2000 gmc safari bucking at part throttle

lone racer

lone racer

Club Member
about a month ago wife had a issue in wet/slushy condition van started misfiring and staled but after a few minutes started,when I got home pulled the dog house noticed the coil wire half off and figured she had 80k on it since we got it and did a new coil,wires,plugs,cap,rotor also fuel filter. No issues till sat night it did the same thing except it backfired when she tried restarting it. It now has a bucking(I don't think ignition break up) it is a erky jerky/ smooth-rough-smooth-rough etc.. when normal driving off idle and a slight bucking at speed. If I dog on it no bucking. fuel pressure guage shows good even when it dose it, haven't found a vacuum leak nor a ignition arching issue. no cel
so many possibilities I started pulling maf plug( it ran better but not 100%) no cel. With maf pluged in pulled tps,crank position sensor and iac and nothing happened at all no cel no change in bucking.
scanner is showing 99.2 stft b2, tps .004 or.04 at idle and barely jumping to .0/.007 for a sec when playing with throttle then settles back to the 4.
I can not interpret what the scanner is telling me, and without a good one and ability to understand it mine will do me more harm than good I think.

With almost 200k should I start with possible dizzy gear being worn, ecm,maf,iac,ETC..r2d2,pms lol.
I really cant just throw money at it in hopes
If you are able to scan and near me I can drive to you and compensate.
If you know any thing im ears.
 
Get a brand new distributor and be done, not a junk yard one. I’ve been down this road with a 01 s10 blazer, they have moisture issues or the screws are loose on the rotor or the body is cracked by the cap screws( plastic housing).
 
4.3
engine off key on = 60 psi
running = 60 psi
during buck session = 60 psi
engine off pressure maintained 60 psi, bled off pressure key off then on = instant 60 psi maintained 58+ while running and bleading off.
 
can you see the MAF wires inside the housing? May be broken. My old iroc had same symptoms with broken maf wire(old style maf with long wires in it)
 
A long while back had a Jimmy that ran like you described. Fuel PSI was no more than 5 psi less than what it should have been. Even during duck season. Changed the fuel filter & pump, it ran as it should... Guzzling fuel without even one-wheel peeling...it couldn't burn the rubber even when new!
 
Also easy to diagnose the distributor with a good dry out with a hair dry are and then hit the inside with some wd-40 and see what it does from there.
 
I have it in the heated garage with dog house out, and heat light for myself plus I spray wd as a routine, cap& dizzy had a squirt with new cap about a month ago
 
not having luck printing data, I have watched videos and have a very small idea what to look for, the cat is empty and oil foulers are used but has been that way for a year or so.
o2b1s3 (v) bounces every frame.
THIS IS WHILE DRIVING! 130,.125,.115.100.130,.095,.105,.295,.105,.130,.120,.195,.510,.675,.490,.220,.240,.195. etc..
SHRTFTB1S3% 99.2
 
Does the truck have EGR? Try unplugging the connector to the valve if it does. I had a car do similar stuff once, and it was EGR.

-Geoff
 
Pulled it and cleaned it but it wasn’t bad at all, no real build up.
Scanner is saying no Egr off idle and failing throttle down test?
The more I play the more I find. Didn’t even realize I could watch live graphing, data yes but graphing no! Gives a little better visual seeing a graph over a number,lol.
I will check the book for test procedures, the springy thing moves easily and seats fully, no carbon build up or binding.
 
CMYZ28 said:
4.3's hate dirty throttle bodies which might make sense with the no issues under full throttle etc.. Didn't see where you'd cleaned it unless i missed it. I'd start there https://youtu.be/lHLZfg5GYoA
Click to expand...

That vid makes it look easy, BUT in a van not so much. I did a sea foam treatment thru the intake tube just before the TB last year, I might go ahead and pull it but really doubt that is the cause, had that issue before with a 5.3 and it was a way different kinda miss off idle to maybe 2000 rpm the van is more like 2000 and up before it starts acting up. But I have wanted to chop off that dohickey on the the blade tho.

I do try to maintain and do preventative maintenance on her vehicle, put fuel cleaner, actually flush systems and ensure I have done my best to keep her safe. My car is another story, but it seems to like no maintenance and full throttle racing to the next light. 214,000 Focus wagon, swear I try but I cannot seem to kill it. Maybe time to quit doing oil changes?
 
lone racer said:
Pulled it and cleaned it but it wasn’t bad at all, no real build up.
Scanner is saying no Egr off idle and failing throttle down test?
The more I play the more I find. Didn’t even realize I could watch live graphing, data yes but graphing no! Gives a little better visual seeing a graph over a number,lol.
I will check the book for test procedures, the springy thing moves easily and seats fully, no carbon build up or binding.
Click to expand...

Just try it unplugged because if it is unplugged, the engine will know it, and run different timing and fuel. You can watch on your scantool too. If the trucks starts bucking when EGR comes on, then unplugging it will fix it.

-Geoff
 
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