Last week I installed a performance prom from Jim at TPIS in my 89 Corvette & it felt even slower, couldn’t even spin the 21 year old tires! So I pulled it out & without it in place it seemed to run better.

Yesterday an elderly friend of mine who’s a retired SAE mechanic hooked up his scanner to my 89 Corvette to see if there was anything out of the ordinary going on with it. He couldn’t get the ECM to communicate with his OBD I scanner. After numerous failed attempts he felt I may have a bad ECM. After I left yesterday he hooked up his scanner to an 88 Chevrolet vehicle of his neighbors & it communicated with out issue.

I got my 89 corvette back running around the 1st of July but have been plagued with drivability problems & lack of power issues. So could I really have a bad ECU? The current one in my corvette is already an AC Delco reman unit, so it wouldn’t surprise me if it failed again. Along these lines someone else said there is usually a cause so be sure to find it. Not sure what I’d be looking for on that one or how to diagnose a bad ecm?

 

Did you also try to scan it with the original prom? Could be an issue with the ALDL connector, wiring, ecm, prom, or scanner. Did you try with 10 k resistor?

 

If the car runs at all, usually its not the ECM. More likely its the prom or the connector or scanner.

I said in the other thread that they don't always like to talk to the scanner. Sometimes you hook up in Run and see if it'll talk, and then fire up the engine.

 

tequilaboy, I pulled the performance prom before I went to have my mechanic friend hook up. He’s not a fan of performance changes & I wanted to avoid an ear full if I still had the performance prom installed! Yeah, I’ve learned with the vette & others that it can be dam near anything. The mechanic tried everything he had & he had it all.

vader86, the corvette does run & “pretty well” overall. My mechanic friend was definitely working the Aldl & was trying it every way possible. It was weird as it would act like it was going to pull the information then just sit & not do anything. No rpm, the temp reading was -40 which he said was a sign of something, don’t recall exactly. He use to work on these corvette when he was at the Chevy dealership & for 81 the guy is crazy sharp too. Looking around it looks like there are ecm’s are around. eBay prices are $400-$600+ and most were just pulled from a wreck so no telling what one would get that route. Summit racing had them in stock. Which I’d lean towards if it turns out to be that.

A few weeks ago I used the paper clip trick to check the codes but nothing engine related. I have my FX3 shock controllers disconnected so I got every code for those! I ordered a Moats Cable setup so I can try to figure that out, should be here by Wednesday. I guess if the moats cable doesn’t end up working (with all the correct software & drivers, etc) then I’m guessing it’s probably time to buy a rebuilt ECM.

 

I doubt Jim at TPIS programmed a chip that made your car go slower with less power. TPIS is a veteran company with the older C4 Corvettes. The computer needs time to learn and build it's fuel trims. When you reset the ECM, you need to drive your car for at least 50-70 miles in and out of WOT along with some hole shot runs. When I tune my 96 and flash a tune into the ECM, it's a process. It takes a minimum of 50-65 miles before I feel or notice the change. If your car is not in good running condition meaning 25-30 year old plugs, O2 Sensor, wires, sensors and switches, your new chip won't do anything but enhance whatever problem is there in the first place. Before you tune, your car needs to run good with no problems. Otherwise, you're chasing yourself and will get frustrated...

 

The first part of diagnosis is will it flash a 12. That would indicate ecm is ready. Checking power and grounds at the ecm. Beyond that you need to follow symptoms chart in the fsm. It's been a minute since I saw a monitor 2000. Does it still have parameters cards? During setup did it ask for body type after asking for engine code

 

I agree Jim is excellent & trust him which I’d why I bought my Cam, Valve Springs, Timing Chain Kit & Performance Prom from him. Your right that the new prom shouldn’t make the car slower & less powerful, which is why I went to my retired mechanic friend to hook up his scanner with only the stock prom in place & see if we could spot anything that was not correct. There’s something I’ve been chasing & could be the reason the ecm isn’t communicating. Thus the reason I reached out on this forum, I need expertise!

 

Yeah I remember him using one of the numbers in the vin, along with year & make of the car. Could have been more he used as well. My friend is an ASE master mechanic & is still very very sharp but he’s also human which is why I wanted to see what others have experienced. I have a FSM & I’ll be honest, it’s a Royal PITA to find anything in it but I’ll fit it up shortly & see if I can find help in it. 🤞🏻

 

I was successful in finding where in the FSM they had “No ALDL Data”. Going through the FSM test procedure with my multi meter I have determined that the ECM or MemCal is bad. Per the FSM directions I’ve ordered a replacement ECM. Also spoke to Jim today & he said the effects of the prom install are immediate & one doesn’t need to drive it any distance or time to notice the changes, they are immediate.