Running rich high rpm missfire

[BDD]

I have 30,000 miles on the stroker in my 98 tj. It has always ran great but lately it seems like the rev limiter moved from 5200 to around 4500. It started breaking up and running rich in the upper rpms a few weeks ago.It seems to go rich on my wideband by 1/2 throttle and continues getting richer the higher it revs,probobly because it is missing?
I started by cleaning my air filter and put new plugs,cap and rotor on it. I thought my convertor could be plugged so I cut off my tail pipe and emptied the cat. It changed nothing.
I installed a new tps,map sensor,coolent temp sensor,crank sensor,cam sensor,upstream02 sensor,oem fuel pump and regulator.
I have checked for vacuum leaks and found none.
I dont normally just replace parts to fix a problem but I thought it would be easy if I replaced my old 160,000 miles parts with new ones,and I would have spares for the trail.

The only thing I havnt replaced is the ecm,and rear o2. I find it weird that I dont get a cel after I emptied my cat?
I should also tell you I am running neon injectors on a mild stroker.It has always run around 14.7 at idle and cruising,and gets to 12.7 after about 2 seconds when you mash the peddle.Last summer I cut my factory muffler and tail pipe off of it and put a cherry bomb on it.I had to put the stock tail pipe back on it to keep it rich enough.Now I have no tail pipe,and no guts in my cat,and it is rich when ever I floor it.
I am wondering if it could be my cam going flat,or weak valve springs,causing float.But it doesnt seem consistent,seems to rev to 5000 clean when I first take off,hit second it breaks up,hit third it breaks up and keeps getting richer on my afr.
I running a505 stage one cam with stock springs.
any ideas? I am at my witts,and wallets end.
.

[gonridnu]

Just for S & G's check your spark color if you would. It could be the coil is going and not able to fully saturate at higher RPM giving a weak spark. Depending on what condition your distributor is in you could be seeing some spark scatter as well if the shaft is super loose.

If you are clean in first and second becomes a problem it indicates there is a problem under load which coincidently creates higher cylinder pressures which create resistance across the gap of the plug and if you have a weak coil voila ... misfire. As you have changed so many other parts it would definitely be worth looking in to. Also check your engine grounds to be sure none have come loose or broken.

That's all I got.....

[BDD]

Just for S & G's check your spark color if you would. It could be the coil is going and not able to fully saturate at higher RPM giving a weak spark. Depending on what condition your distributor is in you could be seeing some spark scatter as well if the shaft is super loose.

If you are clean in first and second becomes a problem it indicates there is a problem under load which coincidently creates higher cylinder pressures which create resistance across the gap of the plug and if you have a weak coil voila ... misfire. As you have changed so many other parts it would definitely be worth looking in to. Also check your engine grounds to be sure none have come loose or broken.

That's all I got.....

Thanks,I am going to try a different coil today.I have been over every connection and replaced every sensor.I have not bought a new map sensor,but the three I have so the same thing.If I unhook vacuum to map the motor almost dies,If I unplug connector from map the motor wont rev above 3000 rpm. I think my map is fine.

[superstingray77]

No signs of cam failure? Wiped exhaust lobes could cause this due to excessive cyl pressures. Oil has no metal in it? Compression test it, did the cam possibly jump time? Check TDC on balancer against the movement of the valve train on #1.

This is all if the coil suggestion fails because it is a good one.

[superstingray77]

No signs of cam failure? Wiped exhaust lobes could cause this due to excessive cyl pressures. Oil has no metal in it? Compression test it, did the cam possibly jump time? Check TDC on balancer against the movement of the valve train on #1.

This is all if the coil suggestion fails because it is a good one.

[doublins]

I always thought that misfires would register lean on a wideband because the o2 sensor would read the unburnt oxygen as a lean condition- the sensor measures oxygen, not hydrocarbons

Correct me if I´m wrong.

Oddly enough, I have the exact same problem as you, but it is not consistent- never happens in 1st gear, sometimes in 2nd, always in third- dramatic power falling off at about 4500rpm

I was thinking it had to be either misfiring due to a problem with the ignition, or some kind of timing jumping problem, or valve float. I hope you figure out what it is so that it might help me to figure my problem out.

THIS is exactly my problem.

