The MegaSquirt Project has experienced explosive growth other the years, with hundreds of new MS installations occurring every week - a phenomenal success! MegaSquirt has been successfully used in all aspects of Internal Combustion engine applications including R&D, Industry, Race, and Research. The MS project has transformed itself from a simple R&D project into a full-featured mature engine control system. To reflect this the support structure has also changed to meet the needs of MegaSquirt Users.
Moving forward, the R&D forums for MegaSquirt project are in a read-only mode - no new forum posts are accepted.
However the forums will remain available for view, they still contain a wealth of information on how MegaSquirt works, how it is installed and used. Feel free to search the forums for information, facts, and overview.While the R&D forum traffic has slowed in recent years, this is not at all a reflection of Megasquirt users, which continue to grow year after year. What has changed is that the method of MegaSquirt support today has rapidly moved to Facebook, this is where the vast majority of interaction is happening now. For those not on Facebook the msextra forums is another place for product support. Finally, for product selection assistance, all of the MegaSquirt vendors are there to help you select a system, along with all of the required pieces to make it complete.
This forum is for discussing ignition setup, tuning, and troubleshooting for MicroSquirt (TM)
Forum rules
Read the manual to see if your question is answered there before posting. If you have questions about MS1/Extra or MS2/Extra or other non-B&G code configuration or tuning, please post them at http://www.msextra.com The full forum rules are here: Forum Rules, be sure to read them all regularly.
Ok, please no crossposting as I really need ideas as to why i'm getting this RPM spike/dropout problem. This is the sort of problem that would make or break an ECU to the general person on the street so any help is much appreciated...
My combo:
400 Pontiac, 42lbs injectors, 78mm LS1 throttle body.
MSD Probillet distributor with VR sensor sent straight to MS2's VR circuit. IGBT driver firing an MSD6AL.
MS2 v3.0, 2.35 code. Fuel pressure set to 44psi at idle, with vacuum line attached it drops to 40psi.
Attached is a zipped datalog, the RPM spike is very noticable at about Record 15000 (see screen trap) and also attached is my MSQ if anyone can find something...
Thanks heaps!
Last edited by krisr on Fri Apr 21, 2006 6:41 am, edited 2 times in total.
Sydney, Australia
Successfully MS2 v3.0 squirted 1971 Holden Monaro HQ
400 Pontiac, ported #16 heads, Tomahawk intake with custom plenum using LS1 78mm throttle body dialed in with a TechEdge 2E0 Wideband Controller.
I replaced the VB921 driver, still no good. Dropped my dwell & spark duration from 25.5 to 2.8-3.5, didn't change. Added some heat insulation behind the MS box where I mounted it on the cabin side of the firewall, still no difference. I upped the fuel pressure to 50psi and reset REQFUEL/ve table, no joy there.
Without having access to a CRO to check the 'cleanliness' of my tach signal, would adjusting the VR pots make any difference? I also added a bit more RTV around the crystal on the mainboard just incase it came loose.
One other symptom I found when coming home just then, after a few violent hesitations, it just shut down. Switched ignition off and it fired right back up fine...
Sydney, Australia
Successfully MS2 v3.0 squirted 1971 Holden Monaro HQ
400 Pontiac, ported #16 heads, Tomahawk intake with custom plenum using LS1 78mm throttle body dialed in with a TechEdge 2E0 Wideband Controller.
I am also experiencing a similar issue with my 4cyl. Big rpm spikes. Thsi only showed up when I started driving a wasted spark setup. With a single coil deriven by a single vb921, it worked great. It has to be noise getting onto teh board either through a sensor, power or ground. I have not yet been able to track it down.
I'm going to buy a new pickup on Tuesday to try as a local speedshop has them on special at the moment, but beyond that, i'm a bit stumped. I replaced the VB921, put a pullup resistor on the output, but the dutycycle going to 0% on each stumble has me believing i'm definately having the problem on the RPM signal side of things...
Sydney, Australia
Successfully MS2 v3.0 squirted 1971 Holden Monaro HQ
400 Pontiac, ported #16 heads, Tomahawk intake with custom plenum using LS1 78mm throttle body dialed in with a TechEdge 2E0 Wideband Controller.
Sounds unlikely I know, but I hd all sorts of rpm spiking problems on my 4cyl VW install. I fitted a set of resistor type plugs and it was like a miracle cure! Runs and idles really smoth now. Worth a try for the sake of the price of a set of plugs!
Thank you Dieselgeek! You've gotten me out of strife again!!!!
I have adjusted the hysteresis pot about 4-5 turns out until the RPM was a bit more smooth, then I even got a bit more creative and adjusted the zero crossing until it picked up RPM slightly, then back it off 1 turn.
Went for a drive, not 1 hesitation or stumble!!
Finaaaaaaally I can finish tuning this thing properly
Sydney, Australia
Successfully MS2 v3.0 squirted 1971 Holden Monaro HQ
400 Pontiac, ported #16 heads, Tomahawk intake with custom plenum using LS1 78mm throttle body dialed in with a TechEdge 2E0 Wideband Controller.
Good timing, we found ourselves in a similar situation this weekend and I was determined to try to figure this out.
ADjusting the pots for the specific VR installatoin seems to really do the trick, I've had a couple other guys comment on this as well.
Playing with the Hysterisis and zero crossing pots (is that what they're called) while having someone slowly spin the distributor until it triggered smoothly at low RPMs really helped us.
Quick one.. Did you ever mess with the reluctor/pickup airgap in your probillet distributors? From memory I set mine to about 0.010" and MSD said it's a bit to close. They recommended about 0.030"...
That might contribute to my noise problem too?
Sydney, Australia
Successfully MS2 v3.0 squirted 1971 Holden Monaro HQ
400 Pontiac, ported #16 heads, Tomahawk intake with custom plenum using LS1 78mm throttle body dialed in with a TechEdge 2E0 Wideband Controller.
I'v enever played with the air gap settings on these distributors.
It would be interesting to see what happens when closing down that gap a bit, using an oscilloscope. My guess is that the A/C signal is higher amplitude? and might contribute to better low RPM performance, but maybe at the trade of high RPm tach spikes or problems?
