BigWalt Posted June 17, 2014 Share Posted June 17, 2014 1994 F-Super Duty..7.3 IDI non turbo.Customer got the dough, said go ahead replaced the motor. Original motor runs but knocks badly.Complete motor was installed today. Starts, runs and has decent power but I notice rough idle, does not feel like misfiring, I cracked loose injector lines one by one, all of them made differences. This ruled out bad injectors. IThen, check the flexplate for missing weight, I did not find any weight on flexplate, is that normal?From my experiences I know 7.3 Powerstroke had weight spot welded to flexplate but not on this non turbo 7.3 IDI. If no weight on flexplate is normal then what can cause rough idle? I only can do basic checks and past knowledge ( If I can remember ), we have no diagnosis equipment is available for this old dinosaur. Quote Link to comment Share on other sites More sharing options...
Chase Posted June 18, 2014 Share Posted June 18, 2014 Fresh pump with engine? Quote Link to comment Share on other sites More sharing options...
BigWalt Posted June 18, 2014 Author Share Posted June 18, 2014 yes, new pump, came with motor. Quote Link to comment Share on other sites More sharing options...
Chase Posted June 18, 2014 Share Posted June 18, 2014 Air intrusion somewhere maybe? how's it start? Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted June 18, 2014 Share Posted June 18, 2014 Blip the throttle and take it quickly to top gov speed and let it snap back to idle. As the engines winds DOWN pay attention to how it feels- if it's a miss it will be smooth here, if it's a balance problem it will shake on its way down as well as on its way up. Do this several times and you'll get the feel for what I'm talking about, I can ID an imbalance very easily this way after many years of doing it. You'll think I'm nuts, but I've balanced many engines by feel using a stack of washers on the PP. This all came from imbalanced Chevy SBCs in the 50's and 60's where a TSB had you put a clip-on weight on the flexplate and move it around until the shake went away. Many times I put a clutch in (or whatever) and balanced it in the shop sitting under the truck behind the FW with the boltholes numbered, moving a stack of washers around, with one of my guys in the cab starting and revving the engine for a couple of seconds, then shutting it off and moving the washers. It sounds hillbilly as hell but I can get rid of 95% of an imbalance within 10 minutes using this method. Good Luck! Edit: Complete motor was installed today. Starts, runs and has decent power but I notice rough idle, does not feel like misfiring, I cracked loose injector lines one by one, all of them made differences. This ruled out bad injectors. IIRC, cracking the line loose on a cyl with no compression will still cause the RPM to drop because it retarded the timing because you're dropping housing pressure (or something silly like that) by cracking the line loose. If it "revs down" smooth indicating a miss, I'd use a temp gun or water bottle on the ex manifolds to find a weak cylinder. 1 Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted June 18, 2014 Share Posted June 18, 2014 That was quite an insightful piece of advice! Quote Link to comment Share on other sites More sharing options...
mrbudge Posted June 19, 2014 Share Posted June 19, 2014 You have probably checked this, but is it possibly way overfull of oil? Quote Link to comment Share on other sites More sharing options...
BigWalt Posted June 19, 2014 Author Share Posted June 19, 2014 That is first thing I check.No, oil level is good.It is confirm rough idle, Reset pump timing made a differences....it is certainly pain in the butt to do the pump timing but it pays off. Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted June 19, 2014 Share Posted June 19, 2014 If the timing is too high it will be loud and rappy, if it's too retarded it will be a dog with no power, IIRC advance is turning the top of the pump towards the driver's side. I remember a special bent 9/16" wrench.......... Good Luck! Quote Link to comment Share on other sites More sharing options...
Chase Posted June 20, 2014 Share Posted June 20, 2014 If the timing is too high it will be loud and rappy, if it's too retarded it will be a dog with no power, IIRC advance is turning the top of the pump towards the driver's side. I remember a special bent 9/16" wrench.......... Good Luck! Passenger side advances. I own 2 IDI's and timing tools. If things were still that simple.... Quote Link to comment Share on other sites More sharing options...
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