Brandt Posted May 20, 2015 Share Posted May 20, 2015 In the morning my truck runs rough and is now starting to backfire. It may have always had a slight backfire, but I notice it more now running straight pipe. This happens between 1200 and 1650rpm when the temp gauge is below 155*. It will spitter and have reduced power. It also blows a lot of smoke (bluish white). From 156* to 180* there is an improvement, then at 180* all is good. If I keep the rpm's up above 1650 the truck runs OK, except in top gear then she falls on her face. Is this typical for a cold engine or is something amiss??'91 RD 690EM7 300 HP1070B 12 spd trans (.78 OD) Quote Link to comment https://www.bigmacktrucks.com/topic/40093-rough-when-cold/ Share on other sites More sharing options...
gearhead204 Posted May 20, 2015 Share Posted May 20, 2015 take a temp gun and shoot the temps at the exhaust ports, it sounds like a bad injector this should help you find the bad one. my guess is that it blew off a tip off of one injector and its spraying nonatomized fuel causing the off color smoke and once hot enough it burns and cleans up 1 Quote Link to comment https://www.bigmacktrucks.com/topic/40093-rough-when-cold/#findComment-290541 Share on other sites More sharing options...
Brandt Posted May 21, 2015 Author Share Posted May 21, 2015 Looks like #1 read 97*, and #3 read 106*. The rest were at 197-210*, while warming up.The old Detroits could get more HP with bigger injectors, can the same be true for 4 stroke Macks?? I'd like to get more HP from this engine and will eventually be getting a larger turbo also. What injector # should I look for??Is this something an average wrech turner (me) can do, or do I have to get everything calibrated to each other? Quote Link to comment https://www.bigmacktrucks.com/topic/40093-rough-when-cold/#findComment-290700 Share on other sites More sharing options...
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