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Old 01-16-2013, 02:33 AM   #1 (permalink)
george116
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p1093, lack of power when towing

Hello all,

I'm trying to figure out what is wrong with my truck. It is a 2003 Sierra 3500. The engine was replaced a few years ago by the previous owner and has ~88k miles on it (Chevy dealer did the work). The rest of the truck has 254k. I bought the truck to tow a fifth wheel RV. The first time I towed it on the interstate I experienced a lack of power when climbing any grade of hill (this was I-20 in Georgia). I lost 15 MPH on some of them if they were sustained. I am towing pretty heavy for the rating of the truck but I did not expect this sort of performance. On some hills I can build a little bit of speed after initial slowdown but it isn't much. I don't think I've experienced the "limp mode" I've read about -- no RPM limiting or anything like that. Also I can get to 65 MPH when not going up a hill.

I had the codes checked and had P1093. I changed the fuel filter, which helped the performance some when not towing. However, towing performance is still bad, and the code is still there. From all the research I've done it seems likely the problem is the CP3. However, the cost to replace that is pretty steep, as I don't have the knowledge/time to do it myself. I've also seen that it could be a problem with the fuel rail, fuel line constriction, fuel pressure regulator, or possibly the fuel pressure relief valve (though from what I read that is unlikely for the LB7s?).

Previous owner had two of the injectors on the new engine replaced before it went out of warranty. I did not smell any fuel when checking the engine oil dipstick. The air intake filter (aFe) is pretty dirty and I'm going to clean it.

This is my first diesel and I don't know a whole lot about them. I need the towing power that I thought I was going to get with this truck, as I've already ended up going 35 MPH on an interstate trying to get up a long hill, and I don't want to repeat the experience.

What steps should I take to diagnose the issue? Cheapest/easiest first. Is the bottle test useful/doable on an LB7?

Side question, does anyone know a good diesel repair place near Montgomery, AL with experience on Duramaxes that could help me for a good price? Or anyone in the area with a scanner that could look at data and help me diagnose?

Thanks!
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Old 01-16-2013, 01:26 PM   #2 (permalink)
D.Camilleri
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Welcome to the diesel place. Do us a favor and fill out your signature line and put your truck specifics in it.

As to your truck, my guess is that your cp3 probalby wasn't replaced when the engine was replaced and is worn out. You can take you truck to a dealer and have them command the rail pressure to 126 mpa and see what the pump is able to produce. Have the return rates on the injectors checked also. This will give you an idea as to the health of the fuel system. Replacement CP3's cost around 5-700.00 install isn't super hard. Sometimes a weak CP3 can be nursed along by adding a lift pump. You can also install a fuel vacuum gauge in the fuel feed line to see if the lift pump in the CP3 is pulling the fuel enough. Kennedy Diesel is a vendor here and you can find more info on his website.
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Old 01-16-2013, 02:36 PM   #3 (permalink)
george116
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Thanks for the reply. The Chevrolet dealer in the area estimated it'd be about $2k to replace the CP3. $1k for the pump, ~$200 for miscellaneous hoses, etc., and 7.3 hours of labor.

What kind of diagnostic fee ought I to expect for having the dealer check those things you mentioned to make sure what the problem is?

I will look around for a "how-to" on the CP3 install. With the dealer estimating about a day's work to do it, I'm guessing it'll be beyond what I can handle with my lack of experience. Where is a good source for CP3s in that range? The cheapest I have found was just short of $700 but I didn't know if the vendor was trustworthy. I'll check out Kennedy as well.
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Last edited by george116; 01-16-2013 at 02:43 PM. Reason: clarity
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Old 01-16-2013, 03:28 PM   #4 (permalink)
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Just called the dealer, they said the high rate fuel test takes about 3 hours and runs $280. I am not sure if they were talking about the same test you mentioned.
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Old 01-16-2013, 07:45 PM   #5 (permalink)
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Your dealer must have a pretty high labor rate. The parts for these trucks aren't cheap, and neither is the labor, but if you can learn to do the work yourself, it makes it a little more bearable. You could search for an independent diesel shop and check their prices. The return rate will tell the condition of your injectors, but it doesn't mean you won't find bad injectors and a bad cp3. I would ask for a vin check here in the proper section and see if your injectors have been replaced under warranty.
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Old 01-17-2013, 11:13 AM   #6 (permalink)
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Can someone point me to where to check for constricted fuel lines? I do not know where they travel on the truck.
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Old 01-17-2013, 04:30 PM   #7 (permalink)
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The fuel lines leave the fuel tank on top and go to a steel line on the frame rail, follow the frame rail to the engine compartment to a quick coupler, then on to the fuel filter. Restrictions can happen in the fuel tank in the pick up, or rubber lines that can colaspe internally. If you had access to an electric fuel pump, you could do a test by hooking it up to the fuel filter feed line and see how much fuel the pump could put out into a container.
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Old 01-17-2013, 05:06 PM   #8 (permalink)
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I do have a transfer pump mounted on a tank in the bed that I might be able to rig something with. I guess you're suggesting unhooking the line near the fuel filter and trying to draw fuel out of the truck's tank via the external pump? How would I evaluate the results?

Thanks for your replies.
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Old 01-17-2013, 07:29 PM   #9 (permalink)
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If you have a large pump on a tank, it would probably be too large to get good results from. A smaller electric pump would be better just to determine flow. But I think I suggested going to Kennedy Diesel's site and check out his fuel vacuum and pressure gauges. If the vacuum gauge gets too high before the filter, it would suggest a restriction in the feed lines. Me personally, I would invest in a lift pump (electric fuel pump) and mount it on the frame rail so it pulls fuel from the tank and feeds it to the cp3. It could possibly fix your problem and if it doesn't, it is still a good upgrade to have.
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Old 01-23-2013, 03:00 PM   #10 (permalink)
george116
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Finally got someone to look at the truck today, they were not able to do much with it because they lacked the right equipment. The guy did have it on a Mentor (?) reader of some sort. We drove it on the interstate and he said the actual fuel pressure did get up above 22,000 psi at times when I was laying on the throttle. Does that shed any light on the subject?
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