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Lost Power And Can"t Find It

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we took our 1995 r model mack and swapped out the 400 motor and droped in a used 427, about three years ago. after some computer issues we finnally got the truck on the road, the 427 was incredably strong, right up till 3 weeks ago. the motor started to hitch and hesitate on hills, so we took it to a mack shop, the mechanic changed the injection pump with a good working used one and sent us on our way. the truck didnt hesitate any more, but lacked power, so he told us to take the original pump to get calibrated. we had the original looked at and calibrated, but there was nothing wrong with the pump, it was working fine, besides a little timing and cleaning. so we put it back on the truck, still lacking power. so they said it wasnt the pump it was the wiring harness to the pump, they changed it with a new one and gave us the truck back. we took the truck on the road with a EMPTY log trailer behind and it didnt just lack power now it could barely haul itself. we had to drop the trailer and take the truck to another mack shop. that shop said our turbo was cracked, so we put a good working used one on and still nothing, changed the air filter and fuel filters and all of the fuel lines, still nothing. new air to air, 6 new injectors, new intake sensors, boost gauge, STILL NO POWER. we can only get 15 to 20 psi boost from the turbo, 2 mechanics say the fuel pressure is fine 1 says it fluctuates. the temp gauge will read 180 after a quick run but the comp hooked up will read 108 and a temp gun shot at the manifold will read 103. first thing tommorrow morning i want to check all connections on the new wiring harness because after it was installed we lost all power. oh and the vavles have been set as well. if anyone has ideas or input please help. thanks frustrated 427. p.s. the turbo for the 427 is actually off of a 400 because the 427 turbo will not fit with the hood closed but the motor had tremendice power before with the other 400 turbo.

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we took our 1995 r model mack and swapped out the 400 motor and droped in a used 427, about three years ago. after some computer issues we finnally got the truck on the road, the 427 was incredably strong, right up till 3 weeks ago. the motor started to hitch and hesitate on hills, so we took it to a mack shop, the mechanic changed the injection pump with a good working used one and sent us on our way. the truck didnt hesitate any more, but lacked power, so he told us to take the original pump to get calibrated. we had the original looked at and calibrated, but there was nothing wrong with the pump, it was working fine, besides a little timing and cleaning. so we put it back on the truck, still lacking power. so they said it wasnt the pump it was the wiring harness to the pump, they changed it with a new one and gave us the truck back. we took the truck on the road with a EMPTY log trailer behind and it didnt just lack power now it could barely haul itself. we had to drop the trailer and take the truck to another mack shop. that shop said our turbo was cracked, so we put a good working used one on and still nothing, changed the air filter and fuel filters and all of the fuel lines, still nothing. new air to air, 6 new injectors, new intake sensors, boost gauge, STILL NO POWER. we can only get 15 to 20 psi boost from the turbo, 2 mechanics say the fuel pressure is fine 1 says it fluctuates. the temp gauge will read 180 after a quick run but the comp hooked up will read 108 and a temp gun shot at the manifold will read 103. first thing tommorrow morning i want to check all connections on the new wiring harness because after it was installed we lost all power. oh and the vavles have been set as well. if anyone has ideas or input please help. thanks frustrated 427. p.s. the turbo for the 427 is actually off of a 400 because the 427 turbo will not fit with the hood closed but the motor had tremendice power before with the other 400 turbo.

Fuel preasure should not be an issue unless its really starving for fuel, it would likly stuter, stumble and miss if it were running out of fuel preasure ,sounds like a programed derate.these are the things to check in order( sounds like they have been checked BUT ya never know!

check 1 - Fault codes (Repair as nessary)

check 2 - fuel preasure 15 to 20 psi under load.

check 3 - re-pin fuel pump plug.

if you have all of the above checked and done heres another place to go.

i ran into this awhile back on an RD!( hicups and hesitations are USUALLY it is the pin conections at the fuel pump!)BUT Having said that ,You now get 1/2 the boost the engine should make ! You likly have a second unrelated problem If you have no faults coming up( No blink codes) , I would check to make sure the wiring to the torque limit switch on the trans is not shorted !The computer will not see a problem with this because it doesnt know theres a problem!(All it sees is a closed switch),

and derates the power by half.

check it out and see if that may lead you to a fix.

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well finally the problem was fixed, after 3 weeks with a truck that was unusable. you were right, the connection at the torque limit switch was bad, we would have never thought to look there nor did the mechanics. they forgot all about it. and the new wiring harness was loose at all connections on the firwall, but the connection at the torque limit switch was the problem. i thank you so much, you have saved us alot more time and money, should have asked 3 weeks ago i guess. anyway untill next time. thank you again. fixed 427

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well finally the problem was fixed, after 3 weeks with a truck that was unusable. you were right, the connection at the torque limit switch was bad, we would have never thought to look there nor did the mechanics. they forgot all about it. and the new wiring harness was loose at all connections on the firwall, but the connection at the torque limit switch was the problem. i thank you so much, you have saved us alot more time and money, should have asked 3 weeks ago i guess. anyway untill next time. thank you again. fixed 427

Glad to help! Ask and you shall recieve! :D

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well finally the problem was fixed, after 3 weeks with a truck that was unusable. you were right, the connection at the torque limit switch was bad, we would have never thought to look there nor did the mechanics. they forgot all about it. and the new wiring harness was loose at all connections on the firwall, but the connection at the torque limit switch was the problem. i thank you so much, you have saved us alot more time and money, should have asked 3 weeks ago i guess. anyway untill next time. thank you again. fixed 427
That is from working on then instead of looking at them and guessing ant it Hand.

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That is from working on then instead of looking at them and guessing ant it Hand.

That fix cost me alot of gray hairs 8hrs worth and the owner a fuel pump check over and all the parts and related sensors plug pins.

YOU Got it for FREE! sort of :( lucky dog. :)

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