New member with a misfire probelm

[Uhvnutn]

I have an 89 cherokee with a 4.0 in it. It has been running really good lately with a super smothe idle. Yesterday i noticed a strong fuel smell and began looking for it. What I found was the rear injector was leaking through the electrical connection. So today I went to the local auto parts store and got a new injector and a set of new O-rings. I replaced the leaking injector and all of the O-rings, and made sure to lube the O-rings before installing them. After buttoning everything up I started the jeep and heard a loud hissing sound and it also had a bad miss. I searched everywhere for a vacuum leak and found nothing. I sprayed either around the engine compartment and there was no change in engine idle. While wiggeling stuff near the map sensor the hiss went away but the miss is still there. I eventualy put the old injector back on and still have the miss. Im at the point that I have no idea what to do next. Someone please help!

 

[XJRubicon]

I have an 89 cherokee with a 4.0 in it. It has been running really good lately with a super smothe idle. Yesterday i noticed a strong fuel smell and began looking for it. What I found was the rear injector was leaking through the electrical connection. So today I went to the local auto parts store and got a new injector and a set of new O-rings. I replaced the leaking injector and all of the O-rings, and made sure to lube the O-rings before installing them. After buttoning everything up I started the jeep and heard a loud hissing sound and it also had a bad miss. I searched everywhere for a vacuum leak and found nothing. I sprayed either around the engine compartment and there was no change in engine idle. While wiggeling stuff near the map sensor the hiss went away but the miss is still there. I eventualy put the old injector back on and still have the miss. Im at the point that I have no idea what to do next. Someone please help!

Hmm you pulled the Vac line going from the throttle body to the MAP sensor.
Or cracked the line...
Sounds very much like MAP sensor line is cracked. The plastic is very brittle.
a few wraps with electrical tap should fix it.

Pull the line off carefuly and inspect it.

XJR

 

[Jess]

Did the gas leak stop when you put the old injector back in? Have you checked the plugs/wires?

If you have a plug not firing and an exhaust leak, that could explain both the misfire and the gas smell.

 

[XJRubicon]

Did the gas leak stop when you put the old injector back in? Have you checked the plugs/wires?

If you have a plug not firing and an exhaust leak, that could explain both the misfire and the gas smell.

The misfire was not present before the injector install.


XJR

 

[Uhvnutn]

Yes when i put the old injector on it still leaked. I checked the map sensor vacume hose and didnt see any problems with it. Also what is suposed to be in the hole right above the map sensor vacume hose at the throttle body?

 

[XJRubicon]

Yes when i put the old injector on it still leaked. I checked the map sensor vacume hose and didnt see any problems with it. Also what is suposed to be in the hole right above the map sensor vacume hose at the throttle body?

That hole should be what the vac line attaches to... the line has a weird end on the Throttle body side. I believe the hole you are talking about is just a spot for the line to secure it self to the throttle body.

I don't remember there being any other hole on the throttle body.
The one I am talking about it just above the MAP vac port and is about 3/8".

Hope this helps,

The reason I am focusing on the MAP vac line is because you stated you sprayed around the intake to see if it would cause any change and nothing happened.

What did you use to spray? carb cleaner? soap?

If the MAP line is cracked, not even carb cleaner will have any effect on the engine because it is probably such a small leak.

It is one cylinder that is not happy or the entire engine?

Have you driven it? any backfiring?

XJR

 

[Uhvnutn]

I usd either to help find the leak, nothing found. I put the new injector back in today and cleaned the throttle body and injector holes in the intake. It seems to run somewhat better but still has a miss. It almost sounds like there is a dead hole. I dont have time tonight to pull the injector and/or plug wires one by one tonight but thats my next step i guess. And yes I drove it to work today.

 

[Uhvnutn]

I drove it about 100 miles yesterday with the same missfire problem. I noticed that it idles rough and kinda chugs when accelerating. Also when the torque converter locks up it chugs badly. And fuel mileage was horable, it used about 17 gallons of fuel during the 100 mile trip. When moveing the throttle position while driving i can hear a slight whistle that wasnt there before this problem. It also seems to run somewhat better when the motor is heat soaked. If anyone can help please do so. Thanks in advance Will

 

[Uhvnutn]

Problem solved!!! It was a bad conection/wire on one of the injectors. Runs like new now. Thanks for all the help pointing me in the right direction.