Stromius

+1 on checking this Steve!

Speedtoys

It didnt.

It got oily as you pulled it -out-.

The oil in the well, may be screwing with the wire to plug interface, causing a misfire.

James Bailey

Driving around on 4 cylinders is said by Porsche to be one reason why the driveshaft in the torque tube breaks. If enough oil is in the sparkplug well it can short out the spark but it is not going to leak down to the electrode....And as I mentioned before being down only one cylinder is only a little power loss and only a noticable miss when at full throttle. So much so that it might not be noticed by many.

stevedavies

Power loss was more than a simple misfire, although cleaning the one plug seemed to cure it. Will investigate ignition more closely this weekend

Hilton

Steve, if/when it happens again, have a look at the clear relay mounted on the side of the ECU's - it has a green and red LED, and each lights up for one or the other bank of cylinders (red for right (5-8) IIRC).

Its possible a misfire was bad enough that the ignition monitoring sensors detected lower exhaust temperatures (there are probes in the manifold at the exhaust ports for cylinders 3 and7 on your car). If it does detect lower temps, it shuts down that bank, rather than dumping raw petrol into your cats where it would cause a major fire (burning cats are a common cause of 928 combustion).

Dictys

I thought the red light was for 1,4,6,7 which is the passenger side coil and cap on a LHD.

I have been chasing a simliar problem with a low idle.

Hilton

IIRC, the ignition monitoring system doesn't shut down the ignition on one bank (i.e. one distributor/coil/amplifier). Instead I thought it shuts down the injectors on the side that has the lower exhaust temps.

The injector harness is partitioned into two, and I vaguely recall the monitoring relay just grounds one or the other bank of injectors to stop them spraying fuel. I don't think it turns off spark.

I could be wrong on all this tho' - its not a system I have on my cars (my 89 is from a country where they didn't have cats, so it wasn't fitted with the monitoring sensors/relay from factory).

edit: just checked and found a post by Alan - it does disable injectors, not spark, so the above holds.

Vlocity

As mentioned previously, if you run a compression test at least you will have eliminated any major problem. With that off the table then you can spend your hard earned cash on maintenance items.

Ken

the flyin' scotsman

Steve,

Lets eliminate the big picture and do a compression test.

All well, I'd concentrate on the ignition maintenance items; rotors, distrib. caps, plug wires and the plugs themselves.

The cam cover gaskets may be leaking also......can you post a pic of the exterior of the plugs and wires?

stevedavies

Ok have been looking more closely at the ignition system today. Several of the plugs holes have a little oil in the holes, but nothing major. I took out all plugs and they look consistent ( one was oily yesterday but now ok). One thing I did find was a disconnected earth strap. Part no on cable is 928 612 814 00. One end is connected to the coil clamp ( drivers side RHD), but the other was neatly tucked out of the way, unconnected. Its not obvious where the disconnected end fits?? Can anyone post pic?

All connections to the coils look good, ie no corrosion. All ignition is old though apart from plugs.

Compression tester on way, should get it this weekend

SteveG

I don't know if the problems (I think there are two) are connected, but I'm betting the coil ground is the cause of the loss of power. I had similar situation. 5-speed would accel OK, but at speed (65) it would not accel. Shift to 4th, no joy. I found corrosion on coil wire connector. Check and clean coil and distributor connections. Even though there is boot on the distributor, this connection seems to promote corrosion.

Speedtoys

That ground wire sneaks down, back, and up to a lug on the pass side engine lift ring.

Chris Buckenham

Hello Steve,

I am based down in Essex and late last year bought a 90GT with about 78,000 miles on the clock . The previous owner had replaced brakes , cambelt , tensioners etc but had done nothing electrical . We considered that it was running "a bit rough" and before taking it over to Paul Anderson for engine mounts we replaced all the electrical components that have been previously mentioned .

All of the parts came from Euro Car Parts at Wembley . We did plugs , leads , rotor arms , caps , coils . The leads were by far the most expensive item but when i said to the chap at ECP that i thought they were a bit pricey he said "hold on " looked at his computer and then knocked about 40% off the price . Needless to say he then reduced everything in price as we went through the list . The caps on the car looked 100% original and had a 1988 mark in the mouldings . The leads were also original looking . tThe replacement Beru set supplied by ECP felt like a very well made quality product , however I stand to be corrected on this . Once all the parts were fitted the car started and ran superbly , all traces of roughness gone instantly .
When and if you have managed a compression test as has been suggested , personally I really would recommend doing a full ignition overhaul . On my car those earth wires went from the coil bracket to bolt onto the engine near to the coil . The old coils were showing a little sign of corrosion and leakage on the lower facing surface where the top joins the metal body .We also cleaned all connections and earths and applied a little copperslip here and there .

Regards

Chris Buckenham

stevedavies

Speedtoys, thanks I can see where it goes now.
Chris, the ignition has moved up to the next thing to replace. I hadnt thought of ECP, will check them out. When I looked at ignition leads from UK sources they are REALLY expensive, better in US. Will check them out tonight

Chris Buckenham

Steve

I will check my bill and see what they charged me , about £200 I think . There is also a particular person there who understands the Porsche parts well and will arrange to have the parts sent to the local branch of ECP from Wembley if required.

Chris