Jeep Strokers

Hello all,

I have about 3000 miles on my stroker so far, and overall I would say it's running well but it has a few quirks that I am becoming concerned about. I am beginning to wonder if these said "quirks" are related to the camshaft that I opted to run. I am still new to engine building and would appreciate some advice on breaking down my camshaft specs and how they could be affecting my engine's performance. The cam is a custom grind comp 163-000-5, I've posted a picture of the cam card with the specs below.

Build summary:
- 4.2L Scat crank and scat rods
- Russ custom dished pistons
- Russ ported promaxx head with upgraded LS valves and valve springs (not certain on the spring specs, can get them if needed)
- Comp 163-000-5 cam with hylift johnson lifters (specs below, I chose this cam because it was the only nitrided option availible to me at the time)
- Stock 1.6 rocker arms
- Banks torque tube exhaust header
- Ford 24lb injectors
- Champion RC9YC spark plugs

The issues that I am having:
- First and most concerning in my opinion, the engine has a stumble/shake to it at idle, resulting in some pretty harsh vibrations in the cab. It almost seems like it has a lope to it but I'm not too sure. I've attached a video link of the engine running below. Its hard to see in the video, but in person I can see the motor shutter in the engine bay every few seconds, giving me the vibration that I feel in the cab. In the cab, can see the rpms constantly fluctuating ~20 rpm on the tach at idle. The exhaust also sounds like it has a periodic "miss" to it that seems to happen at the same time a stumble occurs.

-Secondly, the engine has a lot of valve train noise, to the point where it almost sounds like a diesel. I would say the noise is pretty consistent, it does not make any out of place knocks or anything, just seems loud compared to what my stock 4.0 used to be. This can easily be heard in the video down below.

- Lastly, the engine's powerband is not quite what I was expecting it to be. Overall the motor seems relatively sluggish at low rpms, less than around 2k. At and above 2k, the motor makes decent power and at higher rpms, around 3k and above the motor REALLY wakes up and pulls hard.

Again, my question is if the cam I selected could be causing the symptoms I described above. If something I said does not make sense or further explanation is needed I would be happy to provide more info. Thank you!

Idling video: https://youtu.be/2X6k_zCy2F8

Yeah I think the symptoms you're experiencing are those of a fairly aggressive cam (for a Jeep) with a slight lope.

What valve springs did you use? Stock valve springs are only good for something like .460 lift with a .060 safety margin.
You need to have the ecm tuned. With the loss of vacuum at idle the engine is probably running really rich. The cam isn’t huge but it definitely is going to need a tune to run correctly.

dwg86 wrote: ↑September 30th, 2024, 9:12 am What valve springs did you use? Stock valve springs are only good for something like .460 lift with a .060 safety margin.
You need to have the ecm tuned. With the loss of vacuum at idle the engine is probably running really rich. The cam isn’t huge but it definitely is going to need a tune to run correctly.

The valve spring is a Comp Cams 26981 and Camshaft is a 163-301-5 that has been nitrided. Static compression ratio is going to be around 9.4:1 to 9.5:1 with a cranking compression of 175ish running a 24 pound Bosch Injector.

Not saying it wouldn’t benefit, but this particular set up his been duplicated approximately 50 times without requiring a tune.

With that said all opinions and input welcomed.

Thank you for posting up that info Russ you beat me to it.

Forgive my ignorance here but running rich at idle: could that be what is triggering my engine stumble? Is there anyway to confirm this other than an AFR gauge? After speaking with Russ over the phone the other day, we are in agreement that neither the idle stumble or valve train noise are grounds for serious concern. The stumble is more of a driving comfort issue for me if anything but I'd still like to get that situated if possible. Who does everyone reccomend for their tuning needs?

Additionally and possibly related, I scrolled through my camera roll and found this picture of my stock champion spark plugs before I swapped them out for the cooler range RC9's few weeks ago. Both sets were gapped at 0.035. Looks to me like the plugs are mostly white indicating a lean condition, with #1 being completely white. #4 and #6 were concerning with those burn marks. Will need to check the new plugs for comparison though. Just something I noticed that could be a contributing factor to the idle stumble. Maybe I'm running the wrong plugs or plug gaps?

It does seem loud but it is a bit hard to tell if it's just the cam giving a loping idle or something else. When a cam is ground to a more aggresive profile, they can have a smaller base circle and need some valve lash adjustment or slightly longer pushrods to compensate. I don't think that this cam is that agressive, but it's not out of the question. If not addressed, the pushrods can tick and you would be off the expected lift. The stock rockers aren't adjustable and adjustable roller rockers will probably require a valve cover spacer with the stamped steel valve cover or the baffles cut out which will result in more oil getting drawn into the intake. Have you used a mechanic stethoscope to check the source of the noise?

Plug 2 and 3 do look lean but the others look rich assuming they were new with less than 3000 miles. How many miles were those run? Aside from that your cherokee sport looks like a later 99-01 with a JTEC/JTEC+ ECM but I'm not sure. Did you tune it or have it tuned after the build? If not that could help get it dialed in. A wideband O2 sensor will be helpful and it would be be beneficial to log that with the engine ODBII data. On whichever bank the lighter plugs came from. The wideband enables the AFR guage. There are a couple models which have the ability to output a narrowband signal for the ECU allowing you to use an existing upper O2 bung for the sensor. PLX and Innovate both make them.