The ignition monitoring system would do more than rough idle, as it knocks out 4 cylinders if tripped. Anyway, you established it isn't a factor with the bypass.

If John Speake's Spanner is saying the WOT position is not working on the throttle switch, even intermitently, snug the first half of the throttle cable if there is any slack there. Verify that the idle switrch still works.

Sorry I don't have anything to add about your problem other than make sure all the relevant grounds are snug.

 

Thanks Bill,
drove the car to work today and it is screaming and runs so strong and then wham out of the blue it looses power and shudders.
I wonder if the ignition modules can be tested or if they are a part you just replace and hope for the best?
The throttle cables has been adjusted so the idle switch clicks with a light touch on the fun pedal(fun most of the time).
And that one works, the WOT works sometimes when testing and then again other times gives an error message when testing the actuators.
(but never generates a stored error code when testing the ECU's)

/Peter

 

I have to beleive this is spark related, it's ONLY thing I can think of that would cause this sudden loss of power. Until you replace that coil wire and rule that out, I think that's youre number one suspect. It's the one thing you have not replaced.

And let me make sure I understand your symptoms. Everything will be running great and then it seems like you've lost half your power or more, but the car does not die... it will continue to idles and run. Is this correct? How about heat? Does it happen when cold or only after it has warmed up?

But let's pretend that you've replaced it and it still gives you these symptoms. What's left?
None of the sensors would (e.g. Temp II, etc) would make it feel like that. They might richen the mixture a bit, but in general, they won't cause a sudden dramatic loss of power like you describe. So let's think in terms of spark and fuel becuase air and compression will not change enough to cause these issues.

Spark: The only thing common that I could see that could take out 1/2 the power would possibly be the EZK (assuming both coils, wires, etc. are good). The Crank Position Sensor would take out ALL saprk, so that cannot be the issue. That's about it for spark, I think.

Fuel: Can't be the fuel pump or fuel filter as those would show as constant problems, not intermittent. If an injector shorts out, it takes them all out, so it's not that, either. The MAF might affect fueling, but I don't think it would to the level that you're describing, but I'd keep it on the list for now. The throttle position switch might also cause this if it were triggering a faulty "Idle" signal, but again, I don't think it would be at the level that you're describing. Finally, the LH could certainly cause these issues and is probably more suspect than the MAF or TPS in this case. I don't think there is anything else fuel-related that would cause the running issue you are describing.

I hope this helps.

 

Hi Andrew,

thanks for helping me think straight and logic about it.
First of all the MAF and LH is newly fixed from John Speake and this probably contributes to the fact that the car runs better than ever when it doesn't show this intermittent issue.(fixing a couple of vacum leaks should also contribute, I have steady 500mm HG in vacum at the intake and idle.)
I had the same intermittent fault last Year so they have not added anything to the problem.
I tested with my old ignition lead from the passenger side on the driver side coil and this made no differense whatso ever.
I should have two new ignition modules in the post tomorrow from a Swedish supplier of spare parts which he was kind enough to offer taking back if not curing the problem.
I agree it feels like spark since a week pump or even a relay cutting out would not give this immediate cutout.(both fuel pumps has been replaced, the inner pump had a broken rubber tube and the outer was Bosch but not 928 specific)
It happend this morning after about 2minutes driving, I can keep the engine running by pressing the clutch and pump with the accelerator pedal but it feels very rough when doing this.
And then out of the blue it runs like a dream for a while, but it came back maybe two or three times on the way to work which takes 12-15 minutes.
It is kind of scary when it happens since in the wrong situation it could be dangerous.
So no long trips until this is pinned down and fixed.

/Peter

 

Ok, so it's not heat related... I've heard of coils going bad but only showing symptoms after getting heat soaked.

The pumping the pedal seems odd... If it were spark related, pumping the pedal wouldn't help. Makes me think relay, relay, relay (or EZK .)

What if... the FP relay is going bad? If it cut the fuel pump, how would the car run? Would it cut like yours? You would have some fuel in the rail that would keep you running for a bit, maybe. Hmmm...

