can not figure rail issues out

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onebaddmaxxx

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Feb 22, 2009
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Cecil County Md
Working on a 2002 gmc at work. Truck is 2wd with utility body and dual tanks. Truck came there running rough and lots of white smoke, had bad balance rates on 2 injectors. Pulled all 8, sent them out to get tested and low and behold 2 were bad. Replaced the bad injectors with new bosch injectors. I then reinstalled the other 6 injectors back into the cylinder they were removed from. The truck started up and ran great it sat there for about 2o minutes idling while i finished some things up and let it warm up to add coolant before i test drove it. I backed out of the shop and had no pedal response. The truck was throwing p0087, p1093, p1094. I did some research and everyone said since it was throwing low rail psi that those codes were usually thrown from needing injectors or cp3. The cp3 had been replaced 3 days prior to coming to our shop by the local gm dealer. Regardless, being it had new injectors i pulled the cp3 and had it tested and it came back good. Upon reassembly, i noticed a strong gas odor. I pulled the brand new fuel filter off and it was completely black inside and smelled like gas. I figured ok lets drop the tanks and clean them. BOTH tanks were filled with gas and very dirty. Cleaned them, reinstalled and filled with diesel and the truck had the SAME symptoms.

At idle, the truck makes 65mpa and desires 40mpa. If you start giving it gas the desired goes up but the actual goes down. I can only get about 2300rpm out of it total, and once the actual goes under the desired it starts smokin heavy white smoke. The injectors were re o ringed, new coppers, new return line washers etc. at full throttle it maxes at about 2300rpms and is at about 26mpa. any ideas on this? I tried looking up how to do a bottle test lb7s but couldnt find any ideas...could the fprv be bad? how common is that? Really stumped on this one thanks in advance....
 
Kappa9012

Kappa9012

MAN.... I Broke it again.
Aug 5, 2008
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was the fuel filter changed, lines etc flushed out? wonder if there's still residual gasoline in the system.
 
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onebaddmaxxx

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Feb 22, 2009
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The lines surprisingly werent that dirty for a truck with 200k on the clock. Plus i cleaned them all before i put them back on and siliconed the tops of lines to prevent dirt from getting in anymore. Fuel temps were reading around 150 when i logged it the first time at idle when i diagnosed the bad injectors....did not think of looking at it again afterwards. When i drove it 2 weeks ago when i diagnosed the injectors, it was around 185 degrees until i stopped and let it idle then it slowly backed down. I wouldnt think it should be that hot. Its been around 70* outside but literally as soon as i got it started last time it did it right away. After the truck runs a while and gets warmed up, it takes about 2 seconds longer to start as well when you crank.
 
prodiesel804

prodiesel804

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Feb 1, 2013
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had one about the same at work, cant remember exactly want to tink it was a ground issue on the rail pressure sensor.
 
x MadMAX DIESEL

x MadMAX DIESEL

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Dec 30, 2008
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That is sorta what mine is doing, that's why I'm pulling my injectors. I think one is hanging wide open not allowing it to hold rail pressure. My balance rates are fine. But with it not holding pressure and white smoking like crazy I think it has to be blowing raw fuel out the exhaust from a cracked injector ball seat or just stuck wide open. I have tested compression and all cylinders are 340-360. You could have them rechecked? When I pulled my glow plugs all tips looked they were burnt normally. But one (#2) was clean for the first half of the tip... The other half had soot on it. I think the front half was just washed off with raw fuel and that's the bad injector.
 
WI Huck

WI Huck

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Feb 8, 2012
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The diesel fuel is the lubricant for the fuel system parts. Put six more injectors in and hope the rest are still good.
 
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onebaddmaxxx

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Feb 22, 2009
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Cecil County Md
x MadMAX DIESEL said:
Mine also does it around 2 grand.. Right when pressure gets to 10k it starts adding this way. Does it look the same as this video? It also "diesels" for alittle after you let off like its still running on all that extra fuel http://m.youtube.com/watch?v=s8F46R2B8ng
Click to expand...

