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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
Hi! I just replaced my Exhaust Manifold on my 1987 Jeep Cherokee XJ 4.0L 6cyl. When I went to start of the jeep the engine started roaring like I was putting the pedal to the metal. I Immediately shut off the truck, and looked under the hood. There was white smoke coming out from the front of the engine and smelt very bad, like burnt plastic. I than did some research and read that it could be because of a faulty fuel injector. Is this the case? Should I replace the fuel injectors? The fuel injector pigtails are all on the right injector... Please help!
Also it is common for white smoke to be present right after doing intake/exhaust gasket or new mainfold. Not the crazy high pedal to the floor board though....
No. A fuel injector will not do that. You can't make the motor run faster (higher RPMs) just by having more fuel added. Your motor runs faster (roars) because it is getting more air. Air is likely getting into the combustion chamber from some source other than the throttle body.
When you put on your new exhaust manifold and re-installed the intake manifold, it probably did not sit flush against the mating surface. So air is getting sucked in around the intake manifold. Usually, this is because the rear portion of the intake manifold is hung up on the rear most locating dowel. It is not easily spotted from the front and/or above. But 9 times out of 10, this is the cause.
^ What he said but still if you have stock injectors I would change them to 746 Bosch injectors from a volvo. Othere will work also bit that's what I used.
"......but my stock injectore are fine......"
Until they ain't. When your 3 hours from home and they start leaking at the seams. It isvery easy to change them over. Then if they start leaking all you need is an O ring. Always keep a pack of fuel injector O rings in your jeep, in case they start leaking when your way away from a store.
^ What he said but still if you have stock injectors I would change them to 746 Bosch injectors from a volvo. Othere will work also bit that's what I used.
"......but my stock injectore are fine......"
Until they ain't. When your 3 hours from home and they start leaking at the seams. It isvery easy to change them over. Then if they start leaking all you need is an O ring. Always keep a pack of fuel injector O rings in your jeep, in case they start leaking when your way away from a store.
That's a good tip. I currently do not carry any. I should remedy that.
If you cover the throttle body and the engine doesnt die you have a large vac leak. Covering the TB will also make the leak more pronounced. Dont cover the TB with anything that is dirty or can break apart. I use a 1/2 plate of aluminum that I keep specifically for this/runaway diesel.
No. A fuel injector will not do that. You can't make the motor run faster (higher RPMs) just by having more fuel added. Your motor runs faster (roars) because it is getting more air. Air is likely getting into the combustion chamber from some source other than the throttle body.
When you put on your new exhaust manifold and re-installed the intake manifold, it probably did not sit flush against the mating surface. So air is getting sucked in around the intake manifold. Usually, this is because the rear portion of the intake manifold is hung up on the rear most locating dowel. It is not easily spotted from the front and/or above. But 9 times out of 10, this is the cause.
I just checked it and it sits on the dowels and looks to be flush. I might need to tighten it better since I only used a wrench. I might really need to crank it down
If you cover the throttle body and the engine doesnt die you have a large vac leak. Covering the TB will also make the leak more pronounced. Dont cover the TB with anything that is dirty or can break apart. I use a 1/2 plate of aluminum that I keep specifically for this/runaway diesel.
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
Originally Posted by TrayXj
I just checked it and it sits on the dowels and looks to be flush. I might need to tighten it better since I only used a wrench. I might really need to crank it down
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
Originally Posted by TrayXj
How do I cover the throttle body?
Remove the air duct from the throttle body. that's the plastic pipe that goes from the air box (where teh air filter lives) to the TB. You'll see the TB intake. It's..... (going from memory) in the neighborhood of 3" diameter. Maybe a bit less. It looks like this:
Now this part is complicated: Stick the palm of your hand over the intake. No 1/2" aluminum plate required. Trust me, it won't suck you in.
Heh. I once got to watch as someone tried to shut down a runaway engine from an M-88 tank recovery vehicle that was sitting on the ground being worked on. We're talking about a twelve hundred cubic inch, 1500 horsepower air-cooled gasser that powers a massive, tank-like vehicle that can TOW a couple of tanks at the same time. The air intake was about 8" across. I know the measurement because what finally worked was a standard clip board, and it barely covered the intake.
That engine ate a t-shirt before someone tried the clip board.
He shouldn't be changing anything until he gets this massive problem solved.
I agree. He mentioned fuel injectors. Was just giving him some advice.....& if the intake wasn't sitting flush and he ended up having to take it back apart, might as well change them while it was back apart......but he said it's flush so he can get to them after he solves this.
Remove the air duct from the throttle body. that's the plastic pipe that goes from the air box (where teh air filter lives) to the TB. You'll see the TB intake. It's..... (going from memory) in the neighborhood of 3" diameter. Maybe a bit less. It looks like this:
Now this part is complicated: Stick the palm of your hand over the intake. No 1/2" aluminum plate required. Trust me, it won't suck you in.
Heh. I once got to watch as someone tried to shut down a runaway engine from an M-88 tank recovery vehicle that was sitting on the ground being worked on. We're talking about a twelve hundred cubic inch, 1500 horsepower air-cooled gasser that powers a massive, tank-like vehicle that can TOW a couple of tanks at the same time. The air intake was about 8" across. I know the measurement because what finally worked was a standard clip board, and it barely covered the intake.
That engine ate a t-shirt before someone tried the clip board.
Awesome thank you! I will try that, I'll torque down the bolts first than do that second.
05-11-2019, 10:05 PM
Very Violent/Rough Idle
