Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 911 Technical Forum


Reply
 
LinkBack Thread Tools Rating: Thread Rating: 1 votes, 1.00 average.
Author
Thread Post New Thread    Reply
Registered User
 
sugarwood's Avatar
 
Join Date: Apr 2014
Posts: 4,909
Garage


I ran the fuel pressure test with the gauge I got from AnnWorx.
With the key turned to Acc position, the fuel pressure was 0.
Once the engine was actually running, the pressure immed. read 32-34 psi.
__________________
1986 3.2 911 coupe.

Last edited by sugarwood; 07-04-2015 at 06:57 PM..
Old 07-04-2015, 06:53 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #41 (permalink)
Registered User
 
sugarwood's Avatar
 
Join Date: Apr 2014
Posts: 4,909
Garage
DONE: Verify Speed/Ref sensors (for correct resistance)

Saw this in another thread, and decided to try it for myself.

I tested a new Ref Sensor in the box.




To test resistance, you need to set the MM to the Omega (horseshoe)
I set mine to 2000 ohms, since reading will be 960.


For those who like a visual:
__________________
1986 3.2 911 coupe.

Last edited by sugarwood; 12-26-2016 at 11:10 AM..
Old 12-26-2016, 11:06 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #42 (permalink)
Registered User
 
sugarwood's Avatar
 
Join Date: Apr 2014
Posts: 4,909
Garage
I can't believe I didn't notice this the first time,
but the MM was on the wrong setting for this current test.
I think I blew the fuse after doing this last year.

Notice the MM is set to Voltage (VDC)
For a current test, it was supposed to be set to Amps (ADC)

Quote:
Originally Posted by sugarwood View Post
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.
__________________
1986 3.2 911 coupe.
Old 12-26-2016, 01:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #43 (permalink)
Registered User
 
Join Date: Oct 2004
Posts: 12,088
Be on the lookout for auto-ranging multimeters. They are easier to use. I have a couple of Fluke ones, but I know that Radio Shack had a very good pocket one, which surprisingly had auto range feature. I wish I still had that little guy - I have no idea where it is.
Old 12-26-2016, 01:54 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #44 (permalink)
Registered User
 
ischmitz's Avatar
 
Join Date: May 2002
Location: Santa Barbara, CA
Posts: 4,508
Garage
Send a message via Skype™ to ischmitz
Just wanted to clarify how a digital multimeter works: Internally a DVM only measures voltages. During a voltage measurement there is almost no current drawn by the DVM as the input impedance of modern DVM is on the order of 1 - 10MOhm or even higher. Therefore it is safe to connect the negative lead to GND and the positive lead (plugged into the VOLT socket) to the battery or any other point on the car. The DVM registers the voltage between these points.

When you want to measure a current there are two common approaches. A contactless measurement requires a current clamp and these devices can be extremely expensive depending on sensitivity and accuracy. A simpler way is to insert a shunt (very small resistor) into the circuit. This is how the DVM works. Typically, there are two more socket for the positive lead for a high current range and a low current range. Internally for each Ampere socket there is a fuse and a very small resistor between that socket and the GND socket. Once the DVM is inserted into the circuit a current through the fuse and shunt results in a very small voltage drop. And the DVM measures that voltage drop and calculates the current according to Ohms law I=U/R. For this it doesn't matter what the DVM dial is set to or whether it is an auto-ranging model or not.

Most DVM have a 200mA range input. The only difference is the shunt resistor value and the value of the fuse protecting this input. Again, it doesn't matter what the dial is set to. As soon as the leads are connected to either the 200mA or 10Amp socket and GND they will form an active part of the circuit. And if the current flowing is too high the respective fuse will go immediately.

There is a special case where you can check whether a current flows in a fused branch (e.g. the fuel pump): You can measure the voltage across the corresponding fuse. Use the voltage socket and GND socket and set the DVM to voltage. Then connect the leads to each side of the fuse. Polarity doesn't really matter.

- If a current flows through the fuse there will be a small voltage drop in the order millivolts. This indicates the fuse is good (acting as a very small resistor).

- If you measure battery voltage across the fuse the relay is trying to energize the branch but the fuse is open (acting as an infinite resistor) and thus all voltage drops at the fuse.

- If you measure zero voltage this means there is zero current flowing. Either the relay is not delivering power or there is an open toward GND past the fuse (bad pump or bad GND).

If you want to measure the current though the fuel pump branch directly you need to use the highAMP socket and GND. In theory that works and in practice it might, too. However, keep in mind the only active fuse now is the internal one in the DVM. If the current draw is higher than the rating of that fuse it will let go. Further, the inrush current can be much higher than the rated current of the pump. So even if the meter can tolerate 10Amp and the fuel pump fuse is 10Amp you might still blow the internal meter fuse because it is super-fast acting. The initial current to start the fuel pump can be much higher than 10Amps.

Ingo
__________________
'74 Targa 3.6 (not stock ) - '01 C4 (almost stock) - '00 ML430 (stock)

I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs
Porsche "Hammer" or Porsche PST2 - I can help!!
How about a NoBadDays DualChip for 964 or '95 993
Old 12-26-2016, 09:37 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #45 (permalink)
Registered User
 
sugarwood's Avatar
 
Join Date: Apr 2014
Posts: 4,909
Garage
Thanks again. I'll read that a few times, and try to understand, but hard to learn this stuff at a PC.

