| Slant Six Forum https://slantsix.org/forum/ |
|
| Electronic Ignition question https://slantsix.org/forum/viewtopic.php?t=58490 |
Page 1 of 1 |
| Author: | crustycar [ Mon Oct 05, 2015 1:12 pm ] |
| Post subject: | Electronic Ignition question |
Vehicle is a 1980 B 100 Van with 225 6 on a 4 speed on the floor. Voltage drop across ballast resistor on Electronic Ignition. I have intermittent moments of what appears to be no spark at high loads. Van runs perfect 90% of the time but in the right conditions of low rpm and high throttle it will fish bite or bursts of misfiring. Get the rpm up above 1800 and problem seems to go away. It's load sensitive. High load she flames out. Spark is there but have to wonder if it's weak. It gives all the indications of something flashing over when it's hardest for the spark to jump. Plugs are not very old. Does not show the behavior until warmed up. Been fully thru the carb and just don't think the problem is there but it is a Holley 1945. The sort of snap off and on makes me think spark. Carb bad lean would just feel flat. Measured the voltage to coil from ballast resistor and found it to be 12 volts. Engine running at idle. This hit's me as a higher than it should be. Figuring on normal points voltages being 6 to 8 at idle. Dwell is the key -- longer ON time lower voltage. Is just a 2 volt drop normal for an Electronic Version ? Does moving the pickup coil closer to the pole change the dwell or is it fixed in the module ? Meter was a Simpson 260 that never lies. The more I think about this the more I wonder ignition coil breaking down but shocking as this may sound the original mopar ignition module is what's under the hood. If there are caps in the module there dust. only 44,000 miles but it's 35 years old. It was parked at 38,000 for 28 years. I hate the shotgun approach so thoughts on all this ? Is 12 volt at ballast resistor too high with engine running and battery at 14. Everything under this hood is OEM on ignition. Nothing has been changed except plugs. And they have crossed my mind too as a possible. |
|
| Author: | SlantSixDan [ Mon Oct 05, 2015 8:02 pm ] |
| Post subject: | |
What's in there for a distributor cap, rotor, plug wires, and spark plugs? |
|
| Author: | crustycar [ Tue Oct 06, 2015 10:17 pm ] |
| Post subject: | ignition question |
All is original Mopar from 1980. Cap looks very good with good carbon button. Rotor is clean with no cracks or black under center contact. Wires are the originals. Plugs are Motorcraft from Autozone. On the hotter side of the range they listed. Plugs have about 4000 miles on them but they have burned thru some pretty bad fuel and crud. They were one of the first things installed when started getting it back to running. I don't think this is plugs unless all 6 are shot. It runs excellent cold and that's where plugs usually show bad. This is like the key going off and on. You loose them all, like flame out then it comes back Fish biting is the term that comes to mind. If you lift your foot just a little bit it all comes back perfectly smooth. This only happens when you make it do tall gear pulls at high throttle and low rpm. Making it pull at 1000 rpm in 3rd gear. Get above 2000 rpm you cant make it happen. Other than this high load at low rpm cutting out it runs perfect. it's related to high dynamic load. One other question not related. I have a new dist gear but not changed it. Are the originals prone to turn to dust over time ? The one in there is 35 years old after all. |
|
| Author: | wjajr [ Wed Oct 07, 2015 5:33 am ] |
| Post subject: | |
Quote: It runs excellent cold and that's where plugs usually show bad
All indicators of lean condition. Check accelerator pump shot for slow to react to throttle movement, and weak squirt. Accelerator pump bridges temporary lean condition during sudden wide throttle openings until main jets and enrichment circuit can come on line. Lean idle mixture will cause stumble at low rpm during transition between idle circuit and main jet, in addition to poorly timed and volume accelerator pump shot.If you lift your foot just a little bit it all comes back perfectly smooth. This only happens when you make it do tall gear pulls at high throttle and low rpm. When throttle is opened wide at low rpm, intake sees a lot of sky, vacuum drops off to near zero, and main jets won't come on until air velocity in venture is great enough to pull fuel from well bowl. (simplified explanation) This process is slowed when lugging engine restricting rpm increase which is needed to get up onto the main jets. Re examine float level, accelerator pump shot, and idle mixture, and stop lugging engine. |
|
| Author: | crustycar [ Wed Oct 07, 2015 11:20 am ] |
| Post subject: | stumble |
I worked the carb pump last week. It helped. Float is set so level in bowel is very high. Above the book setting. This helped a little too. Could this be power jet vacuum plunger sticking ? it's annoying as some days it never happens and next day it's there all day. What ever it is - it's slowly getting worse. Gets far more pronounced when puling trailer. |
|
| Author: | wjajr [ Wed Oct 07, 2015 5:18 pm ] |
| Post subject: | |
There are several thing one can do to accommodate high load conditions, or in other words constant low vacuum condition. Going up four jet sizes from stock carburetor tune will help reduce lean condition when pulling a load under low vacuum condition. What power valve is installed? Is it a two stage? Holley made provisions to accommodate low power to weigh vehicles with a two stage power valve. When manifold vacuum begins to drop, a two stage PV will provide partial addition enrichment at a fairly high vacuum say 10 "Hg. and as vacuum continues to drop off when pull up a hill, or getting started the second stage kicks in say at 6"Hg giving full enrichment. I think you are going to have to do a little experimenting with jetting and power valve selection. I recommend you acquire two books titled: Super Tuning and Modifying Holley Carburetors by Dave Emanuel, and Holley Carburetor Handbook 4150 & 4160. I had to read & reread these two authors more than several times before the theory sunk in to my thick skull. |
|
| Author: | Sam Powell [ Wed Oct 07, 2015 7:44 pm ] |
| Post subject: | |
One side of your ballast resistir should read 6-8 volts, the other 12 . |
|
| Author: | crustycar [ Sun Oct 25, 2015 11:33 pm ] |
| Post subject: | found the problem |
this was the problem. The vacuum hose to the carb preheat sensor and flap was split right where it slid on the carb. it was split up past the barb and clearly leaking. Cut a new piece of hose. Just like magic the problem is gone. I actually did not expect this to make any difference in how it ran but it sure did. Explains the slowly getting worse too -- hose was not bad back this spring. |
|
| Page 1 of 1 | All times are UTC-08:00 |
| Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/ |
|