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1994 Mack RD6886 Loss of power.


741samuel
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Hello I am new to the forums and have two truck that's constantly keep me busy with questions. I have a 1994 Mack RD6886 E7400 tandem rollback. This truck starts and runs fine and at times will loose power and not hardly pull out of its own tracks. I was replacing the fuel filters and then it would take right back off fine. It may run for a day or two weeks before what seems like it goes into some type of limp mode. Change the filters filters and take off off again. Right before this all started I started buying fuel at a new station thinking I would get a cleaner fuel. Well since the problem started after getting fuel at the new station I blamed it on the fuel. I kept dumping the old filters in a pickle Jar looking for water and even cut one of the filters in half. Everything has always been really clean. So after knowing that the fuel seemed to be fine and fueling again at my old location I called several "Buddys" to get other ideas. Many said to make sure the fuel lines from the tank to the pump were clean and open which I did. Next was told to try replacing the lift pump. That did not fix it either. So after getting tired of buying fuel filters the next time it powered out I just turned it off and just set there about as long as it takes to change the filters. Hit the key and it was OK again. When it powers out it idles fine and and the engine revs just fine. Try to take off and no power. After replacing the mechanical lift pump it idles like its about to die. I checked the fuel lines again and blew the line to make sure nothing was restricting fuel. I hope this is enough information and someone has the cure before I take it to the shop. It is electronic throttle and the engine light or buzzer comes on when this happens. I also replaced the turbo with an Oem Mack October 2013 but it ran fine until recently. Thank you for any comments good or bad!

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is the vent plugged on tanks, could be pulling a vacuum on tanks and starving for fuel. know of a guy that had one do it on a ford and started to collapes tank

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We the unwilling, Lead by the unqualified, are doing the impossible, for the ungrateful.

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OK I checked the vents on the tank by blowing back through the return line and air easily comes out of the vent so I am moving and looking at the small return lines. I did check that fuel was returning back out of the small one that comes from the back of the injector pump and tee's into the fitting on the big return line that goes back to the tank. It has pretty good pressure on it. I am not finding any banjo fitting just yet.

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Check your tank for trash.. Don't laugh but I found a ping pong ball in a tank one time. It would bounce around in tank until getting lodge on the suction line and once stopped it would fall off. This was a long diagnosis. DONT KNOW HOW IT GOT THERE....some things will never be explained..

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It could be the fuel, I had this problem after filling at a spinx, my mech told me that the additives in their fuel,

does help clean the system. but the accumulation that has built up in the tanks will be cleaned off also and you will

have to go through about a dozen fuel filters until it is completely cleaned. I carried filters with me and never filled again at that station havent had problem since.

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  • 2 weeks later...

It could be the fuel, I had this problem after filling at a spinx, my mech told me that the additives in their fuel,

does help clean the system. but the accumulation that has built up in the tanks will be cleaned off also and you will

have to go through about a dozen fuel filters until it is completely cleaned. I carried filters with me and never filled again at that station havent had problem since.

Could also happen if you filled up with a bio diesel blend. Bio will clean things out too!

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