1996 JGC Weak Valve Springs

[hoofan]

Guys,

4.0, V6 1996 JGC

I have been fighting this Mult Random Cyl Misfire problem for months now and the Jeep mechanic that I know has said that the only thing left is to replace the valve springs. He said he normally sees this in 96-98 JGC's within 30-50K and mine is about 110K. Each time he has done this as well, the Jeeps do not come back in again.

I have done everything else that would be obvious regarding ignition and sensors are concerned and it is only throwing out misfire codes at random that bounce all around to each cylinder. No pattern.

Does anyone have any experience with this? I do trust this guy, he has helped both my brother and me before (both own JGC's) but I don't want to throw 300+ at it if it is a shot in the dark.

I originally thought that the new CPS I got back in December might be bad again, but he (my Jeep guy) said he doubts that is the problem at all and a full scan of the PCM showed no hints of the CPS having any issues.

Thanks for the help.

Bryan

[JDPascal]

Are the misfire's at idle, acceleration or cruising speed??

Valve springs would not be a common cause with a stock vehicle in any case but especially at idle. Acceleration and cruise conditions might be affected especially if the valves are carboned up under the valve head next to the guide....

Check the injector connections. Sometimes the contacts corrode up (you can't even see it) and a cleaning and sealing with a dielectric grease will help.

Just some random thot's.

JD

[hoofan]

The misfires occur on accel, decel from dead stops or slow speeds and cruising speed at as much as 70mph on the highway. Barely noticable at low, flat crusing speeds of 25-45 mph around town, especially when you don't have to "get" on the gas at all.

The explanation I got today was that they basically the valave springs in "some" of the 96-98 JGC's get weak (not often common, but he has done 30 or so of these in the past) and that of course doesn't allow them to open fully and results in a random misfire.

When he took it out for a drive today, it was on a steep grade up and a steep grade down really getting on the gas where he saw them all take place.
He ran it with the scanner hooked up and watched the misfires go from zero at idle to multiple across Cyl 2, 4-6 (on this particular trip) and then back to zero again at idle.

That's the skinny anyway......

Bryan

[JDPascal]

Well...... ...... this sounds like he is saying it is a valve sealing problem. The purpose of the springs is to close the valves. Normally valve springs cause a problem at high revs (valve float) but combined with valve head and maybe seat deposits this might be something to consider as a solution.

Does your mechanic plan on removing the head for a complete cleaning or quick spring swap?? For $300, it sounds more like a straight spring swap is what he is going on about.

Let us know how it turns out....

JD

[xj31]

There is actually a bulletin about this,# 18-22-98.it involves decarbonizing the combustion chambers and replacing the valve springs.Its surprising yours went this long before it acted up.

[hoofan]

Soem things that really keep running across my mind here.

Since I am really down to 2 things for this problem IMO: New CPS being a bad or intermittment bad part and the weak valve springs (Short history is that my Jeep was running like a top until I had the CPS replaced because it was shutting me down back in December).

The valve spring thing still seems odd to me, even though I trust this guy. I mean, would I be able to detect misfires by watching the TAC and would the vavle springs really cause great fluctuations in the TAC? Would the valve springs not closing properly cause the Jeep to "buck" really hard on an incline from time to time? My inclination is that the valve spring issue causing a misfire would be pretty subtle and hard to detect by "feel".

Regarding the CPS. Let's just say it was "acting up" and not shutting down the vehicle, similar to some of the causes expressed in thread at the top of the page. Couldn't it starve the engine of fuel or "fool" the computer without actually setting a fault code? Would a quirky CPS register any irregularities in the computer when scanned (not code-wise, but other indications) that would show that the part is not operating effectively?

I guess what I am getting at here is that it is MUCH cheaper for me to throw another CPS on here and give that a shot then to do the valve springs. My GUT has always been that the CPS was either not a good part when I had it changed in December OR it was not installed properly at my regular mechanic's shop.

It seems highly unlikely to me that having not had ANY misfire problems until I had the new CPS put on is suddenly a valve problem at 110K miles.

Anybody got any thoughts or suggestions and what is more realible if I try a new CPS, MOPAR, Echlin or another preference??

