Okay I have a 1998 GMC Jimmy SLT 4x4 with the 4.3 vin W motor and 4L60E auto tranny.

The truck revs great in park/neutral, however taking off and accelerating it had a hesitation small misfire and sometimes a little bit of backfire. Almost kind of like its bogging out. It is lacking power quite bad. Sometimes its fine but quite often it does this. Doesnt matter on the temp, initially I thought it was doing it when it warmed up, however that doesnt seem to be the case now. Im familiar with these trucks as I have owned several and I can not figure it out for the life of me.

It has solid 60psi fuel pressure @ idle.
I have replaced the plugs, wires, cap/rotor, distributor, cam position sensor, and ignition control module. Its improved a little but not much. It is not throwing any codes. Also it does have a new transmission in it. It was doing this a bit prior to the tranny being rebuilt.

Any suggestions where to go from here?

 

I have a 2000 blazer with 120,000 miles that does the same thing, no codes, and its only under hard initial acceleration. Did you ever find out what it was? I dont know where to start.

 

Ahh I'm having the same problem I wish someone had some help

 

I'm having the same problem on my 97 4x4 blazer it only seems to do it under normal acceleration. Under light and heavy acceleration its fine, but under normal acceleration it seems to miss fire around 2500 Tom's.

 

mine will only accelerate ever so lightly, i can floor it and the rpms stay at 1.5, 2 and it revs but doesn't accelerate.. I'm thinking it could be the CAT I don't know though.

 

I made a post about this too mine only hesitates for a second at about 750-1000 rpm then runs fine. I was told to clean the MAF sensor. I'll do that today and let you guys know if it helps.

 

This is an issue that many have faught with and I did everything under the stars trying to solve mine. If you want, look up my post, or just make it easy on yourself.
If you replaced your cap, rotor, and wires with anything other than AC/Delco, and are not running AC/Delco platnums then be prepared to chase this gremlin for a long time.

 

Try the crank position sensor I read it on a chevy forum thing. guy had the same problem. replaced everything that had to do with the ignition. changed the Crankshaft position sensor fixed it right up

 

Go back and replace the plugs with ACDELCO Professional & Belden Edge Wires from Nappa! Sensor to the Cat I found many plugs don't relate to the W engine like the professional acdelco ones do!

 

my 00` blazer stared to not start at running temp whenever parked on a sleght hill or incline like in parking lots,let it cool off it`d start then started running like i had 2 cyl`s other times fine,but i was at 100K even by the time i had money so i did the cat 1st,but i had ordered a new disty from ebay 8 months b4 just never put it in.well the cat didnt do nothing,finally i put the new disty in and did cap/rotor/wires/and all plugs but the idiot plug behind the stering rack,and for almost 2 years if i hit 3K or more rpms it`d drop like you threw bucket of air in it n act like i had only 2 cyls again,finaly i just went and screwed with the wires nd smaked the cap and rotor assemby few times real good and problem solved.Never thru a code but now keeps telling my something bout the cat.