 

Well I barely made it home from work today, the car ran like crap most of the time.
Most relays that has with ignition, injection and fuel pump has been replaced at an early stage in this ghost hunt.
When I came home the idle was hunting up and down from almost dying to ~1000 revs, the FP meeter on the rail showed FP fluctuations in rythm with the surging from 42 PSI up to the normal 48 PSI.(when shutting down it was 51PSI)
If it is fuel related and relay is involved my guess would be that there is something funky in the wiring or fuse/relay board.
I will take the lid over pumps down and check the leads for continuity tonight.

/Peter

 

Surging at idles sounds like the throttle position switch to me or some type of unmetered air getting into the system, but that shouldn't cause your other issues. You know... it is possible that your recently rebuilt MAF is causing the problem. Try unplugging it and see if there is any difference.

 

Would the FP meeters behaviour be normal with a surging condition.
(when car runs fine it is rock steady at 48 PSI idling and vacum applied)

/Peter

 

Yes...

 

Keep chcecking for fault codes with the Spanner, Peter. Just in case one pops up there....

When the engine dies, does the rev counter drop as the engine revs drop, or does it drop instantly ?

 

Started the car cold and drove it into the garage and idle was calm.
Stopped engine and FP gauge now showed 54PSI at shutdown as specified.
I checked vacum on the white line going under the intake and vacum was not steady but variating up and down, average was 200mm HG at idle.
Hooked the vac meeter to the black line going in on the passenger side of the intake and it show 0 vacum.(checked and it is still connected under the intake)
Is this normal?
Not sure John, need to check tomorrow but what is the difference indicating?

/Peter

 

My 91 GT (which now has the violent vibration above 5K rpm, btw) used to have a similar cutout problem where it would only run on 4 cylinders. Sometimes, when I shut it of and restarted the problem went away and soometime it returned. It eventually was happening quite often and it turned out to be an intermittent relay in the ignition circuit, located in the passenger side kick panel. I recall talking to Mark Anderson and he metioned that he had bypassed that circuit on his track car but that he didn't recommend it be bypassed for a street car. Replacing the relay fixed the issue for me.

I considering looking into the ignition control to see if that is what is causing my severe vibration in the higher revs.

 

Quote:
When the engine dies, does the rev counter drop as the engine revs drop, or does it drop instantly ?


Not sure John, need to check tomorrow but what is the difference indicating?

Hi Peter
If rev counter drops like a stone, this indicates EZK rpm signal has died, and so is the cause of the drop out. (No spark, and LH fuel pump is switched off)

This could be due to faulty flywheel speed sensor, EZK ECU or EZK relay.

Igntion drop out of course could be final ignition stages, but they rarely fail. Have you checked the test connctors to these, which are near the fuse/relay panel ? (see WSM page D 28-14 and Page 28-63)

 

Ok,
latest update on this issue, got the new ignition stages with the post today.
(great Service from the local vendor Utzon here in Sweden )
Last night I took the MAF off and checked all vacum connections under the intake and they were all ok.
I did notice a small crack on the edge of the rubber between the intake and MAF.(did not seem to go all the way though, but new one on order)
Put all back together and munted the new final stages for ignition.
Good and steady fuel pressure and took the car for a spin around the local area.(around 49PSI and steady calm needle on the FP gauge)
The car ran much better than Yesterday and did not cutout like it did then.
Need to drive more though to say the cutout issue is gone completely.
I did notice some hesitation on one occasion after the car had warmed up and popped the hood, FP gauge had dropped down to 42-43PSI and when switching off it showed ~50PSI.
So could it be a combination of one or both of the final stages was bad and the FPR sticking sometimes when engine gets hot?
I have a new FPR on order from 928 Specialist and hope it will ship any day soon.(waiting for another part that delays the shipping)

/Peter

 

Hello Peter
Have you checked the two ground conenctions that are on top of the engine under the engine airfilter housing ? A poor connection on those can cause strange problems like you are having.

The problem you have sounds more like a intermittant joint somewhere rather than other causes.