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**Gmtech1005** · 11-30-2002, 08:03 AM

hi, thanks
I don't think that it is the fuel pump that the pcm turns off, but I checked out the system on SI2000..(GM's online sevice information site)anyway and found the following.

Fuel Cut Off Mode
The PCM has the ability to shut OFF the fuel injectors completely or selectively when certain conditions are met. This fuel shut off mode allows the powertrain to protect itself from damage and also improve its driveability.

The PCM will disable the injectors under the following conditions.

Ignition OFF (prevents engine run-on).
Ignition ON but no ignition reference signal (prevents flooding or backfiring).
High engine speed (above red line).
High vehicle speed (above rated tire speed).
Extended high speed closed throttle coastdown (reduce emissions and increases engine braking).

Fuel RPM cut off ranges:

Important
These RPM cut off ranges may vary according to PCM calibration, axle ratio, tire size, and tire rating.

Park and Neutral - 4000 RPM
Reverse - 4000 RPM
Drive - 5950 RPM

© Copyright General Motors Corporation. All Rights Reserved.
1998 Pontiac Firebird

that was directly from GM, and it is a 1998. The systems work the same though. The pcm turns off your injectors. The computer is factory programmed on my 1997 firebird for 115mph tires. It shuts off injectors at 117mph, even though i have z rated tires on it. I'll look at the schematics and try to figure out a way to get around it, but it doesn't look too good. I'll keep ya posted if I find anything.

**Gmtech1005** · 11-30-2002, 08:35 AM

ok, found some info about the injectors that might help. From your underhood electrical center, you have a 15A mini fuse which is hot in run, bulb test, and start and is labled " inj 1" which spans from terminal j9 to j8. J8 is a 0.8 pink and white wire #639 which goes into connector c100. From there the wire becomes just pink and enters splice pack s102. From that splice pack the pink wire..still #639, feeds every injector. So basically they all get their power through fuse "inj 1". Now, from injector #1, you have black wire going to the pcm. From injector #2 you have a light green and black going to the pcm. From injector #3, you have a pink and black wire going to the pcm. From injector #4, you have a light blue and black wire going to the pcm. From injector #5, you have a black and white wire going to the pcm, and from injector #6 you have a yellow and black wire going to the pcm. What all this means is, each fuel injector has a common power wire coming in (in this case pink) and from there a different wire going to the pcm. The pcm controls the injectors through grounds. Each injector has a fuel injector driver inside the pcm (basically a switch that either closes and grounds the injector causing it to turn on, or if opens killing the injector circuit, turning the injector off). The pcm controls your injectors by turning on and off its internal drivers. The pcm gets its vehicle speed info from your vehicle speed sensors. When they reach a certin factory preset speed, the pcm recognizes it, and turns off some of its injector drivers to slow the car down. This is a tough one to get around. But I'll keep trying to find a fix

**chazz** · 12-01-2002, 01:58 PM

Hi,

I really appreciate you taking the time to
answer my question in such detail!

Thank You,

Chazz

**Gmtech1005** · 12-01-2002, 05:16 PM

not a problem, glad i could help answer it for ya

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