BarryMckociner Posted Tuesday at 02:27 PM Share Posted Tuesday at 02:27 PM I’ve got a 2003 RB688S with electronic (EUP’s) E7 400 engine in my dumptruck that is low on power and has a miss around 1,200-1,400 rpm. Miss is slight first thing in the morning but gets worse once warmed up. Truck idles fine and runs down the road okay once you get above 1,400rpm but as soon as you hit a hill loaded it slows down quick. Boost lags as well until I get to 1,600rpm. I’m leaning towards fuel return restrictor or lift pump. What are the specs for fuel pressure? Any help is appreciated Quote Link to comment https://www.bigmacktrucks.com/topic/75702-2003-mack-e7-low-power/ Share on other sites More sharing options...
Joey Mack Posted Tuesday at 06:19 PM Share Posted Tuesday at 06:19 PM 60-80 psi. Definitely check that. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75702-2003-mack-e7-low-power/#findComment-578013 Share on other sites More sharing options...
fjh Posted Tuesday at 07:00 PM Share Posted Tuesday at 07:00 PM Yup check that ! Any other symptoms? Smoke ? Color of smoke at what rpm ect all help with diagnosis! Quote Link to comment https://www.bigmacktrucks.com/topic/75702-2003-mack-e7-low-power/#findComment-578015 Share on other sites More sharing options...
BarryMckociner Posted Saturday at 08:06 PM Author Share Posted Saturday at 08:06 PM On 6/24/2025 at 2:00 PM, fjh said: Yup check that ! Any other symptoms? Smoke ? Color of smoke at what rpm ect all help with diagnosis! No noticeable smoke at any rpm. Starts easy at any temperature. Quote Link to comment https://www.bigmacktrucks.com/topic/75702-2003-mack-e7-low-power/#findComment-578197 Share on other sites More sharing options...
JoeH Posted Saturday at 11:19 PM Share Posted Saturday at 11:19 PM Any fault codes? Does your lightning bolt work? Quote Link to comment https://www.bigmacktrucks.com/topic/75702-2003-mack-e7-low-power/#findComment-578205 Share on other sites More sharing options...
BarryMckociner Posted yesterday at 01:23 AM Author Share Posted yesterday at 01:23 AM 2 hours ago, JoeH said: Any fault codes? Does your lightning bolt work? No fault codes or symbols on dash. All lights function. Quote Link to comment https://www.bigmacktrucks.com/topic/75702-2003-mack-e7-low-power/#findComment-578210 Share on other sites More sharing options...
fjh Posted 15 hours ago Share Posted 15 hours ago Well in My mind you either got to check the fuel pressure Or get out the Parts Canon your choice! You need to get facts ! Or just start throwing things at it and hope! If you are also dealing with a miss or partial miss there is a possibility of a broken EUP Spring! Just sayin! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75702-2003-mack-e7-low-power/#findComment-578216 Share on other sites More sharing options...
JoeH Posted 2 hours ago Share Posted 2 hours ago Pull heat shields covering the EUPs. Warm up engine, loosen one wire screw on each EUP, one a time. (Don't remove screw, just loosen. They're not designed to come out). Remove wire, you'll get a spark, no big deal. Listen for an EUP that doesn't make a change in engine sound. This is how you do an injector cutout test on these engines. Not a bad idea to pull all the EUPs and inspect. Pull the EUP cam followers as well. My 2003 engine had 3 bad EUPs, 2 had broken springs, one failed electrical component. 2 of my cam followers were bad, almost lost the camshaft but caught it just before major damage was done. Quote Link to comment https://www.bigmacktrucks.com/topic/75702-2003-mack-e7-low-power/#findComment-578246 Share on other sites More sharing options...
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