articfriends

iTrader: (1)

Fuel pressure is very important, I get alot of phone calls from people wanting to "buy a replacement mefi ecm", after I talk to them a good part of time their issue goes back to low fuel pressure, idle fuel pressure with a accurate gauge will at least tell you IF your close BUT you REALLY need to see the fuel pressure at wot as at idle your injectors are open like 1.2 milliseconds at idle and accounting for dead band, more like .7 ms , at wot more like 10 MS (10 times more) so extend gauges temporarily to near helm with hoses or something as you could chase things in wrong direction without that data! those two ashy plugs in first pic look like they have saw quite alot of oil, does that motor use alot of oil, more than the other? does it ever idle to high (bad pcv) which will draw alot more oil in and maybe it gets to those two cylinders

SB

iTrader: (1)

Even a cheap bluetooth wifi boroscope / endoscope

DrFeelgood

Appreciate the info. The boat is new to me so I don't have any data on oil consumption yet. PO told me he added a quart to each, fairly consistently, but I don't recall how often he said that was.
No high idle noted thus far. PCV valves replaced last week.

Gimme Fuel

Do yourself a favor and just ditch the tiny PCV system and go with a catch can breather setup. I got some cheap Chinese ones for ~$50 each and plumbed them straight to each valve cover and capped off vacuum port on plenum. My 960+ hour 502MPI's went from burning a quart every weekend to burning a whole quart over the entire season just by letting them breathe. Mount the cans near the arrestors/TB to help suck in some of the fumes.

I also recommend having Smitty (Articfriends) flow your injectors. I learned the hard way with a melted piston from bad injector. These things are still original (sans a used piston/ring set to replace melted one) and run like swiss watches with Smitty's injectors and tuning and I actually picked up several MPH afterwards.

TomZ

iTrader: (2)

How are you limiting the vacuum draw?

*f’ing autocorrect

DrFeelgood

Tested my Stbd fuel pressure regulator today, with compressed air. Blew off at 33-34 psi, far short of the 43 psi spec. Replaced with new Merc unit.
Also determined my distributors are in rough shape, significant corrosion, modules questionable, probably will replace both.

Gimme Fuel

I put the Davis Unified distributor modules and coils on my motors. Been running on them several years now after Smitty (Articfriends) recommendation from his dyno escapades. I also included the part number for a very reasonably priced spark plug wire set that fits these perfectly and has great quality for the price. Both of my fuel regulators were bypassing with low fuel pressure however are basically inaccessible without pulling engines or doing serious disassembly to access. Put a secondary universal regulator on the return line which has worked very well.

Summit Racing part #'s:
DUI-000444 Davis Unified Ignition Ignition Dyna-Module
DUI-31723 Davis Unified Ignition Screamin Demon Coil
FST-255-2416 FAST FireWire Spark Plug Wire Set

TomZ

iTrader: (2)

Anyone know if the DUI modules have a built-in advance curve and what it is? I'd like to update mine - I'm carbureted now but using the Delco distributors. The modules appear to be factory original though their characteristics seem to be a little different from one another. Sorry for hijacking a little.

articfriends

iTrader: (1)

Sb has told me multiple times that different variations of 8 pin small cap efi/hei modules have different advance curves BUT I have never found them to have ANY advance curve. IE, you set base timing in a mefi ecm at 8 degrees, the wot timing at 34 degrees at 50 KPA/5000 rpms and the factory default setting in the MEFI " FALLING REFERENCE ANGLE IN REGARDS TO NEXT PHYSICAL TDC" TO 8.1 degrees and aside from timing chain stretch, cam deflection/twist, when you rev it up to 5000 at 15" of vacuum you will pretty much see that 34, if you change it in the programming to 20, you will see 20, if you change it to 40, you will see 40. Now, the saturation time, dwell time, storage time then realease, whatever you want to call it when module converts the signal of rotor passing and sends it out , is ever so slightly different on some modules. What I mean by THAT is say a merc module is in dist and set to 8 base, you put a dui module in, base might change to 9, 9.5, put a weak standard module in, might change to 7 or 10, but again at that point the cap was just off and disturbed too.
so after changing module, I have had to adjust base 1, 2 degrees before to get it back to the correct base number (8 degrees on most mefis) that makes the tables correct, Smitty

SB

iTrader: (1)

8 pin GM modules . Can’t vouch for the DUI replacement.
When you remove the 4 wires attached to right side of dist, as we do for cabureted app’s, you lose the 5 volt ref and ecm ‘timing’ wire connection. When those aren’t there, the module uses it’s own advance curve.

For carbs, we just run + and - to coil, then attach two other terminals on coil to two wire connector on dist. Again, nothing plugged into 4 wire connection on dist.

Now, so much of the advance is under 1000rpm and alot under 600 rpm, most with a timing light don’t see this and think the module has no advance.

Diagram shows hook up. Diff fist but same deal. GM est/voyager dist just plugs in with two wire connector.