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Burning super rich

2

242_cherokee

NAXJA Forum User
Location
Howard, Ohio
I have a 99 xj 4.0 aw4 231. I was replacing my broken muffler with a cherrybomb glasspack :viking: and i noticed that from the cat back the inside of my tail pipe is black. pitch caked on black. im only getting barely 200 miles out of a tank of gas driving extremely sensibly... no idea. my rocker arms are wore out so my valves may not be working properly.. recent tune up.. no codes.the o2 sensor behind the cat looked fine - no black on it. any ideas? thanks guys.
 
JJacobs said:
Rocker arms are worn out? Why do you say that?
Click to expand...

Where the push rods hit the rocker arm the rod has almost put a hole through the arm. On several of them. So next months project is changing the arms and rods.. How do I check for a bad sensor dirty tv and cracked manifold? :soapbox:
 
No amount of cleaning this and adjusting that is going to overcome a base engine problem. If the rockers are burned up, what's the rest of it look like inside? Get the rockers fixed and check compression then see how it runs.
 
everything else looked pretty good for the most part. nice and clean. no obvious signs of wear or tear. just the rocker arms and rods are worn. my guess is (im no mechanic) since the push rods and arms are wore the valves aren't operating properly. is that safe to assume? and could this be the root of the problem?
 
I'd bet on it, get the valves/rockers/everything else fixed and it should help a lot.
 
Mr 242, how many miles? Is it tapping, or running rough, due to collapsed lifters? Good oil flow on top end? Rocker arms shouldn't just wear out. If they're worn or damaged, there is a reason.
And all the usual stuff-tune up, O2 sensor, cracked manifold, etc. Sounds like a good indoor project for the winter.
 
It makes a knocking sound and the higher the rev the more knocking. I'm positive it's the arms because there is a gap between the rods and where it hits the arm cause the arms are wore. I'm almost positive that is the problem. I don't think my valves are getting the proper workout. The o2 sensors have never been changed. 126k miles.
 
AJTorris said:
Is there anything else that could cause this? I am running rich and have low rpms.
Click to expand...

Excessive fuel pressure, coolant temperature sensor, thermostat, efan stuck on.
 
242_cherokee said:
It makes a knocking sound and the higher the rev the more knocking. I'm positive it's the arms because there is a gap between the rods and where it hits the arm cause the arms are wore. I'm almost positive that is the problem. I don't think my valves are getting the proper workout. The o2 sensors have never been changed. 126k miles.
Click to expand...

OK, you have rockers that need replacement. Worn rockers did not cause worn rockers. Sounds like either no oil to top end, or a few bunged up lifters. Have you tried to tighten down the nuts. I've seen them work loose, but it's not common.
 
It seems like the lifters should be able to take up any gap from worn rocker arms. More likely that you have collapsed lifters. Have you decided that the rockers are worn out because there is a gap between the pushrods and the lifters or have you pulled the rocker arms off and looked at them compared to one that isn't worn?

Anyway, before trying to chase down electrical, fuel, etc. issues, it is a good idea to do a compression test to evaluate the sealing of the rings and valves. Without good compression, it won't run right and you will change other parts for nothing.
 
i think a leak down test would be better. if there is a problem and the valves are not operating properly, the compression test may be off even though the rings and valves are fine. have you checked the adjustment of the tv cable for the transmission? if that is out of adjustment it could cause poor gas mileage/excessive consumption.

zedpapa
 
I compared Arms. Mine are definately worn. Probly from the two years and 40k miles with no oil change when my mom owned it (what is it with vehicles and women?). Never thought about the TV cable. How Do you adjust it?
 
Rocker arms can wear, but usually it is caused by something else. No oil change is a good cause, but mostly it would cause the lifters not to pump up, leaving you the space you describe. By all means do the rocker arms, but if it doesn't help, you'll probably be looking at new lifters and pushrods also. And then you'll have to deal with most people saying you shouldn't replace the lifters without a new cam also. But, one step at a time! I put new lifters and rockers in my '92 six years and 70k miles ago, but didn't replace the cam. Now, with over 200k miles on it, it still runs fine. I was having the same problems you describe, but at least half of my lifters wouldn't pump up, and the engine tapped like crazy and ran rough, even after warm, and a good run on the Interstate. Yes, mine was also owned by a woman! It sounds like this is where you're heading.
 
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It idles a bit smoother after a little drive.. i cranked the engine with the v cover off to check for oil. it looked satisfactory. plenty of oil was getting up there. put the v cap back on and fired it up. tapping seems to come from the top of the engine. i'll change my arms and rods come next month. the ends of a few of the push fods are kinda blunted with some shiney showing... not chunks mising just wore a bit excessively. I havent noticed really any metal in my oil chenges ( magnet method) the rest were flat. I'm beginning to think that its getting revenge for going without an oil change for two years.. I run castrol Full Syn every 3 months regardless if i hit 3k miles or not. I remember when i changed the oil in in a long time ago when mom had it.. The oil strongly resembled molasses... I ran dino oil in it after than then went two oil changes with syntec blend then went full syn. ARR.. We'll see how it goes..
Also i think my intake could be loose or the gasket could be bad.. I keep hering they can come loose.. Should i try to tighten it down? or maybe some RTV lol.
 
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