Manfred

Thread Hijacking in progress....

OK, so I've had this happen to me twice last year ('91 GT). Both times in extremely cold weather; both times when I stopped the car and restarted it fired up and drove normally. So, would it be fair to say that I have a problem in one of the coil systems that occurs in cold weather and that my IMS is appropriately shutting that bank down? Also, if I'm going to check my relay and see which light is on so I can figure out which side is causing the problem, do I need to do this with the car running before I shut it off? Can I shut the engine off by turning the key one click and then look at the relay or do I need to leave it running in neutral while I look at the circuit board.

Thanks,
Dan

AO

You need to look at it before you turn the motor off. One you turn it off, the relay will reset itself - which really isnt' a bad thing. Another casue for tripping the relay can be soot buildup on the ends of the EGT's. A good cleaning can help eliminate this.

Manfred

Thanks Andrew but you got me on EGTs. I found another post talking about them which has me guessing that they're temp sensors in the exhaust but I couldn't find out exactly what the letters stand for. Exhaust Gas Temperature sensors? Do they screw into the headers like the O2 sensors screw into the exhaust?

Dan

SharkSkin

Dan & Wally, one additional factor is that the cylinders that are not firing are still compressing air, so the working cylinders are each firing then there is significant drag slowing the crank between each firing cylinder, which only exaggerates the problem.

James Bailey

They screw into the cylinder heads near the exhaust port on cylinders #4 and #8 for 89 then #3 and #7 for 1990 > and updated 89s as Porsche recommends. The 944 drive line Porsche felt the need to use a large rubber disc to absorb some of the vibration /pulsing to protect the driveshaft. Few 4 cylinder cars use such a small driveshaft. And yes a six cylinder engine is a much smoother design the V 12 on a flat crank even better. Four cylinder engines are rough also why the 944 has a balance shaft spinning a large counter weight at 1/2 engine speed (under license from Mitsubishi) to cancel the FEEL of the vibration. The V-8 running on 4 cylinders has those dead cylinders working as big air compressor ....

Manfred

Yeah, for me since just shutting off the engine and restarting seems to take care of it it seems like a no-brainer that I should be pulling over and turning off the car. The first time it happened I thought I was in limp home mood and I was afraid if I turned off the car it wouldn't restart so I did what just what the name implies--I limped home and then shut off the car.

Manfred

Thanks--what does EGT stand for though? Was I right with my Exhaust Gas Temperature sensor guess?

Dan

James Bailey

yes

Manfred

VehiGAZ

+1.

The connector on one of these sensors (found behind/aft of each valve cover) could also be dirty or oxidized, causing faulty readings to the ignition circuit protection relay (ICPR), which causes it to shut down cylinders.

I traced each temp sensor wire from the exhaust manifold to the connector aft of the valve covers, then disconnected them and cleaned them. That seemed to sort out this problem for me (which I'd been having intermittently for almost two years). That said, I also had an intake R&R done last year, which also may have fixed the problem

You can also buy a pre-1989 ignition relay, which bypasses the ignition monitoring circuit, so if you get caught in the ignition protection mode you can always bypass it in 2 minutes on the side of the road.

Good luck!!

WallyP

"You can also buy a pre-1989 ignition relay, which bypasses the ignition monitoring circuit, so if you get caught in the ignition protection mode you can always bypass it in 2 minutes on the side of the road."

Haven't heard of that - are you sure?

VehiGAZ

Yes, I am sure that this is supposed to work, but I haven't actually tried mine out yet. For $17 it's certainly worth keeping on hand.

The part number is 928 615 175 00, available at 928intl.com.

Manfred

Thanks; sounds like I found myself my next project...

VehiGAZ

It takes very little time, actually. IIRC, you will need to remove the air filter housing to get a hand back there. They are a little tricky to get at for big butcher's hands like mine, but still doable. Got kids? Have one of them give daddy a hand...

If one of these temp sensors appears to have failed (no signal) or has a low temp reading, it will switch to the 4-cylinder mode. A dirty contact can cause this.

WallyP

"Yes, I am sure that this is supposed to work, but I haven't actually tried mine out yet. For $17 it's certainly worth keeping on hand.

The part number is 928 615 175 00, available at 928intl.com."

OK, that explains it. That isn't the ignition relay - that is a bridge to tell the ECU that the car is not equipped with cats. You pull the clear relay and replace with the bridge.

Be aware that if the Ignition Monitoring System is working correctly when it goes on four cylinders and you then bypass it, you will probably burn the car to the ground.

If it is a false warning, then all is well...