EFI/ITB "4k" rev limit issue

[Chrisyoung808]

Aloha Pelicans,

I am currently chasing an issue with my car not being able to rev past 4k rpm. The only time I'm able to go above 4k is downshifting. When accelerating/revving in neutral, I can reach about 4k, then it seems like it's hitting a limiter. I'm thinking I'm getting some kind of signal interference. My tachometer bounces around 3500-4500, and Tuner Studio goes crazy, all the way past 8k+. I'm able to drive normally, but short freeway onramps are a bit challenging and I'd like to get the full potential out of the car. I've tried a few things, but nothing has seemed to work.

Current setup: Distributor wire (signal, ground) to a terminal board located between the shock mounts, and Megasquirt wires (white/black in shield) to the other end of the board. Stock internals 3.0L, X-Faktory ITB kit, Megasquirt, MSD ignition, headers & megaphone exhaust (no crossover). New plugs, wires, injectors, fuel lines, and rebuilt distributor.

1. Talking with Al Kosmal, I tried wiring a resistor inline between the distributor and the Megasquirt. No luck. Tried a potentiometer and increasing resistance, nothing either.

2. Connected the distributor wire to the Megasquirt wires directly instead of the terminal board.

3. Thought maybe the distributor wire was bad. Cut a spare shielded wire and wired dizzy to Megasquirt directly and via terminal board.

4. Routed the wire away from everything and wrapped the whole wire in aluminum foil (I was/am desperate).

5. Checked Tuner Studio rev limit settings. Put rev limit from "Normal" to "Coolant Temp" and adjusted all values to 6000. Engine was warm when I did this to make sure I'm not redlining a cold engine. Still could only get to 4k. Played around with all the rev limit settings, resetting to my original values each time.

Been talking to a couple guys who's worked with standalone ECUs & ITBs (not specifically on Porsches) and I'm being told that adding a Hall Effect sensor + crank pulley toothed gear would give a more reliable signal than the distributor, which I'm assuming is a mag sensor type. Ideally I would like to refrain from buying more things and trying to make what I have work, but if it comes to it, gotta do what I gotta do, right? So I do have a couple questions to ask:

a. Would it be worth it to convert to Hall sensor & crank gear over trying to use the existing dizzy setup & signal wire? My distributor has been completely rebuilt & cleaned/tested, so there shouldn't be anything wrong internally.

b. What values of ignition advance should I be looking for at each rev? 2k, 3k, all the way to 7k? Looking for 0-25% TPS, so I could have a good baseline to go off. Or if anyone could share their ignition table with a car similar setup to mine, that would be much appreciated. I'll upload my tune in a few hours when I have access to my tuning laptop.

c. How do you all have the patience and willpower to work through your car's issues? Admittedly, I was/am naive to think going EFI/ITB would have been simple and straightforward, but boy there have been times where I thought about giving up. Don't get me wrong, I am learning a lot and somewhat enjoy the process, but sometimes ask if it's worth it when I had a perfectly running car with a completely rebuilt CIS system and could've spent all this time driving instead of being frustrated and broke (mentally and wallet).

Thanks in advance!
Chris

[na2ub]

What year car are u working with?

I am doing a similar conversion with a 79, using the dizzy as tac signal, but i have yet to get all installed.

Do you have mechanical / vacuum advance on the distributor in good shape?

Also, after reading some of these threads, don’t overlook basic maintenance items.

Are your plugs, wires, coil in good order? Fuel filter? The last thread like this needed a new cap and rotor.

Just guessing. Im only a backyard mechanic.

[timmy2]

Did you adjust/set the rev limiter on the MSD 6AL?
Did you cut the small red or blue wire to put the MSD in 6 cylinder mode?

Are you using the MS2 unit to drive the MSD for spark, or just running fuel only?

[Chrisyoung808]

Originally Posted by na2ub

What year car are u working with?

I am doing a similar conversion with a 79, using the dizzy as tac signal, but i have yet to get all installed.

Do you have mechanical / vacuum advance on the distributor in good shape?

Also, after reading some of these threads, don’t overlook basic maintenance items.

Are your plugs, wires, coil in good order? Fuel filter? The last thread like this needed a new cap and rotor.

Just guessing. Im only a backyard mechanic.

My car is a 1979, using dizzy as tac signal as well. Distributor is completely rebuilt with new cap, and everything's in good order. Brand new plugs, wires, fuel lines, fuel filter, fuel pump. Basically anything that should be replaced or rebuilt has been.

[Chrisyoung808]

Originally Posted by timmy2

Did you adjust/set the rev limiter on the MSD 6AL?
Did you cut the small red or blue wire to put the MSD in 6 cylinder mode?

Are you using the MS2 unit to drive the MSD for spark, or just running fuel only?

I haven't touched/enabled the MSD rev limiter settings, as I planned to have everything controlled via Megasquirt. I haven't cut either wire in the loop, I do remember reading about that.. that could be one issue.

The last question, I'm honestly not too sure how to answer. Everything's pretty much wired/installed per Al's guide. Reading the MSD manual, I have the magnetic pickup wires (green/violet) disconnected/tied aside, and the amplifier output (white) hooked up to the ignition wire on the Megasquirt (brown wire, pin 36).

