Need a diagnosis

[dracing70]

I will try to make this quick my lb7 had a htt turbo on it the cp 3 is modded. It has all the other usual bells and whistles it had 65over injectors. I returned the turbo and injectors back to stock as well as removed the mp8 and kept all basic mods. I had a injector issue so we put in eight new ones. Actually the dealer did. I am running the same ppe tuning I Have ran for years and occasionally efi. So hear is the prob. I have yet to log the truck however it runs ok but not like before it used to smoke like a freight train even with stock injectors prior to the 65 overs and now even on a monster tune it barely does even under massive load. What could b the prob. Does this sound like a ECM issue or a fuel issue. Keep in mind even back in the day before all mods with a big tune it would role coal. Sorry for the novel.

 

[McRat]

You need to log the truck. Is it getting the fuel? It's the fuel that makes smoke.

List of things:

Fuel Filter dirty
Lift pump bad
Air leak in lines
Regulator sticking closed
CP3 failing
Programming
etc.

 

[The Neens]

Log actual & desired rail pressure, then go over what McRat posted...

 

[othrgrl]

Fuel or tuning issue. Check rail pressure at WOT.

 

[dracing70]

yeah i know i need to log it and i will soon as i get it back. what i dont understand though is it was perfectly fine prior to changin turbo and injectors. the cp3 is freshly done and the fass lift pump is prob 8 months old. it just baffles me and is a bit frustrating.

 

[The Neens]

what i dont understand though is it was perfectly fine prior to changin turbo and injectors.

You've changed the setup, things are gonna be different now...

 

[dracing70]

Yes I know I understand that. The problem though neens my truck only had those two items I removed on it for about two weeks so I remember exactly how it ran and as I stated stock injectors stock turbo plus big tune used to equal lots of coal. Now I get a puff at take off and that is about it. I get a lil haze on through the gears on the big tune

 

[Redbowties88]

its the mp-8 that was making you smoke like a train....

 

[S Phinney]

It has got to be a fueling issue. Just because GM changed the injectors doent mean they are good. Log everything and you will get insight into your problem.

 

[dracing70]

Well here is what I found so far I will log while driving sometime later today however everything looks pretty good at idle although I did locate a code it is p1093 and it says low fuel rail pressure during power enrichment. Any advice or suggestions???

 

[TNRGreene]

Is the valve shimmed?

 

[dracing70]

Which valve is that? Lb7 Does not have a relief valve

 

[JoshH]

Yes they do. It's in a banjo bolt somewhere. I think guys have been plugging with an allen screw or welding the end of the bolt. There are threads talking about it.

 

[dracing70]

Ok then next question why if this valve is failing would it do it all of a sudden. Prior to it's new life as a hauler this truck was a contending pulling truck that ran quite hard. Would the fact that it went from modded cp3 and large nozzles to modded cp3 and stock nozzles cause more pressure due to lack of flow therefore causing the valve to bypass be the prob? It will build smoke at takeoff but then right away quit and it has a hint of a shutter at 1500-1600 rpm but still has decent power????? Tell me what ya think

 

[McRat]

The P1093 is a good start, but all that tells you is that you are right, there is a problem in the fuel supply system that is reducing power.

Check inlet pressure at CP3. If it is a vacuum, it's on that side. Next, check actual rail vs. desired at 1500-3000 rpm with moderate load. If that is OK, it's "probably" not the regulator. Next take a TechII, and exercise the CP3 at idle. If it cannot hit 23,000psi, the CP3 cannot make pressure, OR the fuel is going back into the tank before you can hit 23k. If all checks out fine, then check actual vs desired at WOT running through the gears up to 80mph. If the pressure suddenly drops to less than 1/2 desired after spiking past 23000, that's a PRV blowing off it's seat. Otherwise, there is probably a piece of debris blocking a small passage on the high pressure side before the sensor.

Asking "why" is a question that only the defective part can answer, and they are pretty tight-lipped.

 

[dracing70]

Well so far my first log under moderate load seems good actual and desired seem to mesh well. What exactly is the tech II?? Also is the prv on a lb7 on the junction block in front of the intake bridge??

 

[paint94979]

Well so far my first log under moderate load seems good actual and desired seem to mesh well. What exactly is the tech II?? Also is the prv on a lb7 on the junction block in front of the intake bridge??

if in your log your rail pressure doesn't drop too far from desired i would doubt your FPRV is popping open... on my truck (LLY) Desired was 23,000 and it would drop to 18,000, so i went with a Race Valve

 

[JoshH]

Well so far my first log under moderate load seems good actual and desired seem to mesh well. What exactly is the tech II?? Also is the prv on a lb7 on the junction block in front of the intake bridge??

You should be able to command rail pressures with the DVT function of EFILive. I don't know what else you would need to do that would require a Tech II (which is a diagnostic tool used by GM dealerships).

 

[dracing70]

I have never tried the dvt Function I will have to experiment with it.

 

[dracing70]

well i finally got a day off to due some testing and here is what i found i ran a couple logs including a 0 to 80 mph run and the desired fuel pressure is askin for 23000 and the cp3 is only supplyin about an average of 12000-13000. it peaked once for a fraction of a second to 19000 but only for a milisecond. so what does everyone think. here is another bit of info i just had this cp3 done in july and should hold 26000 all day.