Starts but won't run

[jimwes55]

I have a 1992 Explorer with the 4.0L engine. The engine starts but won't run. The fiberglass insulation under the hood, just above the EDIS (coil) has been eaten away as if spark has been jumping to the hood. Has anyone seen this and could this be my problem? I changed the spark plug wires but that didn't help.
Thanks for any help
Jimwes55

 

[wood1]

Hey Jim. Welcome. I suggest you spray a salt water solution on the coil and crank the engine (in the dark) and see if your coil is grounding out.

 

[arco777]

Without more information it's hard to diagnose the no-start.

1. Do you have fuel? Turn the key to ON without starting it. Listen near the rear drivers side seat for the whine of the fuel pump. It should run for a moment and then shut off when you turn key ON to prime the system. You can also use a fuel pressure gauge connected to the fuel rail and check for 35-40 PSI of fuel pressure after priming the system. The pressure should stay pumped up at 35-40 PSI for over 15 minutes. If it leaks down quickly, or doesn't ever build pressure, check your fuel pump and fuel pressure regulator. The pump should pressurize the system, and the regulator should keep the pressure at 35-40 PSI and hold it. If the pump never runs, check for a failed fuel pump relay or fuse, or the PCM is not commanding the fuel pump to run - see #3 below.

2. Do you have spark? Check for spark at the plugs by removing one plug or taking a spare, connect one of the spark plug wires to it and touch the end of the plug to a ground like the block. With the fuel pump relay disconnected (so engine won't start), crank over the engine and see if spark is jumping across the plug. This verifies if your ignition is firing.

3. If you have no fuel pump activation AND no spark, chances are that your PCM (computer) isn't getting power. In this case check for a failed EEC relay or blown fuse.

Note that all the relays in the power distribution box are interchangeable, so you can swap out an ABS or horn relay if needed for testing.

 

[jimwes55]

I can hear the fuel pump and I'm getting fuel but the pump cycles in two different tones and does not stop after the system has been pressurized. Measured the fuel pressure and it's within spec. Changed to a different fuel pressure regulator and changed the air intake air temp sensor, because the PCM uses this input to control fuel flow, but the engine still starts but won't continue to run unless I feather the throttle. Unplugged the AC compressor and it does run better but still dies. The fuel pump is still cycling, non stop, in two different tones. The fuel pump is about 8 months old. Also, changed the fuel filter. Help me OB 1, you're my only hope!

 

[MrShorty]

Measured the fuel pressure and it's within spec.

Did you also measure the fuel pressure when it wants to stall?

I can hear the fuel pump and I'm getting fuel but the pump cycles in two different tones and does not stop after the system has been pressurized.

If the pump is not shutting off after a few seconds KOEO, that suggests some kind of wiring fault in the fuel pump circuit. Is the relay stuck closed? Occasionally, it seems like these kind of symptoms seem to be caused by some internal circuit fault inside the PCM causing the fuel pump relay to stick on and other problems. At this point, I think I would try to ascertain why the fuel pump runs continuously KOEO. The pump should run continuously while the engine is running, but it should shut off when the engine is not running.

 

[jimwes55]

Thank you Mr. Shorty, I think you've got it. I did change the fuel relay a week ago and the situation didn't change. Is there a way the test the fuel pump in place by supplying power from an external source? I guess it would just continue to run because it wouldn't get a signal to stop pumping like KOEO. What is the sequence that tells the fuel pump to stop? Is there a sensor that detects enough fuel pressure and allows the PCM to remove power from the pump? Thank.

Jimwes55

 

[MrShorty]

Is there a way the test the fuel pump in place by supplying power from an external source?

One of the leads in the self-test connector is a fuel pump test lead. Grounding this lead is supposed to close the fuel pump relay (KOEO). This will allow you to use a voltmeter and a wiring diagram to test the fuel pump circuit.

What is the sequence that tells the fuel pump to stop? Is there a sensor that detects enough fuel pressure and allows the PCM to remove power from the pump?

Nothing near that complicated. It's a simple timer. If the computer does not see the signal from the crank sensor indicating engine rotation, it runs the pump a further 2-3 seconds, then shuts it off. There is no sensor telling the computer fuel pressure.

 

[jimwes55]

I check the compression on the engine and got average 90 lbs on initial stroke and built to average 160 lbs on all cylinders. I assume this is good. The crank sensor was changed with not change in performance. I disconnected the catalytic converter to see if I had a clogged exhaust system. Still no change. Oh yea, the noisy from the fuel pump turned out to be the rear window washer system, man was that embarrassing. This truck still won't idle at all. If I could run it at 4000rpms all the time I'd be in business. I'm thinking about vacuum leaks, maybe in unusual locations. Can the vacuum canister be bypassed to verify that it doesn't have a leak? This is kicking my butt. Any suggestions would be appreciated.

Jimwes55

 

[arco777]

Compression sounds fine.

Vacuum can be troubleshooted by capping off or plugging all the lines at the source; the upper intake manifold has a tree that the vac-operated stuff comes off of. Plug those hoses or put a cap over the fittings on the manifold vac tree and see if there's any change.

 

[jimwes55]

Checked the vacuum as suggested and found no change. I had someone else check the fuel pressure for me before and was told it was good. I checked it myself and found the following. With KOEO the best it registered was about 10 lbs. When running it would go up to 40 psi. I disconnected the vacuum line to the pressure regulator and it made no difference. The engine starts fine but won't keep running. Even at a higher RPM the engine lops like it has a race cam. I read something about a leaking fuel injector, does that sound like a possibility? Any suggestions are greatly appreciated.

Jimwes55

 

[arco777]

When the key is turned on the system should pressurize to 35-40psi immediately. If it is only pressurizing to 10psi, you have a problem.

Can you get the system primed to 40psi by repeated priming without starting the engine (key on, key off, key on, key off, key on)?

When primed, does the pressure leak down quickly? It should hold fuel pressure for at least 20 minutes.

Try driving with the fuel pressure gauge in sight (some have suggested tying it to the radio antenna or a wiper blade). How does the fuel pressure look while driving?

 

[jimwes55]

The pressure did build to 12 psi after 4 or 5 key key off sequences. The pressure did seem to hold at 40 psi after the engine died. The truck doesn't run well enough to drive. Tonight I removed the intake manifold and did ohm readings on the fuel injectors. They all read 16.8. They were very dirty. Is there a method for cleaning them off the vehicle? Also, is there a way to check the input to the injector, to make sure adequate voltage is being delivered?
Thanks for any help you offer.

Jimwes55

 

[arco777]

If you can only prime to 12psi, you have a problem. You should see priming pressure jump to 30-40psi on the first turn of the key. If pressure is reaching 40psi while running and holding, then your regulator is working fine and fuel injectors aren't leaking. I think your fuel pump is shot.

The injectors can be checked using noid lights, which are simply 12v bulbs hooked inline. They are probably being driven fine. You can use a stethoscope to listen to the injectors while the engine runs, they should be clicking along. If they are dirty you can send them off for cleaning. You can try cleaning them yourself with an ultrasonic jewelry cleaner or soaking in fluids like seafoam but most people have mixed success with self cleaning.