NAXJA Forums -::- North American XJ Association  

Go Back   NAXJA Forums -::- North American XJ Association > NAXJA Unibody Jeep Technical Forums > Jeep Cherokee XJ (1984 - 2001) > Modified Tech Discussion
HOME Member FAQ Sponsor Info Rules Bylaws E-Mail

Modified Tech Discussion Forum for Tech related discussion for Modified XJ's and MJ's.

Reply
 
Thread Tools Display Modes
  #1  
Old January 1st, 2009, 20:06
jeeperguy21's Avatar
jeeperguy21 jeeperguy21 is offline
NAXJA Forum User
 
Join Date: Jun 2007
Location: Syracuse, UT
Posts: 786
Replaced exhaust manifold, start engine and the RPM's go out of control!

I was so happy to have finally gotten the new exhaust manifold put on my '99 XJ. After I finally got done hooking up everything the way it was before, I started it up and the engine will rev out of control.

It does the same thing after multiple starts. I have to kill the engine immediately because the engine wants to blow itself up. What is wrong?!

Let me know if you know what causes this or have had the same problem. I gotta drive this thing to work in the morning!
Reply With Quote
  #2  
Old January 1st, 2009, 20:14
ECKSJAY's Avatar
ECKSJAY ECKSJAY is offline
Water is dirty
 
Join Date: Jun 2003
Location: Covington, WA
Posts: 13,008
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

You've got a leak somewhere in the intake. Take a few mins off, go with a flashlight and a deep breath, and look at the seams. Happened to a buddy of mine after an engine swap and his intake was just a slight bit crooked at one end. Loosened up a few bolts, tapped it in place, tightened down, and it worked fine. Check out the throttle body and all the vac hoses on the intake manifold, too. Good luck!
Reply With Quote
  #3  
Old January 1st, 2009, 20:24
jeeperguy21's Avatar
jeeperguy21 jeeperguy21 is offline
NAXJA Forum User
 
Join Date: Jun 2007
Location: Syracuse, UT
Posts: 786
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

I'm gonna shoot myself. Already been working on this thing for 8+ hours. It looked and felt like it was seated properly when i installed it. So with the intake being a little crooked, like your buddy's was, why would that cause the RPMs to be so high?
Reply With Quote
  #4  
Old January 1st, 2009, 20:27
ECKSJAY's Avatar
ECKSJAY ECKSJAY is offline
Water is dirty
 
Join Date: Jun 2003
Location: Covington, WA
Posts: 13,008
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

Because it's letting too much air in. When you step on the gas, it opens the butterfly in the throttle body, right? That lets more air in, but it's under a controlled manner. If you've got half of the intake away from the head, you've got a MASSIVE intake leak...which is letting a ridiculous amount of air in...which also makes the engine race.
Reply With Quote
  #5  
Old January 1st, 2009, 20:45
jeeperguy21's Avatar
jeeperguy21 jeeperguy21 is offline
NAXJA Forum User
 
Join Date: Jun 2007
Location: Syracuse, UT
Posts: 786
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

After looking it over, I found something broken, but I don't know what purpose it serves. What is this and could it be causing the problem or not? Here are 2 pics of it:



Reply With Quote
  #6  
Old January 1st, 2009, 20:51
bigfrd8's Avatar
bigfrd8 bigfrd8 is offline
NAXJA Forum User
 
Join Date: Aug 2008
Location: Florence, AL
Posts: 7
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

That is part of your crankcase vent system. it will not cause RPM problems. like the others said you either don't have the manifold seated properly or you left some vacuum lines loose.
Reply With Quote
  #7  
Old January 1st, 2009, 20:53
hubs97xj's Avatar
hubs97xj hubs97xj is offline
NAXJA Forum User
 
Join Date: May 2008
Location: Fort Wayne, IN
Posts: 4,433
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

CCV. Big freakin vacuum leak. Could be your culprit.
Reply With Quote
  #8  
Old January 1st, 2009, 20:58
ERratIC's Avatar
ERratIC ERratIC is offline
NAXJA Forum User
 
Join Date: Dec 2008
Location: Sooke, BC, Canada
Posts: 59
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

The other end of the hose goes to the airbox or intake pipe...I think. Which would not cause your problem since the air leak is before the throttle body. Should still be fixed though.
Reply With Quote
  #9  
Old January 1st, 2009, 21:02
hubs97xj's Avatar
hubs97xj hubs97xj is offline
NAXJA Forum User
 
Join Date: May 2008
Location: Fort Wayne, IN
Posts: 4,433
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

That tubing runs to the intake manifold. <edit> come to think of it, when I had the booster hose off the manifold, the idle jumped, but it didn't runaway completely. I'm thinking you've got a bigger leak, and a guess would be that the manifold isn't seated fully on the alignment pins. It can appear to be fully seated looking down on it, and still be open along the bottom.

