i have an 87 f150 with a 302 efi, 4 speed on the floor, its symptoms are bucking/jerking under acceleration/load. ive checked the timing and fuel pressure which are both fine. ive replaced the fuel filter, throttle postion sensor (tps) coolent temp sensor and a new air filter.. the OBDI codes for it are 25- system running lean and 41- bad knock sensor.. would these codes cause problems such as loss of power, hesitation, and bucking/jerking under acceleration? im stumped at this point and any input would be greatly appreciated!

 

Where this codes KOEO, CM, or KOER?

Either way am not sure they would cause the symptoms you have. Have you checked for vacuum leaks as this would cause these symptoms. If vacuum is OK, I would look into crossfire on the plug wires or an electrical component failing.

If it is a gentle surge look towards a fuel system problem. If the surge is sharp and abrupt look towards an ignition problem. One very quick check for weak ignition is to load the motor by doing the following: (1) with the motor running and auto trans in drive put one foot on the brake pedal (2) while holding the brake firmly press slightly on the accelerator pedal with the other foot, hold the break hard enough to prevent the truck from rolling and rear tires from spinning. This creates more demand on the ignition system and weak components will cause the motor to have sharp abrupt skips (missfires). Doing this with the motor cold creates an even larger demand on the ignition system.

I had similar symptoms on my 1987 F-150 and it turned out to be the PIP inside the distributor.

I read a Ford Technical Bulletin released, regarding a situation with our generation of trucks, specifically v8's, where the PIP spikes the timing every 8th firing, causing a miss.

It's a condition with how the PIP & the distributor inter-react, so replacement of the PIP alone won't cure the problem. Recommendation is to replace the Distributor ( which by doing so, replaces the PIP also). Replacement of the distributor is a lot less hassle than dealing with replacement of the PIP, so many people opt to replace the distributor as a unit anyway.

If this is the case with yours, just replacing the PIP could prove a fruitless effort. I also recommend TFI module (ICM) replacement at the same time, as it shares the same power & ground with the PIP. So they tend to share the same service life expectancy. Like an old married couple, one usually goes, soon after the other.

Here is some info about the PIP: Ford Fuel Injection » Stator (RPM)


Hope this help

 

A couple more possibilities.

Do you have what sounds like an exhaust leak that you can't find? If so it's likely coming from the air injection(smog) tube at the back of the motor, these often rust out or crack and this results in an exhaust leak upstream of the O2 sensor which creates a lean condition and that produces a misfire under load(bucking).

Another possibility is arcing between the plug wire or the wires and a metal engine part. Start the engine up in a dark garage or somewhere without ambient lighting and look for the lightshow as the motor is loaded down, it's usually real obvious if you have this problem.

 

Run a compression test, if your problem is at low rpms, you may have low compression on a cyl, my 88 did.

 

KOEO had a system pass (11), KOER had 41, 25. i forgot to add that i had also replaced a bad TFI module a couple months ago. the truck does fine at lower rpms but for example when i go to pass someone at highway speed, i shift down to 3rd and give it some throttle and attempt to reach higher rpms is when it starts bucking and almost feels like a lack of fuel. i have not ran a vaccum guage on it yet... is there any way i can determine if the PIP/distributer is malfunctioning before replacing it?

 

subscribing~~~~