i have a 94 boosted gsr. the car will run great for about 30-45 minutes of drive time then it just starts missing on cylinder 4, got spark but no fuel. so i got my volt meter out and check the power going to the injector harness, i have a constant 12.5 volts coming out of both sides of the pigtail. if im correct one should be a "signal/ground" for pulse or what not? so i checked the other pigtails and they are all reading 12.5 and .0009 or some some number in that nature. i figured if it was a short in the harness it wouldnt have any power to the pigtail, correct? so i put the factory ecu back in and volts show to be fine on both side of the pigtail, then i put the neptune ecu back in and it runs fine again for another 30-45 minutes or so. someone please shed some light on this please. anything will be greatly appreciated...

its bone stock on 10lbs with a precision 5731 billet wheel, rc 750cc's and a walbro 255.

 

ECU switches ground to injectors by the way. Your problem sounds like a ignition problem. Either the coil or ICM is failing once it heats up.

 

so would a new dizzy resolve the issue? like i said tho ive got spark. the dizzy thats on there is only 6 months old. and its just the one (#4) cylinder..

 

I know you said you have spark but you didnt say how you confirmed that. So I didnt trust it. A simple dist swap would eliminate alot of variables. If you still think its injector related you can swap injector to another cylinder and see if the problem follows the injector.

 

problem does not follow injector. that was my first test. i tested spark by pulling a plug wire and putting a plug that i was not using in the wire and held it against clean metal and had a blue spark.

 

anyone?

 

If you swapped all the plugs, the injector driver circuit could be done for #4. Have you visually inspected the ECU for any signs of burnt pieces or the likes. Do you know anyone that has equipment to test the ECU? I have been seeing a fair amount of Demons dieing lately as well...

 

i pulled the casing off the ecu and it has a vague scent of being burnt, but i thought it may have been from the socket being soldered in. visibly the computer does not seem burnt. thats what i was leaning towards was that injector driver being bad. i traced the entire harness and could not find any problems. i figured if there was a break in the harness i wouldnt be getting any thing to that injector on either side, power or ground (depending on whichever wire that would have the short). and what kind of equipment is needed to test it?