Astra 1997 GSi 16v 2.0 - Loss of power, and sudden jerking

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Thu 23 Jun 2011 05:39
Astra 1997 GSi 16v 2.0 - Loss of power, and sudden jerking - Ryan2.0

Hi All,

Hope someone can help a bit with this one.

The car is a 1997 Astra GSI 2.0 16v Ecotec engine, with about 108000km on the clock.

When I drive, the car is fine up to about 2000rpm, when I go over it, it is not a problem, but if I press the accelerator past about the first 20% throttle, then the car becomes jerky and the power disappears.

When I shift from 1st, to 2nd or 2nd to 3rd when the car is cold, I always hear a backfire noise coming from the back, it is soft, not a big bang, but it is there.

It also has a problem when idling when cold. If I get to a corner, and put my foot on the clutch, the revs just drop and it dies, unless I slowly let the revs come down to about 1k manually. This only happens when it is cold, then it seems fine.

If I have no load on the engine, i.e. just parked in the driveway, then the engine runs up to 6k rpm without any hesitation and it sounds perfect.

To exclude the EGR, I blocked it off, and it is exactly the same symptoms, and no engine light, or error codes from the ECU.

Thanks,

Ryan.

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Fri 24 Jun 2011 01:12
Astra 1997 GSi 16v 2.0 - Loss of power, and sudden jerking - Ryan2.0

Ok, so I took the MAF sensor off, blew into it to see if there was anything I could get off (If it was dirty, but I don't think that would have done much.

Then As I was putting it back, I noticed the IAT sensor before the MAF sensor, and it was turned so that the plastic was guarding it from the ariflow. I turned it 90 degrees, so that the air can run straight over it. The flat bit on the sensor now matches the flat bit on the rubber outside.

Made a huge difference, so is the orientation of the IAT sensor important?

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Fri 24 Jun 2011 02:20
Astra 1997 GSi 16v 2.0 - Loss of power, and sudden jerking - unthrottled

Very interesting observation.

IAT works is essentialy a temperature sensitive resistor. High temperatures=low resistence, low temperatures high resistence. If you get a short in the circuit, the resistence is low so the ECU thinks the intake temperature is very hot. If you get a broken circuit, the ECU thinks the temperature is very cold. I reckon you had a short. The ECU thinks the engine was taking in air at over 100C and pulled the timing which killed the power. Temperature sensitive spark retard is much more sensitive at low RPM when detonation poses its greatest threat.

By overestimating the air temperature, the MAF/MAP can't work properly because the ECU has misjudged the density of the air (goes down with temperature). This causes the ECU to supply a lean mixture which misfires and causes the jerking. Under steady state driving, the lambda sensor can correct the mixture, but when you tip-in tip-out during gear changes the lambda sensor readings are ignored and the mixture goes out again and you get the popping/stalling.

I think by bending the IAT sensor 90 degrees-you fixed the short! Well spotted. That's going in the memory bank.

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