Hi all;

No real problems for a while now. Did a long trip one week, made it home with about a 1/2 gallon of fuel left in the tank. Let it sit a few days. Filled the tank. Within minutes, the car started to act, on and off, like it was just running on a few cylinders. Within an hour of driving, it was normal again, for the duration of that tank... (exhaust sounded extra loud whenever it was acting weird...)

Another full tank - no problems at all.

Again, almost out of fuel. (1 gallon or so at most - let it sit a few days...) Car died feet from the pump. Filled it. Wouldn't start. Cranked on and off until the battery was dead.

Used jumper cables. Apparently flooded it. At one point, the rear muffler smoked extensively - seems to have had a fire inside of it for a bit...

Eventually, the car started and after a minute or two of running, it acted perfectly normal.

Used 1/4 tank - let it sit 2 days. It barely started and ran CONSTANTLY like it wasn't firing all cylinders for a 25 mile trip. Made it, but it sounded weird and acted like it was just running on 4...

An hour later - started normally... Ran fine. Shut it off...

2 hours after that, it again started normally and more or less ran properly. There were SOME moments where it hesitated a bit, and made the noise, but pretty much was fine...

I have a 12 hour drive coming up on the 29th. A trusted expert said after hearing the first symptoms that it sounded like the aux fuel pump. When it broke down at the gas station, I did swap the horn and fuel pump relays - no change...

Does this sound like that aux pump failing? What should I check? I'm torn about driving it out of state Sunday - it seems like it would make it, but who knows?

If I can confirm this diagnosis, I'd like to get the needed parts rushed to me and swap that pump before the trip. Can it be a plugged fuel filter? Computers? Anything else worth mentioning? Any advice would be most appreciated. That weekend trip has been planned for months and I'd hate to not take the 928 if possible. Arrrrrrrrrgh...

Of course, if there's anything else I can mention, please ask. I'll be monitoring this post as much as possible. Need to act very fast if it sounds like a bad choice to drive it as such...

Remember - I've been through 2 tanks without issue since I first noticed this... Thanks so much...











Nick - Hazleton, Pennsylvania

1989 928S4 - Auto

 

Hi Nick, have you confirmed that you do have a 2 pump system?? its easy remove the fuel pump cover under the right rear of the car and see if there are 2 wires connected to the outlet fitting at the bottom of the tank.
Usually on a 2 pump system if one pump fails its wise to replace both of them. Also it is common to have the inner pump hose fail and cause the inner pump to not function. So it could be a pull the inner pump and fix a hose or worst case replacing both pumps , that is if you do in fact have 2.
If you only have one pump then you might try adding some marvel mystery oil and running it backwards this can flush out the pump .
And replace the fuel filter

 

I'll check ASAP, probably in the AM. I thought ALL 89 S4's have two???

 

This is the same behavior that I had when my MAF (mass airflow meter) died.

Smoke from the tail pipe, and felt like it was only running on a couple of cylinders.

Did you also get a funny smell from the tailpipe?

When I had the problem, I unplugged my MAF and then started the car. It ran better off the failsafe map. Would not run when the MAF was plugged. it.

I had to get a rebuild (928Intl) to fix my problem. Hopefully your fix is less expensive.

Good luck

 

The MAF was replaced with a questionable used one a few months ago when it was claimed that the 1st of 2 shops had "lost it..." It IS intermittent though - if it's a bad MAF, wouldn't it be "on or off" rather than sporadic?

(I'll try disconnecting it if this happens again though...) : )

I have put about 3,000 miles on the car since that MAF was changed. The problem just started recently and seemed related to low fuel levels until today.

Aaaarrrrrrgh!!! : ( Worried about that out of state mini-vacation coming up Sunday...










Nick - Hazleton, Pa. - 928S4

 

LISTEN to the car. It is trying to tell you something. It may be telling you that you have a failing coil or some other problem with the ignition system.

Your car has the ignition monitoring circuit. Do a search for "Green" and "Red" LEDs and use the results to learn what the IMU does and why. You need to determine why your car runs intermittently on fewer than 8 cylinders. It isn't a failed fuel pump.

Or keep doing what you're doing with 4 cylinders worth of fuel burning in your exhaust and you'll be able to park the smoking remains of your 928 next to Joey's burnt out hulk - that is, if you manage to get out of the car before you are a crispy critter too.

SRLSY.

 

When that had happened - smoking exhaust after lots of cranking - some stranger stopped by and claimed to used to work on foreign cars like this one. He said that the ignition system won't fire without 10 volts minimum, and that it probably wasn't getting a spark because I had drained the battery.

I hadn't thought though about 25 miles of gas intended for 4 cylinders getting through the system.

Honestly, I felt that it was ignition related at first. I checked visually for obvious problems but found nothing.

