Valve question

Hi everyone,
I'm having a misfire issue that is coming back. Specifically on cylinder 6, 4 and occasionally 2. It's really subtle, and shows up at idle. When a reader is plugged in it clocks misfires only at idle. When the engine is revved the cylinders no longer misfire.

The mechanic thinks the valves are the issue. My question is, wouldn't the valves still misfire when the engine is being revved? Also if it was the IAC wouldn't it affect all cylinders as well? Also, the jeep has never been overheated.

If I do need to have the valves done, what else should be done when they are inside the engine? It's a 2005 renegade 3.7 with 92k.


What's been done:
-new spark plugs
-new tps
-recently replaced cool packs
-fuel pressure is good and the injectors are checking out.
-injector cleaner


Thanks!


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Ya lots of shake at idle for some KJ folks, been there...-odd fire V-6 and lifters were sticking for me-bad news.
Now I change oil at 2500 miles and add Lubegard Bio tech engine treatment, which also quiets & lubes lifter after the engine was cleaned as per link below.
Have you cleaned the throttle body/ IAC and the ports? I ended up replacing the IAC as well as the TPS too etc.
Many pics missing due to PB removing em all but this link of mine tells a story..
LINK: http://www.jeepkj.com/forum/f196/3-7-engine-slight-shake-57700/
Jeep likes Mopar coil packs and all the other sensors in Mopar. Aftermarket stuff hit and miss oh oh..

LibertyTC said:

Ya lots of shake at idle for some KJ folks, been there...-odd fire V-6 and lifters were sticking for me-bad news.
Now I change oil at 2500 miles and add Lubegard Bio tech engine treatment, which also quiets & lubes lifter after the engine was cleaned as per link below.
Have you cleaned the throttle body/ IAC and the ports? I ended up replacing the IAC as well as the TPS too etc.
Many pics missing due to PB removing em all but this link of mine tells a story..
LINK: http://www.jeepkj.com/forum/f196/3-7-engine-slight-shake-57700/
Jeep likes Mopar coil packs and all the other sensors in Mopar. Aftermarket stuff hit and miss oh oh..

Click to expand...

Thanks for the reply.
I change my oil at 2500 miles to, I've always babied it. I did clean the throttle body, but maybe I should do it again. All parts I've used have been mopar. Thanks for the link.

I'm not a mechanic but wouldn't the misfire get worse when revving if the valves were bad?


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Not necessarily ...is the engine light coming on?
Any smoke out tailpipe after sitting all night or..?? Valve train quiet or a bit rattling?
Keep in mind that if the scanner is just doing the misfire count from idle, it can take hundreds of counts or more my guess to set a code.
The IAC intake air control - controls the idle. What is your jeep idle rpm when hot?
Finding someone that can really interpret the fuel injectors diagnostics/live data may point to it being the real culprit too.
I hope TJKJ can have some input here as well. Lots of the KJ's do suffer from a misfire/s at idle or just above.
Mine still does it at just above idle, but does not turn the light on, low miss counts.
I wish I could monkey with the fuel trim levels.

Lots of 3.7 & 4.7 have idle issues, they like a very low idle something like 550 rpm. It often dips from there closer to 450-500 where it'll surge back to above 550 then settle down.
Plenty of Commander and liberty owners trying to find why it'll sometimes stall at idle.

For that problem transmission Fluid level can make a difference, sometimes torque converter is bad. Cam position and crank sensors being changed can sometimes help.

Only mention this because it is another erratic problem that is hard to trace with no error codes.

I had a miss on my f150 I couldn't find no matter what I did, replaced the throttle body assembly twice, o2 sensors and anything I thought was related, did all kinds of stuff, it finally got worse doing at speed while driving. Finally I replaced the injectors which cost a bit to get all 8 with Ford "quality" injectors. That fixed it, idles smoother and no longer has that missing feel at speed. Never had a code

On our commander I had to replace the catalytic converter assembly and o2 sensors, also put a proper mopar cam sensor in while I was at it. During the motor swap I had to make due with a car quest part.
Reset the computer and after relearning it is running so freaking smooth I take the long way back but I'm a geek about engines when they run right.

I'm not sure about bad or leaking valves and what they can do but just wanted to mention a few other possibilities.


