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2003 Chevy Tracker 2.5l Idle Misfire/Hard starting when hot

posted May 09, 2016 02:55:37 by Jerry Hardway
I have a 2003 Chevy Tracker with the 2.5L V6 and auto transmission, the guys on the suzuki forum sent me here. Just got it from a buddy who has spent about $2000 trying to fix the problem between the dealership and another garage. Just about every sensor on the engine has been replaced as well as fuel pump and fuel regulator. The only codes it has consistently thrown are lean codes for both banks. Yesterday it finally stored a random misfire code in pending codes.

When it goes closed loop it has short term fuel trims at 19.5% for both banks and long term fuel trims around 15% for both banks. When in closed loop it idles smooth as glass, but as soon as it tries to idle in open loop it starts loping and missing, it sounds almost exactly like a motor with a performance camshaft.

Also, after it gets warm and you shut it off for 10 minutes or so it is very hard to start. I have been probing around with my oscilloscope for the past couple of days and figured out that during the no start condition the computer isn't sending trigger signal to the coil packs.

After some more testing on the Crank and Cam sensors I believe my Cam sensor is faulty causing the no start condition. The cam sensor on this car has two channels, one with 6 pulses per cam revolution and varied pulse width to signal ignition timing and the second with 360 pulses per cam revolution with constant pulse width to give a time reference to the computer.

When I crank the motor over with the injectors unhooked cold the 360 and 6 pulse signals are all there and clean, when it is warm the 6 pulse signal is still good but the 360 pulse signal is very choppy. I checked the voltage and ground to the sensor when it was cranking as well and they were both good.

The strange thing is the cam sensor was just replaced and is still producing the seemingly bad signal. I guess the new sensor could be bad, but I don't want to be too willing to just throw money at it. I've attached snapshots of the scope view during both cases. The 6 pulse signal is in blue and the 360 pulse signal is in red for both pictures.

Just wanted to get another opinion on it and see what you thought.

Thanks.

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33 replies
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JerryHardway said Jul 03, 2016 21:05:55

Also, I was talking to the previous owner and he said that the mechanic at the dealership thought it was an internal problem in the ECM.

Anybody ever heard of an ECM failure causing anything like this?
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Chris said Jul 05, 2016 18:05:25
I think you need to revisit the MAF sensor. Reading back you stated at idle it was reading 1.85 volts which is way to high. It should read around 1volt at idle and jump to around 4 on a wide open snap. Having a high idle reading will cause the computer to add fuel in closed loop because it's believing there is a lot of extra air to be burned.
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JerryHardway said Jul 06, 2016 02:48:34
Well, according to the factory manual the reading is supposed to be between 1.5 and 1.8 volts at idle so it isn't that far out. I would say the slightly high voltage is accurate because it is having to open the IAC more to maintain the desired idle speed since it isn't running right.
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