Hey all I have a 2000 GMC 1500 4x2 4.3L Vortec. I have a misfire on light accleration about 1500-2200 RPM and when in Park or Netural lightly pressing gas. I just lost the coil so replaced coil,Dist cap, Rotor button, Wires and Plugs (Delco Plat).

Which brings me to this I had on a scan tool and my friend said you got what looks like a dead miss on 135 and real bad on 246 when its happening. So I told him unplug the tps and it goes away, he didn't believe me. So I unplug it and truck revs fine. I can drive it with it unplugged and get very little missing of the engine. Plug it in and returns to bad miss. Scan tool said tps working and nothing throwing codes.. NO LIGHTS AT ALL??

Now when u press brake and put engine under load no miss at all. same with driving light on the gas and misses and heavy it goes away. This has me stumped. Things possible? Distrubitor gear, o2 sensor?

Plz help

 

It should of turned cel when you unplugged tps. Vacuum leak or maf sensor needs cleaned or bad. You can take maf off spray with cleaner you can get at auto parts store.
Be real careful with it do not touch filaments on bottom. Just spray them , let dry good put back on. When you unplug any sensor disconnect battery first. Try this first go from there.

 

Thanks i'll try that tomorrow!! By they way I have had 4 yrs in parts at gm dealership and 6mths in ford.. got everyone stumped around here.

 

Tried cleaning and still the same. I have a Distributor gear on order and let you know what happens....Seems to be leading in the direction!!

Keep ya posted

 

On your truck if the dist.cap not good and tight will draw moisture. Also i belive one of the ac lines drips on the dist. Make sure vent hole on dist. housing is clear. Can put a little bead silicone on cap , then tighten good. Only things i can think of .

 

Is the throttle body clean?
I had a 4.3 miss that was bad and I had everyone stumped as well and it ended up being the rail that the rocker arms ride on was cracked right under the #1 rocker and it wasn't allowing the valve to close all the way. My GM parts guy told me it was the first one he had ever ordered at their store. I pulled my hair out and did a lot of unecessary repairs (including pulling the head) before I found the issue. If I never would have pulled the head I would have never found it though. It ran great after that $5 part was installed.

 

Yeah the body is clean, just finished cleaning it. It could be same issue as yours, but i'm leaning toward the Dist gear. Seems to be fairly common and same symptoms (although they are the same as 1000's of others). Right now its -10c and snowing so I'm putting the project on hold for a few days till it warms up a little...supposed to be in the plus later in the week.

Keep ya posted.

P.S. I got my Dist gear today so we'll see what happens.

 

Its fixed finally. It was the gear, there were no teeth chipped or anything but small amount of wear on it. Replaced and better than ever!!

Cmenchion

 

Im New To All Of This Stuff....Where Would I Begin To Check For A Vaccuum Leak?

 

You'll get more responses if you start your own thread, but you can start looking for vacuum leaks around your intake and throttle body as well as check all vacuum lines for cracks. If you have a good ear sometimes you'll be able to hear it sucking air.