1988
F-150
351
Automatic
A/C
Unknown actual mileage. Odo said 2,000 when I got it.

Problem:

Truck ran fine for years. All of the sudden, it started running poorly. So does anyone know what could cause that?

JUST KIDDING.... Yes, I will list the symptoms.

Starts up easily every time and has a slightly higher idle for about 30 seconds then idle drops down a little, except now it wont drop the idle like it used to, unless I tap the gas a couple times.

Upon acceleration, it hesitates a little and "doesnt kick in" at less than 15-20% throttle. Once I press the throttle further, it takes off and acts normal.

Driving down the road, it starts to spudder and not run right, loses some power- (10-15% throttle range). I press the peddle down further and "poof", its running better and accelerates. Maybe something to do with the TPS failing in the 0-15% throttle position range?? No idea......

When I come up to a stop sign, its fine for a second, then starts to surge. It surges harder and harder until it kills itself. If I put it in neutral, it will stay running without the surging.

Exhaust system is pumping out a lot of very toxic smelling exhaust. No like eggs, but just nasty heavy thick exhaust smell, maybe a lot of unburnt fuel in the exhaust?

I looked around for vacuum leaks, and this is what I found:

The two plastic vacuum tubes that go to the "coffee can" aka "vacuum reservoir", were burnt completely through and hissing. BINGO! So I fixed those lines and plugged the connection back into the coffee can..... and that caused it to run 10 times worse!?!?!? With those lines attached, the engine is unpredictable, bucks, stalls, spudders etc. Undrivable, so I had to disconnect them just to get the thing drivable again.

Please advise ! What do I do - oh gurus of engine wisdom.

 

If the ignition system (plugs, wires, cap, rotor, coil) is in good shape I'd suspect the O2 sensor. Have you tried to read codes?

Other possibilities are excessive fuel pressure (FPR) or possibly the IAC. TPS is a possibility, as is the MAP sensor.

Without codes, it's tough to nail it down.

 

Sounds like it is running rich. TWO WILD GUESSES the MAP sensor or the coolant temperature sensor.

 

No "check engine" light is currently on. Will it still throw codes without triggering that dash light? Also, I think I would have to reset the system and wait for the new codes to show as it has not been cleared in years.

Keep the info coming guys, I need all I can get. Where do I start? Try replacing the MAP sensor? Clear the codes and wait for new ones? Hit it with a hammer?

 

Now that glc mentions it the fuel pressure regulator is a good possibility. They say pull the vacuum hose off it and see if it is sucking gas into the intake.

 

Sucking gas into the intake? I don't understand. What? I unhook the vacuum hose, then what?

 

Something I've only read about. There should be a vacuum hose on the fuel pressure regulator and if the fuel pressure regulator goes bad the vacuum hose will suck gas into the intake and this gas will end up in the cylinders of the engine, along with the air that is naturally needed for the engine, thus a rich fuel mixture.

 

If you unhook the vacuum hose right after the engine has been ran, and the regulator is in fact bad, the inside of the vacuum hose may appear wet with gas.

 

So check for the Wet vacuum hose then check the codes, then replace the Map Sensor?

 

Without codes, it's a crapshoot.

The codes were cleared the last time the battery was disconnected.

 

I have not cleared the codes since I have owned the truck. Never disconnected the battery in the last 2 or 3 years. I will disconnect the battery and leave the headlights on over night. Any idea how many minutes/hours of driving it will take to trigger the codes again?

 

If it's a hard failure, it should be within the first few minutes.

I'd read them out before clearing to have a point of reference. You don't have to leave the headlights on - they will clear by themselves within a few minutes of disconnecting the battery.

 

Code 34 came up. Could that cause the surging at stop signs?

Also, I plugged the vacuum hoses back in and it ran SUPER rich for a bit. Reeked of fuel and ran poorly but it seemed to adjust the fuel mixtures by itself and now it not running so bad with the lines attached. Still surges and has problems in the lower throttle range. After plugging the vacuum lines back in the trans is acting weird. It is not shifting right. It always had a problem shifting from 2 to 3rd, where it would try to get into 3rd but would not make it in if it was under load. It would just bump in and out of 3rd with hard shuddering. If I let off the gas it would shift into 3rd and then I could give it gas again and it would be fine. Anyway, now its has weird symptoms when shifting into all the gear if its under load. I have to manually shift it through the gears if I want it to act normally. Ideas? Oh - and the trans problems are not there when the engine is cold. They get worse the more it heats up.

 

The vacuum modulator might be bad on your transmission. If you replace that it may help your shifting problem. I think it's mounted on the side of your transmission and has a vacuum hose going to it. I'm pretty sure you would have a C6 transmission.

 

Ok. I will replace that gizmo on the trans and see if it helps.