Robmaxfli

I bought a 1981 Corvette only to find that the reason that the check engine light is coming on is because the PROM chip is bad. Chevy doesn't make these anymore for my rare 4spd. Manual Trans. (only for auto). Does anyone know where I can find one of these PROMs. Also , Hypertech chips does make a replacement chip for about $160 and a few extra horses but it isn't a factory correct chip. Does anyine have any experience with these Hypertech chips and how they are?

Dalannex

I don't have an answer, but would like to add to the question. What exactly does the hypertech chip control? Does it make the mixture control selenoid pulse faster, or is it responsible for a different fuel mixture, or does it control the lockup on the converter or what? The computer on an 81' doesn't control enough that I could believe it does a whole lot.

UKPaul

Hi,
If you get really stuck I could copy the chip in my '81 for you, but it would probably only be of use if you've got an Auto (not sure if the rear ratio would have any effect on it - can't think wht it should). There must be somebody over there who could copy theirs for you? Or if you know anybody who can "blow" EPROMS I could email you a dump of mine.
From what I've managed to find out (which isn't a lot) the performance chips alter the advance curve & carb mixture (fuel map) at WOT (they also control the TCC lockup, but I don't know if it is controlled any differently to the standard chip). I think that operation at anything other than WOT is the same as the standard chip. The control granularity (pulsing) is the same as standard for the M/C solenoid (10 pulses/sec?).
It's very difficult trying to get some in depth info on these aftermarket chips, but I've seen opinions of them ranging from excellent to crap. They do a version for use with a low temp stat (160) which has probably got another fuel map & maybe a different advance curve. Personally I'd use that with a 180 stat, as I don't think a 160 would work very well in our climate. If somebody could convince me that one would dramatically improve performance, then I'd probably get one. But, for roughly the same price I could get a Crane cam designed for use with a computer.....
:cheers:
Paul

CHEESERAL

I have an 81 that was originally a 4spd and is now a auto, TH350 non lockup. The only difference I found in the wiring harness is that the manual lacks the wires that control the lockup. My computer was shot and not doing anything, I got a whole new computer from Napa, I think, for about fifty bucks. Plugged it in and everything works great, no more watering eyes from running so rich.

Good luck

adam

Hi Rob;

I have the chip, it's in my car...

If its a standard eprom style, then burning one should be easy around
here. If not, getting an older carb and distributor may be another
option. I've been looking at that idea...

Robmaxfli

Hi Adam,

I'm in Plano. Are you in Allen?.
Are you saying that there is a way to make a copy of your chip that I could use for my '81. I would gladly take you up on that if that's the case. Please let me know if you know someone that knows how to burn these. Or I will gladly investigate this. Mine is a stock Prom chip. My phone number is 972-669-4119. Thanks, Rob

Chris69

Hey Cheeseral, let's get together soon and do some checks on our '81's. I have the Hypertech stage 2 chip (runs the 160 stat). This chip was in the car when I bought it and would like to do some timing checks just for grins. You say you got a whole new box with chip for $50?

As for the other question, I have no way of knowing if this chip actually improved anything. I've heard mostly not. Car seems to run fine with it, but it's frustrating not being able to set your total advance. With 12 degrees initial, total is 44. On the dyno, peak power is reached at 4200 rpm's instead of the spec'ed 5200 rpm's, but not sure how or if that relates...

UKPaul

You just need access to an EPROM blower/burner, or somebody who has one. Once you've got you hands on one, then copying PROMs is easy (it would be sensible to do a couple of spares as well).
Paul

CHEESERAL

Hey Chris, yeah, I took mine to Tiger when I found out the whole thing wasn't working, he got me a whole new computer and put it in, about 50 bucks for the part, took the old one out, threw it in the trash, plugged the new one in, how sweet it ran.

Robmaxfli

Does anyone know what the symptoms are for a failing ECM computer and/or Prom chip? My mechanic is telling me that my ECM is storing codes like "speedometer sensor" while the speedo seems ok, its also storing a variety of others like Solenoid codes . My mechanic is leaning toward replacing the computer. The car has no pickup either even though the carb was just overhauled and the car has only 23K org. miles. My check engine light comes on occasionally prompting these codes. Also, if anyone is interested in making a copy of their Prom chip for me, I would gladly compensate that person. "81 Proms for Man trans. are discontinued. Thanks, Rob

adam

Hi Rob;

Do lunch friday, we'll talk about the Prom.
I get the speedo sensor code occasionally. Unless it's hard I wouldn't worry
about it.

UKPaul

I was getting these intermittant error codes regularly. It was due to bad connectors (corrosion/dirt). As there are very small currents flowing then the connectors need to be good. The speedo sender connector behind the gage cluster on the drivers side just needed a clean to solve the speedo sensor problem. Also try cleaning the M/C solenoid connector & the connectors to the ECU.
Good luck,
Paul

Gator81

I've got a Hypertech chip in my 4-speed '81. My understanding of the performance aspect of the Hypertech modification is that it provides a faster timing advance curve and more total advance. My chip is the Stage II model, which is intended to be used with a 160-degree thermostat; however, I encountered substantial drivability problems with the 160, so I changed up to a 180 and the problems went away. The choke, various smog controls, and thermal vacuum switches (TVS) just wouldn't settle down and stabilize with the 160. The fuel mileage sucked, too.

Changing out the chips was a simple process, no problems, and I've had no trouble with the Hypertech modification in the 6 years or so I've had it.

As far as codes go.... let's see if I can find that old document I downloaded form the Forum way back when... I think it was CheeserAl (Chuck) who posted this.

Get the 5 terminal connector located in the center console under the ashtray. The test terminal is D and the ground is E. With the ignition on, jumper the test terminal to ground. The Check Engine light will begin to flash, one flash, a short pause, then two flashes would be code 12. 12 just says the self-diagnostic system is working. If more than one code is stored in memory the lowest code will flash 3 times followed by the next highest code until all faults have been flashed.

Here are some code explanations:

12 No reference pules to the ECM. This code is not stored in memory and will only flash while the fault is present.

13 Oxygen Sensor Circuit.

14 Shorted coolant sensor circuit

15 Open coolant sensor circuit

21 Throttle position circuit

23 Open or grounded M/C solenoid circuit

24 Vehicle speed sensor circuit

34 vacuum sensor circuit

42 Electronic Spark Timing bypass circuit grounded

There are more codes but you get the idea.

======================================== ===========

There is a complete diagnostic procedure with a catalog of codes in the '81 Shop Manual, available from Mid-America.

Good luck! :seeya

Robmaxfli

Ok Adam , why don't you give me a call @972-669-4119 or let me know a place and time in our area. Thanks, Rob

adam

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