limp home - self cure?
Racer
Joined: Oct 2010
Posts: 384
Likes: 1
From: Seattle, WA
Similar thing happened to me coming down from Shasta, and again at the Grapevine. Conditions were a cold, coasting/braking descent where the temp sensors in the head on either side sensed enough difference in temperature that the relay tripped and went into 4cyl mode. Stopped, scratched my head, started it up find a better place to park and it ran fine. Drove around the lot a few times and decided to keep going. Met up with the group driving to Sharktoberfest and Bill Ball explained what probably happened and told me that his failed so often he pulled the relay at one point.
I understand there are another pair of sensor locations more forward, and that sometimes fixes the issue.
I now find places in a long, cold descent to accelerate and put a little more heat into the engine.
I understand there are another pair of sensor locations more forward, and that sometimes fixes the issue.
I now find places in a long, cold descent to accelerate and put a little more heat into the engine.
Nordschleife Master
Joined: Apr 2003
Posts: 9,601
Likes: 39
From: Abbotsford B.C.
Next time it happens, pull the LH/EZK cover, the IMS relay sits right below it and if one bank is activated it will have a green or red LED. Alternatively, make up a 3 wire bypass, or buy a bypass relay, next time it happens, unplug, and use the bypass. Does the problem come back?
You can pull the cover off and clean all the contact paths and rerun all the solder joints, or just buy a new relay, or bypass it.
You can pull the cover off and clean all the contact paths and rerun all the solder joints, or just buy a new relay, or bypass it.
Thread Starter
Rennlist Member
Joined: Oct 2004
Posts: 10,717
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From: Southern Alberta, Canada
Hi Malcolm,
The IMS relay on my '89 S4 acted up like that intermittently over a period of 10 years. Sometimes it would go 2-3 years without any problems, other times it would happen twice in one month. Once on a long trip to California it acted up...then reset and I went another 2500 KM's without a problem. Mine eventually failed to the point where it was happening all the time. Best to check out your system first for any possible problems, but if it is the relay you can either get a new IMS relay (BIG $$$), a lower cost bypass relay (P/N 928.615.175.00), or make jumper wire to bypass the system:
https://rennlist.com/forums/928-foru...ing-relay.html
The IMS relay on my '89 S4 acted up like that intermittently over a period of 10 years. Sometimes it would go 2-3 years without any problems, other times it would happen twice in one month. Once on a long trip to California it acted up...then reset and I went another 2500 KM's without a problem. Mine eventually failed to the point where it was happening all the time. Best to check out your system first for any possible problems, but if it is the relay you can either get a new IMS relay (BIG $$$), a lower cost bypass relay (P/N 928.615.175.00), or make jumper wire to bypass the system:
https://rennlist.com/forums/928-foru...ing-relay.html
Thread Starter
Rennlist Member
Joined: Oct 2004
Posts: 10,717
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From: Southern Alberta, Canada
Malcolm--
Your symptom is typical to first signs of MAF failure.
The "ignition protection relay" lives on the face of the controller mounting bracket in the passenger's footwell. It has red and green LED's that give you an indication when it is active, and which set of cylinders it is protecting. If/when the condition repeats, unsnap and remove that side cover over the controllers, and look for one of those LED's. If none are lit, your problem is elsewhere. If one is lit, look for an ignition fault first, like a coil wire loose.
The protection is self-reinforcing, in that it shuts off fuel to cylinders it feels are too cold. Those then become colder, making it a little tougher to find using a temp gun on exhaust header pipes. The relay also has an initial time delay built in, allowing the engine to run for about 5 mins before it goes active.
I'm not at all a fan of just arbitrarily disabling the system. As much as some see the system as a problem itself, it does work to keep the car from going up in flames from catalyst overheating from eating raw fuel. Unless disturbed, the thermocouple probes last a really long time. The electronics in the relay are relatively bulletproof (simple low-voltage comparitor), and the contacts don't actively switch under load.
Regardless, look for the telltale LED'S on the relay next time the symptom shows up.
Meanwhile, MAF is still my first suspect. You have a spare in the other car to test with.
Your symptom is typical to first signs of MAF failure.
The "ignition protection relay" lives on the face of the controller mounting bracket in the passenger's footwell. It has red and green LED's that give you an indication when it is active, and which set of cylinders it is protecting. If/when the condition repeats, unsnap and remove that side cover over the controllers, and look for one of those LED's. If none are lit, your problem is elsewhere. If one is lit, look for an ignition fault first, like a coil wire loose.
The protection is self-reinforcing, in that it shuts off fuel to cylinders it feels are too cold. Those then become colder, making it a little tougher to find using a temp gun on exhaust header pipes. The relay also has an initial time delay built in, allowing the engine to run for about 5 mins before it goes active.
I'm not at all a fan of just arbitrarily disabling the system. As much as some see the system as a problem itself, it does work to keep the car from going up in flames from catalyst overheating from eating raw fuel. Unless disturbed, the thermocouple probes last a really long time. The electronics in the relay are relatively bulletproof (simple low-voltage comparitor), and the contacts don't actively switch under load.
Regardless, look for the telltale LED'S on the relay next time the symptom shows up.
