Eng Prob - U never heard of this one
11-08-2013, 03:15 PM
#63
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I appreciate all the posts and thoughts on how to fix my problem - you guys are great. Here are a couple more points.
1. I did not see the old set of plugs, and therefore cannot take a pic.
2. The gap on the new plugs did not close. Therefore I agree the plugs should not be an issue.
3. The borescope was clean.
4. I don't know if they ever looked at the MAF or the ignition protection relay, although I sent them an e-mail containing all your suggestions so they would have that as a reference.
5. I also don't know if they ever cleaned/checked the exhaust sensors. However, I did call 928 International and the exhaust sensors is what they thought the problem would be, and I did mention that to the mechanic.
As it stands now, the car is in the hands of the previous mechanic who did all the wiring work. Let's see what he comes up with.
1. I did not see the old set of plugs, and therefore cannot take a pic.
2. The gap on the new plugs did not close. Therefore I agree the plugs should not be an issue.
3. The borescope was clean.
4. I don't know if they ever looked at the MAF or the ignition protection relay, although I sent them an e-mail containing all your suggestions so they would have that as a reference.
5. I also don't know if they ever cleaned/checked the exhaust sensors. However, I did call 928 International and the exhaust sensors is what they thought the problem would be, and I did mention that to the mechanic.
As it stands now, the car is in the hands of the previous mechanic who did all the wiring work. Let's see what he comes up with.
11-08-2013, 04:00 PM
#65
Race Car
I appreciate all the posts and thoughts on how to fix my problem - you guys are great. Here are a couple more points.
1. I did not see the old set of plugs, and therefore cannot take a pic.
2. The gap on the new plugs did not close. Therefore I agree the plugs should not be an issue.
3. The borescope was clean.
4. I don't know if they ever looked at the MAF or the ignition protection relay, although I sent them an e-mail containing all your suggestions so they would have that as a reference.
5. I also don't know if they ever cleaned/checked the exhaust sensors. However, I did call 928 International and the exhaust sensors is what they thought the problem would be, and I did mention that to the mechanic.
As it stands now, the car is in the hands of the previous mechanic who did all the wiring work. Let's see what he comes up with.
1. I did not see the old set of plugs, and therefore cannot take a pic.
2. The gap on the new plugs did not close. Therefore I agree the plugs should not be an issue.
3. The borescope was clean.
4. I don't know if they ever looked at the MAF or the ignition protection relay, although I sent them an e-mail containing all your suggestions so they would have that as a reference.
5. I also don't know if they ever cleaned/checked the exhaust sensors. However, I did call 928 International and the exhaust sensors is what they thought the problem would be, and I did mention that to the mechanic.
As it stands now, the car is in the hands of the previous mechanic who did all the wiring work. Let's see what he comes up with.
Dan
'91 928GT S/C
475hp/460lb.ft
11-08-2013, 04:54 PM
#66
Paul, as others have said, you are not experiencing MAF related limp-home (misnomer) mode if your ignition monitoring system is triggering. You are experiencing "please stop driving me or my driveshaft will break" mode and / or "please make sure I am fully insured because I am going to catch fire" mode.
Others have mentioned the led lights on the ignition monitoring system relay. Look for these when the car runs rough (assuming the little men have stopped hammering your spark gaps closed).
Now this whole relay assembly, job lot, intact, nothing removed or added, no wires disconneced, etc can be unbolted from its hidden location and can be carefully pulled rearward into the passenger's footwell where it can be seen while you are driving the car. For the abundance of caution when I did this I added an earth wire between the relocated relay and the car, by connecting the original mounting points with a decent and properly attached wire.
I reckon if you can start to do some of the simple step by step forensics yourself - note, simple and step by step - with guidance from this forum, you'll get your car repaired sooner and more cheaply than employing a 'let's put a washer under the spark plug' mechanic, and you'll also find you'll start to enjoy the ownership more and fear the car less.
Good luck,
Dave
Others have mentioned the led lights on the ignition monitoring system relay. Look for these when the car runs rough (assuming the little men have stopped hammering your spark gaps closed).
Now this whole relay assembly, job lot, intact, nothing removed or added, no wires disconneced, etc can be unbolted from its hidden location and can be carefully pulled rearward into the passenger's footwell where it can be seen while you are driving the car. For the abundance of caution when I did this I added an earth wire between the relocated relay and the car, by connecting the original mounting points with a decent and properly attached wire.
