| Re: Timing and Overheating with the Howell EFI [message #370303 is a reply to message #370266] |
Sun, 07 August 2022 07:36   |
 |
RF_Burns
Messages: 2276
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
|
Senior Member |
|
|
Fun Fact:
In an Electronic Spark Controlled (ESC) system, the ECM doesn't use the distributor pulse for the current cylinder to Fire, it's used to fire the next cylinder in the firing order!
When cranking, the distributor uses it's position pulse internally to fire the spark plugs at its set advance position (say 6 degrees). Once the engine starts and reaches 400RPM, the ECM sends 5 volts on the bypass wire to the distributor. This commands the Distributor to use the pulse from the ECM to Fire the plugs.
When the distributor sends its pulse at say 6 degrees BTDC and the desired advance is 20 degrees BTDC, that reference pulse is already 14 degrees too late. So the ECM uses that pulse as a reference to fire the next cylinder.
So, if you want 20 degrees advance and a V8 fires every 90 degrees, then:
90 - (20-6) = 90-14 = 76 degrees of delay before firing the next cylinder.
So the ECM figures out the time to delay the spark based on current RPM and degrees to delay.
So at 600RPM = 10 revolutions/second = 100mS/revolution, divided by 360 degrees = 0.278mS/degree times 76 degrees (desired delay) = 21.1mS
So the ECM in this case will delay the pulse 21.1Ms before sending the pulse to the distributor to fire the next cylinder.
I expect the Engineer types have a fancy software algorithm to figure the delay more eloquently.
Disconnecting the distributor Bypass wire forces the distributor to fire from its own reference pulse so you can set the initial timing with the engine running above 400 rpm.
Howell has a spark advance table set in their PROM which will use a different initial spark setting. With the EBL board installed, you can use more initial advance. Just set it to whatever is in the EBL Bin you are using.
Just my Ex farmboy shade-tree mechanic with 50+ years in electronics way of seeing things, or I could be all wrong!
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
|
|
|
|
| Re: Timing and Overheating with the Howell EFI [message #370305 is a reply to message #370303] |
Sun, 07 August 2022 11:04 |
 |
Richard RV
Messages: 631
Registered: July 2012
Location: Full-timer for 12 years, ...
Karma: -17
|
Senior Member |
|
|
RF_Burns wrote on Sun, 07 August 2022 08:36Disconnecting the distributor Bypass wire forces the distributor to fire from its own reference pulse so you can set the initial timing with the engine running above 400 rpm.
Howell has a spark advance table set in their PROM which will use a different initial spark setting. With the EBL board installed, you can use more initial advance. Just set it to whatever is in the EBL Bin you are using.
Bruce,
Thank you for your clear explanations. They are appreciated! I also understand that the initial timing in the ECM table and that done with the timing light must agree.
I would like you to clarify something, please. The GMC MH manual says to set carbureted initial timing to 8° at ~650 rpm. Over the years I've seen the gurus say to push it to 10° initial. In seminars and conversations Dick Paterson said 12° is good.
My question: if 8/10/12 is good carbureted, what's different with Howell EFI and a throttle body that would suggest dropping the initial timing down to 6°? It seems to me that since the EFI and/or ESC doesn't take over until sometime after the engine is kicked over and certain conditions are met that the initial timing shouldn't be lower than the manual's 8°. What an I missing?
TIA
Richard
'77 Birchaven TZE...777;
'76 Palm Beach under construction;
‘76 Edgemont waiting its turn
|
|
|
|
| Re: Timing and Overheating with the Howell EFI [message #370306 is a reply to message #370266] |
Sun, 07 August 2022 13:08 |
Tom Katzenberger
Messages: 399
Registered: June 2019
Location: Kingsville, MD
Karma: 4
|
Senior Member |
|
|
Bruce,
Thank you for the great information. My FlowKooer 330-195 thermostat arrives on Tuesday. I will install it immediately.
The WUD has the temp at 212 degrees and runs +- 7 degrees generally. The funny thing is that the engine runs cooler in stop and go traffic and while idling. The temps rise on the highway.
My friend who rebuilds engines has an antifreeze supplement which supposedly lowers the water temperatures up to 30 degree. He said it is used in street rods.
With all that was done, I am also hopeful that the previously installed new thermostat is the issue and replacing it with the new flowKooler thermostat may solve all my problems. As I stated earlier, at this point I am replacing new parts with new parts.
I had the radiator re-cored, but was thinking that I may have to replace it with an aluminum one. Hopefully all will be well after Tuesday.
Thank you for sharing your input and sharing you knowledge.
Take care and stay healthy,
Tom K.
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D., Micro Level, Howell EBL-EFI Spark Control, Macerator, York Air Compressor, 6 Wheel Disc, Quadra Bag, Onan W/Bovee Ignition
|
|
|
|
| Re: Timing and Overheating with the Howell EFI [message #370307 is a reply to message #370266] |
Sun, 07 August 2022 14:04 |
|
RF_Burns
Messages: 2276
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
|
Senior Member |
|
|
Tom,
I would suggest you test the new thermostat in some hot water in a pot on the stove with a candy thermometer. Test the thermometer itself by making sure it reads ~212F with boiling water.
Richard,
A standard distributor has its advance curve pretty much set in stone. It will start into centrifugal advance just above idle. Setting the initial advance also moves the whole advance curve for any RPM/vacuum level. Setting it too far in advance will make for hard starting, but restarting it too much and you will lose advance at higher RPM levels. So you might want to set it at 10-12 degrees to get maximum advance at higher RPMs.
An Electronic Spark Controlled distributor has the advantage of being able to set the initial advance closer to TDC for easy-spin starting. But then when the engine starts, you can advance it up for best operation from idle on up. EBL also lets you set a fixed idle advance, or one that moves with RPM & Vacuum. A fixed idle advance might give a smoother idle. So you can set it to start at 6 degrees BTDC, then immediately jump to 20 degrees BTDC when it starts to idle.
If you set the initial too low, the rotor might not be in the correct position in the cap to fire the right plug. It may fire the previous cylinder. Contacts are 45 degrees apart on the rotor but you are moving the spark advance 1/2 of about 45 degrees as well so the rotor could be getting close to the adjacent cylinder contact on the distributor cap. I've never investigated this because it never seems to be an issue.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
