4911 Inner Workings

[jmiller]

I know this post is three months old but since no one else replied here is my two cents. The only screw that I would mess with is the Fuel Screw. Alot of people feel that messing the inlet screw gives them more power. It can but all it does is advance the timing on the injection pump by increasing the housing pressure. The biggest problem with adjusting this screw as that it moves the timing curve to a different area in the RPM range. If you were placing it on a motor that had a different operating window it may not be a problem. Increased wear and tear are also problems with the higher pressures. Most of the "Gain" people feel when messing with this screw is due to them reclaiming lost advance due to worn engine and pump components. Without a test bench it is anybodies guess as to what is a safe rate to increase this.

Honestly, I wouldn't make any pump adjustment without being on a test bench to verify what in the hell I'm changing.

If really required, idle and max RPM ok to make. But pressure and advance changes can make for more trouble than pulling the pump and taking it to a shop.

About the time you shear a pump drive or get thing out far enough to damage the engine, then what do you have? A steaming pile of :shiiiiiite:

If you want to boost fuel output, change the torque curve or timing curve, find a pump shop that will make those changes (some won't). They will make sure you have a pump that will be up to the challenge and verify that it will operate in the desired manor.

Unless you are really interested in just breaking things.

Trust me, I get great pleasure I pushing things and fixing them when the break. Just make sure you understand what will eventually break and be able to afford the loss when it does. 6.5 Carnage =< $7,000

 

[turbovanman]

Great thread and pics. Ok, my current pump is a dog, feels very flat like no advance, how much can I safely turn the screw inside the fuel fitting? I would like to try 1/8th or 1/4 to see if she wakes up?

Also, what is the max advance our engines like, I am getting another pump tested so I will turn up the screw before I take it there then I know who much the adjustment affected it.

 

[WarWagon]

Side arm is to roll on timing as you add throttle. The screw for case pressure is in the fuel inlet port. You have to remove the fuel fitting to get to it. The case pressure also controls timing by RPM.

Add more case pressure and the timing advance, like weaker distributor springs, comes on sooner. The extra case pressure also fills the plungers more/faster. I have read if you overdo it the pump locks up and breaks the driveshaft.

The next adjustment is the RPM governor screw above the fuel distributor head. Usually has a plastic tamper cover over it. This controls the top engine RPM and is known to start to cut fuel early costing you top end power.

Let me correct myself here. the side arm is a timing "retard". More throttle= more load so it retards the timing. Like vacuum advance where more throttle kills advance on gas engines.

Great thread and pics. Ok, my current pump is a dog, feels very flat like no advance, how much can I safely turn the screw inside the fuel fitting? I would like to try 1/8th or 1/4 to see if she wakes up?

Also, what is the max advance our engines like, I am getting another pump tested so I will turn up the screw before I take it there then I know who much the adjustment affected it.

1/4 turn will wake up a stock 6.5 turbo. But the SOTP is at low RPM off the line. Going NA to turbo takes 1/4 turn. So 1/2 turn from NA to power turbo. On a 6.2 pump this usually is the limit of the fuel screw: 1/2 turn. A .31 plunger 6.5 pump has more room for power.

Feeling flat is one of three things
1) Timing advance piston worn out or locked up.
2) running out of fuel: weak lift pump, plugged tank sock, 0 PSI at fuel filter WOT at max RPM...
3) That small factory turbo having an asthma attack over 2200 RPM.

 

[turbovanman]

1/4 turn will wake up a stock 6.5 turbo. But the SOTP is at low RPM off the line. Going NA to turbo takes 1/4 turn. So 1/2 turn from NA to power turbo. On a 6.2 pump this usually is the limit of the fuel screw: 1/2 turn. A .31 plunger 6.5 pump has more room for power.

Feeling flat is one of three things
1) Timing advance piston worn out or locked up.
2) running out of fuel: weak lift pump, plugged tank sock, 0 PSI at fuel filter WOT at max RPM...
3) That small factory turbo having an asthma attack over 2200 RPM.

Ok, just to clarify, not the fuel screw but the screw inside the feed fitting, you said it fills the plungers faster and adds more advance.

This was supposed to be a rebuilt pump so who knows, getting at the screw shouldn't be too hard, figured out a fast way to adjust the fuel screw without taking out the metering rod. See sig for my mods. :thumbsup:

 

[WarWagon]

The screw you get to through the top or the side of the pump is the fuel limit screw. It limits how far the plungers travel. It is the most adjusted as described above.

The screw at the fuel inlet is the transfer pump pressure screw. It affects timing more than filling the plungers from higher pressure. I have not had good results from messing with that screw.

 

[turbovanman]

The screw you get to through the top or the side of the pump is the fuel limit screw. It limits how far the plungers travel. It is the most adjusted as described above.

The screw at the fuel inlet is the transfer pump pressure screw. It affects timing more than filling the plungers from higher pressure. I have not had good results from messing with that screw.

First screw I know about, 2nd one is the one I want to play with, maybe I still will on the 4544 pump before she's tested, I"ll just mark where it is now and note the difference from spec.

Thanks.

 

[Will L.]

Thank you guys so much for this one. I forgot completely about this when I put on my turbo!

