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Discussion Starter · #1 ·
We have a 98 GMC Jimmy SFI and when hot or cold you try to rev it, it hesitates at 2-2500rpm and wont go past and when it does this it pops or backfires out of the throttle body. Now if you step on the gas real easy and bring the R's up slow it'll rev fine but under a load driving it hesitates if you demand any power out of it. Of course there are no codes that have been thrown, we had it tested anyway to see if there were any stored codes and there were none. We have replaced the follow parts since the issue started occurring:

Plugs
Wires
Distributor Cap
Rotor Button
Cam Sensor (On the disty)
Map Sensor
Throttle Poisition Sensor
Crank sensor checked out to be good
Cleaned up the intake on the inside

We also tested the fuel pressure, priming was 55psi and at idle it was 53psi. We dont know where to go next, check timing? Could still be a clogged injector or something? If anyone has any ideas let us know. Thanks in advanced.
 

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Sometimes I'm mean...alot
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Did you check for a clogged fuel filter?

Possibly a clogged Catalytic Convertor as well, try removing the O2 sensors ahead of the cat and run it. If it rev's like it should....there's your answer!
 

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Discussion Starter · #3 ·
Did you check for a clogged fuel filter?

Possibly a clogged Catalytic Convertor as well, try removing the O2 sensors ahead of the cat and run it. If it rev's like it should....there's your answer!
Cat is newer but could be the problem I guess and there is a new fuel filter, I should add that to the list.
 

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Discussion Starter · #4 ·
Well we tested the voltage to the IAT and the resistance and it checked out good. Also tested the resistance of all the injectors and they appear to be good at 11.8-11.9 on all. We are thinking it needs a timing chain at this point and it looks to be a pain in the ass to change because of the oil pan. Any one have any other suggestions?
 

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Sometimes I'm mean...alot
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We are thinking it needs a timing chain at this point and it looks to be a pain in the ass to change because of the oil pan. Any one have any other suggestions?
Timing chains never go bad on these engines...keep looking

Pull those O2 sensors and see what happens.
 
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