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

[sugarwood]

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

[m962b]

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!

[sugarwood]

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.

[sugarwood]

Ok, I did the first one.
I felt a very slight vibration.

[sugarwood]

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.

[sugarwood]

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)



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)

[Autoban]

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

[Derek911]

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.

[T77911S]

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.

[sugarwood]

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?

[Derek911]

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.

[sugarwood]

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

[winders]

Originally Posted by sugarwood

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.

[sugarwood]

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

[winders]

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....

[T77911S]

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.

[TheSt|G]

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

[Socbum]

Signing on to do the same

[sugarwood]

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.


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--


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.

[sugarwood]

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?


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.



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.


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.