Getting to know our 911's: Performing some basic tests before there is a problem
 

It's winter, and the 911 is mostly parked, and maybe I'm looking for an excuse to get in the garage with some micro-projects.

Don't laugh, but I'd like to try out some of the more common "no start" test diagnoses before my car has a problem.
A low-stress opportunity to learn how to diagnose my car.
Plus, I'll have something to compare to when there is an actual problem. Like a baseline physical of sorts.

Any new guys want to try some stuff with me?
Any veterans willing to guide us?

We can document and photograph whatever we explore.
I'm sure this stuff is covered in the archives, but are there other new guys here who might want to learn some tricks that are 2nd nature to the veterans here.

We can discuss each item in detail, as we progress down the list.
I'd like to work through the list during February.

To start, here is a list of items that have been mentioned in other threads.
Does the list look complete? Any big items missing?

1. DONE: Check Idle Control Valve (for correct buzzing)
2. DONE: Check DME relay (Dual relay. Power to DME/injectors and power to fuel pump)
3. DONE: Check Fuel Pump voltage and current (at fuse #6)
   
4. CURRENT TOPIC: Check Fuel Pressure (at fuel rail)
   
5. CURRENT TOPIC: Check for spark
6. Check Reference sensors. Speed & Position.
7. Check Coil
8. Check Air intake (?)
9. Check relays (which ones?)
10. Check ignition switch

I'm up for whatever. Mines currently down with an Alternator bearing issue, but after that I'd live to learn on my newest toy!

DONE: Check Idle Control Valve (for correct buzzing)

Ok, tonight's task will be to verify the Idle Control Valve.

You turn the ignition to on, but don't actually start the motor.
Now, pop the lid, and check the engine compartment.
The ICV with 2 hoses going into it is in the middle of the photo.
It should be vibrating slightly.

http://rennlist.com/forums/attachmen...socket-003.jpg

Ok, I did the first one.
I felt a very slight vibration.
<iframe width="420" height="315" src="https://www.youtube.com/embed/pPv40JF3-Rk" frameborder="0" allowfullscreen></iframe>

DONE: Check DME relay (Dual relay. Power to DME/injectors and power to fuel pump)

Ok, I am moving onto the DME relay.
It is located under the driver's seat.

To remove it, first slide the seat back to loosen the nut. (10mm)
Then slide the seat forward to unplug the wiring harness from behind.

https://i.imgur.com/ZhT8BiG.jpg
https://i.imgur.com/QfPLdJw.jpg

Let's understand how the DME relay works and test it.

Following the diagram, power 12V is hardwired into 30 and switched into 86 via the ignition switch
Powering a closed 86->85 coil circuit with 12V closes the first switch.
When that happens, 30->87 is now a live circuit (DME and injectors are live)
This also allows 30->85b to close the 2nd switch
When that happens, 30->87b is now a live circuit (Fuel pump is live)

https://i.imgur.com/RvkuG1M.jpg

If you have electrical test leads (aligator clips, wires, and 9V battery), let's test our relay, since we know it works.

1. Connect 86 and 30 to (+) and 85 to (-) of your battery. This will click the first switch closed.
2. Now connect the (+) for a test light to 87, and ground the (-) side. Light should work. (Simulates power to DME)
3. Leaving the above connections in place, connect 85b to (-) of your battery. This will click the 2nd switch closed since 30->85b is a live circuit.
4. Now connect the (+) for a test light to 87b, and ground the (-) side. Light should work. (Simulates power to fuel pump)

This is a great thread, I do all the maintenance once a year during the winter time using the Bentley manual. I will add this to my check list.

Juergen

Sugar is the man. Your pics are very clear. Does anyone know of a picture of a 3.2 engine with every component labeled? I have seen one for the 964 but not the Carrera.

you really want to do the easy stuff first.

the ICV WILL NOT keep it from starting. putting your foot on the gas bypasses the function of the ICV.

first thing is to split the problem in half. is it fuel or ignition.
ignition is the easiest test and if ti passes it rules out a lot of stuff.
take a spare sparkplug (you can keep one in the car) and connect it to a plug wire, ground it and start the car to check for spark.
if that passes you can rule out the CPS, speed sensor, DME, coil.

