91 explorer vapor lock issue.

[lmatt]

Hello, I have posted this before, but still looking for answers. I have a 91 Explorer. Yes its old and high mileage, but other than that all new parts and in very good shape. The problem is that after it sits for about 15 minutes, and then go to re-start it, it sputters and misses. Bacicly a hot sarting condition even when the outside temp is cold. It has new plugs, wires, fuel injectors, fuel pump, regulator,alt, all temp sensors, MAF sensor, fuel filter. Checked all the fuel lines. No check engine light or codes at all. All of you are going to think im nuts and say it cant be, but, this issue does not occur when it gets fuel that is not blened with 10% ethanol. But, this is getting hard to find and soon ALL fuel will have ethanol in it. I have checked with major refiners and they have all said the same thing, ALL fuel will have ethanol in it by 2010. Any ideas as to what this problem is, other than the ethanol issue if any?? PLEASE ADVISE. I want to shoot this explorer. Thanks, trouble in Kansas.

 

[BeetleBailey]

I would have the exhaust system checked. I think you may have a catalytic converter stopping up.

 

[lofton316]

Mine use to do that until i replaced the pcv value

 

[lmatt]

The PCV vale is also new. Any ideas regarding how I could keep the fuel rail cooler? I have found this is where the fuel is boiling at. I talked to fuel reps from BP/ Amoco fuels Wednesday, and they said that ethanol boils at 140 degrees. Heck, the fuel rail gets up to 160 deg. And I had never thought about the converter being pluged up. If it is, wouldnt the performance be affected? Thanks

 

[lmatt]

All of the first gen Explorer's and no one else is having or had this problem? I cant belive this. Does nobody go and re-start their explorers after just sitting for 10-15 minutes? I cannot find ANYTHING mechanical wrong with it at all. PLEASE HELP. This is to good of an explorer to part out.

 

[lgreenough]

We have an explorer that is doing the SAME exact thing and it also in GREAT working contionion as well!!! I have no idea how to fix it!!!! Know it is not the Catalytic Converter because my hubby took all the stuff from inside ours out. So it is NOT cloged! I wonder if there is a product on the market to sablize the fuel like a High temp fuel stabilizer???? Also thinking maybe make a heat shield for the fuel line where it comes in contact with the source of heat???? Some suggestions I am going to try.

 

[Maniak]

I doubt very much that it is vapor lock. That is virtually impossible to get on a fuel injected vehicle running 30psi+ pressures.

The symptom you described is somewhat common on here, at least I've read about it a bunch and we had it on our X for a while. (We didn't do anything "specific" to fix it)

You may have a leaking injector so when the truck is off/hot its leaking fuel into a cylinder. That will not only throw lots of extra fuel into the cylinder but it will also mean you will most likely try to start with low fuel pressure. If you cycle the key from off to on a few times and then try to start it you will have your fuel pressure back up before you try to start it.

Other things I'd check would be the IAC (handles the no touch start), Coolant and air temp sensors (the 2 wire coolant sensor). If those are reading wrong the ECM will throw the wrong mixture/timing combo and make it hard to start.

~Mark

 

[Roadrunner777]

I have this problem too; it's my current working problem, as a matter of fact. I think the idea IS to try to get fresher cooler fuel into the rail before starting. Maniak's idea of turning the key to on a few times would basically do this. I would be very interested in anybody's results to this procedure! Also, it might be interesting to rig up a fuel pressure gauge somehow so you can see it from the cab at start-up. I think this would tell the whole story.

 

[jyro]

ranger vapor lock

I have this problem too; it's my current working problem, as a matter of fact. I think the idea IS to try to get fresher cooler fuel into the rail before starting. Maniak's idea of turning the key to on a few times would basically do this. I would be very interested in anybody's results to this procedure! Also, it might be interesting to rig up a fuel pressure gauge somehow so you can see it from the cab at start-up. I think this would tell the whole story.

it is vapor lock, ford went to a higher presure fuel pump with no return system on later rangers to overcome this issue. I have the exact problem on my 1991 4.0 auto 2wd ranger. I wonder if you could put a higher presure pump on off a later Ranger to overcome it. or a adjustable regulator, or a heatshield for the fuel lines at the motor.

 

[hawkfire1]

hello,

Can you explain how you came your conclusion of vapor lock?

I am extremely curious to know your method of diagnosis.

Did you use a fuel pressure gauge when this problem occurs or are you just guessing and diagnosing by replacing parts based on the symptoms and circumstances?

It could be a partially clogged fuel pump sock or filter, fuel injectors stuck open and bleeding down, a bad fuel pump checkvalve or just a partially faulty fuel pump.

