XJ engine instantly revs out at start up
 

Hi all, was trying to be a good brother today doing a major service
and repairing the cracked exhaust manifold on my sisters 99XJ.
Repairing the exhaust manifold obviously entails taking of the inlet
manifold, unplugging all the wires, fuel line off the fuel rail etc.
Everything went back together ok but when I fired it up, the engine
raced to max revs instantly, pretty sure it would rev till blew up
from the sound of it if I didn't switch it off. I can't understand how
it could do this, particularly since the throttle butterfly does not
open at all. I tried resetting the computer, no luck, I'm out of ideas
at the moment other than towing it to the nearest Jeep dealer, Any
idea's anyone???

Re: XJ engine instantly revs out at start up
 

Glenn wrote:
> Hi all, was trying to be a good brother today doing a major service
> and repairing the cracked exhaust manifold on my sisters 99XJ.
> Repairing the exhaust manifold obviously entails taking of the inlet
> manifold, unplugging all the wires, fuel line off the fuel rail etc.
> Everything went back together ok but when I fired it up, the engine
> raced to max revs instantly, pretty sure it would rev till blew up
> from the sound of it if I didn't switch it off. I can't understand how
> it could do this, particularly since the throttle butterfly does not
> open at all. I tried resetting the computer, no luck, I'm out of ideas
> at the moment other than towing it to the nearest Jeep dealer, Any
> idea's anyone???

You have an air leak in the intake plenum. Either the gasket is not
seated properly or you forgot a hose, especially the one that runs to
the brake booster.

Did you use a new gasket and clean the block/intake plenum of any
old bits that got stuck.

--
DougW

Re: XJ engine instantly revs out at start up
 

Glenn wrote:
> Hi all, was trying to be a good brother today doing a major service
> and repairing the cracked exhaust manifold on my sisters 99XJ.
> Repairing the exhaust manifold obviously entails taking of the inlet
> manifold, unplugging all the wires, fuel line off the fuel rail etc.
> Everything went back together ok but when I fired it up, the engine
> raced to max revs instantly, pretty sure it would rev till blew up
> from the sound of it if I didn't switch it off. I can't understand how
> it could do this, particularly since the throttle butterfly does not
> open at all. I tried resetting the computer, no luck, I'm out of ideas
> at the moment other than towing it to the nearest Jeep dealer, Any
> idea's anyone???

You have an air leak in the intake plenum. Either the gasket is not
seated properly or you forgot a hose, especially the one that runs to
the brake booster.

Did you use a new gasket and clean the block/intake plenum of any
old bits that got stuck.

--
DougW

Re: XJ engine instantly revs out at start up
 

Glenn wrote:
> Hi all, was trying to be a good brother today doing a major service
> and repairing the cracked exhaust manifold on my sisters 99XJ.
> Repairing the exhaust manifold obviously entails taking of the inlet
> manifold, unplugging all the wires, fuel line off the fuel rail etc.
> Everything went back together ok but when I fired it up, the engine
> raced to max revs instantly, pretty sure it would rev till blew up
> from the sound of it if I didn't switch it off. I can't understand how
> it could do this, particularly since the throttle butterfly does not
> open at all. I tried resetting the computer, no luck, I'm out of ideas
> at the moment other than towing it to the nearest Jeep dealer, Any
> idea's anyone???

You have an air leak in the intake plenum. Either the gasket is not
seated properly or you forgot a hose, especially the one that runs to
the brake booster.

Did you use a new gasket and clean the block/intake plenum of any
old bits that got stuck.

--
DougW

Re: XJ engine instantly revs out at start up
 

Glenn wrote:
> Hi all, was trying to be a good brother today doing a major service
> and repairing the cracked exhaust manifold on my sisters 99XJ.
> Repairing the exhaust manifold obviously entails taking of the inlet
> manifold, unplugging all the wires, fuel line off the fuel rail etc.
> Everything went back together ok but when I fired it up, the engine
> raced to max revs instantly, pretty sure it would rev till blew up
> from the sound of it if I didn't switch it off. I can't understand how
> it could do this, particularly since the throttle butterfly does not
> open at all. I tried resetting the computer, no luck, I'm out of ideas
> at the moment other than towing it to the nearest Jeep dealer, Any
> idea's anyone???

