3000 RPM limiter and detonating

[FlyinRyan]

Have you set fuel sync yet.

[superstingray77]

Just my .02 here but it sounds like you have VERY Excessive cylinder pressures. Check the cam timing and verify the lift @ the proper crank degrees.
Specifically I am leaning towards and exhaust restriction which will be present either in the system itself or the cam lift/timing not opening the exhaust valves enough.
For grins have you done a test run without the cats/down pipe/pipes connected?

The symptoms you describe are identical to when my first stroker wiped out the cam lobes. Under any load it would detonate and it would break up like a soft touch rev control at 3k. It did make the 300 mile trip home with black metallic nail polish for oil still getting 20+ on the hwy. (stock tires and no lift then)

[Rinkrat456]

Have you set fuel sync yet.

How does one do this?

[Rinkrat456]

Just my .02 here but it sounds like you have VERY Excessive cylinder pressures. Check the cam timing and verify the lift @ the proper crank degrees.
Specifically I am leaning towards and exhaust restriction which will be present either in the system itself or the cam lift/timing not opening the exhaust valves enough.
For grins have you done a test run without the cats/down pipe/pipes connected?

The symptoms you describe are identical to when my first stroker wiped out the cam lobes. Under any load it would detonate and it would break up like a soft touch rev control at 3k. It did make the 300 mile trip home with black metallic nail polish for oil still getting 20+ on the hwy. (stock tires and no lift then)

The cat is a Magnaflow universal, with a Magnaflow muffler after that. The exhaust note now has had a few months to settle in and it got louder than what we would like so we will most likely be bringing it back to the muffler shop to have a small 4" round Magnaflow bullet muffler added to quiet it down a touch. However, to answer your question, no we have not had the engine running without the downpipe. The closest test to that is just running an open pipe without cat or muffler. I cut the exhaust system off before the cat and we ran it on that for a short while. Detonating and 3000rpm limiter remained.

I don't mind checking the cam timing again but I need to know if the symptoms I'm experiencing are more susceptible to the cam being advanced one tooth, or retarded one tooth.

[FlyinRyan]

Fuel sync is something I adjust on EVERY cammed and or stroked OBD2 vehicle I tune. It is a crude way of adjusting injector timing.

You'll need a DRB3 or Snap on SOLUS/MT2500/etc type scanner to adjust it with any real precision.

I recently worked with an early 80s CJ that used a OBD1 harness, and OBD2 PCM out of a 5 spd TJ. Even with my base tune, the truck would backfire above 2200. Had great torque below that, but would miss and buck and backfire BAD if you tried to push beyond 2200 rpms. At my insistence, the shop that put it together finally adjusted the distrubutor to see if that made any difference. After some playing around with it (no scan tool), they got rid of the bucking. Truck runs better than ever. We still need to finalize the setting but even so, fuel sync NEEDS to be adjusted, and not just using "the toothpick method". Why this forum seems to think this is an elective procedure baffles me. I hope this helps.

[Rinkrat456]

Well, with tail tucked between our legs, my wife and I dropped the Jeep off to a local Mopar specialty shop and we discovered the timing set was off - despite all of our attempts to degree the cam properly. The shop fixed the issue and we are dyno tuning later this afternoon.

I'm getting antsy to see what this 1.5yr struggle will actually feel like. The shop has had the Jeep all week so I'm excited to drive it tonight.

[SilverXJ]

Did you use a degree wheel to set the cam?

[Rinkrat456]

The shop degreed the cam and buttoned everything back up. We ended up buying an SCT handheld through the shop, who dynod it and tuned it for 87 octane and 100% reliability with 25* of timing (I think he started at 33, then 28, then settled on 25 after a few test drives on the road listening for detonation). It made 173.08hp and 295.7lb-ft of torque at the wheels on a Dynojet.

This Jeep pulls like a bat out of hell in 2nd gear all the way to 85mph.