Here is Peter's response to the idea of switching the leads on the VR:

HI Sam
You can try switching the VR leads, but I checked it on the bench and verified that spark was happening at the correct time relative to the VR waveform. If it's incorrect, timing will not be stable even with bypass disconnected, so it's easy to check with a timing light. Plus I think you'd have to change the distributor position about 45 degrees crank, which is a lot. This makes me feel that the current polarity is correct; because the timing was so close in bypass

Send me the current tune when you get a chance; I think I can predict fuel use at higher KPA if you have the lower KPA dialed in, for a given RPM column
Peter

This morning I sent him the same tune file George has.

Sam

_________________

Pierre, I posted before reading your post. Thanks for the link. That is a big help. I had already gone to Radio Shack, (is that Rat Shack?) and the guy there had no idea what I was talking about, and I did not know what to ask for specifically. He pointed me to the audio connector cables section, and saw nothing that looks like this stuff you linked me to. I certainly do not need 1000 feet of it, so hopefully can find it at a local merchant.

I will check the spark plug wires. They are Magnicore wires which are only a few years old, with no miles on them to speak of. I wonder if there is a better spark plug wire for this application. Even if they are not "leaking" there is going to be a fair amount of electromagnetic energy around them. I will start it in the dark and take a look. Thanks again.

Sam

_________________

I would still try switching the VR leads, since it is dead simple.

Too bad that the HEI (or MSII) is so apparently susceptible to interference. That is discouraging. I would bet it is not the Magnecore wires. The MSI and ignitions I have run (MSD and Jacobs) have not shown any noise problems in almost 10 yrs of running.

Great idea to check/set the reluctor air gap. If the VR signal is weak (too wide a gap), you will be in for trouble.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Hes's using an HEI module so he can do timing control from the MSII and the version board he has.

_________________
It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

Not to belabor the point, and I always get messed up on this point: having excess oxygen in the exhaust will show lean, meaning all the fuel was burned before the O2 was. Conversely, having less O2 shows as rich, meaning all the O2 was consumed before the fuel was. When speaking of misfiring, it gets confusing, because if ignition does not happen, you would rightly think all the fuel from that cycle will go out the exhaust, and show rich. But the O2 sensor does not measure fuel, it only measures oxygen, and all the oxygen from that cycle goes out too, which will show up on the O2 gauge as lean. It is somewhat counterintuitive (to me anyway) and I continually make that mistake.

Now, with that said, referring to Sam's datalog I posted above. The vertical blue line through the image shows that slice of time. You will see that the RPM is over 6000, but both the duty cycle and pulsewidth for the injectors are 0, which tells me the rev limiter is doing its thing and shutting off the fuel. SO, I don't see the CPU putting 6000 RPM worth of fuel in. Be that as it may, I can't account for why the AFR is so rich, unless it's the residual shot of fuel that was put in by the CPU as the RPM spike climbed up to the point it was shut off. I don't think the engine was running at that moment, which the driver would interpret as a misfire. Disabling the rev limiter, I think, will eliminate this.

Regardless, the root problem is the crank signal breaking up. Fix that, and it fixes a lot of these issues.

_________________
It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

George, I think your idea is spot on. It felt exactly like a rev limiter was in place and doing its job. I understand your idea that the dying may stop but that the noisy signal still needs to be dealt with. Tonight I purchased a microphone cable with is shielded, and should help with the noise. But, before I install this, I will try disabling the rev limiter. I hope you are a genius. Lucky would also be OK. I will not get to this until tomorrow evening at the earliest. This is a good thought.

Thanks, Sam

_________________

I turned off the rev limiter, and so will drive it to work today and give you a report later in the evening. In the mean time, I would like to be thinking about the nature of our noise fix. I purchased a microphone cable last evening, and will wire it in some time in the next few days. A deeper understanding of the nature of EMI would help me design a "fix" and route the wire.

Does this EMI penetrate metal? Or does it bounce around and reflect off of things. Or it is absorbed by metal and dissipated? I was thinking of making a small aluminum shield down low on the inner fender for the wire to sit behind as it moves forward toward the radiator core. Would this help? Or is EMI not stopped by such a shield?