check for fuel. is pump getting power. you can check for power at the fuse. if all that is good the DME relay is good. the other check that you can do now is the current for the fuel pump. remove the fuse and set your meter up for current. connect it in place of the fuse and run the pump. pumps are usually around 7-8 amps.

other than that take a resistance reading of the CPS and speed sensor for future reference. i think they are in the 500-700 ohm range. the thing with these sensors is they can cause bad running or they can fail when they get hot and work when cold.

carry a spare coil. you can check for 12v at the coil. does not confirm the coil thought. thats about all you can do for a coil. they can work when cold and fail when hot.

a CHT can cause bad running but not sure if would keep you from starting.
same with the O2. it will not keep it from starting but can make it run bad.

to sum it up, keep a spare plug for testing for spark, a coil and a DME relay in the car.
you can carry a test light for doing electrical work too.

as preventive maint i would pull the relay and hit all the joints with a soldering iron. thats the biggest failure on these things is bad solder joints.

i am not big on the motronic for porsches so if i missed anything let me know.

i did not tace it out but i saw a speed shutoff relay. i dont know if that would keep it from running or not.

one last thing, car alarms. after market alarms are crap and WILL keep it from starting.

one more last thing. battery and grounds. make sure the battery is fully charged and make sure all connections, including grounds are clean. grounds are a big one. most people over look them and only clean the positives. also the grounds for the injection system. they need to be good and clean.

Thanks for the tips! I have a few stupid questions about testing for spark.

Is there a way for only 1 person to test for spark?
(Instead of one to crank the ignition, and one to hold the spark plug?)

Here is my major confusion. How do you prevent the engine from actually STARTING when you just want to test for spark? (Or is the engine supposed to idle with one spark plug removed?)
If I turn my engine over for more than 1-2 seconds, my engine fires up.
Is it dangerous if the engine starts running while the spark plug is removed like that?
Won't unused gas start accumulating in the cylinder?

Most people test for spark by removing an existing spark plug. How does that work, exactly?
Doesn't oil or gas get blown out of the open spark plug hole when the engine is cranked?

It's always a 5,000 poster that throws a wrench in a thread. Not that T77's wisdom is not welcome, but maybe we wanted to go through the journey with sugar. Maybe we liked his clear pictures. I was looking forward to the fuel pressure test pictures.

LOL, I was unable to get to the garage tonight.
Here is what I've got so far on the fuel stuff.

Fuel voltage is tested by checking current on fuse #6.
I will report back tomorrow evening, as I'm still unclear on the steps.

Fuel pressure at the fuel rail / Schreder Valve seems less straight forward on these 3.2s
It seems you can either buy the $100 fuel pressure kit from HarborFreight or make your own.

Here is some reading from the archives:
link 1
link 2
link 3

Or, you can buy a fuel pressure gauge here:

Fuel Pressure Guage / Tester (12mm) [FPT1 (12mm)] - $35.00 : ArnnWorx Specialty Tools

I bought one of these and it works well. Just make sure you find out if you need the 12mm or 14mm version. Oh, ask them to make the hose as long as it is in the photo. The one I bought came with a 6" hose. Long enough but longer would be better I think.

Great find, winders! I read about 30 fuel pressure threads tonight, and none mentioned this custom tool.

I am glad I could help. I bought an adjustable fuel pressure regulator for my race car and needed to find a fuel pressure gauge to set the pressure to the same as the fixed regulator for a starting point. I managed to find this source within 5 minutes of search. Just lucky I guess! Lol....

usually when you are checking for spark the car wont start, so thats not an issue. but, you can pull the FP fuse.

there is absolutely nothing wrong in what the OP is doing, in fact it is great. but for real world troubling shooting there is a certain order of things to do.

i kind of did the same thing when i bought my 930 but for more of a baseline of where the car is when i got it. checking fuel pressure is a great thing to do. it is always best to know what it is when it is running right. i checked all the fuel pressures but also did a leak down test and a compression test.


voltage and current are 2 different things. you can check voltage with the fuse installed. (12v).
current has to go thru the meter for it to measure it so the fuse is removed and the meter is connected in place of the fuse. (normally about 7-8amp).
get familiar with a test light. it is much easier to use and cheaper. check it across the battery for a refernce of how bright it is.

Keep up the good work Sugar. Your clear photos and explanations are an excellent resource.

