A bunch of questions

Hello everyone, I just joined this forum after getting an 87 XJ, 4.0, AW4, NP231 with 236k miles and it seems to be running strong. I just have a few questions.

The engine runs what I would call well for have so many miles on it. The engine always starts the first time, but it hesitates after a handful of cranks. The engine makes a sound that's kind of hard to describe. Its one that speeds up with rpm. It's just the sound of a tired engine. Well, I've been looking into different things I should check to get things perked up.

1. I was looking into a timing chain/sprokets because I don't know if that's ever been replaced.
2. When reading about replacing the timing chain I read that cam shafts can wear out. Have any of you experienced that?
3. I wanted to check valve clearances and adjust accordingly. I thought that valve clap might be the sound I've been hearing.

Does any of this sound reasonable to check? I'm good with my hands, but I don't have a lot of experience wrenching on engines. Thanks for any advise regarding something to revive my engine.

I dont know about the guys on here with a clue, but I for one feel that would be a waste of time. With an engine with that many miles on it, I would think the engine has worn both topend and bottomend, equally. Id just drive it, I am of the mindset if it aint broke dont fix it. Long as oil PSI is fine and it isnt running hot... just my opinion.

That engine will keep going until it dies. duh.

Keep after the fluids religiously, especially oil changes.

No matter what you fix (e.g., timing chain), something else will become the weak link.
The 236k is good; it might make 300k, might let go at 250.

Yes camshafts wear, but not so much as to be noticeable above the general wear of the other components. You have hydraulic lifters, which automatically adjust for any wear in the valves, pushrods, and cam lobes. There isn't any valve adjustment possible, because there is no need.

Plan on a whole new rebuilt long block within the next year or two, and you'll have a dependable rig for years.

First things first. Remove the throttle body and clean it on a bench with a good carb/FI cleaner, careful of the sensors, most of those cleaner are not plastic safe. Then use some chrysler top end cleaner, Gm top end cleaner, etc to get any carbon build up out of the valves and head. Then do a complete tune up, plugs, wires, cap, rotor.
The engine fires from a little sensor on the bell housing, it's called a crank position sensor, magnetic, more or less tells the computer when to inject fuel and fire the plugs. They do go and usually result in a no start. The fuel system works off of high pressure constant flow with a return of unused fuel, when you shut the engine off it is supposed to maintain pressure for about 30 min but maintain fuel in the line for alot longer, there is an anti drain back valve that if bad will allow all the fuel to drain back into the tank and when cold starting you end up cranking the motor over till the fuel system repressurizes again. Generally they start after the engine turns over 2-3 times. Test is to turn your key on when it's cold and count to 30, then move it one more position to the start position, if it fires right up that is the problem. That check valve is part of the fuel pump.
You could also start adding some synthetic oil, synthetic is high detergent and will clean out any sludge that might have built up in the lifters and other areas. The other method is to use one of the internal engine cleaners, much faster than using syn oil but if I went that route I think I would do a couple of quick oil changes after using it.
As for the timeing chain, AFAIK the jeep timeing chain is all metal/steel, not like a GM350 with nylon gears that wear out in 100K.
I also recommend all mopar parts for the tune up, Mopar makes some nice high performance wires for the 4.0 that are actually cheaper than the OEM wires.
Also seeing as how it is new to you I would do all the fluids, engine oil, transfer case, both diffs and I would do a good cooling systems flush, refill with Mopar coolant and distilled water, new mopar thermostat and pressure cap. Yea, I like the mopar stuff, it always fits and always works in my experience

Check it out

It's all good advice and should get you going. Do a compression check to see where you're at. If you can't afford the full synthetic oils try some of the blends. You have hydraulic lifters so if there is valve clack then you can replace them by pulling the valve cover and loosening the rocker arms. Take one thing at a time and we'll help with what we can. Good luck.

Re: Check it out

HossHoffer said:

You have hydraulic lifters so if there is valve clack then you can replace them by pulling the valve cover and loosening the rocker arms.

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Spoken (written) like a true 2.5L 4-cylinder man.

The problem is that for some inexplicable reason, although the 2.5L and 4.0L are very VERY similar engines, you can replace the lifters in the 4-banger without removing the head, but on the 6-cylinder the head has to come off.

Don't use the syn/organic blend oils, it's a waste of money, don't even think for a minute that they do a 50/50 mix. If you ask the manufacturer they will tell you the blend ratio is 'proprietary', which means that it could be 1/99 or some other blend. If you want to run a blend add 3 quarts of Mobil-1 or Syntec and 3 quarts of organic, you will be ahead money wise.

Wow, I really appreciate all of the great advice you guys have! I'll definitely finish up a tune up as Rich has suggested. Where is a good place to get mopar parts? the dealer?
I've allready started to replace the fluids. You can flame me if you like , but I put z-max in the car and it seems to have fixed another problem in the tranny. Prior to it's application, the tranny would always shift at fixed speeds: 15, 30, 45 mph no matter how hard I would press the gas. It would never downshift if I mashed the gas either so I couldn't pass or go uphill. Since the application, it seems to be shifting extremely smooth and at the appropriate rpms based on how much gas I give it. It also downshifts to pass and climb. I am very pleased about that. Anyway, would this product be comparable to the christler top end cleaner you mentioned?

Another problem I solved was the sound the engine makes. A tired sound. Well, I started up the engine and put my ear to it only to realize it was louder towards the back near cyl 6. I checked the bolts on the exhast manifold there and it was very loose. Luckily it was a top bold and the engine noise is gone. The fumes I assumed were caused by the engine being tired are gone too. I'm thinking of replaceing the O2 sensor to see if the exhast leak was hurting performance. It's kind of strange what a sound can do to make you think your motor isn't running well. There are no abnormal sounds now and it feels like this motor is running very strong.

As for the timeing chain, AFAIK the jeep timeing chain is all metal/steel, not like a GM350 with nylon gears that wear out in 100K.

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I don't follow you about the AFAIK. Is that the type of chain it uses? I'm gathering that you're saying it's very durable.

In regards to doing a compression check. Assuming I find a problem, what are typical solutions to having poor compression?

Again, thank you all for all the great advise and help. It's nice to find a great group like this!

AFAIK. As far as I know.

Re: the compression test -- get the results, then look for solutions IF[/b[] there is a problem.

According to the 1988 Factory Service Manual (which you'll see us refer to as "FSM"), compression pressure should be 120 psi to 150 psi, with a maximum variation between cylinders of 30 psi. That doesn't mean necessarily the difference between adjacent cylinders, it just means your lowest cylinder should not be more than 30 psi below the highest reading.

Unless you have extremely low readings, consistency from one cylinder to the next is probably more important than raw numbers, especially with a high-mileage engine. If you have three cylinders at, say, 125, a couple at 115 and one at 110, I would not consider that you have a "problem," even though technically the lower three would be out of spec.

Do the test once. If all or several cylinders are below the minimum, run the test again but before teasting each cylinder squirt some oil in through the spark plug hole. If the oil causes an increase in compression, this suggests that the rings have a problem. If the oil doesn't make much difference, you may have leakage at the valves.

Be sure to use a compression tester that screws into the spark plug hole. The kind you just press in place (if the even make them) are difficult to use and not accurate because it's so tough to hold them without letting some leakage occur.

Do the test, then post your results.

Oops

Thanks Eagle for catching that on the lifters. Having done work on the 6 cyls I should have known better and always appreciate when others make sure I don't steer anyone the wrong way. My son has taken on the build-up of a 4.0 in his advanced auto class to drop into our '85 with the 2.8 so we need to keep it straight too!