I'm tuning on a 1991 Corvette with a 0122 7727 ECM. I use a Moates ZIF socket, a 27SF512 chip, and tuner cat.

The other day, I was changing some of the values associated with the VSS sensor in an effort to get my speedometer to read correctly with the 4.10 gears I've installed. Specifically, I was changing "Instrument Panel VSS Pulse Divisor." I was using the trial and error method, and trying to come up with a value for this field that would yield something close to the correct speed on the speedometer.

After making 3 or 4 changes, it looked like I was making headway and might be able to get the speedo pretty close. I changed the value for what I hoped would be the final time, burned the chip, and installed the chip in my ECM.

Once I turned the key on, the ECM immediately went into some kind of panic mode because both cooling fans came on. I started the car, and the 'SES' light immediately lit and the idle went to 1500 RPMs. I shut the car off and checked the orientation of the chip in the ECM, it was installed properly. Next, I thought it might of been something with the new value I inserted in the 'instrument panel VSS pulse divisor' field so I swapped back to a tune where the value was unchanged from stock. Still the same problem, immediate SES light, high idle, and instant cooling fans with the key on. I also noticed that my engine temperature reading on my scan too was -36 C. That reading rose at the rate of one degree per second until 91 C, where that value stopped changing.

Next, I dug out an old hyper tech power chip that I had laying around from a few years ago. I installed that and the symptoms changed.

The cooling fans behave normally, the car idles at 800 RPM's or so like it should, but the check engine light blinks rapidly.

When I bought this car a few years ago, it had the hyper tech chip in it and what appears to be a hyper tech brand chip socket. The socket has 'hyper tech' typed on it, so I am fairly confident that it's not the stock socket. I thought my ZIF socket might be causing the problems, so I pulled it out and reinstalled this hyper tech chip socket. The problems changed again:

With the hyper tech socket and hyper tech chip installed, the car would barely run. It idled really low, 400 RPMs or so, and would not rev above 700 RPMs no matter how much throttle I gave it.

I tried my 27 SF512 chip and the hyper tech socket as well. With this combination, the car wouldn't even start.

So, any thought's on where to go from here? New ECM?

 

I also noticed that the ALDL port is now dead. I can't get my tech 2 or my scan tool to read anything from the ALDL. I tried jumping pins A and B on the ALDL connector to get the ECM to flash codes, and I get nothing. At the very least it should of flashed code 12.

Since the ALDL port seems to be dead, I am leaning towards a bad ECM. I do flip and flop it quite a bit when I swap chips, so I don't suppose it's out of the question that it took a hard enough whack to crap out, but I'm always pretty careful with it.

I'm also wondering if by installing a faulty chip I could of caused some kind of permanent damage to the ECM. The 27SF512 chip that I've been using has been erased and burned probably 100 times, so I guess it could of been on it's way out.