Very Wierd "Hunting" Problem
Discussion
This S2 owner posted on the "Scotland" forum:
http://www.pistonheads.co.uk/gassing/topic.asp?h=0...
His problem was that the car was hunting badly, running rich, backfiring etc. He has replaced the injectors, plugs, leads, dizzy cap, air flow meters, and even substituted another ecu. No difference.
Suggestions over on the other forum included air leak, or the coolant temp sensor, or the throttle pot.
I thought I'd move it over here so that the S gurus could maybe help. Here goes.
I went to look at the car yesterday, and I found that unplugging the ISCV made the car run evenly. Now I know that doesn't mean that it's the ISCV that's at fault, it just means that the ecu can't bleed air to compensate for another fault, but at least it shows that the engine is basically fine, it was probably an ecu signal somewhere.
So - we disconnected the air flow meters, the coolant sensor, the fuel temp sensor, and the big connector under the coil, cleaned up the terminals with emery, then a spray of contact cleaner then some waterproof dielectric grease, and put them back together. The ISCV and TP connectors looked fine.
We took the ISCV apart and cleaned it out with carb cleaner.
We also checked that the plug leads were in the right order!
After all that, the engine was idling perfectly - smooth as a baby's. We thought we had cracked it. The radiator fan cut in, then off again - perfect. We were standing chatting, and the fan cut in a second time, then as it went off, the engine hunted and stumbled to a complete stop.
It started right away though, and soon settled down smooth. Fan cuts in twice, and as it goes off the second time, the engine again stumbles and hunts to a halt.
When the engine is going perfectly, a vacuum gauge plugged into the servo connection on the plenum, gives a reading of 18" Hg, which is right in the range for a healthy engine. When it's hunting and farting about, the reading drops to 15 - which indicates an air leak (or faulty ignition timing - but I can't see why the ignition timing would be related to engine temperature at idle - unless the ignition module was breaking down under heat - but only the second time it gets hot!).
We did find that when it was hunting one time, wiggling the non-retun vacuum valve at the servo restored normal operation - but later, with the vacuum gauge connected and that hose therefore out of the equation, it was still doing it.
I also tried unplugging the ISCV now, as it was hunting, and it made no difference - it still stumbled to a halt.
The other thing I noticed - he said he couldn't remember which way round the AFMs had been connected before he changed them, and I can't help because mine is an S3C and doesn't have any. He has the white connector to the top one, black connector to the bottom - is that right?
I think that we have fixed whatever the ECU signal problem was, but there is still some intermittent more fundamental fault. He's happy enough that the car is at least running right for a while, so it's much better than it was. He's going to get it MOTd so that he can try it on the road.
I suggested that he tries spraying "Easy Start" around all the inlet joints and see if the revs rise momentarily - either that or trickle redex on, and see if it gets sucked into the joint. He's also going to change the coolant sensor.
Other than that, I'm stumped - why would a fault occur as the fans switch off for the second time - 3 times it did exactly that?
Sorry about the length of the post, but it's a difficult problem to explain, and I wanted to show that we had eliminated the obvious (well, obvious to me at least)!
Any thoughts?
http://www.pistonheads.co.uk/gassing/topic.asp?h=0...
His problem was that the car was hunting badly, running rich, backfiring etc. He has replaced the injectors, plugs, leads, dizzy cap, air flow meters, and even substituted another ecu. No difference.
Suggestions over on the other forum included air leak, or the coolant temp sensor, or the throttle pot.
I thought I'd move it over here so that the S gurus could maybe help. Here goes.
I went to look at the car yesterday, and I found that unplugging the ISCV made the car run evenly. Now I know that doesn't mean that it's the ISCV that's at fault, it just means that the ecu can't bleed air to compensate for another fault, but at least it shows that the engine is basically fine, it was probably an ecu signal somewhere.
So - we disconnected the air flow meters, the coolant sensor, the fuel temp sensor, and the big connector under the coil, cleaned up the terminals with emery, then a spray of contact cleaner then some waterproof dielectric grease, and put them back together. The ISCV and TP connectors looked fine.
We took the ISCV apart and cleaned it out with carb cleaner.
We also checked that the plug leads were in the right order!
