low fuel pressure

[kyle830]

i have posted this on other websites and have yet to find whats wrong. i have a 96 5 speed with the 215 pump. everything is stock besides the fuel plate which is a #0 and i have low fuel pressure under load. at idle its about 24 psi and while revving in neutral to 2000 rpms i have 30-35 psi. while accelerating or climbing a hill the fuel pressure drops to 10-15 psi. i have an adjustable over flow valve which will increase the pressure at idle and revving in neutral but will still drop down to 10-15 psi while driving. ive changed the fuel filter multiple times, cleaned the pre filter screen multiple times but its never been that dirty, deleted the fuel heater, i have checked the fuel shutoff solenoid for the right adjustment and making sure its pulling up all the way, ive replaced the lift pump twice once with a cummins one from genos and another time with a hot rod one from power driven. the hot rod pump raised my idle pressure to 30 psi but under load it would still drop to 10-15 psi. ive replaced the fuel line with 3/8 marine grade hose and put a new sending unit in the tank but nothing has fixed the low fuel pressure issue. ive used multiple gauges to make sure the gauges isnt bad and they have all read the same. at 15 psi the truck still runs somewhat decent but once it drops below 15 the engine starts sounding different and loses power.

[Vincejax]

I would clamp off the overflow completely and go for a short test run with a mechanical gauge on it. Have a buddy watch or even better film the gauge next to your tach so you can see fuel pressure compared to rpm. Rule out the ofv being your problem and take it from there.

[kyle830]

Originally Posted by Vincejax

I would clamp off the overflow completely and go for a short test run with a mechanical gauge on it. Have a buddy watch or even better film the gauge next to your tach so you can see fuel pressure compared to rpm. Rule out the ofv being your problem and take it from there.

My gauge in the cab only goes to 35 psi so i cant see how high the pressure goes but it pegs the gauge when i clamp the return line. i havnt driven it while clamped but at idle and when i let the rpms climb slowly the gauge stays pegged but when i stepped on it and let it rev up fast it blew some black smoke and the pressure dropped

[jasonc]

Normal for a stock lift pump and stock fuel system. Which is fine for 500hp or over.

What's the timing of the engine set at, being you say it plays over up top.

[kyle830]

Originally Posted by jasonc

Normal for a stock lift pump and stock fuel system. Which is fine for 500hp or over.

What's the timing of the engine set at, being you say it plays over up top.

stock timing at 12.5 degrees. checked it and it hasnt slipped

[jasonc]

Your loss of power at the upper rpm range is due to the stock timing and not your drop of fuel pressure. About 2500 is all it will pull to at 12.5° no matter what gov springs it has in the pump.

Now it may rev up in neutral past that with no load, but isn't gonna make any power up there.

[Snedge]

Originally Posted by jasonc

Your loss of power at the upper rpm range is due to the stock timing and not your drop of fuel pressure. About 2500 is all it will pull to at 12.5° no matter what gov springs it has in the pump.

Now it may rev up in neutral past that with no load, but isn't gonna make any power up there.

Jason is correct as usual.
You need to get that timing bumped to 18-20. Completely different animal when you do that. You'll lose a pinch of snap on the bottom end, but the increase in the torque curve will make you happy.

Plus-- I hope the deleted fuel filter as been un-deleted.

[Vincejax]

Originally Posted by jasonc

Your loss of power at the upper rpm range is due to the stock timing and not your drop of fuel pressure. About 2500 is all it will pull to at 12.5° no matter what gov springs it has in the pump.

Now it may rev up in neutral past that with no load, but isn't gonna make any power up there.

agreed x2

[Mark Nixon]

Originally Posted by Snedge

...Plus-- I hope the deleted fuel filter as been un-deleted.

Where did he say he deleted the filter?
I saw a HEATER delete mentioned.

Mark.

[Snedge]

Originally Posted by Mark Nixon

Where did he say he deleted the filter?
I saw a HEATER delete mentioned.

Mark.

Well ****... I is rataded. Reading is hard. My bad.

[Mark Nixon]

It's good, Jeff, we all have our moments.

Mark.

[kyle830]

Originally Posted by jasonc

Your loss of power at the upper rpm range is due to the stock timing and not your drop of fuel pressure. About 2500 is all it will pull to at 12.5° no matter what gov springs it has in the pump.

Now it may rev up in neutral past that with no load, but isn't gonna make any power up there.

the truck has stock head bolts. im planning on getting studs in the future but for now would you say around 16 degrees would be good?

[jasonc]

Be just fine at 16

[Red Sleeper]

Originally Posted by kyle830

the truck has stock head bolts. im planning on getting studs in the future but for now would you say around 16 degrees would be good?

I’m pretty sure Jason is the king of stock head bolt limits. Correct me if I’m wrong.

[jasonc]

Originally Posted by Red Sleeper

I’m pretty sure Jason is the king of stock head bolt limits. Correct me if I’m wrong.

Mr Garmon is the king of stock bolts, I just copied his ways.

[kyle830]

Originally Posted by jasonc

Mr Garmon is the king of stock bolts, I just copied his ways.

do you retorque the original bolts or buy new bolts and torque them down past what the manual says? ive read a lot of mixed opinions about retorquing them and even though people are successful with stock bolts a lot of guys still say to buy studs instead.

[Mark Nixon]

Interesting schools of thought.
One school is head studs, with multiple hot retorques.
Are y'all doing multiple hot retorques on head bolts?

Mark.

[Snedge]

Originally Posted by Mark Nixon

Interesting schools of thought.
One school is head studs, with multiple hot retorques.
Are y'all doing multiple hot retorques on head bolts?

Mark.

We run new bolts and over tighten them once.
No secret moon dances or sacrifices.
I never talk anyone out of studs though. It's futile to argue with the internet. ARP studs are quality material, but they are not flexible.

[95cummins5.9]

5 lb increments from 100ftlbs to 150 ftlbs with plenty of time between each 5lbs with arp stud lube always does the trick for me with stock bolts.

[Red Sleeper]

Originally Posted by kyle830

do you retorque the original bolts or buy new bolts and torque them down past what the manual says? ive read a lot of mixed opinions about retorquing them and even though people are successful with stock bolts a lot of guys still say to buy studs instead.

At the end of the day, studs are cheap insurance for any more than stock power application.

I prefer studs but not their new price. Running used 625’s has served me well.