HEI7 Dwell Misfire ??

[oldskool]

Hi, got car running this week with MS3/MS3X, starts good, drives good except at light throttle 13-15% in OD doing 50mph, at that TP & speed, I get a misfire. During misfire AFR, RPM bounces around, give little more throttle, misfire goes away. Checking Datalog, noticed Dwell drops as low as 0.1 - 1.0 , running good at 3.8(set at 3.5 max in ignition settings).
Thanks,
David


77 Pontiac 400 stock 190HP test engine,
HEI7 controlled w/MS3X,
bank 2 bank port w/38's,
LS1 75mm TB,
GM 4 wire stepper IAC,
5,000 Altitude,
91 octane
200 4R

[Matt Cramer]

You're getting RPM spikes. How do you have the RPM input set up?

[oldskool]

Matt, Thanks for the reply. Can you view tune & see my settings? During assembly of MS3, testing with Stim, R56 pot had to be adjusted different than VR input. I had a post Feb 27th about this. At first Stim would see tach signal if I turned R56 in 6 turns, later after backing off R56 adjustment all way for VR in car, wouldn't get siganl from HEI7. Turned R56 back in 6 turns for Stim to test, wouldn't get signal, tried all way from full couterclockwise to 6 turns, couldn't get tach input from stim. Finally put in car, left cover off MS3 being careful to avoid grounding board & shorts. I turned R56 all way counter clockwise, then cranked engine over while turning slowly clockwise till my NOID lite flashed, same time LED blinked. (about 2.5 - 3 turns). I left adjustment alone. Could the R56 be the problem? Thanks,
David


77 Pontiac 400 stock 190HP test engine,
HEI7 controlled w/MS3X,
bank 2 bank port w/38's,
LS1 75mm TB,
GM 4 wire stepper IAC,
5,000 Altitude,
91 octane
200 4R

[Matt Cramer]

It's probably not the MSQ. I think you may need to adjust your VR trim pots until the noise disappears.

[oldskool]

Hi Matt, since I last posted about misfire, I corrected phasing of my rotor, slotted screw tab on pickup coil to rotate. That took out low speed misfire. Have maybe another problem? Still related to dwell? I'm sending some datalogs & tunes. Today, 6-3-12 I roadtested with higher ignition timing, I was able to run this amount of timing with points distributor with blow thru carb, this added timing feels like it really helped. Checking in MegaLogViewer, as RPM goes hi, dwell drops & gets erratic, MAP, Duty cycle, AFR, timing get erratic same time, this all was same before advacing timing. Datalog with unser.msl has a good cruise log. Is this a normal dwell variation? kPa with engine off is 83-84 (5,000) altitude. Please let me know, Thanks for you help.
David

I'm sending few more in another reply, Thanks

[oldskool]

Here's 2 more

[oldskool]

Matt, I'm not sure if I mentioned it has 7psi boost, earlier posts I didn't have the charge pipe to TB fabricated yet, Thanks,
David