delco1946

So sad. These trucks are very restorable, and forest green and nutmeg are rare colors.

Well I need to do some more investigating but it does seem to be the oil sender wire. It is toast and I know I hit it while checking spark plugs. Lots of oil around the sender its self. Not sure where the oil was coming ( dripping from valve cover?) from but yuck what a mess. Not sure how to replace the sender wire as it merges into a larger wire harness ( I hate splicing 😂). The harness looks toasty too but that’s gonna to expensive to try and replace. It’s so hard to see and get to. No wonder I’ve never paid attention to it before! Thanks for the lead.

Why would my oil pressure gauge suddenly be reading low. Yes, I know it always reads low but now it’s reading lower than usual and is no longer responsive when I rev the engine. It also isn’t reading as high upon startup when cold. Any tips to diagnose this? It seems like either of the gauge is now malfunctioning although none of my other gauges are, or else it’s reading is accurate and which case something is wrong with my engine now.

Ope! Looks like someone marked something! I’ll look underside to see if I can find other marks!

I love how none of these parts are easily visible or accessible. Sigh. Is this the distributor bolt to loosen? Balancer isn’t even visible from the top 🫠

Thanks Jim!

I’ve been searching and not finding what I’d like to see - are there any videos of timing for a 351m? I’m not sure I fully understand what bolt to loosen before I start turning the distributer. I’ll have to check on a different day, but is there an obvious pointer? Not sure I’ve ever noticed one. After some googling it sounds like I’ll need to sand my balancer to find the old timing marks? And how many are there - ie does it go high enough to timing total timing (so 30 to 40?). Thanks!

Sorry y’all. I resorted to inaccurate shorthands Increase in pressure = increase in absolute pressure ( just how my mind was thinking since these are consistently negative pressures (aka vacuum). I may have also been saying idle and meaning mixture screws or vice versa. Bad habit of mine to be less than accurate. I have to adjust the mixture screws to get the carb running as lean as possible, just before dying in order to pass emissions. My truck won’t even idle on less than 2 to 2.5 turns (manual says start w 1.5!). Not sure why she runs so rich compared to what the manual suggests, but I score high on hydrocarbons as a result. In Oregon, only vehicles older than 1975 are exempt. My Datsun also has challenges passing. Doesn’t help that my renewal date is February so it’s hard to really get the engine roaring hot. I’m a nut - I like all things vintage hence a pretty sweet vintage Sun tune up set which includes a timing gun ( don’t know how to really use this yet), but it has a cylinder compression gauge (never used), dwell/ rpm meter, vacuum gauge, remote starter and the original instructions and such. Pretty neat find from an estate sale. My truck has a New catalytic converter, egr, etc prolly all from around 2019ish. Doesn’t make it easier to pass emissions tho! The air dump system only operates at rpm’s above idle (deq only tests that after you failed the idle emissions so it’s a moot point), egr only operates above idle etc.

3.5 turns but higher pressure and better idle….

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.

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

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?)

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 :/

It did rattle when I shook it, yes.

Well, it shouldn’t be vacuum related ( to carb/ emissions devices) since I pinched off the entire source of vacuum to all emissions related devices, and it made no change, (including thermostat controlled switches). I checked all my spark plugs, and some didn’t look fabulous, however, I think they generally fit within a normal tolerance. I tightened down the valve covers, put a new gasket under the breather filter that mounts to the driver side valve cover. However, I did just check my PCV at idle. It’s pulling a lot of suction which makes me think it’s no longer functioning? It’s not that old 1yr?), but it’s got full manifold vacuum going through to the valve cover, which, if I understand how the system works, it should be closed with that high of suction and open up as the vacuum gets weaker. The engine ran noticeably smoother when I put my thumb over the valve and plugged it.