I am working on a 2001 Saleen mustang with the little eaton blower on it. The car came into the shop as the customer attempted to install a battery tender then the car would not start. It had a fried ECU as the tender was hooked up incorrectly (cross polarity). We had a new ecu programmed then sent to Saleen for their programming. We got the ECU back and the car ran great, returned the vehicle to the customer and he came back the next day with a misfire. Sent the ecu out for a rebuild, came back car ran good for 30 min the started to miss on cylinder 8 again. We completed a compression test 135 PSI on #8, swapped the plug, coil, and injector with no change. Checked continuity from the ECU pin #98 (injector #8 wire) and the injector. It had .03 ohms of resistance. Then I checked resistance among the drivers side red injector wires. They had .03 ohms of resistance as well. I then pulled the valve cover just to verify the valve train was in place, it is. I am at a loss aside from trying another ECU. Any other ideas would be greatly appreciated. Thank you.

 

i have had this problem before and it was a bad 30lb injector on a s281, just do the process of elimination

verify cylinder with misfire, obd test may not help since the last one i did had the misfire monitor shut off in the programming, so verify by this procedure

1. with car running, remove injector connector at each cylinder (one at a time obviously), verify idle/rpm drop, if cylinder isnt affected by unplugging fuel source, that is the faulty cylinder
2. after misfire cylinder is found, remove plug check compression (cam followers have been know to fall off and still show good compression)
3. verify that the coil connector and injector is pulsing while running ( i use a noid light kit, plugs into coil harness and injector harness, and should flash while running)
4. check coil by replacing with know good cop or switch with know good cylinder and see if the misfire follows that cylinder
5. if misfire remains at same cylinder verify injector by replacing with know good one, or switching with another cylinder, now the only reason i say this is that i have had 4 injectors that have passed resistance tests in the past and had some that had actually broken appart inside and intermittently causing issues, also had one on a 2 valve gt that actually had some crap on the inside of the rail blocking the fuel going into the injector at the feed side of the injector, so the resistance test would not show this and niether would it process a misfire code in the processor.

and last but not least if all fails verify that the crank trigger wheel is broken or missing any teeth, but that would be ultra rare and i have only ever seen one on a mod motor, but had many other issues as well.

i really hope this helps man.

 

jmstekguy thank you for your reply. I did get the car fixed. The ECU was bad. The car did not miss when the ECU was cold, on a mormal drive the ecu would get warm and the mis in cylinder # 8 would develop. Took the ecu out and stuck it in the freezer and the miss went away. Once it heated back up to operating temperatire the miss would return. I cooled the ECU with compressed air and the miss went away while the car was running. Remove the cooling air and the miss would return. Swapped ECU's and the miss was gone for good.

 

bad injector or coil driver... good call man