I wanted to recap, just to make sure I captured the practical side of it.
Is the following correct?

Fuel pump voltage test.
MM is set to DC Voltage. (I set it to 20V range)
Red lead connects above the #6 fuse.
Black lead goes to ground.
When you crank, you should see 13.5V. This tells you power is getting to the fuse.
If I get no volts, then power is not getting to the fuse.

But, you can get power, but have no current (open circuit somewhere)

Fuel pump currenttest.
Remove Fuse #6.
Red lead connects above the #6 fuse.
Black lead connects below the #6 fuse.
MM is now in the the circuit.
MM is set to DC Amps (current). (I set it to 10a range)
When I crank, I should see something like 8amps. (Fuse is 25amps)
If I get 0 amps, there is no current, and this tells you the circuit is open (for example, a broken ground wire for fuel pump)

Is this about right?
__________________
1986 3.2 911 coupe.
Old 12-27-2016, 08:29 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #46 (permalink)
 
Hey, nice marmot.
 
tirwin's Avatar
 
Join Date: Feb 2011
Location: Marietta, GA
Posts: 4,888
Garage
sugarwood,

One thing to clarify in your fuel pump current test. You want to make sure that the red lead on the meter is plugged into the correct spot on your meter. If this is your meter, then it should be plugged into the empty 10A spot on the left.

For most tests the red lead is plugged into the red location on the right. For testing current draw (amperage) up to 10A you would plug the red lead into the location on the left.

If you'll notice the meter has it color coded. The AC and DC 10A settings on the dial are the grayish white color and that corresponds to the color of the terminal on the left. All the other dial positions are red which corresponds to the red terminal position on the right. Black is "common" (noted as COM) and it doesn't move.

Hopefully that makes sense.

__________________
There are those who call me... Tim
'83 911 SC 3.0 coupe (NA)

You can't buy happiness, but you can buy car parts which is kind of the same thing.

Last edited by tirwin; 12-27-2016 at 09:41 AM..
Old 12-27-2016, 09:36 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #47 (permalink)
Registered User
 
ischmitz's Avatar
 
Join Date: May 2002
Location: Santa Barbara, CA
Posts: 4,508
Garage
Send a message via Skype™ to ischmitz
What tirwin said. However, reading zero Amp with the meter connected could also mean its internal fuse is busted. That's why your car fuse is rated at 25Amp even though the pump only draws 8A. At startup for a very short time there is a higher draw. And the meter fuse acts much faster to that.
__________________
'74 Targa 3.6 (not stock ) - '01 C4 (almost stock) - '00 ML430 (stock)

I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs
Porsche "Hammer" or Porsche PST2 - I can help!!
How about a NoBadDays DualChip for 964 or '95 993
Old 12-27-2016, 01:00 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #48 (permalink)
Registered User
 
sugarwood's Avatar
 
Join Date: Apr 2014
Posts: 4,909
Garage
My battery is dead, so I wasn't able to do this.
I did blow the fuse last time I tried this, and have since replaced it.
I will double check it before I try again.

And yes, I now see the red should be in the grey 10A jack.
Thanks, current test means switch the red lead jack.
__________________
1986 3.2 911 coupe.
Old 12-27-2016, 02:02 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #49 (permalink)
Registered User
 
sugarwood's Avatar
 
Join Date: Apr 2014
Posts: 4,909
Garage
Ok, I went back to this test.
Verified both fuses are intact (continuity test)

Does the following seem like expected results for a properly working car?

First, I re-did the fuel pump fuse #6 voltage test.
MM is set to DC Voltage. (I set it to 20V range)
Red lead connects above the #6 fuse.
Black lead goes to ground.
With engine at rest, I got 0V
When I cranked, I got 13.6V

I then tried the current test.
Remove Fuse #6.
Red lead connects above the #6 fuse.
Black lead connects below the #6 fuse.
MM is now in the the circuit.
MM is set to DC Amps (current). (I set it to 10a range)
Red lead plugged into GREY 10A JACK
At rest, I see 0.
With engine running, I saw about 5 amps.
__________________
1986 3.2 911 coupe.

Last edited by sugarwood; 12-28-2016 at 02:21 PM..
Old 12-28-2016, 02:14 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #50 (permalink)
Registered User
 
ischmitz's Avatar
 
Join Date: May 2002
Location: Santa Barbara, CA
Posts: 4,508
Garage
Send a message via Skype™ to ischmitz
Measurements sound reasonable.

Now insert the fuse again, leave the leads on either side of the fuse and connect them to Volt and GND on the meter. Then set the range to 1V and crank. In that configuration you'll measure the voltage drop across the intact fuse #6.

BTW: As I said earlier, the fuel pump can draw much more current in the initial startup phase and that can be enough to burn the fuse. You are lucky that you didn't burn the internal fuse in the digital multi-meter. Just saying......
__________________
'74 Targa 3.6 (not stock ) - '01 C4 (almost stock) - '00 ML430 (stock)

I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs
Porsche "Hammer" or Porsche PST2 - I can help!!
How about a NoBadDays DualChip for 964 or '95 993
Old 12-28-2016, 04:53 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #51 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 06:42 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.