High tach signal on startup
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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.
High tach signal on startup
I didn't want to hijack another users thread, so I started another one. I am datalogging my startups and getting very high tach signals on startup. Matt had mentioned a Zener diode in line with the tach signal could help with erratic tach signals while the engine is running. Could it help during startup to? I am also firing from the coil. This is happening on two MS-II projects i have going on right now. Hmmmm.....
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
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Matt Cramer
- Super Squirter
- Posts: 2951
- Joined: Sat Jul 03, 2004 11:35 am
Re: High tach signal on startup
Sure, noise can be a problem any time. I'd add the Zener diode.
Re: High tach signal on startup
Installed the diode (36 volt) and still gets high RPM on startup. I think I may need to add a cap to the MS power. I did not mention this before, but my ASE randomly turns on sometimes during throttle movements. I will rev it slightly and ase turns on then revs high for a bit. I think this is all due to the RPM signal? I may try shielded wire on the coil wire next. This problem is on a boat I'm working on with wire lengths of roughly 24', so there may be some places it's picking up noise from.
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: High tach signal on startup
Could you post a data log showing the ASE randomly turning on?
Re: High tach signal on startup
Thanks for the reply Matt.
It looks like at about time 213.327 the tach signal drops to 0 and ASE starts over and the engine runs as it had just started (IAC opens up, idles high for a few seconds, etc, etc). This happens a few times, mostly right after I rev it up a little. I'm currently looking for a scope to try and narrow down some noise issues. I did a quick shielded wire install from the coil directly to MS-II with no change in the erratic tach signal!
By the way, I have a 4 conductor shielded cable. Can I run my 3 TPS wires and 1 Tach wire in the same cable? I don't have a 1 conductor shielded available for the tach. This is what was available from work. Thanks.
It looks like at about time 213.327 the tach signal drops to 0 and ASE starts over and the engine runs as it had just started (IAC opens up, idles high for a few seconds, etc, etc). This happens a few times, mostly right after I rev it up a little. I'm currently looking for a scope to try and narrow down some noise issues. I did a quick shielded wire install from the coil directly to MS-II with no change in the erratic tach signal!
By the way, I have a 4 conductor shielded cable. Can I run my 3 TPS wires and 1 Tach wire in the same cable? I don't have a 1 conductor shielded available for the tach. This is what was available from work. 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: High tach signal on startup
I don't see a problem with putting TPS and tach in the same shield - not ideal but there shouldn't be too much noise in there. Having the RPM fall to zero is what turned on ASE.
Re: High tach signal on startup
That's what I had noticed, which led me to these last few posts. Now I have to find out why it's dropping to zero. I will permanently install shielded cable (and reinstall the zener diode) today and re-log to see if it's any better. I will post my findings. Until I get a hold of a scope, should I even bother throwing caps in on the MS power to see if that helps? Any idea on a value?
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: High tach signal on startup
Power is unlikely to be the problem - it's the signal off the coil, which is pretty noisy.
Re: High tach signal on startup
Update, last night: I installed the shielded cable for the tach wire and TPS wires. It didn't seem to help too much. I'm still seeing erratic tach signals during startup AND tach is dropping to 0 after a throttle rev.
This morning: Looked over my msq file and noticed and changed the lag factor for the RPM from 5 to 30. Seemed to be an improvement in the beginning, but after a few minutes and revving the throttle, it did it again. I don't know if that really made a difference but ASE did not turn on until later on. I datalogged this morning's attempt and the tach is all over the place during startups and quick throttle movements. Any suggestions on my next option/attempt?
This morning: Looked over my msq file and noticed and changed the lag factor for the RPM from 5 to 30. Seemed to be an improvement in the beginning, but after a few minutes and revving the throttle, it did it again. I don't know if that really made a difference but ASE did not turn on until later on. I datalogged this morning's attempt and the tach is all over the place during startups and quick throttle movements. Any suggestions on my next option/attempt?
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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
Re: High tach signal on startup
Ford 351 v8, MS-II version 2.89 firing off coil negative
Update: I installed a 36volt Zener diode with the band pointing to the coil negative. This combined with the shielded cable on the tach wire to MS at first did not seem like it did anything. I still had high tach spikes on startup and RPM dropped to zero after hitting the throttle (causing a sync problem?) and having MS thinks it's restarting....ie, ASE kicks in, IAC opens up and idles high for a few seconds. Try pulling out of a parking spot and having the engine suddenly rev up while you're in drive! Not good.