None of these issues will trigger a cel on a 92.

Neither will a failing IAT or ECT if it passes the preliminary PCM check

Just because parts are new or replaced doesn't rule out defective parts so it would be a good idea to double check and make sure the replaced parts are functioning properly.

One thing that baffles me is people who ask for assistance or help for a problem they CANNOT find an answer to yet INSIST they know for sure what the problem is.

After all, if they know what the problem is, they surely know the answer to the problem at hand so why post to begin with?

 

[hawkfire1]

One other thing to consider is a faulty or failing PCM.

Best to get it tested if possible.

 

[jyro]

Sure , and I'll overlook your attitude

hello,

Can you explain how you came your conclusion of vapor lock?

I am extremely curious to know your method of diagnosis.

Did you use a fuel pressure gauge when this problem occurs or are you just guessing and diagnosing by replacing parts based on the symptoms and circumstances?

It could be a partially clogged fuel pump sock or filter, fuel injectors stuck open and bleeding down, a bad fuel pump checkvalve or just a partially faulty fuel pump.

None of these issues will trigger a cel on a 92.

Neither will a failing IAT or ECT if it passes the preliminary PCM check

Just because parts are new or replaced doesn't rule out defective parts so it would be a good idea to double check and make sure the replaced parts are functioning properly.

One thing that baffles me is people who ask for assistance or help for a problem they CANNOT find an answer to yet INSIST they know for sure what the problem is.

After all, if they know what the problem is, they surely know the answer to the problem at hand so why post to begin with?

It only does it after it's shut off hot, the plugs are not wet when is doing it, it will run for 15 seconds barely and clearup and run like nothing is wrong. it gets 19 mpg on the highway and never misses, the filter has been replaced. When it's doing it there is no black smoke, or any smoke at all or fuel smell. Ford changed the fuel system on later Rangers to a higher pressure pump and a no return system to overcome vapor lock on earlier rangers. it passed emissions testing last month with zero problems and it would still do it when hot and parked. If you let it sit overnight after shutting off hot it starts and runs fine.
I'm thinking of trying a adjustabe regulator for the higher pressure. One thing I don't know and maybe you do-- does the regulator bypass with the motor not running and the pump on, if it did, it shouldn't vapor lock since the fuel would refill the pipes and push the vapor back to the tank.

Many people have this same problem and have for years with no resolution. I am also going to insulate the fuel line where it's about 6 inches from the exhaust on the drivers side floor but I suspect it's related to the injectors and their close proximity to the block and heat soak combined with the design of the ranger fuel system.
the truck runs great under full throttle so I don't suspect a bad pump, no I never have checked the fuel pressure. no matter how many times you turn the key off and on to fill the lines before you try to crank it, it will still miss on all 6 till it runs for about 15-20 seconds so I don't suspect a check valve issue.

 

[MrShorty]

One thing I don't know and maybe you do-- does the regulator bypass with the motor not running and the pump on, if it did, it shouldn't vapor lock since the fuel would refill the pipes and push the vapor back to the tank.

This question doesn't make any sense to me unless I assume you don't understand the type of regulator being used. The fuel pressure regulator on these is a pretty basic mechanical back pressure regulator. As the pump runs, pressure builds until the system pressure reaches the specified pressure (30-40 psi depending on vacuum level applied to the regulator). When the pressure reaches the desired value, the regulator opens, and the "excess" fuel is bled off to return to the tank. In this way, the fuel is constantly "recirculating." In this way, there is nothing to "bypass."

IMO, if the gasoline is really boiling (at 40 psig pressure) in the fuel rail, either the top of the engine is too hot, or the fuel pump isn't putting out enough. It is really difficult, IMO, to say much of anything conclusive without putting a fuel pressure gauge on it.

An adjustable regulator could be used to increase the pressure if you really wanted to. It would only work up to a point. From what others have reported when their regulators have failed closed, above ~60 psi, the PCM can no longer compensate for the increased pressure and can't properly regulate the A/F mixture. I might also worry about the pump longevity -- is the pump overdesigned enough to continuously pump against those higher than spec pressures.

 

[coco944x4s]

I had the same problem with my 94 up until i replaced my leaking lower intake gasket. While i had everything apart i also took the time to polish my fuel rail. Since i completed the gasket repair, i have had minimal if no issue with the problem if a rough idle/hard start that you mention. My wifes 92 does the same exact thing, and i am pretty sure that her intake isnt leaking as i had the transmission out in may to replace the front pump seal after it blew out, and the pressure tested held for 10 mins when i just replaced the radiator in it a few weeks ago. Since you obviously seem very mechanically inclined, or have a good mechanic one, i would suggest pulling the upper intake and fuel rail and giving it a good shine to see if that helps alleviate the situation. I took the time to do it since i also painted my intakes and valve covers and had spare time while watching paint dry. I figured it couldnt hurt anything and that the shiny rail would be less likely to absorb heat and more likely to reflect it. Just my $.02, hope you find a cure for your problem.

