4.0 Hesitation

[blackhawkmike44]

i am still experiacing this same issue i have replaced and checked everything suggested and found no reasons for this sysmtom if anyone has been able to fix this i would love to know what is causing this problem

 

[99TJMA]

I'm having the same problem and I still can't find out what's wrong. I keep throwing In new parts and nothing.. Let me know if you can find the fix.. It's been a few months now and she still keeps acting up..

 

[69jeepcj]

It does sound like mybe a low fuel situation. If you have a vac gauge, most can be used as a pressure gauge too. Take a fuel line apart and put the vac gauge on it and crank the engine to see how much pressure your pump is putting out. That will eliminate the pump if its good.

 

[99TJMA]

Did the fuel pressure test and the pressure was fine. Even when it started to act up .. It would be nice if it threw a code but nothing.

 

[Utah_jeepster]

Check your evap emission purge valve, this is a known problem of being stuck open giving you a vacuum leak that doesn't throw a code. without starting the jeep pull the valve and see if you can blow through it. You shouldn't while is closed.

 

[greg92jeepxj]

Check your evap emission purge valve, this is a known problem of being stuck open giving you a vacuum leak that doesn't throw a code. without starting the jeep pull the valve and see if you can blow through it. You shouldn't while is closed.

Good call Utah_Jeepster , this happened to an '83 pontiac gran prix v6 I once owned . If these members are describing it as a hesitation , to me , my problem was much more severe. The canister stole vacuum from the engine and returned it with an overly rich vapor which bogged the engine something horrible ! Even though the carb was electronic and not dependent on vacuum to control a power piston , performance suffered majorly since air/fuel mixture was not being introduced efficiently to the engine.
I haven't had that car in years and forgot some of the found lessons from it. Electronic fuel injection covers up too much of the errors and faults on modern engines and an wreak havoc on diagnostic troubleshooting unless we make a check list and start with basics. I try to practice what I preach in that we must start from scratch and many times it yields positive results.
The one thing I have learned over the years in terms of diagnostics is that there is no magic pill , only hard work.
Back then , I only found the cause when I was trying to find the source of rich mixture showing up on plugs and the useless OBD 1 ECM didn't even throw a O2 rich code. I just wrote in another post , we have to go back to basics or we just chase our tail assuming . Glad good people like yourself remind people like when needed. Thanks again, greg