PCM after engine swap...CASE relearn???

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budh420
Posts: 7
Joined: Thu Nov 25, 2010 3:50 am

PCM after engine swap...CASE relearn???

Unread post by budh420 » Tue Nov 30, 2010 12:50 am

I have a 97 chevy malibu v6 3.1 and did a engine swap (complete used engine, used nothing on my old engine) I cant get it to idle right and not getting good gas mileage around city ( tons of traffic and lots of stop and go, CA) I read on the internet that if you do a engine swap you need to do a pcm reflash or a CASE relearn. I have a scan tool and its not picking up any codes and ses or check engine light is not on. Even though there is no ses or check engine light on or fault codes set can this still cause my problem? If it is off an idle at like a grand it is fine, also I was driving on the freeway the other day at about 70 and all of a sudden my gas guage, temp guage, went to 0 and my ses, abs, anti theft lights came on and my mph went to like 110 mph for about a mile I was getting ready to pull off the freeway then every thing went back to normal, this has happend 3 times now in about 4 months, I got the car with a bad engine so I have only drove it with the motor I bought, this was my cousins car and she said she never have these problems, but she also had a coolant leak and burned up her engine, any help would be greatly apprecited. Thanks

The Genreal2tcd

Re: PCM after engine swap...CASE relearn???

Unread post by The Genreal2tcd » Wed Dec 01, 2010 1:05 am

Even if there are no codes, the PCM may need to be flashed.
The gauges problem, ABS, SES, etc are related to the Body Control Module (BCM). You may have a bad unit, or a wiring problem.

protech

Re: PCM after engine swap...CASE relearn???

Unread post by protech » Wed Jan 26, 2011 9:52 pm

If you got the used engine from a similar model and year, you should have no PCM issues at all. All the sensors and wiring would be the same, so there is no reason you would need a reflash after an engine swap. As for the driveability problem, and depending on the condition of the used engine, it could be as simple as just being worn out. You could have clogged fuel injectors or a throttle body with excessive carbon build up. An idle problem can be due to a faulty idle air control valve, or throttle position sensor, although they usually will set a code if they are bad, but still need checking. The exhaust could be plugged up, including a bad catalytic converter. Lots to check for this kind of problem.

Now with the problem you encountered with all the lights coming on the dash and the gauges acting erratically, I'd bet there is a wiring problem somewhere. I'd start by checking all the connections you made when you took out and replaced the engine. A loose ground can cause this issue, as well as a power wire that might be shorting out on a metal bracket somewhere. A general look around and tug at all the harnesses is an easy way to do a first check.

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