bulldogfan Posted March 1, 2019 Share Posted March 1, 2019 I have a real head scratcher! I replaced the two fuel filters a week ago. Truck fired up, did the usual stumble than seemed to run okay. Idle seemed a little rough though the next day. Then, I parked truck with driver side leaning down a bit to unload. Would not fire. Cranked great, but no fire? This is where I get confused, we dragged truck backwards to other side of road so that now passenger side was leaning downwards a bit. sat for a minute, cranked truck and fired right up! Been running truck all week, seems fine, except first thing in morning spins over well, but takes just a bit longer to fire. Then today, truck starts good, drove for 3 hours, perfectly, had to park with driver side leaning slightly again, get in to move and will not fire. Spins over great, but doesn't even attempt to start? So far, I have opened hood and pumped hand primer. It feels to have little to no resistance. So I replaced hand primer. Still has little to no resistance. Truck is almost full of fuel (single tank). If truck runs fine, shut off for five mins, get back in and then cranks great, but no fire? Seems electrical? But then why no firmness in hand primer? Help!! Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/ Share on other sites More sharing options...
fjh Posted March 1, 2019 Share Posted March 1, 2019 Gray or red engine?? Do you have a plugged fuel vent try cracking the fuel cap see if that makes the diffrence! So also Gray or red engine?? RED Injector cup issues if a red engine! MP 7 MP8? If gray faulty fuel supply pump could also be an issue! Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-416923 Share on other sites More sharing options...
bulldogfan Posted March 1, 2019 Author Share Posted March 1, 2019 Hello, It is a gray engine. And I am thinking fuel supply pump also, but do you think the pump would fail intermittently? And if so, would that cause the hand primer to be pretty spongy? Thanks. Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-416925 Share on other sites More sharing options...
fjh Posted March 1, 2019 Share Posted March 1, 2019 (edited) make sure the vents clear anything is possible, fuel return check / drain back valve also can cause this! Drain back is cheaper than the pump if you going to throw parts I would go there first! Edited March 1, 2019 by fjh Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-416928 Share on other sites More sharing options...
bulldogfan Posted March 1, 2019 Author Share Posted March 1, 2019 Thanks. Drain back valve? Is it also called check valve? Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-416932 Share on other sites More sharing options...
fjh Posted March 1, 2019 Share Posted March 1, 2019 Yes Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-416934 Share on other sites More sharing options...
bulldogfan Posted March 1, 2019 Author Share Posted March 1, 2019 Just left mack with$1000 in parts. I will keep updating this post... Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-416937 Share on other sites More sharing options...
bulldogfan Posted March 2, 2019 Author Share Posted March 2, 2019 I replaced the transfer pump. Also installed factory fuel filters. Took a while to get all the air to purge. But truck finally fired "rough at first" than smoothed out. Actually seems to idle a lot smoother now too. I bought a new check valve, but don't see where it goes? Is it behind the egr cooler? Thanks. Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-417011 Share on other sites More sharing options...
JoeH Posted March 3, 2019 Share Posted March 3, 2019 Might be one in the fuel filter housing? I've never worked on one this new. 😊 Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-417051 Share on other sites More sharing options...
bulldogfan Posted March 3, 2019 Author Share Posted March 3, 2019 Dealer sold me a checkvalve. It looks like a hydraulic coupling? Can't seem to locate it. I am sure it's not attached to filter housing. Going to get my bore scope and look behind the egr cooler. And hope it's not back there! Lol. Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-417075 Share on other sites More sharing options...
Macktech689 Posted March 3, 2019 Share Posted March 3, 2019 If you are looking for the overflow valve it's in the block above the front of the head on the air compressor. Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-417077 Share on other sites More sharing options...
bulldogfan Posted March 3, 2019 Author Share Posted March 3, 2019 I am now wondering about the fuel line that runs from primary filter to the back of computer? It has swivel fittings, and they have slop in them. Not leaking fuel, but maybe letting air in? Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-417081 Share on other sites More sharing options...
bulldogfan Posted March 10, 2019 Author Share Posted March 10, 2019 For future reference... something that I have replaced seems to have fixed issue. Fingers crossed. Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-417909 Share on other sites More sharing options...
mrsmackpaul Posted March 11, 2019 Share Posted March 11, 2019 Sounds like air was getting in The easiest way I have found to find these problems is get a bit of old inner tube and a couple of big flat washers and some air fittings and put them through the tube Next get a big hose clamp and clamp it onto the filler neck of the tank and pressurize the tank a bit and and leaks will show right away Sounds like its fixed though, good luck with it Paul Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-417942 Share on other sites More sharing options...
fjh Posted March 11, 2019 Share Posted March 11, 2019 6 hours ago, mrsmackpaul said: Sounds like air was getting in The easiest way I have found to find these problems is get a bit of old inner tube and a couple of big flat washers and some air fittings and put them through the tube Next get a big hose clamp and clamp it onto the filler neck of the tank and pressurize the tank a bit and and leaks will show right away Sounds like its fixed though, good luck with it Paul Yup agree with Paul a little Preasure will find a leak where Vacuam not so much! How ever changing things one a a time is sometimes all you can do! Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-417974 Share on other sites More sharing options...
bulldogfan Posted March 14, 2019 Author Share Posted March 14, 2019 Thanks for that! I'll keep it in mind incase the problem comes back. Still curious about the fuel line between primary filter and ecm. Makes sense that I first noticed a hard start and rough idle immediately after service, including changing the centrifuge oil filter. Which you have to move fuel line out of way, to change. Ever heard of the swivel fittings going bad on fuel lines? Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-418127 Share on other sites More sharing options...
bulldogfan Posted August 19, 2020 Author Share Posted August 19, 2020 I finally replaced the fuel lines that run from primary filter to ecm then to the mechanical lift pump. Problem solved. If you have the quick connect fuel fittings, it will be the issue with truck losing prime...Go, with regular hydraulic style fittings. Quote Link to comment https://www.bigmacktrucks.com/topic/55888-06-aset-hand-primer-question/#findComment-459032 Share on other sites More sharing options...
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