Zj 1998 running issues
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Joined: Jul 2017
Posts: 6
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Model: Cherokee
Zj 1998 running issues
Hi Guys..
Just wondering if any of you wise owls can point me in the right direction with a bit of fault finding..
Got a 1998 ZJ 4.0 Which starts first time and when going runs really smoothly..
Did you notice the ...When Going bit...
So she starts perfect and runs at idle for a few minutes normally.. Then she starts dropping revs and kicking back in every few seconds...
To clear it i would put the gas on and it would lag but kick in a blow clear and run normally.
If i start driving straight away, it starts the stall thing after about 30 seconds and again, foot down ,clears through and she runs perfectly whether it be 10 miles or 300 miles.( straight running)
If i stop longer than 30 minutes( engine off) , the same symptoms....but if i only stop for about 10( engine off) it doesnt come back when i start going again..
Changed the radiator the other day, nice easy job apart from the AT port being metric instead of imperial and trying to find adaptor.... when i stumbled onto something...
Whilst running the radiator up to temp, it again started the stall thing, i decided to pull the injector feeds one at a time..
As soon as i pulled No2...(second in from front) it cleared itself straight away and ran fine...plugged 2 back in and still ran fine...
Changed injector 2 and 1 round to see if the symptom followed it...but it didnt, still only cleared itself when 2 plug pulled ...
Same supply v at no2 as their is at the others....
Could their be something wrong with the ecu or can you reset the chip..
Anyway guys, hoping one of you can help me out...
Just wondering if any of you wise owls can point me in the right direction with a bit of fault finding..
Got a 1998 ZJ 4.0 Which starts first time and when going runs really smoothly..
Did you notice the ...When Going bit...
So she starts perfect and runs at idle for a few minutes normally.. Then she starts dropping revs and kicking back in every few seconds...
To clear it i would put the gas on and it would lag but kick in a blow clear and run normally.
If i start driving straight away, it starts the stall thing after about 30 seconds and again, foot down ,clears through and she runs perfectly whether it be 10 miles or 300 miles.( straight running)
If i stop longer than 30 minutes( engine off) , the same symptoms....but if i only stop for about 10( engine off) it doesnt come back when i start going again..
Changed the radiator the other day, nice easy job apart from the AT port being metric instead of imperial and trying to find adaptor.... when i stumbled onto something...
Whilst running the radiator up to temp, it again started the stall thing, i decided to pull the injector feeds one at a time..
As soon as i pulled No2...(second in from front) it cleared itself straight away and ran fine...plugged 2 back in and still ran fine...
Changed injector 2 and 1 round to see if the symptom followed it...but it didnt, still only cleared itself when 2 plug pulled ...
Same supply v at no2 as their is at the others....
Could their be something wrong with the ecu or can you reset the chip..
Anyway guys, hoping one of you can help me out...
Old fart with a wrench
Joined: Nov 2010
Posts: 14,398
Likes: 741
From: Manlius, east of Syracuse, NY
Year: 2000 XJ Sport & WJ Laredo
Model: Grand Cherokee (WJ)
Engine: 4.0L
Okay, here's the thing. The injectors are powered up with 12 volts constantly and the individual injectors are triggered by drivers in the PCM by grounding them when needed to spray fuel. There is a thing called a "noid" light that clips on the injector and flashes as the coil is energized. First, check the wire harness where it goes behind the valve cover for damage or fraying. Also, check the pins in the cable sockets at the PCM.
I had a similar problem with my WJ 4.0 and I noticed my #2 injector's body was cracked. I replaced them all with a reconditioned set of Bosch 4-holers. Mine was the opposite. It ran ragged until it warmed up, then it was fine. I'm figuring moisture got into the coil and had to evaporate before to worked properly. Yours may be leaking fuel after shutdown. Check the fuel pressure and see if it holds after shutdown.
I had a similar problem with my WJ 4.0 and I noticed my #2 injector's body was cracked. I replaced them all with a reconditioned set of Bosch 4-holers. Mine was the opposite. It ran ragged until it warmed up, then it was fine. I'm figuring moisture got into the coil and had to evaporate before to worked properly. Yours may be leaking fuel after shutdown. Check the fuel pressure and see if it holds after shutdown.