Thanks for the help!!!

Bryan

[rksnc]

The most common problems is valves. This is a fat fuel system. Decarbonize may help but most of time valve job is the fix. I could not believe it myself until I made the repair. Every test I would run seems just fine. But misfire come and go, and would see 1 or 2 cylinders that show more than others but always random.

[hoofan]

Thank you. That's good info to know.

Now I have to decide whether I want to do the valves or just upgrade to a later model Jeep anyway. I have been considering that for a few months.

If I can get a guy to do it on the side for less than 300, I might go ahead and do it anyway. The stealership is going to want 500. I am just afraid that I might do it and the problem will still be there. I'm thinking I might rather throw the 300-500 at another Jeep.

Who knows???

Thanks for all the input though. If anyone else has any ideas, please let me know.

Bryan

[hoofan]

Guys,

I just finally put 2 and 2 together on this one and now it is beginning to make sense. I got this from the thumbnail at the top of the page and I have read it before, but I thought I would go through them again. This is EXACTLY my symptoms and after looking at my Haynes Manual a little closer, I can now see that this very well may be the cause of my problem after all.

(Copied from above)

The jeep shake or shudder, misfire may occur when the vehicle is operated between 50 - 70 MPH

I tried 2 jeep dealers and they could not fix this, one said it was the coil, replaced it no help, and tune up, injectors cleaned too no help. The other on said it was the torque converter and pump it was under warranty, no help. So I think they just want to sell you something or they don’t know any more then we do, or maybe they throw the service bulletins away. So I did some research on the internet and this is what I found the trouble. So far
I have paid a lot of money at the dealers.

Late closure of an exhaust valve may be the result of no valve rotation and associated build up of carbon on the exhaust valve stem.

So I bought a 16 oz. bottle of Marvel Mystery Oil, put half in the gas tank and the other half in the oil. No more jeep shake or shudder or misfires.

By the way the $500 at the dealer for decarburizing



4.0L MULTIPLE CYLINDER MISFIRE
Date: 08/01/03
Model Year(s): 1999-2004

Description: NOTE: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 4.0L ENGINE. This bulletin involves inspection of all engine exhaust valves and a decarbonizing procedure if necessary.

Details: The customer may experience an incident of engine misfire during certain vehicle operating conditions. The misfire may occur when the vehicle is operated between 50 - 70 MPH and under light loading conditions, e.g. slight uphill road grades. This condition may occur at all ambient conditions, but is more noticeable when ambient conditions are less than 0 C (32 F).

If the vehicle is equipped with On-Board Diagnostic (OBD), a MIL illumination may also have occurred due to Diagnostic Trouble Code (DTC) P0300 - Multiple Cylinder Misfire. Various single cylinder misfire DTC?s may also be present. If the frequency of misfire is high the Powertrain Control Module (PCM) may place the engine in ?Limp-In? mode.

The misfire condition may be caused by one or more engine exhaust valves that are slow to close. Late closure of an exhaust valve may be the result of no valve rotation and associated build up of carbon on the exhaust valve stem.

This condition may occur when the engine is not allowed to run at engine RPM?s that are greater than 3,200 RPM. At 3,200 RPM or higher the engine exhaust valves will rotate if not impeded by high carbon deposits. Low engine RPM?s and high carbon deposits are associated with short trip driving where the vehicle engine is not allowed to fully warm to normal engine operating temperatures. Cold ambient temperatures will increase engine warm-up time and add to the opportunity of carbon deposit build-up on the stem of the engine exhaust valve.

[Caribbean ZJ]

NIce Research. How much a Qrt for the Marvel oil?

[hoofan]

I am not going to use the MM Oil.

I just see that this points directly to what my mechanic and I have been discussing for a few months. Even though the model years are listed as 99-04, there still appears to be some history of this with the 96-98 JGC 4.0L as well.

I'll pass along the results when I have them. I'm hoping to get the valve springs doen next weekend.