Signing on to do the same :)

Ok, I tried 2 different MM (multimeter) tests at the fuel pump fuse.
I am not 100% sure I understand the concepts, I just sort of know the steps I was advised of.
Maybe someone more experienced can clarify what is going on with these 2 tests, and also can point out errors, as well
As as well explain the difference between current and voltage (flow in amps vs. pushing power)

FIRST TEST
I tried to verify the #6 fuel pump fuse is getting 12V when cranking/running
I clipped the red test lead to one of #6 fuse block screws.
I clipped the black test lead to chassis ground to the left of the fuse block
The #6 fuel pump fuse is not removed, and is left in place.
Does this allow the full 12V+ to flow thru the MM, as well as 12V through the fuse?
I believe this is a voltage test, not a current test.
http://i60.tinypic.com/dc63w5.jpg

I set the MM to DC 20V since I was expecting a reading of 13V or so.
On some MM's this may be labelled as V--
http://i60.tinypic.com/o797vn.jpg

Since my car runs properly, the engine actually started up.
If this was a real no start, you're looking to see the voltage level as the car cranks.
Notice how the voltage only registers during cranking?
It's still 0 when the key is moved to the start position.
This reading showed about 13.5V.
<iframe width="420" height="315" src="https://www.youtube.com/embed/AxlqdMUndkc" frameborder="0" allowfullscreen></iframe>

The second test was a current test.
I clipped each test lead on either side of #6 fuse block screws.
The fuse is not removed, and is left in place.
This now makes the MM part of the circuit, right?
I think the MM has a very low wattage rating, so it draws very little current, and most of the current still goes through the fuse and to the fuel pump.
Should I have removed the fuse for this test, so the entire current has to flow through the MM?
http://i57.tinypic.com/25pn29f.jpg

I set the MM to DC 200m since I was expecting a reading of 20-40mV.
Is this right setting for the dial?
Should I have been using a the other 10A port on the MM for a current test?
I have no idea if this 2nd test was correctly set up.
http://i62.tinypic.com/1z1h8bp.jpg


Notice how the current only registers during cranking ?
It's still 0 when the key is moved to the start position.
This reading showed about 165. In what units is this 165?
Is this right? I guess it has to be right, since the car is running.
<iframe width="420" height="315" src="https://www.youtube.com/embed/-QSw23nczsw" frameborder="0" allowfullscreen></iframe>

For the last thing, just out of curiosity, I tried to start the car with the #6 fuse removed.
It idled for about 1-2 seconds before dying.

Ok, the first test tells you that the pin of the fuse block where the red lead is attached to is getting +12V once you crank or the engine runs. Think of this test as testing the pressure of a garden hose. The pressure (+12V) registers on the MM.

The second test is a pressure difference on a small restriction (fuse) in the garden hose. You measure before and after the restriction. Once water (current) flows through the restriction (fuse) there is a little pressure difference. This pressure difference (voltage drop) proves there is current going through the fuse and into the fuel pump.

The second test is helpful to diagnose a potential bad fuel pump. Imagine the wire from the fuel pump to chassis GND is broken. When you crank you will still see +12V at the fuse (1st test). But no current will flow. The second test will read zero at all times.

Ingo

Thanks Ingo.

I am having trouble understanding test #2.
Test #1 makes sense to me: There is 12V of "pressure" in the circuit, and the MM splices into the circuit and sees the same 12V.

Why doesn't test #2 also see 12V? It's part of the circuit, isn't it?
Can you explain why I am not getting the identical reading for both tests?
What is fundamentally different about them?
Why does one see the full 12V while the other does not?

http://i61.tinypic.com/2rmwdv9.jpg

Both sides of the fuse have almost the same voltage with reference to GND. A voltage is a potential (pressure) difference. Convention is that voltages are reported referenced to GND and GND is at zero. For this you put the negative lead of the DVM to the chassis. If you repeat test 1 on the other side of the fuse you will see a slightly different value.

In the second test you measure +13.20V on one side and +13.04V on the other side of the fuse (both referenced to GND). If you measure on either side you measure 13.20V - 13.04V = 0.16V

Does that explain it better?

Ok, so I need to think of a D-- DC voltage test as the difference between the pressure (voltage) read by both leads ?

