Has anyone ever had a problem with the ECM being stuck in test mode fan is on when key is on and check engine light flashes, car will not start. It is a 91 formula 350 I just installed headers last weekend along with cool fan switch, and a new O2 sensor. Anyone have any ideas I don't know what to think.

 

Probably not an ECM problem, but a wiring problem. Look for a short between the wiring leading to your A & B terminals of your ALDL and the ECM. If there's no short, then start looking at the ECM.

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Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, MSD 6AL, Aluminum Driveshaft, TB Coolant Bypass, Ported Plenum, Modified MAF, Syclone Fuel Pump, JET Airfoil

15.556 @ 86.65mph, Nov 10, 2000.... I know it sucks.. but it will get better!

http://www.geocities.com/transam85tpi/

 

Better yet, unplug the ECM from both harnesses, and then check for continuity while probing the ALDL A & B terminals. If you get continuity, you have a short somewhere in the wiring. If you don't have continuity, then it's the ECM.

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Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, MSD 6AL, Aluminum Driveshaft, TB Coolant Bypass, Ported Plenum, Modified MAF, Syclone Fuel Pump, JET Airfoil

15.556 @ 86.65mph, Nov 10, 2000.... I know it sucks.. but it will get better!

http://www.geocities.com/transam85tpi/

 

91,

This could also be the result of a PROM that is inserted incorectly or not fully seated in the socket. Before you order a new ECM, you might want to check that and the other connections to the ECM edge connectors.

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Later,
Vader
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"I'm'a do Things My Way - It's My way or the Highway."
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well new discovery it finally started and ran all day yesterday just fine then last night I was leaving and it died again so I finally got it to start and made it back home. at home I started it and it would run for less than five minutes then die, when it dies the fan, EGR solenoid and Charcol cannister sol all stay on and you can hear them all turn off at the same time about once a second, and the SES light flashes each time the sol's/relays turn off. this all happens with the key in the run position it will not start I even tried to jump the fuel pump relay that did not help. then after I let it sit for about ten minutes it will start and run for a couple more minutes. Please offer any insight.