Strange F-150 problem

[Sous]

So I have a 1992 F-150 with the 4.9L straight six. It has fuel injection and is an automatic. Every once in a while the truck will not start, but it cranks/turns over just fine and will continue to do so. I have thought it was the battery being drained from sitting for a month or so and tried to jump it. I have thought maybe the starter had a dead spot, but beating the starter did not work either.

This has only happened twice in the past year and I have only come up with one solution. When I have it towed via a strap for a couple of miles and then park it, the truck fires up just fine. So, I am at a loss here and thought maybe it was vapor lock, but as I understand it that typically happens to vehicles that are running hard/hot. I have replaced the battery and the truck starts fine 99% of the time, just every once in a while it needs some help via a tow/moving around a lot.

Thoughts, ideas, suggestions?

 

[Sous]

A friend of mine suggested the neutral safety may be going bad, but I thought that it would not even crank if that was the case. I was under the impression if the safety was bad, when you go to start the vehicle it would act as if the battery was dead and just make a click noise.

 

[dadofthree]

If the starter solenoid is clicking and nothing else, I'd suggest you need a battery. Doesn't really fit in with the tow fix though

 

[BoostCreep]

I'd have to see a wiring diagram but normally a neutral safety switch won't allow the truck to even turn over. Since it's turning over fine, the next time this happens take a spark plug out right away, look at it, smell it, does it have a ton of fuel on it or is it bone dry? Then lay the spark plug on something metal (ground the plug), turn the engine over and see if it sparks or not.

This will tell you if you have fuel and ignition. From there we can work backwards a little bit. Also, does this happen only during a cold start or does it only happen when the engine is warm?

 

[chrisjp]

ford...nuf said? lol

 

[BoostCreep]

ford...nuf said? lol

Which means it's got half a million miles on it and this is its first problem.

 

[mistaforty]

its your key...you try to start and nothing...then it starts like nothing was ever wrong. ive seen and had it happen especially if youre using a duplicate key. for whatever reason the computer stops recognizing the security chip and wont start. when it picks it up it starts. if it happens theres also a reset that can be done to get it started right away.

acually now thats just a theory as i did not see the year you mentioned...ive had explorers and expeditions (currently an 07 EL) but im not sure if the same chip was used in 92. my first expedition was 96 (M.Y. 97) but not sure that the f150 prior had that key/security

 

[StromBusa]

check if the throttle body is loose to the intake

 

[Sous]

If the starter solenoid is clicking and nothing else, I'd suggest you need a battery. Doesn't really fit in with the tow fix though

Battery was replaced about 3 months ago due to a very old one being in there. The truck will try to start by cranking over and over, and once I have pulled it a couple of miles it fires right up without a boost or anything. It is strange and I am 99.9% sure it is not the battery and that is good enough in a court of law.

 

[Sous]

I'd have to see a wiring diagram but normally a neutral safety switch won't allow the truck to even turn over. Since it's turning over fine, the next time this happens take a spark plug out right away, look at it, smell it, does it have a ton of fuel on it or is it bone dry? Then lay the spark plug on something metal (ground the plug), turn the engine over and see if it sparks or not.

This will tell you if you have fuel and ignition. From there we can work backwards a little bit. Also, does this happen only during a cold start or does it only happen when the engine is warm?

This only happens when the truck sits for a while, like a month or so. The last time it happened it was in the sun and I thought maybe there was pressure build up in the fuel tanks or something that prevented fuel from being pushed into the lines, but had no idea. I pulled it up to the front gate so a tow truck could get to it and tried to fire it up one last time, and it did. It has been fine since then and sits for long periods of time as this is our work horse to take stuff to the county dump.

I don't think there is an ignition problem or neutral safety issue as the starter is turning over. Normally with an issue with the neutral safety the symptoms will be similar to a dead battery.

 

[Sous]

ford...nuf said? lol

As KooK mentioned, I got this truck for free when my father passed away and it has 189,xxx miles and this is the first problem it has had that I know of. It is a beast and has only not started on me two times because of this ghost problem.

 

[Sous]

its your key...you try to start and nothing...then it starts like nothing was ever wrong. ive seen and had it happen especially if youre using a duplicate key. for whatever reason the computer stops recognizing the security chip and wont start. when it picks it up it starts. if it happens theres also a reset that can be done to get it started right away.

acually now thats just a theory as i did not see the year you mentioned...ive had explorers and expeditions (currently an 07 EL) but im not sure if the same chip was used in 92. my first expedition was 96 (M.Y. 97) but not sure that the f150 prior had that key/security

Thanks for the theory, but this is a 1992 F-150 and there is no chip in the key. The key is a genuine Ford key and it does not even have keyless entry. I don't think the key is the problem as it starts just fine most of the time, just those two. But, after having a friend pull it a couple of miles toward the mechanic shop, it fires right up.

 

[Sous]

check if the throttle body is loose to the intake

Everything appears to be as it should be. All vacuum hoses are attached and no dry rotting that I can see.

Anyone else have thoughts or ideas? Very strange problem if you ask me and I don't want to take it to the mechanic as it may be fine for the next year or so before the same thing happens.

EDIT: It does have dual tanks, one was full and the other was 1/4 tank at the time. Even when switching to the full tank, the problem persisted. Once the truck was pulled for a bit and fired right up, I went and filled both tanks to full again just to get it out on the road a bit. It was too late to take my remodeling scraps to the dump.

