3000 RPM limiter and detonating

[Rinkrat456]

JEEP....Just empty every pocket right? Seems there is no end to this stroker fighting me and my wife the entire way. '98 XJ, '97 block made into a 4.7L stroker.

I'm starting a new thread instead of going along with this one because I want to focus on the main symptoms rather than reading through all of the previous ones. See this thread for further details if needed though.
http://www.jeepstrokers.com/forum/viewt ... f=5&t=4212

My wife and I are still battling a strict 3000 RPM limiter and detonation under load. We have recently replaced the entire ignition system with quality parts.
- Distributor
- Coil
- Cap
- Rotor
- Plug wires
- Plugs
During this we also replaced both O2 sensors with new Denso brand sensors.

The low end feels awesome now and we're averaging 16-17mpg on the highway going 60mph. Any faster and there's enough load on the engine to detonate regularly while cruising. We have over 1000 miles on the stroker and gain more daily. After replacing the distributor and hooking everything back up, I did an 1800rpm burnout and one-wheel-peeled out of my driveway with ease....but of course it can't rev past 3000 still in any gear. I'm starting to suspect the actual PCM itself. That's next to get replaced if I don't figure this out soon. We need to drive this Jeep 38-40 hours coming up in 3 weeks on our trip home for Christmas so it is paramount we get this figured out. Keep in mind from the previous threads we were battling a horrible camshaft to timing set relationship over the summer and even after degreeing the cam with 95% confidence, there's still that doubt in the back of my mind we're 1 tooth off in either direction. My wife did her best to figure out all the geometry/trig and math but this sure sounds timing related. What are the symptoms of being 1 tooth ahead? What are the symptoms of being 1 tooth behind?

Here are the major symptoms:
- Strict RPM limit of 3000, seems to be bouncing off a rev limiter in all gears PRND321.
- Nearly full power loss while accelerating as RPM's climb above 2000 and on up to 3000. Engine continues to climb in RPM's but much MUCH slower than from idle to 2000.
- Detonating/pinging at higher throttle loads while accelerating or maintaining cruising speed above 65mph.
- An RPM that bounces off of idle when coasting, RPM's will drop and bounce up and down ever so slightly (less than 100rpms of bounce total but noticeable on the tach and audible).

What I need is a hypothesis, a way of testing that hypothesis, and I will post back with results. I will Paypal someone $5 to whomever has the winning hypothesis which solves our issues - no joke - it's that annoying now at this point as we've been dealing with various little things on this engine for months and we just want it running right.

I can get videos, audio clips & pictures. For testing equipment I have a fuel pressure tester, cylinder compression tester, cheap multi-meter with basic functions and a simple lighted circuit tester.

Put me to work!

[shawnxj]

did you check your cam and crank sensor signals?

[Rinkrat456]

did you check your cam and crank sensor signals?

Can you elaborate on how I go about this at home? I did however have a shop hook up their diagnostics machines to the Jeep and the cam and crank were in sync with each other if that's what you're asking.

[shawnxj]

put a meter on them and see what the signals say. if the voltage isn't high enough it could lose the signal at higher rpm's

[sly-jeeper]

have you figured anything else out yet?....your running an 8 degree retarded cam in it...did you phase the distributor properly to compensate?

[SilverXJ]

your running an 8 degree retarded cam in it

Why is your cam retarded 8*?

[Cheromaniac]

He's running a Melling MC809 cam which is a stock replacement for the '87-'95 4.0 with an LSA of 112* and an ICA of 110.5*. Installed dot-to-dot, it'll be 1.5* advanced. The question is whether the timing set was installed correctly. One tooth off on the cam sprocket is a difference of 7.5 degrees, whereas one tooth off on the crank sprocket is a difference of 15 degrees.

[sly-jeeper]

for some reason i thought that cam was retarded i guess im retarded 8 degrees lol

[sly-jeeper]

i just found another of his threads on here...it really does sound like hes off a tooth or the distributor isnt phased right

[ruffy01]

I just replaced my throttle body with a 68mm unit AND experienced pinging with a 3000RPM rev limit!
I replaced the IAC & TPS with my old ones BUT then noticed no vacuum line between the bottom of the MAP sensor & the port at the base of the throttle body, which the old throttle body had.
I hooked up that little vacuum line & problem solved

I hope this may be your solution.

[Mr.Justimizer]

If you haven't ground the locking tab's off of the distributor you need to do that. I had the same issue you are describing with my first stroker. What happens is the computer tries to retard the timing but the stock rotor only has enough surface to allow it to retard so far so it has to jump off the edge of the rotor. I bet if you look at the rotor (if it has a few miles on it) the trailing edge will have a lot more wear (burning) than the center. Grind the locking tab off so you can rotate your distributor forward just a little and it will probly work great. This was my experience anyways.

[Rinkrat456]

Sorry guys I haven't checked this website in awhile until I got ruffy01's PM sent to my email.

Jeep is still being a big pile of manure. Nothing much has changed since I posted this thread, except the Jeep is daily driven...granted I know it's probably not the best idea but we're out of vehicles to drive during this cold snap of weather. My wife drives the Jeep about 3 miles to work so it's not that far each day.

One thing we DID test just today was replacing the PCM...and by replace I mean I found an identical model year PCM from a junkyard, paid $65 and swapped it in while trying to defeat the 3000rpm limiter and detonating. No bueno, everything is the same. So...I'm willing to try whatever is next.

I have a spare distributor, and can do whatever you guys want me to do with it. Please explain further this whole "grinding down the locking tabs" thing.

[Rinkrat456]

I just replaced my throttle body with a 68mm unit AND experienced pinging with a 3000RPM rev limit!
I replaced the IAC & TPS with my old ones BUT then noticed no vacuum line between the bottom of the MAP sensor & the port at the base of the throttle body, which the old throttle body had.
I hooked up that little vacuum line & problem solved

I hope this may be your solution.

Thanks for the thought. I'm not opposed to trying a new IAC or TPS but I know we've checked vacuum lines 1000000 times and all are in good shape. Interesting that you experienced the exact same symptoms though. Gives me something else to check considering the IAC and TPS that is currently on the Jeep are only a year or so old.

[ruffy01]

Hey mate.
The TPS & IAC weren't the culprits, sorry badly worded perhaps.
It was the 'very little' rubber line, not visible without removing the throttle body, from the base of the throttle body venturi to the underside of the map sensor.
When removed, I couldn't get above 3000RPM & the engine pinged really bad.

[Rinkrat456]

Well, I took the MAP sensor off and everything appears to be in working order. The little 90 degree right angle vacuum elbow is in near perfect condition with no visible cracks. The suction around the seal was tight to pull the MAP sensor off from the throttle body.

What are the symptoms of a MAP sensor that's not getting a correct reading?

My wife likes this smiley....


And I want to do this to the Jeep.