Diagnostics help, please - sputtering, crazy tach signal

[opethmike]

I unhooked the grey/slate tap from the relay board, and ran a wire directly from coil negative. No change at all. Starting to get annoyed.

How can I test the MS ECU?

[Spittybug]

Other than swapping with a known good one for testing purposes.... you need a stim. I don't own one or I'd send it to you. You may need to get DIY on the phone. Matt can be very helpful. Try posting on the Megasquirt boards?

Double check that your MAP vacuum line hasn't kinked, cracked or otherwise come loose. That can do weird things. Have you tried a recalibration on your O2 sensor?

[opethmike]

The same is being posted on the Megasquirt boards, but I figured it would be smart to post here as well.

I do have a stim. I "ran" the ECU for a brief while on it, but I couldn't reproduce the issue there. The maximum RPM Dot was 200; that was without moving the RPM knob on the stim. In the car, I will see RPM Dot spikes of 1,500 to 3,000.

I actually did check the MAP line since I had the parcel shelf out to take the ECU out of the car. MAP line looks fine.

I'll try recalibrating the O2 sensor, but I'm not sure I understand how that would affect the RPM spikes?

To review:

Problem seems to get worse the longer the car is driven (this is the part that stands out the most to me, but not sure what to make of it)
Several different ignition coils have been tried with no improvement
Noise filters in MS have been tried with no improvement
New wire has been run directly from relay board to coil negative terminal with no improvement

[opethmike]

Well, screwed up the distributor tach wire trying to get a different signal, so I will have to order a new one of those. I'll get back to it once I have that in my hands. One of the guys on the MSExtra boards rather sternly pointed out I shouldn't be using battery for ground, so I'll try a different ground as well. Not sure why it would work for 1 1/2 years then get problematic, but.....

[AdmiralSenn]

Well, screwed up the distributor tach wire trying to get a different signal, so I will have to order a new one of those. I'll get back to it once I have that in my hands. One of the guys on the MSExtra boards rather sternly pointed out I shouldn't be using battery for ground, so I'll try a different ground as well. Not sure why it would work for 1 1/2 years then get problematic, but.....

If you're worried about damaging the tach wire (once you have the new one) you could try tapping into the relevant wires next to the ignition ECU. Should be a little easier to solder to.

[opethmike]

Got my replacement tach wire installed in the DeLorean. But cranking, I am only seeing ~150 RPM. Me thinks I have run down the battery from my starting attempts the other day. On the charger it goes.

[opethmike]

Root cause of sputtering resolved, and it was embarrassingly stupid. Turns out at some point I had way overtightened the negative terminal bolt on my battery, which stripped the threads, and it was slowly untightening itself. When I pulled the battery out of its cubby to unbolt it, the freaking bolt literally just fell out. When I looked at it, the threads were stripped.

Replaced that, and all good to go. Wow.

[Bitsyncmaster]

Root cause of sputtering resolved, and it was embarrassingly stupid. Turns out at some point I had way overtightened the negative terminal bolt on my battery, which stripped the threads, and it was slowly untightening itself. When I pulled the battery out of its cubby to unbolt it, the freaking bolt literally just fell out. When I looked at it, the threads were stripped.

Replaced that, and all good to go. Wow.

What I use are long allen head cap bolts with a nut. That way I screw the bolt in finger tight to get all the threads and then use the nut to clamp the terminal. The allen head is small enough to slip a boxed end wrench over the head to tighten the nut.

[Spittybug]

Isn't it amazing how we humans tend to overthink a problem? I'm as guilty as the next guy and I confess that I too have had the 'old terminal at the battery' issue previously. It's very hard to make yourself check the obvious first when they are so well hidden in plain sight that they are no longer obvious!

Good to hear that it isn't a black mark against Megasquirt too! Same old story, going this route WILL find all of your other issues sooner or later.

[opethmike]

Thanks for the support guys, I appreciate it.