Ignition Misfire Diagnostics

[hefavitzen]

Hey guys, It has been a while since my last post but a lot has been going on. Besides the family growing and kids getting older and more active, my Jeep project has also continued on.

Two years ago(?!?!?) when I came up to the Sand Blast event, a few of you pointed out that my ride was smoking and you were not wrong! In fact, I had F'ed the timing up something fierce and just hadn't realized it yet. So, I've been working on that and have some questions.

Here is the situation again: Gen 1 SBC stroked to a 383. Vortec heads. Holley 750 carb (yes, I know it's too big, but it is what I have at the moment), MSD Street Fire HEI.
Timing is currently set to 32 degrees advance.

My issue is that I have a misfire. I say this because all of my spark plugs look fabulous except for #8, which is fuel fowled.

Here is what I've done to try to diagnose the issue:
1) Checked spark with a spark tester - PASS. All cylinders check with spark at a pretty good gap; far greater than a spark plug could be gapped.
2) Pulled the valve cover and all "looks" normal, and no excessive lash in the rockers. I have not pulled the head though.
3) With the engine running, I pulled the #8 wire from the distributor and the engine didn't miss a beat. I put it back and pulled #6 and the engine chugged. I put it back and pulled #3 and the engine chugged. I put it back and pulled #8 again and the engine didn't miss a beat.
4) With the spark plug tester, I tested at the distributor - #8 has spark.
5) I swapped the #6 and #8 wires and did the "pull" test and the same results. #8, with the #6 wire, when pulled, the engine didn't miss a beat. I put it back on, pulled the #6 wire and the engine chugged.
6) I had put on a new distributor cap last summer as I have been fighting this issue for years. I pulled the cap to inspect it and found no weirdness. The spark is hitting in the center of all 8 of the pickups in the cap and there doesn't appear to be a difference between any of the pickups impact points, even on #8.
7) While I had the cap off, I cleaned off the pickups with some light filing and when I put it back on and started it up, it ran really smooth for about a minute even after a rev or two. Then, it was back to its tricks of being a little rough, a little spitty and a tiny bit of back talk from the tailpipe when coming down off of a throttle goose.

8) I forgot to also say that I did a compression test of all cylinders and they all shows 180 PSI and held there. I didn't hold it for a long time, just a few minutes each cylinder, but they didn't seem to leak, even #8.

So, I'm stumped.

I'm of two minds and would like your opinion:

Option 1: Swap in a new MSD Billet and 6A control box and see if that fixes it. - this is the $900 option
Option 2: Pull the head and see what is going on with the valves such as something sticking the intake valve open a bit letting stuff through that is fowling the plug. (this is a wild ass guess...I have no idea if that is even realistic)
Option 3: Take it to a shop and let a mechanic tinker with it.

Anyone have any idea what the heck I should do next? Thanks in advance!

 

[hefavitzen]

Here are the plugs I pulled... I broke #1 when I was pulling them so I just replaced all of them.

 

[hefavitzen]

I keep coming back to maybe it is the valve guides that are worn out on the #8 cylinder on the new heads that were installed in 2015.

If that is the case, how can you tell without pulling the head? I'd like to avoid pulling the head if possible since it doesn't leak at the moment. I am afraid I am being intimidated by having never pulled a head before or ever set valve lash before. Ugh.

 

[CJ7Pilot]

It does look oily to me. Maybe start with replacing valve guide seals (under the valve springs).

How does it run with the new spark plugs? It should take a little time for a new plug to foul.

 

[hefavitzen]

It does look oily to me. Maybe start with replacing valve guide seals (under the valve springs).

How does it run with the new spark plugs? It should take a little time for a new plug to foul.

I did change the spark plugs before I did all of the diagnostics I listed out. The photo is the set I pulled out, not the set I put back in. The new set though does show fouling of the #8 plug even with only about 10 miles of driving.

I've been dreading actually having to dig into the head, but I am leaning in that direction too...

 

[mysunnshine]

I'd start with a set of intake gaskets. Is it an aluminum manifold?

 

[jammer1]

On my cj7 - Cj8, I have a chevy 350 (engine factory made engine) with vortec heads. I started having a minor miss that drove me crazy for over a year. My mechanic couldn't figure it out. Number 3 cylinder would get oil fouled (like your number 8 plug, just a little cleaner). The mechanic even installed a new distributor (minor bounce in timing). Finally I was done with it and had him pull the intake. Found #3 gasket dried and pulled into the runner just enough to give a minor intake leak. Didn't like the no name intake manifold and so went with a Edelbrock intake with their intake gaskets. Needless to say fixed the problem. Six months later it started again, this time with #4 plug. Do a search on the vortec intake leaks. It's very common. This time I did the research and found a felpro gasket that is designed to fix this problem with the vortec heads. So far (knock on wood), solved the problem. Yours sounds very much like my problem.

 

[jammer1]

Back at my computer with pics. First set was the engine factory no name intake and their gaskets. These were removed in 2020. A edelbrock intake and edelbrock gasket set was installed.