In test #1, the red lead reads 13.2V, and the black lead reads 0V. Hence the difference (voltage) is 13.2V

In test #2, the red lead reads 13.2V, and the black lead reads 13.04V. Hence the difference (voltage) is .16V = 160mV. And the fuse has introduced a little bit of resistance (heat dissipates or faint light, like a filament.)

http://i61.tinypic.com/2rmwdv9.jpg

I will now re-read your fuel pump example below and make sense of it.

So, if the fuel pump GND wire is broken, the circuit is broken.
However, doing test #1 at the fuse and chassis will show a pressure difference of 12V b/c power is still being supplied, even though it's not being used.
So, when a broken circuit is being powered, you will still see a 12V difference when you compare pressure in the wire vs. the chassis.
Doing test #2 will show the same voltage before and after the fuse, b/c there is no current flowing, so the fuse doesn't act as a resistor.
Since there is no voltage difference, test #2 would read 0V. Is that about right?

What kind of test is test #1 called?
What kind of test is test #2 called?

your way of looking at it to me is screwy but it works.

your statement here is very good.

"So, if the fuel pump GND wire is broken, the circuit is broken.
However, doing test #1 at the fuse and chassis will show a pressure difference of 12V b/c power is still being supplied, even though it's not being used. "

this can be true. and even though this test does not mean there is voltage AT the pump, it is really to verify that the DME relay is working and providing power to the fuse.
troublshooting comes down to checking easy things and the most likely things that go bad first. its also about starting at a place that will cut things in half. like checking for spark first.

both tests are VOLTAGE tests.
the other test i told you to do is a CURRENT test.
to do this test the fuse has to be REMOVED. the red lead on the MM needs to be moved to the 10A connection and the meter set to A-DC10. (the pump current is right at the limit of the meter. if it is too high it will just blow a fuse in the meter). connect the leads to each clip of the fuse holder like you did. run the pump. the current actually goes THROUGH the meter now.

just remember this. measure voltage reference to ground. IE, connect one lead to gnd.
current has to go thru the meter. so something has to be removed. a fuse, one end of a wire.
like remove the neg cable on the battery and connect the meter to the cable and the post. but the meter has to be set up to read current.

here is how a test light can be used. connect it to the body. then just probe what ever you want to see votlage on. the actual voltage is not really impotant. charging problems you need the voltage. the other way a test light can be used os to connect it to 12v, then probe and check for ground.
here is the problem with a MM. a MM is a hi resistance device. IE, it does not need really any current to measure voltage. this can send you down the worng road. a test light (TL) is a low resistance and needs current to light the bulb.
i have seen severla people here working on a brake light (or some light) problem. they measure 12v at the light and the ground is good but the brake light will not work. thats becuase there is a hii resistance due to a bad connection that reduces the current so the light will not light but the MM reads 12v. if they had used a TL, the TL would not light (after all it is light bulb too) and they would know power is bad at the bulb and they would not be pulling their hair out trying to figure out why it does not work.
checking for shorts.
if a fuse is blowing you cant put power to the circuit, obviouly. buy you can remove the fuse and connect the TL in place of the fuse. now the TL is a load that reduces the current so wires dont melt and you can look for the short. a MM will do the same thing here, but what is easier to read, a light bulb or a number. OR, you can connect the TL to 12v and look for what is shorted to ground.

i hope this is not too much info but you seem like you are getting a graps of things.

Even inserting an Amp meter instead of the fuse is a voltage test as the Amp meter has an internal shunt and measures the voltage across that shunt. Test #2 uses the fuse as shunt.

Doing test #1 is great for checking the DME relay. This cuts the fuel pump branch in half. If #1 passes #2 is the quickest and most telling as it shows a bad fuse (measure +12V), a working circuit (measure ~ 0.1V - 0.2V) or bad pump/open wiring downstream (measure 0 volts).

The problem with a test light is that it itself has an appreciable internal resistance and alters the circuit to much once serious currents flow. Image using in inline with the battery and then crank. SmileWavy

Ingo, I am just going to paste some personal notes here, as a way of archiving these thoughts.
Anyone is welcome to comment or correct. To review,

http://i61.tinypic.com/2rmwdv9.jpg
Test 1: So, if I "splice" my red lead into any active wire and ground my black lead, I will be "observing" how much pressure is in the live circuit. This is a voltage test, and simply tells me if the wire is being supplied with power.

