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Discussion Starter #1
I'm looking at a friends 94 F-150 5.0 2wd. I'd like a second opinion before I suggest they buy a new ignition module.

Engine starts and runs good cold. Misfire occurs only when engine thoroughly warmed up.

When misfire occurs, tach jumps, and timing light reflects misfire when hooked up to coil wire.

Swapped coil with known good with no change in symptoms.

Several cylinder balance tests reflects different cylinder faults.

No other codes showing up.

continuity checks and power checks to ignition module are good.

do they buy a new ignition module?

Cheers

Steve
 

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I'm looking at a friends 94 F-150 5.0 2wd. I'd like a second opinion before I suggest they buy a new ignition module.

Engine starts and runs good cold. Misfire occurs only when engine thoroughly warmed up.

When misfire occurs, tach jumps, and timing light reflects misfire when hooked up to coil wire.

Swapped coil with known good with no change in symptoms.

Several cylinder balance tests reflects different cylinder faults.

No other codes showing up.

continuity checks and power checks to ignition module are good.

do they buy a new ignition module?

Cheers

Steve

Have you checked proper routing of plug wires and their condition? How's the distributor cap?

"Several cylinder balance tests reflects different cylinder faults."

Does this statement mean you've done a compression check? If so, what were the results?

Were the plugs pulled and checked?
 

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Discussion Starter #3
symptoms are leading me toward ignition system, since the misfire is showing up with the timing light. misfire is showing the same when I place the timing light on each spark plug, and coil wire.

Cylinder balance test I'm referring to is the EEC test mode. I would get codes 20,50,60 one time, and 10,40,70 and then other cylinder codes.

Steve
 

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I want to know how you can see a misfire with a timing light. A timing light shows timing and spark to cylinder #1. I think that you should replace your wires first. Spark plug wires seem to work better when they are cold and after they heat up they tend to misfire if they are bad. Just seen this on an escort 2 days ago. Maybe your seeing the misfire because you didn't pull the spout connecter, since this will throw your timing mark all over the place.
 

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Discussion Starter #6
Good point on the spout. I'll warm it up and recheck that today. Plug wire routing is horrible, and they were zip tied and such. There was dielectric grease on the metal contacts of the coil wire only. :twak

It's taken me a half a days work to get to the point I'm comfortable diagnosing instead of chasing myself with the simple stuff.

I'll try to get some video today of what I'm talking about.

Thanks!

Steve
 

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Discussion Starter #8
When misfire occurs, tach jumps, and timing light reflects misfire when hooked up to coil wire.
also i read you had the timing light hooked to the coil wire, it needs to be on number one wire.
umm, yea thanks. I'm using the timing light as a diagnostic to indicate the spark event not to check timing which is 10* with spout disconnected.
 

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The plug wire routing is critical on the 5.0. It's very easy to get crossfire on a couple of the cylinder pairs that fire sequentially. Check Steve83's diagrams on supermotors for a view of the label that should be under the hood showing the proper routing. Get some cheap wire separators, too.
 

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Discussion Starter #10
Thanks SEWIV, I've already picked up the separators, and rerouted the wires per the vehicle diagram. pulled plugs and they looked good. all the same color (ashy white w/ no deposits), no tip erosion, and the wires ohmed out per specs in haynes. I didn't regap, but they all looked about right to my uncalibrated eye.

Started the engine, and same miss.

Right now, I'm freezing the ignition module (have I mentioned how awesome my wife is?) and once that is good and cold, I'll retest with the module cold.

Cheers

Steve
 

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Discussion Starter #11
The ignition module was as cold as my beer, and still missing.

I ran the timing light once more around the engine with it warmed up and missing. got a steady miss on #7 Swapped in a known good wire and the same miss.

looked at the distributor, and decided to correct it to #1. it had the correct firing order, just didn't start where the cap was marked #1. pulled the dizzy and moved it one tooth, reassembled and retimed, and the miss followed to #3.

now I'm looking at the cap, or the trigger. The cap ohms out good. Gonna have to try a cap next.

At least I didn't jump on the module and waste $100.

Cheers

Steve
 

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Discussion Starter #12
Changed cap rotor and adapter. mostly cause I broke the adapter...

ran again, and on warmup, had same misfire.

Today I pulled the Dizzy, and sure enough, the Dizzy shaft is bent. causing the rotor to contact the inside sensor.



The wear pattern continues all the way around the rotor. Looks like it has been doing the wobble for some time. It's almost worn through in some spots.

Will be getting a new(rebuilt) one soon as the owner orders it.

Cheers

Steve
 

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Looks like you may have found the culprit.

Just for my own curiosity, couldn't a vacuum leak produce similar symptoms (aside from the miss following the new wire orientation you mentioned)?

It's been my experience that alot of times a "small" vacuum leak isn't very noticeable on a cold engine, I guess because the RPMS are higher, mixture is richer etc. but once it idles down and warms up, the missing becomes apparent.

Just wondering
 

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Discussion Starter #14
yeah, I suppose a vacuum leak would appear as "phantom air" to the MAF system in this 94 and cause a lean condition. I doubt a MAP or speed density system would do anything more that idle high. :shrug

I intend to change the distributor and retest. might find something else...who knows. This engine is SEFI and the distributor was one wire off proper firing order, and I'm sure that didn't help.

Come to find out the PO was having problems with misfire, and would pop the hood and HIT the distributor with a broomstick.

And I was getting to the point I thought I had seen most of it all...

I'll keep ya posted

Cheers

Steve
 

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Discussion Starter #15
replaced Dizzy, retimed, warmed the engine at retested.

ALL GOOD :chili:

I took the truck for a road test, and hiding behind the engine misfire is a transmission problem. :doh0715:

1st gear shudder and slipping. Fluid is fairly fresh, and proper level. trans does ok at speed above 35. :banghead

>edit< This looks to be an E4OD with the OD switch on the shifter.

any suggestions on where to go read on troubleshooting this one? I'm just trying to help a retired guy out here. This is getting to be too much.

Cheers

Steve
 

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Discussion Starter #16
bah.

I have returned the truck to the current owner. I fixed the original ignition issue, and I'm not running a garage. I told him about the transmission problems, and suggested he take it to someone who can diagnose that problem.

I feel like I have not done all I could. But I was getting in over my head quickly.

Did I do the right thing?

Cheers

Steve
 

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Sure, you're not a transmission shop. You were able to find and fix the misfire problem and you probably did it with no labor fee?
 
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