Couple of PROM questions for you guys about my 91 6spd vert;

Here is the story: Earlier this year, I was having problems which turned out to be injectors. After many weeks of not being able to figure it out, I got frustrated and sent it to the stealership. Their "troubleshooting" determined it was the ECM. Wrong. Then he says it must be the PROM, but they can't get one. Well, the tech eventually produces one in an old box that he says is used, so he just gave it to me. Turned out not to be the problem, but I still kept it after getting towed away from the dealer.

Originally (from the PO), my car had a hypertech chip, though I never looked at it. I retained it as well. After replacing the injectors, I started back driving, now with the second hand chip from the dealer.

So now for the questions:

1. Is there some kind of power throttling that changes over at 2000-2500ish rpm? Kind of like the lower RPMs are just kinda weak, but with constant pressure on the gas pedal, it kicks into an extra juice mode when the rpms climb to a certain point. I assumed at first that this was some GM gas saving feature that I didn't have with the hypertech chip before.

2. If this is not standard behavior, is it possible to reprogram the factory PROM? I imagine the possibility that whoever was the PO of that chip has programed a wacky tune on it. I've read on here about people changing parameters, but I'm not clear on whether that is using a stock PROM.

3. I would like to go with a factory chip, but don't have anything against how it ran with they hypertech, so if there is something fishy about my current chip, I'm not above swapping back. However, after looking at my original chip, it looks to me like the factory PROM is just piggy-backing the hypertech chip. This would lead me to believe that I can just unplug the top half and use it. Is this the case, or has something been modified about my "original" chip?



Thanks for any help you guys can provide. I've already learned a wealth of info just by lurking around this forum.

SteelBlue91

 

your factory chip is piggy back on the hypertech
you can remove it and install it into the computer.

I would not use the chip you got from the dealer since it sounds like it is not right.
there is no power reduction in the lower rpms. not on a tpi.

the chip in the hypertech is the one that is burnable. someone can make a tune, burn it to a chip, and you can swap this chip into the hypertech. This is what I have.

 

I have a '93 which has a weird ecm and chip that makes it harder to change out and reprogram, I'm just not sure how it is to be done without having a spare oem on hand in case something goes wrong. Where can you find the parameters of what is oem settings and what settings will do what when you program them. It would seem better to pull the ecm out and install a newer version with a factory programable chip. My neighbor says I should not mess with it as the factory setting is best overall, they know what they were doing. Yea like changing the sparkplugs! I may have to break down and get the tunercat, chip burner etc and see if I can find a used ecm off a lt1 that would work. Not sure if the ones that were used in buick roadmater, cadillac limos would be a source for one. I just want to improve my fuel economy.

 

I dont know what the 93 computer is like on the inside.
Do you have a chip like the one above?

I also had one of those factory chips made for my car based on my combo, it sucked.

 

OK, so I tried swapping back to my original chip and got some unexpected results: (I disconnected the battery for each swap)

With my original chip right in the ECM, I get a SYS on the speedo. The car will crank but no fire. The car will also not enter diagnostic mode (no SES light).

With my original chip/hypertech assembly, The car will run (rough) but throws a code 41, faulty MEM-CAL. I assume it is running limp-home mode here.

In the ordeal with the dealership, I ended up with a new ECM. I am wondering if there is something confused with it; like maybe it is really for a camaro or something...

Under code 41 in the FSM it states:

"The ECM used for this engine can also be used for other engines, and the difference is in the MEM-CAL. If a Code 41 sets, the incorrect MEM-CAL has been installed, may not be installed properly, or it is faulty and it must be replaced."

This would lead me to believe that perhaps my ECM is for another car and doesn't agree with my old chip somehow? But if the ECM is used for other engines, how does it know that my MEM-CAL is not the right one??

SB91

 

code 41 or code 51?

because 51 is faulty mem cal.

41 is Cylinder Select Error.


Are you sure you hve the chip all the way into the ECM?
you even have the little arms on the sides clipped into it?

I got code 51 before and it was my chip that came loose.

 

As stated the ECM was used in multiple cars. The memcal programming is what makes it unique to a particular car / engine / trans combo.
The crank / no start is most likely VATS related; your stock memcal is looking for a set VATS resistance and the Hypertech chip probably has the VATS deleted

'92-'93 LT1 cars were the last of the ECM's (# 16159278 ) with a removible chip. As these were on used in Vette '92-'93 and F-bodies in '93 there is very little support out there compared to the later LT1 cars.
94 went to the alum case PCM with flash memory built in.

 

The weird ECM is functional similar to all the previous ones and totally programable using the right equipment .$175 and a old laptop gets you in
http://www.moates.net/product_info.p...roducts_id=169

Has been done; need PCM and all engine wiring from later Vette.

