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E7 400 Mack, Misfire, seems to Move, need help


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Hi, new to Mack and need help

I have a E7 400 Mack with a jaccob Brake set up, here's the story  the truck had a head gasket problem that was building coolant pressure that we were adding coolant hopping to get a few more weeks out if it till we had time to get the truck in the shop, then we noticed a lack of power and noticed a misfire it seemed to be cylinder 2 and 3 we checked this by cracking the fuel lines loose one at a time, when removing the valve cover we found cylinder 3 exhaust yoke broken, from there we, 

Replaced both heads, gaskets , all 6 injectors , and injector lines , and the one broken yoke, piston's and cylinders seemed fine on visual inspection, adjusted valve timing according to the book and have rechecked since 16 on intake and 24 on exhaust, put all back together there is no more coolant pressure problem to still has a misfire , we checked compression and leak down all seem ok, we tried checking witch cylinder the misfire is from by disconnecting each individual fuel pump wire one at a time and it seems that the misfire jumps around, OHM checked all fuel pump wires seems to be ok , swapped the computer with another truck and other truck ran fine with computer not sure where to go next    

Edited by rspatola88
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  • rspatola88 changed the title to E7 400 Mack, Misfire, seems to Move, need help

How many miles are on this engine? Are all the valves adjusted about the same.... as in you didn’t have to crank one to the end of threads to get adjustment correct? Were the lifters or the EUP lifters checked? The ceramic rollers break or the metal rollers score up and cause a miss that way, especially if you had broken valve train components

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So this comment holds some weight being as you had a yoke failure  to begin with you should check the lifters !on the failed yoke cyl! That being said the fact that the miss seems to jump around sort of indicates the computer is possibly trying to compensate for irregularity in engine rpm smoothness not sure on this! But I have been personally involved in chasing this issue several times wasting time To no avail ! My advice is  After you check the lifter! if the engine is only doing this at Idle and is not effecting performance, Leave the dam thing alone and drive it! Its an annoyance thing only!  Not an indication of a failure of any sort! 

Just an opinion 

Edited by fjh
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  • 4 weeks later...

You can use a vise grip and squeeze the fuel hose that is after the regulator. it comes out of the block below #3+4...  be careful not to cut the hose.. also if the fuel hose is hard like dry rot, dont do this test... without replacing the line when you are done...... so your truck is probably set to 625 RPM's... it will flucuate about 25 RPM's during the rough idle condition.. if squeezing the line smooths out the idle and you get a firm 625 RPM's, then replace the regulator.... Ok my Canadian friends and Glenn,,, please advise... Jojo ✌️

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Joe in my opinion You got to be carefull with that test! I have seen more than one pump shaft seal blown out due to over pressuring the system ! had it happen to me more than once!  Wern't a happy camper!😡

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👍yes sir,, it does take some care, and i dont actually close it off completely, but yes it is risky... Thank you for youre opinion..jojo

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Hey Joey, That test is a good test to see if the regulated pressure is set too low for the fuel system.  I would squeeze the return line slowly until the idle stabilizes. Yes F is correct, care has to be taken. If the idle does smooth out then the higher regulated pressure check valve can be installed. But this may lead to other issues such as diesel fuel diluting into the engine oil. I used to recommend installing the updated delta seals on the EUP once the fuel pressure was at 100 psi. Here is the Delta Seal part# 1899-071356. Also there were datafiles that were released by Mack that tried to solve this issue. I say try because it worked sometimes. 

V

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Yes sir... I use a needlenose vise grip, because I can preset the gap in the jaws so that it doesnt completly cut off the return flow. and if its too loose, i turn the knob slowly to set it right... thanks sir.. I like other opinions, I certainly dont want to offer bad advice.. and I also like to learn more, even if it means my way is the wrong way....🤔  Jojo

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👍 "V"   you always come up with Stats and Mack Info.. and part #'s...  I'm quite sure you have helped many here.. jojo

Edited by Joey Mack
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