Have you tried disconnecting the O2 sensor? Isolate that issue if you can. Comparing apples to oranges here maybe; but I had a similar problem occur with a hacked O2 sensor on an '88 BMW. I suspected the butt connectors were crossed. The symptoms you're describing were exactly what caused the car to buck and stumble...but only after it warmed up. He gave me the car back with the O2 sensor disconnected and it ran fine. I finally installed a factory correct Bosch sensor to make that problem go away for good.

 

John SCB: I will disconnect the O2 sensor. And that is not a bad idea because when I bought the Bosch sensor for my truck the wires were too short to connect the plug to the receptical, so I soldered them to the old plug effectively lengthening the wire. I could've crossed the wires I guess, but I saved the Bosch plug (somewhere?) which I cut off leaving a little pig tail, so I could get some extra wire and some butt connectors and match those wires up (they will be the same color) and try it.

Today I did the window regulator repair (putting new gear plugs in the front door window regulators from "Stans the Man for Window Regulator Gear Plugs," so tomorrow the Bronco work may be limited to buttoning up the front door panels and also the tailgate door panel from the previous tailgate window regulator gear plug repair. But if I have time, I will look into the O2 sensor. Thanks!

 

You can also buy an O2 sensor for the 300 instead of the V8 302 or 351. Its several inches longer.

Just wanted to throw that out there.

 

Many times you can unwrap the cable bundle to find 18 - 20 inches more O2 sensor wiring folded back on the transmission wiring harness. No soldering required.

 

OK, guys. Conanski and others suggested that I look for possible arcing between plug wires. So at night I ran the engine and didn't see any arcing. So I replaced my EGR sensor and it didn't fix it (I don't think it needed replacement). I replaced my frame rail fuel filter (it really needed it) and my in-tank fuel pump (it needed that too). Nothing helped.

So, I pulled my PCM and opened it up to look for leaking/bulging of the three (now 20-year old) capacitors which notoriously fail in my EEC-IV PCM and the capacitors looked good, so I didn't replace them (although I will eventually). Pictures here:

https://www.ford-trucks.com/forums/1...uestion-4.html

After early morning Easter resurrection services (man those Presbyterians can sing!) at my mother in laws (because I had nothing to do) I was looking closely at the spark plug wires and I could see and feel roughness on the wire rubber where one wire was crossing over another wire. So I separated that wire from crossing over the other by stretching it over the valve cover plastic oil fill cap.

And the miss instantly was reduced.

Since then I installed a 9mm Ford Racing Spark Plug Wire Set* (from Summit Racing for $43) and two sets of Ford Racing Wire Separators ($14 ea. for plastic! but they look and work good), and guess what?

I HAVE NO MORE MISS OR HESITATION OR STUMBLING WHATSO-FRIGGIN'- EVER !!!

Let me repeat that for emphasis:

I HAVE NO MORE MISS OR HESITATION OR STUMBLING WHATSO-FRIGGIN'- EVER !!!

Finally, if you do this make, sure that you get a copy of your SPARK PLUG WIRE ROUTING DIAGRAM and follow it!!! Because of the firing order, certain wires have to run cross-ways to others (not parallel) so follow the routing diagram to a "T" and make sure you use wire separators (generics are half the price at Pep Boys) to keep the routed wires in place.

Just two cents from a guy who assumed it was the PCM and was about to replace it.

And finally, there is no substitute for pulling your PCM if you want to know its number. And if you can, photocopy or photograph the bar code and numbers on the exterior of the PCM. Otherwise, you are just guessing.

And one more thing, I attribute this all to the Easter Morning services. So go to church.


* The 9mm Ford Racing Spark Plug Wire set is really nice. Not only are the wires bigger than stock, but each wire for a specified engine is already fabricated in the correct length for that numbered cylinder (no need for you to cut and fabricate) and check this out: EACH WIRE IS NUMBERED ALONG ITS LENGTH WITH THE NUMBER OF THE CYLINDER IT GOES TO !!! (Even I couldn't screw this up.)

Ford Racing Spark Plug Wire Sets M-12259-C301 9MM wires

http://www.summitracing.com/parts/fm...c301/overview/

Proform Ford Racing Licensed Spark Plug Wire Dividers 302-637

http://www.summitracing.com/parts/pro-302-637/overview/

MSD Spark Guard Dielectric Grease 8804 (didn't end up using it, the boots has a light grease already.)

 

Great news Tim! Glad to hear you fixed it. Yeah plug wires play tricks. Mine are still original but 23 years later, I know it's time for new ones. Thanks for posting the update.

 

I have seen a frozen belt tensioner kill an engine and prevent the car from being restarted.

I first saw this when a poor soul had the engine die on his Silverado when passing the Ford dealer where I worked… he glided into our lot with a dead engine. The damn thing would not crank.

I called the Chevy shop right down the road and he told me they see that happen pretty often… I towed him the two blocks to the dealer and parked right in front of the showroom for all to see… my Ranger demo pulling a Chevy!

The whole sales crew flipped me the bird…hahaha.

 

You're such a troublemaker/instigator, I would've done the same thing!

 

So after reading all these threads about the hesitation on my 93 5.8l bronco, I disconnected the plug to the ac compressor and that cleared up the problem mostly....does that mean the ignition coil is weak?