deercreek Posted February 9, 2012 Share Posted February 9, 2012 Decided to start a new thread on this as I really need some help. Have an 08 Mack granite gu713 that has been giving some grief. Its giving this code MID 128 PID 94 FMI 7 which appears to be related to the fuel system. We have replaced the fuel filters about 3 times, blew out the accesible fuel lines countless times. It is an intermediate problem. Sometimes it will work great with no problems and other times it will act like its starving for fuel and hiccup/carry on and even shut off sometimes. The truck is currently at our local diesel truck mechanic, he is now thinking it might be electrical, I have had it down there like 3 times already, seems it always works good when he drives it. Does anyone have any suggestions on what it might be? Quote Link to comment https://www.bigmacktrucks.com/topic/23164-2008-mack-granite-fuel-issue/ Share on other sites More sharing options...
Mackpro Posted February 10, 2012 Share Posted February 10, 2012 The easiest thing to check is the fuel pressure relief valve on the front of the head ( had one with the end broke out last week). Also , if there is a Tee on top of the 7th injector this is a check valve that can go bad and air can be forced back into the fuel system. Also check where the fuel supply pump bolts to the power steering pump and make sure it not dripping fuelor seeping from where they mate together. Check the plastic fuel lines and plastic fittings at the fuel tanks and make sure their not cracked. We have had a few filter stands go bad and start sucking air but in reality it probably the injector cups bad, the symtoms vary greatly when it comes to bad injector cups. Done 2 sets in the last 3 weeks and got another GU sitting in my bay to start on tommorrow. There is a test we do to check for air in the return fuel. If there is alot of air bubbles then it's the cups. I would call a dealer and give him the VIN , miles and engine hrs and see if its still under warranty. If still under warranty get the conical (stainless)cups and injectors installed (If there not on backorder) . If not under warranty you can just replaced the copper cup that went bad to get by cheaply. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/23164-2008-mack-granite-fuel-issue/#findComment-101633 Share on other sites More sharing options...
deercreek Posted February 22, 2012 Author Share Posted February 22, 2012 Thanks alot for all the info. We ended up taking the truck to our local Mack Dealership. They finally got to it and called today. They said there was some oil in the engine harness and where the connector connects into the ecm? They were thinking that might be part of the problem. Have you heard of something like that? Replacing all that won't be cheap. They were going to do a test to check for air in the fuel lines and havent heard back from them yet. I just can't quite see how it would be the ecm, would think it would cause more random issues. Quote Link to comment https://www.bigmacktrucks.com/topic/23164-2008-mack-granite-fuel-issue/#findComment-103283 Share on other sites More sharing options...
Mackpro Posted February 22, 2012 Share Posted February 22, 2012 Yes, the oil temp/oil level sensor in the oil pan is known to push oil up the engine harness into the engine ECM, we actually had one today. The oil in the ECM /harness causes all kinds of weird codes. We usually wash out the ECM, replace the sensor and enine wiring harness and test drive to see if the ECM is OK, About 90% of the time the ECM is OK. Quote Link to comment https://www.bigmacktrucks.com/topic/23164-2008-mack-granite-fuel-issue/#findComment-103320 Share on other sites More sharing options...
deercreek Posted February 22, 2012 Author Share Posted February 22, 2012 Okay, thanks for the helpfull info. They also found some debris in the fuel lines and tank so we may have two things going on here. Thats good news on the ecm, hopefully a washing out will be good enough for it. Its sorta spendy. They are saying they first want to replace the harness and then see what the ecm does after replacing it. So hopefully it will be all good.The truck was one that we rebuilt, it had layed over(I think) on the drivers side, so maybe that is part of the reason there was oil coming up that harness, beings the ecm is on the drivers side Quote Link to comment https://www.bigmacktrucks.com/topic/23164-2008-mack-granite-fuel-issue/#findComment-103397 Share on other sites More sharing options...
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