Hi fellow MegaSquirters,
I've got a quick question regarding sensors:
I was wondering if the MSII will work ok if I haven't connected TPS, temp sensors, etc..... I am only controlling the ignition at the moment and I haven't connected any sensors except for the MAP sensor; direct coil control using a VR dizzy.
I've managed to get the engine started and running but when I let it sit for a couple of days, it doesn't want to start..... not sure if it has anything to do with sensors not being connected???
I thought my tripple carbies may be the problem, but the car would start first shot before I installed the MSII. I have removed the tripple carbs and installed the standard twin carbs.... still no luck. I am organising the fuel injection, but in the meantime, I want to make sure that the car starts without fail.
Any help/advice would appreciated.
Thanks.
Marc.
Sensors
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.
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.
-
Bernard Fife
- Super Squirter
- Posts: 1009
- Joined: Mon Feb 16, 2004 3:15 pm
Marc,
At very least you need to ground the TPS signal (not the Vref) to ground through a 1K Ohm resistor (otherwise the voltage can creep up on the disconnected pin and put you into 'flood clear mode' in which no fuel is injected). <edit>Just realized you aren't using fuel - d'oh! In that case, I *think* you are okay, but I haven't actually tried ignition control with no sensors myself...</edit>
If it were mine, I'd also ground the CLT sensor pin through a 390 Ohm resistor, to give you a constant ~165°F reading.
You also need a crank position signal (distributor or crank wheel, etc.), but I assume you knew that.
Lance.
At very least you need to ground the TPS signal (not the Vref) to ground through a 1K Ohm resistor (otherwise the voltage can creep up on the disconnected pin and put you into 'flood clear mode' in which no fuel is injected). <edit>Just realized you aren't using fuel - d'oh! In that case, I *think* you are okay, but I haven't actually tried ignition control with no sensors myself...</edit>
If it were mine, I'd also ground the CLT sensor pin through a 390 Ohm resistor, to give you a constant ~165°F reading.
You also need a crank position signal (distributor or crank wheel, etc.), but I assume you knew that.
Lance.
Thanks for the prompt response Lance, much appreciated!
I played around with the MSII yesterday and made some progress.....
I believe I have solved the hard starting problem I was experiencing; I changed the cranking rpm to a lower value and this seemed to work. I've decreased the value to 120rpm and it starts almost every time I turn the key...... small problem with dwell (mentioned below).
I'm using the VR sensor from the distributor which seems to be working quite well; the only problem that I experience is that the signal seems to cut off below 700rpm; I can hear the relays turn off and the LED stops flashing momentarily..... sometimes the engine will stop and other times it will continue to run..... I've increased the idle to 750rpm to prevent this.
I connected a coolant temp sensor and the MSII was going into warm up mode and working normal as expected....
I'm still getting a spike once every so often; I noticed that when the rpm spikes (~10,000rpm) the dwell drops. I had the dwell set to 3.1ms and when a spike occurred, the dwell dropped to ~1.30ms. I reduced the dwell to 2.1 and the spikes seem to have stopped. I'm still trying to grasp the concept of dwell and how it affects the ignition.
Besides the dwell settings, is there any other parameters in the MSII that vary the dwell? I noted that sometimes when I am starting the car, the dwell jumps up (between 7.0-9.6ms) and the engine seems to struggle when turning over and then a puff of smoke comes out of the carbs. I then re-attempt to start the engine and it will start. I set all of the voltage compensation values to 0 to see if this was the cause, but the dwell still reached high values when cranking.
Look forward to any suggestions???
Marc.
I played around with the MSII yesterday and made some progress.....
I believe I have solved the hard starting problem I was experiencing; I changed the cranking rpm to a lower value and this seemed to work. I've decreased the value to 120rpm and it starts almost every time I turn the key...... small problem with dwell (mentioned below).
I'm using the VR sensor from the distributor which seems to be working quite well; the only problem that I experience is that the signal seems to cut off below 700rpm; I can hear the relays turn off and the LED stops flashing momentarily..... sometimes the engine will stop and other times it will continue to run..... I've increased the idle to 750rpm to prevent this.
I connected a coolant temp sensor and the MSII was going into warm up mode and working normal as expected....
I'm still getting a spike once every so often; I noticed that when the rpm spikes (~10,000rpm) the dwell drops. I had the dwell set to 3.1ms and when a spike occurred, the dwell dropped to ~1.30ms. I reduced the dwell to 2.1 and the spikes seem to have stopped. I'm still trying to grasp the concept of dwell and how it affects the ignition.
