TheatreJunkie

Just bought a 92 cherokee 4.0 for $700 and am super happy with it. It's got a lot of problems and is in dire need of some tlc, which it is now receiving, but over all it's a super fun vehicle to drive and will make a fantastic beater up off roader after a few months as a daily driverd, but first I need to get her registered and inspected. After repairs to tail lights, horn, cooling fan, tire, brake bleeding, replacing the bypassed NSS, oil change, and a radiator flush I've finally gotten her to stay on the dyno for long enough to get through a test without overheating! But she failed emissions. Here are the results...
High speed (25mph) Low speed (15mph)
Standard/Current Standard/Current
HC(PPM) 159/128 163/119
CO(%) 1.78/0.66 1.38/0.67
NOx(ppm) 1014/1613 1110/1498
DILUTION(&) <6 14.5 <6 14.5

Gas cap integrity: FAIL

Based on a whim I pulled off my airbox and checked the Intake manifold. Through the throttle body I can see an unhealthy coat of oil all over the inside of my intake manifold. I also pulled the front two spark plugs. I didn't measure the gap on either, however it was noticeably very different between the two. Not good. Those will hopefully be replaced tomorrow morning. I also saw black build up inside the front cylinder (cylinder #1 I think?) My oil pressure runs low at maybe 5 psi at a hot idle. I'm still getting oil flow though as I can see it in the valve cover through the oil fill cap with the engine running. Upon start up it appears to be burning oil too. The smoke is more white in color which I believe indicates coolant, but it doesn't smell sweet at all. I think higher NOx is a hotter burning combustion, but since fixing the cooling fan and flushing the radiator it holds steady right at the top of the temp gauge. And that's about all the info I can think of at the time. Hopefully someone can advise me on what's going on so I can really start using her as the daily driver I bought her for.

Bustedback

Run some Seafoam, or combustion chamber cleaner through the engine and make sure you have a good working cooling system with a 50/50 mix. NOX is caused by high combustion chamber temperatures.

TheatreJunkie

I'll use Sea foam soon, but I also want to address the issue. Without knowing how the oil is getting inside the intake manifold won't it just gunk up again?

mschi772

Seafoam might address the issue. Carbon buildup in the cylinders can raise temps too high resulting in NOx production.

NOx is also cleaned-up in the cat. You might need a new one.

Oil in the intake might just be blow-by from the PCV. There are homemade blow-by collectors you can make to put between the PCV and your intake.

XJGHZ7ST

Alos make sure your timing is right. Maybe your not firing when your supposed tooooooooo

XJGHZ7ST

Also oil pressure low , change that pump.

Bustedback

Stop giving bad advice. Pumps don't make pressure, restrictions in the oil flow path (bearings and lifters) make pressure.

TheatreJunkie

I do understand that, which is why I stated that I am still getting flow, just not pressure. Thanks for looking out for bad advise!

Bobolink

All right, you two...how do you know you have ADEQUATE flow? That is also required for sufficient pressure. Bearing wear is not the ONLY cause of low oil pressure. There are any number of causes. A pump that has too much wear will not build adequate pressure even in a brand new engine in which all other specs are perfect. A pump makes pressure when pushing against restriction. All the restriction in the world will not cause pressure unless something is trying to push something through it. So quit with the semantics game. It's not bad advice.

Bustedback

Changing the oil pump because of low oil pressure is not good advice. Verify the cause and fix it the right way, don't just replace parts just because.

Bobolink

My point is that it's not bad advice to consider the pump; incomplete, perhaps, but no more incompelete than your advice to pull the head and replace the lifters of drop the pan and change the mains and/or rod bearings. In that light your advice is just as bad.

Bustedback

Where did I say to pull the head and replace the lifters, or replace the bearings? I simply said those are two things that can cause low oil pressure. End of argument.

Bobolink

Even the consideration of wear of the oil pump was bad advice, by your words. The truth is, all these things need to be pursued if you have a problem with low oil pressure. Every time someone on this forum mentions the words "oil pump" in the same post as "low oil pressure" you try to start a monkey dance by implying that they are lying, or are stupid. End of argument.

Bustedback

Just let it go!

Bobolink

Agreed, and done.