amailloux Posted May 20, 2014 Share Posted May 20, 2014 I have a 99 7.3. ran koeo and koer, no codes. Cylinder contribution test pass. had a p0603 stored and exhaust backpressure valve unplugged. Cleared p0603 and it has not returned. when cold or hot, I can hold it at 1700 rpm and it has a buck. Feels like key is shut off and then back on real quick. Scan data rpm is the only pid that moves, but I can't tell if it is in response to the issue, or creating the issue. gray cam senso in it. I scoped the cam sensor when the buck happened and it looked ok, but it is so fast it was hard to tell. When I mat it, it will buck all the way up to the shift point. Never had a buck under 1500 rpm. chacked codes again and ran buzz test ok. I am leaning towards an idm, but don't have another one to test with. Any other things I should check. has good power other than the buck. Does this sound like a failing idm. I have only worked on a dozen or so 7.3s and am looking for any information I can get. Thanks. Quote Link to comment Share on other sites More sharing options...
Aaron Posted May 21, 2014 Share Posted May 21, 2014 Does it do it with the EBP sensor unplugged? Quote Link to comment Share on other sites More sharing options...
amailloux Posted May 21, 2014 Author Share Posted May 21, 2014 Unplugged ebp, no change. I then pulled out the idm. tested voltage with my lab scope and had no dropout when the condition occurred. then I threw my amp clamp on the ground wire and had all 8 injectors. I had a large section of 6 or so missed injections when the buck occurs. I then backprobed the cid circuit and it had no dropouts when the buck happens, and then I backprobed the fuel command and there were no lost events, just 1 higher demand event I am guessing is right after the buck to get the engine back up. The only odd thing I noticed was the tach does drop sharply when it happens. I believe the tach comes from the pcm as indicated by the cam sensor. Could just be the lack of processing speed from my eyes to my brain also. Quote Link to comment Share on other sites More sharing options...
Aaron Posted May 21, 2014 Share Posted May 21, 2014 Swap a known good cam sensor in. I had an e van kicking my ass last week doing something similar. Quote Link to comment Share on other sites More sharing options...
ktmlew Posted May 26, 2014 Share Posted May 26, 2014 Check charging voltage when misfire happens. There is a relay behind the dash that will drop out if voltage drops and tach will drop. I can't remember what relay it is though. Quote Link to comment Share on other sites More sharing options...
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