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gomi_otaku
gomi_otaku, Technician
Category: Audi
Satisfied Customers: 3431
Experience:  VW certified technician, Chicago VW/Audi Training Center, Seattle VW/Audi Academy
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1993 Audi 90 CS 5 Spd, 84,000 orig miles = Replaced the fuel

Customer Question

1993 Audi 90 CS 5 Spd, 84,000 orig miles = Replaced the fuel pump about a year ago, car has been running great! Suddenly, when accelerating normally from an intersection it quit. Cranks fine; can hear the fuel pump cycle when the key is turned on; does not even try to start; when I spray gas into the intake - after the air cleaner assy - it starts and runs fine... IMMEDIATELY; therefore, not an ignition problem. Don't know what the fuel pressure requirement is or how to check it and with what (?). Or where the fuel filter is in order to
check/replace it...which could be the problem(?). Except it was running perfectly and then stopped and now won't start/run. It seems that if it was a filter and/or low fuel pressure that there would have been symptoms before it stopped.
Any Ideas??? Is there possibly anything electrical having to do with the fuel system, including injection that could have failed? The sudden stop and not run seems like an electrical failure.
Submitted: 1 year ago.
Category: Audi
Expert:  gomi_otaku replied 1 year ago.

You can pull the fuel line off the rail, and direct it into a glass jar, and see if you get flow while cranking. I understand what you are saying about sudden failure, it seems odd with a fuel pump, especially a new one. So if you get no flow, I would check power at the fuel pump connector while cranking, if you have no power you have an issue with the fuel pump relay or something.

When it starts on starting fluid, it just runs until the fluid spray is gone, correct? So you know you have spark, so your crank sensor is not the issue.

Customer: replied 1 year ago.
Hi,
Thanks for getting back. Actually, I sprayed gasoline from a spray bottle in to the intake just after the air cleaner assy
and IT STARTED AND RAN IMMEDIATELY until it used up the fuel. So, not an ignition or compression problem {2 out of 3 things to make an engine run} . Earlier that day I ran it to red line in 1 - 2 & 3 gears. It ran perfectly! Where, specifically, is the fuel line that I should take off and how is it attached? There is power to the fuel pump, as I said, because I can hear it cycle - come up to pressure, I believe, - when I turn on the key to the start position which is normal, and the fuel pump relay clicks at the same time. Is there a specific fuel pressure PSI required?
Expert:  gomi_otaku replied 1 year ago.

But it won't stay running with the key in the run position, correct? Just making sure that it isn't the ignition switch, cutting off the pump in the start position, but allowing it to run in the run position. Typically when this happens you get a "stumble" like it is going to start, just as you let off the key.

Customer: replied 1 year ago.
Re: "But it won't stay running with the key in the run position, correct? NO! Just making sure that it isn't the ignition switch, cutting off the pump in the start position, but allowing it to run in the run position. Typically when this happens you get a "stumble" like it is going to start, just as you let off the key."NO.
As I stated previously {read again the original email} it does not start OR EVEN TRY TO - cranks perfectly!It only starts and runs when gas is sprayed into the intake. AND, IT WAS RUNNING when it just stopped and has not started
on it's own since. Therefore, it has nothing to do with the ignition switch.
AGAIN...is there a specific fuel pressure required in the system in order for it to run and how can that be checked and where is the fuel filter in order to check it / replace it? It seems that if it was a filter and/or low fuel pressure that there would have been symptoms before it stopped." Re: "Earlier that day I ran it to red line in 1 - 2 & 3 gears. It ran perfectly!"
"It was running perfectly and then just stopped and now won't start/run!"
What could have failed completely - - - - suddenly in the fuel system? Ignition & compression are OK otherwise it would not start immediately and run on the gas sprayed into the intake!
Larry
Expert:  gomi_otaku replied 1 year ago.

Yes, I am just clarifying. You do need to have about 30psi of fuel pressure on these. When you hear the pump cycle, you are hearing the actual pump in the rear, not just the relay under the dash, correct?

Expert:  gomi_otaku replied 1 year ago.

Have you checked the fuses for the fuel pump (s17, 15a) and for the injectors (s72, 12a) It could be that you are getting pressure to the rail, but the injectors are not opening.

Customer: replied 1 year ago.
Re: "When you hear the pump cycle, you are hearing the actual pump in the rear, not just the relay under the dash, correct?"
Correct! And, I checked with the fuel pump plug unplugged using a test light, that power was going to the plug. I checked all
applicable fuses also {don't remember the actual numbers}. Where, on the system do I check pressure? Is a special tool required? The fuel filter...where is it located? It is possible, I suppose, that the filter is keeping the injectors from getting the
30 PSI and yet the pump is cycling??? It seems peculiar though that, that would cause it to just Shut Off without any symptoms like down on power or missing before stopping complete! Are the injectors activated by any electronics or electrical connections? It seems to me like something electrical failed because of the SUDDEN Stopping of the motor and the fact that
right away it did not and still does not even try to start on it's own.
Expert:  gomi_otaku replied 1 year ago.

Yes, the injectors are fed constant power through fuse 72- and then grounded in turn by the ECM in order for them to open. You would need to check pressure with a gauge on the fuel line- but like I said, you can just look for the injectors, follow the fuel line back, and find a place to disconnect it and route it into a glass jar or bottle and make sure it is pumping when you are cranking.

Customer: replied 1 year ago.
OK. But where is fuse "72"? The fuse block under the hood does not have any numbers even close to that!
Is there another fuse block/location somewhere? Maybe specific to the F I?
Expert:  gomi_otaku replied 1 year ago.

Take a look at page 29-30 of this fuse listing- the "electronic box" behind the center dash holds the fuse s72.

Customer: replied 1 year ago.
Hello,
Please excuse my not answering right away but I have to fit in time, when I am not working, to repair the Audi.THANKS for the extensive wiring diagram! But I do not understand: where the "electronic box" is located. Do I have to
disassemble the dash to find it...in order to check a fuse?/!/? And none of the pages you referenced 28; 29; 30 show anything
about fuse 72s. Please provide more info on the above. This situation/problem is a bit more complicated than usual it appears.
That is OK but it is why I ask for more complete information.Regards,
Larry
Expert:  gomi_otaku replied 1 year ago.

Sorry, should have said pages 30- 31, not 29-30 One more page would have shown you where it was. If you look at page 30, it shows the ECM and circuit breakers, the one that is listed in the wiring diagrams as S72 is the circuit breaker in position 5 there.

And yes, it is inside the dash area. This is what mechanics do all day, dig in deep!

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