So here's a little background.....

I scored an 89 vert that has a 91 TPI vette engine in it. Someone hacked the wire harness so I'm trying to clean it up. I converted it to an 7730 ecm and have an old version of EASE scan software laying around. The problem I'm having is it recognizes the ALDL cable is hooked up but it never establishes connection.

I need to get some good scans to clean up the tune and make sure it is going in closed loop. It has a rough start problem and the check engine light doesn't come on so I assume someone hacked it up.

How can I test that the ALDL port is working correctly so I can determine if it is a car/wiring issue or a scan software/cable problem. I'm leaning towards a car/wiring issue.

Suggestions?

 

Using a DMM, measure the voltage at the ALDL serial data pin with the ALDL cable not connected. A pull up resistor should be pulling this voltage up to +5 volts. If you see the +5 volts, I think you might have an issue with the ALDL cable and software. If you don't see the +5 volts, then the issue is with the car.

If you know anyone who has an oscilloscope, you can also connect that at the same time the ALDL cable is connected and see if it is send data request commands. I don't know the ECMs by year, but if it is an 8192 baud ECM, the software has to send a data request command and wait for the ECM to respond.

 

I tested the voltage for both the serial (E) and diagnostic (B) ports and both are reading 5 volts.

I went through the gauges and made sure all the gauges lights were working. When I start the car the engine light now comes on immediately and stays on. When I ground out the diagnostic port (A & B) the engine light stays on steady with no flashing.

VATS has been bypassed on this car also.

Could it be an issue between ALDL connector and ECM? Can I wire it directly from the ECM to rule out a wiring issue?

I need more suggestions on next things to check. I know it needs a tune but it runs terrible and is barely drivable.

 

Have you ruled out bad ecm?? If ecm is not going into diag mode with a&b jumped that could be the $100 prob

 

I thought about it but I have swapped it with another 730 ECM I have with the same results. I swapped the memcal also with another I have. Wouldn't it shut down after a few seconds due to the VATS being disconnected? The chip I burned disables VATS.

The car will start then die unless you throttle it up. If you throttle it up it will eventually idle after it warms up. Once it warms up and is idling the throttle response is terrible.

 

You have a tough one on your hands! I would try ruling out your computer and cable too. Do you have any friends with a GM car you could scan to verify your computer and cable? That way you at least know that side of the problem is working

The fact that the Check Engine light works but doesn't flash codes is concerning. Did you trace out and ohm out all of those wire paths? The fact that you see 5 volts does give you a warm and fuzzy. Did you check ground on pin A? Does that ohm out good?

My last shot in the dark would be that I think these cars go into a very basic limp mode if the ECM detects a PROM error. Can anyone else chime in and verify? Could it be in that limp mode?

 

Car will go into limp with PROM error. Amazingly, these cars run pretty good when the ECM goes bad. I drove my car, on and off, for months chasing down problems before I replaced the ECM. Like the OP stated. Once the car warmed up, it ran pretty good. But getting it to start at first was the problem.

My tell tale sign the it was the ECM was not reading any data through ALDL, yet it showed "connected" and not having the SES light flash off when I turned the key.

 

I checked voltage but not the ohms. I'm going to focus on getting the ses light working again before I mess with the data logging. I'm thinking if I fix one I may resolve the other issue. I am going to reburn the prom again also to see if that changes anything.

 

If you are pulling the PROM to burn it again, go ahead and power up the car with the PROM removed. Verify the voltages on pins M and B to be 5 volts again. Try the paper clip to see if the light stays solid still. If so, that would lead me to believe that the PROM might be bad.

Lastly, you might want to try to start it with the PROM out.

With the PROM out I would read what is stored on it. Ask around for the stock bin file from someone else and do a compare between the two files.

 

I tried another quick test this evening and I think I narrowed it down to memcal/prom.

I was able to borrow an untouched AUJP memcal and plugged it in. The car wouldn't start (due to VATS enabled) but I was able to bridge terminals A&B and have it flash error codes back.

I fired up the old laptop and scan software which connected immediately and reported a VATS error code back after attempting to start it.

This is frustrating but at least I think I've narrowed it down. I have to figure out if it's the memcal or prom. I'm thinking most likely prom and if so why? I'm using AT29C256 chips.

I also ordered a moates adapter. Anyone have a stock AUJP memcal for sale?

Thanks for all the suggestions.

 

Update - I think I found the root problem.... I feel like such a noob. I'm using a pocket programmer and I noticed when I pulled the file off of the original AUJP it was larger than 32kb. I also noticed the checksum was coming out all zeros so I went through the settings and it looks like it was in hex mode even though the files were saved as bin. I was able to burn a new bin without vats and started the car up. It started but ran like crap.....I knew it was going to need tuning but it ran like a different kind of crap than before. I was able to also bridge A&B terminals and have it flash back the codes.

I'll be hooking up the scan software this weekend to do some tuning. Also I'm still needing a stock AUJP memcal if anyone has one.

Thanks again for the help.