Strange and horrible sounding '87 Renix 4.0 I6

[matt0106]

Hey all. Thanks for reading.

I'm having a really hard time figuring what my 4.0 is doing. It sounds really horrible when it's running. Almost as if it's not running on all cylinders/misfiring. 1987 Cherokee Laredo, Auto, 4.0 I6, lifted.
Recently changed spark plugs and oil. Also checked fuel injectors, all are working properly.
I made a YouTube video to give y'all an idea of the sound.
http://youtu.be/fnZMIlqwgVI

[matt0106]

Anyone? No ideas?

[4.3LXJ]

Kinda hard to tell, but sounds like typical 4.0 high mileage lifters to me

[matt0106]

Well, whenever I start my jeep when it's cold, it won't run for more than a minute. It'll run for about 30-40 seconds, then it'll just sputter out and die. I'm thinking it's got something to do with fuel/spark.

[Brasscatz]

Well the sputter and dying could be your fuel pressure regulator. How's the idle on it normally? Constant bad idle is most likely your IAC valve

Sent from my Samsung Galaxy S4 because my microwave couldn't do it

[4.3LXJ]

I vote IAC too. Clean it and see what happens. Won't cost you anything hardly

[matt0106]

Cleaned it and the throttle body like 2.5-3 months back.

[XJ Wheeler]

Hmmm, it does sound like its not happy. It does sound a bit like a misfire. I would check the fuel pressure and do a compression test just to be sure.

[ParadiseXJ]

Some questions:

What did it sound like before you changed plugs
Did you change plug WIRES too? Cap? and if so,what kind of cap, brass contacts or aluminum? Rotor?
What kind of plugs? Fancy platinum quad contacts or regular old copper plugs .35 gap

Have you tested the spark coming from the coil? Snappy & blue...or just kind of half a$$ yellow?

How's the oil pressure?

How do all your grounds look, greasy or shiny?

[matt0106]

It didn't really sound like it does now, it was just typical 4.0 sounds

No, didn't change wires, cap, or rotor. I'm going to change those whenever I get the chance. Plugs are regular old champion coppers set as close to .35 as possible.

I tested the spark coming off of one of the plug wires, it wasn't blue or snappy, kinda slow and, yeah, an off yellow.

Oil pressure I'm not so positive on, the gauge always reads over half of it, so I think that's 40 psi or more, all the time.

I refreshed my grounds , so they should be good. They aren't the stupid flimsy crap that it came with.

[ParadiseXJ]

The weakish yellowish spark could be caused by a few things.

A weak or poorly connected/grounded ICM
The ICM itself
The sensor ground in the harness.
Plug wires/Rotor etc.

[matt0106]

Could it also be a bad coil? And, this sensor ground in the harness that you speak of, where is it?

[matt0106]

Hmmm, it does sound like its not happy. It does sound a bit like a misfire. I would check the fuel pressure and do a compression test just to be sure.

Ok, so, I did this "http://www.xjtalk.com/showthread.php?t=13190," and it is always close to 40psi+/-1.
I will borrow a compression tester and do that too.

[matt0106]

Ok. So I went and got my battery checked, just so I could rule it out, it wasn't it.
Tested the spark coming from the coil, it's not "blue and snappy," it's "sluggish and yellow."
Cleaned up the contacts on the coil and ICM, didn't change anything.

Oh, forgot to mention, it starts but won't run for more than a minute.

[matt0106]

I'm going to test the coil and ICM to see if they're good or not. Then I think, the fuel pressure regulator and vacuum lines are next to be checked.

All that sound good to ANYONE on the forum?

[4.3LXJ]

I was thinking you should check the fuel pressure too. Do you have a gauge?

[matt0106]

Ok, so, I did this "http://www.xjtalk.com/showthread.php?t=13190," and it is always close to 40psi+/-1.
I will borrow a compression tester and do that too.

I did the permanent fuel pressure gauge mentioned in this, while it's running it says about 40psi+/-1 or 2, when the key is just in the on position, not running, about 35psi+/-1.

[4.3LXJ]

If it stays at 40 psi, then you don't need to check the regulator. It is fine

[matt0106]

Ok. So what else could be causing my jeep to start but not run for very long? The only things I can think of are related to fuel and spark.

My step dad mentioned an intake manifold leak. Is that possible?

[4.3LXJ]

Get that O2 sensor nailed down yet. If you put one in out of a non running vehicle, I would be suspect of that. Here is how it works. The first few minutes the computer provides a rich mixture. Once the heated O2 sensor is supposedly heated up, then it begins relying on that. It it is not working, then it will not run.

[matt0106]

No, I don't think anyone mentioned checking the O2 sensor. The current one in there is probably pretty old, so it could be bad. Would an exhaust leak cause one to go bad quicker?

[4.3LXJ]

No, but typically it will cause the mixture to become too rich from fresh air getting sucked into the exhaust

[matt0106]

Ok. Is there a way to test the O2 sensor? Or do I just have to flat out replace it?

And I was thinking, that maybe background info as to how this may have happened, might help people understand what's wrong.

[4.3LXJ]

If it hasn't been replaced in a long time, replace it. They wear out and the sensing function cannot be tested

[matt0106]

Ok. Is there a brand I should stay away from? Where should I get it?

Also, thank you for helping me out. The Cherokee veterans over at Cherokee forum are giving me crap for asking suggestions.

[4.3LXJ]

OEM I think is probably the best. I have had good luck with Bosch, but others haven't.

[matt0106]

So if I got a Bosch one at AutoZone, I could return it if I need to?

[4.3LXJ]

I don't think you can do that once installed. Besides, you need to put antisieze on the treads that should come with it. I understand the cost issue, but they really need to be changed every 50K anyway to maintain your fuel economy

[matt0106]

Ok. Because I never replaced it and it can't hurt to replace it. Thanks.

[XJ Wheeler]

A suggestion... I just searched around for my O2 sensor and found Rock Auto to be the cheapest. No, you can't walk in to return/warranty it but the warranties suck anyways and the savings made up for it in my opinion.

[matt0106]

A suggestion... I just searched around for my O2 sensor and found Rock Auto to be the cheapest. No, you can't walk in to return/warranty it but the warranties suck anyways and the savings made up for it in my opinion.

The only reason I'd get it somewhere local is the not waiting for shipping part.

[ParadiseXJ]

Look through this post by Cruiser54 on ComancheClub.com. Some very good tips for the Renix years. It should address the slow, weak spark issue as well as alot of other cheap, easy diagnostic stuff.

http://comancheclub.com/topic/43770-88-no-start-after-engine-swap/

Scroll down to post #5 and click on the link to "Cruisers Renix Tips"

The O2 sensor issue MIGHT cause it to run rough (or just lean/rich). You've already looked at the fuel pressure. Most of the information in the link concerns electrical issues, which are many, and by following them you can rule out ALOT of gremlins. Especially the sensor grounds, TPS adjustment, CPS modification(s) and throttle issues.

The start up and then dies immediately issue is most likely something to do with ballast resistor, slow spark is likely CPS related since you've cleaned and checked your coil, ICM etc.

Give it a look. You'll learn alot. I know I did. My MJ runs like butter now and has more power and uses less gas than ever before.

[XJ Wheeler]

The only reason I'd get it somewhere local is the not waiting for shipping part.

True. Many times I have done the same.

[matt0106]

I checked to see if mine had a fuel pump ballast resistor, it doesn't. Nor do I see wires where one might have been.

[matt0106]

I think I found my problem.

http://i493.photobucket.com/albums/rr299/matt0108/Mobile%20Uploads/image1.jpg (http://s493.photobucket.com/user/matt0108/media/Mobile%20Uploads/image1.jpg.html)

http://i493.photobucket.com/albums/rr299/matt0108/Mobile%20Uploads/image1-2.jpg (http://s493.photobucket.com/user/matt0108/media/Mobile%20Uploads/image1-2.jpg.html)

http://i493.photobucket.com/albums/rr299/matt0108/Mobile%20Uploads/image1-1.jpg (http://s493.photobucket.com/user/matt0108/media/Mobile%20Uploads/image1-1.jpg.html)

[matt0106]

Ok, so replacing the CPS didn't help at all. It's still doing the same thing. The first thing I'm going to do next is a compression test. I know that's really the first thing I should've done, but I was hoping that it was something small and easy. I noticed something today while I had it running, for the short time it will actually run, there was what I am assuming smoke coming from the crankcase, the oil filler hole to be more precise.

[matt0106]

Also, while it runs for the very short amount of time, it's making weird noises the whole time.

[matt0106]

Thank the lord in the heavens above. I got it running.

I took off the exhaust from where the cat connects back, and I started it and it ran fine. The cat melted and was causing a huge exhaust restriction.http://i493.photobucket.com/albums/rr299/matt0108/Mobile%20Uploads/image1-3.jpg (http://s493.photobucket.com/user/matt0108/media/Mobile%20Uploads/image1-3.jpg.html)
That's a piece out of the cat.
So now I'm going to go cat-less because I don't have emissions testing on it anymore. Thanks for all the help everybody. Y'all are great.

[XJ Wheeler]

Thank the lord in the heavens above. I got it running.

I took off the exhaust from where the cat connects back, and I started it and it ran fine. The cat melted and was causing a huge exhaust restriction.http://i493.photobucket.com/albums/rr299/matt0108/Mobile%20Uploads/image1-3.jpg (http://s493.photobucket.com/user/matt0108/media/Mobile%20Uploads/image1-3.jpg.html)
That's a piece out of the cat.
So now I'm going to go cat-less because I don't have emissions testing on it anymore. Thanks for all the help everybody. Y'all are great.

Glad you got it fixed up! We've had a plugged cat before, not fun!