Hello chaps

Now I have rebodied my car with a fury tub, all wired up and the engine runs very badly.

Looking at the screen the RPM is leaping all over the place, spiking up to 12,000 just looking at the display.

I am taking the feed off the tachometer output from the bikes CDI unit, it worked perfectly well before, same wires etc (only 4" long) has just been relocated, does anyone know how to filter the signal?

Cheers Mark

If it's a megasquirt 2, pop open the top cover and there are two potentiometers that are used to adjust the VR signal. Use tuner studio with composite logger or tooth logger to adjust them correctly

Unfortunately megasquirt 1, I made it maybe 10 years ago.

Thank you anyway.

Disturbed an earth maybe during the relocation?

That is a possibility, food for thought thanks.

My MS1 V3 has the same two adjustment pots referred to above. But that may not be the issue. Have you used the correct type of screened cable for the input signal and is the screen connected at one end only? I had reset issues following an engine change. Like you, I had re-used the entire MS setup, wiring and everything. Strange.
Relocating the ground connections together with a home-wound inductor in the 12V feed sorted mine out. I also fitted little clip-on ferrite rings to all the ins and outs from the ecu.
RPM spikes can be caused by almost any part of the system. There are plenty of threads on the net regarding RPM spikes.
Get googling.
I have read about similar problems caused by...
Dodgy temp sensor (when cold)
Sensor wires near ignition wires
Poor battery connections
Poor engine earth strap

If your ecu does indeed have the two VR conditioner pots inside, if you do adjust them keep track of the number of clicks so you can go back.
You could try disconnecting sensors one by one.

Apart from the position of the parts the ECU wiring is untouched however the lowcost bulkhead was aluminium, the CDI unit and megasquirt were under the scuttle with the coils near the engine, these are now all under the bonnet so not separated by metal.

All the sensors look clean on the display.

The tachometer wire is not shielded so something to consider tomorrow thanks.

run new earth strap to it and make sure it doesnt earth on the body that way you can rule out other electrical items like on mine the earth was shared with a new usb cig lighter thing which caused temps and a few readings to go nuts. removed the cig lighter usb feed and all back to normal. So since then I have removed it from chasssis ground using rubber grommets to mount and now used its own ground straight to battery just in case.
DJ

Been hard at it today, mixed resuts.

Unwrapped all sensor wires, & TPS wires, they were all straight so twisted up and rewrapped.
Replaced the CDI signal with with co-ax, single earth from the megasquirt Earth point.

Opened the megasquirt, installed a Dave capacitor, cut the link on the diode and reconfigured for an external earth.

Ran new earth from the megasquirt back to the engine block rather than the chassis.

Replaced the tachometer wire with co-ax

Ran the CDI battery back to the switched source as I had megasquirt and the CDI on the same fuse.

New set of plugs.

Car now starts and runs, however it still occasionally misses, unable to screen capture data as I left my laptop charger at work so I do not know if it's still spiking, it does however now seem to be running cleanly, I am not convinced that it's all resolved.

Next weekend is sprint day, I will drop a big capacitor over the battery to see if this cleans up any spurious noise from the alternator etc.

Bit bored with it now to be honest....

That aside thanks for the advice chaps, before the laptop died I could see gains with each step, I can now simple turn the key and it idles not trying to catch a stall or watch flames exit the exhaust + it is running much cooler.

It also seems a little better than I remember it from before, I do wonder if I have always had a bit of a problem.

[Edited on 17/4/16 by mark chandler]

Have you introduced electrical interference by removing the ally scuttle panel? In the late 60s early 70s our local police force were using Volvos with ECUs , when using the police radio the cars lost power/cut out . Swedish engineers got to the bottom of the problem by wrapping the ECU in Bacofoil

The ECU is enclosed in a nice aluminium box, when it was in the locost bulkhead the CDI unit and Megasquirt ECU were 'inside', the coil packs under the bonnet so seperate.

When my laptop is charged up I will know more about what is going on, I need to make a waterproof box to go over the ECU,s as the wheel will splash them in rain so may make a metal lid which will provide additional shielding.

You could rule out the alternator by starting the car with it disconnected. Don't connect or disconnect it with the engine running. My mates car suffered resets due to a noisy alternator output. Sorted it with a new diode pack.

Get some "clip on ferrite" noise filters. Cheap and effective. I've got them on all the wires going to and from the ecu.
And the coil feeds. And the fuel pumps.

Great, thank you eBay purchase made

QUANTITY 4 CLIP ON FERRITE CLAMP CABLE NOISE SUPPRESSOR MEDIUM SIZE 9MM

Pass the wire through the ferrite more than once if you can.

Update on this post

Ferrite cores fitted, I am still seeing occasional spikes but these do not seem to affect the engine anymore, car starts on the button every time

I have an additional problem however, I cannot get the tachometer to work off either the coils or CDI output needle stays on zero. If I take the tachometer feed and take around 6 turns around the HT lead it shows idle but does not track the engine when revving, just drops down so off to maplins for a Zener diode although not hopeful.

Update on this post, went to Rockingham last weekend, car was terrible would not go on boost, massive flat spots hopeless ....

Plugged in my laptop and the RPM was spiking worse than ever before so removed the rev limiter which helped a little and swapped out the CDI sensor off the end of the crank, no real improvement then started to push and pull things about and found the culprit.

The spade connector on one of the coil packs felt slightly loose, when the engine revs it wobbled slightly on its post which is the root of my problems so crushed slightly and away it went, check the basics !

Bad news, sorted it out at 3pm, 20 minutes driving and the rain started so packed up and went home.

Rev counter is still rubbish however but at least the odometer works, will attack that again over the weekend.