89 928S4. Had the radiator replaced, car drove fine for about 30 miles or so. Parked it, got in it a few hours later and at around 30mph car feels and sounds like it's running on four cylinders. Fuel pump and filter were changed about 1500 miles ago by the way. So, I pull over, look underneath, cats are not glowing red and I proceed to limp the car home. Get it in the garage, fire it back up, it runs on all cylinders. Drive it some more, it makes it about 4 miles further than it did and cuts powe againr. Turn and limp it home while pulling over a few times to cut the engine. Each time it fires up all cylinders but quickly cuts to four cylinders running. No power drain on battery, lights don't flicker and PO installed a fuel meter which for reasons beyond me I didn't look at. It stayed red on a total lean condition. So my question is what wires could the radiator tech have jiggled around or what coincidence of a new busted thingamajig might I have stumbled on. Where should I start checking?

Funny enough while I was limping it home, the car out of first cruises kind of ok, just sounds terrible. Like an old school Viper almost.


Thanks

 

If there were some hands moving around the rad area - check the primary and secondary coil wires: often that could be a loose secondary either at the coil or distributor cap. Also, the wire harness to the dual ignition modules (~2x6" black plastic cover, drivers side in front of the rad) could have been disturbed.
In the passenger footwell, unclip the rug cover over the 'brains': when it again runs "on all four", check the relay attached to the EZK to see if either a red or green led is energized ....

 

Kaz,
IIRC on the 89+ there is a system that will shut one bank of cylinders if the temperature varies by a given amount from the other bank or a set temperature. It seems that something is activating this system.
Look just below the LH module and you should find a clear relay. Start the car and immediately watch the relay. If a light comes on in the relay as the car switches to "4 cylinder" mode then the system is being activated.
You'll need to figure out whats' causing it but seems that it has to be temperature related. Could be something like an injector gone bad or unplugged.
I don't have a solution, but this should give you something to work with.
You can disable the system by jumpering 2,4, and 5 together.
HTH,
Andy K

OK now I see that Garth has already coverd this.

 

Thanks guys, I just checked and sure enough, a few minutes after start up that little green light comes on.

 

.... which indicates that if this protective relay is working correctly ( and not the failure spot itself), then one of the 2 exhaust manifold temp sensors is reading a low temp - and shutting down fire to cyls 2,3,5,8.
Still the same things to check as before - coils, coil wires ( clean contacts) , and the 2 modules on the rad support. If nothing obvious turns up quickly, just for giggles, swap the connectors on the 2 modules. If the red light then comes on, one of the modules may be fried.

 

Like I said last night Kaz - if that light is on it is going to be dumping fuel.

If its dumping fuel the stoich would be RICH. And your meter is saying LEAN.

To me, these two things don't match.

 

Thanks Garth, I swapped the connectors and still the greenlight came on so it appears the modules are fine.

Yeah Brendan, it was just really hard hearing you in that place I was in and yes the meter is still showing a lean condition but the green light in the relay lights up. I'll fiddle with it some more later today, give me more suggestions.


Thanks!

 

Hmmm. Maybe swap coils? If that coil is a problem then that means the OTHER colored light will go on right guys?

 

I just RTFM, and it says on page D28-12 that those lights indicate that the INJECTION circuit shuts down and not the ignition circuit.

If this wordings is correct, then that makes sense on the leanb reading Kaz is getting on the 02 readout.

 

The (O2) sensor cannot read unburned fuel, so is seeing 4 cylinders burning, and averaging them as if they were 8 = ~ 1/2 stoich = lean.

 

Great! then, that points more to the driver's side coil or its secondary wire to the dist. cap.

 

It could also be one of the injector wires. Each circuit controls two middle injectors on one side and two outside injectors on the other side and I don't remember which circuit controls which. Check that your inlector wires are connected. IIRC the sensors in your car are at cyllinders 3 and 7 (second from the rear on both sides).

 

So just to be clear, the ignition system may have faults, which cause a temp change in the manifold, which will trigger a shutdown of the INJECTION circuit.

We we are looking for a fault in the Green light side, which is injection circuit II, - we are looking for a problem on THAT side of the car in the ignition system.

What side that is it does not state.

 

Hi Brendan -
Injector circuit 2 is cylinders 2,3,5 & 8.

Regards

 

If I recall, Porsche adopted the mariner's light codes for these fault indicators - red = port (left), green = starboard (right).