Audi A8 with LOTS of new parts soon parting out - Page 3 - AudiWorld Forums

Go Back  AudiWorld Forums > Audi Models > Audi A8 / S8 > A8 / S8 (D2 Platform) Discussion
Reload this Page >

Audi A8 with LOTS of new parts soon parting out

Notices
A8 / S8 (D2 Platform) Discussion Discussion forum for the D2 Audi A8 and S8 produced from 1994-2002

Audi A8 with LOTS of new parts soon parting out

Old 08-29-2018, 01:05 PM
  #21  
AudiWorld Member
Thread Starter
 
Join Date: May 2018
Posts: 53
Default

Originally Posted by BrianC72gt View Post
The fuel pump has a specific output of liters or gallons per minute. Dunno the exact measurement. if you are opening lines, ONLY use fuel injection clamps, not worm gear clamps. Worm gear will leak and... Carbecue.

The pump powers up momentarily on cranking then doesn't stay on until the ecu believes the engine is running...probably crank sensor signal of RPMs over a few hundred. To power it continuously, you could look for the two fattest wires int the connector under the carpet, right side of the trunk. One has continuity to ground, the other is a switched hot from the relay under the passenger side (right U.S. cars) footwell. You can remove the floor mat, three screws on the incline portion of the floor, one or two fasteners to slide out the relay tray, pop cover off of Fuel Pump relay, Key in RUN position, push FP contacts points closed with a folded matchbook or folded piece of soft plastic fuel line, or the rubber handle on a pair of pliers. Very lightly. Then the fuel pump should run continuously.
So I did the following so far:
adjusted the timing to be so dead on it can't
​​​possibly be off.

Two new power output stages

Swapped out old fuel filter, it was the original from 97

Checked all my coils, got zapped so they work

Checked spark plugs, they make noise and zap so they work

Idk what else it could be. I did get a throttle position sensor error code, or something like that, I believe pedal position sensor, but I doubt thats it.

Could the fuel pump really cause just one side to not fire at all?

​​​​​
Captain Sweeney is offline  
Old 08-29-2018, 04:17 PM
  #22  
AudiWorld Member
 
Join Date: Jan 2004
Posts: 585
Default

Does it run at all? Or does it run badly? Inconsistently, like stumbles, then good, then stumbles again?
After clearing codes, do the multiple misfire codes come back?
I don't know if a defective TPS would cause the car not to run. Would a bad TPS cut power to the fuel pump? Dunno.
What makes you think one bank is not firing at all? Do the headers on that side get hot?

Next steps: Clear the codes, crank and see which codes come back. Are any of the codes deal breakers? Next Check fuel pump output and pressure, then noid lights on the injectors.

I would test the fuel pump output next. An Yes, I've seen misfires just on some cylinders with a bad fuel pump that is in the throes of dying. Hotwire it in the trunk (or wedge the FP relay contact points closed and key in RUN to power pump continuously), pump out at the fuel rail hose in the engine compartment. It should pump out fast and forcefully. A pressure gauge would be better still. Never used one myself. Do local auto parts stores rent those out? If the gas is a couple years old, it could be off. If the pump works and the gas is more than a few years old, pump it all out to gas cans, and put some clean gas in the tank - a few gallons.

How is your fuel pump flow? I've done some sketchy things to clean injectors removed from the car, like filled a length of fuel hose with lacquer thinner, stick 50 psi of air hose blower on one end, an injector on the other, and battery voltage to the injector with alligator clips and speaker wire to a battery and blown it through to clean them out. That was right around 1990 on a Sterling 827SL, what a heap of crap. Many braincells died to clean those injectors. I mention this stupid story because I always wondered if you could do something similar to test for a bad pump. Maybe unplug the fuel pump, open the fuel line at the rail, add a few feet of hose filled with gas to briefly feed the injectors, compressor hose on the other end with a blow gun around 50 psi and fire it up for testing purposes.. This is likely a really bad idea, but it sounds like something I would do. So don't do it, because it might be awesome or carebecue.

If the fuel pump is good, and the timing is good and the spark is good, then compression or fuel injectors. The fuel injectors are always getting battery voltage once the ignition is in the RUN position. The ECU operates the injectors by rapidly opening and closing the ground side of the circuit. You can check for power between the hot side of each injector and a ground to the block with a multimeter, but the ground side of the circuit switches too fast to tell if the ECU is opening/closing them. But, you can visually inspect the operation of the injectors with a NOID light. it slips into the wires on the injector connector and flashes every time the injector opens and closes. If it doesn't flash then the ECU is not switching the ground or the ECU has a bad ground connection.
BrianC72gt is offline  
Old 08-29-2018, 05:13 PM
  #23  
AudiWorld Member
Thread Starter
 
Join Date: May 2018
Posts: 53
Default

Originally Posted by BrianC72gt View Post
Does it run at all? Or does it run badly? Inconsistently, like stumbles, then good, then stumbles again?
After clearing codes, do the multiple misfire codes come back?
I don't know if a defective TPS would cause the car not to run. Would a bad TPS cut power to the fuel pump? Dunno.
What makes you think one bank is not firing at all? Do the headers on that side get hot?

