And after performing like a new truck in the mountains this weekend it stumbled a bunch going to work on the flats in Sacramento this morning. Go figure. Now it is an intermittent problem.

One thing I did when I replaced my catalytic converter on it this Summer was solder the new Bosch O2 sensor to the wires on the existing plug, because the new Bosch sensor wouldn't reach without the extra length of the old plug wires (with the old sensor clipped off).

I read not to solder but to use butt connectors. Could this be contributing to the problem?

In other words, I guess I am leaning towards a sensor/PCM-ECM computer problem rather than a fuel, spark or AIC problem first. (I have no doubt I will be chasing down each one of those separately to rule them out one by one.)

Edit the next morning:

So same drive to work this morning as yesterday. Same warm up prior to leaving home as yesterday. Not one hint of stumble during the drive to work this morning! So not like yesterday, when it stumbled multiple times on the freeway on the flats.

I watched the engine compartment when it was warming up in the dark this morning and didn't see any hint of arcing spark plug wire. I know it wasn't under load, so this raises a question.*

Does the spark voltage or amperage increase (i.e., does the coil put out more electricity through the spark plug wires) when the engine is under load? Is this why an arcing spark plug wire would be more visible under load?

* I think it is Greystreak who's signature says "the only stupid question is the one you don't ask." In my case, we can change that to "the stupid questions are the one's I ask..."

Conanski: There is that A.I.R. pump. I don't know what it does, but I will start looking at the hoses that come off it. This Summer I replaced the Y-pipe with catalytic converter, and I haven't heard any click, click, click indicative of a warped exhaust manifold, so I doubt I have an exhaust leak upstream of the single O2 sensor. But this weekend I will check where the Y-Pipe bolts to each exhaust manifold. Hopefully I will also be able to your spark plug wire observation under load this weekend too.

 

I am unsure if the coil puts out more spark under load or not, but I'm bringing up another thing you may want to check out if your original problem persists.

First off though, let me try and go over what was done to get my mind straight, correct me if I'm wrong on anything.

- You replaced your catalytic converter/s and O2 sensors
- You disabled your AC compressor and replaced belt/pulleys that were suspect on serpentine system
- You checked for codes (some codes may be stored even without the light so still check that if you have not yet)

You have NOT yet

- Checked timing
- Checked/replaced distributor cap/rotor/wires
- Fuel filter
- Checked fuel pressure


If what I stated above is correct, then I'll try to say what I may do next if the truck was stumbling. Checking timing and fuel pressure is a great thing to do if you have the tools, and its pretty fast. I would start there to rule out other branches of issues it may be. I'm thinking the timing is probably okay, and usually failing fuel pumps would behave differently, but checking the fuel pressure won't hurt, especially if we're coming across more dead ends.

The stumbling to me sounds like it may be an ignition related problem if it happens intermediately and on flat roads/highway. I think you're on the right track to check for spark plug wire arcing, but you can also check to see if there are any scorch marks or discoloration on any of the wires. Sometimes you won't be able to see the arcing well enough, but the wires' insulation will leave hints of arcing. check especially near where any wires could be touching other metal pieces such as the manifolds or frame.

If you never have replaced the wires since owning the truck, and have had them for over two years, it probably would be a safe bet to replace them because they could be pretty old. I know you are trying not to spend money on spare parts though but I would plan on replacing them with your next tune up for sure.

If the wires seem to check out okay, my next guess would be a distributor related issue. I've been reading up a lot about distributor issues lately and experienced some of my own (on my Camaro, I know I know! It's not a Ford, but I like the 80-90s style camaros and it was cheap!) so my mind is sort of fixated on problems they can cause when acting up.

The things to check on the distributor would be first, the cap and rotor. If the contact points on cap have lots of build up, definitely try and clean them off. I think you are safe cleaning them off with a brass brush, but don't quote me on that. If the cap contact points and rotor both look pretty dirty and have a bit of wear, replacing them would be a very good step that may help reduce the issue you are having.

Now if both the cap and rotor check out good or you replace them and the issue persists, you could have a pickup coil going bad in the distributor. The pickup coil is an electromagnetic sensor that's inside the distributor that controls spark and I believe has a play in injector firing also. When these start to go bad, you often time get intermittent issues such as hesitation/bucking, and then eventually stalling and no starts. I don't know any good way to test these, usually replacing the distributor is best when this is the case. I probably would save this step for last though if it were the case, because a new distributor would be a semi pricey item. Someone may know of a good way to test the pickup coil too, I just never bother to see if there was a way and replaced my distributor (both in my Bronco and Camaro, they both had bad pickup coils in their lives.)

