Engine/Transmission (1994 - 1998) Crazy Fuel Pressure??

[cumminsgetme]

This is somewhat of a follow up to my problem with engine stutter at 2600rpm. Chris and I checked the fuel pressure today and found something interesting. My truck showed to have an idle pressure of 7psi, I then reved it to 2000rpm and got a new idle pressure of 12 psi. When testing the pressure under driving conditions, both under load and at constant speed it never exceeded 20psi. We then took the overflow valve from his truck and placed it on mine to see if that could be the problem. The numbers came out to 28psi at idle, and reached a maximum of 40psi at 2000rpm under constant speed. Much better! It also seemed to run smoother and cure some of my stutter problem. However, during heavy acceleration pressures dropped significantly using both overflow valves (dropped to about 20psi using Chris's overflow). Chris didn't recall seeing this drop in pressure when testing his truck under acceleration. Has anyone seen this? Is it normal? If not, any ideas. Thanks
-Cord

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94' 2wd,5spd,#5TST,15%pump mod,K&N,imellmoke

 

[illflem]

Cord, It sounds like both you and Chris have messed up overflow valves, did he stretch his out or something? My pressure runs at 22 almost always, idle or load, the only time it goes up is going downhill at idle sometimes, then it hits 28. Having high pressures is no benefit at all, 20-25 is fine, it's just making your lift pump work harder than it needs to and risking a fuel filter rupture or rip from the high pressure. One of your filters, there are three, could also be clogged causing the high acceleration drop off. A partially kinked or collapsed fuel line can also do it.

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95' 25004X4,AT,Driftwood,Banks Stinger,Warn fender flairs and running boards(work truck)
95 3500,5 speed 3:54,BD E-brake,Driftwood,Banks&Psycotty,34,000 GCVW apple and tractor hauler(works harder truck)

 

[DieselB59]

For some additional fuel pressure fixes see my post in the Products/Accessories forum.
www.turbodieselregister.com/ubb//Forum3/HTML/003449.html

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Chris Timochko
*Association of Diesel Specialists Certified*
AUTO WURKS DIESEL R&D TEAM
1997 5sp 4X4, Rhino Linings, Espar Heater, A. W. D. HX40 turbo, ATS 3pc Manifold, BD 4" Brake, Marine Compression, A. W. D. Custom Tuned Injection Pump, A. W. D. Intercooler, A. W. D. 370B Injection Nozzles, Delivery Valves, Governor & AFC Spring Kit, Psychotty Air, A. W. D. Water Injection, NOS Diesel Kit, A. W. D. 6" Chrome Exhaust System, BD No Smoke Valet Switch, McLeod Dual Disc Clutch, Mag-Hytec Rear Cover, Cummins Chrome Kit, Optima Red Tops, Hadley Bully Horns, Hurst Line Loc, Goodyear Wrangler AT/S 305/70/16s. 15. 50@97mph on Goodyear All-Terrain tires.
****************************************************************************
Project U96 - 1996 3500 2WD racer. A. W. D. Marine Ultra Low Compression, A. W. D. Teflon-coated Pistons, A. W. D. High Lift Camshaft, Ported and Honed Cylinder Head, Intake and Exhaust manifold; A. W. D. HX40 Turbocharger, ATS 3pc Exhaust Manifold, A. W. D. Water Injection, A. W. D. Custom Fabricated Fuel System, Race Spec A. W. D. /BD P7100 Injection Pump, A. W. D. Custom High Flow Fuel Injection Nozzles, BD Auto transmission and Custom TC, Weld Draglites, Goodyear Eagle Drag Slicks, 5" Single Stack Through The Bed, Mag-Hytec on Rear and Transmission. 11. 54@115mph

 

[cumminsgetme]

illflem-I definately think that mine is bad, however, Chris's is new. That doesn't mean that he couldn't have gotten a bad one. Hovever he doesn't see the fluctuation in pressure on his truck and his readouts seem to be a little more normal. If I remember correctly his truck hits 22 at idle and 36 under acceleration, with no psi drop under heavy acceleration. Maybe he can correct me if I got some of that wrong. I haven't found any bad lines yet, pre-screen is clean and I put a new fuel filter on about 10 days ago. DieselB59, keep us posted when you get it on the dyno, I think you've got some interesting stuff going on there.

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94' 2wd,5spd,#5TST,15%pump mod,K&N,imellmoke

 

[Strick-9]

illflem,

This quote is taken directly from the TST website about fuel pressure.

"Typical value should be about 20 psi at idle and 30-35 psi at rated speed. "

My specs seem to be right in line what Mark Chapple suggests. I doubt my overflow valve is bad, but I've been wrong before.

Can someone please comment on whether the pressure should drop under WOT acceleration for a heavily fueled Ram (~350hp). If not, I'll hook up my pressure gage in the next few days and see for myself.

-Chris

 

[cumminsgetme]

Chris-
Thanks for the info. It sounds like we've found the culprit! I stoppped by the dodge house to pick up interior paint for my pillar mount and decided to go ahead and get a new overflow valve. After reading your post I'm glad I decided to cough, choke and spit out the $93 to get it. I'm assuming what little sputtering is left is due to delivery valves. BTW, I ordered a can of interior paint... . they sent me a relay... . idiots!

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94' 2wd,5spd,#5TST,15%pump mod,K&N,imellmoke

 

[illflem]

Has anyone found a source for just the spring yet? Sure could save some money.

 

[Strick-9]

illflem,

Unfortunately, Cord and I both had the original sealed overflow valves. We have no choice but to cough up the $93 for a new one the first time. The next time mine fails you can bet I'll find a $2 spring instead of an entire new valve.

-Chris

 

[Deezul1]

Try your local fuel injection shop, mine will sell me a Bosch overflow valve for $60. 00

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96 SLT Laramie CC 5spd, 3. 54, no muff, no cat, 5"turn down tip. (its for sale)
. Member NRA/USPSA

 

[illflem]

With all the overflow valve problems I hear of I just wonder why the stock valve couldn't be replaced with a 1/4" hydraulic pressure relief valve in the return line? I have some on farm equipment that are adjustable from 0- 2000 psi, they are cheaper and hold up very well.

 

[Strick-9]

Cord,

I just installed my fuel pressure gage and went for a few runs.

Idle: 27psi
High RPM no load: 38psi
Moderate acceleration (up to 25psi boost): 26-30 psi.

Under HARD acceleration (38-40psi boost)the needle did drop to 20-22psi. I hit 18psi one time from a dead stop at WOT, but it climbed back to 20 and held there until I backed out of it at 1500°F exh. temp.

Basically, it acted the same way your truck did with my overflow vavle in it.

-Chris

 

[Andy Redmond]

On the overflow valve spring. . I am testing one made from some spare springs. I'll let you know how it lasts, if at all over time.

Make sure you have a fuel psi gauge to test afterward, if you are playing with it.
A new overflow valve will return 28-30 psi at idle, with a fresh filter.

I also have a bag of 1/4" ball bearings, illflem; however, the Bosch unit is a metric size check ball.

I beleive you will also find the pump is tapped with a metric thread pitch.

Do your hydralic(sp) valves, have a metric pitch to thread into the pump?

Chris, ck my posts in the past for the Bosch number if you are sourcing at a Bosch shop.

 

[illflem]

Andy, they are pipe thread. I was thinking you would eliminate the ball and spring and tap into the return line with flare fittings for a relief valve.

 

[Strokercummins]

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