I have a 1990 F250 / 302 (5.0L) and the CEL has been on for a while. I had some leaks at the manifold, so I decided to have those fixed before I resolved the CEL. I have also had problems with idle. It will often just go up to 2500 or so RPM at idle. I've changed the TPS but it hasn't completely resolved it. I'm sure its not something sticking now because when it goes to 2500ish RPM at idle, if you quickly turn the key to OFF then immediately back ON (so fast that engine's own rotation starts it back up) the idle comes back to normal. But NOW, post exhaust manifold repairs, the idle is constantly messing up to the low side ALSO. It will go down to 400 RPM as well. Then it started bogging down as soon as you put a load on the engine, even at 700 ish RPM, unless you get it manually (with accelerator) to approx 1500 RPM first. Then it will drive normally except the occasional roars to 2500RPM's when you shift gears. Finally, it just quit. Drove it to Lowe's and went to start it and it ran terribly till it finally quit and died within a couple of minutes. We thought there was no spark but that might have been just a mistake in the bright sunlight. But changed the ignition module and the coil. Had it towed to a shop. He said the timing was messed up and, though hard to believe, it ran relatively ok but with the same idle problems. A couple of days later, it quit again. Drove it to do some work. Went to re-start it, and it just turns over and over, not catching at all. This time, I have checked and am for sure that I have spark. I pulled the OBD I codes from the flashing CEL method and get the following:

KOEO: 63
CM: 31, 41, 63

I changed the TPS again just to be sure. But still, after 3 days of sitting, the truck turns over and makes not the slightest signs of firing. I'm out of ideas and I have so much work I'm falling behind on with the truck stuck. I appreciate any help.

 

Also, I haven't checked the exact fuel pressure at the schrader valve on the fuel line going along the top of the engine, but when I press it down, the fuel shoots up about 2' or so. So I know I have fuel there.

 

[The following definitions are according to my service manual.]

Code 31: PFE, EVP or EVR circuit below minimum voltage.

This refers to the EGR positioning sensor. I'm not entirely sure what below minimum voltage indicates, but it could be that the EGR is stuck open or closed. Here's a link to more info on the EGR. Ford Fuel Injection EGR Valve Position sensor (EVP)

Code 41: HEGO sensor circuit indicates system lean AND/OR No HEGO switching detected.

If the system is running lean, the o2 sensor itself could be the cause. You never mentioned how many miles are on the engine, but I'm going to assume it's enough to have worn out the o2 sensor. Bad o2 sensors send incorrect info to the computer, which in turn incorrectly adjusts the air/fuel ratio. Before you outright replace it, here's a web page that shows you how to test it and has other technical info. Ford Fuel Injection Oxygen Sensor (HEGO)

Code 63: TP circuit below minimum voltage.

Is the TPS on your engine adjustable? If so, this problem is easily remedied. You'll need to turn the key to the "ON" position, then backprobe the connector in the wiring harness to read the voltage output. This can be kind of a pain in the ***. What I've done in the past is put those quick splice connectors on the wires, then measured the voltage from those instead. Much easier. If your TP sensor is not adjustable, it can easily be modified to make it adjustable. It should be reading somewhere between 0.06-1v in the closed position- and 0.09v is a good reference. Again, here's a link with more info, which you'll need to match up the correct wires in your TPS connector. Ford Fuel Injection Throttle Position Sensor (TPS)

 

Still no change on the truck. I have checked fuel pressure at the fuel rail. Its 40 psi during start attempts. Still getting sparks. Checked the TPS and have 5v ref, 1.0V throttle closed. Checked HEGO. Have 12V and good ground. Still no idea, but those are the latest things I've checked. Thanks, DBGrif91, but no idea what to try next. I'm leaving the battery disconnected overnight to try to clear the PCM? Well, that's the idea anyway.

 

And I guess a dumb question would be, could I be getting spark with a bad EEC relay or does the existence of spark mean the EEC relay is providing power to the EEC?

 

Well, I guess I don't feel so bad if nobody else has any ideas on this. EEC relay checked good in any event. I've cleared the EEC by disconnecting battery overnight. Now it gives code 11 11. I'm thinking maybe narrowed down to EEC or PIP sensor?

 

Have you checked and/or cleaned the IAC valve?

Ford Fuel Injection Idle Air Bypass (IAB)

 

The idling issue could be related to a faulty iac motor or a bad egr valve. A stuck open egr will cause havoc on your motor.

 

Do you think either the IAC or EGR would cause it to not start and not even slightly fire?

 

EGR, probably not.

IAC, on the other hand, could. The computer and engine rely on the IAC to open 100% at start up. If it's not opening enough or at all, the engine isn't getting air and thus, no air=no fire.

 

Actually, it turned out to be no compression on most of the cylinders. I was kind of surprised that it happened so fast with no other signs of a problem other than it wouldn't start. The shop wanted to buy my truck, but I'm attached to it. I towed it home and am researching buying and installing a new engine in it. Thanks for everyone's help though.