But it doesnt seem consistent, seems to rev to 5000 clean when I first take off,hit second it breaks up,hit third it breaks up and keeps getting richer on my afr.

[CobraMarty]

What's your plug gap? Maybe narrow it to .032" and try.
Running rich is an incomplete burn.

[doublins]

What's your plug gap? Maybe narrow it to .032" and try.
Running rich is an incomplete burn.

Good idea, I will measure and then close gap if need be.


A total aside... (well not totally considering I brought it up, lol) As far as incomplete burn goes that means there are more reactants left over afterwards, which would include oxygen. When there is more oxygen in the exhaust flow, the o2 sensor would record it as a lean mixture, yes? In a rich (yet combusted) mixture, there is a higher ratio of hydrocarbons : o2, so the o2 is completely consumed in the process. In a lean mixture, there is not enough hydrocarbons to completely react with the o2, so there is extra o2 in the exhaust, hence, anything (such as a misfire) that would result in oxygen remaining in the exhaust flow, would register as lean, yes?

I´m kind of thinking out loud here, but in terms of what the o2 sensor is sensing and reporting, it stands to reason that an un-combusted a/f mixture would register as lean no matter how much fuel was present.

Now, mind you that my o2 sensor shows proper a/f under wot of about 12.3-12.8, so I don´t even necessarily know why I´m having an open debate with myself on the internet, but... well, when I don´t understand something I become obsessed with trying to make sense of it.

[superstingray77]

Also depends on how many cylinders are affected. My cam was destroyed and the symptoms were the same, cylinder pressure could not escape thus blowing out the spark. Engine was done at 3000 rpm and would crap out bad between gears. Pull the valve cover and check the travel on the valve train, check cranking pressures see if there is any massive variance.

[doublins]

Also depends on how many cylinders are affected. My cam was destroyed and the symptoms were the same, cylinder pressure could not escape thus blowing out the spark. Engine was done at 3000 rpm and would crap out bad between gears. Pull the valve cover and check the travel on the valve train, check cranking pressures see if there is any massive variance.

I pulled the valve cover yesterday- all rockers fully actuate, so the cam isn´t wiped.

Next idea? This is driving me nuts.

Note that I have an onboard wideband and it´s not a lean-mixture cutout. A/F shows 12:1 while it´s hitting the wall.

[dwg86]

I find it weird that I dont get a cel after I emptied my cat?
.

What do you mean by emptied the cat?

[doublins]

Also depends on how many cylinders are affected. My cam was destroyed and the symptoms were the same, cylinder pressure could not escape thus blowing out the spark. Engine was done at 3000 rpm and would crap out bad between gears. Pull the valve cover and check the travel on the valve train, check cranking pressures see if there is any massive variance.

I pulled the valve cover yesterday- all rockers fully actuate, so the cam isn´t wiped.

Next idea? This is driving me nuts.

Note that I have an onboard wideband and it´s not a lean-mixture cutout. A/F shows 12:1 while it´s hitting the wall.

So... I lied. I busted out the dial indicator last night. My cam is wiped- lift is only about 0.300¨ on a few of the lobes according to a dial indicator placed on top of the valve retainer..

I tried to measure my preload and when I went to do so, I realized that EVERY SINGLE lifter core is bottomed out and my preload is set to the max physical number, essentially making my hydraulic lifters solid lifters. my shop is going to have a lot of explaining to do on this...

This makes the THIRD time in a year and a half that my cam has failed. At this point I don´t trust that the machine shop has any idea what they are doing when they set up my valvetrain, this is completely unacceptable.

[Cheromaniac]

This makes the THIRD time in a year and a half that my cam has failed. At this point I don´t trust that the machine shop has any idea what they are doing when they set up my valvetrain, this is completely unacceptable.

I'm sorry to hear that. Looks like you're gonna have to give your machine shop hell.

[superstingray77]

Sorry to hear the news. I nitrided this cam and went solid lifter (more for power and sound) this round. My first one wiped because titan built and shipped me a new head w my first kit that had the seat pressures over 135#. All the metal in my engine destroyed the oil pump, rings, bearings. I had crank micro polished and rehoned the block.

[superstingray77]

I also had the lifter bores honed. If they stop turning the cam is toast.