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Engine stumbles - EFI Question

2284 Views 9 Replies 3 Participants Last post by  zwede
Sorry not sure this is the right area to post this question. I know this is not exactly a Chevelle question, but I'm sure someone here can answer my question.

My daily driver for going to work is a 95 Cutlass Cerria that I inherited from my mother. The engine is a four cylinder 2.2L. It has a severe stumble/hesitation at highway speed. This happens during crusing, light/medium accelleration and light deaccelleration. The engine just runs horrible with a jerking/stumble or hesitation. At WOT it runs fine, I don't feel any stumble, good power at least for a four banger. Idle is smooth.

The check engine light is NOT on and when scanned there are not any codes. I've had a Chevy dealer and a local repair shop look at this. Both acknowledge the problem and both are completely clueless. Without any codes showing they just say "can't do anything without knowing a trouble code". Whatever happened to doing real trouble shooting without a computer?

I've replaced a few of the simple and cheap things, spark plugs, spark plug wires and fuel filter. Didn't help anything.

I don't want just to throw expensive parts at it hoping something works. The cheapest injectors I've found run about $70 each. My EFI knowledge is severly limited as is test equipment other than a simple volt/ohm meter.

So where do I start trouble shooting this? This car only has 86k miles on it, so there is still a lot of life left in it. I just can't stand a horrible running car.

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I'd use an OBDII scanner (not a simple code reader) and look at the live data while the problem is happening. I have an Actron CP9575 and it does a good job for ~$100. I'd look at what the O2 sensors are doing (lean/rich), is the computer pulling timing due to false knock readings, is the intake air temp suddenly reading 255F due to a short, etc, etc. So many possible problems you can check with live data.

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Sorry, missed the 1995 part!

Well, 95 was a transition year for GM. Many 95 Chevys have OBDII connectors and will talk to OBDII scantools. But I can't say for sure that your Ciera will.

You could go to an autoparts store like Advance/Autozone/Oreillys and ask them to scan your car (they do it for free). If their OBDII scantool connects and reads you should be able to scan it with the CP9575.

I haven't heard anything about the '95 GM PCMs being limited in capabilities? My experience is with Camaros and the PCMs were almost the same between 95 and 96. The OBDII capable PCM came in 94 on the Camaro.
Read my first post again. You're not looking for codes, you need to look at live data.
Maybe not with the scanner you bought, but OBD1 does provide live data.
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