Is cracked manifold causing rough idle? - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Grand Cherokee & Commander Forums > ZJ Grand Cherokee Forum > Is cracked manifold causing rough idle?

Stainless Steel Door Hinge PinsPoly Door Hinge BushingsSteinjager TJ tube doors

Reply
Unread 09-18-2003, 10:50 AM   #1
skyguy
Registered User
 
Join Date: Sep 2003
Posts: 4
Is cracked manifold causing rough idle?

I recently posted a thread on a mystery vibration in my '93 ZJ with the 4.0 I-6 at low idle. The only thing I can find that might be a problem is the cracked exhaust manifold. My question is:

CAN THIS CAUSE THE I-6 TO RUN ROUGHLY BY MESSING UP THE READING TO THE OXYGEN SENSOR?

The vibration becomes tolerable if I take it out of drive and put it in neutral and turn off the AC, thus effectively raising the rpm's by a few and allowing the engine to run a bit smoother. It seems like the rpm's increase and decrease slightly every few seconds while idling also. Could this be the computer picking up conflicting info from the O2 sensor and other EFI sensors?

Thanks for any suggestions.

skyguy is offline   Reply With Quote
Unread 09-18-2003, 03:17 PM   #2
Big Dumb White Guy
Registered User
 
Join Date: Dec 2001
Posts: 254
here's what happened to me...

mine ran like crap - cracked manifold - it causes the O2 sensor to "see" more O2, then pours the gas in. you end up with a folded out spark plug. that's what the bad idle is from. just fixed it all. ebay has a stainless steel exhaust manifold for $150 (or so). you could go with header(s), if you have the cash..... check the plugs...

let me know how it turns out for you.

good luck!
__________________
repost Nazi's suck!

A guy walks into the psychiatrist office wearing only Glad Wrap shorts. The shrink says, "Well, I can clearly see you're nuts."
Big Dumb White Guy is offline   Reply With Quote
Unread 09-18-2003, 06:09 PM   #3
RockPaws
Registered User
 
Join Date: Jun 2003
Location: Pahrump, NV
Posts: 830
If the exhaust manifold is cracked, get it fixed very soon. Its also a safety concern. An exhaust leak in the engine compartment can get into the cabin from the fresh air intake below the windshield. And you can't smell carbon monxide...bad to breath.
If the manifold is cracked bad enough, it will cause a rough idle. I would also check the ignition system for problems.

When you have your manifold replaced, use either a new one from the Jeep dealer or install a Banks or Borla header. The aftermarket "Cheep" manifold are just that ....Cheep. I have installed a number of them, They usuall come back .. cracked.
__________________
[FONT=Trebuchet MS]01' Jeep TJ (Jeep #5)
3.5 RE Custom SuperFlex, Raingler, Kilby, Currie, Banks, Borla, American Racing, Custom mods, Always more in the works.
[URL=http://www.redrock4x4.com][COLOR=Blue]www.redrock4x4.com Rocks![/COLOR][/URL]
[URL=www.needhim.org/][COLOR=Blue]Need Him?[/COLOR][/URL][/FONT]
RockPaws is offline   Reply With Quote
Unread 09-18-2003, 07:45 PM   #4
demtjcj
Registered User
 
Join Date: Aug 2002
Location: greensburg, pa
Posts: 361
i am having the same problem. what ignition parts do you think you should check. thanks
__________________
2004- Wrangler X stock

1977 full size cherokee-401 v8, quadratrac dana 44s

prev. jeeps: 98TJ on 33s, 00TJ on 35s, 01TJ on 35s, 78CJ on 31s, 85XJ stock, 94ZJ stock, 97 TJ on 35s, 03 on 35s, 93 GC on 33s
demtjcj is offline   Reply With Quote
Unread 09-19-2003, 03:29 PM   #5
demtjcj
Registered User
 
Join Date: Aug 2002
Location: greensburg, pa
Posts: 361
can naybody help with this. or have a suggestion
__________________
2004- Wrangler X stock

1977 full size cherokee-401 v8, quadratrac dana 44s

prev. jeeps: 98TJ on 33s, 00TJ on 35s, 01TJ on 35s, 78CJ on 31s, 85XJ stock, 94ZJ stock, 97 TJ on 35s, 03 on 35s, 93 GC on 33s
demtjcj is offline   Reply With Quote
Reply
Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.