91 fj80 cutting out and dying (1 Viewer)

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Mar 4, 2006
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I have read all the posts I can find here regarding this issue. Here is what I am dealing with. engine runs fine while idling in park. While accelerating (in drive) and doesn't seem to matter about rpm's the engine starts cutting out, seems like it completely dies off and on. The check engine light will blink as its doing this. And will stall out if going slow enough.

Here's what I've done so far in order: new air filter, new fuel filter (frame), dist. cap, rotor, wires, and plugs. Problem was still present. Then I disconnected the battery and pulled the MAF connector and cleaned it. Also cleaned the connector right at the intake/ throttle body. Not sure what sensor that is.

After doing that, I took it for a test drive around the block and it seemed fine. An hour later I took it for another spin around the block and the problem was back. It's so bad that I cannot drive the rig at all. Any ideas would be great. Thanks,

Jeff
 
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Also, I have inspected all vacuum lines and intake tubes for cracks. All seems fine.
 
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I seem to remember reading somewhere that a flashing CEL sometimes means a misfire, not sure if this is true to the 80 or not.
 
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Well its only flashing because the engine is completely stalling out. It's like ignition is turning on and off, but only while in gear. It will run all day in the driveway.
 
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Just drove it around the block again, and it seems to do it while coasting in gear to. I have grabbed and wiggled every hose, wire, and connection under the hood while running and it doesn't miss a beat. I am stumped, seems like it has to be electrical though.
 
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Couple of thoughts:

Fusible links off of the positive battery terminal. These can become intermittant and cause silly issues. One guy had his truck stall only when making right turns.

Fuel pump wiring might be suspect depending on vehicle history. There is an access plate under the second row seats. Fuel pump is fired by the circuit opening relay in the dirver's kick panel and the flap switch in the AFM (you don't have a MAF on a 3FE).

In-line fuel filter and fuel pump pre-filter might be clogged. If this only happens when there's a load on the motor, I would change these out.

Possible bad connections on the EFI main relay under the hood. While the truck is idling, perform some percussive engineering on or about the fusebox.
 
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May be a dumb question but was it doing this before you changed plugs wires etc? Specifically was it doing it before you messed with the MAF plug?
 
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no, it was doing it before i did anything. changing fuel pump sock in the morning.
 
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Apr 13, 2007
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Might not be the problem at all but my MAF had a wire that came loose inside. Actually looked like a piece of aluminum foil. It exhibited similar symptoms. I cut the silicone carefully around the top of the black cover cap and pulled it out and that is how I found it. I soldered it back in place and it has run great for the last 5k. Might want to look at that before you tear into the tank. Here is the link:

https://forum.ih8mud.com/80-series-...g-really-dumb-truck-wont-start-maf-issue.html
 
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More details needed.

With the vehicle stationary, with the transmission in PARK, the truck will start and run and get up to NORMAL OPERATING TEMPERATURE. Is this correct?

In the above state, with the truck at NORMAL OPERATING TEMPERATURE, you can freely rev the motor throughout the RPM range and it will act normally. Is this correct?

With the vehicle stationary, wheels chocked, handbrake on, brake pedal depressed, engine at NORMAL OPERATING TEMPERATURE, put the transmission into DRIVE and give small, increasing amounts of throttle until you feel the RPMs stop increasing with throttle input (torque converter stall). Can the motor hold this for a FEW SECONDS without exhibiting symptoms? Don't do this too much longer as it's not great for the transmission.

Try the very same thing with the transmission in REVERSE.
 
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Mar 4, 2006
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Jon, yes to everything you just said. I can only get the problem to occur while driving.
 
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I think if the o2 sensor is bad it would just throw a code and not effect the engine running.

I have another issue I hope someone can help me figure out. I disconnected the negative side of the battery and to check for current draw because I noticed that every time I would disconnect it would spark a good deal.

What I found was with my volt meter connected from the neg. terminal to the neg. cable i read 12volts! I know I should not be getting this. What would cause this, and could this be causing the cutting out and stalling?

Charging system is working correctly. Thanks,

Jeff
 
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(you don't have a MAF on a 3FE).
i am confused as to why you would say this? I am pretty certain i do have one, and I have cleaned it twice. Is this not the big chunk of aluminum between the air filter and throttle body unit?
 
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Feb 25, 2007
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McDonough, Georgia
 
 
I had this issue except the vehicle every once and a while would completely stall. Found the fusible link chaffed where it passes thru the hole in the battery holder. I had to actually cut, strip and twist the wire together inorder to get a restart.
 
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i am confused as to why you would say this? I am pretty certain i do have one, and I have cleaned it twice. Is this not the big chunk of aluminum between the air filter and throttle body unit?
What you cleaned is called an air flow meter, not a mass air flow sensor. I said, "Fuel pump is fired by the circuit opening relay in the driver's kick panel and the flap switch in the AFM (you don't have a MAF on a 3FE)."
I was simply correcting the terminology used. The MAF is a different box on a different motor. Sorry for the confusion.

Getting back into it, I would like you to try the stall test with the transfer case in low range. This will put a very large amount of torque on the motor mounts and will cause everything in the engine bay to flex. That was the point of the other exercise. I was hoping that putting the motor under load would reveal the issue in a controlled fashion.

If that reveals nothing, I would poke around the fuel pump wiring and control circuits while the engine is running and see if you can stir up the intermittent. Control is from the AFM and the COR in the driver's kick panel.

Make sure the coil/igniter on the right fender is mounted securely. The mounting bracket is the ground path for both.

There is a wiring harness that runs on the injector side of the intake. Very close to the firewall, at the end of the fuel rail, there is a metal support bracket with a single 12mm bolt holding it in place. Give that a looksee.
 
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I think if the o2 sensor is bad it would just throw a code and not effect the engine running.

I have another issue I hope someone can help me figure out. I disconnected the negative side of the battery and to check for current draw because I noticed that every time I would disconnect it would spark a good deal.

What I found was with my volt meter connected from the neg. terminal to the neg. cable i read 12volts! I know I should not be getting this. What would cause this, and could this be causing the cutting out and stalling?

Charging system is working correctly. Thanks,

Jeff
By pulling the negative terminal, you have now floated the vehicles ground path. A more useful test would be to check the amount of current draw. You will almost always get a small spark even when the vehicle is at rest. My truck draws 20-25 mA at rest IIRC.
 

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