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1993 EM7 300 engine . . . . . computerized or mechanical?


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I have a question about a truck I drive at work, the beast at question is a 1993 Mack DM 690 SX, 58K rears, double frame, MaxiTorq Extended Range 7 speed, 317K miles, tag on motor says EM7 300. What I have read online is the EM7 is a computerized motor, but this one appears to be a mechanical beast having fuel lines going between each injector to fuel pump / governor. Accelerator pedal uses a mechanical bell crank & rod setup that rivals the complexity of a Rube Goldberg Invention to get power from governor. So my question is was the EM7 a mechanical motor in 1993? Or is it computerized and I just do not realize it.

Also, anyone have good experiences with these motors?? This one drives like a real dog, no power whether empty or loaded, shows no unusual signs of smoke, pyrometer never reads above 750 deg F, coolant temp never above 180 deg F, just CANNOT climb a hill on the highway to save it's life. All filters / oil serviced regularly in the last 7 years that we have had the truck.

Can I expect this kind of performance from this engine / tran combo or am I in need of some major repairs in the road ahead????

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It is a mechanical engine. The first computerized engines that we have are 99 and up e7's .. I don't know why it doesn't run good we have two 95 mechanical rd's with e7's in them and they will pull just as well as the computerized dogs, if not better. I prefer a mechanical engine.. Either way these are great engine's ... The trucks we run are mixers and dumps that gross anywhere from 50,000 to 63,000 .

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Great point david... now that i remember when i drove the 98 rd that was a mechanical engine, we had two times that i remember the truck slowly getting less and less power... each time it was the linkage on the throttle where it pinches the shaft on the pump, had gotten loose... If that makes sense ... the truck would only run around 54 mph and wouldn't get out of its own way before we found it the first time, and once fixed/tightened it would pull much harder and run right around 68-70 mph loaded ... Its worth a shot and an easy fix :twothumbsup:

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I have changed some of the pedal linkage parts but I've never thought to check the "clamp" at the end of the pump shaft, I'll take a look at that. As for checking pump pressure we don't have any fuel injection tools, that's something we'd probably send to the shop for.

Thanks for the advice I'll let you know what I find.

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Is the linkage moving the lever all the way open?

Took the words right out of my mouth , if it was loose it probably isn,t in the right spot to open the throttle all the way .. Have someone hold the pedal down, and then see if you can open it any further on the pump, if it moves a little farther adjust it again , it's night and day power difference

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Well there is half an inch of space between the floor boards and the accelerator pedal when pushed down all the way against the "spring lever" on the governor shaft with the engine not running so I think the linkage is in the right spot but maybe it needs to be adjusted more. When I tightened it down was while the engine was not running and the governor lever all the way back against the engine brake switch. Should it tightened down and adjusted in a different manner?

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Took a closer look at everything this evening and it seems the pedal opens the throttle lever all the way to an adjustable throttle stop (set screw). Does anyone have advice on the proper way to adjust that throttle stop? I'm wondering if somehow along the line somebody tried to throttle back the engine to keep the drivers from getting into trouble with speed since the truck belonged to a large trash fleet originally. The governor says BOSCH on the casting and there is a MACK reman tag on the fuel rack if that makes any difference.

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I have a question about a truck I drive at work, the beast at question is a 1993 Mack DM 690 SX, 58K rears, double frame, MaxiTorq Extended Range 7 speed, 317K miles, tag on motor says EM7 300. What I have read online is the EM7 is a computerized motor, but this one appears to be a mechanical beast having fuel lines going between each injector to fuel pump / governor. Accelerator pedal uses a mechanical bell crank & rod setup that rivals the complexity of a Rube Goldberg Invention to get power from governor. So my question is was the EM7 a mechanical motor in 1993? Or is it computerized and I just do not realize it.

Also, anyone have good experiences with these motors?? This one drives like a real dog, no power whether empty or loaded, shows no unusual signs of smoke, pyrometer never reads above 750 deg F, coolant temp never above 180 deg F, just CANNOT climb a hill on the highway to save it's life. All filters / oil serviced regularly in the last 7 years that we have had the truck.

Can I expect this kind of performance from this engine / tran combo or am I in need of some major repairs in the road ahead????

This engine runs 1050rpm's to 1750rpm's (It is gutless) the 7spd goes from 1:1 to .60 overdrive you most likly have 5.02 rear,,

but will not help when you shift to high gear

look at it this way you now know what we had to deal with years ago with a 237 and 5spd on a long hill

gallery_133_137_10125.jpg

Thanks for hearing me out.

You can have the soap box now---------JIM

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  • 3 weeks later...

OK So I did some research in this forum about the puff limit valve and took a closer look on the engine and found a 1/4" air line between the intake manifold and what must be the reversing relay was rubbing against the top of the firewall and had a large hole rubbed through it. When I started the engine I didn't feel any pressure escaping but said "what the heck, lets change it anyway" and WOW did it bring that puppy to life! The dog growls now at low RPM and I can see smoke out the passenger mirror and the pyrometer will climb an extra 50 F on a hill (close to the 800 - 825 F mark) and the water temp moves towards the 190 F mark also now. I can now understand why they call it a MAXIDYNE :) Still loses a few mph on a hill at 65 mph but with the torque curve I've seen i can expect that much, just happy it will actually PULL when leaving the stop lights! For the first time since I've started driving this truck in 2007 it actually has some BARK :) Thanks for all the great posts in this forum and hope this helps someone else!

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