After all that, the engine was idling perfectly - smooth as a baby's. We thought we had cracked it. The radiator fan cut in, then off again - perfect. We were standing chatting, and the fan cut in a second time, then as it went off, the engine hunted and stumbled to a complete stop.
It started right away though, and soon settled down smooth. Fan cuts in twice, and as it goes off the second time, the engine again stumbles and hunts to a halt.
When the engine is going perfectly, a vacuum gauge plugged into the servo connection on the plenum, gives a reading of 18" Hg, which is right in the range for a healthy engine. When it's hunting and farting about, the reading drops to 15 - which indicates an air leak (or faulty ignition timing - but I can't see why the ignition timing would be related to engine temperature at idle - unless the ignition module was breaking down under heat - but only the second time it gets hot!).
We did find that when it was hunting one time, wiggling the non-retun vacuum valve at the servo restored normal operation - but later, with the vacuum gauge connected and that hose therefore out of the equation, it was still doing it.
I also tried unplugging the ISCV now, as it was hunting, and it made no difference - it still stumbled to a halt.
The other thing I noticed - he said he couldn't remember which way round the AFMs had been connected before he changed them, and I can't help because mine is an S3C and doesn't have any. He has the white connector to the top one, black connector to the bottom - is that right?
I think that we have fixed whatever the ECU signal problem was, but there is still some intermittent more fundamental fault. He's happy enough that the car is at least running right for a while, so it's much better than it was. He's going to get it MOTd so that he can try it on the road.
I suggested that he tries spraying "Easy Start" around all the inlet joints and see if the revs rise momentarily - either that or trickle redex on, and see if it gets sucked into the joint. He's also going to change the coolant sensor.
Other than that, I'm stumped - why would a fault occur as the fans switch off for the second time - 3 times it did exactly that?
Sorry about the length of the post, but it's a difficult problem to explain, and I wanted to show that we had eliminated the obvious (well, obvious to me at least)!
Any thoughts?
Griffinr said:
Just a thought, could it be a yellow connector problem as the fan cut in would apply an addition load to the electrics.
Rob.
Good thinking, and I even talked about the yellow connector to him yesterday - except that it's not when the fan cuts in, it's as it goes off - and not the first time, but as it goes off the second time. It was getting late so I didn't actually check the connector though.Rob.
See if giving the alternator a good solid earth makes any difference. The alternator body has to be earthed to get a good voltage reference, but the earth is only via those nasty cr@ppy mounting bolts and stay none of which are reliable on an old engine. If the alternator isn't earthed and the battery voltage is jumping around, this can result in very strange behaviour at the ECU as the input voltage does silly things.
What state is the battery in? Reading between the lines this car hasn't been run much has it?
A poorly battery can cause allsorts of wierd goings on even if it has enough strength to start the engine.
I understand that there's a big multiway connector on top of the engine to one side - worth checking that out.
There's a star tester for the Ford V6 that has a wire 'wiggle test' function that sounds like it could be worth checking out. One or two forum members have one that they lend out for the postage, they do also turn up on ebay.
Chris
A poorly battery can cause allsorts of wierd goings on even if it has enough strength to start the engine.
I understand that there's a big multiway connector on top of the engine to one side - worth checking that out.
There's a star tester for the Ford V6 that has a wire 'wiggle test' function that sounds like it could be worth checking out. One or two forum members have one that they lend out for the postage, they do also turn up on ebay.
Chris
All good ideas guys, thanks.
With regard to the Star Tester, I have my own 15-year-old fault code reader, which also includes that "wiggle test" - unfortunately we couldn't plug that in because my tester has a standard Ford OBD1 3-pin triangular connector, and there isn't a corresponding connector on the car. There is a round 3-pin connector, and a 5-pin almost-triangular one, but not an OBD one. One of those two might well be the diagnostic connector, but I would need to check the wiring colours and make up an adaptor.
With regard to the Star Tester, I have my own 15-year-old fault code reader, which also includes that "wiggle test" - unfortunately we couldn't plug that in because my tester has a standard Ford OBD1 3-pin triangular connector, and there isn't a corresponding connector on the car. There is a round 3-pin connector, and a 5-pin almost-triangular one, but not an OBD one. One of those two might well be the diagnostic connector, but I would need to check the wiring colours and make up an adaptor.
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