9C1 computers

[1968 Pontiac]

The odd time I see 1989-96 police cruisers in the bone yard. I've been tempted to take a computer and throw it into my 91 Caprice, but was wondering if the computer was swapped out before the car was turned over to civilian use. Does anyone know what the part numbers are of the 9C1 computers? Thanks.

[silicon212]

Doesn't matter, they're the same as in a civilian car. The "cop chip" theory is a myth.

[Blue Bowtie]

You couldn't use a '94-'96 PCM anyway. The 1993 and earlier ECMs might be compatible. Some of the 9C1s had no speed limiter, a different DFCO, target idle, TCC thresholds, different fan temps, different injector constant due to a different pod and injectors (TBI), WOT TCC lockup enabled, and a few other changes. You most likely wouldn't be able to tell just by looking which cars had it or didn't. None of the factory programs had Highway Modes enabled, even though the highway patrol cop cars could have saved a lot of fuel that way.

It doesn't matter much anyway, since you can program them a lot better than the factory did in either case.

You likely have a 1227747 ECM in your '91. That uses a 2732 EPROM. That's a plain old, 4K PROM. You can find the same ECM with no speed limiter in many 305 TBI F-bodies from 1987-93, L03s, L05s, 454 Truck TBIs, 262 V6 trucks, so long as they were equipped with 16" wheels. That's still not a great deal better.

There are a half-million places on the web to find good binary files, and you can find the software to write your own in another half-dozen places. It's all free, except for the PROM writer and the $6 PROM itself. If you need a burn, just ask around.

[Blue Bowtie]

FWIW, with just a cursory search, I found one of my favorite haunts has no fewer than NINE different binaries for the L05 alone, and that's not counting a few F-Cars that might have have a manual trans. There are a few differences. As Silicon mentioned, however, there is no mythical "Cop Program" that went in all SEO cars. They probably run the gamut like any other family of vehicles. I know that the '94-96 LT1s are identical between the intended vehicle customer.

[1968 Pontiac]

Thanks for all the info.

[HLandin]

Originally Posted by Blue Bowtie

None of the factory programs had Highway Modes enabled, even though the highway patrol cop cars could have saved a lot of fuel that way.

What is this Highway Mode your referring to? This is the first I've ever heard of that.

[Blue Bowtie]

If you want a full rundown of the capabilities of the C3 and P4 GM ECMs, go to the "Center of the Universe" for information regarding them - www.ThirdGen.org, and visit the DIY-PROM message board. Craig Moates' message forums are catching up, and lots of threads are cross-posted between the two sites, but ThirdGen.org is still the largest information clearinghouse of the ECMs used in this vintage of vehicle. People with ThirdGens have explored all the known capabilities and limits of the hardware, and many times surpassed the original capabilities. Moates' "Ostrich" and other special hardware was a direct result of the discussions at TGO.

Incidentally, "Highway Fuel Mode" is programming that GM Powertrain/Delco Electronic (before they were Delphi) provided in every EFI engine ECM. It allows light load cruise fuel mixture up to 18:1 for maximum mileage. GM effectively disabled this programming by setting the minimum MPH for invocation of the routine at a ridiculously high number, where the load value (LV8) would be above what would allow the routine to execute.

There is also a "Highway Spark Mode" which is similarly disabled. It is a table of ignition advance adders at various RPMs and Load Values which can effectively increase light load, low RPM spark advance to over 50° BTDC. Combined with Highway Fuel Mode, this can allow a relatively potent 350/L98 to sip fuel at the rate of over 30 MPH highway. Many people there have done it.

The suspicion is that GM disabled the programming since they had no control of the conditions under which the vehicle may operate, and the remote possibility of going too lean and burning a piston or valve was not worth the warranty risk of potential repairs in exchange for really good fuel mileage in a mid-80s vintage vehicle. I have an '86 Trans Am that easily does 31 highway MPG at 75 MPH. As long as the EGR system is operational, there are no problems. My peak advance is 48°. HFM target mixture is open loop and over 17:1. I played with several programs to get to that point.