Now another thing you can and should check is your igntion control module. This is the black or grey "card" like looking thing that has a small/thick heat sink mounted to it. I believe on your truck, it will be mounted on the drivers side fender close to the firewall, but some are mounted on the distributor themselves with older Broncos. These apparently have semi-high failure rates on older vehicles, especially if they get too hot over their lifespan. These can be taken off and tested at parts stores. If you do get this tested, make sure the part is pretty warm before testing it (leave it secure in your ride's engine bay on the way to the tester place or have the store test it a whole bunch, like 10 times, to get it hot.) When these are taken off, you will want to get thermal paste to put back on the control module and heatsink. Make sure to clean off the old "paste" (it won't be very pasting when it's old) before putting the new/original one on. If you do get a new one, make sure it's the same color. I think I read that the black and gray ones are not quite the same and can cause unoptimal driving conditions if the wrong one is used.







I think I covered a bit of stuff, rambled a bit too long again like usual, but hopefully the information I posted can be of some help! Let us know what you do and find out so we can better pinpoint and find what's causing your issue!

 

BubbaJ ones: I have not pulled codes with a code reader yet. I am borrowing my buddy's this Friday morning. However, this was the OBD flash code I was previously having:


<table width="566" border="1"><tbody><tr><td width="28" align="center">34
</td><td width="63" align="center">(R)
</td><td width="453" align="center"></td></tr><tr><td width="28" align="center">
</td><td width="63" align="center"> (O,R,M)
</td><td width="453" align="center"></td></tr><tr><td width="28" align="center">
</td><td width="63" align="center">(O,R,M)
</td><td width="453" align="center"></td></tr></tbody></table>

 

Update: I found the old O2 sensor, and contrary to my previous posts, I did not use the old plug on the new Bosch O2 sensor to make the wire longer. Rather, I cut and added new wire between the plug and the O2 sensor on the new Bosch O2 sensor, so unless soldering the connections is causing the problem as opposed to using butt connectors as recommended but which I ignored, the O2 sensor should not be the problem. (Just to be sure, I will soon cut the soldered connections and reconnect them with butt connectors.)


(BTW, door panels, window regulators and thin film plastic dust vapor barrier all came out great. And Mile Marker manual hubs arrived today.)

 

many have complained about having bad o2 sensors from the autoparts store.

 

Kemicalburns: I bought it from Amazon which may or may not be better than the local retailer. Do you think I should buy the O2 Sensor from Ford?

The stumbling persists, but is absolutely intermittent now. Yesterday no problem. Today multiple stumbles. Same drive.

I am focused on installing the Mile Marker stainless hubs and replacing the front brake hoses and calipers now, but still background processing the stumbling issue...

 

have you double checked your TPS is in spec?

 

Kemicalburns: I have not checked that the TPS is in spec. My guess that involves a multi-meter and a volt reading? If any one has a good thread on how to test the TPS, I would appreciate it. Otherwise, I know how to use the search feature hear and I will look it up.

BTW, I borrowed my buddy's code reader, and guess what? It doesn't even fit our OBDI plugs (I am sure you guys expected that). So, I dowloaded a good tutorial on how to make the jumper and how to read codes, but I haven't had time to do that yet.

 

ive never done this myself, just know it can cause what you describe. its been talked about a lot along with the necessary process and what you should get. I also believe there are some youtube on it.

 

OK, guys. Conanski, BubbaJones 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.)

 

excellent news. the wires that had been touching, where they cylinder 7 & 8 by chance? if so this is a known issue that frankly I forgot to even think about. they must not touch in any fashion otherwise the spark will jump which you figured out. I imagine the wires were worn as well which could contribute to this occurring on other wires that were touching.

 

Kemicalburns: It was either 8 and 7 or 8 and 6. I was such a bone head that I forgot to determine definitely which. If the wire routing scheme which Conanski pm'd me was followed I can tell from that. But better yet, I took a picture before I started taking the wires out, so I may be able to tell from that. I will update this thread.

 

Tim, the thread title has been updated per your request. If you'd like some other variation, let me know.

 

Bronco stumbles/misses/bucks
so your saying its a bucking bronco?

 

chadjones99: I don't think Ford meant it that way...


powerstroke72: Thank you! Perfect! (and even if it wasn't I don't mess with people who have avatars like yours...)