Next steps: Clear the codes, crank and see which codes come back. Are any of the codes deal breakers? Next Check fuel pump output and pressure, then noid lights on the injectors.

I would test the fuel pump output next. An Yes, I've seen misfires just on some cylinders with a bad fuel pump that is in the throes of dying. Hotwire it in the trunk (or wedge the FP relay contact points closed and key in RUN to power pump continuously), pump out at the fuel rail hose in the engine compartment. It should pump out fast and forcefully. A pressure gauge would be better still. Never used one myself. Do local auto parts stores rent those out? If the gas is a couple years old, it could be off. If the pump works and the gas is more than a few years old, pump it all out to gas cans, and put some clean gas in the tank - a few gallons.

How is your fuel pump flow? I've done some sketchy things to clean injectors removed from the car, like filled a length of fuel hose with lacquer thinner, stick 50 psi of air hose blower on one end, an injector on the other, and battery voltage to the injector with alligator clips and speaker wire to a battery and blown it through to clean them out. That was right around 1990 on a Sterling 827SL, what a heap of crap. Many braincells died to clean those injectors. I mention this stupid story because I always wondered if you could do something similar to test for a bad pump. Maybe unplug the fuel pump, open the fuel line at the rail, add a few feet of hose filled with gas to briefly feed the injectors, compressor hose on the other end with a blow gun around 50 psi and fire it up for testing purposes.. This is likely a really bad idea, but it sounds like something I would do. So don't do it, because it might be awesome or carebecue.

If the fuel pump is good, and the timing is good and the spark is good, then compression or fuel injectors. The fuel injectors are always getting battery voltage once the ignition is in the RUN position. The ECU operates the injectors by rapidly opening and closing the ground side of the circuit. You can check for power between the hot side of each injector and a ground to the block with a multimeter, but the ground side of the circuit switches too fast to tell if the ECU is opening/closing them. But, you can visually inspect the operation of the injectors with a NOID light. it slips into the wires on the injector connector and flashes every time the injector opens and closes. If it doesn't flash then the ECU is not switching the ground or the ECU has a bad ground connection.
At times it has jumped up a few RPM, it only runs when I keep my foot on the gas. Yes it runs, and reason why I say only one side does is because the codes tell me it doesnt, it says cylinders 5,6,7,8 are misfiring, and also I hear popping in the exhaust which means fuel isn't burning in the cylinders.

Also only one catalytic converter gets smoky, the other one gets warm but not nearly as hot.

I would be astounded if the fuel pump was my problem. But i feel like giving it a shot now...
Captain Sweeney is offline  
Old 08-29-2018, 05:36 PM
  #24  
AudiWorld Member
 
Oxnardo Ring's Avatar
 
Join Date: Jul 2018
Location: SoCal and On The Road
Posts: 91
Default

The fact that it's only on one bank should be a strong clue... meaning "What is it that only affects one side?". So I'd work through the list of things that run off different hardware from right to left.

Such as.

There are two banks of those coil drivers, but you've addressed those (although I'd double check the wiring). You could always swap back.

Do the fuel injectors have different fuses for right and left bank? NO. At least on the Motronic system all fusing is on the primary power for the ECU. So, no separation of fusing for those. It's probably worth checking the footwell fuses, down where the fuel pump relay is. Ignition power-distribution is via those two panels.
It seems pretty implausible that you'd have enough fuel pressure on one side of the fuel rail but not enough on the opposing bank.... unless you had a huge issue with the rail clogged/gunked/varnished from sitting.

O2 sensors are in Right and Left bank too....

Will keep thinking of stuff that separates "left" and "right" banks.

Tom

Last edited by Oxnardo Ring; 08-29-2018 at 06:02 PM. Reason: Editing for completeness.
Oxnardo Ring is offline  
Old 08-29-2018, 09:30 PM
  #25  
AudiWorld Member
 
Join Date: Jan 2004
Posts: 585
Default

I still wouldn't rule out the fuel pump. At this age it could start to be crazy stuff like the ECU has two sets of injector drivers and one set is on the fritz. But it was running fine intermittently not long ago, and the car's history is a mystery. I don't want to hurt my head with exotic failures. Every A8 fuel pump dies around 100k miles. Some freaks have made 150, but that is the far end of the distribution curve. The most common no start on all D2s is the fuel pump, unless it is a pre FL model, then it is 1) POS, and 2) fuel pump. As to one bank misfiring and not the other, I'm sure on a dying pump, the injector closest to the Fuel Pressure Regulator sees the highest or lowest pressure of all 8 and the farthest vice versa. Or a bunch of valves are bent, but that is poop, so let's say fuel pump. And you cleared all the stored codes, then new ones came back, Yes?

While at Kierstin's Biergarten tonight, wolfing down some tasty Jagerschnitzel, I drank a big stein of german beer while meditating "think german, think german" to aid in empathic diagnosis while the Kraftwerk burbled from the speakers on the paito. That Kierstin is a feisty one. I explained the whole problem to the beer and sent it on its way. It fizzed knowingly. Not sure it fully understood, I sent in some reinforcements. I mentioned the pressurized fuel line trick and it said,"Nein, Das Auto nicht in brand setzen" Which means: " That is an awesome idea, you should do it!" or somethng about smores.

