westexhunt

I am cheap, let's get that out first and that may be the root of my problems, read on and you will see what I mean. I lost the stock HO vp at 170K miles, after pulling it and putting it up I see that the Juice wire tap had "sawed" the vp wire in two pieces and I more than likely could have fixed the wire and gone on down the road. But, I had a older reman Bosch pump that had 3-4k miles on it and was supposed to be for a HO engine in the garage. I put it on, power was down just slightly (sop), and mpg was without a doubt down 2+ mpg across the board. It had decent power to about 2600 rpms (still smoking) then from 2600 to 2850 low power (no smoke at all) then from 2850 to redline bigger power and smoke. Tried this in on every Edge setting with an without a trailer and watched the egt's react exactly like the smoke (climb to 1250-1300 at 2600 drop to 1150-1200, then climb back to 1250-1300 around 2800-2850 rpm to redline (defuel), this is on 5/5, but similar results on any setting. I thought this pump was the problem as I never noticed any of this with the stock pump. I read over and over on here to put a SO pump on my HO truck, so instead of buying a new pump I cheap out. Today I took a SO pump off a 120k mile 2002 that ran perfect (no codes, no nothing, owner just wanted to put on a new pump because the VP usually dies and he did not want to walk) I put this SO pump on my HO truck. It runs exactly like the replacement pump I took off. So my conclusion, either I need to try a "new" SO pump, I do not have enough fuel to use a SO pump on my HO truck, or the SO pump at some point in the rpms make more power than a HO pump but in a daily driver at 400hp it runs pretty crappy. I know I am cheap but a VP swap at my pace takes about 2hrs and even being self employed, I dont quite knock down the $1000+ I saved on trying a used VP instead of a new one. I really want real world SO to HO swap experience stories if you have them.

afoulk

I just swapped a "new" rebuilt SO pump onto my HO about 400miles ago. I've also noticed a drop in fuel mileage and drastic drop in power below 2300rpms. My max boost has dropped from 21psi to 19psi but I can still hit the same max with my egt's (950-1k) if I really try. I also used to get a puff of smoke when pulling out and when shifting when I wind it out, don't get that at all now. I think the fuel mileage has dropped because I have to beat the snot out of it to get it to accelerate. But now, I am stock yet, so I was expecting this, although not this bad. I figure things will get much better once I start "bombing" it. My goal in the end is between 500-550 hp, so I feel it'll pay off eventually. If I'm correct, I think the HO's actually run a slightly smaller injector than the SO's, so maybe that has more to do with it than anything. I think the HO's made their extra power with higher fuel pressure and 1point higher compression pistons. If your only making 400hp and thats all you ever plan to make, I would definately stick with a HO pump....they're usually good up to about 500.

B-Peterson

I thought you had to change the ecm when changing to a so pump?

westexhunt

Sounds like mine almost to a T. I will have to go to a larger turbo for 500hp, this one is maxed out EGT wise and I will not run it over 1250. I may sell this truck and go to a 3rd gen, I need the 4 doors now anyway.

westexhunt

I had not heard this, many folks have switched from HO to SO pump and are really pleased with no ECM swap.

GFB

Do the HO injectors have a higher pop-off than the SO injectors? If so, that could be some of your problem. I think a lot of guys that switch to the SO are doing so because their mods have already maxed out the HO pump (they already have injectors and box).

afoulk

well, my original IP took a dump, so I figured I might as well switch to the SO now than have to change my pump again fruther down the road.