Engine/Transmission (1994 - 1998) 97 seems low on power... lift pump?

[Forrest Nearing]

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!

 

[BTanzini]

Forrest Nearing-mine did that a couple of months ago so I replaced the over flow valve and problem solved.

 

[Forrest Nearing]

well, like I said, I really don't think it's the overflow valve, but I'll keep it in mind if everything else checks out.

 

[bmoeller]

Curious why you cut a coil out of the spring, when you want to lengthen it to increase the pressure.

Did you check the pre-filter screen yet?

How are the rubber hoses?

Fuel heater leaking air?

 

[The patriot]

Mine was acting the same way, all of a sudden.

I did the fuel filters and it that was it.

Eric

 

[Forrest Nearing]

Curious why you cut a coil out of the spring, when you want to lengthen it to increase the pressure.



Did you check the pre-filter screen yet?



How are the rubber hoses?



Fuel heater leaking air?

I didn't even think of the fuel filter! duh! I'll do that before I do anything else. it's not stumbling like it's got air in the system.



when you cut a spring you increase it's tension. I also stretched it out, but I cut a coil to increase the spring rate... make it stiffer. also took a shim off of the other OF valve and put it on there. the OF won't be causing low pressure problems for the time being!

 

[Forrest Nearing]

dang, just talked to the PO... said he changed the filter very recently

 

[WDixon27]

my old lift pump would hold decent pressure at idle and crap out as soon as you hit the throttle even out of gear, it was hitting maybe 20 at idle but drop like a stone from there and hold maybe 10, new pump same of valve (mutant of valve made from dodge and mercedes parts ) 20 at idle and 30 running, in the year and a half since i changed the lift pump i have tweaked the of valve spring to about 27 idle and a max of 36 at high rpm, seem to like the slightly higher pressures

 

[Forrest Nearing]

good to hear! similar simptoms? the truck runs 'fine', it just doesn't have the cashews I know it should... doesn't sputter/stumble like it's sucking air, just doesn't have that GO like it's starving for fuel

 

[Howard Durand]

Put a fuel pressure gauge on. It can tell you if the system is holding fuel pressure under different driving conditions. Mine was fluctuating between 20#and 32# just driving down the road.

I had a combination of weak spring in the OF valve and air leak in the feeder hoses.

I am still fighting the hose problem but the OF valve maiintains about 32# constant at highway speed.



I have a question to add to this. Has anyone noticed the plastic inside liner in the hoses that come from Larry B at Foster Truck? I am not sure if that is helping with assembly or is causing problems. I know for sure, I can't push one on the steel line past the hump in the line. One of the lines has a hump right at the mouth and I had to cut that off before I could get the hose on.

 

[hsmith]

I quit using Larry's just for that reason. The liner folds too easily, making it impossible to slip on.

 

[BigPapa]

I didn't even think of the fuel filter! duh!

Mine was clogged up with the goo suddenly only 500 miles after changing. I think it was from the USLD changeover. I'd still check it.

when you cut a spring you increase it's tension.

This sounds a little like picking up your feet to lighten your load. Seriously, I've never heard of this. Could you explain it a little more or quote some law of physics that might explain it.



Scott

 

[Forrest Nearing]

I can't explain the physics, but it's true... take a 10ft length of 1" schedule 40 pipe. I bet you can bend it. Not to the extent of putting a kink in it, but I bet you can put a little arc in it. Now cut that down to a 1ft length. bet you can't bend it.



if you look in a spring catalog, you'll note that for a given wire diameter and given coil diameter, as the spring gets shorter (fewer coils) the spring rate increases



I put a gauge on the truck today. it did 28-29psi at idle, and it would suck down to 18-19psi at WOT. Not great, but not bad enough to cause the low power issue IMO.

 

[BigPapa]

But, if that length of pipe HAD to be 10' long, cutting it down to stiffen it wouldn't help.

I may be wrong, but if I took a rear shock spring for a particular ATV or dirt bike and tested the spring rate, then cut off a coil and stretched it out to the proper length, I don't think it would be any stronger. I would thing it would be weaker.

Oh well, sometimes you just can't teach an old dog new tricks. Maybe my skull is too thick.

Scott

 

[champspa]

stretch it Forest, then run Forest run, just like you used to. lol :-laf:-laf

 

[The patriot]

Overflow valve springs are like a box of chocolates... ... ..... :-laf

 

[Forrest Nearing]

But, if that length of pipe HAD to be 10' long, cutting it down to stiffen it wouldn't help.



I may be wrong, but if I took a rear shock spring for a particular ATV or dirt bike and tested the spring rate, then cut off a coil and stretched it out to the proper length, I don't think it would be any stronger. I would thing it would be weaker.



Oh well, sometimes you just can't teach an old dog new tricks. Maybe my skull is too thick.



Scott

do a web search on coil springs, it's true

 

[Don Tanklage]

shorter spring has higher spring rate



spring rate is the term used to measure how the force increases as a spring is compressed



forrest is right - if you cut a spring the spring rate increases



but springs dont exert any force until they are compressed



that is where the installed height comes into play



when using a spring to regulate pressure of a fluid the spring rate really doesnt have much to do with it - you can take any spring that will physically fit the application, put it in a tester, pull it down to the pressure you want, note at what height that pressure occurs - and then shim the spring housing to that installed height

 

[Hammer]

What your describing Forrest sounds like a bad load of fuel to me. Usually when you get one you know it not long afterwards. Mushy pedal,dead on power,lazy no boost,nasty smell out exhaust and a host of others. I have seen it cause motors to skip and stumble,knock or ping and just be a PIA to drive. Might be something to consider... ... ... . Andy

 

[Forrest Nearing]

nah, the fuel is good... throttle response is excellent, 40-42psi of boost. the needle is swinging a lot harder now that I fixed the boost leak. exhaust smells normal. and like I said, engine runs smooth, no stumbling or breaking up.



the conclusion I've come to is:



either the injection pump is getting 'weak' (278k miles... been turned up w/ 370's since about 130k)



OR



I've grown used to the feeling of 500+rwhp trucks and a little 370 injected truck w/ a 12cm HX35 turbine on it just isn't passing muster