Engine swap- is there an ECU change too?

[jgiedt]

I bought a '94 Buick PA that had a Supercharged engine, but was swapped to a normal aspiratoin engine. The engine has always idled a little rough at low rpm's, but this week it started throwing codes and the check engine light comes on w/i the first 5 miles of driving.

My mechanic told me that there are too many codes to sort through and he believes that the ECU is bad or perhaps the wrong ECU for the engine.

How can I troubleshoot this w/o taking this to a dealer. Is there a serial number code on the ECU that can tell me if I have the correct ECU or not? Where is the ECU on this car?

All information and ideas are welcome! I need to get this fixed "on the cheap".

Thanks- jg

[maxwedge]

What were the codes, need this info for starters.

[HotZ28]

It is obvious why you have so many codes. One thing for sure, if the prom (chip) was not reprogrammed, or changed from SC to NA parameters, the settings are incorrect and you will have an abundance of erroneous engine control functions. Furthermore, the ECM cannot monitor current engine functions using an SC/ECM (prom). It just will not function properly! You need to change the prom to settings programmed with NA settings!

[jgiedt]

So am I to understand that the existing ECU can be reprogrammed? That would be much better than replacing it.

FWIW, I do not KNOW that the guy that made the engine swap did or did not program the ECU, but am assuming not by the performance. There where 9+ codes, and they where not all provided to me, as it was obvious to the mechanic that the issue was not actually the codes, but the ECU. The one he did mention was crank position sensor if memory serves.

It sounds like this is a job for the dealer- reprogramming?

TIA-jg

[HotZ28]

Actually, the dealer does not reprogram proms (chips), they simply replace them with a pre-programmed prom. Starting with the 1996 models, the PCM can be reflashed (reprogrammed).

You should be able to get a correct programmed prom from your dealer and install it in the ECM yourself. This is a very simple procedure.

If your car is OBDI, the ECM will be located under the dash on the passenger side. Remove the wiring harness from the ECM and remove it from under the dash. You will see two small bolts on the back side, holding a small cover on. When you remove the screws and cover, the prom will be in front of you and inserted into the PC board. Slide the clips back on each side and lift up, to remove the prom. Install the new prom in reverse, be sure to insert the prom in the right direction and press down until both clips lock into place! Reinstall ECM in reverse order and you are done!

BTW, do not confuse the ECM with the prom or (chip). They are two different parts. The newer cars (96) up do not use a prom! In addition, do not forget to disconnect the negative battery terminal, before removing the ECM!

[jgiedt]

Yep- This sounds simple enough. I've changed LOTS of proms on digital audio equipment before, so this should be simple stuff. I'll take it by a dealer to verify that the prom is SC and should be normal aspiration. If it is incorrect, I'll just buy the prom and do it myself. Thanks for the info!-jg

Originally Posted by HotZ28

Actually, the dealer does not reprogram proms (chips), they simply replace them with a pre-programmed prom. Starting with the 1996 models, the PCM can be reflashed (reprogrammed).

You should be able to get a correct programmed prom from your dealer and install it in the ECM yourself. This is a very simple procedure...

BTW, do not confuse the ECM with the prom or (chip). They are two different parts. The newer cars (96) up do not use a prom! In addition, do not forget to disconnect the negative battery terminal, before removing the ECM!