Stroker Spark Plugs

[IH 392]

Tip style really doesn't have jack to do with the heat range, the projected tips run rather cool due to the intake charge cooling them, but in higher than stock compression ratio engines they can cause detnation and blow holes right threw the tops of the pistons!, I've seen that first hand, in an AMC/Jeep 4.6 stroker motor!it was an expensive lesson, custom flat top pistons for AMC's aint cheap!

[gradon]

Here's what the RC9 looks like:

From my experience with the Champions, colder heat range plugs have ceramics that don't protrude as much as the hotter ones. Anyhow, I just tried to see how the NGK worked and they're no different than the RC9s.

[W_A_Watson_II]

First, it's amazing how much quieter the Jeep is with the tail pipe and the plug gap closed down a little. It still sounds good, just not as bad ass as before.
Based on how the Jeep ran yesterday, and that the miss seems to come on after the engine was well warmed up, and the miss was present at any engine load/speed and not consistent, I believe the issue is plugs and not fuel. So I pulled the plugs. They were a strong 0.055" gap that I initially set them at, and looked decent. Plug 3 looks whiter, while plug 5 is darker, but "I" don't see anything that tells me anything. Based on others knowledge and comments, I decided to close the gap up some, so I re-gaped them to a strong 0.040". So I start the Jeep up, and the A/F ratio gauge doesn't bounce around nearly like it did before at idle. So I take it out for a test drive. Everything seems good, the Jeep sounds quieter, and the A/F ratio gauge doesn't bounce near as bad as it did before, even at engine speed. Well, once the Engine was well warmed, the miss was back, and again at all engine loads and speeds. Not consistent like it's a single cylinder, and it's very very bad at had acceleration once it tries to exceed 4,000 RPM. I watched the A/F ratio gauge and when it misses now it seems to bounce more to the rich side, suggesting (to me) that it's still a plug problem. The plugs are NGK BKR6E-11 (yes "E", not "3" as written on the cardboard). The stock plugs would be Champion RC12LC4. Based on what I've found the NGK's I'm using are one temperature range cooler, which is what was a recommended starting point for my stoker. So now do I go one more step cooler?





Suggestions or recommendations?

Thanks,
Will

[SilverXJ]

What is the stock gap?

[W_A_Watson_II]

The NGK Stock gap is stated to be 0.044".

[SilverXJ]

Its interesting that after the re gap that the AFR didn't bounce as much. Really can't tell much from the plugs. 1 & 3 look a bit oily or more carbon then then the rest. Do you have the stock coil to swap back in? I've never been a fan of any of those after market "hotter" coils for Jeeps.

[W_A_Watson_II]

Yes I do, it's got some bad cracks in it, but was working before the build.

[W_A_Watson_II]

After installing the NGK BKR7E-11 (Gaped at 0.044”) I took the Jeep out for a spin. A/F Ratio seems even more stable. However it started missing even before it warmed up. Might have just been new plugs, but nope. A few miles down the road I got on it. Missed at high RPM, at 4,000+ RPM, A/F ratio in 10-11.5 range (rich).

Here is a video, you don’t hear the miss in 2nd at 5,000 RPM and 80 MPH: http://www.youtube.com/watch?v=fhNnI5RTJ4w

Here is another video of the same, I let off the throttle so it would shift into 3rd, as it wasn’t in the previous video: http://www.youtube.com/watch?v=eZsmQXNfjVY

Here are three videos at road speed 50-55 MPH, you can kind of hear the miss and see the A/F ration swing left (rich) when it does, at least that’s how I read it:
http://www.youtube.com/watch?v=8tZlC6At9cU
http://www.youtube.com/watch?v=EXUcQip7qdw
http://www.youtube.com/watch?v=tB8zs9Z-Qto



Above is a random plug (#5) I pulled after getting home. Engine was well warmed, and missing, and running at 2,250 RPM when I shut it off and pulled the plug.

Now I wonder where I go next? A/F Ratio at High RPM is Rich, and in the normal range while driving, so I’m still not convinced the miss is fuel related.

Will

[SilverXJ]

Have you checked the fuel pressure while driving? What injectors? Have you tried the stock coil?

[W_A_Watson_II]

Not yet, tried the plugs first. Need to get a gauge and see what it says. My Injectors are the VENOM High Performance Fuel Injectors Part No. HP-624-8 with stock 39psi FPR (24 lbs/hr). Will try the stock coil next.

Are you thinking I'm lean?

[jbxx]

What's the A/F saying when the miss happens?

[W_A_Watson_II]

It looks to bounce Rich, the lean but you can look at the last three videos above and see what you think.

[jbxx]

Do you have an o'scope that you could hook up during the miss?
Wrap a wire around the coil wire if you do to make an inductive pickup. Then if you see an anomaly, do the same for each wire.

[W_A_Watson_II]

Sorry, no Oscilloscope.

[SilverXJ]

Not yet, tried the plugs first. Need to get a gauge and see what it says. My Injectors are the VENOM High Performance Fuel Injectors Part No. HP-624-8 with stock 39psi FPR (24 lbs/hr). Will try the stock coil next.

Are you thinking I'm lean?

Your injectors are 24 [email protected] PSI. At 39 psi they are around 22.7 lbs. Lean is an option, however I don't think so. You would have be running insanely lean to create a misfire. You should see the lean AFR on the wideband just before the misfire. I don't think that is the case. I wouldn't go messing with the injectors just yet. They may fit pretty well.

Keep in mine a misfire will show up as a rich condition on the wideband. Not because there is unburnt fuel, but because of unburnt oxygen.