Computer problems?
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Joined: Jun 1999
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From: Durham
Computer problems?
Just rebuilt a 302 in an '88 4X4. We got it running long enough to break in the cam, but now the thing won't run worth crap.
It will just sit and sputter and even backfire through the throttle body. When we dump fuel through the vacuum port, it runs fine. Pulled the intake back off and found one injector not firing, but that's not enough to keep it from running...fuel pressure is good...spark is good...it's like the computer doesn't want it to run and tries to shut it down as soon as we start it...any suggestions???? 
It will just sit and sputter and even backfire through the throttle body. When we dump fuel through the vacuum port, it runs fine. Pulled the intake back off and found one injector not firing, but that's not enough to keep it from running...fuel pressure is good...spark is good...it's like the computer doesn't want it to run and tries to shut it down as soon as we start it...any suggestions????
Hotshot
Joined: Jul 2002
Posts: 14,285
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From: Bend,OR
you are sure about the cam. reason i say is speed density wont run if the cam has a lobe seperation less then 114*. you might also check your distributor to make sure its not 180* out and the timing is set at 10*btdc with spout connector removed this is very important. also are you using the correct firing order?
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From: Durham
Checked all of those up front...we fired it up with the spout connector disconnected, set the advance at about 25 degrees and ran the cam in for twenty minutes at 2000 to 2200 rpms....shut it down, set the timing to 10 btdc, and it would run for a while, then sputter, pop, and die, finally got it running with the snout connected for about 15 minutes before it sputtered and died again...since then we can only get it to start and then it sputters and pops and does not want to come much off idle before dieing...we poured fuel into the vacuum port and the engine fired right up...we checked each injector and found injector #6 was not firing (wiring problem somewhere), we checked fuel pressure and got about 38 lbs pressure when running,,,man I really am not sure where to look next...we even changed out computers with another truck and still the same thing...
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Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
i will bet your distributor is not set correctly. best way to check is put cylinder 1 at TDC and take off dizzy cap and make sure the rotor is pointing to number 1 on the cap.
why did you advance the timing 25* for break in. i have never heard that.
why did you advance the timing 25* for break in. i have never heard that.
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From: Durham
We try and keep the rpms up over 2000 rpm (for breaking in the cam) and when you have the snout plug out, the computer won't advance the dizzy, total advance should be close 28-30 by 2500-3000 rpms so we just set it at 25 to make sure we were in range at 2000 rpms..and I guarantee it is not the timing, the timing is set right...we tore off the plenum and intake and pulled the wiring harness this afternoon and found a burned wire on the injector harness, that could be the culprit for everything...also, we were told to check the MAP sensor, sometimes they tend to short out or it could even be that the short in the wiring harness fried the computer....anyway, we'll start checking those items when we get it back together...BTW, it runs good and does not get hot when it does run, I believe there is a sensor telling the computer to shut the engine down somehow. And, if you pour fuel through the vacuum port, the engine runs great (bypasses the injectors)....