New PCM = Less power? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 10-01-2006, 08:54 PM   #1
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Default New PCM = Less power?

Okay, so I've gotten my Bonneville back from the dealer with a new computer installed and programmed. And she runs perfect... except that she doesn't seem to have the same kick she used to have. In fact, it runs about like it did when I drove it for a few weeks with the Supercharger belt off. I'm going to call the dealer back, and see what he thinks, but I thought I'd run it past you guys first.

This car is a '96 SE, upgraded with the L67, supercharged engine. It is badged with a "Supercharged" emblem on the trunk, but other than that, it looks like a typical SE car. There isn't even a boost guage in the dash. If he programed the new computer like a normally aspirated one, failing to notice the SC, would I see basically weaker performance like that? (Just a thought)

Is it possible that the old PCM was not a stock unit and had been upgraded to something aftermarket that was making her run faster... and now I've got a stock one?

Again... she runs good..... just about 20% less kick in the pants than she used to have.

A side note: The dealer told me the car needed a new O2 sensor, and I should bring it back in. The CEL was not on, he says, because the sensor was stuck in the middle range and thus still sending a signal. The next day, the light came on and there is a strange smell upon turning the car off. (symptomatic of a bad O2, I understand). It ran weaker from the time I picked her up, though.

Any thoughts appreciated, as always!

--Mike
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Old 10-01-2006, 09:01 PM   #2
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You'll have a learning period of about 100 miles while the new PCM learns the way you drive

An NA pcm wouldn't work in your car due to boost control etc.

If you have known issues, get them cleared up and give the car 100 miles before worrying about how it really feels. It'* probably just learning.
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Old 10-01-2006, 11:29 PM   #3
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Bill Boostie is right.... time and mileage will tell.
Also, the o2 sensor can have a big effect on performance. If you have a bad one and then you put a good one in you will notice a difference almost immediately, and the power will return as the computer adjust itself back to it proper settings for fuel and spark.

If you need the front o2 sensor you will need AFS75 (also AFS 75) and you should be able to get one on ebay for about 1/3-1/2 of dealer price.
If/when you do replace the o2 sensors the only one that is fit for your car ....OEM GM AC Delco o2 sensors.
Other brands such as Belkin, Bosch, etc... have proven to be not a very good brand in our cars, not giving good mpgs, and poorer performance.
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Old 10-02-2006, 02:42 AM   #4
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I believe some members have had luck with Denso sensors as well, there was a thread about them a while back and they seemed to be thought of rather well.
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Old 10-02-2006, 07:10 AM   #5
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Hey, thanks guys! I'll get the O2 checked out and verifty that it was causing the light and give her another hunred or so.

Mike
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