I have a 1999 jimmy. it seems to idle fine, maybe a little higher than normal (1100ish) , the problem i have is when im driving. for the most part it seems normal, but when the engine gets put under more load (road inclines, and the truck slows down, so i push a little more on the gas to maintain speed, but not enough to make it downshift) the closer i get to the point of it needing to downshift to accelerate as fast as i want it to, it begins hesitating or stumbling. like it cant accelerate at all, it stutters. It only does this as it reaches heavier load on the engine, once it downshifts it is fine. It will stutter in any gear, once the engine is under enough stress.

im trying to rule out possibilities.

i dont smell any fuel in the engine bay or anywhere for that matter, so (rule out fuel pressure regulator, fuel spider?) can the spider just be clogged but not leaking and cause it to not inject enough fuel as the engine requires a lot under load?

Ive done a new fuel filter, so not that

cap and rotor look like they should not be having any problems at all, very minor wear on them, previous owner probably did it recently.

so whats left? distributor ?, i feel like that would be a more constant problem regardless of being under load or not, idle/acceleration etc would all be crap if the timing was off

any ideas of where i should look now? i was thinking about renting a fuel pressure gauge at the auto part store to check that out.

supposedly the spark plugs are recently done (all of them) and being as hard as they are to check, i am curious, where to go next.

 

I would go ahead and do the fuel pressure and leakdown test. To rule it out. Your idle is pretty high, when warm it should be more like 550. So it could be an ignition issue as well, but start at the fuel.

 

fuel pressure test seems easier than a leakdown so i will start there and report back. thanks for pointing me in a direction =)

 

You do both at the same time. To do the test, turn the key on but engine off! It should be about 60 to 65 and shouldn't go below 55 for 10 minutes. So post back your initial number and the number after 10 minutes.

 

alright, well i tried to record the fuel pressure gauge with my phone. Then my battery died and it wouldnt start. So i figure, it dies alot, i went to the store and bought this compact jump start battery you plug into the cigarette lighter. i came home, the battery was so dead it wouldnt accept the charge. so i pushed the truck out of the garage, then jumped it with my gf's car. then i drove around the block a couple times and came back. Now the thing i bought was working, so i had it trickle charging my blazers battery, i hooked up the fuel pressure gauge and tried video recording it again, now the fuel pressure gauge reads 0 no matter what. this job has turned into the biggest f'ing nightmare. so i head back up to the auto parts store to return the fuel pressure gauge and along the drive there the truck is sputtering along and running like ****, like its running on 5 cylinders or something. it seemed like it had a misfire on maybe one cylinder while idling. and a hesitation upon initial acceleration from the stop light, and if i press hard on the gas pedal it really sputters and doesnt accelerate very well at all.

I didnt really get a chance to do a good fuel pressure test, i will have to do it again. when i first turned the key on, the pressure gauge went to 59, then slowly worked its way down to 53psi. after all the bull**** that happened, i finally got it started and the gauge no longer worked, it was 0psi and never moved.

 

Sorry to hear about all of the trouble. Another thing you can do before the fuel test again is go threw all of the vaccum lines and make sure there isn't a leak. Also, try cleaning the egr valve.

 

what really sucks with this whole thing is i have no CEL so i have no idea whats going on. Just randomly looking at possible things until something seems wrong. I will take my egr valve off today and clean it out, and look at vacuum lines. is there any diagrams of where the lines run to and from so i dont have to guess? ive never done anything with vacuum lines before. appreciate all your help thus far

also, about checking for vacuum leaks, ive heard you can spray something along all the vacuum lines as well as the intake manifold gaskets etc and if the idle changes youve found a leak. is there a recommended liquid i should be spraying? ive seen someone online say water, but wouldnt i not want to get water sucked into the engine, or, i could spray carb cleaner in there but is there risk im gonna blow my *** up? lol

 

Starby spraying the carb spray around the base of the throttle body. Do it when the engine is warm and idling. If the rpms go up or it about to stall you have a leak. As far as the lines, I've heard really soapy water will work but the best way is just a close physical exam. It sucks that it takes some time but I have found it to be the best.
I'm on the mobile right now and my service sucks but do some searching on here for the diagram, I'm sure its here somewhere. If you don't have any luck I will look when I get home tonight.

 

im not hearing any vacuum leaks, i sprayed carb cleaner around the base of the throttle body, and then i looked at the little picture of the vacuum diagram on the radiator fan cowl and tried to follow the vacuum lines. I will take a closer look tomorrow when i take it to my dads shop to have them hook up the scan tool. I did find a bad vacuum line but i dont think it has anything to do with driveability. It is on the right side of the engine bay (looking at the front of the vehicle) close to the firewall, there is a T fitting with some vacuum lines and one of them is split, i believe its for the climate control system too change where the air is blowing. but i could be wrong. it was not affected by carb cleaner, or by closing and opening the hole.

would it be worth my time to scan for codes? i know my check engine light is not burned out cause i see it when i turn the key. but it has not been on in a long time, several months.

 

Did you get this problem figured out?