RPM's Fluctuating
 

1995 S10 Blazer 4.3 V6 (W)

Ok, this engine came from the local Salvage Yard and I replaced all the seals, water pump, intake manifold gaskets, nut kit, plugs, rotor, wires, dist. cap. I inspected the distributor gear before reassembling everything and it looked fairly new.

The truck fires right up and idles very good but, I noticed that if I hold the accelerator at a constant RPM....it will start to fluctuate down 100-200RPM's and then go up to the original RPM.

It sounds like it has a miss at idle but I am unsure, I have not been able to drive it yet cause I have the front end torn apart at the moment. I have included a video so you all can see what it is doing. I am hoping that driving it will help clear it up cause it has not been driven in about 8 months.

If anyone thinks I have a problem and might know what it is please feel free to let me know.

Thanks,
Frog


YouTube - RPMs ???


http://www.youtube.com/watch?v=N0tmvM8BOcE

Hmmmm....well, I finished installing the intake after work today and while the truck was idling I could hear a faint popping sound at the intake filter. Then also about 5 minutes after I started it I could actually hear the injector pulse (spider)...is that normal?

I revved the engine slowly and the buzzing/ticking sound of the spider changed with the throttle application.

I think it is backfiring thru the intake a little and that is what I think the popping sound I hear in the intake is. Timing???

The large drop in RPM's at 33 seconds in the first vid is me letting off the throttle some.

No input...from anyone?? Hmmmmm

Either I don't have a problem or this is a tough one to answer.

does it always do it around 2000 rpms?

I wouldn't call that a problem... Probably just slight changes in throttle position given that it doesn't take much throttle angle to alter RPM in neutral/park.

If, after you have driven it, there is a noticeable hesitation under load, then that is a different story, but no use speculating until you have put some seat time into it while moving down the road.

Does it at most RPM's above 1000 if throttle is held steady.

Ok, thanks. I will let you know. As for being able to hear the injector assembly....is that normal?

Oh, and the popping in the intake....would/could that be more of a timing issue?

Could be a number of things. Improper spray pattern from the poppet nozzles, timing, plugs, EGR stuck partially open, etc.

mine has the hesitation bad at 2000 rpms when trying to shift . it feels like it doesnt know if it wants to shift or not . it only really does it if im light on the gas , if i floor it it takes off and skips the hesitation. i tried seafoaming it but it didnt really help :(

Ok, so I checked the timing and it was dead on. So, I checked for vacuum leaks and did not find any. I made another video and removed some of the variables and you can clearly see that the RPM's are dropping with steady throttle input.

http://www.youtube.com/watch?v=aOOvpI0EcKw

At idle I still hear a slight popping in the intake and the engine jerks/shakes a little. I took it around the block (could not get above 40mph...residential streets) and it seemed ok...shifted good all the way to 3rd...did not have enough street to get it in OD.

It does seem to lag a little from a stopping start while accelerating briskly. But, I do not know if it will do the fluctuating while held at a steady RPM while driving. Could it be TPS, EGR or etc....I have no CEL on either.

Thanks