94 ford ranger 4.0l intermit stall

ok here is the problem

truck stalls very intermittently always when hot out and truck has been running all day. let it sit for 15 to 20 min and it starts and runs fine.

i have replaced the crank sensor, tps, map, iac, ign mod, coil pack, plugs, wires, fuel pump, fuel filter, all relays, fuel shut off sw, and ecm.

there is no loss in power prior to stall and no check engine lights no codes and gives no warning. i have noticed i can reproduce problem if i sit and idle for 30 to 45 min on a hot day..

could it be a vapor lock, there is a small leak in fuel tank right at the top only leaks when full could that be the problem? no egr valve on engine

im stumped

happened again yesterday

talked to an old guy that had about 50 years experience with cars and trucks and he said it could be the ignition switch..


what do you think?

Do the gauges go off?
If not then ignition switch would be a long shot, but you seemed to have tried most other things
In the old days there were two separate circuits to power the coil from the key switch, but now there is just the one that controls the EEC relay that turns everything on, so you would see other signs if key switch was the issue.

Vapor lock was usually only seen on the older lower pressure returnless fuel systems, fuel would be sitting in the fuel lines and get heated up.
Gasoline is a good cooler, and at 35psi flowing thru the system and back to the tank(at idle) it cools the fuel lines pretty well, I don't recall any vapor lock issues with the high pressure systems??

So if it stalls there is no restart for 15-20 minutes?
Have you tried starting fluid after it stalls to see if it's fuel or spark that is not working?

And does it just stall instantly like no spark or does idle go down a bit like it is running out of fuel.

Because it is an intermittent issue it makes it that much harder to find the cause.
You could hook up a few test lights.
One connected to the 12v wire at the coil
And one connected to the inertia switch(fuel cut off)
The inertia switch only has power when computer activates relay so it would be off and on as normal but if it stayed off for awhile and engine stalled......

The EEC relay and wiring turns on most things when key is turned on, coil power and fuel pump relay power are two of those.
If there is a corroded wire the resistance would get higher as it gets hotter, this lowers the voltage to that device.
If you have a volt meter I would test battery voltage, thats the reference voltage the rest of the circuits should have.
So if battery is 12.7v, then with key on the coil should have 12.7v, as should fuel pump relay, on the fuel pump relay base there will be a contact with 12v all the time, that's from the fuel pump fuse.
But there will be another contact that should have 12v only when key is on(EEC relay closed), that's the one to test.
I have seen corroded wires show only 8-10volts cold, when hot the voltage drops enough so device can not work.

Also if you get a heat gun(hair drier, lol) you can test voltage then watch it as you heat up an area, see if it is dropping.

gauge stay on

"So if it stalls there is no restart for 15-20 minutes?" will turn over and try to catch but wont start...


Have you tried starting fluid after it stalls to see if it's fuel or spark that is not working? no it always catches me when i least expect it .. i t does however have fuel pressure 30 psi as i recall and spark just wont start

And does it just stall instantly like no spark or does idle go down a bit like it is running out of fuel. i get a sudden loss of power (wont accelerate) and it just dies. sometimes i can keep it running for a few seconds if i floor it just wont go


inertia switch was bad when i got it and has been bypassed (you just reminded me i need to get a new one kind of forgot about it)


could it be the small crack in the top of the gas tank (only leaks when it is all the way full) going to fix this weekend


ill check the other things that you suggested also this weekend and post results..


thanks for the reply

im beginning to think this truck belongs to a union LOL runs 8 hours and just quits

A full 8 hours would be pushing it for union work

No, a hole in the top of the tank wouldn't stall it, might get a CEL from the EVAP system, it would be like driving without a gas cap, never heard of that causing a stall out.

Reads like fuel is the issue though, if pumping the gas pedal keeps it running a bit longer, with a spark issue it would just die, maybe injectors shutting off, they also run off the EEC relay, but then pumping the gas pedal wouldn't help.

I don't want to say FPR(fuel pressure regulator) because I can't see it causing this unless it has fuel in the vacuum line and is flooding out the engine.
You may want to check that, just pull off that vacuum line and see if it has gas in it or smells of gas.
Vacuum is highest at idle so that would be the time it would suck fuel in if the FPR diaphragm was leaking.

The egr should be on a 94
its on the drivers side near the exhaust manifold

After some research that's what I found so hope the helps. ( stated that Cali made ford had them). Not 100% positive though .


-gil-

Gilbee01 said:

The egr should be on a 94
its on the drivers side near the exhaust manifold

After some research that's what I found so hope the helps. ( stated that Cali made ford had them). Not 100% positive though .


