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I have a '95 F150 XLT. Here are the relevant facts about it:
351W run off a 302 computer. EGR blocked off. New plugs and wires. New rotor and cap. New IAC and all new vacuum lines. Automatic transmission. New alternator that reads a healthy 14v when running. New fuel pumps, cleaned and restored injectors, new fuel filters. New fuel pressure regulator.
So I'm slowly developing what feels like an intermittent misfire. It doesn't matter if it's idling or under load. Under load, when the misfire starts it feels like hard bucking. At first I thought it was transmission related because the bucking can be quite hard depending on the load. However I've ruled that out. The transmission runs perfectly. I'm starting to wonder if my PIP sensor (has close to 280k miles on the thing) is starting to go, or if possibly my main coil is going. Perhaps I should just change them both as they both are original to the engine.
My only other symptom of note is my tach started to bounce at the same time. It's rock solid until the engine starts to miss. Then it bounces like the signal's bad. This is nearly the same while driving. Not sure if this is related. The tach is not original to the truck. It is an OEM tach that I added, and had to splice a signal wire in through the firewall. I wonder if something under the hood is causing my tach to get a bad signal causing it to bounce. As the misfire has worsened, the bouncing has increased.
What do you guys think? I daily the truck so I've pretty much been waiting for it to get worse as it is pretty difficult to tell what's going on at the moment.
Run the Key On Engine Off (KOEO) tests and Stored Code display. There is a Stored Code (CM) for an erratic PIP signal (Code 211). This is only displayed in the CM codes and it will not trigger a Check Engine Light (CEL). Your symptoms are very similar to a failing PIP, but advised to check for codes first.
I ran one a few weeks ago with no results, but that was when I first noticed the problem. Perhaps as it worsens it'll finally throw a code. I'll check it again today just to be sure it hasn't happened already. Appreciate the reply!
I'd suggest starting with the most simple of things...check the routing of your spark plug wires. My experience has been that many a misfire is due to improper placement of wires and a cross fire. Curious, why the 30 PCM for your 351?
I don't think the PIP sensor/Hall effect switch is bad. They very rarely go out. If the PIP signal is wonky it's more likely the culprit would be worn dizzy bushings allowing the metal ring to walk far enough away that it doesn't activate the switching action. You probably would have noticed this much play when you replaced the rotor. You can check the PIP signal, though. IIRC, you remove the fuel pump relay and test the PIP wire with a multimeter while cranking, and it's supposed to put out less than 10 volts AC.
More likely the culprit is a failing ignition control module. The ICM fires the coil from the negative side, and the tach signal is taken off the same wire. If the truck is misfiring and the tach is acting up simultaneously, the ICM would be where I'd check. You should also wiggle the wires and connectors to see if the misfire can be traced to a bad connection. However, if your new ignition wires run close to the PIP and Spout wiring they can interfere with the signal.
It is weird that you had to run a tach wire. There should have been one in the harness already.
So the truck began its life with a 302. When I got the truck the 302 block was cracked. So, I dove into these forums, got tons of great advice and made the switch to the 351w. I use the old 302 computer, MAF system and all that to run the 351. I kept the 351 dizzy with the block so I didn't do anything weird like swap the 302 dizzy over to the 351. It was all nearly plug and play with a few exceptions I don't need to get into here.
When I initially made the swap, I had read that crossfire was a potential problem. So I was very meticulous with my routing. I used lots of zip ties as wire separators as well as isolators to keep the wires away from the block. I did suspect that perhaps my tach signal wire was picking up some weird signals by laying against a plug wire or something, but no dice. Very well isolated from anything like that.
The original instrument cluster that the truck came with had no tach. I ended up finding a different cluster at a salvage yard in Fairbanks, AK that had the tach and made the swap (the mileage on the 'new' tach was only 5k miles over what mine was. Lucky!). For whatever reason I had to run a new tach signal wire in order to get it to function. I had also read about that somewhere which was how I figured out where to tap in for my tach signal.
In the end, I'm thinking about refurbishing my ignition system. I'm starting to look into getting a new ICM, new coil, and looking into options for my dizzy. If we're talking worn bushings inside the dizzy, it's sounding like an entirely new dizzy might be in order, PIP and all. Again, I wouldn't discount that as the truck has fairly high mileage, and many of those miles have not been gentle. These parts don't last indefinitely. I'm amazed they've lasted this long already!
I went through the run/die/cool/run cycle with progressively longer periods before the engine would run. Replaced ICM & it continued.
Replaced PIP & never happened again. Never once threw a PIP code. A few years later I did have capacitor leakage & multiple no code issues in the computer.
A few years later a chapter bud had all manner of not starting problems unless the SPOUT was pulled. He replaced his whole distributor & I opened up his original:
I recommend pulling the rotor, shutter wheel & blowing/brushing with a shot of electrical cleaner as a "what the hell" attempt.
Great idea! I'm certainly down to try something like that while I gather my resources and find a suitable replacement that fits my budget. I'm not interested in getting anything high performance or anything. Just something that will carry me another 200,000 really.
Alright so I finally got around to performing the work. Everything was very easy to do with one exception being getting the original body module off of the heatsink. Once I got the two fasteners out, I cut slots into them so I could use a regular screwdriver if ever occasion dictated... I kept everything except my old distributor. It was quite wobbly, dirty and full of corrosion.
This greatly improved a few other aspects I had learned to live with. However, the stumble unfortunately is still there. I'm starting to look elsewhere for potential causes.
I'm ordering 9mm plug wires to give myself better piece of mind over that area. I tried unplugging my o2 sensor to see if perhaps I had cracked/leaking exhaust manifolds (the extra fresh air from outside could fool the o2 sensor, giving a false reading), or even a bad o2 sensor in general (it's 3 years old so I doubted it). I drove the truck like this 30 miles and experienced no change in the stumbling.
The only update I can provide is that the stumble occurs most often when the engine lugs in O/D at lower speeds. If I give it enough gas to cause a downshift into lower gear, it seems to smooth out completely. It also occurs most often when I first start out in 1st gear. Other than that, it's just an occasional miss now and again, whether at idle or cruising down the freeway.
When I get my new plug wires, I am going to pull my plugs and take a look at them. I am starting to dread something like low compression in a cylinder or worn valve guides. I do consume oil, but I always figured it was the old valve stem seals leaking. My spark plugs always show signs of that (that slightly pitted, sandy look). I also dread something like a bad ground or failing connection in a wire connector. There seem to be so many different possibilities it's almost overwhelming.
In the end, I'm thinking about refurbishing my ignition system. I'm starting to look into getting a new ICM, new coil, and looking into options for my dizzy. If we're talking worn bushings inside the dizzy, it's sounding like an entirely new dizzy might be in order, PIP and all.
Originally Posted by loud41
Alright so I finally got around to performing the work. Everything was very easy to do with one exception being getting the original body module off of the heatsink. Once I got the two fasteners out, I cut slots into them so I could use a regular screwdriver if ever occasion dictated... I kept everything except my old distributor. It was quite wobbly, dirty and full of corrosion.
so what if any codes are you getting now, after changing all that out, I think mary-kate is asking did you get a new 'new dizzy' or a new 'reman dizzy' because the reman dizzy's are know to have bad PIPS from the start, but the new 'new dizzy has new 'new PIP' and maybe even name brand of dizzy, have you cleaned/checked your MAF, I had mustang that had wire almost broke into, would miss then hunt for idle, then miss, miss, miss, hunt for idle
