Diagnostics help, please - sputtering, crazy tach signal

[opethmike]

For the last few weeks, I have been having some issues with 1049 that are making the car near unusable. The following things happen:

1. When I go wide open throttle, or heavy throttle, the car will sputter real hard, almost as if hitting a rev limiter (which I don't have set). It will do this usually between 3,500 and 4,500 RPM.

2. The AFR will oscillate widely from lean to rich to lean, etc. As you can imagine, the car doesn't exactly drive smoothly when that happens.

I have observed in the data logs that I have examined that when these things are going on, that the RPMs that Megasquirt is reading/TunerStudio is displaying will jump around wildly. The dash tach does NOT - it stays steady.

I've tried some of the Tuner Studio noise filter seemingly to no difference. I've also checked the wiring where I get the inside of the car (white/slate which normally goes into the idle ECU), and at the ignition coil end. Soldering/crimping all look good.

I'm at a loss, so any help would be appreciated. My current tune file and a data log from a drive tonight are attached.

[Bitsyncmaster]

Sounds like the EFI ECU is getting a noisy tach signal. So if yours was working and suddenly started this problem, I would first check the ECU for a bad solder joint and or burned component (cap or diode). Is your alternator voltage running normal? Is your battery getting old?

[Spittybug]

I just looked at your files Mike... You are running fuel only? (look at the tach/ignition settings tab). I though you went full control..... So your timing is still dizzy controlled - funny, I don't know why when I loaded your .msq into the megalog viewer it popped up a spark table too??? Yet I can't see one when looking only at your .msq file in tuner studio.

Can you confirm?

[opethmike]

I just looked at your files Mike... You are running fuel only? (look at the tach/ignition settings tab). I though you went full control..... So your timing is still dizzy controlled - funny, I don't know why when I loaded your .msq into the megalog viewer it popped up a spark table too??? Yet I can't see one when looking only at your .msq file in tuner studio.

Can you confirm?

Owen,

I am still running fuel only. Confirmed.

-Mike

[opethmike]

Sounds like the EFI ECU is getting a noisy tach signal. So if yours was working and suddenly started this problem, I would first check the ECU for a bad solder joint and or burned component (cap or diode). Is your alternator voltage running normal? Is your battery getting old?

Battery is about five months old. I haven't checked voltage with my DMM yet, but the dash gauge and the tuning software both show ~14 volts while running. I'm VERY rookie at looking at circuit boards, so I'm not quite sure what to look at there, but I will follow your suggestion and see if I can find anything. I'll also hook it up to the simulator board that I have to see if the tach gets funny then.

Thought/question - I could be wrong, but it SEEMS that this problem starts happening/gets worse when the car has been running for a while. Maybe a bad solder joint on the ECU board is loosening up when the ECU warms up from running?

[AdmiralSenn]

How are you getting your tach signal? Gray/white wire from coil negative? Are you using the VR conditioner circuit or the hall/optical circuit?

My first few attempts to tune Christine yielded horrible noise on the tach signal. I pulled a new tach signal off the distributor lead and used the VR circuit to condition the signal and my tach input is probably about as clean as they get on these cars.

[opethmike]

Coil negative. I have the 3.57 box from DIYAutoTune as it comes, I have not touched the insides of the box. The car has run without these issues for about a year and a half; they are a few weeks new.

[opethmike]

Also to note, I've tried three different ignition coils, and the issue was the same. So I seriously doubt a coil issue. Right now, I have the tach wire from the MS relay board soldered onto the grey/slate wire. To eliminate that wiring circuit as a cause, I am going to try running a wire from the MS relay board directly to the coil negative.

If that still has issues, I would have to think that something is wrong with the MS unit, but I don't know how to test that.

[Spittybug]

Also to note, I've tried three different ignition coils, and the issue was the same. So I seriously doubt a coil issue. Right now, I have the tach wire from the MS relay board soldered onto the grey/slate wire. To eliminate that wiring circuit as a cause, I am going to try running a wire from the MS relay board directly to the coil negative.

If that still has issues, I would have to think that something is wrong with the MS unit, but I don't know how to test that.


Do indeed try running directly to the coil. I vaguely remember when I was having my issues converting that there was a difference in where I grabbed the tach signal. Although it is odd that it should just stop working properly...... Could be something else in the car that has "changed" in some way and is now creating noise.

[Bitsyncmaster]

Another long shot guess is that capacitor on the coil could have gone bad. It's good you tried other coils.

[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.