I've recently been having some problems with my truck - acting like a fuel problem only to find out the oxygen sensor was completely shorted and running on default. I changed the sensor and decided to give the truck a tune up as I bought it with 100,000 miles on it last year and have put 28k on it. I changed the spark plugs, wires, distributor cap and rotor - made the mistake of having two wires swapped and fixed it after initial start up. Truck was idling and reving fine after start up and i took it for a test drive.

On the test drive it rode fine for about 10-15 minutes and then the rpm almost bottomed out in less than a second and then just as quickly picked up again (causing the truck to buck). This was happening occasionally when it was under a load - taking a turn and goosing it. Also happened once while just slowly accelerating. After getting back to the apartment I had the truck idling while I looked at the engine and then the engine stalls (twice). I tried reving it while in park to see if it made a difference and it does the same thing but it's not constant.

Any and all help with be appreciated. I'm going to go clean out the MAF sensor (i disconnected it to give me more room while I was changing the plugs) and see if that helps anything.

 

after cleaning the MAF sensor and checking all the plugs, wires, distributor cap and rotor again the truck seemed to be running fine. Yesterday it ran fine, and then today while making a small trip around town the truck began to lose rpm sporadically again... Truck would drop rpm and then buck when it caught up again.

I'm at a complete loss as to what is causing it..

 

Try driving around with the MAF disconnected. It won't run well at all, but if the truck stops dying/bucking, then you know it's the MAF.

As always, check your air filter, change fuel filter, and check fuel pressure.

 

I'll do that sometime today after work. Fuel filter was changed two weeks ago, and fuel pressure was checked a couple days ago and it was within spec ranges. The air filter was cleaned and recharged about a month ago (k&n) filter.

 

If you have a K&N, it wouldn't surprise me if your MAF was dirty.

Do not use carb cleaner on a MAF sensor. They have special "sensor safe" cleaner you can use.

 

Well i ran to an auto parts store and got them to run a computer on the car before i ran with the MAF sensor unplugged. It pulled three codes

157 MAF low voltage
211 PIP Circuit Fault
212 Spout Circuit Grounded

I drove around a bit with the MAF unplugged and it did run worse like expected (idling up and down and what not) and then it started bucking again and when stopped it would kill. Got to the point it killed every stop and sometimes would start right back up and then others it took about 10-15 minutes before it would start up again.

I got back to the auto store, disconnected the battery to clear codes, and when the computer was run on it again it just pulled a 156 MAF sensor fault - low or high

Had to double peddle the ride home to prevent the engine from killing when stopping.

 

Spout grounded and pip circuit fault are probably not unrelated. Check the wiring around the distributor and the ignition module for signs of chaffing or shorting out. I believe for your truck the module will be on the drivers side fender towards the firewall.

Also check any and all grounds you can find.

 

you are correct about that. I looked over everything twice and couldn't see any wires that were messed up. After not finding anything wrong with them I was going to trace the wires from the spout with a voltmeter, but I just don't have the time in the day to do that with work. So i decided to give in and bring it to my uncle's shop in new orleans. He thinks he knows what wrong with it and has basically said what you have, plus a possibility of the pick up coil in the distributor acting up.

I appreciate the help!

 

I realize this forum is several years old, Ive had this issue with my 1995 f150 xlt efi 5.0 with 4r70w transmission. I replaced pcm tps egr complete tune up new plugged swapped iac valve fuel injection cleaner in both tanks as is long bed single cab truck new cap rotor plugs wires cleaned hall effect inside distributor and pip sensor inside distributor new fuel filter as old one was muddy fuel going towards the engine. Going highway speeds just for it to lose power bog stall under load stall in gear except park and neutral. Did compression check came out good checked timing thats good. cleaned mass air flow sensor thats good. Finally pulled my Upper intake plenum off pulled injectors out to find........tada!!!! all of the injectors completely clogged with mud have new injectors and plenum gasket on the way now yes also checked the fpr which is also good. So my advice before you think its something its not such acting like miss fire and stall under load...replace fuel filter do compression check and check your injectors will save you hundreds if not thousands of dollars.

 

fuel pressure gauges work wonders, in check sequence.