I am hoping Gunpilot's suggestion moves us forward big time.

I want to reiterate, I have seldom accomplished anything of real value on this car without the support of you guys on this forum. The contributions have been too numerous to mention. Not that it is that great. It is just better than it would be working alone. In fact, I would likely have sold it several times without the support of the forum. Thanks.

Sam

_________________

EMI will be "absorbed" (not reflected) by metal that is well grounded, and the metal will act as a sheild for anything inside it. You might google "Faraday cage" for more info. However, if the metal does not completely surround the signal wire of interest, it may only give small or partial shielding.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Ha ha, Sam, I'm no genius. I get lucky sometimes, and I'd rather be lucky than good.

I will say that noise suppression on the tach (crank) signal line has traditionally been a lively and much discussed topic on the MSEFI forums. Frankly I've been surprised that I have not run into it before, just lucky I guess.

BTW, looking at the manifold pressure curve in your datalog gets me all excited. Look at that boost coming in at low RPM and low throttle opening! And it stays nice and flat over the RPM you ran. Can't wait to get my GN turbo hooked up.

_________________
It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

Its better, but no cigar yet. I could run up to 3Krpm at 10" of vacuum, (70KPA or so) in second andn 3rd, which is a new high, with nary a miss, but floored in 2nd and it falls flat on its face. This is with over rev limit turned off.

Yes, the turbo set up has almost NO appreciable lag. Am eager to get this fixed. Would a trigger wheel and pickup be less prone to this kind of noise. It would all be up front and away from the spark.

Good shielding is a simple next step. I was just starting to wonder..........It seems I am only a really excellent ignition away from success here.

Car starts and drives better than ever. That is ever, including all the various carbs.

Sam

_________________

I would see if we can't sort out the problem with your setup before swapping to another pickup type. I'm also running off the VR in the distributor with no noise, so I know it's possible. Unrelated to that, I do want to go to a pickup wheel later, simply for more stable timing.

I'd like to see another datalog - one where you run it up to higher RPM without it breaking up, and then where you floor it and have it break up as it did today.

Also, does the signal break up if you run the RPM up in neutral? If you can include that in the datalog, there may be some interesting info.

Also, not related to this problem - I noticed baro correction was turned off in your tuning file. Turning it on may help with smoother running, starts, etc. I always have it on.

On your next run, you may wish to see if turning the tach filter on makes any difference...

We'll get it worked out and running right. I have no doubt of that.

_________________
It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

Agreed on fixing what I have first. Just thinking ahead. I will get you another data log within a few days. And, thanks.

Sam

_________________

What settings should I specify with the tac filter. How does this effect things? Is this a deal where you can select more than one type of filter? I just went with what Peter chose. However we were working late, and were tired. I don't think this was the best or final choice in many cases. It was just something to try and get me home.
Sam

_________________

Under Noise Filtering in the general setup, the Noise Filter Enabled setting is currently set to OFF. Try setting it to ON and see if that helps.

_________________
It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

I decided to go ahead and stay up late, and patch in the VR signal wires with the shielded microphone cable.

It feels like this is not so good. It could be just my imagination, but it seems there is a small miss at idle. It revs smoothly, but I did not take it out and drive it. I checked the timing and it is on where it belongs, so I know the wires are the same as before. I think I did a good job of soldering and heat shrink tubing it. The wire looks to be size 20 stranded. And I did ground the shield.

As an answer to a previous question you had, the HEI module is grounded with number 12 wire to the head where everything else is grounded.

Just for the heck of it, I switched VR leads once, and it ran very poorly. It actually died before I could get the timing light on it. Now just to be fair, it sounded quite retarded, so perhaps if it were timed right, it would actually be better. I am not writing this one off entirely. But for now, I think the leads are properly oriented.

George, I will give you several data logs tomorrow. I will warm it up, and simply idle it for a minute or two, and rev it a few times and let you see how it behaves. Then I will drive it and try to get it to act up for a data log.

Oh Yes, I have not checked the reluctor gap. I will do that.

Sam

_________________