 

[jyro]

This question doesn't make any sense to me unless I assume you don't understand the type of regulator being used. The fuel pressure regulator on these is a pretty basic mechanical back pressure regulator. As the pump runs, pressure builds until the system pressure reaches the specified pressure (30-40 psi depending on vacuum level applied to the regulator). When the pressure reaches the desired value, the regulator opens, and the "excess" fuel is bled off to return to the tank. In this way, the fuel is constantly "recirculating." In this way, there is nothing to "bypass."

IMO, if the gasoline is really boiling (at 40 psig pressure) in the fuel rail, either the top of the engine is too hot, or the fuel pump isn't putting out enough. It is really difficult, IMO, to say much of anything conclusive without putting a fuel pressure gauge on it.

An adjustable regulator could be used to increase the pressure if you really wanted to. It would only work up to a point. From what others have reported when their regulators have failed closed, above ~60 psi, the PCM can no longer compensate for the increased pressure and can't properly regulate the A/F mixture. I might also worry about the pump longevity -- is the pump overdesigned enough to continuously pump against those higher than spec pressures.

In my way of thinking bypass=recirculate, when there is no vac. what does the regulator do, I am new to Rangers and EFI in general, my last truck was a 1966 F-100 with a 351w and a afb. I have built race cars for many years. I'll buy a gauge adapter and check the pressure.

 

[Maniak]

Low to no vacuum with the fuel pump running raises the bypassing pressure to about 40 psi. With full vacuum it bypasses at around 34. I can say 60 psi is too much as when our regulator went bad we were runnimg 60 psi all the time which
made for black exhaust and rough idle.

~Mark

 

[MrShorty]

In my way of thinking bypass=recirculate, when there is no vac. what does the regulator do,

When we say this is a "continuously recirculating" system, that is what we mean. When there is no vacuum, the system is still recirculating, and it should be at ~40 psi.

 

[hawkfire1]

Ok, now we have a few details more than was originally provided.

Not much to go on since I think you have it set in your head that your 4.0 OHV is suffering from vapor lock.

I can sort of see your line of reasoning, but without temperature readings from the block, fuel lines and fuel rail and FUEL PRESSURE GAUGE readings when this is hot restart problem is occuring, well it is just guesswork or speculation on your part.

A vapor lock issue is possible, but I think not probable under the provided circumstances until other possibilities have been ruled out.

Since you wish to speculate about heat being an issue have you inspected the fuel pump relay and socket/wiring located under the fuse box in the engine compartment?

The theory is that a 19-20 year old 5 prong socket holding the relay in is fine during a cold start but heats up and expands when the engine is at running temperature and stays expanded causing an intermittant or bad contact.

When it cools off the metal sockets contract forming a solid contact and no problem starting the engine.

OF course, these are just suggestions. YMMV.

 

[Roadrunner777]

I'm just going to toss this in, see what you guys think. First, mine is not vapor lock, it happened 2 nights ago in below freezing weather.

If conditions permit (engine temp, so forth) can the engine start directly into closed-loop mode? I can probably research that myself this week, just wondering if anyone has a quick definitive answer. If so, then I start thinking my oxygen sensors are too slow to heat up, or the bandwidth is just too wide due to sensor age. Any thoughts?

I'm going to hook up a fuel pressure gauge next week and see if I can get definitive readings.

 

[jyro]

Ok, now we have a few details more than was originally provided.

Not much to go on since I think you have it set in your head that your 4.0 OHV is suffering from vapor lock.

I can sort of see your line of reasoning, but without temperature readings from the block, fuel lines and fuel rail and FUEL PRESSURE GAUGE readings when this is hot restart problem is occuring, well it is just guesswork or speculation on your part.

A vapor lock issue is possible, but I think not probable under the provided circumstances until other possibilities have been ruled out.

Since you wish to speculate about heat being an issue have you inspected the fuel pump relay and socket/wiring located under the fuse box in the engine compartment?

The theory is that a 19-20 year old 5 prong socket holding the relay in is fine during a cold start but heats up and expands when the engine is at running temperature and stays expanded causing an intermittant or bad contact.

When it cools off the metal sockets contract forming a solid contact and no problem starting the engine.

OF course, these are just suggestions. YMMV.

I have several infared guns and I'll dig one out to test the temps . I can hear the pump run when the key is turned to on for about 3 seconds every time.