Hi,

something strange is growing at the moment : at iddle, the engine suddenly bounces up to 800~900 rpms then goes back to normal 600 rpms.
When cruising, it seems that sometimes the engine accelerate itself, a few seconds, then go back to normal.
At the same time, I don't know if it is my imagination, it seems the engine is making a louder noise.

This doesn't last for now, but I've been looking everywhere and everything looks normal.

Did that happen to some of you? Should I worry because it should announc a bigger problem?

Hi,

Should I worry because it should announce a bigger problem?

Yes

I'm not an expert, but the IP sounds like it may be on it's way out.

b4 my ip went on me i would be sitting at a light and the engine would surge. on another day i was standing at the back of the truck while the engine was running, it gave 3 short bursts of rpm increase in rapid succesion and spewed some black smoke. was i ever mystified at that since no one was in the truck. on yet another day i had to hit the brakes as the truck rpm's increased that i thought i'd rear end the dude in front of me wile at a light. on other occasions it would be like someone turned of the key but never enough to stall it till it started getting worse. gm warrantied the pump with code 1216. whether that is ip or pmd related is unknown 2 me. best you go thru the diagnostic. Ed

Doesn't sound good. Santa is not fair :mad:

I'm running 8 oz of 2 stroke oil in each tank refill. The oil I use is almost dark. The blend itself is just a little greenish, but should it be enough to fool the optic sensor of the IP and make it working bad?

Check wiring to the CTS first....I had similar problems with my 94....the truck would move from high to low idle and the timing would change rapidly....wound up being the pigtail to the CTS...

Check wiring to the CTS first....I had similar problems with my 94....the truck would move from high to low idle and the timing would change rapidly....wound up being the pigtail to the CTS...

CTS? or CPS (Crank Position Sensor) :cool:

If you're checking the IP out as a possiable problem, check the distributor rotor.
"GM had a few complaints about engine surging, possibly due to some wear on the rotor where it contacts the rotor retainers. Excessive wear in that area would increase the poppet valve stroke which would cause the fuel delivery to increase beyond specification. Wasn't seen oftan, but other issues related to rotor wear was black smoke, bucking, rough idle, harsh shifting and engine overspeed.
When rotor wear is the root cause of an engine surge complaint, an "idle fuel rate" of 0-3 cubic millimeters / stroke is displayed when checked with tech 1 or 2 scan tool"

6.5L Turbo Diesel Volume II

I was reading about the DS4 pumps, not sure how similar it is to your issue, worth checking out though. I have no clue how to check though, besides the scan tool.

Hope it helps.

Maybe also check that AC compressor is not siezing. Doesnt sound like a complete runaway that would indicate a for sure pump failure.

CTS? or CPS (Crank Position Sensor) :cool:

CTS - coolant temp sensor aka ECT - engine coolant temp sensor....

CTS - coolant temp sensor aka ECT - engine coolant temp sensor....

Thanks all for taking time in helping me.

I have cleaned all grounds (except the one close to the downpipe) will do oil change in days coming and will do it at this time).
Also, I had the negative terminals on the 2 batteries full of a kind of white and green powder. I've clean them and put some dielectric grease on them.

I also check the CTS, unpluged the pigtail and carefully replug it. The CTS itself is only 1.5 month old, so I hope it's not a factory defect.

At the moment, everything seems to go back to normal. Grounds or CTS pigtail. I bet pigtail. Anyways, I cross fingers, and will have a look at the codes as soon as possible. ;)

BTW, what should mean this powder on negative terminals? By the same time, I remark that my crancking speed is low.
Luckely for me, my truck starts very easy, but if I should have to cranck a long time, not sure I will have enough power.
Should that mean that my batteries are slowly dying?

White powder is corrosion....I would place bets that the corrosion is in the battery cables themselves....only cure is to replace them...

If the truck acts up again - pop the hood and play around with the wiring to the CTS with the truck running - if the CTS or the pigtail are causing issues you will find out quickly....

Baking soda and boiling water in a glass, be careful when you mix the two, it can bubble over the glass, so don't hold it, it will burn you. Take that, pour it over the terminals with the white/green corrosion, and it'll disappear.
Dielectric grease is a very wise investment for any terminals, I use it in my parking/turning lamp sockets too.