You have an air leak in the intake plenum. Either the gasket is not
seated properly or you forgot a hose, especially the one that runs to
the brake booster.

Did you use a new gasket and clean the block/intake plenum of any
old bits that got stuck.

--
DougW

Re: XJ engine instantly revs out at start up
 

That usually means you forgot to hook up a vacuum line. You have an air
leak into the intake someplace likely.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Glenn wrote:
> Hi all, was trying to be a good brother today doing a major service
> and repairing the cracked exhaust manifold on my sisters 99XJ.
> Repairing the exhaust manifold obviously entails taking of the inlet
> manifold, unplugging all the wires, fuel line off the fuel rail etc.
> Everything went back together ok but when I fired it up, the engine
> raced to max revs instantly, pretty sure it would rev till blew up
> from the sound of it if I didn't switch it off. I can't understand how
> it could do this, particularly since the throttle butterfly does not
> open at all. I tried resetting the computer, no luck, I'm out of ideas
> at the moment other than towing it to the nearest Jeep dealer, Any
> idea's anyone???
>

Re: XJ engine instantly revs out at start up
 

That usually means you forgot to hook up a vacuum line. You have an air
leak into the intake someplace likely.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Glenn wrote:
> Hi all, was trying to be a good brother today doing a major service
> and repairing the cracked exhaust manifold on my sisters 99XJ.
> Repairing the exhaust manifold obviously entails taking of the inlet
> manifold, unplugging all the wires, fuel line off the fuel rail etc.
> Everything went back together ok but when I fired it up, the engine
> raced to max revs instantly, pretty sure it would rev till blew up
> from the sound of it if I didn't switch it off. I can't understand how
> it could do this, particularly since the throttle butterfly does not
> open at all. I tried resetting the computer, no luck, I'm out of ideas
> at the moment other than towing it to the nearest Jeep dealer, Any
> idea's anyone???
>

Re: XJ engine instantly revs out at start up
 

That usually means you forgot to hook up a vacuum line. You have an air
leak into the intake someplace likely.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Glenn wrote:
> Hi all, was trying to be a good brother today doing a major service
> and repairing the cracked exhaust manifold on my sisters 99XJ.
> Repairing the exhaust manifold obviously entails taking of the inlet
> manifold, unplugging all the wires, fuel line off the fuel rail etc.
> Everything went back together ok but when I fired it up, the engine
> raced to max revs instantly, pretty sure it would rev till blew up
> from the sound of it if I didn't switch it off. I can't understand how
> it could do this, particularly since the throttle butterfly does not
> open at all. I tried resetting the computer, no luck, I'm out of ideas
> at the moment other than towing it to the nearest Jeep dealer, Any
> idea's anyone???
>

Re: XJ engine instantly revs out at start up
 

That usually means you forgot to hook up a vacuum line. You have an air
leak into the intake someplace likely.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Glenn wrote:
> Hi all, was trying to be a good brother today doing a major service
> and repairing the cracked exhaust manifold on my sisters 99XJ.
> Repairing the exhaust manifold obviously entails taking of the inlet
> manifold, unplugging all the wires, fuel line off the fuel rail etc.
> Everything went back together ok but when I fired it up, the engine
> raced to max revs instantly, pretty sure it would rev till blew up
> from the sound of it if I didn't switch it off. I can't understand how
> it could do this, particularly since the throttle butterfly does not
> open at all. I tried resetting the computer, no luck, I'm out of ideas
> at the moment other than towing it to the nearest Jeep dealer, Any
> idea's anyone???
>

Re: XJ engine instantly revs out at start up
 

the intake manifold is not on the pegsand not matting flat to the head and
you have a major vacumm leak

Glenn wrote:

> Hi all, was trying to be a good brother today doing a major service
> and repairing the cracked exhaust manifold on my sisters 99XJ.
> Repairing the exhaust manifold obviously entails taking of the inlet
> manifold, unplugging all the wires, fuel line off the fuel rail etc.
> Everything went back together ok but when I fired it up, the engine
> raced to max revs instantly, pretty sure it would rev till blew up
> from the sound of it if I didn't switch it off. I can't understand how
> it could do this, particularly since the throttle butterfly does not
> open at all. I tried resetting the computer, no luck, I'm out of ideas
> at the moment other than towing it to the nearest Jeep dealer, Any
> idea's anyone???