You need a program like TunerPro or TunerCats to access original settings.Not for the faint hearted.
Read
http://www.thirdgen.org/techboard/di...uide-book.html

 

41 for sure. FSM says 41 is "Cylinder Select Error (Faulty or Incorrect MEM-CAL)". I am about 99% sure I had it seated well, but I will check it out.

The VATS possibility occurred to me, though I don't know how it would have gotten off. I did notice that I got a dash ding sound each time I would reconnect the battery with the old chip installed without the hypertech. So I think something is off before the key is involved. I didn't consider it at the time, but maybe if I activate and then reactivate the alarm? (of course this wasn't necessary with the dealer's chip, and doesn't explain the SYS reading) I will give it a try this weekend.

SB91

 

What are the broadcast codes on the two memcals;
4 letter code visible through a hole in the blue cover ?
They identify exactly what the original memcal program was for.

 

My original chip: DELCO BDBK 4779
Dealer's chip:
The sticker on the chip says "DELCO R665 R665"
There is a duplicate sticker up on the blue cover "DELCO AXCN 9806"

SB91

 

Very strange, I wonder where you got your original chip from?
BDBK is an AUTO LT1 code, AXCN is correct for 91 stick.

The BDBK should be missing the 2 calpak ICs under the knock sensor circuit board, containing the limp home calibrations.

 

It would explain why it would not run with the BDBK memcal (without the Hypertech) as the LT1 calibation is wrong for your L98.
How about trying the Hypertech with the AXCN memcal.That should give you the Hypertech programming in addition to the correct factory calibration.

 

Will do... Unfortunately I won't have a chance to get at it until tomorrow.

I wonder how in the world I was running before. Is the LT1 chip reprogrammable? Perhaps the guy who installed it for the PO used an LT1 chip with an L98 program on it?

Thanks for help guys. Is there some reference on the web somewhere that lists the different prom IDs?

EDIT: Nevermind, found it at chevythunder.com

SB91

 

All of the factory memcals can be reprogrammed; a rather tedious method which is why everybody uses the flash memory chips as you have on the Hypertech.
The only way you could tell would be to get someone with the rightequipment to read the memcal.
As the piggyback runs the engine with the original memcal used for limp home function it could be ( don't quote me) that the LT1 programming was close enough to work in your car.
The late L98's and early LT1's are similar; MAP , batch fire ,etc.

 

Well, I installed the working dealer chip behind the hypertech and everything works more like it was last year before my injector problems. Throttle is much more snappy right at the beginning (coming right off idle), and there doesn't appear to be any powerband issues, though I defer to more thorough testing

I will be contacting hypertech to see if they can confirm that my chip is made for my engine, based off of the model/serial #s. I have a weird feeling since the chip from the PO was not correct for the car, the hypertech is not either, even though it seems to run quite well.

I would prefer, however, to just be running a stock chip. Does anyone know where to get a factory PROM replacement? I had seen someone mention BlueStreak here before, but my dad tried to get in contact with them about his and could never get a response.

Also, does anyone know where the PROM broadcast code goes so that the car knows it is right/wrong? I'm thinking it has to be the CCM, but maybe not?

Edit: always answer my own question as soon as I open my mouth .... looks like a search on the PN off of my chip has revealed that it is indeed for a 1991 manual.

SB91

 

I have and 86 Vert that had a similar problems. PO replaced the stock prom with a hypertech. Ran OK for more than a year and suddenly code 41 and ran really bad. I could not find a stock replacement after more than a month of searching ... had to replace the hypertech with an exact replacement. $200 later car runs great. If I had been the original ower the hypertech would have been free under warranty.

If your car was running with the 91 Prom and no code41 then it has gone bad. You might as well find a stock chip or get the right hypertech chip.

Good luck

 

I forgot to mention that hypertec will bench test your PROM for free. Unless you were the orignial owner they won't replace it for free.

Cyl. Select error = bad prom
Good luck.

 

Well, I've been running for several days now with the PROM from the dealer behind the hypertech. I feel pretty good about the hypertech since the part number matches what it is supposed to be for my year/trans. Car runs great, very punchy.

I still plan on tracking down a known good factory PROM. Anybody have any good sources?

SB91

 

The AXCN is as stock as it gets. Try the AXCN memcal without the Hypertech adapter.
The LT1 BDBK won't work! It has its own knock sensor circuit and is missing the limp home calpaks, needed for the earlier 90 and 91 ECMs.

Is the AXCN yours for good or do you have to give it back? If it's yours you should be fine just like you're using it now.