Voltage drop causing rpm spikes on startup
Forum rules
Read the manual to see if your question is answered there before posting. Many users will not reply if the answer is already available in the manual.
If your question is about troubleshooting, configuration, or tuning, you MUST include your processor type (MS-I or MS-II) and code version in your post. If your question is about PCB assembly or modifications, you must also include the main board version number (1.01, 2.2 or 3.0). For tuning/troubleshooting questions, please attached a datalog and your MSQ file to your post.
If you have questions about MS1/Extra or MS2/Extra code configuration or tuning, please post them at www.msextra.com Such questions posted here will be moved to: a temporary MSextra sub-forum, where they will be removed after 7 days
The full forum rules are here: Forum Rules, be sure to read them all regularly.
Read the manual to see if your question is answered there before posting. Many users will not reply if the answer is already available in the manual.
If your question is about troubleshooting, configuration, or tuning, you MUST include your processor type (MS-I or MS-II) and code version in your post. If your question is about PCB assembly or modifications, you must also include the main board version number (1.01, 2.2 or 3.0). For tuning/troubleshooting questions, please attached a datalog and your MSQ file to your post.
If you have questions about MS1/Extra or MS2/Extra code configuration or tuning, please post them at www.msextra.com Such questions posted here will be moved to: a temporary MSextra sub-forum, where they will be removed after 7 days
The full forum rules are here: Forum Rules, be sure to read them all regularly.
Voltage drop causing rpm spikes on startup
I made some progress on an issue I've been having during startup with my car. I've had rpm spikes during cranking, sometimes reaching 9000rpm. I've tried modifying the tach circuit with the help of other members, shielded wire, rerouting wire, etc...with no luck. I reviewed one of my datalogs and noticed it happens when the battery voltage drops to around 8-9volts. I put a battery charger on and tried again, this time there were no spikes at all. None. I tried this about 5 or 6 times and there was not a single spike. I also have the battery mounted in the trunk (1000 cranking amp battery with 0 gauge cables running up to the engine/starter. I'm debating whether I should try a larger cap or just move the battery back to the engine bay. There's nothing I can do about the voltage drop regarding the physical setup (battery, cables, etc). Any opinions? I can post a datalog when I get to work if anybody would like to see. Thanks.
1962 Buick Skylark 215 V8
Bored and stroked to 266, Port Injection, Pertronix ignition AEM WB 02
1977 28' Mercruiser 351Windsor, TBI, Pertronix ignition, NB o2
Both MS-II 2.891 , V-3 board
Bored and stroked to 266, Port Injection, Pertronix ignition AEM WB 02
1977 28' Mercruiser 351Windsor, TBI, Pertronix ignition, NB o2
Both MS-II 2.891 , V-3 board
-
Matt Cramer
- Super Squirter
- Posts: 2951
- Joined: Sat Jul 03, 2004 11:35 am
Re: Voltage drop causing rpm spikes on startup
You might want to try more skip pulses; this can often fix an initial startup RPM spike.
