89FrontPorsche

89 S4, ~180,000 miles. Was driving home, started "cutting out" for about 1/2 second then recovers, then does it more frequently as time passes (over 5-10 minutes) then no acceleration, won't idle but on a few cylinders, then dies. Attempted re-starts "sort of" successful. Might start and begin to idle fine then over a half-minute, goes to running very roughly, then dies.

First instinct is ignition control unit/module. Very reminiscent of what my '87 did when that board died. Porsche technician (friend of mine...factory-trained) says to spray mass flow cleaner over the wire in the intake, might be rpm sensor on bell-housing. Wants me to check those before spending big bucks on a replacement computer.

If these symptoms seem familiar to anyone, let me know. I'd be most grateful. Car is sitting, I killed the battery with numerous re-start attempts. Relays on the board are doing their clicking and seem to operate normally. Fuel pump is working. Maybe clogged fuel filter?

Car did this once before a week ago. Let it sit then after 15 minutes, it started up, ran fine and I drove it around for several days with no trouble...then it did it again yesterday with the barely noticeable half-second cut-out then increase in frequency of that until it cuts off when accelerator pressed down and then it just runs very badly and quits. I'm having a funny notion that after the battery is charged up, I'll go to start it and it'll start right up, thus making the mystery even worse. But my instinct is telling me that the ECU is probably lunched.

Any suggestions/help is welcome

89FP

Stromius

CPS / CPS Connector, coil connections for corrosion for starters. For grins check resistance on the Temp II pins to ground.

Bill Ball

If it's the CPS, you will get no spark. And there will be no tach signal. That doesn't rule out the EZK or, I suppose the ignition final stage, but they rarely fail. With a final stage failure, you would still have spark on 1/2 of the cylinders.

If it's still "dead", I would pull some spark plugs and see if there is spark when you crank the starter. If there is, then I would determine if fuel delivery is the issue. If after cranking but not starting you pull a spark plug and find it dry, that would argue the injectors are not firing, which is likely with a failing LH or a short anywhere in the injector harness. BUT, first, even though the LH, EZK and fuel pump relays are clicking, swap them out with other known-working "53"s, such as the horn and ventilation blower.

The car will run with a dirty or failed MAF, although not well. I know, I drove 20 miles home with a failed MAF in the limited "limp home" mode that the LH provides in that circumstance.

928 GT R

I had similar symptoms on my 90 GT. After much consternation it turned out to be the MAF...

89FrontPorsche

Near as I can tell, the whole problem is due to bad electrical connections with the relays. I took out all relays that had anything to do with fuel delivery and the LH relay and the ignition control relay and cleaned all the terminals both male and female.

The LH relay had one terminal that was black. Almost as if it had paint on it. (Arcing?) I sanded them all to a shine as well as the receivers and sprayed contact/electrical cleaner in all the slots and the car has run fine for today.

After I charged the battery up, I installed it and the car ran fine. This was before I cleaned all the relay and fuse terminals. Knowing this car has had intermittent electrical gremlins...I decided to examine all of the connections as well as some in the engine compartment.

As I said, runs, drives fine now. I have so far saved some money by not having to replace the MAF or the LH computer.

We'll see how it goes. Thanks everyone for the advice. Seems fine for now.

89FP

Mrmerlin

if you have not already done this then clean all of the fuses as well,
and the battery terminals,
and the 14 pin connector under the hood

Landseer

I'd replace the battery ground strap.

Immediately, based on what we have collectively seen here regarding failure modes for the symptoms described.

89FrontPorsche

OK, here's the latest. Replaced the MAF. Given the car's undocumented maintenance history, I was gonna change it anyhow. Some may say this is foolish but I'm in aviation and changing a part before it fails is a good way to keep motoring about happily.

I did notice that the car ran much better...uh...at first. Started right up then, it stumbled and idled poorly. Then it cleared itself up and I took it for a short test drive. Halfway through that it went into limp-home-mode. I got it home, examined for loose connections, found none and shut it down. Gave it a five count and started it back up. It then ran just fine.

Drove it to the store to pick up my dinner and when I got home, (now here's the A-HA! moment), I was sitting there letting it idle and as I listened to the fuel pump, it started whining higher in pitch then stopped whining altogether. Simultaneous with this, the engine ran poorly. (Of course) Then, the fuel pump started whining again and all was well...but the problem persisted and I'm thinking a ready-to-fail fuel pump is the bigger culprit.

