This is a 98 12 valve : The engine is slowly getting louder and louder.Taping and clacking.I can hear the exhaust more than usual.Starts fine,idles fine,does not miss,no exhaust smoke unless i get on it, its quieter when cold.Replaced the overflow valve this weekend.(20 lbs at idle and 2k)helped some but after 100 miles the noise is back.New fuel filter but the strainer is unknown. I can sure use some help on this one.





!998, 3500, drw, 4500, 85k miles, kdp tabbed ,bone stock.

 

might want to have the overhead run on it.

 

Sounds like it is time for a valve adjustment.

 

lift pump and possibly timing

 

Can the timing move on the ctd? With the fuel presure guage connected I have about 37 lbs at idle with the guage holding steady. with the engine at temp the guage is jumpimg around so bad I dont know what the pressure is.(What does that tell you?)Using a flow control in line with the guage still does not help. Will do the valves this weekend and go from there.Thanks for the help,keep it coming.

 

Yes, you can set the timing on a 12 valve. The lift pump not keeping steady pressure indicates a problem. What kind of problem I don't know, most of my knowledge lies over with the 24V engine.

 

If your fuel pressure is 37 at idle it has to be way too high at higher rpms.
This will definitely cause performance problems, replace the overflow valve.
The reason the pressure is all over the place is because a 12 valve lift pump pulsates quite a bit, not because it's bad. If you allowed the gauge to jump around for very long it is likely damaged and can't be trusted.

 

The overflow valve is a new one from Precision Diesel,just replaced last week.The o/f valve is a pressure relief valve.I believe It is dumping at 37 lbs and should dump at that pressure what ever the rpm.The gauge was installed only to check fuel pressure.I just finished adjusting the valves,sounds a little better.i drive 35 miles to work so i'll see how things work when i get a little heat into it.

 

Reguarding the timing question, my question was, can it move.( IE jump time.)

 

I have only seen it slip (dramtically) after advancing the timing and usually caused by not cleaning the taper seat on the shaft & gear or the bolt wasn't torqued enough.

Many reported the timing will slowly retard with time & miles on the engine.

 

The lift pump is positive displacement meaning flow increases as the engine rpm increases.

The overflow valve is a pressure relief as well as flow regulator. The relief trips at approximately the same psi, but the flow regulator does raise the overall pressure when the lift pump is flowing more.

The best way to see this is while the engine or entire truck is on a dyno.
The pressure will climb significantly with higher rpm, but dip again when loaded ie burning more fuel.

 

It's not all that uncommon for a new OF valve to be bad. Every 12 valve whose pressure I've measured jumps about 10-15 psi from idle to 2500 rpm.
You are looking at blowing some expensive to replace seals in your injection pump if you continue to run it with fuel pressure in excess of 45 psi. Normal fuel lift pump pressure specifications are 17 - 22 psi at idle and 25 - 35 psi at 2500 rpm

High fuel pressure can be caused by installing the overflow valve in the inlet (where it fits perfectly) rather than the outlet of the injection pump.

 

I will reinstall the pressure gauge and double check the pressures.
The o/f valve is installed in the return line.I had to use a die grinder to provide clearence for r&r.

 

I stand corrected,thanks

 

I took Infidels advise and put a needle valve before the guage. The guage fluctuations were no longer a problem. Just crack it open, worked very well.