S5 Turbo Fuel Issues

[JL1RX7]

I bought a S5 turbo awhile back. Started and ran like a champ for a few months. Then it started acting like it had no fuel when running, stalling out etc. Previous owner was a flipper who told me it had fuel pump replaced. From the condition of the tire's it looked like it sat in a garage for a extremely long time.

Well I could see that there was an extra unused factory patch cable which ran from the stock location to the pump. Other than that nothing looked like it was replaced. So I purchased a brand new factory pump kit.

Replaced said pump and now the car won't start period. I ran through all the FSM stuff, all OHM readings are within spec, as are voltage's. I have a few S5's so swapped out the main fuel relay and AFM with one that works. No joy.

Cleaned most of the grounds around the engine etc. Only things not replaced yet are plugs/wires.(look brand new) and fuel filter.

Completely out of places to look to see what could be causing this. Any one have any ideas?

[Pete_89T2]

Hmm, not sure. I'm assuming the car is cranking strong, just not starting, and you checked for any stored CEL codes.

My best guess at this point is it's a wiring harness issue - something is preventing the either the fuel pump from running OR the FIs from firing. Time to crack out the FSM schematic diagrams & go to war.

Couple of ideas to try to troubleshoot further:

1. Try jumping the yellow 2 pin fuel pump test connector. It's located on the passenger side strut tower off of the main ECU harness. With the key in the "run" position, you should hear the pump running constantly when it's jumped.

2. Also with the key in run, check voltages between each FI's "A" terminal pin (per FSM schematic) and ground. All should be reading +12V. If you're not seeing +12V, none of the injectors will fire. If you look at the FSM schematics, you'll see that all of the FI's share a common +12VDC, supplied thru the main relay.

[JL1RX7]

Yep did all of that. Battery fully charged, etc. When you use the jumper on the yellow connector it purrs like a kitten. When checking the voltages across all the relays they all read like they should. All OHM readings check good per FSM. Used my other FC's for spare relays, etc to swap in. Still nothing. Which is why I am stumped as hell.

[Pete_89T2]

So when you jump the yellow check connector the FP runs as it should. Have you tried starting & running the car with the check connector jumped? If so, what happens?

And just to be clear, you checked the voltages between each FI connector terminal & ground, and are reading +12V on the "A" terminal, and 0V on the "B" terminal of each FI?

[JL1RX7]

Even tried that. It still wouldn't start more than a second. It seems that it's not switching from start to run. Just changed plugs for shits and giggles. Still doing the same thing.

Yes on the switching relay under the steering wheel it has voltages where it should according to the FSM.

About to change the fuel filter today, again to eliminate any thing else.

[Pete_89T2]

Even tried that. It still wouldn't start more than a second. It seems that it's not switching from start to run. Just changed plugs for shits and giggles. Still doing the same thing.

Yes on the switching relay under the steering wheel it has voltages where it should according to the FSM.

About to change the fuel filter today, again to eliminate any thing else.

^That's not where I said to measure it - you need to measure AT each FI connector to rule out a FUBAR'ed ECU harness wiring to the injectors. Which sucks because you have to pull the UIM to get in there, but that should be pretty easy for you by now. ;)

A harness failure on a 25+ year old T2 isn't uncommon, and I have a hunch that the common +12V source to the injectors may be open somewhere - that would show up as a sudden no start/no run symptom. With the key in "run", you should be seeing +12V at the "A" terminal of all 4 injectors, and 0 at all the "B" terminals. Just use a paper clip to back-probe the connectors with your DVM, measure between each terminal and ground.

[vrracing]

It's really hard to tell from the posts what is actually happening.

"When you use the jumper on the yellow connector it purrs like a kitten."

suggests that it runs fine if the jumper is connected.

But then right after that...

"Pete_89T2 -So when you jump the yellow check connector the FP runs as it should."

to which you respond...

"Even tried that. It still wouldn't start more than a second."

If it "purrs like a kitten" with the yellow jumped but dies if you pull out the jumper, I'd look at the AFM. IIRC, there is a safety feature that if the AFM isn't telling the ECU there is air flowing (that is, the engine is running) then the ECU cuts the fuel pump. That way, if you wreck with the key on, the fuel pump doesnt feed gas to the impending explosion. That is disabled when the key is in "start" as opposed to run because obviously the engine isnt turning over enough to activate the AFM.

Hope that helps.

[JL1RX7]

Sorry should have made that more clear, when you put the jumper in the yellow connector, the fuel pump runs like it should. Now even leaving that jumper in there the car starts for a second then dies.

I agree with you on the AFM. But putting a known good one should have made that go away. But it didn't. I don't have a spare turbo ECU to swap that out to cross that off the list.


Pete haven't pulled those yet. Trying everything else before I did that. Going to the store to buy new hose clamps before I dive down that rabbit hole.

[vrracing]

Have you put a fuel pressure gauge on the system?

[JL1RX7]

I don't have a gauge yet for that. Otherwise I would have. I have all kinds of gauges to measure air volume, but not fluid pressure or volume.

[Pete_89T2]

Sorry should have made that more clear, when you put the jumper in the yellow connector, the fuel pump runs like it should. Now even leaving that jumper in there the car starts for a second then dies.

I agree with you on the AFM. But putting a known good one should have made that go away. But it didn't. I don't have a spare turbo ECU to swap that out to cross that off the list.

^It should have unless there's a open circuit in the harness wiring somewhere between the AFM safety switch and the ECU. Swapping out a good AFM in that case wouldn't isolate that problem.

[JL1RX7]

I would like to agree, but unless the break is on the injectors then everything else works. All relays have correct voltages. If there was a broken wire, one wouldn't. I haven't gone all crazy and rang out each wire in the circuit. But if it ran before changing the pump, then the only common would be the pump. Not the wiring. This doesn't mean that old wiring couldn't be the culprit. This car is so close to factory I wouldn't think this. It spent most of its life in a garage with some climate control.

Almost nothing is dry rotted or broken. Even the foam around the radiator was is reasonable shape. It didn't crumble in my fingers. To give you an idea. The foam inside the door cards was in good shape. Only in bad thing on the car is the speakers. They rotted out. Which for its age isn't a big deal.

I am leaning bad ground somewhere. When I started cleaning a few it would at least try to start for a second, better than acting like its flooded out.

Tomorrow I will change the fuel filter and check voltages t the injectors. Once I check those that should tell me what's wrong.

[TitaniumTT]

Fuel pump feed line leaking, fuel pump lines backwards, bad fpd, bad reg. Pressure Guage will eliminate or find all those

[JL1RX7]

Took the alternator out, failed the OHM check per FSM, and at Advanced. So ordered a new one. Swapped out another unit from one of my other FC's and still couldn't get it to stay started. Still need to rip the intake off to measure the injector's. At this point, might still and send them off to get cleaned along with a few other's for my FC's.

[TitaniumTT]

Dude..... FPSI gauge on the feed line between the primary and secondary rails first ;)

[JL1RX7]

Don't worry I will. Buying a gauge this week. Not like I need an excuse to buy more tools.