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poor throttle response

bigin1978

NAXJA Forum User
Location
florence ky
i have a 87 cherokee , it takes a few seconds more than i think it should to start ,( but I am really a gm guy . this jeep thing is new to me ), anyway it will idle ok and if the trottle is moved slowly it is fine , but if i have to mash it to the floor fast it hesitates real bad for a second then picks up , almost like the timing isn't advancing fast enough , i have replaced the tps and set it , cleaned the iac and replaced the crank positon sensor and the map sensor , no vacum leaks to be found , the cap and rotor both look to be in good shape no coorsion , wear or carbon tracking, I am at a loss. I just got this thing and i don't want to put anymore money in it than i have to , being that it is going to be a dedicate woods rider , any help would be apprciated thank you
 
The slower start on Renix Cherokees (that is up to 1990) is normal. They are designed to 'get organized' (reach a minimum RPM and read such by the engine computer, if I remember correctly) before they can produce a spark. They also sometimes loose the ability to hold fuel pressure (check valve problem), so may take a couple of seconds to rebuild pressure, some vehicles not all. For that hesitation when trying to accelerate, I would look at the EGR next. It is vacuum controlled via an electronic solenoid on the left front fender. If it is opening a bit when you hit the gas, the engine will stumble. Usually they fail by sticking open, and it runs great at mid and high rpm, but idles real low or stalls at idle.
 
Definitely gotta agree with 4xBob. The check valve in the fuel pump lets pressure bleed back into the tank. It then has to rebuild that pressure. And the EGR valves were definitely a problem after a while. '90 and up don't even have EGR because they found the 4.0L didn't need it.
 
today I bought a fuel pressure gauge and found the pressure was reading only 18 lbs. so i went out and bought a new pump from advance master p/n7006 , unfortunatly it is slightly diffrent than the original , i tried to make it fit the sending unit , but ended up braking the upper bracket atteact bolt . I had to order the whole unit which will be in tommarow . it was only 90.99 for the whole unit (they price matced autozone)the bosch pump which is a close proximity to the origianl , sells for 154, so i went with the whole new unit , hopefully it will be a good fit and function . i will return with another post if when installed this fixes my problem thanks for all the help . by the way the egr valve wasn't sticking , it was a bit clogged with carbon, but didn't seem to make much diffffrence when cleaned .
 
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