 

[BoostCreep]

Oh hell, only happens when you let it sit for a few months? This may be one of those really crappy things to try and diagnose. I would give it a light, healthy tuneup (fuel filter, air filter, spark plugs, check the wires, dist. cap, rotor), although this isn't going to solve your problem, it's where I start on something like this because it gets your hands in things and allows you to jiggle stuff around. After that I would do a light cleaning to some of the connections. Take the wires that power the ignition coil and blow them out with some electrical cleaner, check to make sure the terminals are clean and in good condition on both ends and plug it back in. Do the same for the fuel pump (a 92 inline 6 motor will have an electrical fuel pump under the bed and inside the tank). If you can't get to the fuel pump connection then just pay attention next time, see if you can hear the fuel pump trying to prime when you first turn the key in the ignition.

But like I said, we're really shooting in the dark without more information. The easiest thing to do is wait until it happens again, take a spark plug out and see if it has a lot of fuel on it. That will mean that it's getting fuel but no spark so there's an ignition issue. If you take the spark plug out and it's dry after trying to turn the engine over, then ground the spark plug to a valve cover (don't hold the wire or the plug, it may shock you) and turn the engine over. If you can see it spark then you have a fuel problem and not an ignition problem. If the sparkplug is dry and you can't get any spark from it, it means the engine computer isn't receiving a signal from a sensor (normally crank sensor) so it doesn't even know the engine is trying to turn over, therefore it's not opening injectors or firing spark plugs. Although if this were the problem, I would def. check the crank sensor wiring first because crank sensors don't fail like that and it could be a weak connection (and you'd just waste money by buying a new one).

When it happens again, do what I say, isolate the problem a little more and we (or I) can give you a better handle on the situation. The good news is, these trucks are very simple and it wont be an expensive fix if you do it yourself.

But I agree, I don't think it's the Neutral safety switch, and it's not going to be the key itself because this truck didn't come with a security system encoded in the key.

Just let us know when it happens again so we can take advantage of the situation.

 

[Skydyvyr]

This may sound stupid, but I wonder if the fuel pickup is getting clogged, or condensation is building in the tank and moving the vehicle sloshes enough fuel around to clear it. In '92 were the tanks metal or plastic? How much fuel do you keep in there normally?

--Sky

 

[superchargedv8]

if it has dual tanks you might have to replace the intake fuel pump assembly. Sometimes they will pour fuel out the filler neck. I believe there was a TSB back in the day to correct it but is no longer in effect and the way to correct it is to install the new revised fuel pump assembly (believe the check valve goes bad). One thing you can try is; turn the key all the way forward several times and make sure the pumps turn on and are priming THEN TRY AND START IT. All im saying is take a look into the fuel system including filters if equipped and go from there.

 

[BoostCreep]

This may sound stupid, but I wonder if the fuel pickup is getting clogged, or condensation is building in the tank and moving the vehicle sloshes enough fuel around to clear it. In '92 were the tanks metal or plastic? How much fuel do you keep in there normally?

--Sky

Ehhhhh, it's a return style fuel system which means the fuel that doesn't go into the injectors gets routed back and into the fuel tank which on its own moves fuel around a bit. The engine would probably at least cough if this were the case.

if it has dual tanks you might have to replace the intake fuel pump assembly. Sometimes they will pour fuel out the filler neck. I believe there was a TSB back in the day to correct it but is no longer in effect and the way to correct it is to install the new revised fuel pump assembly (believe the check valve goes bad). One thing you can try is; turn the key all the way forward several times and make sure the pumps turn on and are priming THEN TRY AND START IT. All im saying is take a look into the fuel system including filters if equipped and go from there.

Well you're right about the check valve, they do tend to go bad which allows the fuel to drain from the rails all the way back into the tank. If he were to sit there and crank it long enough or bump the ignition a few times, the fuel would work it's way into the rails again. However I'm assuming that he's been cranking it a couple times over and has done it long enough for fuel to reach the injectors, but it's possible he hasn't. But like I said, I wouldn't run out and buy a $200 POS Airtex fuel pump quite yet until this happens again and you can better diagnose a problem that may only cost you $10. By the way, stay away from Airtex, biggest piles of **** that you will warranty time and again (until the 1 year warranty is up, then you just buy another one).

Edit: I'm also going out on a limb here and saying it doesn't have dual fuel tanks considering it's a half ton 6 cylinder.

 

[t5stang91]

I would put a fuel pressure gauge into the shrader valve and when it happens check pressure against what it should be when it happens. I also think it is fuel related. do these still have brains on the fender well? I had a old ford that would crank but nothing would happen once and a while, brain seemed to fix it.

 

[Sous]

It does have dual tanks, one of which is only about 15 gallons and the second is around 20 gallons I think. The tank it was on was at 1/4 when I tried to start it yesterday, but plenty enough that it should have been feeding fuel to the engine. All in all, while trying to start the vehicle I bet it was cranking for about 5 minutes total. Of course I didn't have the key turned to start for 5 minutes straight, but while trying to figure out what was going on. The last time I started it was about a month ago, and that is normal. It gets ran about once a month, but has sat as long as 3 months and would start just fine.

I believe it is fuel related as well due to the truck being jostled around when being pulled. I will probably take it to the mechanic and have them replace the plugs, fuel filter (if accessable) and clean the throttle body/intake. Just a strange problem as it hardly ever happens and when it does it is cured by moving it around a bit.

Thanks for the suggestions.

 

[VIPER]

What you need to check is the crank sensor. If you have fuel pressure on the fuel rail and its cranking but wont start most of the time it is the crank sensor. You also need to check the ground to the pcm. I have a van that did the same thing replaced the pcm worked for a bit then did the same thing. Finally found the ground wire had a ton of corrosion on it and was half disconnected. Once i put a clean ground and tightened everything up i never had another problem with the vehicle.