evening,

i have a 91 F150 5spd manual 4x4, 302 engine, just replaced the starter solenoid, had a problem with the alt not recharging the battery, fixed that and now it won't stay running for more than 5 mins, then it acts like its not getting fuel or its choking, not sure. i've checked the fuel pump relay, replaced the TPS, cleaned out the throttle body and intake manifold. i'm at the end of my rope here, when i got the truck it was missing all vacuum hoses relating to emmissions, when its about to die theres a very noticable sucking sound. but i'm usually in the cab so i can't pinpoint where its coming from because i'm trying to keep it running. fuel pump is activating, i have fuel coming from the check valve on the rail. its not squirting the hood or anything seems kinda week to me but i don't have a gauge to put on it. the check engine light goes off after ignition. doesn't come on again untill key on position prior to crank. it is missing the exhaust system and the air filter. i have a cat converter but its not on. i'm farly new to the mechanics deal but i'm out of probable causes for the rough idle/dying. i wish i could link an audio file. i imagine anyone with experience with these things would be able to tell what it is by listening to it. thanks for any help at all.

 

Maybe start with the fuel pressure, you can rent/borrow a tester at Auto Zone or O'Riley's. Might (just for S&G) go ahead and replace the fuel filter.

If all the emission stuff was taken off then you need to track that down to be sure everything is connected right.

Another thing to check would be the EGR. If it's clogged or broken it will jack up the way it runs.

Start with that stuff and I'm sure someone else will chime in soon.

Good luck and Welcome to the site.

 

Good idea on the EGR checked it this morning and it looks horrendous, when I get home this evening I'll take it off and see if it will actuate after a good cleaning. I was also wondering, I recently replaced the starter solenoid, placed the wires back where I took them off from. There was one wire coming from the alt going to the starter side of the solenoid, before I switched it to the battery side of the solenoid it ran done but didn't charge, now that I've switched it, it's charging but won't stay running. So I might have a bad ground to the starter from the batt

 

Man I have a 1996 F150 4x4 with the 302 it was doing the same thing so I replaced the spark plugs,wires,distributor cap, rotor button, coil, idle air control valve, throttle Position sensor, checked the timing, checked all the fuel injectors, the O2 sensors and still couldn't figure it out then I thought the distributor was bad so pulled it only to find out it was good also. Just discovered the other day I tooke the upper intake off and the gasket was broke into like 9 different parts and that fixed her up. I know yours is an ODB-1 but maybe that will help.

 

so i have replaced a few more sensors, still no change. it makes no sense, before i had a problem with the alt not charging the battery but it ran fine. my problem there was there was a large, fusible link green wire that i had on the starter side of the starter relay/solinoid. i switched that to the battery side, and when running it charges the battery. but now it won't stay running long enough to check anything. not idling and after a few minutes even with the pedel to the floor it will rev up and then nothing then rev again, almost like the fuel pedel isn't controlling the fuel. i've replaced the fuel pressure regulator, did the ground out test on the fuel pump and it works fine. took the fuel tank down and cleaned it out as well as new fuel filter and the siphon filter on the bottom of the pump. the other day i was able to get it to hold around 3k rpms for a good 5 min. very irratic symptoms so its making it hard to rule out things and diognose properly. ruled out timing simply because i was able to hold it at 3k rpms for a good bit. i keep thinking about that wire from the alt on the wrong side of the solinoid " it ran fine before i switched it" so maybe i'm chasing a bad ground? seeing as its so irratic. i'm out of sensors to replace that deal with air/fuel ratio. i'm also considering fuel return or vapor lock. i'm trying to think simple before i jump to injectors/valves, and maybe the cam position sensor. also the deverter valve isn't on it, i'm not sure that would have any thing to do with it seeing as it deals with the smog pump and the tad,tab lines. i'm running out of options before i decide to tear it all down and rebuild it.

 

You said you don't have an air filter - is the whole intake tube gone? Is the MAP sensor missing?

 

brand new map sensor, i have the air tub but because i'm all over the engine it keeps getting in the way so i have it off. would that little bit of air restriction from the air filter cause it to do all this?

 

Pull your air bypass valve off and check see if plunger is stuck or if it has bunch of crud in it check for vacum leaks would b pretty major one if there was make sure all your sensors are hooked up around your air tube

 

Okay, I have the same problem. Replaced all the sensors, new exhaust, new injectors (tested), new EGR valve, and even a new comp. It has the local shop stumped (been there a month). The only thing that was done to this engine (while being rebuilt) was a mild RV cam was installed.Have you figured out what the problem is yet?

 

I know this is an old post but I was wondering if you ever figured out what was wrong with your truck. I'm having almost the same problem with my 89 although mine runs great right up til it dies. I can go a couple miles and it just shuts off like fuel or spark is getting cut. I've replaced a lot of stuff trying to track it down also.

 

It's a vacuum leak somewhere. You mentioned the vacuum lines are missing, start there...