I reckon if you can start to do some of the simple step by step forensics yourself - note, simple and step by step - with guidance from this forum, you'll get your car repaired sooner and more cheaply than employing a 'let's put a washer under the spark plug' mechanic, and you'll also find you'll start to enjoy the ownership more and fear the car less.
Good luck,
Dave
11-08-2013, 06:32 PM
#67
Under the Lift
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If you get this to someone familiar with the IMS, they will rule that in or out including figuring out the underlying cause in less than than an hour. As Dan said, you can rule this out yourself by watching for the a relay LED while driving. If they don't light, move on to something else. If one does, then the diagnostic thinking cap needs to go on.
The system measures the exhaust temperature difference between cylinders 4 and 8 which are served by different ignition banks (coils, distributors, output stages). So, say one of the two coils goes out or a coil wire falls off or goes bad, then one of these two cylinders (as well as the others served by that coil) will be colder. Now, since the IMS measures only 2 cylinders, a single plug wire issue to one of these two will be interpreted in the same way by the IMS. So, in practice it can be an entire ignition bank or just one cylinder at fault. Also, it doesn't have to be an ignition failure - if say an injector were not firing to either cylinder 4 or 8 (say an electrical lead fell off it or the injector was just plugged), so no fuel was going to one of these cylinders, the IMS would detect one cylinder as colder and trip. Additionally, the sensors themselves are famous for failing leading to false tripping of the IMS.
When the IMS trips it cuts fuel to the 4 cylinders served by the ignition bank it thinks may have failed. As others have mentioned, this lights either a red or green LED mounted inside the clear IMS relay case, visible if you remove the passenger well carpet and CE panel cover.
So, lets say the car runs just fine and all cylinders are verified to be firing initially but after some time the system trips, cutting fuel to 4 cylinders and displaying a lit LED. That would indicate a bad sensor most likely leading to a false alarm. The sensors can be removed from the exhaust manifold and cleaned. Sometimes this will eliminate the false alarms. The sensors can be tested directly and if faulty can be replaced at a cost of more than $200 each (and that price was 10 years ago). Or the system relay can be bypassed disabling the IMS, at some risk of a cat fire should there be a real ignition failure at some point that you do not detect.
If there is some engine problem, say a miss, initially but then the IMS trips, and the running condition gets far worse, then there is either an ignition or fuel supply problem problem at least to cylinder 4 or 8. The color of the lit LED would direct you to which is at fault. Red LED would indicate cylinder 4 or the right side ignition. Green LED would indicate cylinder 8 or the left side ignition. Also, there is a mode wherein if the IMS sees a condition indicating a total failure of one sensor or the sensor circuit, it will always trip the Green LED and cut fuel to the 4 cylinders served by the left side ignition circuit (5,3,2,8).
Note the IMS resets each time you turn the ignition off and there is a small delay after start up before it is active.
So, you can see the system is a bit complicated and subject to different types of faults that need to be evaluated by someone who has plenty of experience with MY89+ 928.
So, with an IMS related issue, we have the commonly called "4 cylinder mode" due to the way it cuts fuel to 4 cylinders. It's not a good idea to run a car in this mode as it puts unusual vibration stress on the driveline that can snap the torque tube shaft.
The spark plug gap closing issue was a total baffler, but that seems to have magically cleared up. Whether you have an IMS related issue, with some ignition or fuel delivery problem as I have outlined above, is not clear yet. There are other things that could be responsible, but I would rule out the IMS and related issues, as it can be done quickly, in only a few minutes if the system does not trip with more time required if it does.
The system measures the exhaust temperature difference between cylinders 4 and 8 which are served by different ignition banks (coils, distributors, output stages). So, say one of the two coils goes out or a coil wire falls off or goes bad, then one of these two cylinders (as well as the others served by that coil) will be colder. Now, since the IMS measures only 2 cylinders, a single plug wire issue to one of these two will be interpreted in the same way by the IMS. So, in practice it can be an entire ignition bank or just one cylinder at fault. Also, it doesn't have to be an ignition failure - if say an injector were not firing to either cylinder 4 or 8 (say an electrical lead fell off it or the injector was just plugged), so no fuel was going to one of these cylinders, the IMS would detect one cylinder as colder and trip. Additionally, the sensors themselves are famous for failing leading to false tripping of the IMS.
