ace4213

First off, let me tell you that I don't have a lot of automotive knowledge, but everything ive done to my vehicle up to the point has been learned from common sense, people who know what they are doing,and how to videos. I have a 2003 Jeep Grand Cherokee 2WD, with the 4.7L V8. One night, I was coming home from work and all of a sudden, I heard a loud belt squeak and the jeep started vibrating like crazy and the check engine light started flashing. I pulled over to the side of the road and the vehicle shut off. I could crank the car back up, but it ran really rough and the idle fluctuated and would eventually shut back off. While the vehicle is running, you can smell raw gas out of the exhaust so I know its running rich. Also, when test driving it, I noticed that a belt squeaks whenever i make a turn. The vehicle has never done this before I started having these issues. I was advised to replace all 4 O2 sensors, so I did. Still same issues. I took it to a Jeep dealership for them to diagnose the program. The issues they came back to me with were:

*The 1/1 O2 sensor connector pigtail(connector socket) wires were skinned and were shorting to each other. Connector needs to be replaced.

*All 4 O2 sensors needed to be replaced again.

*Needed all new spark plugs

*2 Coil Packs were bad.

I taped up the wires on the harness so they were no longer shorting out. I replaced all 8 of the spark plugs. They were all black so it means the engine is running rich on all cylinders. I also changed the two bad coil packs. I also only changed the 1/1 O2 sensor (The one that shorted out because of the bad pigtail.) No change. Still runs the same.

Here is a list of the codes from before and after the repairs I did.

Before:
P0031
P0113
P0353
P0051
P0113
P0355
P0138
P0131
P0132
P1499
P0523
P0136

After Repairs:
P1499
P0523
P0136

I trusted the dealership to help me diagnose the problem, and its cost me $250 and I'm still having the same problems. My dad and I are stumped about what it could be that's causing the engine to run rich. Because it all happened so suddenly, I wouldn't think it was a major mechanical break but I could be wrong. Any help is greatly appreciated.

Cherryokee

Ace4213, Welcome to CF!

Wow! This one sounds tough, but nice going so-far.

Remember that the tape solution may be only a temporary solution until you can nail the final fix.

How many miles are on the Jeep? Do you recall having ever seen or experienced any indications of erratic functions prior (but within recent history) to that grand event?

Pardon my random questions but I'm only on my first coffee...

My knee-jerk reaction to your description is one of a timing chain (that's why mileage is important to note).
How does the oil and antifreeze look. Any chance they've mixed?
Status of your electrical system, grounds, alternator and battery? (One bad ground, especially in the ECM, can send your systems all to hell and you down a troubleshooting rat-hole.)

You're doing well. It's admirable that you would delve into this with (admittedly) limited working knowledge. Get into the basics before you go too far throwing parts and extensive labor dollars into it. If you haven't got a Factory Service Manual then it's time to get one. Thanks to the guidance of a terrific forum member (tip o' the hat to Dave1123) I got mine on-line from Pacific Coast Manuals for $8.99 and I'm using it now. My manual is for a 2000 so may lack details for yours, but with it, I can see that many of your codes indicate or suggest output voltages are too high. When that happens in groups then it usually indicates loss of a ground - in this case possible loss of a sensor reference (ground) which is likely part of, or located within, the ECM.

Fred/N0AZZ

Hopefully Dave will address this as he is the expert on the WJ's as suggested get the FSM pdf. it will help you a lot.


I have an 04 WJ with the 4.7HO and I'm at a loss also but throwing parts at it only to replace them again becomes very costly. I have a Jeep dealership and service manager that I trust who still have people working that are true mechanics not just parts replacers. I take my WJ to them when I have an issue that I can't find or repair, in fact they have installed parts and removed them when they didn't fix the problem not many places do that any more just tell you it was needed.

dave1123

Okay guys. I know the 4.0 very well, but until the other day, I hadn't even touched a 4.7 (I put a finger on one's valve cover just to say I had!)

