Hi everyone. I've been working on this truck for two weeks now and have reached a point of frustration. It's an 89, 4.9. It was running rough at lower speeds but evened out at about 25mph. I broke down at lowe's and had to return $500 of lumber! At any rate, it would chug that night but never catch. The next day, and every day since, it just keeps cranking. I have put all new plugs, wires, cap, rotor, coil. Ran test and came back with some codes, so i replaced air temp sensor, throttle position sensor, egr valve. fuel pump turns on, and smells of fuel when trying to start. Compression ranges from 125-145, all fine. Tried turning the dist while starting. Can't put light on it because it won't start. No change there. It's just acting like it's not getting fuel. Spark grounds on block. No obvious vacuum leaks, but can't fully test with carb cleaner because it won't start. I'm at a loss. What the hell is wrong with this truck!?

 

Got to pull codes.

 

Cannot be sure because I don't know any codes it is throwing but places to look are at your engine control computer, sensors, and grounds. The computer needs to get information from your sensors and then sends fuel and spark to the engine at the right time and place. I am not sure if you are getting spark from your post. If computer is broken or it is not getting readings from sensors, it doesn't know where to send the spark. If your grounds are dirty or corroded, they won't send a good signal. I would inspect and, if necessary, clean the grounds first. Sometimes you computer will burn when it fails, (did you smell anything burning in the cab?). You can test your sensors if you have the tools. Sometimes you can inspect them and see that they are very dirty which will cause you to suspect they are bad.

If you have spark and fuel, it should start although it might not run very well.

 

Hi again. Here are the codes:

21 coolant Temp Sensor out of range
23 Throttle Position Sensor out of range
24 Intake Air Temp Sensor out of range
32 EGR Valve not seated; closed voltage low
67 Neutral Drive Switch circuit open

I replace all three of the sensors, was trying to get the egr off to clean and broke flange, so i replaced with new. Which grounds are you referring to? I don't understand why it wont even hit at all now, like it's out of gas, but it's not. fuel pump turning on and working properly. Hope this helps narrow it down. I'm lost. Like I said, the spark plugs are grounding orangish blue, maybe that's the prob, but everything's new....plugs, wires, cap/button, coil....

 

Check codes.. Mine needed a cam sensor to start

 

If your truck has dual tanks perhaps the tank selector switch on the dash has broke.

Mine went out last week. The engine would turn over but not start.

You could try spraying starting fluid into the throttle body to see if it will start.

That would narrow down the search for the problem.

 

I can't imagine that all those sensors would fail at once. Maybe something in common with all of them like the ground circuit, ref volt circuit, PCM or PCM connector.

 

Thanks everybody. I'm not quite a mechanic. haha. What grounds are you all referring to? and I keep coming across PCM. What exactly does that do? The intake air sensor was covered in sludge and it looks really sludgy down in the hole. Could air flow be a problem? What are the odds of that?

 

And how can I test the tank switch? I sprayed ether in the air intake and no luck there either.

 

There are 3 grounds to be concerned with, 1 on each side of the radiator, make sure they are clean and secure, take them apart, clean all of it with a piece of scotch bright and put it back together. The other is on the driver side fender in the engine bay near the hinge. Do the same with that. The PCM is the computer that controls the engine, its located in cabin side of the firewall on the drivers side, in the engine bay, it will appear as a big rectangular plug. Take it off and clean both sides with a good contact cleaner, make sure you disconnect the negative wire on the battery first.

See if any of that gets you anywhere.