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mk_v said:

Hi everyone,
I'm having a misfire issue that is coming back. Specifically on cylinder 6, 4 and occasionally 2. It's really subtle, and shows up at idle. When a reader is plugged in it clocks misfires only at idle. When the engine is revved the cylinders no longer misfire.

The mechanic thinks the valves are the issue. My question is, wouldn't the valves still misfire when the engine is being revved? Also if it was the IAC wouldn't it affect all cylinders as well? Also, the jeep has never been overheated.

If I do need to have the valves done, what else should be done when they are inside the engine? It's a 2005 renegade 3.7 with 92k.


What's been done:
-new spark plugs
-new tps
-recently replaced cool packs
-fuel pressure is good and the injectors are checking out.
-injector cleaner


Thanks!


Sent from my iPhone using Tapatalk

Click to expand...

Compression test...............................

Injector cleaner only cleans the injectors,maybe.You need upper cylinder cleaner or a professional induction cleaning done to get most of the built up carbon removed.A few fill ups with premium gas and very spirited driving down the highway helps also,and when I mean "spirited driving" I mean you need alot of WOT and hitting that rev limiter.

I have run into a few 4.7/3.7's that will have a slight miss at idle only caused by a bad cat(s),all have been in the 80k-120k range for miles.


Plus the 3.7/4.7 is a odd fire V6/V8 and will always shake at idle,nothing will ever change that but you should not have any misfires being recorded.

tjkj2002 said:

Compression test...............................



Injector cleaner only cleans the injectors,maybe.You need upper cylinder cleaner or a professional induction cleaning done to get most of the built up carbon removed.A few fill ups with premium gas and very spirited driving down the highway helps also,and when I mean "spirited driving" I mean you need alot of WOT and hitting that rev limiter.



I have run into a few 4.7/3.7's that will have a slight miss at idle only caused by a bad cat(s),all have been in the 80k-120k range for miles.





Plus the 3.7/4.7 is a odd fire V6/V8 and will always shake at idle,nothing will ever change that but you should not have any misfires being recorded.

Click to expand...

The injector cleaner was a formula the mechanic used. He disconnected the fuel and ran a can through pressurized snap on machine. Was that was the induction cleaning you were referring to? Costed about a $100.

I asked him about doing s compression test. He said with how subtle the misfire is, the test might not show a bad valve because the valve would have to be lined up just right to produce the misfire. Does that sound right? When the reader was plugged in while idling, it was clocking at most 6 misfires on cylinder 6 and 3-5 on cylinder 4 and every once and a while 1 would show up on cylinder 2.

I read about the cat possibly being a problem but the mechanic didn't really consider it. Maybe I should take it to a exhaust shop to look at that. I also always have run ethanal free gas.

Thank you for the reply!


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mk_v said:

The injector cleaner was a formula the mechanic used. He disconnected the fuel and ran a can through pressurized snap on machine. Was that was the induction cleaning you were referring to? Costed about a $100.

I asked him about doing s compression test. He said with how subtle the misfire is, the test might not show a bad valve because the valve would have to be lined up just right to produce the misfire. Does that sound right? When the reader was plugged in while idling, it was clocking at most 6 misfires on cylinder 6 and 3-5 on cylinder 4 and every once and a while 1 would show up on cylinder 2.

I read about the cat possibly being a problem but the mechanic didn't really consider it. Maybe I should take it to a exhaust shop to look at that. I also always have run ethanal free gas.

Thank you for the reply!


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Click to expand...

Valve issues mainly effect cylinder #2 on a KJ,for some reason 99% of all valve seat failures have been #2.

Another quick way to test for any valve train issues is to hook a vacuum gauge to the intake(brake booster hose is a good line to tap) and start the engine,the gauge needle should be rock steady at idle and somewhere in the 14-16in-hg(depends on altitude) but that needle should never flutter.If it does flutter a few in-hg's at idle you have a valve train issue.

tjkj2002 said:

Valve issues mainly effect cylinder #2 on a KJ,for some reason 99% of all valve seat failures have been #2.



Another quick way to test for any valve train issues is to hook a vacuum gauge to the intake(brake booster hose is a good line to tap) and start the engine,the gauge needle should be rock steady at idle and somewhere in the 14-16in-hg(depends on altitude) but that needle should never flutter.If it does flutter a few in-hg's at idle you have a valve train issue.

Click to expand...

Thank you! I'll try that


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