Need serious oppinion about engine problem

Hi everybody! I'm from Argentina, and a proud owner of a 1991 Cherokee Limited. I've recently had problems with the Jeep with no possible answers,and I really need one.
We have been experiencing great loss of power driving at 120 kph (the engine dies with no reason and comes working again as nothing had happened).The problem was in an obstructed catalytic converter and an old fuel pump, but not for too long. A couple of months later I saw smoke coming out of the exhaust in a small amount, we checked for it but there was not evident failures (maybe the pistons rings). We made a 1000k trip and when we returned, the smoke was gone for 3 months. The last time it came out, it was serious. Huge amunts of dense smoke formed a cloud arround the Jeep. Again, no failures, even NO oil consumption. We checked again the fuel delivery system, the valve cover and the pressure inside the block(that was a bit under the specs), the brake booster, the transmission and cooling system, and every possible fluid that could get into the combustion chamber. And again, the loss of power came into scene. This problem is getting me crazy, so I was told about the site, and desperately I'm here looking for an answer! I hope anybody can give me a clue, I'll be really thanked. 'Til the, greetings from Argentina!

If I understand correctly, you did a compression test of the cylinders. Can you post the numbers for each cylinder? If you are getting engine coolant into the cylinders, the most common failure is a head gasket. The compression numbers are normally a good indicator. In most cases a single cylinder will have reduced numbers.

Pulling the sparkplugs and examining them can yield a large amount of information. Can you pull them and post some pictures? This will be the single best troubleshooting info you can provide.

If you are burning antifreeze, you will normally find a thin oily film on the rear hatch window. Smelling the exhaust can answer a lot of questions if you have a trained nose. If the smell is somewhat sweet, it is most likely antifreeze.

Also, please post the year and engine size.

If it was black smoke coming out of the tailpipe then I would guess a bad O2 sensor. If it was white smoke, I would guess oil getting into the intake due to a bad crankcase vent, or the vac booster sucking brake fluid due to a bad master cylinder. How are the brakes?

Thanks for the quick reply old_man!
Sadly I don't kept the numbers of the test, but about a month I'm getting a new one (i hope so). But as far as I know, we didn't find "compression" in the cooling system. There is, beside, a little amount of coolant missing in the bottle so I will check it again and have it seen also. I will try to post some pictures of each single sparkplug. And, before I forget it, the smoke is not white, but a bit grey, and I don't if smells sweet, what I can say abou it is that you can feel the smell it strong in your throat, leaving your hands like if you just touched something covered with oil (but it is not burning it). Finally, it is a 1991 Cherokee with the 4.0L H.O. I6 (not the one of the Renix) with an AW4 and NP242 transfer case -w/o A.B.S.-.
I'll try to post some pictures of the engine bay and the points I consider problematic.
Thank you very much, you have been of GREAT help and I look forward to your answer!

Well, jeeperjohn, there was an error code, i don't remeber it so much-the 52 or 42- that was O2 sensor stuck in "rich mixture" for more than x seconds. I will look again to the crankcase vent. About the brakes, we experienced big problems: the front part of the reseirvor was continuously empty, and there was no clues where the brake fluid went as the vacuum hoose was completely dry. The problem was a bent cover, but there is no reason why the only part of the reseirvor that lost brake fluid was the front one, so we are checking it every 15 days after the repair. But I'll keep it in mind and check it also. Thank you very much! I'll be waiting for your reply!

Bzamora, I'll have thar sensors checked as soon as possible. Thanks for your reply!

JeepArg. said:

Well, jeeperjohn, there was an error code, i don't remeber it so much-the 52 or 42- that was O2 sensor stuck in "rich mixture" for more than x seconds. I will look again to the crankcase vent. About the brakes, we experienced big problems: the front part of the reseirvor was continuously empty, and there was no clues where the brake fluid went as the vacuum hoose was completely dry. The problem was a bent cover, but there is no reason why the only part of the reseirvor that lost brake fluid was the front one, so we are checking it every 15 days after the repair. But I'll keep it in mind and check it also. Thank you very much! I'll be waiting for your reply!

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I would replace the O2 sensor and still check the master cylinder for leaks at the piston seals. The air flowing through the hose as it sucks vaccum into the manifold could dry out the brake fluid from the hose. It may only get brake fluid when enough of it builds up in the booster to get sucked into the vaccum hose. This would also account for the intermittant nature of the problem. Also the way the smoke hurts your throat tells me it could be brake fluid.

We extensively tested the booster, and there was no problem with it, but, there was a small leak on the seal between the master cylinder and the booster. Beside this, all the seals were replaced and the master cylinder was checked for proper functioning. We are still awaiting for the smoke to come back as I made the same 1000k trip 3 weeks ago and it dissapeared. I will have the O2 sensor replaced and "I make you a call". Thanks.

JeepArg. said:

We extensively tested the booster, and there was no problem with it, but, there was a small leak on the seal between the master cylinder and the booster. Beside this, all the seals were replaced and the master cylinder was checked for proper functioning. We are still awaiting for the smoke to come back as I made the same 1000k trip 3 weeks ago and it dissapeared. I will have the O2 sensor replaced and "I make you a call". Thanks.

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I've never heard of brake fluid getting sucked into the brake booster vacuum line before. Isn't their a barrier between the two systems so that brake fluid leaks externally onto the outside of the brake booster if the master cylinder seals go bad?

It would explain some issues I had a while back, but seems like it would take an external brake booster diaphram seal leak and a master cylinder seal leak at the same time, which would be obvious by the sound of the external vacuum leak, and would also cause a high idle.

If brake fluid did get into the intake the silicone in the brake fluid mean instant death for the O2 sensors.

