Porsche Enthusiasts Club Forum

Hi All,

I'm just sitting in a hotel in France since the 928 has been unwell and dumped me and my wife here. We wondered if anyone can shed some light on our failure?

We were doing quite well, 200 miles in from Calais, when overtaking a lorry doing around 90mph, the car shifted into top gear (which it never really does) followed by some more acceleration, then suddenly there was a loss of power.

I noticed straight away that something was wrong and backed off. The car went from sounding smooth and thrusty to boomy and lumpy instantly. We coasted down to 65mph and i tried to see what was wrong. I listened and noticed the sound was completely different, louder than normal and there was just no power so we coasted into a lay by.

The car was pretty hot underneath but all dials read normal with no warning lights. There may at this point have been some smoke from the exhaust under the car, maybe oil landing on it causing it to smoke.... I checked the oil later on and it did need topping up but wasnt empty. I also noticed a tiny oil puddle of about 10ml near and to the right of the water pump in the engine, not on the floor.

I started the car again to inspect the engine. It sounded pretty rubbish, not smooth and purry like a v8 but more like a straight 4... bland and very lumpy. It also makes a loud hissing noise from the top left of the inlet manifold on idle, around two or maybe 4 of the left hand side down pipes if you can call them that... but there is no smoke, no steam and all dials are fine!?

We got towed to a renault garage who offered us no help as its obviously not a renault..... and left us to it.

So now we are stuck and im not sure how bad this problem is... can ANYONE help with any suggestions to what it might be? Anything would be greatly appreciated.....

Thanks in advance,

Mark and Amy (on the a26)

Hi MARK

It sounds like possibly an intake manifold or inlet pipe leak....what model 928 ? 16 valve or 32 valve ?

You can test this with either a can of ether (Easy start) or at a push with WD 40...

If you use Easy start (with the engine running, even if badly) the idle WILL INCREASE if you spray anywhere near the leak as it will draw the ether in the spray into the cylinders....

If you use WD40 the idle will DECREASE .....

Thats about all I can suggest without knowing which model ?

All the best Brett

Sounds to me like you've lost one bank. Air leak, belt slipped, sparks?
Renault garages obviously have the contract as my TR7 V8 was recovered to one after the pinion bearing collapsed. Funnily enough the guys were quite happy to get stuck in! And checked various transmission levels etc.

Hi guys,

Thanks for coming back to me. . . its a 32 valve s4 1991.
The cam belt and water pump were replaced around 500 miles ago but it has been running perfectly since.... the car is locked in their overnight storage so i will try the leak idea tomorrow. Any other possible things to look for?

M

Does sound like its running on 4 cylinders.

Hi

Have you got a SINGLE Distributor cap or TWIN caps (4 cylinders each cap)

If twin then there is a small rubber belt that connects both of them that can break....

By the way,,,,when were the dizzy cap or caps and rotor arms last CHANGED (not checked but actually changed) ???

All the best Brett

?? Eh ??

On 32 valve 1991 S4 there are 2 distributor caps, one at the end of each bank.

Hi Lee

Oops...brain freeze...lol.....

Mark ignore the dizzy belt thing...but when were they last changed ?

And yes, the S4 has a "limp home mode" if you get a major problem...runs on 4 cylinders ONLY...

All the best Brett

On the left of the passenger footwell there is a small box of carpet with a cstud clip. Behind it there I'd a relay, which will light up an LED when running on 4 cylinders. Green if the left bank has failed and red if the right bank has failed, or vice versa? Remove the carpet and see what's going on.

I'd PM JDSPorsche on this forum and look up his website tonight for the exact information you need. It was John who helped me when mine went down to 4 cylinders.

Hi, the rotor arms and dist caps havent been changed for maybe 6 years... would they just give up like that under load suddenly? if so, is this why the car has dropped to 4 cylinders?

Lee - thanks for the tip - i will check the LED's in the morning. . . if its down to half an engine, will this be the 'limp home' mode and the reason for the noisy inlet manifold?

Thanks again!

Yes it will, if you look back on this forum for posts I've started, there's one called air leak. I had your exact symptoms and I thought it was an air leak. You shouldn't drive in limp home mode above 3000 rpm as it destroys the torque tube bearings.

The idea of the limp home mode is to stop fuel to the bank that's not firing correctly. If unburnt fuel gets to the catalytic converters, they glow red, overheat and set fire to the car.

There is a jumper cable you can fit to see if it's a plug lead or plug, but you can't run for long if you still have cat's fitted. I had an x-pipe, so I had more time to diagnose. JDS explained it to me, but can't remember how to?

The limp home mode is activated by a temperature differential between both banks. There is a temp sensor on each and if they don't read the same, then it activates. You might get to the car in the morning, while cold and it will run fine, but once warmed up it will go back. I'm sure the first time it happened to me, it was one of my king leads off the dizzy?

Hi Lee,
If it is indeed just a matter of putting a lead back on i will be over the moon!
Right. Fingers crossed for the morning.
I will check the LED codes, cold start, all leads and if they are all fine, check for an air leak in the inlet man with some WD40 or cold start spray. if still no joy.... its off to a 'porsche' garage in Reims.....

Let me know if im missing anything

Thanks all, you have been great.
MnA

I've just been prompted to read on with Fast and Furious on in the background in french .... 'plus vitte' .......and I think from reading other threads that it has definitely jumped into limp home mode. If this IS the case, then from what i can work out, i THINK i just have to check the ignition system.... leads etc
will update tomorrow morning.
Thanks again

I don't understand this. Are you saying your S4 never selects top gear? If that's the case we're looking at a lot more problems!

If you can confirm via relay LEDs on the board in passenger footwell holding ECUs that one cylinder bank is not running (this is 4-cylinder mode, different from limp home mode where the pulse width of injectors is fixed and all cylinders run), then as well as possible failure of one of the coil-distributor leads, you may have lost one of the ignition amps (stand in front of car looking at windscreen, on RHS at front you'll see 2 thick leads disappearing into black plastic rectangular cover. This just clips on, and underneath you will find the 2 ignition amps. You can confirm one is faulty by swapping the leads over (they are identical parts).

The good news is they are used in Citroens too, so should not be too rare in la belle France.

Cheers

Adrian