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6.2 and vacuum regulating valve ?s

8

851009

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My 6.2 has 92k on it,runs and starts good,but idles a bit rough.It has electric lift pump,spin on fuel filter,new fuel lines from tank to filter,new injectors,fuel pressure into spin on filter is 6-8 lbs. same coming out of filter,I think IP is good because truck starts and drives down the road at 65 plus mph with no lift pump.(I forgot to turn on a few times) It only smokes a little bit at top of shift points when floored.Recently did compression test all cylinders 395-405 psi,motor runs smooth but at exhaust sounds like a big block with a big cam,at idle especially when cold truck will jump a bit in gear at idle.above idle all is perfect,smooth,good mpg..Most people love the sound of it but it kinda bothers me as it only idles ruff. Also I just installed new vac.regulating valve,it seems to have two adjustments on it,one for the whole body of it,one where the center section shifts.Is one for shift points and one for firmness of shift?
 
Your vac pump and shift valve is unrelated to the rough idle. Reason; diesel engines have no throttle plates thus create no vacuum.

The valve will vary the shift points relative to throttle position. Some fiddling is required.

The rough idle could be a number of things but I suspect air entering your fuel system somewhere.

Welcome to TTS.
 
Thankyou,I knew I should have started 2 threads for 2 separate questions,I do realize vacuum has no affect on my rough idle.Im gonna try a clear fuel line on IP return line,I bought wrong size today.I am curious about the adjustment of the vacuum regulating valve on the IP.It seems to have 2 adj. points,main body and center of main assembly.
 
3500GMC said:
Your vac pump and shift valve is unrelated to the rough idle. Reason; diesel engines have no throttle plates thus create no vacuum.

The valve will vary the shift points relative to throttle position. Some fiddling is required.

The rough idle could be a number of things but I suspect air entering your fuel system somewhere.

Welcome to TTS.
Click to expand...
Thanks,I installed a clear fuel line on return line,no air bubbles at all,next step is rebuilt IP,but I cant believe its bad because truck runs and starts so good,and doesn't smoke. If you search rsh4364 on youtube then 1009 rough idle you can see it idling,any input appreciated.
 
I wouldn't go after ip yet. Have you tried cracking injector nuts one at a time so here any weaker firing cylinders? If you find a weaker cylinder, swap that injector with a stronger cylinder injector and see id the drop power cylinder moves to the new location. If your not afraid to shotgun some $ after it, I would hit new injectors on that before an IP. I have not seen an IP that caused one to lope like that.

3 other things to check: tps setting, where is your idle set, and your timing?
 
If you try retiming it, remember to make the timing adjustment with the engine off then restart. Do not move it with the engine running.
How many miles on the engine? I would be more suspect to a worn camshaft or dished lifters than an db2 IP causing uneven feed to cylinders.

If it is running smooth, just hearing the lope, could be just a critical ear maybe? I hear it, but it's still on a laptop so it's hard to tell.
 
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