Combinemack Posted November 17, 2020 Share Posted November 17, 2020 I have a 1997 mack medium duty truck, it runs great but if the truck has air pressure built up it won't start. Pump the air pressure down with the brake pedal and then it starts right up. Any suggestions? Thanks Quote Link to comment Share on other sites More sharing options...
doubleclutchinweasel Posted November 17, 2020 Share Posted November 17, 2020 Welcome to the jungle! When you say "won't start", what exactly do you mean? Will it turn over okay but not light? Will it not turn over at all? Does it turn, but turn slowly? The more details, the easier it will be for one of the guys to zero in on it. Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment Share on other sites More sharing options...
Combinemack Posted November 17, 2020 Author Share Posted November 17, 2020 It turns over perfect and just like it should, it just doesn't take off. But if we pump the air pressure down it cranks over and fires right up Quote Link to comment Share on other sites More sharing options...
doubleclutchinweasel Posted November 17, 2020 Share Posted November 17, 2020 Is there any way there could be an air pressure switch shutting off the fuel supply? Not sure if that would be intentional or accidental. But, it sure sounds like the two are connected, doesn't it? Maybe check voltage at a fuel shutoff solenoid (I am assuming there is one). Sounds like a good one for one of the Mack technicians to answer...if any of them are still around! This is a little (lot!) out of my field! Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment Share on other sites More sharing options...
Brian L Blaylock Posted November 18, 2020 Share Posted November 18, 2020 I don’t have any knowledge of medium duty trucks but if it would happen to have an air accelerator as did some Superliner you might check there Quote Link to comment Share on other sites More sharing options...
41chevy Posted November 18, 2020 Share Posted November 18, 2020 (edited) What model Midliner is it? Automatic transmission too? Some of the Midliners had a brake interlock switch, which made it so the engine would not start unless the foot brake was applied. Edited November 18, 2020 by 41chevy Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment Share on other sites More sharing options...
Combinemack Posted November 18, 2020 Author Share Posted November 18, 2020 I guess its a renault, and its a standard trans Quote Link to comment Share on other sites More sharing options...
fjh Posted November 18, 2020 Share Posted November 18, 2020 some of these had and air shut down cyl on the side of the fuel pump it may be sticking ! or the air supply solenoid is not working correctly! 2 Quote Link to comment Share on other sites More sharing options...
doubleclutchinweasel Posted November 23, 2020 Share Posted November 23, 2020 On 11/17/2020 at 2:10 PM, Combinemack said: I have a 1997 mack medium duty truck, it runs great but if the truck has air pressure built up it won't start. Pump the air pressure down with the brake pedal and then it starts right up. Any suggestions? Thanks You ever get this sorted out??? Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment Share on other sites More sharing options...
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