 

[jammer1]

This is the result of the edelbrock gasket set with less than 300 miles and just over 6 mths. Without the center bolts in the intake the intake doesn't seem to clamp down enough and allows the gasket to get sucked into the runner. You can see the movement of the gasket (2 gaskets bonded together). The stock gasket uses plastic bonded in the gasket with silicone around the runners. Over time the plastic becomes brittle from the hot/cold cycling. Fel pro makes a gasket set that used metal instead of the plastic and seems to be the fix for this problem. I only have around 600 miles or so on them so time will tell (edelbrocks gasket shocked the hell out of me when I saw the results in only 300 miles. Here's the gasket I'm currently running.

FEL-PRO MS 98000 T Intake Manifold Gasket Set​

 

[hefavitzen]

I'd start with a set of intake gaskets. Is it an aluminum manifold?

Yes, Edelbrock Performer 21163

 

[hefavitzen]

This is the result of the edelbrock gasket set with less than 300 miles and just over 6 mths. Without the center bolts in the intake the intake doesn't seem to clamp down enough and allows the gasket to get sucked into the runner. You can see the movement of the gasket (2 gaskets bonded together). The stock gasket uses plastic bonded in the gasket with silicone around the runners. Over time the plastic becomes brittle from the hot/cold cycling. Fel pro makes a gasket set that used metal instead of the plastic and seems to be the fix for this problem. I only have around 600 miles or so on them so time will tell (edelbrocks gasket shocked the hell out of me when I saw the results in only 300 miles. Here's the gasket I'm currently running.

FEL-PRO MS 98000 T Intake Manifold Gasket Set​

I'll try these! I hope that is all it is. I looked back at some emails with the place that built my engine and I had brought this issue up back in 2015 but we couldn't figure it out. I am way too nice and just lived with it thinking, "maybe this is ok?" Ugh. I wish I had brought this up on here a loooonnnngggg time ago.

I'll take photos and post them! Thanks again!!! CJ-8.com ROCKS!!!!

 

[hefavitzen]

This is the result of the edelbrock gasket set with less than 300 miles and just over 6 mths. Without the center bolts in the intake the intake doesn't seem to clamp down enough and allows the gasket to get sucked into the runner. You can see the movement of the gasket (2 gaskets bonded together). The stock gasket uses plastic bonded in the gasket with silicone around the runners. Over time the plastic becomes brittle from the hot/cold cycling. Fel pro makes a gasket set that used metal instead of the plastic and seems to be the fix for this problem. I only have around 600 miles or so on them so time will tell (edelbrocks gasket shocked the hell out of me when I saw the results in only 300 miles. Here's the gasket I'm currently running.

FEL-PRO MS 98000 T Intake Manifold Gasket Set​

Do you have to pull the heads to replace the intake gasket?!?!? I've never replaced one before!

 

[mysunnshine]

You need to use the steel shim gaskets with aluminum manifolds because the expansion and contraction of the aluminum intake will walk the edges of the gaskets away from the port edges. Fel pro has S3 after the part number to indicate the steel shim gasket style such as 1205-S3 as an example.

 

[hefavitzen]

You need to use the steel shim gaskets with aluminum manifolds because the expansion and contraction of the aluminum intake will walk the edges of the gaskets away from the port edges. Fel pro has S3 after the part number to indicate the steel shim gasket style such as 1205-S3 as an example.

So what if I cannot find gaskets who's ports are the correct size? The Edelbrock Performer 21163 Intake instructions "recommended gasket" has a Port size of 1.08 x 2.11

Here is a screenshot of the instructions for the manifold that state the port size:

 

[mysunnshine]

I highly doubt that you have unicorn heads so there should be a steel shim gasket that should work for you.

 

[mysunnshine]

Your also need to verify the gaskets against the cylinder head ports and against the intake manifold ports.

 

[hefavitzen]

I am positive I have run of the mill heads and have ordered a Fel-Pro set. I'll take some pics of the whole operation as I pull the intake, looking for obvious issues and check the gasket fitment and putting it back together praying it fixes the problem. Gaskets should be here today so more to come really soon.

Thank you guys for all of your input (help) and knowledge sharing. I'd be far poorer without it.

 

[hefavitzen]

I moved my updates to my build thread. I hope that is ok.

 

[hefavitzen]

Ok, so I installed new intake gaskets and a new distributor that doesn't bang into the firewall and I still have a misfire issue on cylinder #8. So, I have pulled the head off to see what is what.

Questions for anyone:
1) Cylinder 2 is very wet looking as is a tiny bit of Cylinder 8 (see the yellow circle on Cyl 8). But, I don't really see a lot of indication of leakage into the cylinder from the sides. Thoughts?

2) Cylinder 8 has a black intake valve which I assume should be very telling? Any ideas on why only one intake valve would be black? I'm researching this, but I haven't found a smoking gun answer yet.

Also, this engine, while having been rebuilt in 2015, doesn't have more than 15,000 miles on it. Should the pistons, cylinders and valve area look this cruddy?

 

[FLCJ8]

Cylinder 8 has a black intake valve which I assume should be very telling? Any ideas on why only one intake valve would be black? I'm researching this, but I haven't found a smoking gun answer yet.

I realize this isn't of any help to your problem (well maybe it is), when you are searching for answers are you looking for black "intake" or "exhaust" valves?
#8 is the only one that has a dark "exhaust" valve, so maybe you mistyped in your searching as well.