Check Engine Light at start up

[sevenmacs]

Left for trip to West Yellowstone, 100 miles into trip stopped and upon starting check engine light came on immediately. Turned mp-8 off and started and it was fine. This has occurred 3 times on trip out of multiple starts, lots stop & go. Planning on leaving mp-8 off at all starts to see if it occurs without it. Mp-8 does trigger light when climbing high passes 10,000 +, when turned up all the way, this has occurred 3 or 4 times. Not sure what altitude has to do with it, startup check engine occurred at 6000 + feet. Just changed oil (mobil ) filters, oil/fuel (wix), before leaving. Oil pressure hot at idle is around 25-25, at speed around 50. Engine runs great no power loss, good fuel mileage (8), has 48000 miles on c-7. We'll see what happens on return trip, 600 miles.

Any ideas ?

[1ciderdog]

I had to turn my MP8 down to about half because the check engine light would come on at the top of a grade but not near the 10,000 feet elevation you mention. It seems to have happened when I back off the throttle as I crossed the summit of the hill.

[sevenmacs]

Yes that's where I keep it when climbing high passes or it cause check engine light just before hitting top. I'm hoping that it is the Mp-8 causing it occasionally at startup, we'll see on trip home. Although I called manufacturer of mp-8 and they said it shouldn't cause check engine when set at full climbing unfortunately it does, unknown why.

[lacdubonnet]

Originally Posted by sevenmacs

Left for trip to West Yellowstone, 100 miles into trip stopped and upon starting check engine light came on immediately. Turned mp-8 off and started and it was fine. This has occurred 3 times on trip out of multiple starts, lots stop & go. Planning on leaving mp-8 off at all starts to see if it occurs without it. Mp-8 does trigger light when climbing high passes 10,000 +, when turned up all the way, this has occurred 3 or 4 times. Not sure what altitude has to do with it, startup check engine occurred at 6000 + feet. Just changed oil (mobil ) filters, oil/fuel (wix), before leaving. Oil pressure hot at idle is around 25-25, at speed around 50. Engine runs great no power loss, good fuel mileage (8), has 48000 miles on c-7. We'll see what happens on return trip, 600 miles.

Any ideas ?

yes i do had this problem along time fixed it today.we have a 2005 fleetwood with a c7 cat.problem was the boost pressure was to high in the motor and was triggering the sensor valve to turn on engine lite,now in simple terms you have to put in on a laptop with proper program and they can measure the psi while you are driving and it should be 25 psi to 26 psi
mine went up to 30psi.replaced sensor valve from cat part 2309944 takes 10 minutes to change on top into manifold price$325.00 good luck

rolandh@mts.net

[lacdubonnet]

Originally Posted by 1ciderdog

I had to turn my MP8 down to about half because the check engine light would come on at the top of a grade but not near the 10,000 feet elevation you mention. It seems to have happened when I back off the throttle as I crossed the summit of the hill.

guys if you have a c7 cat get a tech to check your boost pressure running through your turbro should not exceed 25 psi

fixed mine today after a year of wrong diagnosis

cat part valve2309944 $350.00

good luck

[sevenmacs]

Thanks, will look into it, going to install EGT & Boost gauge, doesn't do it when mp-8 is off.