I have one on the way that I ordered some days ago along with a new filter. I will check the strainer screen, etc and make sure all is well. Seems to answer my hesitation problem while at cruise and the flat out not running at all.

I think sometimes a fuel pump can sound like it's running but if the internals are in bad shape or there's a clog, it can kill the whole thing....obviously. But...it was a planned change item anyhow, again, due to the no-maintenance history on this car.

I also did the oil treatment thing and the noisy lifter shut up. I have oil filters and am a fan of 20W-50. It gets toasty here this time of year and all my front-engine cars have liked the heavier grade oil. Helmut Breitfeldt, an old friend of mine from Tucson (long passed away) swore by it. He was the dealership's oldest mechanic and --- used to be Rommel's staff car driver.

He would scold me about things and I would listen very carefully to what he told me. He was a very good mechanic, to say the least. I still miss him to this day.

So, in a few days I'll change the fuel pump. Hopefully that will return the car to normal drivability.

worf928

You may have an in-tank pump also (OE for '89+). It's likes to disintegrate and send bits through the main pump.

Also note that the LH is adaptive. If you disconnect the battery or replace any component in the fuel/air system (like the MAF) you should expect some oddities at idle until it adapts again.

At 180k-miles - and no documented history - you have a lot of potential for lots of things to be 'ready-to-go.' A good on-the-bench cleaning of the fuse panel is a good start and picks up where you left off. You can likely find a number of threads on this. Here are the high-points:

- remove the fuse panel and ECU brain case and take digital pictures of how everything is routed.
- throw away all the fuses, but note which fuses are the worst.
- remove all the relays. Throw away any '53' relays with a metal shell (those are OE and 25 years old) and replace them with new relays. Check the pins of the other more-expensive relays. The EZK relay is a 53 relay with a fuse tester. It's expensive. You can replace it with a normal 53 relay if you are not inclined to buy the OEM relay.
- using a contact file and/or 2000 grit sandpaper, clean oxidation from every female spade connector on the panel and every male connector for the harness plugs. Pay special attention to any connectors that correspond to fuses or relays that were bad.
- clean the ecu pins
- use a good 'conditioner' on the pins like Stabilant or something similar that will prevent corrosion and enhance contact.
- check the back side of the panel for evidence of shorts, broken insulation, loose connections etc.
- look for a signs of moisture. If you find any, you'll need to do some 'water tests' to find the source.

89FrontPorsche

Thanks Worf, very sage recommendations. Most of the cleaning of posts, etc in the board has been done by me. I've also replaced many 53's already.

I'm curious as to how I would figure out if my car had the in-tank pump. Is it a VIN # thing and/or any give-aways when the cover is removed? I'm pretty sure it's a &#@& to change, no? Not that I can't do it...just hate the smell of gasoline. It makes me sick.

Can I hold a flame over the open fuel sender hole to see if it's down there? (just kidding. Would never do such a thing...although I've known some fellers who might)

928 Intl has an internal pump but it's listed as "954" and I have no idea what that means.

http://www.mailordercentral.com/928i...608%20013%2000

Looks like it goes in a hole in the bottom of the tank and is sealed with an o-ring with the electrical terminals external to the tank.

Naturally, this can all turn out to be much more complicated than what's in the brochure. However, I'm used to that and "really look forward" to being under my car on a hot day and having my car run properly. Any photos or links as to where this little critter might be?

Thanks very much. Oh how in the 80's I could've used the internet for my 944 problems and rebuilding my first 928. Guys like you and everyone who's responded are perhaps the latest proof that humans do actually endeavor to help one-another. I, for one, am truly grateful.

89FP

In my reading so far, 89's don't have but one pump. Or am I missing something?

MainePorsche

Look to the fuel line that exits the tank and goes to the external fuel pump. If there are two (I believe) electrical connections at the union where this line meets the tank, then you have an in tank pump.

89FrontPorsche

Roger, copy that. Will have a look-see. (hoping not to find one)

MainePorsche

Found a pic of what you would if in tank pump present. There are two electrical contacts.

newworld

Curious...when u run car with maf and maf unplugged what was difference in idle and car running?

worf928

What MainePorsche wrote above.

It has two connections that are in parallel with the fuel pump connections. So, if the leads terminate at the pump you don't have one. If they split at the pump and one side runs over to the other side of the pump then you'll see the connections where the supply hose to the pump exits from the tank.

PET indicates '89+. Might be a mid-year thing.