mat in tn Posted August 11 Share Posted August 11 1. I replaced the pcv valve since it’s only $3. 2. Never could find a video that illustrated what pinging sounds like so I don’t know. 3. When I say hot, I don’t mean over heated but just fully warmed, parked on a hot day ( still well within the normal range - let’s say over the “r”. ) 4. i can assure you it is running lean since that’s the only way I can get it to pass emissions. I could enrichen the a/f screws on the carb to see if that helps? 5. I’ll try connecting vacuum directly to the distributer and see what happens. I’ll add that I know squat about timing so I can’t really offer much in that department :/ since you have this tuned for the emissions test, It is a great time to verify vacuum leaks. they should be easier to sort out. one simple test, find the smallest direct vacuum port preferably manifold vacuum. and uncap it while running and warmed up. if it is truly lean then the idle will reduce. if it is rich it will speed up. in the best case you will have a timing light/ tach hooked up to watch. at this time you could adjust the idle mixture screws. And watch the tach. only adjust enough for it to smooth out then recap the port. if capped or uncapped no longer makes a difference, stop there. Link to comment Share on other sites More sharing options...
delco1946 Posted August 11 Author Share Posted August 11 since you have this tuned for the emissions test, It is a great time to verify vacuum leaks. they should be easier to sort out. one simple test, find the smallest direct vacuum port preferably manifold vacuum. and uncap it while running and warmed up. if it is truly lean then the idle will reduce. if it is rich it will speed up. in the best case you will have a timing light/ tach hooked up to watch. at this time you could adjust the idle mixture screws. And watch the tach. only adjust enough for it to smooth out then recap the port. if capped or uncapped no longer makes a difference, stop there. Matt - if I introduce an air leak the idle definitely stumbles. Are you saying to adjust the mixture screw while artificially inducing a leak? Why do that? ( just trying to understand what that accomplishes or diagnoses?) Link to comment Share on other sites More sharing options...
delco1946 Posted August 11 Author Share Posted August 11 Matt - if I introduce an air leak the idle definitely stumbles. Are you saying to adjust the mixture screw while artificially inducing a leak? Why do that? ( just trying to understand what that accomplishes or diagnoses?) I hooked up manifold vacuum to the distributor. This results in immediate increase in rpm’s. I wouldn’t say the engine idles smoother tho, just faster with the same slight lopsided-ness. Interestingly, with the new pcv valve I can now hear it rattling very quickly with the engine running. Don’t recall hearing that before. Also, I do have a timing gun, but I don’t really understand how to use it. Yet. Vacuum pressure vid: https://youtube.com/shorts/xzuh5YOWxI0?si=BGTWw-K0Q8SQSQGh Link to comment Share on other sites More sharing options...
mat in tn Posted August 11 Share Posted August 11 Matt - if I introduce an air leak the idle definitely stumbles. Are you saying to adjust the mixture screw while artificially inducing a leak? Why do that? ( just trying to understand what that accomplishes or diagnoses?) I'm assuming (and we all know better) that you unplugged a very small port. like 1/8". if you were to back out the idle mixture screws say 1/2 round each, does it smooth out? my concern is that it is leaned out too much in the attempt to pass the test. ironically this can lower one reading yet raise another. are you certain that the egr valve is fully closed. at idle this will result in a vacuum leak. if this truck sat for an extended period before being resurrected there are many items like this to prove. Link to comment Share on other sites More sharing options...
viven44 Posted August 11 Share Posted August 11 I hooked up manifold vacuum to the distributor. This results in immediate increase in rpm’s. I wouldn’t say the engine idles smoother tho, just faster with the same slight lopsided-ness. Interestingly, with the new pcv valve I can now hear it rattling very quickly with the engine running. Don’t recall hearing that before. Also, I do have a timing gun, but I don’t really understand how to use it. Yet. Vacuum pressure vid: https://youtube.com/shorts/xzuh5YOWxI0?si=BGTWw-K0Q8SQSQGh Video is not available Link to comment Share on other sites More sharing options...
delco1946 Posted August 11 Author Share Posted August 11 Video is not available I’ve tested the egr and actually installed it circa 2020. I definitely did not induce a vacuum leak when I leaned the screws to pass deq. I basically turned it down so that it just barely ran in Feb. Link to comment Share on other sites More sharing options...
viven44 Posted August 11 Share Posted August 11 I’ve tested the egr and actually installed it circa 2020. I definitely did not induce a vacuum leak when I leaned the screws to pass deq. I basically turned it down so that it just barely ran in Feb. Brand new spark plugs ? When was the last time you compression tested all cylinders ? I wonder if one of them is falling off the lower cliff when things get hot. When I had Big Red, looking at my notes when things got hot all the cylinders lost some compression when hot (as might be typical).. cylinders 2 and 6 had barely over 80 PSI when things warmed up. I just don't think the valves seated all that well... maybe a over-torqued rocker arm?... I never got to the bottom of it before I sold Big Red. I actually put Big Red up for sale and someone wanted me to show compression values so thats when I realized things were close to cliff. Big Red was still a torque monster... but was running real close to the cliff... Rear 120 119 120 120 91 99 120 122 Front Link to comment Share on other sites More sharing options...
delco1946 Posted August 11 Author Share Posted August 11 Brand new spark plugs ? When was the last time you compression tested all cylinders ? I wonder if one of them is falling off the lower cliff when things get hot. When I had Big Red, looking at my notes when things got hot all the cylinders lost some compression when hot (as might be typical).. cylinders 2 and 6 had barely over 80 PSI when things warmed up. I just don't think the valves seated all that well... maybe a over-torqued rocker arm?... I never got to the bottom of it before I sold Big Red. I actually put Big Red up for sale and someone wanted me to show compression values so thats when I realized things were close to cliff. Big Red was still a torque monster... but was running real close to the cliff... Rear 120 119 120 120 91 99 120 122 Front 3.5 turns but higher pressure and better idle…. Link to comment Share on other sites More sharing options...
85lebaront2 Posted August 12 Share Posted August 12 3.5 turns but higher pressure and better idle…. That is an excellent idle for a 351M or 400. Link to comment Share on other sites More sharing options...
viven44 Posted August 12 Share Posted August 12 3.5 turns but higher pressure and better idle…. Yes that looks great. Maybe I jumped to conclusions. I had already assumed the idle screws were adjusted. Link to comment Share on other sites More sharing options...
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