[mikesarge]

Originally Posted by Chrisyoung808

I haven't cut either wire in the loop, I do remember reading about that.. that could be one issue.

This is almost certainly the issue. You need to set up the MSD for a 6-cylinder

[winders]

[timmy2]

Cut the wire, set the MSD rev limiter to 6500.
See if it fixes the issue.

[Chrisyoung808]

I've just performed the recommended. Cut red loop per MSD Streetfire manual (PN 5520) and verified rev limiter is set at 6600. Still only able to get up to 4k.

[timmy2]

Try reversing the black and white wires to the MS2 from the Dizzy. Or change the input trigger angle from climbing to falling?

[Chrisyoung808]

Originally Posted by timmy2

Try reversing the black and white wires to the MS2 from the Dizzy. Or change the input trigger angle from climbing to falling?

Thanks Dennis, I'll take a crack at it tomorrow and let you know where I'm at. Work starts soon and I can't mess with it at night or I'll have some very unhappy neighbors

[timmy2]

Maybe read through this: https://www.megamanual.com/ms2/pickups.htm
Your dizzy is a reluctor type (VR) and needs the right settings in MS.

[al lkosmal]

Chris,
I am away for a few days...but just tapped into your thread. Dennis is providing good recommendations....the fact that your tach signal "goes nuts" in TunerStudio leads me to believe that the VR pots need adjusting. If you go on the DIYAutotune website, they have a good tech article regarding the setting of the VR conditioner.
Also, i would recommend that you email the techs at DIYAutotune. Matt and the crew at DIY are a very good resource for debugging.

rgards,
al

PS: your dizzy sensor is a VR sensor......the faster it spins, the higher the voltage it puts out....sometimes too high for the VR Conditioner....a resistor will often help here, but not always. I actually have an engine on my test bench (Dual dizzy signal into the M'squirt, with the M'squirt controlling the MSD, etc.) Running great...but rev limiting......as soon as I am back in the shop...I will be tweaking the VR conditioner.

[Chrisyoung808]

Originally Posted by timmy2

Maybe read through this: https://www.megamanual.com/ms2/pickups.htm
Your dizzy is a reluctor type (VR) and needs the right settings in MS.

Dennis, I appreciate the link to the manual. Will be divulging myself in this tonight.

[Chrisyoung808]

Originally Posted by al lkosmal

Chris,
I am away for a few days...but just tapped into your thread. Dennis is providing good recommendations....the fact that your tach signal "goes nuts" in TunerStudio leads me to believe that the VR pots need adjusting. If you go on the DIYAutotune website, they have a good tech article regarding the setting of the VR conditioner.
Also, i would recommend that you email the techs at DIYAutotune. Matt and the crew at DIY are a very good resource for debugging.

rgards,
al

PS: your dizzy sensor is a VR sensor......the faster it spins, the higher the voltage it puts out....sometimes too high for the VR Conditioner....a resistor will often help here, but not always. I actually have an engine on my test bench (Dual dizzy signal into the M'squirt, with the M'squirt controlling the MSD, etc.) Running great...but rev limiting......as soon as I am back in the shop...I will be tweaking the VR conditioner.

Al, thanks as always for your knowledge and insight. Hopefully this will be the end of my rev woes.

[jpnovak]

Yes, Since you have a VR sensor and you are sending this signal directly to the MS ECU you need to adjust R52 and R56.

Alternatively, you can send the VR signal directly to the MSD and then send the MSD Tach signal to the ECU as a trigger for fuel only. This will increase your signal to noise ratio by a factor of 10 and reduce the chance of fuel issues related to signal conditioning noise.

[timmy2]

I think this may be the write up Al was referring to:
https://www.diyautotune.com/support/tech/other/megasquirt-vr/

[jpnovak]

2 other things to check.

1. Go to "ignition settings > Noise filtering" and make sure this is set to OFF.

2. go to the tab "diagnostic and high speed logger" and check the input signal. You can use trigger log and/or tooth log. As you raise the rpm you should see if you get signal drop out or you get extra signals (noise). this will help you identify which of the two circuit conditioning trim pots need to be adjusted. this will help you get a better understanding of what this does.

Adjusting the V3 Main Board VR Input Circuit Potentiometers

BTW, This adjustment is well within the normal setup of the ECU. While it may seem frustrating it will run great once you spend a few moments to optimize correctly.

[al lkosmal]

Chris,
Jamie's comments on going fuel only and running the dizzy VR directly to the MSD and the MSD tachout to drive the M'squirt (which will control the injectors) is a good alternative to think about. While you lose some flexibility related timing/advance tuning....the MSD typically accepts the incoming VR signal with no fuss and you would be up and running more quickly.

My recommendation is to follow the procedures for VR conditioning of the megasquirt circuit and....very likely you will be up & running.....if not nd you want to put that particular debug procedure aside and save it for another day....go to plan B ang fuel only
regards,
al

[jpnovak]

From the description I thought this was fuel only.