Bryan

[xj31]

it sounds like you are on the right track.The bulletin you quoted is for newer models,the one I mentioned does say to replace the springs also.I tried to paste it in but couldn't get it to work.I'll give it another try
NO: 18-22-98
SUBJECT: OBD II Misfire Monitor
DATE: Jun. 12, 1998
THIS BULLETIN SUPERSEDES TECHNICAL SERVICE BULLETIN 18-31-97, WITH EFFECTIVE DATE OF JAN. 30, 1998 WHICH SHOULD BE REMOVED FROM YOUR FILES AND NOTED IN THE 1997 TECHNICAL SERVICE BULLETIN MANUAL (PUBLICATION NO. 81-699-98004). THE DECARBONIZING PROCEDURE HAS BEEN REVISED ALONG WITH THE LABOR OPERATION TIME ALLOWANCE. ALL REVISIONS ARE HIGHLIGHTED WITH **ASTERISKS**.

NOTE: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH THE 4.0L ENGINE.

SYMPTOM/CONDITION:
Malfunction Indicator Lamp (MIL) illuminated with either a Multiple Misfire or individual Cylinder (1-6) Misfire Diagnostic Trouble Code (DTC) recorded in the Powertrain Control Module’s (PCM) memory. The MIL illumination may be accompanied by engine vibration.

DIAGNOSIS:
Refer to the 1998 2.5L/4.0L/5.2L/5.9L SFI Jeep Powertrain Diagnostic Procedures Manual (Publication No. 81-699-97019), test TC-106A for the Multiple Cylinder Misfire DTC or test TC-107A for the Cylinder #(1-6) Misfire DTC. For any future reference, record and document Freeze Frame data.

NOTE: BOTH TEST TC-106A AND TC-107A ARE REVISED WITH TECHNICAL SERVICE BULLETIN 26-12-97 RELEASED DECEMBER 1997. DO NOT USE THE PROCEDURE LISTED IN THE DIAGNOSTIC PROCEDURE MANUAL UNLESS THE REVISED PAGES HAVE BEEN INSERTED.

Perform the repair procedure identified in the Powertrain Diagnostic Procedures Manual unless your diagnosis identifies that an engine mechanical problem could be causing the OBD II Misfire DTC. If the Powertrain Diagnostic Procedures Manual identifies a possible engine mechanical problem, perform the Repair Procedure.

PARTS REQUIRED:
Qty Part No. Description
12 53010388 Springs, Valve
1 04318001 Mopar Combustion Cleaner


REPAIR PROCEDURE:
This bulletin involves installing revised valve springs and decarbonizing the combustion chamber.

Use the procedure outlined in the appropriate 1998 Service Manual, Group 9, 4.0L Engine, RemovalAnd Installation, Valve Stem Seal And Spring, to remove and install the revised valve springs (p/n 53010388).
Perform the following Decarbonizing Procedure.
Decarbonizing Procedure
Operate the vehicle until the vehicle reaches operating temperature.
Remove the air tube from the throttle body
With the engine at an idle, spray the entire contents of Mopar Combustion Cleaner, p/n 04318001, directly into the throttle body. Allow the vehicle to load up with the cleaner to the point of almost stalling out.
Shut the engine OFF after the entire can is ingested.
With the hood closed and the vehicle parked inside the garage, allow the vehicle to soak for two to three hours. This will ensure that the engine will maintain its temperature and will allow proper solvent penetration.
**Drive the vehicle to fully warm up the engine.
If the vehicle is equipped with an automatic transmission, place the gear selector into L, if the vehicle is equipped with a manual transmission, place the transmission into first gear.
On a suitable road that will allow the vehicle to be driven safely at the posted speed limit, accelerate the vehicle until the engine reaches 4500 rpm.
Hold the engine speed at this rpm for 15 seconds.
Slow down and pull to the side of the road, then allow the engine to idle for five seconds.
Repeat Steps 7 through 10 two more times.**
With the vehicle at operating temperature and within the freeze frame data recorded for the diagnostic test, verify that the misfire condition has been corrected.
POLICY:
Reimbursable within the provisions of the warranty.

TIME ALLOWANCE:
Labor Operation No. Time
**09-95-20-92 3.1 Hrs.**


FAILURE CODE:
Code Description
XX Service Adjustment