munyanb

I just got a jeep that has a 4.0 in it. It makes a horrible knocking sound that comes and goes a little , it is definitely not running on all cylinders, the guy I just got it from thinks it is a lifter, but I don't think a lifter could be so loud. It seems like it comes from the front, but the guy says he removed the belt and it still does it. He also says he removed the pan and found no bad main bearings, he said he changed the oil and didn't find any metal shavings, he says he removed the valve cover and no loose rockers were found. I know I have to check it out myself but he swears it is not a rod or any major part. I was thinking the timing chain but it runs so rough I don't know. Now I'm asking to see if anyone has run across these symptoms before. It really sounds like a wobbling fan scraping and banging, but since he removed the belt I don't think that could be it. And the terrible miss.

munyanb

I know im going to have to dig into it, I was just wondering if I could get a head start with someone that's had a similar issue. Is there a sticky or post on here about common 4.0 problems?

dave1123

Pull and inspect the spark plugs. That should tell you a lot about weither you have a cracked piston, bad rings or whatever, and which cylinder(s) it's in. It sounds to me like a cracked piston.

munyanb

yes I thought of that, I would love for that to be the problem. I was also thinking timing chain, but the miss is so bad that it shouldn't run at all if the chain were making so much noise. I can change a piston from the bottom right? Oh I saw on here a post where a guy put a supercharger on a jeep 4.0 that was bored and stroked to a 4.6 , and being that this is a 2wd in pretty good condition how do you guys think this vehicle would do as a street dragster? And I still think I could somehow rig a homemade supercharger , not to get boost so much as just decrease vacuum which would increase flow. By the way I now own three jeeps just picked up a 96 in really good shape with a rough country 3" lift and good 31's but it has a 5.2 that is said to be blown up. You will see me on here a lot hopefully, if I get time to do something with these jeeps. I'm skeptical of that lift though because the springs seem to have a bend and only the bottom control arms are aftermarket. I will be on here hopefully with pics , and results and 2 jeeps for sale lol

Bustedback

Check the flex plate/torque converter bolts before tearing the engine apart.

munyanb

The noise seems to be coming from the front top. Now im seeing the radiator has stop leak or something in it, it gets really hot before the water begins to circulate, like 210. So I pulled the plug rail off and turned it over just to listen for it turning over funny. it seems to turn over in uniform believe it or not. But amazingly it tried to start with the plugs all unhooked. perhaps extremely hot? I hooked up my code reader also , it say governor pressure sensor voltage low. What is the governor? I feel stupid but I haven't ran into that just yet

munyanb

this thing is leaking badly from the valve cover I assume. its kinda hard to tell lol

munyanb

So far I pulled the first three plugs, all three were black , they are bosch R3 plugs with an electrode in center and 4 grounds. the electrodes are white. they are covered in carbon but it looks like they were firing and running the same. This noise almost seems to go away at times but not quite. it's dark now so ill get back to it tomorrow.

munyanb

I wonder if the miss and noise are unrelated? tomorrow I will do a compression test , but it really seems like it has uniform compression from listening to it but it did sound like it was firing with no plug wires attached. this is wierd

munyanb

oil remains clean, no oil in water that I can tell, no blow by coming from the valve cover, oil pressure is correct, I guess I check compression tomorrow. it just sounds way to loud to be a lifter. but it does get louder and quieter almost going away sometimes. From further away it sounds like a main getting ready to throw a rod but it seems to be in the top.

munyanb

I will check the flex plate as well even though it doesn't sound like it's coming from there, but the timing sensor on this is coming from where a distributor would normally be. it's been awhile since I got into a 4.0, come to think of it they used to have CPS's on the bell housing, and a distributor? Even the late 80's had the CPS on the bell housing if I remember right.

Bustedback

There is still a crank sensor.

munyanb

so a loose flex plate could cause a miss. I will check it but I really don't think the noise is coming from the rear. I know sounds can be "pitched " and fool you sometimes though.

munyanb

So I looked up the code and it is a tranny pressure sensor. P 1764 governor pressure sensor voltage to low. would this make an engine run badly? I think its unrelated.

Bustedback

No, it may cause shifting issues though.