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Old 03-13-2011, 10:21 PM   #1
oilytony
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cat c7 loss of acceleration

i have a 2004 freightliner with a cat c7 on it, experiencing strange loss of acceleration after it warms past 150 degrees. freightliner replaced ecu and sensors recently and i already changed fuel pump and fuel lines and filters and the very same sensors freightliner changed and changed injector seals oil and oil filter and so far it is sthe the same. engine runs fine while warming up but as soon as it gets up to 150 degrees it loses acceleration and i try to drive it it hesitates and can't get passed 35 miles /hr.
would appreciate any sugestions.
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Old 03-13-2011, 10:49 PM   #2
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If it was a 3126 I would say loss of oil pressure, but the C7 is a common rail so it would have to be loss of fuel pressure. It should bring up a code, loss of power, diagnostic usually starts, low boost, test the CAC, low fuel pressure, change the filters and be sure they are on properly, and the right ones, and proper pressure. The air system filter plugged, or exhaust. Turbo seized or malfunctioning, Valve set to tight. Many of the early ones had problems with the pump, and it was upgraded, Call Cat and see if there are any updates pertaining to that serial number.
Just a thought!
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Old 03-15-2011, 02:11 AM   #3
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The early C7 engines were HEUI.
They also had the fairly early version of the HEP HEUI pump, and were prone to breaking springs on the delivery valves of the high pressure pump.
Your symptoms sound about right for a HEUI pump problem.
The dealer should have the tools to dead head the pump and check to see what the maximum pressure it will build. Ideally do this at the temp you are having the problem at.
If the pump will not build the specified pressure, then it gets replaced. If it is not building enough pressure, they may notice the gear is slipping on the shaft, and per Cat the pump should be replaced as this is a sign of partial pump seizure.
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Old 03-16-2011, 04:14 AM   #4
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C7 HEUI engines were notorious for the hp oil pump bearing and pistons failing and passing metal in the HP Oil system and wiping out injectors and huei pump. The best way to check is to inspect the IPR which in built inside the huei pump, and also pull the big plug on the pack of the cylinder head for the oil rail and catch the oil and inspect for metal and brass.
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Old 03-16-2011, 05:05 AM   #5
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I did not do a lot of them, C7's but the 3126's I did from day 1. I take it the C7 was the one I use to get the pleasure of changing the 9 little pistons 8 on the swash plate and the main one. Those having a problem was not unusual, that is why I recommended calling Cat, or any truck dealer, and seeing if there is any updates available for that unit. Free is good. From memory I believe low injection oil pressure many times did not register a code but would show low pressure when hooked up to the "E" cap, or lap-top.
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Old 03-18-2011, 01:55 AM   #6
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Angry 3126 has a fuel issue lack of power

I am new here and I'm not sure where to post this question, I know this is a reply but where do I start a new post? Anyway I have a 2002 GMC T-7500 with a cat 3126. about 3 weeks ago I noticed a loss of power so I thought ok well I will get a fuel filter tomorrow. here's what happens when I first start the truck it is very choppy when I go thru the rpm's putting my foot down on the gas in nueteral. Then when it warms up its way less choppy, but getting speed is like watching paint dry. I can not get to the upper rpm's in 5th and 6th gear and sometimes not even in 4th. I have very limited power even with no load going up a slight grade and can only get to 60 when going downhill. The truck is a 1 fuel filter system. So I got the filter, my mechanic put it on bled the air out same problem. Anyway I don't even know what I did first but here's what was changed the fuel filter was changed 2 times, the housing of the fuel filter was cleaned out, both tanks were cleaned out, the secondary speed sensor was changed, the lift pump was changed, then I brought it to cat here in the Bronx. H.O Penn, and they tested it out and said for me to change the steel fuel lines to rubber ones and pulled a code which was the IAP valve. I bought the valve and changed the fuel line, only the line from the tank to the engine not the return line (my mechanic did the work). And its still the same!!!! By the way I have good fuel pressure. Whats wrong!!!!
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Old 03-18-2011, 03:06 AM   #7
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I would remove the valve cover and check to see if you are losing actuation pressure. You should be able to see the oil loss even cranking, and when you stop. Look for excessive oil from a solenoid stuck or the seal ring, at the top.
Most times you will not need any parts to look the gasket should be OK.
When you have a problem it is better to give the model and serial of the engine. Every little bit of information helps
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Old 12-17-2012, 03:35 PM   #8
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Has anyone found a solution to this issue. I have a C7 that has the same power loss problems as Oilytony has described.
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Old 12-19-2012, 01:36 PM   #9
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Power loss

I have a 3126 in my fl70 had same issue it was allergie in my fuel system
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Old 12-19-2012, 01:50 PM   #10
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I just changed the fuel filters and they were clean and it didn't run any better with the new filters. I don't understand why it runs so well up to 150 degrees if its a filter problem? Somethings going on when it come out of cold mode.
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