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ClaytonH729, Mechanic
Category: Medium and Heavy Trucks
Satisfied Customers: 755
Experience:  Expert in Freightliner trucks, From the Engine, to the taillights. Hit me with the most complex electrical problem also
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I have a power loss on a Detroit 60 series engine its in a

Customer Question

I have a power loss on a Detroit 60 series engine its in a freightliner classic 2003. The motor works fine there is no proble in the fuel lines collapsing and the pressure valve on the return line is ok
I've changed out the trs and srs sensors and air to air was replaced, but still I'm losing power at the end of the high gears when driving with or without a load very slow acceleration but motor runs fine no shutters what so ever
Submitted: 5 years ago.
Category: Medium and Heavy Trucks
Expert:  ClaytonH729 replied 5 years ago.
Hi, Welcome to Just Answer, I can help you with this. So I can safely assume you drove the truck with a fuel gauge on it to see what the pressure is while you are driving? Low power could be quite a few reasons. Low boost, exhaust leaks before the turbo, boost leaks, and/or bad turbo Air in the fuel due to injector o-rings, crack in the suction line, etc etc. Faulty sensor- Usually followed by a check engine light, and the engine will derate. I drove a truck the other day that had a low power complaint, checked everything but air in the fuel, put a fuel gauge on it, and the pressure would spike to 100 psi when under boost. Would act fine driving easy, but once it was under boost, it would fall on its face. This was bad injector o-rings. Compression was blowing past the first o-ring sealing off the combustion chamber. This might be your problem, and a fuel pressure gauge can tell this.
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Customer: replied 5 years ago.
Hi Clayton thank you for the information. today I did a cutt off test on the injector and found the injector number three would not cause a proper shut off like the other injectors. when administering the test, I did run a pressure gauge and drove truck with the computer on nexiq. andvno codes came up even driving. and the fuel pressure was at 80-90 psi I was told the pressure from the mechanical pump was about 60 psi at 1500 rpm. Have you ever came across the speedometer falling when you release the accelerator and could this be the problem.
Expert:  ClaytonH729 replied 5 years ago.

Never heard of that problem before, it should not do that. Some of these trucks are configured with a speed sensor that splits off and goes to the ECM, and the other goes to the speedo head.

It is possible the speed sensor could be falling out, but a way to prove that is to watch your vehicle speed on Nexiq to see if it also falls off. If it does not fall off in the ecm, but falls off on the speedo, there should be 2 connectors coming off of the speed sensor, you can swap those to see if you lose vehicle speed in the engine ecm, but hold vehicle speed on the speedo head.

When I use Detroit Diesel for a cylinder cut out, you look at the baseline pulse width, and if any injector goes below the baseline, it could be 1 of two things, air in the fuel, low fuel pressure, faulty injector. None of these symptoms could cause a fault code. The only way a fault code will show in the ecm is if the response time of the injector is long or short. This is typically a injector solenoid, or harness issue.

As far as fuel pressure, depending on where you put your gauge, Detroit recommends you put it where the fuel temp sensor is.

At idle, 600 rpm, you should have 15-22 psi

1200-1300, you should have 30-45 psi

1800-2100, you should have 65-80 psi

If the fuel pressure is high, I would suspect a plugged fuel filters or faulty fuel pressure regulator. If the guage is really bouncy, and unstable, especially under boost, then compression could be leaking past the injector o-rings. Or air is getting in the fuel somehow. Which you eliminated the suction line by going straight to the fuel tank.

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