Hey all,

I was talking with a local shop today, and they said that these engines routinely slip time on the pumps, and a good way to tell is start the truck up relatively cold (sitting a few hours), let the oil pressure come up, then drop the pedal to the floor (in neutral.) He said if it stumbles and smokes, the pump timing is off..

When I talked with Cummins NW, they didn't agree. They said that advancing the timing on these pumps is a method they use to compensate for wear, but at 130k miles, I should be fine.


My truck DOES miss and act up for a minute or two when cold. The white smoke doesn't occur unless I really nail the throttle within the first min or 2 of operation. If I don't feather the throttle when cold, it'll die. If I set the idle speed up so I don't have to feather the throttle (700-750), when the engine warms up I'm idling way too high. (Just shy of 1000 rpms in gear)

What gives? Opinions?

 

From the problems you describe, timing can be affected by a bad Overflow Valve.

The low pressure release of the overflow valve due to normal wear will slowly degrade and in essence retard the timing of the injection sequence due to a lower inlet pressure to the injector pump. This late timing will cause studdering, and misfire when cold. Also mileage may be an indicator.

My rig this year was starting more like a bear than last year. Similar symptoms to yours with misfire and white smoke under light load over 1500 rpm when very cold out.

Firstly I went and changed out the fuel lines to the engine as they were old and rotted. That was of some benifit.

Just recently I replaced the overflow valve and that cleared up alot of my problems. Before you pay for a timing adjustment I would definitely go and spend the $75 on an overflow valve and see if it changes anything.. I would bet it would make a significant difference.

J-eh

 

I do agree that it is common for the timing to slip but the symptoms they listed there can overlap with other things as well.

The OF valve is probably the single item the wears out most often on a 12 valve.
Precision Diesel Injection and Turbo Inc.
Marty Tompkins
888-734-7349
$35 + $5 shipping and handling.
Replacement takes one wrench and five minutes.

If you don't have a gauge symptoms are:
low RPM miss/instability
white smoke
hard starting
engine dies at idle
low power
fuel filter cracking

 

I'm curious as to how a bad overflow valve leads to the fuel filter cracking?

 

If the o/f valve fails in the closed position the pressure can go really high blowing out the filter and rubber lines. Over pressure can also allow air entrained in diesel fuel to separate and cause air bubbles, the specs that Cummins recommends of 35 psi max should be adhered to for a reason. Our lift pump is easily capable of putting out in excess of 100psi. What happens sometimes on a high mileage o/f valve is the ball seat inside gets worn and enlarged to the point that the ball gets stuck and won't release the excess pressure.
Over pressure is one of the reasons I don't recommend people fixing the valve by stretching the spring unless they have a fuel pressure gauge.

 

1)If your timing is late, the engine will stumble and smoke when revved up WARM.

2)Set your idle to about 850rpm in neutral on a warm engine.

3)Even if your timing hasn't fallen off from its factory setting, it would still likely benefit from a couple more degrees.

 

Also if the truck is equiped with A/C it should be on when setting idle speed.

Yes a couple degrees of advance may help make the motor feel a good deal peppier off the line.

 

Well, I've also noticed recently that if I stomp on the throttle while going ~65 and uphill, it tends to vibrate, almost like its missing.

Another thing that's happening recently that wasn't happening before is turbo bark. Maybe it's just cause I never abruptly let up on the pedal during high boost, but that seems unlikely. I'm not sure exactly, just know it does do it now.

 

" if I stomp on the throttle while going ~65 and uphill, it tends to vibrate, almost like its missing"

This sounds like shudder, the automatic trans slipping. I had it, an aftermarket trans cured it. I don't mean to alarm you, but like the doctor said "don't do that." 65 MPH in OD isn't enough revs for the transmission to have enough line pressure to transmit the torque you are making. Do a search for several days' reading on this topic.

 

Well, I did some reading on trans/converter shudder, and it doesn't seem like thats it. It's quite mild, you only feel it in the floor. It doesn't shake the dash or buck or anything like that. Also, the RPMs dont go up without a corresponding increase in road speed..

Just had the trans serviced last month, and he said the pan looked pretty clean. I did ask and make sure he refilled it with ATF+3, btw.

 

I thought the fluid supposed to be in it is ATF+4, granted not very many manufacturers carry it.

 

ATF+3 or Dexron works great in a '96.
+4 is a dollarship only item

 

I haven't heard that one yet, dollarship. Nice. I normally use *********** but the word steal-er-ship catches a cuss filter.

I presume it is the same in all 47REs? I heard Redline C+ is supposed to be good for this, anyone else hear the same?

 

Now that's odd.. I wonder why they'd care about the word stealrship ?

 

I stopped using it a couple months ago and it was just the word steal-er so maybe they got sick of seeing ******ship?