Timothy B Demarco Posted March 14, 2010 Share Posted March 14, 2010 I have Mack CH-600 with a mack 300 motor. We have difficulty starting it when it is warm and cold. It's wierd you spray either to it and it fires right up. Fuel filters are tight, no leaks on any fuel lines, it has a new drainback valve. So I got curious and tap on the actuator on the fuel pump and it started. Now was that just luck or could that actuator be bad. If it is bad how do you test it. Quote Link to comment Share on other sites More sharing options...
Rob Posted March 14, 2010 Share Posted March 14, 2010 I have Mack CH-600 with a mack 300 motor. We have difficulty starting it when it is warm and cold. It's wierd you spray either to it and it fires right up. Fuel filters are tight, no leaks on any fuel lines, it has a new drainback valve. So I got curious and tap on the actuator on the fuel pump and it started. Now was that just luck or could that actuator be bad. If it is bad how do you test it.I'm assuming you have an electric solenoid mounted to the injection pump governor: This solenoid would pull the fuel rack that is internal to the pump to the no fuel position to shut down the engine by starving it for fuel. Usually when these work correctly power supplied by the ignition switch releases this hold on the fuel rack allowing the governor to control curb idle. If this solenoid is sticking in the off position you can have the problems you experience. When you hit the engine with a shot of ether you have supplied fuel to it and the engine vibration probably causes the solenoid plunger to release. This is just a guess and again an assumption. In this case you would be best replacing the shutdown solenoid and not screwing around. Citing the engine does start and not shut back down until you want it to lends creedance to the ignition switch is supplying power to this solenoid. The same scenario could play out with a manual cable shutdown also if it is out of adjustment.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
cgallamore Posted March 14, 2010 Share Posted March 14, 2010 i was driving a 1996 dm688 had the same problem they put a cable shut off on it. they had about 20 trucks like that, it was a common problem, they kept cables in stock.hope this helps.the first time it happened to me me they told me to tap on the pump.. Quote http://www.bigmacktrucks.com/uploads/1272400769/gallery_4852_794_314995.jpg Link to comment Share on other sites More sharing options...
Timothy B Demarco Posted March 14, 2010 Author Share Posted March 14, 2010 I'm assuming you have an electric solenoid mounted to the injection pump governor: This solenoid would pull the fuel rack that is internal to the pump to the no fuel position to shut down the engine by starving it for fuel. Usually when these work correctly power supplied by the ignition switch releases this hold on the fuel rack allowing the governor to control curb idle. If this solenoid is sticking in the off position you can have the problems you experience. When you hit the engine with a shot of ether you have supplied fuel to it and the engine vibration probably causes the solenoid plunger to release. This is just a guess and again an assumption. In this case you would be best replacing the shutdown solenoid and not screwing around. Citing the engine does start and not shut back down until you want it to lends creedance to the ignition switch is supplying power to this solenoid. The same scenario could play out with a manual cable shutdown also if it is out of adjustment.RobWhat about a ground relay on the firewall next to the starter soleniod, could that be a problem to, because it smokes sometimes and I'm replacing that. Quote Link to comment Share on other sites More sharing options...
Rob Posted March 14, 2010 Share Posted March 14, 2010 What about a ground relay on the firewall next to the starter soleniod, could that be a problem to, because it smokes sometimes and I'm replacing that.Generally speaking an electrical component that smokes is usually no good itself, or a component it supplies current for has gone bad. In you application I do not know for sure. Mack did in many applications use a large, round metal cased contactor referred to as a power relay. These usually audibly clunked upon turning the ignition key to the run position. Electrical power was then routed throughout the truck via this contactor.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
HK Trucking Posted March 15, 2010 Share Posted March 15, 2010 That relay on the firewall would be the starter relay. It receives it's "signal" when the key switch is twisted all the way to the start position,at that point the starter relay relays current to the large solenoid on the starter, thereby activating the starter.The accessory relay (the one that "clunks" when you turn the key to the "run" position) is under the dash.. Quote "If You Can't Shift It Smoothly, You Shouldn't Be Driving It" Link to comment Share on other sites More sharing options...
