1985 burn off module
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
They don't hardly ever go bad - I've heard them described as "about as reliable as the Frame". This is unlike the "improved" '86 and newer design that uses two relays for the same functionality...
Thread Starter
Cruising
Joined: Feb 2004
Posts: 12
Likes: 0
1985 burn off module
Yes it is discontinued, so I have to scrounge on ebay. I opened the "can" as it were and the circuit doesn't look to complicated. Couple of logic chips, couple of transistors and a few diodes. One very large power rectifier, relay and lots of passive components. My guess is a diode, transistor or power rectifier has pooped out. I don't see any burns or obvious signs of a meltdown. Being an electrical engineer, I am almost tempted to re-design the control circuit as it looks fairly simple by today's standards. I also looked at a post somewhere that talked about changing the ECM for an 86-89 unit and using the external (in the engine compartment) relays. Don't know if anyone has tried it. The other advantage was supposed to be that the 85 ECM is very slow and that improved performance/responsiveness was also possible. Sorry for the length but once I got going, I kind of got into it.
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
I swapped my 85 ECM to a 1986-89 ECM, all you need is the ECM with Chip, got mine on Ebay.
Then re-pin the pigtail, then you can use all of the newer relays in place of the outdated stuff.
BUT if you can redo it, more power to you!
http://www.eecis.udel.edu/~davis/z28/ecm_swap_730/
Then re-pin the pigtail, then you can use all of the newer relays in place of the outdated stuff.
BUT if you can redo it, more power to you!
http://www.eecis.udel.edu/~davis/z28/ecm_swap_730/
Thread Starter
Cruising
Joined: Feb 2004
Posts: 12
Likes: 0
1985 burn off module
Great site, and thanks. Wow, you sure put a lot of effort and work in, and nicely documented. Do you think it be possible to make a converter harness to do the re-pinning, and have the car cables hook to it (like the 85 ECM) and then wire to the new connnector to connect to the 86 ECM? I am thinking just a short unit like 4 inches long or something like that.
I have checked the price of a used ECM, and with the relays this could be less than the 85 module. I have a performance chip in my 85 ECM (hypertech 11551), I wonder if that can just plug into the 86.
I have checked the price of a used ECM, and with the relays this could be less than the 85 module. I have a performance chip in my 85 ECM (hypertech 11551), I wonder if that can just plug into the 86.
Le Mans Master
Joined: Jul 2001
Posts: 6,252
Likes: 2
From: Silicon Valley Kalifornia
What I've done on mine is to bypass the onboard relay in the burnoff module. It does all the work. Actually I tapped into this relay and now the only actual "work" it does is to power an external 30amp relay I got from radio shack. The external relay runs the MAF and performs the burnoff duty too. They're about ~$4. Much cheaper than an 85 burnoff module! Just some simple cuts and jumpers on the module printed circuit board and I'll probably never need to replace it. Got 3 modules cheap from a wrecking yard that didn't realize what he was selling. Years ago before being discontinued the 85 modules were like $700 new....if memory serves correctly.
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Le Mans Master
Joined: Jul 2001
Posts: 6,252
Likes: 2
From: Silicon Valley Kalifornia
Great site, and thanks. Wow, you sure put a lot of effort and work in, and nicely documented. Do you think it be possible to make a converter harness to do the re-pinning, and have the car cables hook to it (like the 85 ECM) and then wire to the new connnector to connect to the 86 ECM? I am thinking just a short unit like 4 inches long or something like that.
I have checked the price of a used ECM, and with the relays this could be less than the 85 module. I have a performance chip in my 85 ECM (hypertech 11551), I wonder if that can just plug into the 86.
I have checked the price of a used ECM, and with the relays this could be less than the 85 module. I have a performance chip in my 85 ECM (hypertech 11551), I wonder if that can just plug into the 86.
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
Great site, and thanks. Wow, you sure put a lot of effort and work in, and nicely documented. Do you think it be possible to make a converter harness to do the re-pinning, and have the car cables hook to it (like the 85 ECM) and then wire to the new connnector to connect to the 86 ECM? I am thinking just a short unit like 4 inches long or something like that.
I have checked the price of a used ECM, and with the relays this could be less than the 85 module. I have a performance chip in my 85 ECM (hypertech 11551), I wonder if that can just plug into the 86.
I have checked the price of a used ECM, and with the relays this could be less than the 85 module. I have a performance chip in my 85 ECM (hypertech 11551), I wonder if that can just plug into the 86.
I bought new pins at my local GM dealer, then cut and solderd longer wires onto to the pin wires I pulled out.
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
NAPA has the burnoff module - I paid $250 or so for one back in 2005 there. Just because the General has discontinued a part doesn't mean there aren't other sources... BTW - I still have the original I took out of the car - Known good, 22 years old...
The '86-'89 ECM is not significantly faster or 'better' than the '85, although it Does have a faster baud rate to the diagnostic link and is therefore better for datalogging. The '85 unit uses a "bare prom" and is therefore a bit simpler to play with chips, not a Big deal either way. Both are still very slow by todays standards, both are still "batch fire" systems and limited in what they can do.
It's an easy enough swap to use the '86-'89 ECM in an '85 - minor wiring changes and it's done. It would also mean buying the correct cables, adapters and mask file for editing the '86-'89 chip (different than what I already have for the '85).
In general the '85 MAF control module is far more reliable than the two relay setup used in the '86-'89 - although it is considerably more expensive if it Should die.
The '86-'89 ECM is not significantly faster or 'better' than the '85, although it Does have a faster baud rate to the diagnostic link and is therefore better for datalogging. The '85 unit uses a "bare prom" and is therefore a bit simpler to play with chips, not a Big deal either way. Both are still very slow by todays standards, both are still "batch fire" systems and limited in what they can do.
It's an easy enough swap to use the '86-'89 ECM in an '85 - minor wiring changes and it's done. It would also mean buying the correct cables, adapters and mask file for editing the '86-'89 chip (different than what I already have for the '85).
In general the '85 MAF control module is far more reliable than the two relay setup used in the '86-'89 - although it is considerably more expensive if it Should die.
