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Junior Member
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Discussion Starter #1
We do some service on a 2000 Kodiak 6500, Cat 3126, Allison, 30,000 miles, but it's a bucket truck so a lot of idle time. They have recently had an engine issue and some other things we've already repaired. All the fluids are fine including fresh oil change (was acting up before the service). Fuel filter is new, air filter is good. It starts and runs fine and runs completely fine while cold or during warm up, but after fully warmed up (at least 10+ miles) it will loose power and develops a miss when subjected to any kind of decent throttle load. As soon as you back off it runs fine. It will run fine at light throttle too (which isn't very effective as underpowered as it is). There is no certain point that it acts up. Sometimes it can run fine up to 2600 (maybe even into 2nd and 3rd gear) and then start missing and drop off. Other times it can run OK for a short time, but then miss and not climb higher than 2000. And still other times it can start acting up shortly after you start accelerating and just not pull above 30-35 mph (maybe 1500 rpm). The check engine light is not on during any of this. Would anyone have a suggestion please? Thanks.
 

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1,138 Posts
You would only be guessing with out using some solftware to monitor the ecm and a gage to put on the fuel system and then you need the troubleshooting guide from cat to tell you what to do. Sounds like a fuel pressure problem but that is guessing. There may be a fuel filter under the battery box that no one has not changed also.
 

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There's your problem.
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220 Posts
Check engine on? Could be a HUEI failure also. On the rear of the cylinder head driver side there should be a hex plug for the HEUI rail. I would open that up and inspect the end for fine pieces of brass, metal, ect. Use a white rag and stick it inside the rail and check the rag for metal. They will be fine pieces so look hard, it will be extremely difficult now though that the oil has been changed. I would take it in to a dealer and do a step up step down via CAT ET to check the actuation of the HUEI pump, and a cylinder cutout. These pumps are prone to failure, causing metal from the HUEI pump entering the HUEI system, and clogging the injectors. Fuel pressure should also be checked, you would check that at the secondary fuel filter base, but the spec range is escaping me at the moment. Maybe Tony or someone else could chime in with it.
 

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Member
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121 Posts
Check engine on? Could be a HUEI failure also. On the rear of the cylinder head driver side there should be a hex plug for the HEUI rail. I would open that up and inspect the end for fine pieces of brass, metal, ect. Use a white rag and stick it inside the rail and check the rag for metal. They will be fine pieces so look hard, it will be extremely difficult now though that the oil has been changed. I would take it in to a dealer and do a step up step down via CAT ET to check the actuation of the HUEI pump, and a cylinder cutout. These pumps are prone to failure, causing metal from the HUEI pump entering the HUEI system, and clogging the injectors. Fuel pressure should also be checked, you would check that at the secondary fuel filter base, but the spec range is escaping me at the moment. Maybe Tony or someone else could chime in with it.
I've got a 4/04 build date C7 that doesn't have the upgraded HEUI pump, and I've been told that the failure mechanism is a bearing that goes bad and sheds metal debris? Does anyone know if this type of failure shows up in an OA report or does the debris get trapped in the HEUI rail and not make it past the injectors?
 

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Discussion Starter #5
Thanks for the advice guys. I took the truck to 2 different truck service garages for scanning with Pro Link, but neither place could do it. It seems it's a GM truck dealer only for the service (unless a Cat dealer is able to do it, but none close by). It has an OBDII connecting port under the dash, but an automotive code reading tool will not work either. Anyways in the middle of all of this, I also changed the water separator under the cab instead of draining it (wasn't that old) and put about 30 miles on it without acting up. I told the owner to give it a try and see if it's gone, but it's been too cold for them to work out of it lately. I guess we'll see what happens. Thanks again.
 

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There's your problem.
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220 Posts
I've got a 4/04 build date C7 that doesn't have the upgraded HEUI pump, and I've been told that the failure mechanism is a bearing that goes bad and sheds metal debris? Does anyone know if this type of failure shows up in an OA report or does the debris get trapped in the HEUI rail and not make it past the injectors?
Ya,one of the bearings go bad inside the pump and contaminates the oil, and copper or brass from the pistons of the internal piston pump wear. Generally if your doing an OA Report, it should come up with elevated iron, copper, and other metal counts. I haven't looked into this because none of the customers i have dealt with do this, and S.O.S samples take too long to get results vs pulling the rail plug. But you still have some metal go past the injectors or something.
 

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Discussion Starter #7
Have there been changes made so that the replacement pumps are an improved design? If so, is it worth changing a pump as a preventative measure? Where is the pump located and how hard is it to change? Thanks.
 

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Have there been changes made so that the replacement pumps are an improved design? If so, is it worth changing a pump as a preventative measure? Where is the pump located and how hard is it to change? Thanks.
I've been spending this winter in Las Vegas and the local CAT dealer maintains a fleet of school buses which have had several HEUI pumps fail in as little as 30K miles! Since my C7 only has 21K miles on it I was interested in changing to the upgraded HEUI pump which I think is standard on late 2005 or 2006 and later engines because I thought it might save a much larger expense if my HEUI pump goes and takes out all the injectors. Then I priced this option at the Las Vegas CAT dealer, then I lost 40% of my retirement nest egg in the stock market melt down, then I decided to just change the engine oil every 6 K and do an OA and hope for the best!

I've also read that my April 2004 C7 was built during a period before CAT discovered problems with their cylinder head casting procedure, and that my head might have small pinholes that can spring leaks resulting in oil in the coolant and/or fuel or coolant in the oil? There's supposed to be a CAT TSB out on this issue and I'd sure like to see a copy of it. The way my luck seems to run lately I'd probably upgrade my HEUI pump and then discover I've got one of the defective cylinder heads!
 

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Discussion Starter #10

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Thanks for the link. The 1st shop didn't have the adapter. The 2nd had an adapter that plugged in fine, but Pro Link still would not read anything from it. It's been too cold for the truck to be put in use recently, but we'll see if the filter took care of it when they do use it again.
To read with prolink you need a version of 1.07 and the newer enginelike the C7 may require 1.11 and you can monitor and do cylinder cut ot selnold test and chane coustomer premeters as well as clear codes.I have both but never used on a C7 glenn
 
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