Ford EEC IV Engine Misfire Video

Mr. Danner, I've just watched your video on the ford EEC  IV  misfire. I have a 1988 F-250 351 W that idles and starts like new but misfires badly on the  road or just revved up. I tried removing the spout but it made no difference. I have been thinking it might be the  distributor. I only have one of the spark test lights that you put in line on plug wire. When I use it on the coil wire (center  of cap) I can  see that  it is failing to fire when it is missing. It  has new TFI module, wires,  rotor, cap and coil. Yea, I know, I'm a parts changer.  Help me stop  .  There is one more detail. When I  probe the green wire that goes to the (-) side of the coil from the  TFI module with an incandescent grounded probe light about 50% of the misfire goes away.
Please Help
Thanks
Jack

I put a rebuilt distributor in yesterday and now it runs worse. Same symptoms just worse. I'm going to put a motorcraft pickup assembly in tomorrow and if that doesn't work, then on to the computer capacitors and what ever I find when I open it up.

Jack

A few days ago the truck ran well enough to drive on the road while skipping. Today it doesn't even idle well though it did before we put the new distributor pickup coil in. It idled so well we haven't checked the plug gaps. I don't think the plug gap would make the coil misfire. The negative coil wire shows to be missing at the same rate as the secondary coil misfire . When we first got the truck it ran and idled perfect with the alternator unplugged. It also ran perfect as long as I probed the negative coil wire (the one that goes to the TFI module) with an incandescent test light to ground. All this is telling me something but I not car smart enough to know what. I suspect computer or ground problems.
These old trucks has plenty ground wires and even the ends show corrosion where the crimp onto the wires. I've spent hours tracing and cleaning connections to no avail. We are now not getting any codes. I will check that again tomorrow. Thanks Monde.

Thanks for any help

Jack

On the other Ford thread you mentioned, "it runs great with alternator unplugged" I would check for a bad rectifier in the alternator, a a/c voltage test

Thanks Mode. I'll try to understand and do what you said. I'll watch the video again.

Thanks for the reply ontheriver, It now has the 3rd alternator on it. The one on it now is not new but is a 3G and it really charges. Would the parts place be able to tell if it has the problem you mentioned?
Thanks again
Jack

Depends on who you go to, my Napa has a machine that came over on the Mayflower, so, no good, I would Google"a/c ripple test on alternator"

Looking in manual, there is a 22k ohm resister in #4 wire from ecm to coil/idm, possible open there

Thanks ontheriver, I will do that
Jack

I checked that resister with an ohm meter and it checked OK.
Thanks

#16, ign ground, from ecm to tfi connector, no resistance?, and/or try the wire wiggle test during intermittent spark, just thinking, if it's worse with distributor change, disturbed/bad wiring is in mix

That's a good thought ontheriver, I've wondered if the TFI module plug is making good contact. I learning about voltage drop testing of wires and plan on trying this. So far every wire has ohm tested good but I've found out that there is more to it than that.
Well, you all have given me plenty to try tomorrow . I'll let you know how it all comes out.
Thanks

Jack.

Finally back too it. Just checking ref voltages and grounds as best I can. Ref volts at sensors are from 4.75 to 5.09.

There are 2 computer grounds that go straight to the battery negative. I unplugged the connector and checked voltage on the two wires with switch on engine off.
They are wires from pin# 40 and #60. One of the wires has 1.49 volts and the other has 8.25 volts. I don't know at this time which of the 2 pins they go to.
Does this voltage seem normal. Just for comparison I checked the same plug on my 1989 F 150 and both wires to ground shows .03 Volts on both wires.

Any thoughts would be appreciated.
Thanks
Jack

Those 2 terminals you checked are bad grounds. Never should have voltage on grounds. Bet if you hook a test light up to battery negative and probe the one you had almost 9 volts on it will light.

Doesn't something have to be wrong in the computer where the 2 wires originate?
The voltage has nowhere else to come from.

Thanks for the reply

Jack

Are they grounds?? The voltage isn’t coming from the computer. Clean where they attach or run redundant grounds directly at the connector on the computer just to prove it. you’ll have no voltage on there.

These 2 wires connect to the battery Negative terminal, so they are grounds. The wiring diagram shows them to be coming from Pins #'s 40 and 60 straight to the battery negative post. They go through a connector. I unplugged the connector and it has voltage when I put one Volt meter lead to the wire and the other to the negative battery post.

Thanks again
Jack

Means those grounds are bad. Use wire piercers or something pierce the wires at the pcm run redundant grounds. Your doing a voltage drop test battery negative to ground is what your seeing

Thank you Cheryl. I'll check that out.

Thanks
Jack

Just to make sure we're on the same page: you disconnected the pcm connector at the pcm and measured voltage on the wires that connect to terminals 40 and 60. Then you disconnected an inline connector further down and still measure voltage on these wires. Do you measure theses voltages between the connector side that goes to the battery and B- or between the connector side that leads to the ecm and B-?

Verify you're measuring the circuits correctly and there's no user or instrumentation error! If your measurements are true then you have a short to voltage in the circuit leg that goes from this in-between connector side where you're test lead is connected to. These voltages would not originate in the ecm as it is disconnected at this instance.