Hi guys. First time poster here. I've got a 94 f150 with a 4.9 I-6 and it has some problems. It takes forever to get the thing where it can even start. It'll stumble for a few minutes and after it warms up it will idle fine and if you slowly try to rev it, it will reach to about 2500rpms before cutting out. If you try to rev it fast then it cuts out as soon as you try it. When driving it, if you get above 40 mph, then you HAVE GOT to be going down a hill. LOL. You can't rev the engine at all and once it's under a load it gets even worse. One thing that does help to get up to speed is to hold the pedal all the way down and pump it really really fast. I know all of you are saying pull the codes, but thats the thing, there aren't any codes. I did the self test and it flashed 11-11. Meaning everything is ok. I haven't got a clue as to where to start. Sensors, timing, fuel pump? I just put a new fuel filter on it. I just don't know.

Thanks guys

 

My first guess is MAP sensor.My 95 did the same thing.

 

I was afaid it might be, but i thought that would throw a code for sure. 130 bucks for one sensor. Ouch!!

 

Adam-check the distributor for bad or broken wires( under the cap) cracks, bad components. Also check for vacuum leaks at the manifold and vacuum lines. If thats all good, check fuel pressure and restrictions in the system.

 

It didnt throw a code on mine either.

 

Karl is right about that dist cap too sometimes bad one look good.

 

Ok guys. I checked the distributor cap and everything looked to be fine except for a little rust. I took sandpaper to the terminals and to the stator to shine them up just to make sure. No change. I just put new plugs and wires on a few hundred miles ago so if figure there ok. Im sure its one of the sensors. Is there any way to check to see if the map sensor is working correctly? Also what are the signs of a bad O2 sensor.

 

With the "stumbling" and all, it does sound like a MAP sensor problem to me as well. When it is in motion (say 30 mph +) and you push in the clutch (or put it in neutral) will it drop right back to an idle like it should?
You didn't mention how these problems (symptoms of the real problem actually) came on. Did this all just start happening at once? Or did it gradually get to this point. There are several things that could be causing it. While I doubt an O2 sensor running a muck would be doing it, a plugged up Catalytic Converter could produce such symptoms. A crack in the underside of the distributor cap can be very hard to see sometimes. A shot of starting fluid into the cap (watch your eyes while shooting it, it shoots back) will usually make even the hardest to see cracks become visible. Another thing to try is run the engine in the dark and look everywhere for loose current (little arcs jumping to a ground). I think you might also want to shop around a bit for a better price for a MAP sensor too. $130.00 for a MAP sensor for a 300 I6 sounds a bit high to me. Seeing how easily they are to remove and replace, if any of your buddies has a similar truck, you may be able to talk him into using his long enough to see if it corrects your problem. Remember to dis-connect, and re-connect the battery to reset the computer for the new sensor.
Hope any of this helps.

Regards,
Daniel J.
LucasOS
The Insane 6
1996 Ford F150 4x2 - Insane 6

 

Yeah, once it's warmed up it idles fine and comes down from higher rpms to idle fine. Just can't rev or accelerate very well . Sorry i didn't mention before, but the truck has ran poorly ever since i got it. I bought it off of a guy for 500 bucks cause it had been sitting in his yard for over a year cause he couldn't figure out why it wouldnt' start. The only thing i did was reverse the wires on the starter relay and i drove it home. It didn't run just the best but i figured i could put a few tanks of fuel and some fuel injector cleaner through it and it would eventually work out all the kinks. Well it did get where it would run pretty decent, not tip top by any means, but drivable none the less. I drove it like this for many many miles due to it not being a daily driver, just a farm truck and hunting truck. A few weeks ago i started to take it out and thats when i noticed the new problems that it had. There weren't any changes or anything made to it to cause the problems, they just started out of the blue.
Today, i think i figured out that the map sensor isn't the problem. My dad has a f350 with a 460 in that looks to have the same map sensor. I changed them around and the 460 continued to run well while the 300 still ran poorly. One thing i did figure out is that if i take the vacuum hose off the map sensor it will rev like it is supposed to, nice and smooth, but will flood out if you let the rpms drop. So i guess this rules out the distributor and all other ignition components and leaves me with the fuel system. I don't know where to go next. It sounds like the map still but the 460 ran great with both sensors. Sorry for the long post guys. Just trying to give you all the details.

 

Well that actually helps! First of all, with the truck sitting for so long, you may have some carbon that shook loose and is plugging some vacuum ports. Second, and this one might be a stretch but I have seen it-if the previous owner had ethanol in the tank and it sat that long there is a chance that the nylon boot in the tank has become "snotty" meaning it has started to deteriorate from the ethanol. This will cause a fuel starvation and or low pressure situation. To fix this you will have to remove the tank then the sending unit and pull the boot off. You can replace it if you want but I usually dont. I do think you may have some vacuum issues though, so I would start by putting a good vacuum guage on the hose to the map sensor, as well as some of the other ports and compare the readings. If they arent coming out, it may be time to remove the manifold and have it cleaned out.

 

Ok i'll try to see if i can round up a gauge somewhere. The ethonol theory is definately a bit of a stretch but good thinking though. I don't think that the guy put ethonol in it but i've been wrong before. I don't think any fuel lines are clogged due to the fact that when i took the vacuum line off the map sensor the truck reved to its full potetial with out hesitation. Thats actually the first time it sounded that strong and it even torqued the truck a little. Definately a first for that motor while ive had it. LOL

 

Ok. I finally hooked a vacuum gauge up to it. Vacuum is fine. I took a long time and went over the entire engine bay looking for anything out of the ordinary. I lifted up to cover on the throttle body and saw what i think is some kind of throttle position sensor unhooked. It piggybacks on the throttle linkage. Anyway after i hooked it back up i unhooked the battery for a while to reset the computer. After i hooked the battery back up i started it and noticed a little difference but that isn't the main problem evidently. Good thing is a finally got some codes when i ran the KOER test. Codes are 72, 213, 225, and 172. I figure im getting the 72 code(Insufficient MAF/MAP change during Dynamic Response Test (user error)) because i can't get the engine to rev up at all. The 213 is spout circuit open. I don't know what that is. 225 is Knock Sensor (KS) signal not sensed during dynamic response test, so i guess i need a knock sensor. And 172 is HEGO sensor circuit indicates system lean (right side).

 

No comments? A bad knock sensor wouldn't cause the lean condition would it? And what would cause the open spout circuit code?

 

Just thought I'd update you guys. Turns out it was a bad fuel pump. Truck runs great now.....all except for a missing cylinder. LOL Fuel pressure is about 90 psi. I guess i need a new regulator. It's cylinder 6 thats missing. It's got good spark and good compression. I think it may be a bad injector, but im not sure till i get the new regulator on. Any chance the high pressure would cause just the one injector to not work and the others work fine?

 

The spout is a two pin jumper by your distributor. The jumper is removed to set base timing. If thats fell out, your timing is gonna be out of whack. I have heard that the computer has modes to try and override it being open but verify the plug is installed. I can see that causing quite a few headaches.

I'd get the regulator installed and then recheck that #6 then. I rigged up a spare injector plug to a battery to test all my injectors after cleaning several years of sitting goo out of them. That worked good.

Brigart