Howdy, a few weeks ago I replaced my intake gasket and while I had it tore apart I done a simple tune up. I replaced the plugs, wires, cap, rotor, pcv, oil and oil filter. Up til then I usually got 12 mpg, but the next week or so i got 13 mpg and the truck seem to run better. But then I was going down the road and it started skipping. All week it has been running fine until it got hot then it would start skipping and jerking. I thought maybe the coil or ignition module was going bad so I replaced them both. With no change. I took my old module and had it tested and it showed pass. This morning when I left it Started skipping 1st thing before it even had time to warm up and the skipping seems worse. I dont think its a fuel issue because the more press the gas the less it seems to skip. Oh and I'm talking about the 88 in my signature. Thanks in advance for your help!!

 

cheap wires? improper plug gap? moisture in the dizzy or cracked cap?

 

sounds like a bad plug wire maybe burnt thru on exhaust manifold

 

They are Auto Zone 8mm wires, but I have already looke in the dark for arching and in the light for signs of touching the manifolds. I checked the gap before installing each plug. Always do, you never know if a box has been dropped. I havnt checked for moisture but I thought that keeps it from cranking not skipping at operating temp. I took the distributor out to replace the ignition module and the cap looked good and dry then. This run great for a week and half after the tune up before it started skipping.

 

Perhaps a bad cap? Also may want to check the center of the cap to the relation of the rotor. Some use a thin piece of metal, and that may actually be causing an intermittent contact. I realized a similar situation with an old Ford tractor, with a replacement coil from the farm store. Luckily it was made in China, so I knew it had to be flawed and once I realized the design difference between US and China made, it was obvious. The center contact was only making partial contact with the pin.

I also had a similar problem with skipping, thinking it was a clogged fuel filter. Changed filter, same problem. Checked wires and plugs, all good. Got my fuel pressure gauge out, and hooked up to find my 18 year old fuel pump was on the fritz. Only had 20 lbs of fuel pressure and the more I punched the pedal, the worst it got. changed fuel pump, not another problem.

The problem may have nothing to do with anything that you did, and think for a minute of you hadn't done anything, do you think it would have started anyway? I think it was coincidence. I would definately check fuel pressure, with engine running and with engine off. That "HUM" from the rear may be a good sign that the pump is starting, but keeping your engine fed with fuel @ 35 lbs, maybe it's telling you, I'm gonna go out on you a 100 miles from home, with it raining and your cell phone dead.

Another thought....perhaps the PIP sensor in the dizzy, but I cannot remember if when the PIP sensor goes bad, whether it will even allow you start the vehicle, as it is a hall effect sensor, IIRC. Also, when running, if you have a stethoscope of piece of tubing, heck even your finger could work, see if all the Injectors are firing. If there is any dead spot from the wiring. Old SD systems use the banking system as odd injectors are fired, then even injectors are fired as 1, 2, 1, 2...
If I'm wrong, hopefully someone will chime in to clarify.

 

I will stick my other cap and rotor back on and see how it runs. I am going to check the fuel pressure, but havnt yet cause it does act like it is starving for fuel. It actually seems to skip less when I gas it. I'm not familiar with the PIP sensor. What is it and can it be tested?

 

Well I put my old dist. cap back on and skip gone. It's running good now. I don't understandthe heat relation to where it was skipping when hot. Expansion? I look on the top of the button and there is a good center marking where it was making contact with the cap. I also still would like to learn a little about the PIP sensor.

 

When you gas it, the RPM's increase, thus "bridging" the gap that is created by a heat related failure. If you have a bad contact, the heat could be causing a separation, or expansion, that is somewhat rectified by the higher rpm's bridging up the gap.

 

I agree with Pope on the expansion/separation. Good to know that you got it back up and running again. Perhaps you can also return the junk cap and get your money back.

As for the PIP sensor, it lies inside the dizzy. It can go out and usually when it does, the truck won't start-up. You could replace the sensor, but IIRC, the consensus is to replace the whole dizzy. If mine were to go out, I would try to replace the sensor before the entire dizzy swap, since I heard of members getting reman distributors from parts store that A. didn't work, or B. didn't last long. I think Andym or Conanski pointed that out to me quite awhile back when I was planning on replacing mine. They said the stock Ford distributor by itself is really good, and there wasn't any need to swap it with a new unit unless it had failed completely or was really building up for more power.

 

Fuel Injection Technical Library » Stator (RPM) aka PIP

 

Cool. Thanks yall!!