Last edited by hubs97xj; January 1st, 2009 at 21:08.
Reply With Quote
  #10  
Old January 1st, 2009, 21:38
StaleAle StaleAle is offline
NAXJA Forum User
 
Join Date: Jan 2008
Location: NV
Posts: 61
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

Fix that because yes it will cause the RPMs to jump to about 2000. Its the EGR system and the front hose to the intake is the crank case breather. Make sure your brake assist hose is connected as well to the manifold.

With the EGR disconnected you should not hit the rev limiter so it could be a gasket (did you put it on backwards) and the EGR being unplugged causing a big vac leak.
Reply With Quote
  #11  
Old January 2nd, 2009, 10:54
dgrigorenko's Avatar
dgrigorenko dgrigorenko is offline
NAXJA Forum User
 
Join Date: Jun 2006
Location: Big Rapids MI
Posts: 1,086
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

You definatly have a leak. i have done mine twice and the first time had no problems, but on the second one my intake manifold was hitting the exhaust manifold ever so slightly causing it to not get a good seal, which caused the exact same issues. i took a ball pein hammer to the exhast manifold and ever so slightly bent the last tube (closest to firewall) and i am talking SLIGHT just a few taps made enough clearance. i was good to go from there. oh while you are in there you might want to think about replacing your motor mounts.... just a thought. i hope this helps


G
Reply With Quote
  #12  
Old January 2nd, 2009, 14:22
igotanxj igotanxj is offline
NAXJA Forum User
 
Join Date: May 2008
Location: Citrus heights
Posts: 1,082
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

Quote:
Originally Posted by jeeperguy21 View Post
After looking it over, I found something broken, but I don't know what purpose it serves. What is this and could it be causing the problem or not? Here are 2 pics of it:



show us where the other end of that hose goes first. im too lazy to go look at my jeep
Reply With Quote
  #13  
Old January 2nd, 2009, 15:31
JeepFreak21's Avatar
JeepFreak21 JeepFreak21 is offline
NAXJA Forum User
 
Join Date: Jun 2002
Location: Cameron Park, CA
Posts: 7,822
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

Quote:
Originally Posted by igotanxj View Post
show us where the other end of that hose goes first. im too lazy to go look at my jeep
It goes to the air box.
Billy
Reply With Quote
  #14  
Old January 2nd, 2009, 15:32
winterbeater's Avatar
winterbeater winterbeater is offline
NAXJA Forum User
 
Join Date: Jul 2008
Location: Royal Oak, Michigan
Posts: 5,315
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

That line sucks the blow-by that collects in the cylinder head into the intake manifold. You could slip a tight piece of hose right over that to fix it. You want to fix it for sure, but I think your intake is probably leaking somewhere else too. But fix it first to find out. Or plug your finger over the part not attached to the valve cover and have someone start it to find out.
Reply With Quote
  #15  
Old January 2nd, 2009, 15:47
igotanxj igotanxj is offline
NAXJA Forum User
 
Join Date: May 2008
Location: Citrus heights
Posts: 1,082
Re: Replaced exhaust manifold, start engine and the RPM's go out of control!

Quote:
Originally Posted by JeepFreak21 View Post
It goes to the air box.
Billy
I thought there were two, one that goes to the airbox and one to the manifold?
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
'91 I6 4.0 4X4 engine knock, increases with RPM's DrRandy OEM Tech Discussion 8 November 28th, 2008 14:56
Replaced plugs, wires, cap, rotor, and battery cables. Clicking from engine on start? Plays For Jeeps OEM Tech Discussion 7 July 11th, 2007 08:15
Jeep wont start. Jump it and it'll run but will die below 1k rpm's. Whats up? Plays For Jeeps OEM Tech Discussion 8 June 28th, 2007 23:37
97+ intake manifold and performance exhaust manifold BigG Wanted: Private Party Only 5 September 22nd, 2006 17:45
weird rpm's at start up, explain? XJ99 Modified Tech Discussion 24 April 23rd, 2006 21:26


All times are GMT -7. The time now is 03:38.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014