+- Rawze.com: Rawze's ISX Technical Discussion and more (http://rawze.com/forums)
+-- Forum: Big Truck Technical Discussion... (/forumdisplay.php?fid=1)
+--- Forum: ISX Related Help (/forumdisplay.php?fid=68)
+--- Thread: Friend with a CM870 having issues (/showthread.php?tid=7282)
Pages: 1 2
Friend with a CM870 having issues - 8042 - 04-21-2021
I haven’t posted in a long time, but have a friend that is having issues with his intact CM870.
He has had problems joining so asked me to post this. I have to admit it is over my head.
Gents,
I have a 2006 Volvo VNL780 with a Cummins ISX15 500 cm870 (egr original)with an Active fault code of 2554 (Insite). In other words, "erratic data" (inactive) and "electrical fault" (active) from the exhaust gas pressure sensor. Upon cold start, engine rpm surges up and down about 200rpm in a rhythmic cycle.
Went to International, got a new exhaust gas pressure sensor, installed it, great. It worked ... for a week. Surging starts once again, and code 2554 comes up again. Measured resistance on the EG pressure sensor and had all reading of infinite ohms across pins 1 to 2, 2 to 3, and 1 to 3 (all open). Ok, figured new sensor was faulty.
Went back to International and got a replacement sensor. Measured resistance of 4.5kOhms on pins 1-2, and 68kOhms on pins 2-3, while pins 1-3, open. Also, checked continuity between ECM harness and exhaust gas pressure sensor: ECM pin 37->1, 47->2, 20->3, all zero ohms. Installed sensor, and all seemed well for another week. Then, surging started once again.
Again, checked resistance of sensor as well as harness continuity, with all values being the same as stated above.
Hooked up to Insite, and noticed that exhaust gas pressure reading was at 48inHg while barometer (ambient) pressure was at 30.2inHg, with engine OFF, key ON.
To my understanding ,the exhaust gas pressure sensor is an absolute reading and should read close to barometric pressure sensor values. However these readings are very different.
Questions:
1) Is it possible that second exhaust gas pressure sensor is a dud? Or are International sensors different in any way? International claims it is the correct sensor (Cummins Dealer)
2) What should the resistance be of the sensor (is this relevant /irrelevant)?
3) Why can't I win the lottery?
.... hmmm
RE: Friend with a CM870 having issues - 8042 - 04-21-2021
Sorry if it’s in the wrong section please move if it’s needed
RE: Friend with a CM870 having issues - Rawze - 04-21-2021
* could be that the ecm is sending +12volts to the sensor sometimes (instead of its normal +5volts) due to the voltage regulator circuit in the ecm failing and causing it to damage the sensor?
* that or perhaps a short in the circuit to +12volts in the harness somewhere?
* Or someone has installed a big illegal CB amplifier or some other device that is causing electrical surges in the ecm and harness?
* maybe a bad run of sensors from the stealers$it?
just some wild guesses.
maybe check to see if the power supply voltage to the sensor is stable at +5 volts or if it is climbing up when the ecm gets hot?
RE: Friend with a CM870 having issues - Nilao - 04-22-2021
Check the muffler, if it's plugged up it will always have a higher than ambient reading, as well as the sensor piping could be plugging up with soot.
RE: Friend with a CM870 having issues - Rss00 - 04-22-2021
Hi all, just joined the forum. I'm the "friend with the cm870 issues".
Forgot to mention one important detail. This problem only occurs in cold weather, with a cold start. Especially once PTO is pushed to engage high idle.
+5v supply coming from the ecm harness is steady and checked
while cold and hot.
Also, cleaned the pressure tube coming off of the exhaust manifold to the sensor housing, as well as checked EGP sensor for variance in pressure while connected to the harness and unscrewed from pressure port. Same high readings on Insite.
No additional +12v accessories on the truck, all original.
As for the plugged exhaust? Got a dual exhaust stack out the back of the cab. New exhaust piping done last year.
I ordered a new Cummins exhaust gas pressure sensor on e-bay and it should be waiting for me at home.
RE: Friend with a CM870 having issues - tree98 - 04-22-2021
Have you ever replaced the small metal tube that feeds that sensor from the exhaust manifold? Could be plugged or almost plugged, especially if it's original.
Don't know if I would trust an ebay sensor
RE: Friend with a CM870 having issues - hookliftpete - 04-22-2021
If you try, it could be very hard to loosen the fitting on the manifold, will needs lots of heat and patience.
RE: Friend with a CM870 having issues - Rawze - 04-22-2021
(04-22-2021 )hookliftpete Wrote: If you try, it could be very hard to loosen the fitting on the manifold, will needs lots of heat and patience.
when they get real bad, cutting the pipe off at the fitting and using a 6-point socket on it, working it a little at a time after getting it glowing dull red with a torch always works. ... then just put a whole new cross-pipe on there from the stealers#it when it needs to go back together.
RE: Friend with a CM870 having issues - Chamberpains - 04-23-2021
^^^^^^^^I dont even play games anymore. This how I do mine^^^^^^
A socket give to better contact. It's better to just jump to this than rounding it off and having to work from there.