ECM swap aftermath

[ChrisWhewell]

Some of you might recall I had an intermittent rpm gauge failure on my 90 that affected the AC functioning.   To remedy it, I did an ECM swap and the display problem went away, hurray.   But, I don't know if its me or if its even true, but I sense the car seems to have less pickup after the ECM swap.   Am I crazy for thinking this, i.e., is there any rational basis for why an ECM swap might make the car perform worse ?  The ECM I swapped was from another 90 model.   I swear it made the car perform worse, but I don't know why that might be the case.... any thoughts appreciated, thank you.

[2seater]

Since the new ECM is starting from scratch it will take a little time correcting the nuances of proper fueling and such but the ECM itself shouldn't have a direct effect unless there is a fault in the information exchange with the sensors. The EEPROM was swapped in from the original ECM, correct? The chip contains the bulk of the performance parameters, including the default or limp-home program. You might take a tour through the ECM diagnostics to see if any readings look out of line. 

[KDirk]

Probably a long shot, but if you used the PROM in the spare ECM make sure it has the same four letter code as the one in the ECM you replaced. I say this because maybe someone put an incorrect PROM in your spare ECM prior to your ownership.

 

Also keep in mind there were two versions for each model year, a federal emissions PROM and a California version. I would expect the Cali version to be decontented in performance versus the federal version to lower the emissions output at the cost of power. Of course, if you reused your editing PROM then all of this is moot.

 

Finally, as already stated, the ECM needs to relearn the operating parameters of the engine when it is replaced. This is usually a short term process (50-100 miles of driving tops) and should sort out rather quickly.

[padgett]

Not only that but some years had revisions to the programming that resulted in a different code. My '88 ANCX was a revision released in late 88 to correct some issues. AFAIR there were later releases in 89 and 90 also (mainly to increase the fuel pump shot when the ignition was turned on to help cold weather starting AFAIR).

 

[ChrisWhewell]

I didn't switch the proms, just the whole ECM.  I read the code for the prom on the old ECM in the past, and also for the new one after installation of the replacement ECM, and they were the same number.  I got it I think it was code 99 in the data retrieval from diagnostics, they were both the 8064 number, the non-California version.   It just idles rougher and doesn't have the pep I perceived it did with the other one.   No problems starting or with any stalling, etc.  Just seems wimpier.    Thanks for the replies

[2seater]

The simplest thing would be to switch PROM's to see if the lost performance returns. Is there any chance one of the proms was reprogrammed at some point? I suggest looking through the various sensor readings as it right now to see if the timing looks correct, check to see the TPS responds properly, the MAF looks about right etc... It may just be coincidence something else has gone astray?

[padgett]

I base my programming for a 90 on the 8064. It has the long crank prime.