I have a 1988 f150 351 w/ aod trans. While accelerating under half throttle or more the truck feels like it is cutting out for a split second, but multiple times while accelerating. I cannot push through as it only makes it worse. If i let out the throttle the condition goes away. Cruising speed is not affected as long as there is no electrical load. I can climb hills as long as the pedal is under half throttle. Within the last two years i've replaced distributor w/ remote mounted tfi module, coil, plugs, wires, tps (@ .97v) idle air control valve, egr, egr position sensor, egr valve solenoid, rubber vacuum hoses replaced all hard plastic lines, fuel pressure is at 34 and only drops to 33 after a minute, 40 psi with vac line to regulator disconnected and when under half throttle. manifold vacuum is at 16 and drops occasionally 1 psi. coil, plugs and wires were tested with ohm meter and came out good. koeo code is 11, continuous code 11, and koer code 44. i noticed that with electrical load like the heater turned on or the headlights makes the cutting out more prominant. any suggestions are appreciated as i have about chewed all the hair off of my tail.

 

I'm sure you have already checked the trans fluid.

I would start by changing the fuel filter assuming it's a fuel related issue. Have you checked your air filter? It could also be your throttle position sensor.

 

So adding more electrical load to the system makes the cutting out worse...

Have you load tested the alternator?
How old is the alternator?
Is it a 2G or 3G alternator? It should be a 2G if you haven't converted it to 3G.

Check the wiring running to the Fender-mounted relay, clean the contacts of the lugs until shiny bright, check the "fire-proned" 2G harness connector, it has 3 big wires running to the alternator.

Reason I asked about the alternator, since if its causing "electrical noise", it can have a detrimental effect on ignition and electrical components. Even bad diodes inside it can cause problems.

That's all I can think of...

 

Fuel filter was replaced 1 month ago. Air filter was not, but looks to be in acceptable condition. I still do have the 2g alternator, did a capacitance test at oreilly's and it came back fine. I will do a diode check, ripple test, and load test within the next couple days and update the post. trans fluid is a little high, but it is not dark, doesn't smell burnt, and there is no foaming. thank you for replies because i need the help now.

 

What is the pressure under load/above half throttle?

 

Have you checked the output voltage while the alternator is installed in the truck?

Those 2Gs are fire prone because of the crappy connectors. The alternator may test fine at the store but fail when installed in the truck because of poor connection(s).

 

Output voltage of alternator is 14.5. I have not checked fuel pressure under actual load. Parked at half throttle or more is 40 psi. I feel like it is missing but under heavy load. The alternator is a 2g.

 

Is your remote TFI module grey in color like the original was?

Two things I can think of are a lean stumble or plug wire cross firing, To test for the lean stumble disconnect the O2 sensor and take it for a drive. To test for plug wire cross firing start up the motor in an area that is completely dark and with all vehicle lights off and observe the engine for tell tale flashes of light as somebody else revs it and put it under load.

 

Steady needle? if so that's a good thing. (If not, if the vacuum reading widely varies you got other issues)

Suggests late ignition timing, late timing can and will cause symptoms you describe, weak under load.

Low vac reading could also point to vac leak/s but you didn't mention high idle along with symptoms.

If haven't checked base timing/set it with a timing light or can't = harmonic wheel to rusty to read timing markings on it for example? you can set the timing using your vac gauge, good option for higher mileage motors regardless.

While idling with gauge so you can read it advance timing until gauge reads as close to 20inHg as you can get it. (end result will depend on over all condition of motor).

Don't go to far right off the bat, easy to go into to far advanced territory, you don't want a faster idle speed advancing the timing. Just the strongest vac reading you can get before idle speed tends to increase.

Will take a little trial and error to get it in the sweet spot but easily doable, you want it advanced as far as possible read highest possible vac reading at an idle and at same time suffer no spark knock.

Take it for a ride see how it runs, if better but spark knocks back off the timing a hair then take it for another ride. If seems good but no spark knock try adding another deg or two until it does, you'll quickly zoom in on its sweet spot adding in or taking out couple degs until you hit it.

Easier/quicker with a timing light but in some cases its not an option at least in the short term.

And don't disregard the importance of a good tune up using quality parts, don't have to be top dollar wires just avoid the auto super mart type cheap crap.

Again you didn't list your location if you live in the rust belt and the heat shields are gone? buy wires rated for headers so they'll survive the heat.

Late ignition timing coupled with zero heat shields protecting the plug wires = toasted plug wires, the boots at the plug end will be fried and leak regardless how the wire tests out for example.

 

Going to check the alternator today, and spray the wires to check for stumble. O2 was disconnected and the truck still ran poorly. Mounted TFI module is grey like the old one. Vacuum is steady at 16 with a drop to 15 about every 10 seconds. base timing is set at 10 btc with spout disconnected and the engine warmed up. After checking alt. and spraying wires, I will advance timing to get to sweet spot.

 

Please advise me how changing the timing work. I've been dealing with lack of power for awhile. At my wits end here.

 

ok so i used a vacuum gauge to adjust timing. any reading over 17inches created pinging. dead on 17 and i get no symptoms until 65 at half throttle. with electrical load engine still runs poorly on acceleration. waiting until tonight to spray plug wires. i did notice that at this new reading the gauge pointer will go up 1 inch about every thirty seconds and about 5 seconds later the needle drops 3-4 inches under 17 then slowly climbs back up to 17. it will stay steady for a good 10-15 seconds and then repeat the process. alternator diodes are working and i have no dim lights to suggest a weak alternator.

 

UPDATE! Hadn't load tested alternator yet so I disconnected the alternator tonight.
Drove around with the headlights on and not a single problem. Gunned it on the freeway up to 85 and nothing. Ran so smooth I almost forgot how beautifully she hummed. Connected alternator and she ran like crud with the lights on almost stalling at 35 and jerking the entire way home. Load testing tomorrow but I feel I will be looking at getting a new alternator.

 

I had problem over 2 day period after I changed plugs but I didn't notice notice that night it was driving me insane it got steadily worse and missing bad it would idle fine and under medium load it would start jerking and lose power and like i said get worse every trip and finally after work i had enough i changed coil cleaned rotor and cap changed wires and tried to plug egr with no change tested pcm tested my tfi tested PIP all was good then when it got dark I seen the new spark plugs I put in the second one right above coil was arcing I took it out and it was cracked so on the ceramic and changed it no problem I still got a fuel pump whining on frame but atleast I don't have to hoof it to work so I'd say check wires at night and look at ur plug wires one little arc will cause one heck of a misfire