Well I acquired a "new to me" ride today and been having fun cruising around getting used to a 12-valve. Quite a change from the 3 "electronic" beasts I have owned/own.

Other than the Rip Rook exhaust and AFE filter the engine hasn't been Bombed, the P7100 is virgin territory. One thing I notice is spoolup seems rather sluggish and power is flat to about 15 psi then all of a sudden it pulls good 'n strong to 3000 RPM. Boost rockets from 15 to about 27psi. Doesn't have a lot of ooomph at lower boost and RPM then really comes alive above 2000 RPM/15psi.

Another thing I notice is even when it starts pulling strong it doesn't emit any smoke to speak of. Then around 2800-3000 at WOT it's a volcano, sudden huge cloud as if someone flipped on the smoke switch. EGTs shoot up but there is no increase in power. . . I am running into the governor right about then. Any ideas what is going on?

I am going to check for boost leaks then try adjusting the star wheel. . . do you crank it toward the front or rear of the engine for more fueling down low to help spoolup?

When I get a chance to look it over good I am going to check for boost leaks, I thought I heard a whistling sound around 25psi.

For an old truck I really like it even though it needs quite a few little "fixits," I'm looking forward to having fun with it. I like the more natural feel and response of a mechanical pump vs. the electronic variety. The other 12-valves I have driven that were basically stock seemed to have more power down low then start to drop off noticeably above 2500, this thing pulls strong to 2900 then hits the governor 200 RPM later.

Vaughn

 

the top of the star wheel turns towards the engine for more smoke-or more power before boost kicks in...

 

Vaughn, does it seem like anyone has been inside the pump, is the break-off screw removed or the retaining wire at the rear of the pump broken?
Reason I ask is because the boost you are seeing and 3000 rpm wouldn't usually happen unless someone had tweaked some adjustments.
Your new ride might not be as stock as you think.
Put in a 3k gov spring kit, a #10 plate and bump the timing to 16.5 and you'll be grinning.

 

That truck does not sound stock, with 27# of boost. Also, are you sure that the turbo hasn't been changed to a larger one with less spool-up?

Just a thought, but try pinching the boost line from the AFC to the wastegate with a pair of vise grips.

 

sounds like the watse gate dumping to me.

 

If the wastegate was dumping/stuck open he'd have a ton of smoke at low rpm

 

Infidel, the top screws including the breakoff still have factory paint on them. I just went out for a look and felt around the back of the pump since it's hard to see back there and felt a piece of small wire with a lead weight. I thought maybe the pump could have been swapped but made to look untouched but everything looks to virgin, no sign of the bolts being tampered with.

The turbo looks pretty virgin too, it appears to be a typical HX35 but not sure what housing it has, whatever comes stock in '96.

I will try squeezing the boost line or testing it with compressed air, but given the fact it makes no smoke when I hit the throttle tells me the AFC needs turned up or maybe the overflow valve is getting weak, or something like that.

I'm not as concerned 'bout this though as I am about sudden heavy smoke near the governor cutoff.

This truck has a lot of miles so the pump is probably due for a good going-over. I don't know how long a P7100 usually goes before it needs a good tune-up or rebuild kit or whatever.

Vaughn

 

The 27 psi and 3000 rpm are not stock values. The stock 215 hp pump should give you 21 psi and 2600 rpm max.

The black smoke above 2900 rpm might be the waste gate finally opening or the pin following the fueling plate going off the end. Does the elbow fitting on the boost pressure line to the turbo have an allen screw in it. The stock elbow on the boost signal line is plain with no added screws or holes.

You need to pull the top off and look at the fuel plate to see if it is stock and in the center position. Some pump kits included a new breakoff screw and matching Cummins paint to cover your tracks.

If worst comes to worst, you may have to take a trip to Wentland Diesel to get the pump calibrated on the pump test stand. If it is set up on the test stand you get the pump timed as a side benefit with no cost increase.

With the 5 speed, you can use the 4000 rpm GSK with new valve springs. (The diesel automatics cannot make good use of the increase over 3000 rpm.)

 

Al that's what I'm thinking to do, take the covers off and look it over. . . maybe I'll have you and Leon come over and show me what to do

Maybe the cam plate or something slipped? I suppose it's possible it was tweaked and then the seal redone at the back, who knows. Nothing like a little mystery to try and solve

Vaughn

 

3000 RPM is what i was seeing in my 97 bone stock. But, the wastegate should have been factory set around 18-21 psi. You might heck the boost line running from the turbo to the AFC housing. It should have a hose barb with no restriction.

Some foks have been known to install a fuel plate and use the breakoff screw provided in the kit then touch it up with the Cummins paint to make it appear stock.

 

Well I tried it again and WOT it maxes @ 24-25psi. Vaughn

 

Well Vaughn, you only have 10 more to go till it runs right

 

LOL Infidel Very true!!

 

Why stop at 10psi more?

 

hey i was just wondering why a stock auto wont turn more than 4k rpms i recently ordered the 4k and 60 # valve springs but everybody ive talked to said i might as well have got the 3k and saved money