Anyway, we all agree you should really test the **** out of that fuel pump on a well charged battery.

Any chance you are in Northern CA? Because I can't give you all this ****ty advice, and not fix your damn car.

Peace,

Brian

Last edited by BrianC72gt; 08-29-2018 at 09:40 PM.
BrianC72gt is offline  
Old 08-30-2018, 06:29 AM
  #26  
AudiWorld Member
Thread Starter
 
Join Date: May 2018
Posts: 53
Default

Originally Posted by BrianC72gt View Post
I still wouldn't rule out the fuel pump. At this age it could start to be crazy stuff like the ECU has two sets of injector drivers and one set is on the fritz. But it was running fine intermittently not long ago, and the car's history is a mystery. I don't want to hurt my head with exotic failures. Every A8 fuel pump dies around 100k miles. Some freaks have made 150, but that is the far end of the distribution curve. The most common no start on all D2s is the fuel pump, unless it is a pre FL model, then it is 1) POS, and 2) fuel pump. As to one bank misfiring and not the other, I'm sure on a dying pump, the injector closest to the Fuel Pressure Regulator sees the highest or lowest pressure of all 8 and the farthest vice versa. Or a bunch of valves are bent, but that is poop, so let's say fuel pump. And you cleared all the stored codes, then new ones came back, Yes?

While at Kierstin's Biergarten tonight, wolfing down some tasty Jagerschnitzel, I drank a big stein of german beer while meditating "think german, think german" to aid in empathic diagnosis while the Kraftwerk burbled from the speakers on the paito. That Kierstin is a feisty one. I explained the whole problem to the beer and sent it on its way. It fizzed knowingly. Not sure it fully understood, I sent in some reinforcements. I mentioned the pressurized fuel line trick and it said,"Nein, Das Auto nicht in brand setzen" Which means: " That is an awesome idea, you should do it!" or somethng about smores.

Anyway, we all agree you should really test the **** out of that fuel pump on a well charged battery.

Any chance you are in Northern CA? Because I can't give you all this ****ty advice, and not fix your damn car.

Peace,

Brian
Lol dude, sadly I'm in Massachusetts. Although I'd love to be in California. I'll give the fuel pump a shot. I'll also check out the ECU, and double check those fuses again. I appreciate all the help, especially that last story lol, you should be a writer. I'll send an update on how it goes by this evening.

​​​​
Captain Sweeney is offline  
Old 08-30-2018, 07:43 AM
  #27  
AudiWorld Member
 
Join Date: Aug 2011
Location: Houston
Posts: 289
Default

How much flow were you getting thru the old filter?
I'd guess, if it was in place for your estimated period of time, that pump is toast.
If the pump has been in place since the D2 came off the line, it wouldn't be a bad move to replace it. The major issues with Audi or any other brand of car, is how many miles are on the car. If you do not have repair records, going 140,150k miles tells me, it's time to renew most everything (except the engine.)
When I located my D2, I factored in that replacing most everything was part of the purchase. Hard to swallow but after it's all over, you can drive for another 7/8 years without the worry of heading anywhere.
pocketchange is offline  
Old 08-30-2018, 08:04 AM
  #28  
AudiWorld Senior Member
 
Join Date: Apr 2001
Posts: 1,762
Default

Originally Posted by pocketchange View Post
How much flow were you getting thru the old filter?
I'd guess, if it was in place for your estimated period of time, that pump is toast.
If the pump has been in place since the D2 came off the line, it wouldn't be a bad move to replace it. The major issues with Audi or any other brand of car, is how many miles are on the car. If you do not have repair records, going 140,150k miles tells me, it's time to renew most everything (except the engine.)
When I located my D2, I factored in that replacing most everything was part of the purchase. Hard to swallow but after it's all over, you can drive for another 7/8 years without the worry of heading anywhere.
Gary, send me your address I found the mount and am prepared to ship it to you.

-Richard
audinutt is offline  
Old 08-30-2018, 11:51 AM
  #29  
AudiWorld Senior Member
 
Join Date: Oct 2005
Posts: 816
Default

It's easy to try a shot of starting fluid to see if it smooths out, or if this has no effect. You can even shoot into a vacuum line if you do not want to take out the air filter.
jfrahm is offline  
Old 08-30-2018, 01:06 PM
  #30  
AudiWorld Member
 
Join Date: Jan 2004
Posts: 585
Default

Originally Posted by jfrahm View Post
It's easy to try a shot of starting fluid to see if it smooths out, or if this has no effect. You can even shoot into a vacuum line if you do not want to take out the air filter.
Speaking of vacuum line, I believe your engine has some hoses for its version of a PCV system in the valley of the intake manifold. They can leak air causing all sorts of lean running/no running.

But at this point my number 1 suspect would be the fuel pump.
BrianC72gt is offline  

Thread Tools
Search this Thread
Quick Reply: Audi A8 with LOTS of new parts soon parting out


Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: