("UPDATE SORT OF")Spark Plug wire hot idling irratic?

[Blue71]

Stock 302 V8, Auto tranny, points, everything was running fine idling smooth until the other day when the Bronco would die when you idled. It progressively got worse during a few hours of running it until it would barely run at all. Start it up and it sounds like it lopes as if it has a huge cam in it. Its stock though. It idles very irratic. I had put new spark plugs in it a week before it did this and it was really smooth. I checked yesterday..and # 2 plug had backed out and was real loose. Hard to tighten because of the headers. I figured that was my prob. Tightened it up and its still rough. Looked at the plug and it looks good. Started it and let it run about 1 min irratically. Felt all of the plug wire caps that fit over the plugs and this # 2 wire was hot. None of the others are even warm yet. Does this mean anything? Let me know your thoughts and what else to check. Points gap and points are new and look good. No sign of vacuum leaks. Timing is set. Liike i said. I started to notice it a bit and then progressively got worse . Humm?

Thanks Much,

Blue71

 

[broncnaz]

Might want replace the spark plug wires if they are the old graphite type they really shouldnt get hot that may just be engine heat. But either way those old stock type wires do go bad and usually after changing plugs as they dont like to be handled much you might of broken the graphite inside causing a gap that the iginition is having a hard time over coming thus you get the miss and possibly a hot wire. Get a good set of spiral core wires and you'll never have another problem.

 

[Blue71]

Thanks broncnaz,

I got a set of premium plug wires and installed them and also got another set of points and changed them. I put a new spark plug in hole #2 and still have the same problem. Any other suggestions?

Thanks Much,

Blue71

 

[Doyle]

Is the plug boot still getting hot with the new wires? Might be blown header or head gasket.

 

[broncnaz]

If its still running like before it might have a stuck, bent or burnt valve that number 2 cylinder would be a good place to start looking. Like was posted might have a exhaust leak and burnt or broke a valve with cold air hitting it.

 

[DirtDonk]

And even though you said it didn't appear that there were any vacuum leaks, look again. It sounds like a classic case of a vacuum leak. Why it did it right after you changed the plugs is just plain luck. Not the good type though.
Not an ucommon Murphy type trait every other mechanical device it seems.

I just finally got an '83 302 running perfectly again after sitting for months with electrical issues. Got it smogged (passed with flying colors) and drove it for a half a day. Within 25 miles it pretty much ran like crap and stopped idleing completely.
Turned out that the intake manifold is leaking around the whole edge on the passenger side!
I've NEVER had an intake leak before, so it was a mystery at first. Then I remembered, this truck is cursed!
Within minutes of discovering the problem, the heater core started leaking on the ground and in the cab! Sheesh.

Good luck on yours. And check again for leaks.
Broncnaz's idea of a bad valve makes sense too.

Paul

 

[Blue71]

Thanks all. Gonna try a compression check first. Dirt Donk. I'm gonna search more for a vacuum leak again. Any other suggestions..let me know.

Thanks again,

Blue71

 

[DebosDave'72]

Did you ever pull the plug wires at the coil one at a time to make sure which cylinder was giving you the miss? Perhaps the hot wire was just a coincidence, and there is a bad plug in one of the other holes....

Just a thought.

Dave

Afterthoughts:

double check the firing order on the replaced plug wires also... If you find which cylinder is missing, and replacing that plug and wire doesn't work, start looking at the valve train...

 

[Blue71]

OK...Did a little work on her today. I checked compression on all 8 cyl. and went ahead and put 8 brand new plugs in. Pretty sure the #2 plug wire was getting hot because of it being right against the header. Here are the results:

1- 145 psi
2- 140 psi
3- 145 psi
4- 140 psi

5- 140 psi
6- 140 psi
7- 150 psi
8- 140 psi

All read great!

I pulled the plug wires one at a time off of the top of the dist cap and all seem to fire well and in a consistant manner. It didn't change the way it ran at all when I pulled the plug wire off the dist. cap and replaced it. Still idles irratic and lopes. Does all of this sound like its running correctly? If so..looks like I am gonna try vacuum leak as my next step. Would a vacuum leak progressively get worse like this did?

Let me know and thanks again,

Blue71

 

[Skuzzlebutt]

I have heard of vacuum leaks caused by heat that seal up when the engine is cold. I don't recall the exact nature of the leaks tho.

 

[broncnaz]

Cylinder readings are all good so the rings and valve are good. The bad is no change in the way it runs when the wires are pulled. I'm thinking timing even though you said it was set usaully 2 things can happen the rubber on the balancer is deteriated and the outer ring has slipped so your timing is not correct or the roll pin that holds the cam gear on the dist has broken and the timing is off because of it. Had a F250 with a 460 that this happened to it would start but ran rough and it wouldnt run like it should when the timing was set at its normal mark. Pulled the dist and found the broken roll pin.

Sometimes with aluminum manifolds you can develop leaks as they heat up/cool down at a different rate than the cast iron block and with the low torque of the bolts they can loosen over time. My intake will seap water when it gets cold. Even when the bolts are tight. Might want to check the torque on the bolts even cast iron manifolds can loosen up over time and if its ever overheated it could be warped or just loose causing a leak.
Same thing with the carb bolts.

 

[Blue71]

Any ideas on this????? Still working on it...It runs a little smoother when I pull the vacuum line off of the vacuum advance nipple. Hummm! What does that mean? Seems to run better with the vacuum leak. Does that make since? Still idles irratic, but just not as bad. Still working on pulling the dizzy.

Thanks Much,

Blue71

 

[DebosDave'72]

It could point to timing, have you checked that? The vacuum advance is advancing the timing, so when you pull it off, it retards a little bit... could be out enough that when you pull it off, it improves, but not enough...

Dave

 

[Blue71]

Thanks Dave,

I checked the timing again. I rotated the dist. clockwise until it really ran bad and died. Restarted it with the dist. in the good running point and turned it slowly counter-clockwise until it ran bad and died. Throughout the entire range it idles horrible. I did notice that when I have my optimum timing setting...I can snap the throttle open to a high RPM and it is very responsive and sounds good and clean. (No hesitation on the throttle when done quick) When I ease the throttle open up to a high RPM..it is a rough climb to the same RPM level as if I snap the throttle quickly. Any ideas? Lemme know. Thanks again for all of the input guys. Gotta get this thing workin somehow.

Blue71

 

[DebosDave'72]

You have not found a vacuum leak either? Also, did you make sure you don't have two plug wires mixed up? If you did, it would have a miss regardless of taking one of them off the dist. cap or not... Other than that, I am not much help...

Dave

 

[Blue71]

Would a broken rocker arm, collapsed lifter,or burnt valve, show up on my compression test? Any idea?

Yep...checked and double checked the wires. I pretty much ruled out the wires since it was running great and then started to do it about 30 minutes later as I stopped originally. I'm gonna conitnue with vacuum leak searches.

Let me know.

Blue71

Thanks for the input. Keep'em comin'

 

[DebosDave'72]

I think anything in the valve train would show up on a compression test... I think the great results on the compression test basically rule out anything in the valvetrain or the engine block...

Dave

I think the only thing outside of a vacuum leak that you can look at is the distributor or the timing chain.. I am not sure what it would do if it jumped a tooth?

 

[DirtDonk]

Refresh my memory (since I'm too tired/lazy to go back and find out), what are you running, carb or EFI?

Are you checking for vacuum leaks using the tried-and-true carb cleaner spray method? Or something else?

Just getting mentally up to date here. Thanks.

Paul

 

[Flash69]

Start it at night when it is really dark and make sure you dont have any plug wires arcking over to the motor.

 

[Doyle]

Is this an original engine, never rebuilt? How many miles? If over 75000 may be the factory fiber cam gear breaing down. Timing would look right with a timing light but would actually be off, due to slack in the timing chain and worn gears.