"the pump on the rail" is most likely an adjustable fuel pressure regulator used when installing "non-stock" higher flowing injectors.

Bob

 

The new computer has seemed to fix my high reving problem. The idle still flucuates sometimes though. It has only been two weeks so Im not sure about long term. Also I will not be driving it as much any more because I got a new truck but I will still keep up on my old truck.

 

Thank you for the update !!!!!
I'm glad you finally have some closure with your truck.

I'd say that your surging problem is still associated with "non-stock" injectors (ie. adjustable FPR) in your truck.

Good Job !!!

Bob

 

Could holes in the gas line be causing an issue like this to? Or would it starve the motor? Im talking about small holes in the line..
My unlce had all kinds of issues with his jeep running and it turned out to be he had small holes in the line and after replaced them it solved all of his problems.

 

You know, I was "enlightened" in a couple of other threads about the possiblity of air entering the fuel lines due to the rubber "O" rings deteriorating because of the ethanol used in gasoline nowdays, and was promptly told that it just couldn't happen.

Was the jeep your uncle had an EFI or a carbed engine ????
That, I suppose COULD be the difference as to being relevant or not.

Let's see what happens.........

Bob

 

His jeep is carbed..

 

Give this a try, as crazy as it sounds.............

Run a temporary heavy guage ground wire from an alternator mounting bolt to the negative battery terminal or to the fender ground next to the battery.

I have a hunch that this is a problem I'm having.

Bob

 

88 F250 XLT Lariat, 5 speed Mazda trans, 4.9l with lots of miles.

I am trying to fix the rev to 2200 rpm on start issue as well.

I bought this truck about 5 years ago for $225, did some quick repairs to get it going and worked it hard for 2 or 3 years, then parked it for another 2 years or so. It now sits in its own bay and I'm fixing it right as time and money allow.

The real problem with the engine is that it needs main bearings, and a new oil pump. Cam bearings too, but it may not get those as I don't have the tool anymore. But it actually runs pretty strong, just rattles on start up because of the crazy 2200 rpm thing. (yes, I have a good oil filter on it) and I can hear the mains when it hits shifting rpm as well.

But before I fix that I want to get all the other odds and ends fixed, then I will go through the engine. So very many odds and ends.

Anyway, the rev on start is not doing whats left of the bearings any good, and won't help the new ones either.

The truck had/has several, err..., modifications prior to my purchasing it. One of those is the extra ground from the alt bracket to the battery, so that doesnt' appear to be the fix.

I replaced the tps sensor because it showed dropout, didn't fix the rev on idle, but did get rid of a slight hesitation off idle. It is set at .96v.

I have another engine and trans from an 89 in the bed, so parts are easy to find.

I switched idle air motors, no difference, cleaned both and tried both, no difference.

I replaced the air charge temp sensor with a cleaned one from the other engine, no difference.

I checked the temp sending unit the goes to the computer and it is working correctly, as is the one for the guage.

I replaced the computer with a rebuilt one from Advance when the old one wouldn't run the fuel pump anymore, had the rev problem both before and after.

The egr threw a code, and I will replace that and clear the code, but I blocked it off temporarily, no difference.

I will check fuel pressure, but I don't believe that is the problem. The truck runs very well other than this rev issue and the main bearing noise, oh, and a very slight lifter tap.

The cat has been removed, don't think it would affect start up surge anyway.

The ignition is hotwired to a toggle switch, and a push button for the starter. They put the ignition slider in run, and disconnected the push rod. The acutator is broken - its on the list to be fixed.

They cut the 2 big yellow wires, twisted the ends together and ran them to the toggle.

They ran wires all the way out to the solenoid for the push button starter.

I have the clutch safety switch jumpered temporarily - you know why.

Once in a great while, for no reason, the truck will only rev to about 1600 rpm on startup.

I live in Florida, so cold is not an issue.

I haven't broken out the vacuum guage yet, but when I cover the tb, it pulls my hand very hard, and dies. Line vacuum feels good as well. I was planning on checking for vacuum issues next, but...

One curious thing, when I unplug the idle air motor while its running it dies instantly, which is good. Then I plug it back in, and If I flip that ignition toggle off and back on, it overrevs as always on start, but if I just leave the toggle on and hit the starter button, it does not overrev on start. It only hits about 1300 to 1600 then.

This seems like a clue to me. If I don't break the power to the ignition switch, the problem doesn't occur.

I guess I will have to have a look at the wiring diagrams to see what powers what exactly, but if this gives anybody who knows this system better than me an idea I would appreciate hearing it.

P.S. Does anybody have one of these trucks that doesn't rev that high on startup?

 

bdelmar2, Is this only on start up, as in during the engines warm up routine? Doesn't matter where you live, an engine is always cold at start up. Also, check your dash tach with a good dwell/tach. My dash tach reads 400 rpm high. Then we can see if it is idling too high on start or if the gauge is indicating high.

-Mike

 

Thank you for the reply, yes the truck only revs high on start up.

It does this cold, hot or inbetween, except when it randomly chooses not to. Then it revs up to around 1600 give or take.

This is according to my dash tach. I used to have a multimeter I could just clip on to read rpm, but haven't seen it in years. I do have an otc genisys scanner - which will read the codes but the eec iv system in the truck doesn't give a datastream.

I will look around the shop and see if I can find something to verify the tach with, but I will say that it sure sounds like every bit of 2200 rpm, it shows the truck idling at @750 rpm other than the initial high rev, and seems to be roughly correct when driving down the road, its probably not dead on, but pretty close.

I didn't get much time today to work on the truck, but I did replace the battery terminals with brass ones and cleaned the extra ground connection and the solenoid connections. I discovered the fusable link for the large yellow ignition wire had been replaced with a regular piece of wire and had a poor connection.

Oh, and checked the return signal line against battery ground in a couple of places, no resistance so the computer should be correctly grounded.

I picked up a new fuse link at napa while getting parts for another job and installed it. The truck started and only rev'ed up to around 1600 for 5 or 6 starts. Thought I had maybe found the problem.

Then it went to 1800 for a couple of starts, and then back to 2200. Disconnected the battery again for a half hour or so, but it continued to rev high on startup.

Switched the map sensor out quick, didn't think it would make a difference, and it didn't.

There is a stack of old computers out back in a storage trailer, I may dig around in there to see if there is one I can try.

Tommorrow I think I will rebuild the starter if its not too far gone, and maybe check the fuel pressure.

Thank you for your help.

 

I think someone has tinkered with the idle "set screw" on your throttle body.
While the truck is idling, (after being warmed up) you should be able to disconnect the IAC and the truck should just barely hold an idle and not die.

Try adjusting the the "set screw" with the IAC unplugged, (after the truck is warmed up), to a slow idle (about 4-500 rpms) then turn off the engine.
Plug the IAC back in and start the truck as if you were using a key.
It should start and idle up to about 1600 rpms then idle back down down to about 550 rpms.

Bob

 

Well, I didn't get a lot of time to play with the truck today, but I did do the procedure you suggested.

I warmed up the truck, disconnected the idle motor and adjusted the stop where it would just idle, around 500 rpm - and shut down the truck and restarted it, no change, still rev'ed to 2200 or so.

Unhooked the bat for a couple hours and then reconnected and drove for about 20 minutes or so, no change. Maybe a little higher actually, 2250 or so.

Voltage reads about .76 on tps now, prior to this I set the idle stop so it read .96. But nothing I adjust or change seems to have any effect on the startup rev, other than temporarily at best.

But I do thank you for the suggestion.