Besides the dwell settings, is there any other parameters in the MSII that vary the dwell? I noted that sometimes when I am starting the car, the dwell jumps up (between 7.0-9.6ms) and the engine seems to struggle when turning over and then a puff of smoke comes out of the carbs. I then re-attempt to start the engine and it will start. I set all of the voltage compensation values to 0 to see if this was the cause, but the dwell still reached high values when cranking.
Look forward to any suggestions???
Marc.
-
Bernard Fife
- Super Squirter
- Posts: 1009
- Joined: Mon Feb 16, 2004 3:15 pm
Marc,
Yes, the dwell is someitimes longer during cranking - this is due to the uncertainty over when the next spark will be (due to crankshaft speed fluctuations). So the dwell is sometimes deliberately longer to be sure of having an adequate spark. This doesn't overheat the coil, since the duty cycle for the coil is very low during cranking.
Are you using 'trigger rise' for the cranking trigger? This will give you a spark while cranking at very nearly your 'trigger offset' and should be pretty constant.
Have you tried adjusting the R56 and R52 pots to see if it helps your under 700 rpm problem? It may be the the signal isn't strong enough to reach your current threshold and that speed.
The dwell is the charge time for the coil. In addition to the base setting, it is affected by the maximum spark duration, the supply voltage (the 12 Volt system), the coolant temperature, and the time available to spark.
MegaSquirt-II attempts to set up a charge/ discharge cycle that charges the coil for the specified charge time, discharges it for at least the specified spark duration time, and then remains in the discharge state until it is time to start charging for the next cylinder. At higher rpm's, there may not be time to fit in the specified charge + discharge times. In this case, MegaSquirt-II scales down both the charge and discharge times proportionally so they just fit within the time between tach pulses.
If you are seeing tach spikes, this reduces the time MegaSquirt thinks it has to spark, so it reduces the dwell (so this is expected, and is a result, not a cause, of the problem).
Lance.
Yes, the dwell is someitimes longer during cranking - this is due to the uncertainty over when the next spark will be (due to crankshaft speed fluctuations). So the dwell is sometimes deliberately longer to be sure of having an adequate spark. This doesn't overheat the coil, since the duty cycle for the coil is very low during cranking.
Are you using 'trigger rise' for the cranking trigger? This will give you a spark while cranking at very nearly your 'trigger offset' and should be pretty constant.
Have you tried adjusting the R56 and R52 pots to see if it helps your under 700 rpm problem? It may be the the signal isn't strong enough to reach your current threshold and that speed.
The dwell is the charge time for the coil. In addition to the base setting, it is affected by the maximum spark duration, the supply voltage (the 12 Volt system), the coolant temperature, and the time available to spark.
MegaSquirt-II attempts to set up a charge/ discharge cycle that charges the coil for the specified charge time, discharges it for at least the specified spark duration time, and then remains in the discharge state until it is time to start charging for the next cylinder. At higher rpm's, there may not be time to fit in the specified charge + discharge times. In this case, MegaSquirt-II scales down both the charge and discharge times proportionally so they just fit within the time between tach pulses.
If you are seeing tach spikes, this reduces the time MegaSquirt thinks it has to spark, so it reduces the dwell (so this is expected, and is a result, not a cause, of the problem).
Lance.
Lance,
thanks for explaining the dwell concept, make sense now!
The cranking trigger is set to 'trigger rise' and my trigger offset is set to 58deg..... I have confirmed that the timing is correct; I used the trigger wizard and checked my timing with the timing light..... values matched. I checked at several rpm's and everything was matching.
I totally forgot about trying to adjust R56 and R52.... I will give that a shot and see how that goes!
Thank you for clarifying the spike situation. Makes sense after your explanation... I was under the impression that the dwell may have caused the spiking.... I will replace the exisiting wiring with a screened cable and also try V2.34 code. Hopefully that will eliminate the rpm spike.
Thank you very much for you help, really appreciate it!
Marc.
thanks for explaining the dwell concept, make sense now!
The cranking trigger is set to 'trigger rise' and my trigger offset is set to 58deg..... I have confirmed that the timing is correct; I used the trigger wizard and checked my timing with the timing light..... values matched. I checked at several rpm's and everything was matching.
I totally forgot about trying to adjust R56 and R52.... I will give that a shot and see how that goes!
Thank you for clarifying the spike situation. Makes sense after your explanation... I was under the impression that the dwell may have caused the spiking.... I will replace the exisiting wiring with a screened cable and also try V2.34 code. Hopefully that will eliminate the rpm spike.
Thank you very much for you help, really appreciate it!
Marc.