Not sounding like it's wise to take this car on a 12 hour drive Sunday, I suppose... : (

Are you certain it's NOT a fuel pump??? BTW - with the FIRST INSTANCE of this problem that I described, I found that flooring the car caused it to suddenly act normal. It would barely move, but if I floored it, it'd hessitate just a little, then go screaming along.

Today though, nothing changed it. And then after just sitting for a bit, it fired right up and ran more or less normally for the return trip...

I'm getting the feeling that there's a million possibilities here. Since it MAY be running normally now, for a while at least, how can one properly diagnose it???

I LOVE this car but a low mileage Lotus Elise is apparently trying to psychically communicate flirtatious words to me... : ( I'm quickly approaching 30K invested in an 89S4 after just 3000 miles of fun...






Nick - Hazleton, Pennsylvania

 

What is driving me crazy here, thinking about things that could be causing this problem, is that one moment it's fine, and without anything changing, other than the minute hand on the clock, that it's bad again. Then, for no logical reason, it's good again...

The first time this happened, higher rev's fixed it more or less. When it got messed up again at the gas station, and I got it running, it would demand to be held at 4000 rpm's. Any lower and it would stall...

At that station, once it stabilized, I just let it idle for 10 minutes perhaps and it acted perfectly for 100 miles of driving. Then, two days later, it ran rough from the start, and stayed rough for 25 miles. THEN, it fixed itself, without touching a thing...

So frustrating... Actually, I'd be fine, but I really hoped to drive it on the vacation on Sunday.

I appreciate all advice, and will try to learn what I need to here, but my own "intuition" tells me that it is indeed related to getting a spark, and perhaps a coil is failing, or even has a bad connection to one of them...







Nick - Hazleton, Pennsylvania - 1989 928S4

 

when the car starts running on 4 cyls stick your head under than car and look at the cats if they are glowing red you have other problems besides the fuel pump

 

Nick,

I think I can understand your frustration. I have been there ...

The behaviours you are identifying are all similar with what I experienced (again) with my MAF.
It was running really well, then started to stumble ... then would barely idle. I had to pump the gas peddle like crazy just to keep it running. Once I got the higher rpms, it started to run (well, more like a surge). I limped home but used quite a bit of gas to get there. Now having benefited from this site, I never would have tried to limp home (it was running real rich). My your daughter was with me so I was important to get home (and I had to refrain from using the Porsche technospeak words that help when repairing the car.)
(Actually research once I got home showed that I would have been better to unplug the MAF and then drive home - would have been better for the car and the catalytic converter).

The more you describe the problem, the more it appears similar to my MAF problem. Good luck ... it does not sound too bad.

Glenn

 

Before you drive the car again, remove the cover over the ECUs - this is the carpeted cover on the passenger's kick panel. Look at the bottom of the ECU package and find the Ignition Monitoring System Relay - a clear box about the size of a pack of cigarettes.

Leave the cover off. When you drive the car, if it starts acting as if it is running on four cylinders, look at the clear relay box and see if there is a red or a green LED shining. If so, one of the two independent ignition systems has failed (or the monitoring system thinks that it has) and the Ignition Monitoring System has killed the injection on those four cylinders to keep you from burning the car to the ground.

Check the coil wires very carefully, and route them away from any metal or wire harnesses.

 

<groan> ... what foreign cars are "like this one?" If the 911 and 944 mechanics can't keep 928s running...

On a 928, at start-up, in general, if there is no spark there is no fuel. If the ignition system (that would be the EZK computer) doesn't have enough electron flow to generate the signal it sends to the ignition amplifiers for spark, it probably isn't going to have sufficient umpf to turn on the fuel computer (LH) which then won't be able to activate the fuel pump relay.

Your description indicates that it is intermittent. It probably isn't something you are going to find with your eyeball.

No.

99% based solely upon the description in your first post. It is possible that your problem is fuel related if you are 100% sure that the car only runs like crap when it has an almost-empty tank. In that case it may be crud from the tank getting ingested into the pumps. But, mostly, a fuel pump is like a rodent. It is either alive. Or it is dead. If it is sick it transitions to the "dead" state very quickly.

This is also inconsistent with a fuel pump problem.

I know you've been through a lot of crap and money with your car.

The next time your car is acting like it is running on 4, remove the carpet section in the passenger foot well that covers the two computers. Look at the bottom of the computers and find a clear plastic relay. This relay as two LEDs - one green and one red. If either are lighting-up then the relay has decided that 1/2 of the ignition system has failed and has therefore cut fuel to 1/2 of the motor. Best find that clear relay now, so that you know where it is.

Regardless if whether one of the LEDs is lit you don't want to run the car for any length of time on only 4 cylinders.

The symptoms you describe are consistent with intermittent failure of 1/2 of the ignition system. Find threads on the the ignition monitoring system (and/or relay). There are plenty of them, and they will give you a good idea of how to isolate the problem.

Last, your 89 has the diagnostic port. Use of the Hammer, Spanner, or the other software tool that cannot be named on Rennlist, with that port has a high probability of pointing you in a useful direction.