Test 2: So, if I "splice" both my red and black leads into any active wire, I will still be "observing" the pressure difference (or voltage drop) in that section of live wire. In this case, I was measuring around the fuse. What is the point of this test again? Was it to verify that, since there IS a voltage drop across the fuse, that means some amount of current has to be flowing through it ?


Let's say we are troubleshooting a no start and think there might be a frayed wire.
When you do a test #1 voltage/pressure test, it will read 12V, b/c there is continuity, and the circuit is closed. This is deceptive.
You would need to do a voltage drop test, like this test #2

http://i61.tinypic.com/123wryd.jpg
To test for a frayed (+) cable on the fuel pump or starter, this is test #2, except you are measuring voltage drop across the start and end of the (+) starter cable, and not a fuse.
With no power applied, if the cable was perfectly intact, you would read 0V since there is no voltage drop.
With no power applied, if there was a frayed wire, you would still read 0V, since there is connectivity, and MM's top lead and bottom lead would both observe 12V volts of pressure?

But, what happens at full load with a frayed wire?
Now, the full pressure can't make it across the frayed part?
So, that's when you'd see a difference, and get a reading?
So, does a voltage drop simply occur when there is resistance (fuse, fray, etc)
This creates 2 different pressure (voltage) readings on either side of the "resistor" ?


So, the question about test #2 (voltage drop) is how MUCH is acceptable? Like in the fuse test, some amount of voltage drop is normal (160mV in the fuse case) This proved current was flowing. But, if there is a frayed wire, there will be a much higher voltage drop reading, since the voltage difference will be greater on either side of the break. So, you need to know X voltage drop means there is a problem in the circuit. Is that on the right track?


CURRENT TEST:
The 911 fuse #6 for fuel pump is 25A, so it sounds like a 10A MM can't handle a current test for fuel pump. But, for learning's sake, for a true current test, you put the MM into current test mode (10A), the MM is now designed to create a draw. This is the difference b/w a voltage test (observe the circuit) vs a current test (create a wattage draw to consume power) and this is what dictates when current will actually flow INTO the MM. Simply being connected to the circuit doesn't mean you will draw current, the device must be designed to "suck in" the current, like fan or bulb or something. What makes the MM "suck in" and draw current when it is in 10A mode? Where does the current go? Heat? Light? Motion?

I am not sure I understand the difference between 2 and 3 above.
When the circuit is broken/open, I won't get ANY voltage drop (resistance) b/c it's not carrying any current at all.
So, on a powered closed circuit, a little resistance means there is current, while zero resistance means the circuit is broken somewhere?

http://i59.tinypic.com/11lloc5.jpg

BAD FUSE TEST: Circuit is powered. Switch is OPEN. I connect the MM to points B & C.
Point B is seeing 12V of pressure, and point C is seeing 0V of pressure.
I should read 12V, since 12V - 0V = 12V, and there is a huge pressure difference (voltage drop).

WORKING CIRCUIT TEST: Circuit is powered. Switch is CLOSED. I connect the MM to points B & C.
Point B is seeing 12V of pressure, and point C is seeing 12V of pressure.
I should read 0V, since 12V - 12V = 0V, since there is no pressure difference (voltage drop) at points B and C.
In reality, I will read some nominal amount of voltage drop, due to resistance like heat loss from wire, etc. (All circuits have some built in resistance?)

OPEN WIRING DOWNSTREAM TEST: Circuit is powered. Switch is OPEN. I connect the MM to points A & B .
Both point A & B are seeing 12V of pressure. I should read 0V, since there is no pressure difference (voltage drop) at A & B.
I don't get ANY resistance b/c the broken circuit is not carrying any current at all.
So, on a powered closed circuit, a small voltage drop (some resistance) means there is current, while zero voltage drop (INFINITE resistance) means the circuit is broken somewhere?

To summarize, a voltage drop test:
12V = Break in wire being tested. Power is supplied. Current not flowing.
.1V = Resistance in wire being tested. Power is supplied. Current is flowing.
0V = Break in downstream wire (but not wire being tested). Current not flowing.

