TDC Posted November 9, 2012 Share Posted November 9, 2012 Hi all. I have a 1998 Mack CL 700 with the 427 motor. Issue arose as it started to get a little colder during the A.M. startup. Truck ran fine all day. Parked it for the night. Started it in the morning and the fuel pedal wouldn't respond, tach wouldn't read, RPM's jumped right up to roughly 900 RPM's and the idle control wouldn't work either. Changed out the pedal and it was cured for 2 days then same thing all over again. Truck was acting up in the morning, come back at noon time when it was 60 degrees out and she'd run all day no issues. Now yesterday it was about 32 degrees out all day. Finally got her to come out of high idle and fuel pedal responding. Going out with a load fuel pedal/tach issue came back roughly a dozen times in a 35 mile round trip. Not pretty! Ground to motor looks good. All electrical connections looked good. No water in harnesses or coolant coming thru harness from temp. sensor. Nothing looked bad on connections to CPU on passenger side under dash. Don't know where to look next. Anyone on here have any ideas or similar issues?Thanks all! Quote Link to comment https://www.bigmacktrucks.com/topic/28232-fuel-pedal-and-tach-not-operating-any-ideas/ Share on other sites More sharing options...
staxx Posted November 9, 2012 Share Posted November 9, 2012 Need to check 1939 communication wires they are on the firewall near brake valve , green and yellow in color with a triangle connection ...check the connection and follow wires in both directions , these wires are the connection between the engine ecu and the vecu. Quote Link to comment https://www.bigmacktrucks.com/topic/28232-fuel-pedal-and-tach-not-operating-any-ideas/#findComment-145147 Share on other sites More sharing options...
TDC Posted November 10, 2012 Author Share Posted November 10, 2012 All the factory tags are on the wires thank god. None of the pins on that triangle connector were corrodeded. didn't have time to trace them back thru the harnesses. Puttin a full day into curing this tomorrow. Will update then. Also bought a new tach sensor today too just to eliminate that possibility.FYI Never codes either. Wish it would! Elecrical sucks!!!!!Thanks Staxx Quote Link to comment https://www.bigmacktrucks.com/topic/28232-fuel-pedal-and-tach-not-operating-any-ideas/#findComment-145280 Share on other sites More sharing options...
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