WHT90F150

I have a 1990 with the 4.9L six and about a week ago it started goofing up. Basically is will start and idle fine. In fact it runs fine while it is cool but as it warms up it gets to where it doesn't want to take the gas. After it reaches operating temperature it only idles and if you give it gas it cuts out and acts like it's flooding out (may be starving, I'm not sure). It will rev if you give it gas very slowly. If you try to drive it it bucks violently.

I've recently dropped the tank and changed the screen on the pump and the fuel filter (another issue, it had crud-rust flakes- in the tank that was sticking to the screen). As long as I kept it over 1/4 tank it ran fine but as it dipped below it ran like crud. So I cleaned everything out, blew out the lines, added injector cleaner, changed the plugs and plug wires and drove it for about a day then this new problem started in.

I changes the TPS and the manifold temp sensor to no avail. It has 300K miles on it and I changed the computer about 2 years ago for a similar issue but then it only lost power as it warmed up. This is different. Timing is okay, air filter okay, air by-pass valve is okay, it's firing on all pistons.

I'm looking for ideas and pointers.

Thanks,
Robert

happyhourhero56

i've been having the same problem i've been trying to figure out for weeks... like to see what's said. do a code scan. make sure your engine is warmed up when you do though.

happyhourhero56

i'd pull the tfi/icm off and take it down to your local parts store and they can test it to see if it's bad or not. i think on your truck it's mounted on the side of the distributor.

flareside_thunder

Yes, it is mounted to the side of the dizzy. I second that... The TFI's go bad and when they get hot they let you know it.

WHT90F150

Swapped the ignition module to no avail. Ran a code reader on it. No codes. Threw a fuel pressure gage on it....20 PSI. Pump was whirring, but not enough pressure. Replaced the pump. Runs like a charm, or like it has 300K more left in it. :-) Thanks for the pointers!

Robert