We are getting into the weeds here. My test #2 was to measure voltage drop across the fuse. The fuse can be modeled as a resistor with about 0.05 Ohm value. If a current flows through that fuse there will be a voltage drop proportional to the current according to Ohms law:

U[Volt]=I[Ampere]*R[Ohm]

In your case lets assume there are 4 Ampere flowing. 0.05 Ohm * 4 Ampere = 0.160V

If the circuit is not flowing current because the pump is broken or not connected to chassis GND the current is zero and thus the voltage drop is zero. The resistance of the fuse isn't changing but since there is no current going through it your voltmeter will measure zero voltage across it. Try this: Connect any resistor to your volt meter in setting VOLT. You will always measure zero. Once you change the setting on your voltmeter to OHM the voltmeter will pass a small current through the resistor and measure the voltage drop.

Cheers,
Ingo

Voltage Drop = .05 ohms X 4 amps = .200 volts (200 mv)

using a MM to measure voltage that way can be confusing to those that dont really have a grasp. plus its really not a GOOD way to do it. if the circuit is open at the load, you could still have power at the fuse but the meter would read 0v and send you down the wrong road so i would never suggest to measure voltage that way. this could lead to replacing the DME relay when it is not bad.

like the MM, to measure voltage with the TL its best to reference ground for the reasons above.

i suggested to use the TL in line or in place of the fuse for checking for current drain or when something is blowing the fuse, not for checking for voltage.


always measure voltage to ground and you can verify grounds by putting 12v on them with a test light.

here is why the last one is partly riight.
you are correct in the A & B are seeing 12v thus you should read 0v.
you are wrong in thinking that the open circuit has anything to do with resistance at A & B.

here is another way to look at it.
THEORETICALLY any point along a wire no matter how long is electrically the same point. thats because in theory that wire has no resistance.
to measure voltage you HAVE to have reistance.
there are 2 extremes. removing a fuse= infinty and putting the fuse back in = zero.
in between these 2 you will measure some voltage drop across the resistance (R).

to measure voltage you have to have resistance. to play with the formula ingo gave you. a fuse has "no" resistance. a wire has "no" resistance.


i am reluctant to say this without a LONG explanation but i am saying it because i am trying to keep electrical trouble shooting simple for now.
for the most part you are only concerned about opens and shorts. here is why i am syaing this. an OPEN (blown fuse, broken wire) will keep something from working. a SHORT will blow fuses. anything in between can do strange things and these problems can be harder to find. here is what hi resistance can do.
slow starting. the clicking of the solenoid with no start. bad charging. dim lights.
and again, with a MM you can measure 12v but not have enough current to operate the load.
load= a light bulb, starter, radio.


some people look at this like water flowing thru pipes.
your pressure gauge is a MM. it is placed before a shut off valve. with the valve open, all the water flows, there is no R (short or fuse) so the gauge reads 0v. turn the valve half way and now you have R. the pressure gauge starts to go up. close the valve. now the gauge reads the full power (12v) that the pump (battery) is supplying.

On a completely different subject, you should take the time to check your distributor bushings for wear.

Remove the cap, and check the rotor for side-to-side movement. Almost any movement will mean that the rotor will strike the inside of the cap, causing the rotor to be destroyed and preventing spark. If this happens while the engine is running, then fuel will continue to flow into the cat - destroying it and stranding your car with a red hot glowing cat.

Preventive maintenance should be done on the fuel lines on top of the engine.

Carry a spare DME relay and fuses.

Useful checks are resistance checks of the speed sensor, reference sensor, CHT sensor, and if you have a wideband O2 gauge, the "lean stop" and "rich stop" tests (remove the oil tank cap and replace. remove the fuel pressure regulator vacuum hose and replace).

You can also peform the voltage output tests on the AFM that are not mentioned in Bentley, but are covered in this forum. There is also a DME test plan that has been posted for "no start" conditions when there is no spark.

I fixed my sentence above:
"So, on a powered closed circuit, a small voltage drop (some resistance) means there is current, while zero voltage drop (INFINITE resistance) means the circuit is broken somewhere?"


Ok, in your pipes example, you're describing test #2 (opposite sides of the fuse/resistor/valve)

With valve open, no resistance, no voltage difference.
So, in a voltage drop test, 0V means full current, provided there is power being supplied.
(Since 0V can also mean no power, no current.)

