Engine cuts out at a specific temperature
Discussion
I have been asked about a petrol engine vehicle that runs a closed loop control system and controls the idle speed with a throttle bypass valve. The car always starts from cold and runs fine until just below normal operating temperature at which point more times than not it cuts out and will not restart until the temperature has dropped (typically two minuets or so). If during the warm up it manages to get past the particular troublesome temperature point it then runs fine. The oxygen sensor has been changed and the throttle bypass disabled also tried a different ECU but no change. It seems it may fail at the point where it is switching from the warm up map to closed loop map.
Any ideas anybody ?
Any ideas anybody ?
GreenV8S said:
Does it only die if if it left to idle while it passes that critical temperature, or is it something that can be overcome by the driver?
No, nothing the driver can do about it. To the driver it feels as if the fuel pump or ignition has been switched off. With a view to eliminating this possibility the supply lines to these now have LEDs fitted for next time it stops, they are both powered from the ECU. If you can reproduce the failure in controlled conditions, see whether the fuel and/or spark change significantly at the moment it stops. This would give you some idea why it's stopping.
A cheap passive strobe serves as a very effective HT test lamp, or you can buy little gadgets specifically for this. Similarly, you can buy NOID test lamps that show when the injectors are open (brighter = more fuel) but being a cheapskate I just bought a bunch of minitimer connectors and some 12v LEDs.
Also test the temp senders (coolant, fuel?) if you can locate them, they will usually be thermisters, see if the resistance varies suddenly when the temperature reaches the critical point.
On some installations, there can be a significant thermal shock the first time the stat opens as the cold coolant from the radiator is dumped into the engine. Stick your hand on the top hose and you should be able to feel it heat up suddenly as the stat cracks open. If the problems occurs shortly afterwards, that gives you a clue what's causing it.
A cheap passive strobe serves as a very effective HT test lamp, or you can buy little gadgets specifically for this. Similarly, you can buy NOID test lamps that show when the injectors are open (brighter = more fuel) but being a cheapskate I just bought a bunch of minitimer connectors and some 12v LEDs.
Also test the temp senders (coolant, fuel?) if you can locate them, they will usually be thermisters, see if the resistance varies suddenly when the temperature reaches the critical point.
On some installations, there can be a significant thermal shock the first time the stat opens as the cold coolant from the radiator is dumped into the engine. Stick your hand on the top hose and you should be able to feel it heat up suddenly as the stat cracks open. If the problems occurs shortly afterwards, that gives you a clue what's causing it.
steve-V8s said:
Mr2Mike was on the money with this one, turned out to be the crank sensor which on this engine actually looks at the flywheel, it repeatably failed at a specific temperature. Diagnosis wasn’t helped by the ECU turning off the fuel after about four seconds of cranking with no result.
Sorry to drag up an old thread, but this is happening on the wifes P.O.S 316 SE. Random times and random speeds, the dash goes xmas tree and the engine just cuts out. Nothing to do then but drift off the road and wait, then restart. Fingers crossed its the same fix.Fault code is the crank sensor and the cam sensors apparently. Getting the crank sensor changed tomorrow - fingers crossed.
A colleague had a similar problem on a BMW many years ago which was reported by the owner as cutting out after a certain number of miles from cold but running fine after that. It turned out to be a coolant temp sensor which shorted out at only one place in its temp range but gave the correct resistances cold or hot in a pan of water which is the usual way of testing them. Took a long time to find because of that but such faults will nearly always be a temp, crank or cam sensor.
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