Here's the weird part. A couple of days after installing the zener diode the IAC/ASE thing seemed to stop no matter how many times I revved the motor. The datalog shows the zero is still there, but the weird idle & ase kicking on doesn't happen.....yet. In the meantime I had my laptop disconnecting from MS - acted as if somebody pulled the db-9 cable out and plugged it back in after a few seconds. This happens on both MS projects I"m working on. I figured it may be a software corruption issue, so I reinstalled MT. No more disconnects but the Tach spikes are still there. The RPM zero drop shows up on the datalog once in a while, without any adverse affects on ASE/IAC. Would adjusting the time mask help with the RPM zero drop?
My next move will be to add a cap to the coil power to see if it helps smooth out the tach signal. I may also get new plug wires too.
Update: I installed a 36volt Zener diode with the band pointing to the coil negative. This combined with the shielded cable on the tach wire to MS at first did not seem like it did anything. I still had high tach spikes on startup and RPM dropped to zero after hitting the throttle (causing a sync problem?) and having MS thinks it's restarting....ie, ASE kicks in, IAC opens up and idles high for a few seconds. Try pulling out of a parking spot and having the engine suddenly rev up while you're in drive! Not good.
Here's the weird part. A couple of days after installing the zener diode the IAC/ASE thing seemed to stop no matter how many times I revved the motor. The datalog shows the zero is still there, but the weird idle & ase kicking on doesn't happen.....yet. In the meantime I had my laptop disconnecting from MS - acted as if somebody pulled the db-9 cable out and plugged it back in after a few seconds. This happens on both MS projects I"m working on. I figured it may be a software corruption issue, so I reinstalled MT. No more disconnects but the Tach spikes are still there. The RPM zero drop shows up on the datalog once in a while, without any adverse affects on ASE/IAC. Would adjusting the time mask help with the RPM zero drop?
My next move will be to add a cap to the coil power to see if it helps smooth out the tach signal. I may also get new plug wires too.
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
Re: High tach signal on startup
Have you looked into (or tried) the Peter Florence Tach input circuit? http://www.megamanual.com/v22manual/PFl ... ch_mod.pdf
Or the similar "Dave Cap" solution that is explained in the MegaManual "Wiring and Sensors" section http://www.megamanual.com/v22manual/mwire.htm. This is also where the reference to the Peter Florence Tach circuit can be found.
Also, in the assembly guide for building up the circuit board for every MegaSquirt version there's a short discussion of triggering off the negative coil terminal.
I've had the same problems you've been having; crazy tach readings at startup and then tach signal dropouts later in the engine run. Now I've got these things mostly solved with a slightly changed version of the Peter Florence circuit. It does seem that a circuit with a capacitor or a combination of two capacitors is the key to smoothing the coil negative input.
Or the similar "Dave Cap" solution that is explained in the MegaManual "Wiring and Sensors" section http://www.megamanual.com/v22manual/mwire.htm. This is also where the reference to the Peter Florence Tach circuit can be found.
Also, in the assembly guide for building up the circuit board for every MegaSquirt version there's a short discussion of triggering off the negative coil terminal.
I've had the same problems you've been having; crazy tach readings at startup and then tach signal dropouts later in the engine run. Now I've got these things mostly solved with a slightly changed version of the Peter Florence circuit. It does seem that a circuit with a capacitor or a combination of two capacitors is the key to smoothing the coil negative input.
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Mike_Robert
- MegaSquirt Guru
- Posts: 84
- Joined: Fri Apr 09, 2004 5:55 am
- Location: FL, USA
Re: High tach signal on startup
Another thing you can easily try is resistance in series with the tach line. I have a couple of old rotary Mazdas whose coil negative was extremely noisy with a couple of ms of high amplitude ringing as evidenced on a scope. I experienced exactly the problems you describe. I placed a linear slope (non-audio) 100K potentiometer in series with the tach line as an experiment and it worked. I increased resistance just until signal was lost, measured that resistance, subtracted 20% or so and replaced the pot with a standard 1/4w resistor (50K or so I recall) under some heatshrink. The one fuel-only install was driven for more than 40K miles with zero further problems. I realize your hardware is nothing like mine, YMMV but this is cheap and easy to try.
-Mike
-Mike