I have a ranger '96 4.0 V6 with 233k miles on it and it runs pretty much like the day I bought it back in 98 when it had 74k miles. Anyhoo, I recently discovered that lately whenever I start my truck up, when it's warmed up, and it's hot outside, the idle needs a little encouragement from the gas pedal or the engine dies out. After about 15-20 seconds of gassing it at about 2k it idles just fine.

But, if it's cold/cool outside the engine starts up and idles just fine with the engine cold or hot. Also, if it' hot outside and the engine has cooled off for about 45-60 minutes, the engine fires right up without a hitch.

Anyone have any ideas on whats causing this weirdness?

Thanx-

 

Welcome to FTE Joe

Could be a number of things. Did this begin after some event????

Being it's the time of year that it is, one of the first things that comes to mind is vapor-lock.

If you've recently filled up at a out of the way station, or one with low voume gas sales, maybe you've gotten a tank of winter (low vapor pressure) gas.

If that is so & in your area it's gotten warmer than usual on your trouble days, under hood temps can cause the winter recipe fuel to vaporize in the lines & cause "vapor-lock" until things cool down. So if you think this might be so, run most of this tank out & fill up somewhere else.

It'll also happen more freqently on return type fuel systems (the ones that route unused fuel back to the gas tank), especially if the tank is low on fuel, say below 1/4 tank. The returning hot fuel just keeps warming up the small ammount of remaining fuel in the tank, so the fuel being pumped to the engine for use, is already hot when it gets there & that makes it ripe for vapor-lock. So keep these fuel systems above the 1/4 remaining level.

If you don't think those are a possibility & seeing as how you've a few miles on your vintage ride, maybe a pesky underhood fuel pump relay is acting out, after it gets hot.

So if you think thats a possibility, you might try swapping the fuel pump relay with a like one, not needed to run the engine, say the A/C relay & see if things improve.

You didn't say if you had a trouble light or not, so I'm assuming you don't, but that doesn't mean you couldn't have a "pending" trouble code stored in the computers memory, that hasn't matured enough to turn on the "check engine" light & that code might offer up a good clue, on where next to look, so have the computer scanned for codes & post ALL the code numbers found.

Most autoparts stores will scan the computer at no charge, if your having problems, so call around & check.

Just some thoughts to ponder.

 

I went to my trusted mechanic and he said the fact that the truck starts up at all and is able to keep going as long as I push on the gas pedal means the fuel pump relay is working just fine. No need to get one, any other ideas?

 

Well you could try a KOEO & KOER fuel pressure test when it's hot & won't start, to make sure you have fuel pressure in in the proper range.

You could also do a spark test with a inductive timing light, to determine if spark output is affected when the engine is hot & won't start.

On the fuel pump relay, if as I suggested, it's heat sensitive, it could cause a problem on hot starts, but be ok on cold starts. So what did your mechanic think may be wong?????

The clue you gave with it starting ok on cold/cool days, when the engine is hot, is a good one, I just can't figure out where that piece of your puzzle fits just yet. It would suggest something is heat sensitive, whe hot & is affected by by warm or hot ambient temps & that made me think vapor-lock, or maybe a heat sensitive fuel pump relay.

I'd not rule anything out at this point, as you've not indicated you've run any kind of basic diagnostic tests, that would rule any one system, or any one thing, out!!!

So if you could do some basic fuel prssure & spark output tests & post te results, maybe the outcome could help us begin looking at the troubled system or part.

Just some more things to ponder.