24v injector pop off press vs. 12 v injector... 24v sticks with a P pump ???

600 Megawatts

600 Megawatts

Many Irons in the Fire
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May 6, 2008
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OK, so my P pump conversion is done !!:rockwoot::rockwoot:

A couple of things.... First of all, I kept my 24v injectors. I understand there is roughly a 3,000 Psi popoff difference (15,000 psi to 18,000 psi ) ??? Is this so??? What are the ramnifications of running the 24v injectors with a P pump?? I know lots of guys have done it with no problems, but long term, is this hard on the pump?

ALso the one and only thing that has been a negative with the conversion is the drastic reduction in low end torque. With the VPI used to be able to let the clutch out at idle in reverse up my very very steep driveway with no issue whatsoever. When I first got the p pump running I couldnt even come close to doing this without stalling. I HAD to feed in some pedal. Now after running it around town a little, the Gov is loosened up and I can do it, but not nearly as effortlessly as before. ALso the torque is WAY WAY down until about 1800 RPM... After that yeeeeehhhaawww look out, the p pump screams and this thing is an animal right up to 3500+. It will flat out embarrass my VP44 with a TST on 9 and stacked with an edge after 1,900 RPM. And I only have the plate midway!!:rockwoot::rockwoot:

But with the VP I could lug the engine at idle up the driveway at 500 RPM and it just pulled as nice as can be... now if I let it droop under about 750 RPM it stalls quick.

What I am wondering is, at the very low RPMs, is the pump getting 'under' the injectors? I mean at the low RPM condition, perhaps the pump is struggling to make the higher popoff pressure of the 24V injectors??

Anybody have any experience with this ??
 
There are a couple of factors.

First, you are right on with the injectors. I would have them modified.

Second, you no longer have the computer fueling the VP as the engine gets close to a stall. Before, if your engine was about to stall out, the ECM would tell the VP to give it more fuel, so YOU wouldn't have to adjust the fuel, the ECM would. That is why you never had to tap it. You obviously lost that by going with the P-Pump.

I noticed that you have an 01.5... Does the cruise still work??? That is one of the biggest concerns (electrical problems) I have with a p-pump conversion.. I'm going to do it if this VP ever craps out, but I want to know what kind of mess I'm getting into.
 
The VP has an electronic govenor and has an anti stall feature on the manual trucks.
 
Your pop off figures are high. 24v at 305bars. 12v 260-280bar.
305 bars is 4423psi.
 
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Well, yes I know that the VP has an electronic gov, and was adding fuel, but so is the gov in the P7100 right ??? And even if I give it some pedal, if I let it lug down under about 750 RPM, it will stall with any amount of pedal... thats why I was thinking about the pump getting under the injectors.... of course, that doesnt make too much sense I suppose, since the pump is positive displacement, and after all it pops off the injectors while cranking the engine with the starter..... so, thats prob not it...

I wonder just what the computer is doing to the VP's timing at those real low RPMS..... perhaps, my static 17° timing is too advanced for that low RPM... Does anybody know the timing range that the ECM/VP44 has to work with? Like from 10 to 20° maybe ??

MD, my 01.5 had totally drive by wire electronic cruise done eith the PCM/ECM VP44. There was no vacuum actuator... so I have no cruise now:(

Ron/BBL, thanks for the pop off pressure info/correction. I saw the injection pressures listed for the pumps, and I mistakenly took that for pop off...
 
I have did a few PPump conversions and I would have the P.O.P lowerd to about 270bar. Long term 305bar will be harder on the pump.
 
Where's the best place to have pop off pressures adjusted? I've got two sets of injectors I need to get changed over for my ppump conversion...
 
I've been having really good luck injector wise with F1's. Don sets them up differently for a p-pump conversion. I've never asked what he sets the pressure at. I had several sets before switching to the F1's and they all tended to smoke more for the power they gave. I imagine there is a bit of trial and error getting things right. Not trying to start another injector war, just saying that there does seem to be a difference in performance between setting them for a vp and setting them for a p-pump.
 
600 Megawatts said:
Well, yes I know that the VP has an electronic gov, and was adding fuel, but so is the gov in the P7100 right ??? And even if I give it some pedal, if I let it lug down under about 750 RPM, it will stall with any amount of pedal... thats why I was thinking about the pump getting under the injectors.... of course, that doesnt make too much sense I suppose, since the pump is positive displacement, and after all it pops off the injectors while cranking the engine with the starter..... so, thats prob not it...

I wonder just what the computer is doing to the VP's timing at those real low RPMS..... perhaps, my static 17° timing is too advanced for that low RPM... Does anybody know the timing range that the ECM/VP44 has to work with? Like from 10 to 20° maybe ??

MD, my 01.5 had totally drive by wire electronic cruise done eith the PCM/ECM VP44. There was no vacuum actuator... so I have no cruise now:(

Ron/BBL, thanks for the pop off pressure info/correction. I saw the injection pressures listed for the pumps, and I mistakenly took that for pop off...
Click to expand...

did you gather your own parts or buy the kit from one of the big name shops? does all your dash gauges still work? i know a special cam position sensor adaptor is needed, where did you get yours?

i cant wait to do mine.
 
I like the pop pressures set around 4000, I even do this on 370's and that makes them cleaner.

Jim
 
My cruise control on my 01 still works since it works off the APPS, It's a lil touchy thoughLOL
 
the gov in the p pump will not add fuel to keep the truck from stalling. the pop press in the inj could be to high and that might effect your low end id pull them and have them reset. it cant hurt.
 
Thanks for all the replies!!!! Yeah, when I get a little time, Ill pull the injectors and get them to the shop for about 270 Bar pop off.

GB5.9, I did the whole deal myself. Didnt buy a single thing from a big name shop. it was lots of fun. Member TATE on here helped me alot with emails and answered questions. I machined my own cam sensor adapter out of aluminim, super easy to do. Made my own lines, bought only the following:

P Pump $700
Pump Gear $180
Timing cover $160
.083" wall SS tubing $180
Shutdown solenoid $150
Throttle cable $22
Mallory Fuel pump $180
knick knacks ~$100


Sold: Edge EZ on Ebay $255
TST PM3 on Ebay $410

So it cost me: $1007:rockwoot::rockwoot::rockwoot::cheer::woohoo::woohoo:



Pensacola diesel took my VP44 as a core for the P7100 which was great.
 
If you're still having issues with the stalling, you may need to adjust your gov springs a bit. The gov springs set your base idle, and your idle screw just bumps it up. I can let the clutch out in my truck and it will generally stay at around 700 rpm, little less if I let it out too quick.
 
what throttle cable is needed? stock 12v?

where did you wire your shut down solenoid into?
 
Also dont forget that pop pressure = timeing. The higher the pop psi the more the pump lobe has to come around to make the psi.
 
I have some 275 rv's in mine and lowering them from the stock 24v pressure to 300bar made a huge differance in the truck.


A factory 24v throttle cable can be made to work.
 
Screw the stock throttle cable (I know, there is no throttle but you know what I mean) its overpriced and junk. I bought a nice Lokar Braided stainless generic throttle cable from Summit with nice aluminum threaded adjusters. Check out the pics of the install in my photo gallery.

Wired the hold coil of the shutdown into an ign on hot line, and the pull coil to the starter motor post (NOT the S terminal, the actual post on the motor itself, and not the starter solenoid).
 
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