This is merely conjecture, but because this engine has 2 timing chains with stationary plastic tensioners, I'm thinking one tensioner is broken throwing the cams out if sync and creating havoc with the 02 sensor reading, resulting in the PCM trying to compensate mixtures, which isn't working.

I may be out in left field, but because it happened all of a sudden, this is what I think. The shorted 02 wiring wasn't helping either. These 02 sensors have 12v heaters in them and shorting that kind of voltage to the PCM is dangerous. The 02 signals are in the millivolt range.

I started thinking the harmonic balancer was sheared, but that wouldn't throw off the timing and mixtures. This problem is common with Ford Exploders! My buddy says "When your engine sounds like a bunch of dimes in a clothes drier, that's the harmonic balancer."

That's about all I've got. I hope it helps point you to places to look.

Just a short tutorial on the PCM. All sensors are 5v at the most and the 12v circuits controlled by the PCM are done by grounding them thru a digital driver. To be more specific, the fuel injectors and ignition coils are hot-wired with 12v constantly and the PCM controls them by making or breaking their grounds.

ace4213

First off, thanks for the reply guys.

Cherryokee:
The tape is definitely a temporary fix. I've got a replacement on order because none of my local auto parts stores seem to carry something like that. Also, my jeep has around 168,000 miles on it, and other than some front end stability issues, ive never had any engine issues before now. Oil was a little low when this happened but didn't look any out of the ordinary. All the electrical connections with the exception of the o2 sensor socket look good. No corrosion on the battery terminals either.

Dave:
My dad is an ex-mechanic but that was over 15 years ago, so his knowledge isn't up to date and he is also unable to do the work physically anymore. With that being said, he also was pondering the idea of the timing chain being the issue.

I know a guy that said he was having somewhat similar issues that he ended up fixing by replacing the Cam Position Sensor. He also said that it never caused an code to put up. They are $25 at my local auto parts store. Would it be worth it to replace this sensor?

dave1123

I'm going to warn you right now about aftermarket sensors. Nobody makes them with the quality and precision that Mopar does. I have had bad luck using anything but Mopar sensors. For instance, the Mopar crank sensor is built with a neodymium magnet and aftermarket ones aren't. With a hall-effect sensor, the magnetic field is important.

IDK enough about the 4.7 to know where the cam sensor is or how it functions to tell you it might be the cause. If it's only reading one cam, it may be involved.

ace4213

Ive got a friend who is a mechanic coming over sometime this week because he wants to do a compression test so I will consult with him and go from there. I will make sure to post what we find afterwards

dave1123

BTW, 4.7s are noted for sticking lash adjusters which cause the rockers to slide off the cams. A problem that's happening at the moment will cause the CEL to flash, like a misfire code.

ace4213

So ive found the problem. Upon pulling the valve cover off on the driver side, I noticed that 6 of the 8 rocker arms had come off. Upon closer inspection, I found out why. There are like 6 "Caps" that hold the cam shaft inplace to the cylinder head. On the last cap, closest to the firewall, one of the bolts sheared off. Every single other cap was either cracked or completely broken in half. Bottom line is, that the cam shaft and the entire cylinder head are completely trashed. The camshaft is scoured really bad where it was rubbing against the caps. Metal was scraped on the head and the camshaft. I can buy a 100% complete cylinder head with camshaft for about $400, but ive been told by a few people that putting a new head on an engine with 168k miles is a bad idea. I guess the next step is to start pricing junkyard motors. FML!!!!

Cleman Simpson

That sucks. It's been my experience over the years that often times you can buy an entire vehicle for what a good replacement engine cost, or very little more, and you get a whole lot of spare parts besides the engine. But then I got 11 acres to sit a couple of parts cars on without bothering nobody.

Fred/N0AZZ

There is a shop in Tulsa, OK. that sells Jeep and other Chrysler rebuilt engines have saw then on craigslist. The 4.7 sells for $2175 with a good core the 4.7HO for a bit more. They have a warranty and a local got a 4.0 from them several yrs. ago in fact he trailered his Jeep to them and they did the swap even, he has drove it about 30,000 mi. no problems about all I know.