I ran with the n/a injectors as a base, then put in the used turbo injectors from my donor engine. It was so starved for fuel w/ the n/a injectors the turbo couldn't do a thing. The correct ones helped but no where what it should be, still starving for fuel Maybe??

I had the ip rebuilt when I dropped in the long block years ago, but cannot remember if the rebuilder set it to stock or gave the extra 1/4 turn back then. Is there a way to make sure? Kind of like air fuel mixture screws in a carb starting at 2 1/4 turns...

Btw if anyone is driving thru Boulder City (Vegas area) and wants a working ds4 w/ good PMD from the donor engine come grab it.

 

[turbovanman]

Thank you guys so much for this one. I forgot completely about this when I put on my turbo!

I ran with the n/a injectors as a base, then put in the used turbo injectors from my donor engine. It was so starved for fuel w/ the n/a injectors the turbo couldn't do a thing. The correct ones helped but no where what it should be, still starving for fuel Maybe??

I had the ip rebuilt when I dropped in the long block years ago, but cannot remember if the rebuilder set it to stock or gave the extra 1/4 turn back then. Is there a way to make sure? Kind of like air fuel mixture screws in a carb starting at 2 1/4 turns...

Btw if anyone is driving thru Boulder City (Vegas area) and wants a working ds4 w/ good PMD from the donor engine come grab it.

There is no difference between n/a and turbo injectors except pop pressure so your old ones might have been worn out.

What are your EGT's? Any smoke while under boost at WOT?

I would only turn up the fuel screw, go 1/4 turn. If your a member on the other site, I figured out an easy way to adjust it, a truck probably in 5 mins after you mark things.

 

[Will L.]

Ya, lower pop Pressure, because 40,000 less miles on the n/a ones than the others. Years ago I rebuilt them at work, I am putting together a pop tester now to rebuild them myself (project #217 on the list).

Egt are at 500?!? Sensor is in pipe in between dr side exhaust manifold and turbo. Only about 2 miles on it since put together. Nothing towed yet for a load just truck weight of about 7000 lbs. No smoke, homemade tm. when I can play with it again I need to put in a heavier spring. I also bought the materials to start my 4" exh.

Not on the other site but I'll go search. What is the story with an ATT to replace the gm6? If I learned about this site before getting started into the gm6 project I might not have done it and would have looked more at remote mounting an ATT.

 

[turbovanman]

Ya, lower pop Pressure, because 40,000 less miles on the n/a ones than the others. Years ago I rebuilt them at work, I am putting together a pop tester now to rebuild them myself (project #217 on the list).

Egt are at 500?!? Sensor is in pipe in between dr side exhaust manifold and turbo. Only about 2 miles on it since put together. Nothing towed yet for a load just truck weight of about 7000 lbs. No smoke, homemade tm. when I can play with it again I need to put in a heavier spring. I also bought the materials to start my 4" exh.

Not on the other site but I'll go search. What is the story with an ATT to replace the gm6? If I learned about this site before getting started into the gm6 project I might not have done it and would have looked more at remote mounting an ATT.

Probably a bit cooler putting the probe there but you can still turn up the pump.

I can post up my thread or make one here.

 

[Will L.]

So I went with WW's call in post 23 and went 1/2 turn. YAHOO!! Boost out the wazoo (12). I'll turn down tm.

I goofed and left the screws loose on my tps so on test drive went into 2nd gear limp mode and had more power off the line than in first gear n/a! A quick reset on tps, tranny is happy and it feels like my 01 suburban 6.0 all the way up to 55mph. EGT's (preturbo)hit 1100 getting there. It's like a whole new truck. I am 1 happy boy.

Next is 4" exhaust from turbo back and see how she does on the freeway at 70mph (3000 rpm).
Thanks again all, and any input is welcome.

 

[turbovanman]

Why turn the fuel down, your perfect at 12 psi and 1100 egts. Give it more boost, :thumbsup:

What turbo?

 

[Will L.]

I was saying turn down boost (maybe). The 1100 got there as fast as the truck got to speed and didn't fall after about 7 seconds, then I had to let off for the turn around on the road. I have not really run it for a sustained test run yet. Should I do that just for diagnostics when fighting EGT's at freeway speed while factory exhaust is still in it before going to the 4"?

 

[Will L.]

Oh, gm 6 turbo with the 3 piece van manifolds all from a 99 savana.

 

[turbovanman]

I was saying turn down boost (maybe). The 1100 got there as fast as the truck got to speed and didn't fall after about 7 seconds, then I had to let off for the turn around on the road. I have not really run it for a sustained test run yet. Should I do that just for diagnostics when fighting EGT's at freeway speed while factory exhaust is still in it before going to the 4"?

Damn, meant boost, lol. I would leave it alone until you do some more testing. There is another thread regarding EGT's and 1100 is still ok.

Oh, gm 6 turbo with the 3 piece van manifolds all from a 99 savana.

Nice, :thumbsup:

Got any pics of it?

 

[Will L.]

I need a new computer before I can download, everything is on an ipad so I don't have a clue how to until then.

 

[turbovanman]

I need a new computer before I can download, everything is on an ipad so I don't have a clue how to until then.

Upload to photobucket then link the IMG tags, simple, :rof: