I own a 1990 F150 less then a year ago the truck was doing fine, then I went to start it, would not start. I had it towed to a garage. It started for the mechanic and he couldn't find nothing wrong. I drove it for a while then one day it wouldnt start. It would start with starting fluid being sprayed in it while cranking, but only run on half the cylinders, and would stay running if you held your foot on the gas pedel. Dianogistcs ran keep giving different codes. The mechanic said he thought but wasn't sure it was the computer. I replaced the computer started and ran fine for less then a year. Started last night I drove it one block shut it off and now won't start, acting same way it did before. I hear the fuel pumps just fine, it seems to have good fuel pressuer.

Note: After adding new computer, the truck would run low idle for a short time after starting. Some time not alot it would run high idle even just after starting from cold start.. any suggestions apprectiated...

 

i dont know but to me replacing the computer sounded kind of drastic. but then it worked for a while? thats wierd. i still have issues with both my car and truck 1988 models. my car had problems just like you described. would crank but not start, then started stalling and wouldnt not start. sometimes it would start if i held the gas down or pumped the gas but would run really rough sometimes it would work it out. my computer gave a code for PIP so i replaced the distrubutor. seems to have helped but now i have an irratic idle i cant figure out.

it may be the TFI ignition module on the distributor ($30). it may be the stator inside the distributor (PIP). it may be the fuel regulator. it may be the fuel lines. it may be the fuel pump (you could get a fuel gauge and check by using the valve on the fuel rail).

i really dont like speed density systems or computer controlled cars. seems like you cant work on them unless you have lots of training.

 

Computer replacement is probably the absolute last thing to consider. Even though problems may seem severe it is generally not the computer. TFI module can be checked, I think Autozone can do that for you. The PIP sensor can also be checked ,but it involves pulling the distributor and having the proper tool. An Actron CP9087 Ignition Module and Sensor tester can check both of these components as well as many more. MAP, ECT, Oxygen, EGR VPS and Throttle Position Sensor. They sell for about $75 and you can buy them at Sears and the Internet.
I believe I would start with the basics and check spark, fuel and compression. Compression last because it is the hardest and involves a compression tester. Spark testers are about $7 or $8 and you may be able to borrow a fuel pressure tester from one of the tool loaner programs at a parts store. You can also clean your IAC(Idle Air Control) valve on the side of the throttle body. When is the last time you tuned up your engine? Tuneup on one of these vehicles usually consists of Spark plugs, Wires, Distributor cap and Rotor. May change PCV valve too. All of this, including a good set of plug wires $35 to $40 minimum, can be gotten for around $75 or so. Regardless of what the initial problem is, if you haven't done a Tuneup in a while you probably should.