Kinda pulling my hair out with this problem: Just put in a '96 engine with 85,000 on it ran great and all that. Just recently it started missing really bad when the engine was cold but once it warmed up it ran beautiful. Now it'll start right up, run good for a few seconds, then sputter and die. Any gas I give it usually kills it. To add to the problem, I noticed if I have my headlights on it doesn't run quite as bad. Still it always smooths out and runs great when the engine warms up. Also the battery drains when it's just sitting there overnight. Computer does not read any codes. This has everyone I ask stumped!

Already replaced mass air flow sensor, coolant temp sensor, IAC valve, spark wires, distributor cap, alternator, and coil. Fortunately most of that came off the '97 engine I jerked out. Also during the engine swap I removed the smog pump and bypassed the EGR valve. It ran beautifully for the first few months after the engine swap and then this problem came about. Any ideas??

 

"Computer does not read any codes", or "Computer does not read any codes other than 111"? There is a difference.

I'd be suspecting the fuel pressure regulator, or FPR. One check I would make is to remove the vacuum line while the engine is running and see if it leaks any gas. If it does it's failed and needs to be replaced.

Next I'd check the fuel pressure with a fuel pressure gauge at the Schraeder test port on the fuel rail. I'd be looking for between 35 and 45 PSI with the ignition on, engine off, and fuel pump line in the EEC test connector grounded. (There is a picture of the connector here, with the fuel pump pin identified.) I'd want to read between 30 and 45 PSI with the engine running and the fuel pump pin ungrounded, and I'd want to see fuel pressure increase between 5 and 10 PSI when I disconnected the vacuum line from the regulator.

 

Pulled the vacuum hose of the FPR and no gas came out. I'll check the fuel pressure next. Do you think maybe it's an electrical problem I'm dealing with?

 

It could be. I'm still wondering about the lack of codes, though.

Just so we're on the same sheet of music -- your truck has a test connector under the hood like the one shown at the top of the page at Fuel Injection Technical Library » How To Run a Self-Test , right? I'd hate to be missing the boat because I'm thinking OBDI when your truck is OBDII.

 

A '97 Mass-Air 460 would be OBD-II.