02 lb7 high rail pressure at idle contaminated oil - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 4 (permalink) Old 08-14-2019, 04:09 PM Thread Starter
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02 lb7 high rail pressure at idle contaminated oil

Having a issuse I cant wrap my head around with my lb7. I did a oil change and filter change a couple months back and noticed very thin oil was also throwing a high rail pressure code. Brought to my buddy's stop and starting looking into problem notice that already oil was getting thin again with very little run time since oil change (towed it with my wrecker to garage). We looked into the fpr thinking it may be the problem, swapped out with a working one problem continued. When reading the pressure levels truck reads around 23000-25000 at idle then cuts out to 0 when on gas. Checked the relief valve rail pressure sensor also replaced and also checked the rubber lines they say can suck flat all good. Injector rates are normal truck does not smoke. Any ideas?!
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post #2 of 4 (permalink) Old 08-15-2019, 06:36 PM
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Welcome to the Forum!

So to be clear, engine idles well, has good balance rates but maxed out rail pressure and cuts out off-idle.

FPR was a good guess on the rail pressure issue, but throwing in oil dilution is a head scratcher, and those would seem to be unrelated problems.

“Having a issuse I can’t wrap my head around with my LB7”

I’d say!

As you know, electrical connections on old machinery can be a source of trouble and I’d suggest you disconnect and inspect connectors to the Fuel Injection Control Module (FICM) and anything else on the engine that may be accessible.

How long were you able to drive your truck with the high rail pressure MIL? Did that problem start after the fuel in oil situation?

Does your friend with the shop have a TECH2 (or similar) that would allow him to command a different rail pressure? That might at least show the CP3 is “following orders”.

Any other clues to share?


2003 GMC Sierra 2500HD SLE ExtCab CA Emissions; 155k; Allison 1000 w/Transynd X2 Flush & Fill; 8' bed; AFE/CAI; MBRP 4" Exhaust; Side Tint, 33% VLT, rear, Limo; Smittybilt Stainless Side Nerf Bars; Sprayed-in Bed Liner; MadJack Fuel Filter Access Door; Regular Used Oil Analysis (latest available on request), Blackstone Labs; EGT/Boost Gauges; Dual Chrome Dipsticks, JC Whitney; Stainless Steel fuel filter head bleeder screw; New WP and Hydroboost; Billet Aluminum Fuel Filter Housing Spacer; Professionally repaired instrument cluster (new steppers and lamps); Does anybody ever read this s%#t?; Injectors under warranty @ 70k; 2nd set DIY @ 155k
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post #3 of 4 (permalink) Old 08-15-2019, 07:02 PM Thread Starter
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I was able to drive truck but seemed to have some lack of power not crazy and alittle fast fuel consumption. Haven't had truck very long so my first order of business was check the fluids and do a change along with the filters I noticed the thin oil at this time. Truck sat in my driveway for about a month after the fluid change not ran until about a week before bringing to my buddy's shop to take a look. At this time he informed me that he noticed the oil seems thin again which like I said truck only ran once or twice before making it to him. I will contact my buddy in the morning to see if he can in fact command rates to check the cp3. Could a tune have messed with something? Had a power pup bully dog when I got it but immediately detuned back to stock upon purchase. Trucks been in my buddy's shop for about 2 weeks chasing dead ends. I will have him check the wiring. But the dulison part of it really has me stumped.
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post #4 of 4 (permalink) Old 08-16-2019, 06:54 AM Thread Starter
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UPDATE my mistake truck is throwing the p1094 code for low rail pressure but everything stated stated remains the same.
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