I recently bought a 1997 Blazer that the engine had been replaced. The guy told me it was from a 2000 and had 80000 miles on the engine. My problem is that with the engine off and key turned to on my SES never comes on.

Another unrelated or related problem is that I have rough idle but rolling down the road it runs great.

I do not think when the engine was replaced they did not replace the computer. Does a 1997 and a 2000 take the same computer?

Open to any suggestions.

 

No, the computers are different. Even without the light the codes will be in there. The mechanic may have disabled the light. Check the codes and post them.

 

P0306
p0141
p0146
p0147

 

PCM's are definitely different, and they are not the only things different between 1997 & 2000. 1997 did not have a BCM, 2000 does. 1996 & 1997 are the only years that used 4 oxygen sensors. 1998 and newer have 3 sensors. P0146 & P0147 both relate to the oxygen sensor behind the catalytic converter.


If they changed the PCM with the engine, there will be continuous secondary air system faults, (1997 did not have it). The check engine light on your 1997 is controlled by the PCM. The check engine light on the 2000 uses data from the PCM and the BCM ultimately sends the data to the instrument cluster for the check engine light. If they did NOT change the PCM, the crankshaft position sensor relearn MUST be performed. The PCM either needs to remain with the engine, or the relearn must be done to the original PCM. If it is not done, the PCM will be using the relearn data from the original engine, which is incorrect for the 2000 engine. Ignition timing, injector timing, and misfire data will all be incorrect. P0306 is indicating a misfire on cylinder #6, however, if the relearn was not done, you can't trust the accuracy of it. Bottom line: The engines can be swapped, but the tech doing the swap needs to be very familiar with the differences. If not, you'll end up with stuff not working right, like the check engine light My advice, take it back to them and have them fix it.

 

Returning it is not an option. I bought it from a private party and drove 600 miles round trip to buy it. The guy I bought it from swapped it out in his garage. Apparently his son had wrecked his 2000 so they got this one I have to put an engine.

I have a decent mechanical knowledge but I will be the first to admit when it comes to car computers I'm at a complete loss.

I understand what a relearn would be but have no idea how it is performed.

My next questions would be how would I go about determining if it is in fact a 2000 engine and if it is would I be able to buy a computer for a 2000 and would it mount with the existing wiring harnesses?

Other than the rough idle [ which is at 500rpm which I think is a little low] and the SES not working this blazer runs like a champ. I get about 19mpg and it actually hums running down the interstate.

Maybe I'm being too much of a perfectionist?

 

Stick with the 97 computer. Too many changes were made. Did you erase those codes you posted? Erase them and start with a clean slate. See if they return. Hopefully, they were from the original motor before it was replaced. For the most part, a humming motor that gets 19 mpg is a winner. The serial number would be the way to determine it's year of manufacture. All my heroes are perfectionists.