The Trash Man Posted November 19, 2011 Share Posted November 19, 2011 Ok I've got a '87 Mack MR that has a EM6-237 engine in it and it's a good sound truck with only a little over 90,000 original miles on it but it has a idle that is very annoying. Now the funny thing is the truck will idle real smooth when it's in neutral but as soon as you put it in drive or reverse it starts idling so rough that it shakes the whole cab. The truck will drive fine when your going down the road and everything it's just when it idles in gear. I recently changed the fuel injectors thinking that might take care of the problem and it did help just a little but the truck still idles too rough for me. I have also turned up the idle screw on the injection pump but that didn't really help either. Right now the truck idles somewhere around 600 rpm but I've noticed the tack needle jumps back and forth about a hundred rpm or so when it's idling. My guess is the problem is in the injection pump? Not sure what else it could be. Quote Link to comment https://www.bigmacktrucks.com/topic/21697-87-mr-with-rough-idle/ Share on other sites More sharing options...
rhasler Posted November 19, 2011 Share Posted November 19, 2011 Does it have a manual or an automatic transmission? Quote "Mebbe I'm too ugly and stupid to give up!" Link to comment https://www.bigmacktrucks.com/topic/21697-87-mr-with-rough-idle/#findComment-91332 Share on other sites More sharing options...
The Trash Man Posted November 19, 2011 Author Share Posted November 19, 2011 It's an automatic, an Allison 654. Quote Link to comment https://www.bigmacktrucks.com/topic/21697-87-mr-with-rough-idle/#findComment-91336 Share on other sites More sharing options...
rhasler Posted November 19, 2011 Share Posted November 19, 2011 I think you should be idling around 700 rpm. Quote "Mebbe I'm too ugly and stupid to give up!" Link to comment https://www.bigmacktrucks.com/topic/21697-87-mr-with-rough-idle/#findComment-91337 Share on other sites More sharing options...
The Trash Man Posted November 19, 2011 Author Share Posted November 19, 2011 Yeah I know I've had international and volvo trucks and they always idled at 700, this is the first mack I've had though so I'm kind of new to them. I did notice the head on the idle screw that the throttle rests against is slightly wore down, maybe I need to replace it with a new one and see what happens. I had a friend of mine whose fairly smart on diesel trucks drive it awhile back and he described the problem as a "roll" in the engine. He said something about there may be a buffer screw on the injection pump that needs adjusted but he didn't really know either. It's a trash truck and alot of times I'll be out on my route and people will stare at it like their thinking "that truck surely shouldn't sound like that." Lol Quote Link to comment https://www.bigmacktrucks.com/topic/21697-87-mr-with-rough-idle/#findComment-91340 Share on other sites More sharing options...
macattack Posted December 10, 2011 Share Posted December 10, 2011 did you get this fixed? Quote Link to comment https://www.bigmacktrucks.com/topic/21697-87-mr-with-rough-idle/#findComment-93476 Share on other sites More sharing options...
The Trash Man Posted December 21, 2011 Author Share Posted December 21, 2011 No not yet, thinking about taking it to a mechanic here before long and seeing what they think. I'm thinking the injection pump probably needs some adjusting done on it or maybe even rebuilt. Sure would like to get the problem fixed, it would make the truck alot more enjoyable to drive. I don't mind my old hot rod '64 chevy having a rough idle but I don't like it on a truck I have to sit in 8 hrs a day. Lol Quote Link to comment https://www.bigmacktrucks.com/topic/21697-87-mr-with-rough-idle/#findComment-94862 Share on other sites More sharing options...
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