Spun

Need help on an 89 S4 auto that is running like it is choking after 1-2 min on the 1st run. It progressively gets worse after turning it off.

I spent a fair amout of time reading and trying things from prior posts (see list below).

I have had a similar problem on my cab when there was a ton of paint dust in the tank... it would run strong for 5 min and then choke. This does not go that long before choking.. and the recovery time and effect differs each time.

Quick situational info on the car is: the owner parked the car two months and the battery drained. She was having big leaks on the tranny fluid cooling lines. I fixed those today and the air pump.

When she fired it up yesterday that is the 1st time with the car running rough. I did all the work on the air pump and tranny lines last night and today, so my work did not cause the issue... I looked for areas the ATF might have coated something causing the issue and I could not see anything...

I have fired up the car many times today working through the list below. On the 1st start of the day, she runs strong, fires up, no hesitation. After about 1-2 min she seems to be choking off. I would not say like running on 4 cylinders, because then she would keep driving. She will eventually choke off completely and die when I let off the gas.

If I let it sit, it will run a little better for a min then repeats. The car will also die some times when coasting. It seams like a fuel pump issue (internal if guessing), but I don't have my pressure gauge with me for the fuel rail or an internal pump here.

For thoroughness I have done the following:
o swapped MAFs for a known good one
o swapped LHs for known good
o Swapped EZ for known good
o checked fuel dampeners
o checked for "sucking sound" at fuel tank
o swapped EZ, LH and fuel pump relays
o checked fuses
o disconnected O2 - no change
o removed the battery for 30 min and rechecked - no change
o checked plug wires
o I cleaned grounds a while back ago, so did not do that again.
o checked power at the two fuel pumps. Both will work (make noise) when I wire up 12V. I let the external pump blow some fuel out in reverse to see if anything would come out. Just clean fuel.

Spoke with Roger at 928rus and I am going to get a strainer for the internal pump replace... I am not positive that is the issue, but it seems to be the logical remaining issue.

I did not check the CPS. Since it is running good first, the choking out and then dying, I did not thing it would be the issue.

Any other thoughts? Thank you
Emerald

Hilton

Your description of the sequence of events sounds like its a problem with the O2 loop. From what you say, and the timings, it runs okay open-loop, and then chokes when it goes closed-loop.

The fact that unplugging the O2 sensor didn't make it run noticeably worse after a minute or two supports that. First culprit would be the O2 sensor itself - check for frayed wires where it passes through the heatshield, and then test for signal from it.

Spun

Will do...

dr bob

Check the vacuum line running to the trans. If you accidentally pulled it off you have a big vacuum leak and the symptoms you describe.

worf928

IMS Relay triggering or not?
Access to a diagnostic tool? ('89 has 19-pin port, reading codes is sometimes useful.)
Have you checked Temp-II resistance at ECU pins?

Spun

Have not on the temp II, on the vacuum line, would that act up after a min or start that way?

In either case, I'll check vacuum.

Spun

Ok, so the solution turned out to be simple. I did crazy on the search and Bille (Chief Turn a Wrench) Ball took a look and found we had big time corrosion in the wires and coils... rookie mistake on my part not to check that the PO did not really put new wires, plug, caps and rotors on..m dee-dee-dee.

Funny part is my trouble lies in the step function that it worked and went to hell-in-a-handbasket...

... so to the simple issue. 928Dame took her baby to a Mercedes mech (good guys really) to look at the car and the did a full eval. ssome how they flipped wire 8 and 3 at the left side cap... and there ya go... really, I'm an idiot...

So three days full crazy Emerald speed labor, all electronic system checks, etc and it's F'N plug wire swap...

Good news is I did a sheet load of other items that needed done like tranny line fizes, cam cover gaskets (more oil in the plug well than I have ever seen), sonnection cleans, ground cleans, plugs, wires, caps, rotors, coils, and much-much more.

This baby is down to a top end refresh from being a new 89!

Anyway, moral of the story is, if a non-928 clown touches a 928, go back to basics and look for stupid first...

On the road now running, err, the speed limit up to sierra Neveada brewing company for a victory beer...

Thank you again Chief Turn-a-wrench... you are one of my 928 heros!

E