Engine/Transmission (1994 - 1998) Sporatic Tapping ?

[Jeff H]

When I get hard on the throttle. I can hear this sporatic tapping. I gotta hit about 20 psi of boost to get it to do it. The rpms up around 1800 on up.

It don't do it cruising at any speed. But just when I get on the throttle hard and accelerating.

 

[Mike Ellis]

I had a loud hammering noise that would come from the driver's side of the engine under heavy load. Illflem suggested it might be the lift pump getting ready to tank. When I next changed the fuel filter, I found brass powder in the bottom of the canister so it seemed that his theory might be correct. I had the lift pump changed out at Cummins and the noise went away.



This wasn't a soft tapping noise, it was a loud "get your attention" hammering sound... .

 

[JJW_ND]

Cold weather noises

Jeff:



It is winter and cold out and our trucks make lots of new noises that seem to always go away when things warm up.



I chased a tick the last two winters on mine. Changed lift pump, old one was fine. Reset valves... . all were where I had set them 25K previousely. Still had click. Would go away when warm out side.



Recent top end work and increased timing made for lots of new noises but no TICK and more even when cold.



I guess that means you need a new headgasket, 60 lbs valve springs and timing bumped to 20. Yet that should make the tick go away. NOT!



jjw

ND

 

[Jeff H]

Hi guys.

This has been going on most of this year. Outside temps don't seam to make any difference. I set the valves a few weeks ago. Still does it.

It don't seam to matter how fast I'm going. Just when I put the throttle to the floor.

Just a question though. How does making the engine work really make the lift pump make noises? Isn't the lift pump working the same whether going down the road or mashing on the go pedal. I have 188,000 on this lift pump. Is this pushing it? Last time I checked the pressure it was well within spec.

 

[illflem]

If you've ever heard an P injection pump on a test stand running without the other engine noises you'd take a step back for fear that the thing is going to fly apart. They are very noisy especially under load. Maybe try some lube type fuel additive and see if the tick goes away.

Sometimes when the actuator arm spring in the lift pump starts getting weak the arm will tick against the cam but it's more of an all the time noise that you notice mainly at idle. You're right, the lift pump works the same all the time no matter what the load.