Engine stalls but will restart when cool

[Jeffrey F.]

Hey everyone, I did a search but was unable to locate my specific problem. I have a stock 1993 Explorer Limited 4x4, well 2” lift, so it’s stock, 160k. Stuff I have replaced since I acquired the car 2 years ago, transmission, entire air conditioning, (except blower), alternator, fuel pump, and battery. I got the car for free and everything works, except for a few rock chips it looks brand new and ran perfectly, until…

Lately it has started stalling after driving for 2 or 3 hours. Something fuel related as I’ve checked and it has spark when this happens. I can turn the key to the on position and hear the pump in the tank building pressure, but acts like it’s out of gas, catches for a second then dies. Yes, there is fuel in the tank and I did replace the fuel filter when I replaced the pump. (pump, sending unit, pickup) Tank vent is good, canister is not clogged, no vacuum or hose leaks. The thing is, it will restart if I let it sit and cool down, about 45 min to an hour. Like nothing happened. Can’t be vapor lock, the pump is in the tank, but that’s what it acts like. I have not checked fuel pressure at the engine yet, you know, side of the road thing. I could put a gauge at the manifold, but I have never had a pump build more pressure after sitting for an hour?

My reliable go anywhere camping buddy needs to be ready for summer. Any help would be greatly appreciated.

Thanks,
Jeff

 

[boominXplorer]

I'd swap out the engine coolant temp sensor for the PCM. There's 2 sensors, one for the dash and one for PCM. The sensor has a bunch to do with fuel delivery.

 

[Jeffrey F.]

Thank-You very much since I was prepared to swap out the PCM next. Always best to start out with the cheap stuff first. Had no idea there were two sensors. Thanks again boominXplorer, will let you know how it works out.

Jeff

 

[Centaurious]

Try reading the codes for a clue.

 

[Jeffrey F.]

Yeah, getting codes was the first thing I tried, sorry didn't mention that. Anyway, further developments. I replaced the sensor and still no start, so I'm starting from scratch. Got spark but no fuel pressure at the fuel rail. Tank gauge reads 1/3 full and I can still hear the pump working in the tank. This differs from before when I was getting 35 psi but it still wouldn't start. Now I'm just trying to get fuel to the fuel rail.
I'm going to the gas station to get 5 gallons of gas in the off chance that the fuel pickup fell off in the tank? Is that possible, has anyone ever had that happen?

 

[Jeffrey F.]

Okay, here’s the update. I am getting 35psi at the fuel rail while cranking. Disregard the earlier post about fuel, I have ignorant friends who can't follow directions, please don't ask. Anyway, now the engine will no longer start when cooled off like it used to. Replaced temp sensor that goes to the PCM, no help, but a nice try. Engine will catch for a second or two then die. Fuses are good, fuel relay is good, fuel cutoff switch button is pushed in, MAF is clean, no codes are coming up-all clear and no air or vacuum leaks.

And one more thing to add, the wife who was driving it last said it was idling about 500rpm higher than normal for a short time, about 30 minutes, it then returned to normal idle and quit for good.

Anyway, thanks for all the help, there are just too many things going on to diagnose over the internet. Should have stopped before I put in the tranny last June, but it was running so well the last 8 months. And the real pisser is the new AC was blowing ice cubes on the warmer days this past winter. Oh well, roll the dice…

Will wait until I win the lottery, and then go buy a new GMC Sierra to tow the Exploder to Pic-n-Pull.

Thanks again for the help,
Jeff

 

[Josh P]

I would check to see if the engine will run on starting fluid.

 

[Centaurious]

There is a relay that powers the ECU that may have gone bad. Do you get the Check Engine light with the key on? Pull the Fuel Pump Relay and feel if the ECU relay clicks when the key is turned on.

Fuel pressure but no fuel is usually ECU, bad or no power. The ECU lights the Check Engine light at key on.

 

[Jeffrey F.]

I would check to see if the engine will run on starting fluid.

Okay, further developments, the check engine light does come on with the key in the on position. Checked the fuel pump relay, checked fuel pump resistance, checked engine ground, PCM ground, and made sure I was getting power through the fuel pump shutoff.

I did find a very small vacuum leak at the brake booster grommet. Took about 3 min to drop from 15” of vacuum to 5. Fixed that, still wouldn’t run.

I then pulled the air intake off the throttle body and peeked inside, not pretty, lots of carbon crap. Shot some brake clean in there and let it sit for a few. I have remote start so I hit the button intending on spraying a little brake clean in there to see if I could keep it running. First two tries no luck. Then it caught for a few seconds, stumbled and died. Soaked it with carb cleaner and let it sit for 5 min at which point it fired right up like it was on the showroom floor.

Intake was cleaned out about 6 months ago, so I was surprised to see all that crap in there. My guess is, and I really hate guessing, is that I got a bad tank of gas? I use name brand, mid-grade fuel so I think my next purchase will be a locking gas cap.

Ran through two tanks on Monday with additive and had no weird idle problems or stalling. But it’s hard to trust it without knowing the cause.

The thing is, it was running fine right up to the time it started stalling. Plenty of power and 19mpg. Injectors were cleaned and tested at the same time the manifold was off. Now I’m thinking I will need to do that all over again, and then keep an eye on it. And I’m still not sure what the cause was….

Still too sketchy to take camping so I guess I’ll spring for that new truck this month.
Thank-You Josh, last resort idea for me, I never would have found the problem since I didn't expect to find that crap in the intake.

Thanks everyone for all your help, and I’ll let you know if I find out exactly what the cause was.

Thanks again,

Jeff

 

[Jeffrey F.]

It stalled again and would not restart. With only one AAA tow left I dropped in a new PCM, and after two weeks of daily driving about 150 miles every day with no problems I'm calling it, it was a bad PCM. I was told by several Ford mechanics that the carbon in the manifold was a by product of the faulty PCM and not a cause of the stalling problem. A recent check confirmed this as the carbon is all but gone now.
How the PCM was stalling the engine is still a mystery as all testing showed the engine was getting correct fuel pressure, spark and air flow. Connecting the dots was quite frustrating as the problem became increasingly random. No engine codes were ever set.
Opening up the PCM showed no damaged circuitry, no loose pins and no burnt smell, and no apparent reason for the malfunction.

Anyway, problem solved, I now have faith once again that it will start every time I turn the key. Time to go camping!!!

Thank-You all for your help.
Jeff

 

[Roadrunner777]

Good deal! Yeah, I used to research the reliability of electronics, not far from you... for HP in Palo Alto. Your PCM, at 26 years old, did pretty well in the scheme of things. If you wanted to go an extra step... you could replace the little can electrolytic capacitors. They are the most likely to fail from old age.

Wow, I saw Santa Cruz in your profile. I used to live in La Honda, and have often talked about retiring back to the coast. Tough finding artichoke soup where I live now!