-gil-

Click to expand...

no egr on this ranger never had it never will

RonD said:

A full 8 hours would be pushing it for union work

No, a hole in the top of the tank wouldn't stall it, might get a CEL from the EVAP system, it would be like driving without a gas cap, never heard of that causing a stall out.

Reads like fuel is the issue though, if pumping the gas pedal keeps it running a bit longer, with a spark issue it would just die, maybe injectors shutting off, they also run off the EEC relay, but then pumping the gas pedal wouldn't help.

I don't want to say FPR(fuel pressure regulator) because I can't see it causing this unless it has fuel in the vacuum line and is flooding out the engine.
You may want to check that, just pull off that vacuum line and see if it has gas in it or smells of gas.
Vacuum is highest at idle so that would be the time it would suck fuel in if the FPR diaphragm was leaking.

Click to expand...

not pumping the gas pedal just holding it to the floor just to clarify

black_demon69 said:

not pumping the gas pedal just holding it to the floor just to clarify

Click to expand...

OK, adding the air would keep it running but only briefly if it was flooding out.
Cold engines can handle rich mix, hot engines die, and would be hard to restart until gas evaporated and engine cooled a bit.


My '94 4.0l has no EGR either, came that way from the factory.

RonD said:

You could hook up a few test lights.
One connected to the 12v wire at the coil
And one connected to the inertia switch(fuel cut off)
The inertia switch only has power when computer activates relay so it would be off and on as normal but if it stayed off for awhile and engine stalled......

The EEC relay and wiring turns on most things when key is turned on, coil power and fuel pump relay power are two of those.
If there is a corroded wire the resistance would get higher as it gets hotter, this lowers the voltage to that device.
If you have a volt meter I would test battery voltage, thats the reference voltage the rest of the circuits should have.
So if battery is 12.7v, then with key on the coil should have 12.7v, as should fuel pump relay, on the fuel pump relay base there will be a contact with 12v all the time, that's from the fuel pump fuse.
But there will be another contact that should have 12v only when key is on(EEC relay closed), that's the one to test.
I have seen corroded wires show only 8-10volts cold, when hot the voltage drops enough so device can not work.

Also if you get a heat gun(hair drier, lol) you can test voltage then watch it as you heat up an area, see if it is dropping.

Click to expand...

ok batt @ 12.7 volt eec relay at 12.7 drops to 12 v when key is on engine not running drops to about 11.5 when cranking starter. doesn't matter what temp it is at tried the hair dryer (got some strange looks from my neighbors though) fp relay also at 12 v

cleaned contacts anyway and there is no corrosion on any of the contacts


isn't there a air temp sensor on the plenum? if so could it cause these symtoms?


just another observation it only happens when temp outside is above 100 degrees

ok new devlopment

stalled again today the temp was 107 and it happened after i got home and went to leave again a few mins later.. got it to catch alittle had no power and was popping through intake. i still suspect that something is getting hot so i hosed down the engine compartment for about 5 min no effect still would not start. let it sit for about an hour and it started right up and ran fine...


this is driving me crazy

Have you tried unplugging the MAF sensor when it won't start?
http://www.therangerstation.com/tech_library/CleanMAF.html

Second have you tried running with gas cap loose, or off/

RonD said:

Have you tried unplugging the MAF sensor when it won't start?
http://www.therangerstation.com/tech_library/CleanMAF.html

Second have you tried running with gas cap loose, or off/

Click to expand...

wont start with maf unplugged if running and unplug maf it dies.. tried cleaning maf already also replaced maf from donor truck that did not have this problem

gas cap loose no but does a crack around filler neck count as loose or off? i have successfully repaired the crack and cap is tight..

could be a bad ground somewhere? doesn't the 4.0 have an air temp sensor on plenum if so could it be wigging out? what about the o2 sensor? or a plugged cat conv?

I'm still stumped

MAF is the air temp sensor, it checks both air flow and air temp.
Engine should run with MAF disconnected, it just runs in open loop and CEL would come on.
I think you may be on to something there.
Maybe PCM(computer) or wiring issue??
And heat does effect both

I would test the voltages at the MAF sensor
http://www.therangerstation.com/tech.../CleanMAF.html


Have you tried starting fluid when you have a no start, that would tell you instantly if fuel or spark was the issue, and then if it was a ground or power issue

O2 sensors are not used at startup, if engine is already warmed up they will be used after about 1 minute of running, if engine is cold they won't be use for 5-10minutes, they require above 650deg operating temp, so they are simply ignored until that temp can be guaranteed.

Cat/exhaust flow issue would usually show itself at higher RPMs first and at any temp, i.e. a power band that ends early as back pressure won't allow as much new fuel/air mix into cylinders, so engine doesn't stall just won't go any faster.