quattro Posted October 20, 2017 Author Share Posted October 20, 2017 I am measuring the voltage at the 86 terminal on the relay with a basic DV Voltmeter. I realise that I am measuring pulses and won't get an accurate reading of voltage, but if one circuit is rapidly jumping around from 0.5V to 9V, and the other is a constant 5.4V, then something is wrong. I suspect the problem is with the bouncing one. I am either using the 1K resistor and 2N2222 in the ECU, or a circuit that I have made using a 1K resistor and a 2N5551 transistor. When using my circuit, I just bypass the ECU circuit and connect directly to JS3. With the home made circuit, the tacho rises when the car is revved, but is not steady. The relay doesn't buzz at all. I am aware that my testing equipment is nowhere near good enough and I'm not entirely sure what to test for anyway, so have now found someone to test the entire thing, ECU, added bits and my home made stuff. Let's hope that sorts it When you said earlier that the MS settings looked fine, did you mean the 7, 1 and 0, or the 5, 2 and 55? Cheers Richard Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted March 8, 2018 Share Posted March 8, 2018 I've only skimmed this but I've seen issues with relay-switching from the MS using this exact style of circuit, the high-voltage spikes make their way back into the ECU's power rails and cause processor resets and other issues. Now, when you just want to switch a relay (EG for a fan) you put a zener diode across the output as near the connector as possible to catch the spikes. BUT, as you apparently want the spikes, you're a bit stymied. I'd be tempted to ditch this and use the diodes-fed-from-the-actual-ignition-coils approach before you fry your ECU. Here's my 4-output setup with 4x Zeners, works very nicely. I'm using a darlington array to drive it, a bit lazy but more robust than the 2n2222's: Quote Link to comment Share on other sites More sharing options...
quattro Posted March 26, 2018 Author Share Posted March 26, 2018 I gave up and got someome else to do it for me Basically, my circuit worked very well, but only for a fraction of a second, until the transistor overheated. So, because it happened so quickly, I didn't see it working at all. When you turn it off and measure stuff, the transistor had cooled down and showed everything was ok. A very handy chap called Dave EFI fixed it with a dirty great transistor which runs all day only without even getting warm, so all is working OK. Just have to get the Jag diff in now Quote Link to comment Share on other sites More sharing options...
pierrel Posted February 18, 2020 Share Posted February 18, 2020 On 3/26/2018 at 4:08 PM, quattro said: I gave up and got someome else to do it for me Basically, my circuit worked very well, but only for a fraction of a second, until the transistor overheated. So, because it happened so quickly, I didn't see it working at all. When you turn it off and measure stuff, the transistor had cooled down and showed everything was ok. A very handy chap called Dave EFI fixed it with a dirty great transistor which runs all day only without even getting warm, so all is working OK. Just have to get the Jag diff in now Hi Quattro, It seems that i suffer the same problem as you did, on my MGB V8. Could you please tell me which transistor you had to replace to get your tacho working ? Many thanks in advance, Pierre Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.