PDA

View Full Version : Misfire detection post 98


DA BIG ONE
02-13-2008, 15:53
I hope someone can describe the misfire detection feature in the 6.5td 98 and newer.
More Power
02-14-2008, 10:32
Monitoring misfire(s) and their related trouble codes were added to the 1996+ OBD II systems for emissions reasons. The PCM monitors the contribution of each cylinder to crankshaft rotation - via the Crankshaft Position Sensor (CKP). The DS4 & PCM have the ability to adjust fueling for each cylinder, to produce a smoother running engine. The trouble codes are also useful to identify a weak cylinder - due to a bad injector, leaking injector fuel line or out of spec cylinder compression.

Jim
DA BIG ONE
02-14-2008, 11:03
My scanner detects a misfire but no codes, no rough running has lots of power what should I be looking for?
More Power
02-14-2008, 14:00
My scanner detects a misfire but no codes, no rough running has lots of power what should I be looking for?

You may be seeing a code stored in history, but not a current DTC. Try resetting the codes, then see if any repeat.

Jim
DA BIG ONE
02-15-2008, 06:32
Runs great, and I'm stumped!

I cleared the ecm and drove awhile and the misfire is again detected only code I have is recurring code DTC 1656 boost solenoid control circuit however this circuit is functioning.

I'm going to change out Heath Stage 3 ecm today and go back to my L65 HD ecm then drop boost and see what happens from there.

I'm curious if the timing gears built in 2deg advance have anything to do with this issue?
DmaxMaverick
02-15-2008, 09:48
The advance won't have any effect on the boost solenoid.

Is your SES on? If not, it could be a glitch code, or an intermittent code the PCM isn't seeing as serious. Many faults require repetition under certain conditions to trigger the SES. Else, it may store a code in history and continue w/o complaining. Your BH program may be the cause of the code, but there may not be a real problem present. If your OEM computer doesn't repeat the problem, then it's probably no problem.
gmctd
02-15-2008, 09:53
Always same cylinder? Might give Bill a call

To enhance Jim's input, PCM uses that function to maintain smooth idle under varying load conditions, such as a\c cycling, shifting into\out of drive range, etc.

To test it, kill each injector, noting and comparing rpm drop of all cylinders - weak cylinder will drop least rpm