convoyduel Posted August 28, 2012 Author Share Posted August 28, 2012 Would broken bolts cause it to run fine and then poorly for no reason? I'm asking because I would think that something mechanical like bolts, studs or physical hardware would cause the issue to be consistent, not random or intermittent to disappear suddenly as fast as it appeared. Quote Link to comment Share on other sites More sharing options...
staxx Posted August 28, 2012 Share Posted August 28, 2012 I have had rocker shaft bolt back out almost broken causing rocker shaft to lift up leaving valves out of adjustment but more likely fuel psi you wouldnt beleive the stuff I have pulled from fuel tanks ....bottle caps fuel cap chains rocks mouse fuel nozzle from ful island could have something in fuel tank when these engine lose fuel psi fast like turned off then back on they backfire . Quote Link to comment Share on other sites More sharing options...
staxx Posted August 28, 2012 Share Posted August 28, 2012 What style fuel supply pump do you have one with fuel filter or without? Quote Link to comment Share on other sites More sharing options...
convoyduel Posted August 28, 2012 Author Share Posted August 28, 2012 Here's a shot of the passenger side showing the filter forward of the EGR cooler. Quote Link to comment Share on other sites More sharing options...
staxx Posted August 28, 2012 Share Posted August 28, 2012 The supply pump is part of that filter assembly have seen alot of those fail gear on shaft sliping or housing sucking air engine looks clean new egr cooler and mass flow pipe on there thats good. Quote Link to comment Share on other sites More sharing options...
staxx Posted August 28, 2012 Share Posted August 28, 2012 Could check overflow valve on fuel return, follow that silver line next to air compresor to block and its the fitting that screws into the block has a spring and valve in it .look in your fuel tank with flash lite at nite and you can see the bottom of tank alot better then in daylite check for debris. Quote Link to comment Share on other sites More sharing options...
Lmackattack Posted August 28, 2012 Share Posted August 28, 2012 Just throwing this out there...I had a backfire issue in a cat motor a day after an injector cup failed. Cups faild ,Filled coolant with fuel and drove 150 miles to a dealer. new cups installed next day, ran fine bob tail, idled fine...I hooked up to trailer and as soon as I got up to about 45mph it started to back fire badly...fire out the stack bad.... Limped 5 miles back to dealer and they did an injector cut out test. Fount 2 bad injectors and a bad jake solenoid. they think the water in the fuel was part to blame and the backfiring killed the jake. Almost sounds like an injector is fireing out of time or fuel is lighting off in the exhaust. If its a electrical issue that will be hard to find unless you can read and record the engine data logs in real time... Quote Link to comment Share on other sites More sharing options...
convoyduel Posted August 28, 2012 Author Share Posted August 28, 2012 Thanks guys. Also forgot to add that the dealer put the truck on the dyno and loaded it down. Didn't backfire once. Quote Link to comment Share on other sites More sharing options...
Lmackattack Posted August 28, 2012 Share Posted August 28, 2012 Another thought... If you pull the air cleaner out,have someone rev the engine and listen to the sound as the revs fall. We had a old r model that had a bad cam and you could hear the slight intermittent miss. That truck also backfired sometimes.. Quote Link to comment Share on other sites More sharing options...
Lmackattack Posted August 28, 2012 Share Posted August 28, 2012 Thanks guys. Also forgot to add that the dealer put the truck on the dyno and loaded it down. Didn't backfire once.Figures......never happens when you want it to... Quote Link to comment Share on other sites More sharing options...
convoyduel Posted August 28, 2012 Author Share Posted August 28, 2012 For the Mack service gurus, we had the dealer print out the Vehicle Data and Settings today and turn off some settings related to mph sensor.The Truck VIN is 1M1AA12Y74N155261. Engine SN is 3A0575, VMAC software version is 1MS379B, Datafile is 1MS380BP4. The EECU software version is 1MS368A. The datafile shows a T310 transmission which is the same transmission that is in the truck, verified by physical inspection. Not sure why the build sheet shows a T309.The VMAC had been programmed "YES" to Detect loss of signal from mph sensor, Limit power if no signal from mph sensor, limit power if electrical fault from mph sensor. All of those were changed today to "NO". The VMAC retained its Engine Load Threshold for no mph signal at 40% and Failed mph sensor engine power limit at 50%. We will try the truck again. The dealer is wanting to start leaning towards the EGR valve. I'm not wanting to keep throwing money at parts replacement guesses, especially when no codes are showing for EGR issues. Quote Link to comment Share on other sites More sharing options...
staxx Posted August 29, 2012 Share Posted August 29, 2012 EGR valve can be physically checked if removed good or bad if its not bad just reinstall egr will just give you low hp and smoke if not working correctly if egr cooler was leaking coolant into mass flow pipe when egr valve opens it would be blown into intake manifold and cause issues when injector cups leak s coolant on a aset engine it leaks out where the fuel line enters the head not into combustion cylinder . If it was electrical should see some codes like 45 or 95 would do this but no codes so has to be mechnical most likely I did have a altinator on a truck once that had one strand or wire shorting to case giving the ecu a heartattack and it only happened after long hot run with no codes .Thought about speed sensor settings last nite but that info goes to the vehical module that just tell engine ecu to limit power to whatever setting is Still think fuel psi see if dealership will hook up external fuel gauge temperory and let you drive and monitor fuel when this happens . 1 Quote Link to comment Share on other sites More sharing options...
staxx Posted August 29, 2012 Share Posted August 29, 2012 Since this is a new truck to you maybe have valves adjusted for maintance and to just inspect valve train suggest replacing rocker shaft bolts and retorqing rockershafts this way you know everything is ok with vavetrain. Quote Link to comment Share on other sites More sharing options...
convoyduel Posted August 30, 2012 Author Share Posted August 30, 2012 After having the dealer turn off the speed sensor junk, the truck ran successfully today for a whole shift with no issues. Fingers crossed. Quote Link to comment Share on other sites More sharing options...
Lmackattack Posted August 30, 2012 Share Posted August 30, 2012 That's good news... Knock on wood! Quote Link to comment Share on other sites More sharing options...
convoyduel Posted August 30, 2012 Author Share Posted August 30, 2012 Yes it is. I really really really love this truck. It's absolutely perfect for us so I'll be glad whenever we are sure to get the issues behind us. Regardless of this being the issue or not, the things that VMAC is monitoring seem rather overkill in my opinion. Now that we've turned most of it off, I'm hoping we have less trouble. Quote Link to comment Share on other sites More sharing options...
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