97 seems low on power... lift pump?

S

Scooter's Roofing

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I picked up my old 97 recently and am working on getting it up and kicking again...

current combo is 215 pump, home ground plate, AFC mods, 370's, and a 35/40 hybrid w/ a 12cm housing.

with a less agressive plate and un-modded AFC, I made 436rwhp w/ this truck w/ a full HX40. I could bury the 1600* pryo and pinched off, the HX40 would do 45psi.

the truck just doesn't seem to have the oomph it should. with the wastegate line disconnected/plugged, I can only get 39-40psi out of it, and it's just barely hitting 1400* at 80mph from a 60 roll...

I checked all the boost hoses and didn't see any nicks/tears/slipped boots, etc. I'm going to make a pressure cap for the turbo and make 100% I don't have a boost leak.

I pulled the overflow valve, but didn't figure that was a problem because I replaced it back when I used to own the truck, and it's got maybe 40k on it? I took the old OF valve and cut a coil out of the spring to up the tension and put an extra shim in it just to bump the pressure a little. no difference.

I don't have a fuel pressure gauge on it. I've never had occasion to put one on a 12v, but now I'm wondering if the lift pump just isn't putting out

something's amiss because this same turbo on my 98 would do 42psi w/ a #10 plate and STOCK 215 injectors!
 
Did ya check the fuel filter? Sounds like it might be something simple like that.
 
going to change it tomorrow, but the guy I bought it from said he replaced it recently. good call though, I didn't even think of that originally!
 
Yeah. I figured it sounded kind of stupid when I typed it, but with me it always turns out to be the cheapest thing after I have already bout something more expensive.
 
Did the other guy maybe slide the plate back a little for less smoke or somethin? You probably already checked that, but it's an idea.

George
 
nah, I set the pump up for him... it should be good to go. I will say it felt kinda soft when I rode in it w/ him after furthur tweaking the pump. at least compared to what I expected.

something's holding it back and it sure feels like it's not getting enough fuel... I was thinking maybe a boost leak was causing the AFC to not go forward or something, but it could be the lift pump... heck, it's the original w/ 278k on it, and the truck has been cranked up pretty good since about 135k! LOL!
 
I guess it could be, I just figured that the lift pump on a 12V was either good or bad, as in it would either pump fuel or not. Never realy thought about them being able to flow enough to run, but not enough to have good power.

Then again there are plenty of things I don't understand (just ask my wife)

George
 
roger that! LOL really I thought the same too... I guess a fuel pressure test will show. I thought about pinching off the return line last night, but it was dark
 
It could still be the AFC. After working mine over a few times it developed a leak past the diaphram around the nut. I dab of RTV on the nut and threads sealed it off and power came up.

Also, would tight valve lash (causing a bit of a leak on either the exhaust or intake) cause such symptoms?

Just some thoughts...
-Jay
 
Fuel pressure gauge for you! didn't solve my problem but atleast now I know my pre-injection pump pressure is good. good luck!
 
I'm going to double check that seal on the nut on the back of the AFC cover... we did mess with that, but it was soft even before we got in there.
 
id pinch the line

and with a makeshift fuel pressure gauge setup see if your pressure shoots up, if if does when u pinch it, its ur OFV.. if it dont its ur lp..

worked for me before... but without the gauge its hard to tell...

Rick
 
I put a gauge on it today... 28-29 at idle and it'd suck down to 18-19 at WOT. didn't seem THAT bad to me.

I did find a little boost leak. one of the plenum bolts was MIA :confused: that picked up 2psi... it'll do 40psi and then creep up to 42 at about 2700. it might creep higher, but I didn't have time or room to take it higher in the higher gears :(
 
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