Meanwhile, MAF is still my first suspect. You have a spare in the other car to test with.
I could swap them over temporarily though on a trial basis. thx again
Thread Starter
Rennlist Member
Joined: Oct 2004
Posts: 10,717
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From: Southern Alberta, Canada
Thread Starter
Rennlist Member
Joined: Oct 2004
Posts: 10,717
Likes: 58
From: Southern Alberta, Canada
Next time it happens, pull the LH/EZK cover, the IMS relay sits right below it and if one bank is activated it will have a green or red LED. Alternatively, make up a 3 wire bypass, or buy a bypass relay, next time it happens, unplug, and use the bypass. Does the problem come back?
You can pull the cover off and clean all the contact paths and rerun all the solder joints, or just buy a new relay, or bypass it.
You can pull the cover off and clean all the contact paths and rerun all the solder joints, or just buy a new relay, or bypass it.
Thread Starter
Rennlist Member
Joined: Oct 2004
Posts: 10,717
Likes: 58
From: Southern Alberta, Canada
Thread Starter
Rennlist Member
Joined: Oct 2004
Posts: 10,717
Likes: 58
From: Southern Alberta, Canada
UPDATE
As the car is now running as it should there's no LEDs on the IMS relay so I pulled the coil wires all good; checked distis, plug wires, 14 pin connector etc etc........nothing amiss.
Removed the air filter housing and checked the MAF connection and all thats in the location.......all good.
Im participating in the local PCA meet tomorrow; approx. 200km round trip.......see how she runs
Removed the air filter housing and checked the MAF connection and all thats in the location.......all good.
Im participating in the local PCA meet tomorrow; approx. 200km round trip.......see how she runs
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Chronic Tool Dropper
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Joined: Oct 2001
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From: Bend, Oregon
thx dr Bob..........the MAF did cross my mind but couldnt rationalize the digital off then on from a running perspective. My S4 did require a JDS rebuild some years ago and failure symptoms were vastly different although I do believe there are many modes to MAFs going South.
I could swap them over temporarily though on a trial basis. thx again
I could swap them over temporarily though on a trial basis. thx again
My suggestion on the MAF is based on an experience with a SoCal local's car that experienced similar failure symptoms. He called on Saturday morning looking for help, stranded on the road on the way back from a PCA breakfast somewhat out of our area. The drive to meet his was a fun jaunt over the hill on Angeles Crest and Angeles Forest highways, making the trip even more worthwhile.
Tested all the normal stuff when I got there, found all OK. So started the car and it ran OK for a while, maybe five miles, then power would fall off and the car would barely run. Stop, headscratch, try again. Car would run OK for a bit then fall off to barely run. Finally, within his towing plan distance, we had the car flatbedded to his favorite mechanic. A couple days later on Monday, the mechanic called to ask if they could "borrow" my MAF for testing. Sure! And that was the answer. MAF rebuild and good to go.
Thread Starter
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Joined: Oct 2004
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From: Southern Alberta, Canada
Just got back from a very short drive this morning; car started acting up again as it did on Sunday.
Pulled the carpet and cover off of the LH/EZK computers and the RED LED was glowing on the IMS relay. We have located the source of the issue as ignition/IMS related.
Pulled the carpet and cover off of the LH/EZK computers and the RED LED was glowing on the IMS relay. We have located the source of the issue as ignition/IMS related.
Rennlist Member
Joined: Jun 2005
Posts: 10,578
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From: Oman
Just got back from a very short drive this morning; car started acting up again as it did on Sunday.
Pulled the carpet and cover off of the LH/EZK computers and the RED LED was glowing on the IMS relay. We have located the source of the issue as ignition/IMS related.
Pulled the carpet and cover off of the LH/EZK computers and the RED LED was glowing on the IMS relay. We have located the source of the issue as ignition/IMS related.
Sounds as though some bits need replacing.
Well if all else fails there is now a real "Flying Scotsman" operational in England once more and attracting record crowds- maybe you should pop over to Blightly and "let the train take the strain".
Some nice videos on Youtub.
Rgds
Fred
Thread Starter
Rennlist Member
Joined: Oct 2004
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From: Southern Alberta, Canada
Malcolm,
Sounds as though some bits need replacing.
Well if all else fails there is now a real "Flying Scotsman" operational in England once more and attracting record crowds- maybe you should pop over to Blightly and "let the train take the strain".
Some nice videos on Youtub.
Rgds
Fred
Sounds as though some bits need replacing.
Well if all else fails there is now a real "Flying Scotsman" operational in England once more and attracting record crowds- maybe you should pop over to Blightly and "let the train take the strain".
Some nice videos on Youtub.
Rgds
Fred
Thread Starter
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Joined: Oct 2004
Posts: 10,717
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From: Southern Alberta, Canada
Thread Starter
Rennlist Member
Joined: Oct 2004
Posts: 10,717
Likes: 58
From: Southern Alberta, Canada
so I worked on the car a little more this aft; does anyone remember the Bill Ball thread re. coils and wires......think I got the same on Ign. Cct. I.........swapping out coil and coil wire that are only 2 years old.