bobo Posted March 15, 2010 Share Posted March 15, 2010 what about the nylon fuel pump gear? seen it where it will run due to torque on gear but would not start. just a guess!? Quote Link to comment Share on other sites More sharing options...
fjh Posted March 16, 2010 Share Posted March 16, 2010 what about the nylon fuel pump gear? seen it where it will run due to torque on gear but would not start. just a guess!?This here is too vague. Is this a VMac engine?What is fairly common on a vmac pump is the rack actuator fails!In this case the pump has to come off to be repaired!HK brings up a good point is the dash lighting up when the key is turned on?The acc relay will cause the heater and dash not to work! And will not let theengine light up! Quote Link to comment Share on other sites More sharing options...
bobo Posted March 16, 2010 Share Posted March 16, 2010 This here is too vague. Is this a VMac engine?What is fairly common on a vmac pump is the rack actuator fails!In this case the pump has to come off to be repaired!HK brings up a good point is the dash lighting up when the key is turned on?The acc relay will cause the heater and dash not to work! And will not let theengine light up!Oh sure center me out! LOL I agree what motor is it? Quote Link to comment Share on other sites More sharing options...
Timothy B Demarco Posted March 16, 2010 Author Share Posted March 16, 2010 Oh sure center me out! LOL I agree what motor is it? I found the problem. Up on the firewall you have your starter relay and beside that is square box that has two prongs and that is a ignition ground relay and that burned up. Quote Link to comment Share on other sites More sharing options...
mackvi Posted May 20, 2011 Share Posted May 20, 2011 I found the problem. Up on the firewall you have your starter relay and beside that is square box that has two prongs and that is a ignition ground relay and that burned up.hello everybody! i have the same problem with my CH 1994, can you tell me please, where the starter relay is?in the cab or under the hood?may be my truck have the same ignition relay burned up, if you can send me a picture pleasethanks for your help Quote Link to comment Share on other sites More sharing options...
mackvi Posted May 21, 2011 Share Posted May 21, 2011 hello Quote Link to comment Share on other sites More sharing options...
mackvi Posted May 24, 2011 Share Posted May 24, 2011 Generally speaking an electrical component that smokes is usually no good itself, or a component it supplies current for has gone bad. In you application I do not know for sure. Mack did in many applications use a large, round metal cased contactor referred to as a power relay. These usually audibly clunked upon turning the ignition key to the run position. Electrical power was then routed throughout the truck via this contactor.Robhello everybody! i have the same problem with my CH 1994, can you tell me please, where the starter relay is?in the cab or under the hood?may be my truck have the same ignition relay burned up, if you can send me a picture pleasethanks for your help Quote Link to comment Share on other sites More sharing options...
mackvi Posted May 24, 2011 Share Posted May 24, 2011 I'm assuming you have an electric solenoid mounted to the injection pump governor: This solenoid would pull the fuel rack that is internal to the pump to the no fuel position to shut down the engine by starving it for fuel. Usually when these work correctly power supplied by the ignition switch releases this hold on the fuel rack allowing the governor to control curb idle. If this solenoid is sticking in the off position you can have the problems you experience. When you hit the engine with a shot of ether you have supplied fuel to it and the engine vibration probably causes the solenoid plunger to release. This is just a guess and again an assumption. In this case you would be best replacing the shutdown solenoid and not screwing around. Citing the engine does start and not shut back down until you want it to lends creedance to the ignition switch is supplying power to this solenoid. The same scenario could play out with a manual cable shutdown also if it is out of adjustment.Robhellowhat tap on the actuator on the fuel pump mean? can you explain?thank you very much Quote Link to comment Share on other sites More sharing options...
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