When the IMS trips it cuts fuel to the 4 cylinders served by the ignition bank it thinks may have failed. As others have mentioned, this lights either a red or green LED mounted inside the clear IMS relay case, visible if you remove the passenger well carpet and CE panel cover.
So, lets say the car runs just fine and all cylinders are verified to be firing initially but after some time the system trips, cutting fuel to 4 cylinders and displaying a lit LED. That would indicate a bad sensor most likely leading to a false alarm. The sensors can be removed from the exhaust manifold and cleaned. Sometimes this will eliminate the false alarms. The sensors can be tested directly and if faulty can be replaced at a cost of more than $200 each (and that price was 10 years ago). Or the system relay can be bypassed disabling the IMS, at some risk of a cat fire should there be a real ignition failure at some point that you do not detect.
If there is some engine problem, say a miss, initially but then the IMS trips, and the running condition gets far worse, then there is either an ignition or fuel supply problem problem at least to cylinder 4 or 8. The color of the lit LED would direct you to which is at fault. Red LED would indicate cylinder 4 or the right side ignition. Green LED would indicate cylinder 8 or the left side ignition. Also, there is a mode wherein if the IMS sees a condition indicating a total failure of one sensor or the sensor circuit, it will always trip the Green LED and cut fuel to the 4 cylinders served by the left side ignition circuit (5,3,2,8).
Note the IMS resets each time you turn the ignition off and there is a small delay after start up before it is active.
So, you can see the system is a bit complicated and subject to different types of faults that need to be evaluated by someone who has plenty of experience with MY89+ 928.
So, with an IMS related issue, we have the commonly called "4 cylinder mode" due to the way it cuts fuel to 4 cylinders. It's not a good idea to run a car in this mode as it puts unusual vibration stress on the driveline that can snap the torque tube shaft.
The spark plug gap closing issue was a total baffler, but that seems to have magically cleared up. Whether you have an IMS related issue, with some ignition or fuel delivery problem as I have outlined above, is not clear yet. There are other things that could be responsible, but I would rule out the IMS and related issues, as it can be done quickly, in only a few minutes if the system does not trip with more time required if it does.
11-08-2013, 08:19 PM
#68
Team Owner
nice post Bill
11-08-2013, 08:32 PM
#69
https://rennlist.com/forums/928-foru...-mechanic.html
Old, but might be worth a few calls.
BTW I'm trying to get him to someone that can fix his car. I don't get the feeling he wants to do it himself.
OP? What do you say?
Old, but might be worth a few calls.
BTW I'm trying to get him to someone that can fix his car. I don't get the feeling he wants to do it himself.
OP? What do you say?
11-08-2013, 09:23 PM
#70
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There is always a logical explanation!! And usually a simple one. Think back to just before the problem started.... what had you done? Maybe bought cheap gas from some random station. If the car still sounds the same and runs the same, when running, when does it mess up. I believe it was when you restarted it. Did you notice any hesitation when first turning the engine over like it was flooded? Does it ever go bad when running, or just on start up?
+1 on hiring Sean to fly over if you have no one reputable in your area... He knows what he is doing, is very fair, and is a straight shooter.
+1 on hiring Sean to fly over if you have no one reputable in your area... He knows what he is doing, is very fair, and is a straight shooter.
11-08-2013, 09:47 PM
#71
Rennlist Member
Ok,
Key points:
I) Mystery gap elimination on the plugs is a non-issue. The little guys with the big hammers belong to a union shop and are on break for the moment. So...likely a faulty plug issue and as mentioned previously, a Red Herring...or most any other shade of herring you'd care to reference.
(Thankfully that's dealt with...I'm on the GB team here...can't possibly imagine another explanation, and now the hammer guys are out.......)
II). The wiring has indeed been recently repaired from another issue...although this may be another herring on it's own.....
III). The advice on the cleaning and testing of the sensors for the ignition monitoring system is where I would focus. Experience dictates that this system that detects and deals with temperature variances is to put it mildly, a little on the sensitive side, like the wife or the friend who may elect to play for the other team.....
IV). Having all three....an IMS, a wife , and the friend.....I'm willing to take a stand here.
v). moving along...that leaves one flashing red light....(on the assumption that all injectors are doing their job in a reasonably efficient manner).
vi). CHECK AND CLEAN THE TEMPERATURE SENSORS AND THEIR CONNECTIONS AND REPORT BACK ON THE RESULTS.
