The $5k mystery noise

[a5redwing]

I haul logs with my 1998 ch 355/380 (last six 107636), and here about a month ago I was loaded in the mid afternoon and the temp was in the mid 90s. Out of nowhere I started to hear a popping and surge in RPMs (about 50 to 100). I've heard this noise before, it sounded like it was firing back out the intake. The water temp had been running warm around 200 the motor derated and struggled. I got to a small town and slowed down trying to find a place to pull over, got stopped looked and listened around got back in and it went away. Next day loaded midafternoon samething. This went on for two weeks so I put it in the shop. First checked the computer, replaced air intake temp sensor and both engine position sensors. Next ran the rack on it, some of the valves were a little tight. Mech. said your fixed and I left. So the next day same thing and still running a little hot, ran it for a while took it to a different shop. Ran the rack again checked the cam kept it for a week and said "I don't know". Ran it for another week and put it back in the shop. Two rebuilt heads, new thermostat, checked cam AGAIN a few other odds and ends and "your fixed". Guess what, it aint. I took it home and cleaned out the rad., intercooler and condensor. The next day it ran cooler, had more power, and did not make the noise again until I ran it hard and came into a mill and lugged it a little and POP. It had gotten where it did it all the time loaded rarely empty and once cool nothing. Now it does it after running down the Hwy. and going back through the gears with temp 180-+. Out 5k not including down time this sucks.

[a5redwing]

Wow, no takers? I think I fixed the problem though. Went in for a leaky injector and found a broke spring on a unit pump.

[j hancock]

Sorry to read about your problem but I guess the rest of us are baffled along with those who have worked on the truck for you.

Nothing worse than changing everything including the kitchen sink only to have the problem persist.

Hopefully, it will be set for you now.

[a5redwing]

Your right, nothing makes you feel much worse than doing all you can and still have the problem.

[thomastractorsvc]

totally agree, hope you got it fixed

[Dirtymilkman]

Did The unit pump cure the problem??

[Mack Doctor Jr.]

What kinda noise was it making? a constant pop or like a loose valve adjustment sound?

[krismoriah]

if u have an econovance..that sounds like a possibility if the injector didnt fix it.

[David]

Have you checked the lift on each push rod. Could be a bad lobe on the cam.

[boyd]

On the eup the rollers have been known to kick sideways making the roller run sideways on the cam lobe. Even after running sideways it could pop back straight and run the correct direction. Even when the lobe is sideways it is still being pumped by the lobe it is just not as fluent as if rolling on roller. You can run the truck if this happens but you will destroy your cam if you run for a extended period of time. You will notice very little difference in power when this happens, but you will hear it when it moves. There is a small roll pin that holds the roller cup on the end of the eup if it is gone this is why it is kicking sideways.. You can remove and if you have a good spring and the cam and roller look good just replace roll pin...

[a5redwing]

Well the problem more or less just went away.?. All the money I threw at it did nothing. I kept running it and one morning I had a 2-3 code show up (intake air temp sensor). Stayed on all day that day with no other problem other than fan runs nonstop. Code comes on erratically sometimes all day sometime not at all, mostly on and off during the day. Since it has been doing this no miss or backfire. I have a new sensor in it and I'm going to get another in case that's the problem.

[a5redwing]

I forgot to mention when code is active truck makes full boost, and a lot of the boost pressure flutter goes away.

[a5redwing]

What kinda noise was it making? a constant pop or like a loose valve adjustment sound?

A pop every second or so, sounding like it was coming out the intake.

[fxfymn]

Have you gone through all of the wiring harness connections to clean and grease them with electrolytic grease? Intermittent issues like this that show codes can come from a wire that is breaking connection. (I had this happen on a 2011 Chevy HD with less than 40k on it)

Are all of the grounds solid?

Has the dealer checked for service bulletins? My Chevy had one, but the first dealer never looked.

The curse of a modern vehicle is everything depends on an electrical connection. The days of looking for a broken piece of linkage are gone.

[staxx]

I have had a cam gear come loose on a cam shaft before that caused low power and popish threw intake before . The keyway had sheared off and the gear was moving back and forth a 1/4 in or more.

[rsb502]

The key or they keyway? The little square stock is the key and the little cutout it fits into is the keyway.

[staxx]

Key was rolled sideways and keyway had bin dug out 1/4 in both directions

[a5redwing]

Crossing my fingers when I say this, I THINK it's fixed. Replacing the air intake temp. sensor again seems to have fixed it. No noises, issues, or codes. Guess the first new sensor was bad. Hard to believe a bad senor could reek that much havoc, but I won't question it. Just happy it's "fixed".