With valve half closed, you have resistance, pressure difference is X.
(There is full pressure/voltage before the valve, and less (?) pressure after the valve)
So, in a voltage drop test, I get some non-zero value.
This means there is a resistor in the circuit, power is supplied, and current is flowing.

With valve totally closed, you have infinite resistance (simulates a break in the current), pressure difference is entire voltage.
(There is full pressure/voltage before the valve, and zero pressure after the valve)
So, in a voltage drop test, full voltage value (12V - 0V = 12V) means break in circuit. Power being supplied, no current flowing.

Right?

To summarize, a voltage drop test:

12V = Break in wire being tested. Power is supplied.
If voltage drop is 12V, that's a huge drop in voltage between points A & B.
Current not flowing.

.1V = Resistance in wire being tested. Power is supplied.
Since a wire has SOME resistance, you will always have a voltage drop in an active current.
Current is flowing.

0V =
Case 1: Power is not flowing at all. No voltage drop, since no voltage.
Case 2: If there is power, and current flowing, then voltage drop of 0V is impossible. There is always some resistance.
If break was within length of wire being tested, you'd see 12V voltage drop.
So, with no voltage drop whatsoever, there must be a break in downstream wire (but not wire being tested).
Current not flowing.

you HAVE to stop trying to test a circuit like this. there are too many variables and interpreting your readings can be hard if you don't have a lot of electrical background.
there are a lot of situations that could come up that i just can't cover or predict.

test for voltage with one lead connected to ground. that will ALWAYS tell you power is good from the battery to where you are testing. (there is the exception that you could still have resistance in the circuit between the battery and the point you are testing) then you move down the circuit and test again. the key to being a good technician is keeping it simple and knowing how to cut the system in half so you don't have to start the battery and test EVERYTHING one part at a time.
i think you are getting a GREAT understanding of voltage drop across a component but this is really only good for testing a single part, like one resister, or a coil like on a relay.
this is the reason a test light is made the way it is with one end having a clip to clip it to ground (or power) and a sharp point to easily probe

i use to do auto electric work for a living and i have worked for the FAA as an electronics tech for over 20yrs.

when i did auto electric work "we" almost never used a MM.
what ever you use connect one lead to ground (the body) and probe for voltage with the other.
test lights are great for checking fuses. just touch the top and bottom of each clip on each fuse. much faster and easier than a MM. this also checks the fuse connection.

here is how i fixed my brothers no start after he put in a new switch and starter.
with a test light, i probed the yellow wire a the starter as he tried to start. the light was kind of dim. i could easily compare it to the battery volt at the start. went to the front trunk and found a relay for the car alarm that had a bad connection. i removed the relay and it has never not started since.
the yellow wire was getting voltage but not enough current to pull in the solenoid. i did not check the voltage but i bet it had 12v there.
the point is all checks were made to ground.

CURRENT TOPIC: Check Fuel Pressure (at fuel rail)

Ok, I decided to move onto this step.
First, determine your fuel rail fitting size.

First remove the air duct.
http://i60.tinypic.com/9s5npt.jpg

Next place a rag, and get your 19mm wrench
http://i60.tinypic.com/4se3hs.jpg

I verified my fitting in M12x1.5
http://i61.tinypic.com/16asmsy.jpg


So, next step is to get a fuel gauge that fits.
1) The $100 Harbor Freight kit supposedly works.
2) Try to make my own female M12x1.5 fitting? Has anyone built their own?
3) Or this option for $35.

Option 3 works fine.......

In the meantime, I would now like to test for spark.
I will need a 7th spark plug. Just get NGK BPR6ES?

Since my car currently runs fine, should I disable the motor somehow before cranking? How?
I just don't know if it's bad to have the engine accidentally start up with the 6th spark plug not connected.

I assume you want to test for spark with a functioning engine by disconnecting one lead from a plug and run a spare plug. For that pretty much any spark plug works. Most use an old discarded one.

I would prevent the engine from getting fuel so it doesn't start while you do the test. Either pull the fuse for the fuel pump or disconnect all six injector connectors.

While you are at it maybe get an LED test light and see how the coil "sees" spark pulses on its primary. And then there are inline spark test lights - they hook into the high-voltage line and have a small discharge lamp that lights up when there is a spark.

Ingo