VII). GO BACK AND READ POST #67.-----CAREFULLY. AND SHARE WITH YOUR MECHANIC OF CHOICE.
Finished capitalizing for "effect" now. rant over.
BTW...Agreed. Great post Bill.
Key points:
I) Mystery gap elimination on the plugs is a non-issue. The little guys with the big hammers belong to a union shop and are on break for the moment. So...likely a faulty plug issue and as mentioned previously, a Red Herring...or most any other shade of herring you'd care to reference.
(Thankfully that's dealt with...I'm on the GB team here...can't possibly imagine another explanation, and now the hammer guys are out.......)
II). The wiring has indeed been recently repaired from another issue...although this may be another herring on it's own.....
III). The advice on the cleaning and testing of the sensors for the ignition monitoring system is where I would focus. Experience dictates that this system that detects and deals with temperature variances is to put it mildly, a little on the sensitive side, like the wife or the friend who may elect to play for the other team.....
IV). Having all three....an IMS, a wife , and the friend.....I'm willing to take a stand here.
v). moving along...that leaves one flashing red light....(on the assumption that all injectors are doing their job in a reasonably efficient manner).
vi). CHECK AND CLEAN THE TEMPERATURE SENSORS AND THEIR CONNECTIONS AND REPORT BACK ON THE RESULTS.
VII). GO BACK AND READ POST #67.-----CAREFULLY. AND SHARE WITH YOUR MECHANIC OF CHOICE.
Finished capitalizing for "effect" now. rant over.
BTW...Agreed. Great post Bill.
11-08-2013, 09:58 PM
#72
[QUOTE=928 at last;10892009II). The wiring has indeed been recently repaired from another issue...although this may be another herring on it's own.....
[/QUOTE]
Disagree
In the absence of other indicators always suspect what was last touched.
[/QUOTE]
Disagree
In the absence of other indicators always suspect what was last touched.
11-09-2013, 04:42 AM
#73
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Just reading through this thread.This may sound really stupid but if the problem keeps coming back after about 15 mins, and there was wiring work done to the car recently, could there be a'timer relay' in a wrong slot that could affect the engine??
11-09-2013, 04:58 AM
#74
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I do not have the car, so I can't check the led's myself.
Since I did not want to drive the car in this condition, I had it towed to Renn Haus. They were able to get it to run normally for about 15 minutes after regapping a few of the plugs, and then it went back into this limp home mode. That is the only time I know of where it ran normally again. I would guess it's still in that mode.
What I am going to do is copy Bill's post - #67 - and e-mail it to the mechanic who now has the car. I'm sure this will help him with his diagnosis, and I'll keep you posted as I hear anything.
However, here is something else. And why is it that these "something elses" keep popping up for me????
When I took the car to Eric, he said the mechanic who worked on my wiring a few months ago is no longer with him - they had a disagreement of sorts - so it will take some time to get to my problem. However, I did not see that I had much of a choice - I had to leave the car with him. I did not have the list of repair facilities mentioned above at that time.
Now I hope this new found information on the led's will help him solve the problem quickly. Thanks again to all of you. I know I keep saying that - but I mean it.
Since I did not want to drive the car in this condition, I had it towed to Renn Haus. They were able to get it to run normally for about 15 minutes after regapping a few of the plugs, and then it went back into this limp home mode. That is the only time I know of where it ran normally again. I would guess it's still in that mode.
What I am going to do is copy Bill's post - #67 - and e-mail it to the mechanic who now has the car. I'm sure this will help him with his diagnosis, and I'll keep you posted as I hear anything.
However, here is something else. And why is it that these "something elses" keep popping up for me????
When I took the car to Eric, he said the mechanic who worked on my wiring a few months ago is no longer with him - they had a disagreement of sorts - so it will take some time to get to my problem. However, I did not see that I had much of a choice - I had to leave the car with him. I did not have the list of repair facilities mentioned above at that time.
Now I hope this new found information on the led's will help him solve the problem quickly. Thanks again to all of you. I know I keep saying that - but I mean it.
11-09-2013, 05:43 AM
#75
Pro
You can jumper that relay using a simple 3 way jumper between pins 4, 2 and 5. Easy for diagnosis and can be made with normal (male) spade connectors.