No it doesnt sound anything like that. The pump hadnt had anything ran thru it except diesel i know because i put the pump back in, and then cleaned the tanks and lines before i started it. So unless something trashed it within the little bit it ran the first time, then i dont know. The other 6 injectors had been tested when I installed the 2 new ones. This one just sounds like a 7.3 at all times. Like it has no pilot injection. But it had a stock tune, i pulled it with EFI and compared it to a stock one i had. I assume its just noisey because its making more than desired rail psi at idle. as soon as you get to about 2300 rpms it quiets up but has no power and has a thicker white haze out of the exhaust. It doesnt blow and smoke or haze at idle though.
 
sweetdiesel

sweetdiesel

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Aug 6, 2006
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The noise could be because you have to high rail press.

Ill try and dig up a old post that is a gm step by step

As for bottle testing a lb7 the relief valve is on the junction block at the ds y bridge. I've personally never done it but you would need a hose off the pop valve to the bottle and then just make sure you plug the hose you remove from the relief valve (pop valve)

Do you have a spare fuel line that you can cut and weld the line shut? Enabling you to screw to the cp3 and each inj line that goes off the rail?

Mike had mentioned earlier about fuel temps as some guys with mostly stock tuning can hqve issue due to GM limiters. Also the rail press sensor can fk you up too.

You need to start at the beginning and just rule out everything.
It could be a regulator sticking from what you said in the first post
 
ripmf666

ripmf666

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Sep 20, 2006
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Wentzville Mo
onebaddmaxxx said:
Working on a 2002 gmc at work. Truck is 2wd with utility body and dual tanks. Truck came there running rough and lots of white smoke, had bad balance rates on 2 injectors. Pulled all 8, sent them out to get tested and low and behold 2 were bad. Replaced the bad injectors with new bosch injectors. I then reinstalled the other 6 injectors back into the cylinder they were removed from. The truck started up and ran great it sat there for about 2o minutes idling while i finished some things up and let it warm up to add coolant before i test drove it. I backed out of the shop and had no pedal response. The truck was throwing p0087, p1093, p1094. I did some research and everyone said since it was throwing low rail psi that those codes were usually thrown from needing injectors or cp3. The cp3 had been replaced 3 days prior to coming to our shop by the local gm dealer. Regardless, being it had new injectors i pulled the cp3 and had it tested and it came back good. Upon reassembly, i noticed a strong gas odor. I pulled the brand new fuel filter off and it was completely black inside and smelled like gas. I figured ok lets drop the tanks and clean them. BOTH tanks were filled with gas and very dirty. Cleaned them, reinstalled and filled with diesel and the truck had the SAME symptoms.

At idle, the truck makes 65mpa and desires 40mpa. If you start giving it gas the desired goes up but the actual goes down. I can only get about 2300rpm out of it total, and once the actual goes under the desired it starts smokin heavy white smoke. The injectors were re o ringed, new coppers, new return line washers etc. at full throttle it maxes at about 2300rpms and is at about 26mpa. any ideas on this? I tried looking up how to do a bottle test lb7s but couldnt find any ideas...could the fprv be bad? how common is that? Really stumped on this one thanks in advance....
Click to expand...

There's a issue after replacing the 2 injectors you installed the 6 back and restarted the truck. Then you pulled the said replaced cp3 by a dealer to get checked a to be safe. At that point you noticed the gas smell and cleaned the tanks and all. The issue is what about the gas that already ran throw those injectors and throw the 2 new ones you just installed.
 
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onebaddmaxxx

Active member
Feb 22, 2009
1,212
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Cecil County Md
Thanks, yesterday I was all caught up and decided to diagnose it some more. The fuel temp was at 60* when i turned the key on that that rules that out. Yesterday it threw a p0089 regulator performance. I assume that the reg must be stuck from everything coming through the system. I talked to the dealer last night they did in fact replace the cp3. He also said the truck was having trouble running there. They went thru 2 regulators, replaced the cp3 and then had to put ANOTHER regulator on the new cp3. He said he went through multiple fuel filters as well so guess he never realized there was gas in the truck. He did say he can warranty me out the regulator so im gonna swap that this morning. I did pull the fuel filter off last night and fill it up with stanadyne and it was alot better but still had some symptoms. Ill report back tonight.. Thanks for the help guys
 
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