1987 F-150 problems Part 2

[mcne]

I ended up changing out my plug wires and hoped that would fix my problem. Of course not. My truck still runs like trash. I am going to take it to another mechanic on Sat. but would like some other advice on what to check. The problem is the engine is missing/hesitating. It will miss/hesitate during low rpm acceleration and if it overcomes this it will do it again during higher rpm's. If I drive the truck in Drive and floor the gas it will start to accelerate then miss/hesitate for a bit then surge in power for a second and seem to run well, then it will miss/hesitate. Then if I let off the gas and coast for a few seconds then slowly push the gas it will slowly accelerate until it reaches a point were the pedal is almost to the floor, then it will again lose power and slow down. My truck does not have a rev limiter so I know it is not being restricted. The weird part is it will run better (but not great) when I manually shift through the gears. If I am at a stop and start out in 1st the truck will accelerate until redline, then I manually shift to second and it will accelerate to redline, then I shift to third/drive and the truck does not have any power and will not rev up very high compared to 1st and 2nd. (it will still hesitate in 1st and 2nd but will eventually overcome it) I talked to a tranny shop today and the mechanic said it is not my tranny causing the problem. I also have good vacuum to the transmission. I guess my question is what else besides bad spark plugs or wires will cause missing or hesitation or lack of power. I know there are probably 10,000 different things that can cause it. Based on what my truck is doing does anyone have any guesses on where I can start? I have good fuel pressure, good vacuum when it is running smooth, and the only code the computer has is the always lean O2 reading. Thanks, about to cry Brian.

[tkr]

The next two easy things I'd check are the cap and rotor. After that I'd look at the throttle position sensor, the oxygen sensor and the MAP sensor.....it does have a MAP sensor and not a mass air flow sensor right?? All three of those require a lab scope for accurate testing though. The always lean O2 code means the computer thinks it can't supply enough gas to the engine. It is possibe it actually has a fuel delivery problem....low fuel pump volume, restricted filter, etc...but its more likely a sensor sending the wrong information to the computer. A bad oxygen sensor is an obvious possibility. If it has more than 60,000 miles on it, it needs a new one anyway. Another possibility is the mass air flow or manifold pressure/vacuum sensor. If they're sending an inaccurate signal to the computer, it will think the engine is getting more or less air intake than it actually is and try to compensate for that by adding or taking away fuel. It basically gets confused when it can't match the demand and stores the lean 02 code.

[ntsqd]

My first thot: Replace the fuel filter. I had a similar problem with my diesel Ribbit. Long story about what was going on, but the short answer was a plugged fuel filter. I know a diesel Ribbit engine isn't exactly the same thing, but your description of the problem is the same. Like the O2, if you don't know the age of the fuel filter or it's original, it's time to replace it anyway. Look for it first, you may need a simple special tool to get it off.

If you still have trouble I would check the fuel pressure under load. The engine's fuel rail has a pressure tap for this purpose (& others).

[matt_helton]

and like tkr said, you may have correct fuel pressure but low volume. volume is just as important as pressure. and ditto on the filter. try to eliminate the simple stuff before before you get into the more complicated parts.

[tre5]

I had similar problems with my '94. Turned out to be fuel pressure. Check or replace your fuel filter as a first step. If thats fine check pump and injectors. I replaced everything in my fuel system, and now it runs perfect.
TRE5

[tedmales]

i do not think that the o2 sensor would cause such problems. even if you unhooked it it might run rich,, but shouldn't cause all this mayhem. i think you could throw money at it all day, but it needs to be hooked up to a scope to see whats going on. if you can eliminate fuel starvation then it could be the ecm, or maybe a cam position sensor it your truck has one. good luck and maybe somebody can recomend an honest mechanic, if one still exists, and they can help you spend less money in the long run

[mcne]

Replying to all. Thanks for the input. I am in the Air Force and took it to the mechanic on base. He seems to be an honest guy and he tried to figure out the problem but could only guess. Like I said earlier in my first post. The diagnostic shows that the engine and related equipment is working well. Fuel pressure was good. Sensors checked out good. Vacuum good. Just high emissions. I guess that is the bad part about plugging in the computer when the truck is sitting still and not driving down the road. It cannot simulate actual driving conditions.
I have replaced two of my three fuel pumps on the truck (I have dual tanks) and also replaced my fuel filter about a year ago. Maybe I will replace the filter again.
One change I noticed today when I checked for codes is my always lean code is now gone. The only code I had was a EGR sensor or actual EGR problem. I have had the EGR code for a long time and I think I had it even when the truck was running perfect years ago. Anyone have any EGR problems before? What kind of symptoms did you have?
Well, thanks again for the help. I am taking the truck to another mechanic tomorrow so hopefully he will find the problem. Brian

[tedmales]

i had a 94 dodge that had egr problems. the egr solenoid was melted to the back of the head and when it tried to open it would just die, or run real bad. what it was doing was creating a huge vacume leak when it opened. it was a dodge so it may not apply to you. on a side note it had to be towed to the dealer 3 times to be fixed. they replaced the cat, fuel pump, injectors , ecm, and were going to replace the engine harness when i decide to look it over real close. it took me less than an hour to find. i was just lucky. i also in that same truck had the coil break down. it would run and miss and sputter, sometimes not start, i figured it out when i was washing the engine that the first drip on it and the motor died. replaced the coil and all that craziness stopped. have you acually hook it up to an ignition scope. like what was said earlier it will give what looks like a heart beat monitor and you can see each individual componet in the ignition system. if that hs not happened, that is what needs to happen next.

[slimjim]

I say fuel filter - you probably have more than one, if so - be sure to check both. The one closer to the fuel tank would most likely be the culprit.

[mcne]

replying to all- I will tell my mechanic to inspect the EGR valve tonight. The ignition system has been checked on the diagnostic and I just had the ignition module checked today so I believe everything is sound. Thanks for the input. Brian