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Poor running 87 S4 after warm up

 
Old 04-09-2019, 01:33 PM
  #16  
Kevin in Atlanta
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New pump and filter - identical results? What am I doing wrong?

Counted to thirty and no improvement.
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Old 04-09-2019, 04:46 PM
  #17  
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Originally Posted by Mrmerlin View Post
how long was the car sitting before the engine repairs took place?
have you taken a fuel sample?
or removed the tank sender to inspect the in tank filter?.
Are any of the fuel lines crushed on the bottom of the car?
A misplaced jack can easily do this
Did you check for a mashed hardline like Stan suggested?
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Old 04-09-2019, 04:53 PM
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Kevin in Atlanta
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I figured it out! A bad ground.


Listening to Kevin Wilson's suggestion I tested the pump directly with the pump disconnected to ground.

Here's what the pump pumped:


Correct amount captured.
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Old 04-09-2019, 09:23 PM
  #19  
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Nice one...
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Old 04-09-2019, 09:40 PM
  #20  
Kevin in Atlanta
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Cleaned the grounds... No improvement. Apply battery voltage to pump and use the pump ground and plenty of fuel. Rules out the ground.

12.02 volts to the pump and at the relay. Battery voltage is 12.36.

Not enough voltage as near as I can tell.

Very strange...
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Old 04-09-2019, 09:50 PM
  #21  
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What is your voltage reading from (+) battery post to a ground point on your body inside the rear hatch? Say, where the hatch release mounts.
If still low....bad battery ground strap?
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Old 04-09-2019, 11:16 PM
  #22  
Kevin in Atlanta
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12.43 from positive to MP VI ground. Same to hatch motor release mounts.
12.36 across the 30-15 on the relay
With relay jumped 11.20(ish) at fuel pump fuse (#42) << Sounds low.

I need to revisit reading at the pump in the morning.
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Old 04-10-2019, 01:39 AM
  #23  
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Interesting. It seems really odd to me that 0.5 volts would cause the pump to run that much slower, but you've already proved that something is different with your comparative jug/30 second tests.

I went back a re-read you original post--a few times. The fact that you are getting 60psi at the rail when hot or cold really adds to the mystery.
Have you ever been able to cause the condition in your garage? Eg., hold the engine at 2500 rpm or so for 60 seconds, and watch the pressure? It certainly make sense that under load (driving around) the fuel pressure could drop enough to lean-out and cause those symptoms, but I would think you could replicate it in the garage if it is indeed a kinked hose causing the drop in flow and eventually pressure.
When you drive around and the symptoms come on, and then you stop and turn the car back on and let it idle, does it start to act normally after 30 seconds or so, presumably allowing the pressure to rebuild up to 60 psi while not under load?
Other than that, I am curious how your LH would do in another car. I fought a very similar situation on a non-928 with Bosch L-Jetronic, but I could get it to replicate in the garage if I raised the rpm up to about 3500. Like you, I installed a FP gauge under the hood, but couldn't watch it on the road. After a lot of what you've already done (checking grounds, injectors, testing TPS measurements, pressure testing, flow per second testing, swapping out pumps and filters, running lines directly to the pump from a gas can, with a remote switch to the pump, etc.)....it ended up being the FI control unit gone mad. Replaced it, and then kicked myself how much time I had spent smelling like gas.
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Old 04-13-2019, 09:11 PM
  #24  
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I decided to investigate a bit more...

I went ahead and did a dry compression test engine warm with some surprising results. 1-4 130, 130, 119, 119 ;5-8 175,170,165,160

I even rented another compression tester - same results.

That lead my wonder if the cams were timed correctly, So, I tore into the PS. Timing on the PS was spot on and the cams were correctly set.

I found the fuel line to the front damper slightly kinked - hoping that was the issue I put it all back together with a new fuel line.

Start it up freely spins up to 6k rpm without any hesitation. Seemed a bit healthier, let it come up to temp and topped off the coolant.

Test drive - same symptoms - runs great for 1/8 of a mile and slowly falls apart. I continue to believe as others do there is a fueling issue.

New symptom was engine stall and instant recovery - dash lights come on and go away. Exhaust pops definitely come from the DS exhaust now. Add an throttle and absolutely no response. Have to give it only light throttle to nurse it home.

In retrospect, I should have done a compression test before I did any work - lesson learned. I've parked it for now. Other projects to finish.

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Old 04-13-2019, 09:38 PM
  #25  
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Wow, that is frustrating. With exhaust pops I certainly think you have a timing and/or fuel starvation/ratio issue.
After you nurse it home, have you figure out how long it has to rest (cool down?) before you can go back and it will start okay? Just curious if that points toward the issue/solution.

Those low compression numbers on one bank are definitely telling you something. Just like you, I would have checked cam timing, which you did.
Beyond that, I'm going to have to leave it to the "engine guys" to diagnose that compression discrepancy. I certainly have read threads about similar readings, and recall the solution getting pretty heavy engine-techie.
(You sound like me...had enough with this frustrating project....let's move on down the list of other projects and come back later!)
Good luck, keep us posted.
Jason
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Old 04-13-2019, 10:26 PM
  #26  
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Are any of the fuel lines crushed on the bottom of the car?
A misplaced jack can easily do this
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Old 04-13-2019, 11:11 PM
  #27  
Kevin in Atlanta
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Originally Posted by Mrmerlin View Post
Are any of the fuel lines crushed on the bottom of the car?
A misplaced jack can easily do this
I will take a look in the morning, thanks.

I need to add the following symptom:

The plugs are a glossy black - all of them pretty much. I replaced the plugs because this is how they looked. Maybe that's a clue.
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Old 04-14-2019, 12:44 AM
  #28  
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check the fuel lines before you chase anything else please
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Old 04-14-2019, 12:57 AM
  #29  
Kevin in Atlanta
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And when I say it runs well for the 1/8 of a mile I mean it runs great. Loads of power, shifts great.
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Old 04-15-2019, 07:11 PM
  #30  
Kevin in Atlanta
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Still chasing stuff. What color should my spark be? Spark tester and even the plug sparks are yellow when the engine spins.
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