I was thinking his problem sounded like a stuck open fuel injector that later starter working again. But it would smell like unburned gas.

You've got an AW-4. An overfull or very warm transmission will vent itself, usually right onto the exhaust. This causes big plumes of smoke and can lead to a fire under the right (wrong?) circumstances. You'll find that as a nice oily film on the rear hatch as well - if you've got a white Jeep like mine you'll notice it has a slightly pink tint to it.

Jim www.yuccaman.com

JeepArg. said:

About the brakes, we experienced big problems: the front part of the reseirvor was continuously empty, and there was no clues where the brake fluid went as the vacuum hoose was completely dry. The problem was a bent cover, but there is no reason why the only part of the reseirvor that lost brake fluid was the front one

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Check the wheel cylinders on the rear axle, and make sure they aren't leaking.

Hey guys, just thought id chime in on this one since I just had the same thing happen to my jeep you can find the thread under MY XJ DECIDED TO TAKE A DUMP ON ME, well anyway this is exactly what was going on with mine, drove me and my wife nuts! turned out to be a screwy upstream o2 sensor. hope this helps

Thank you all for the information! I'll update everything concerning the test in about 3 or 4 weeks, when I get figures, pictures and more opppinions. I'm running a cylinder compression test and I think that the fumes smells like burning too much fuel.
I've went to the Jeep Service and they told me it was a piston ring problem and the engine should be rebuilt, but, as I know they only want to get it replace it I searched for more answers to the problem. They said that the O2 sensor was useless and that the SBEC (ECU) was running in an emergency mode so the M.A.T. sensor was the responsible of the injector cut (no signal to them) as the temperature in the intake raised a lot out of the chart. But, as I said, many mechanics told me it could be a part of the problem, but a hole new engine would not be a solution. By the way, I'm avoiding that idea because I need about 20000$ Argentine Pesos (about 6000US$) for the parts needed.
I'm going to get it done and tested in my uncle's garage the next month so, if any more ideas comes up, I'll be pleased to hear them. So wait for a month to get pictures and info of the tests and disassembly of part odf the engine.
Thank you all very much!

Don't waste time and money on the fuel pump. The black carbon in the exhuast is a sign that it is running rich, meaning the O2 sensor is probably bad. These engines run very ruch, wasting gas if the O2 senosr is not working properly. The O2 sensor is not useless! With out the O2 sensor (a working one) the engine uses twice as much gas. Ask me how I know?

If it is running OK right now, I would leave it alone and blame it on a temporarily stuck fuel injector, or maybe a batch of poor quality contaminated gas, or the transmission fluid leak suggested by others.

The mechanical parts of engines do not intermitently blow smoke, they either work right or they don't, in other words they don't fix themselves. Fuel injectors can get stuck, and then get unstuck as some trash lodges and then unlodges in the tip. A stuck fuel injector would cause smoke until it unstuck itself, which can happen.

JeepArg. said:

I was forgetting it, about a month or so, we rebuilt the brake system and we replaced all seals and a cylinder of the rear axle and checked the other and the calipers for porpper functioning. Also I noticed like carbon building up near the exhaust pipe and I was told this was caused by excess of fuel burning in the combustion chamber so, again, in a month, I'm getting the fuel system out for service (including pump, injectors, O-rings, etc.) as well as the brake system again. Bye!

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Hi everybody again! I've been abscent for a while, but I bring new info and news. Well, to begin with, I fixed the brake problem, it was a simple O-ring when I realised what was I couldn't believe how much trouble a tiny part could cause. Well, leaving the brakes apart, there's more info about the engine. I finally recognised the exhaust smell: excess of fuel. A guy with an older XJ told me he had the same problem, it was a stuck injector. So, I'm getting the fuel rail taken out for service.
Well, I've also got the faults from the SBEC II, there're 2 errors, both of the 02 sensor, so again, I'm getting it replaced next week I hope.
All this leaves me with a doubt: what about the smoke? Well I've measured the oil since the oil change and it has lowered about 3-4mm from the full (safe) position. I'think this is not caused by ebgine oil consumption as the Jeep service said. There're two possible explanations that I'll show with pictures: a broken vacuum hose, and the old seals (just common wear leaks).

Well, as I'm new, I'm a bit scared to ask this but, can anybody tell me how can I show the pics so I can share them with you please?THANKS!

There are several free internet web sites that allow you to post pictures in your own archive for free. Then you can post the link to the photos on that web site in a post here.

I am currently using http://my.imageshack.us/
There are others you could locate by searching google

The oil may have been diluted, thinned out by the excess gas causing the oil/gas mix to leak past the piston rings where it go burned. If it got thinned enough it would increase oil burning and any leaks would leak faster.

So, here are the photos! By the way, thank you very much Ecomike!
Well, the first 2 photos show what is supposed to be a leaking injector (#3), but I think it's oil coming from the seal that had found the way to get there as you can see it all around the valve cover in the engine bay photo.



The next photos shows the leaks of the top seals and the rear main seal-I guess-. One from the valve cover seal, leaking over the thermostat hausing, and the other over the spark plugs.



Well, this might have been the main responsible of the smoke problem: I noticed the stain, still wet, while changing the engine coolant. It came from a cracked CCV hose(the one carrying vapors to the intake manifold), and the vacuum port was covered with oil, still dropping out of the hose. So, I realise what you lately adviced about the CCV system, and the following pictures show the leaking, and the CCV system inlets.



Well, I hope this gives you an idea or details of the situation. I'm concerned the engine is "dirty" but, believe it or not, this working jeep's engine bay was never cleaned since import, and it looks worse in the photos than you may think. JAJAJAJAJA. Thanks again all you guys! Hope, more ideas comes to you!