GM 350 V8, TBI, HEI with 8 tooth VR

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RonnieBe
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GM 350 V8, TBI, HEI with 8 tooth VR

Post by RonnieBe »

Hi everybody,
I'm helping a friend of mine to start up a GM 350 TBI engine with a MS1 Extra controller rev 029y4 . We got the engine running but it was jumping a lot on the ignition point, the RPM signal was very unsteady and the injectors can be activated even if the engine is standing still.
I tried to adjust R52 and R56 without success so today I used a oscilloscope to log the signals directly on the board.

The megasquirt is running in distributor mode, using a 8 tooth VR sensor.
The ignition control was originally a HEI distributor with 8 pin module, but the module is removed and the VR sensor is wired into the MS and the coil is controlled by the MS.
VR-sensor.png
This is how I wired the oscilloscope to analyze the VR signal and the TSEL.
OSC-wiring.jpg
One of my problem is that I can not get the right polarity on the VR signal compared to the trigger output.
If I set the right polarity then the trigger will be activated on the long slope when the signal is above R56 setpoint. The timing will be irregular and the RPM indication is jumping a lot even if the motor sounds to run steady.

If I change the VR polarity then I can get the trigger to be activated when the VR signal have a sharp slope. So it's better timing to the 0-level crossing, but the curves are opposite the manual example. In this setup we will have spark generated from the coil to the distributor but no spark out to the spark plugs.
I assume it's a timing problem so the arm inside the distributor is not in physical connection with any of the 8 plugs the the spark is generated?

I hope someone can help me with some hints how it should be wired to get a steady trigger signal and if I'm right about the timing how to adjust it so correctly.
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ashford
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Re: GM 350 V8, TBI, HEI with 8 tooth VR

Post by ashford »

you are missing c31
Matt Cramer
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Re: GM 350 V8, TBI, HEI with 8 tooth VR

Post by Matt Cramer »

:msq:
Matt Cramer -1966 Dodge Dart slant six running on MS3X
Six_Shooter
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Re: GM 350 V8, TBI, HEI with 8 tooth VR

Post by Six_Shooter »

Why not use the HEI8 module?
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RonnieBe
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Re: GM 350 V8, TBI, HEI with 8 tooth VR

Post by RonnieBe »

Thanks for the help.

@ashford, the C31 solved a lot of the noise so it's much better now. Thanks!

@Matt Cramer, we have not been able to run the motor for the 2-5 minutes recommended for a log. As soon as we have it up and running I will make a log. But here I will upload the MSQ now when I have it in my computer. :-)

@Six_Shoter, my friend had been recommended to remove the module so when I came it was already done and he had resolder the inside of the distributor.

Status as of today.
We got the engine started but it wont run good, and when I use the stroboscope light to adjust the ignition I can see the position is jumping a lot.
When looking on the VR and TSEL I think they are not that bad, or?
VR-square-OK.jpg
Another problem is that sometimes after turning off the engine, D14 will remain lighted and there will be a injector and spark pulse every 3-4 seconds even if the VR and TSEL signals are flat. Also because the D14 is lighted I assume the ignition coil is powered, the result was that one coil got so hot so the plastic melted. :? Any idea how come the D14 can remain on?

Idle valve, on the TBI there is a Stepper Motor Idle Valve, but the MS1 can only run a coil. Any good solution for this? Possible to adjust the enrichment so no valve is needed? Now we need to use starter gas to start the motor if it's cold outside. Winter in Sweden is now about -25'C/-10'F.

Hope someone have some ideas regarding my problems. :)

MSQ file
GM_350_V8_TBI_HEI_with_8_tooth_VR.msq
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ashford
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Re: GM 350 V8, TBI, HEI with 8 tooth VR

Post by ashford »

if the coil is "on" when key on engine off the spark output is inverted.

if the scope is setup how i think tach input should be triggered of of rising edge
RonnieBe
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Re: GM 350 V8, TBI, HEI with 8 tooth VR

Post by RonnieBe »

ashford wrote:if the coil is "on" when key on engine off the spark output is inverted.

if the scope is setup how i think tach input should be triggered of of rising edge
It's only occasionally the D14 is kept on, 9 times out of 10 if will turn off.

On MS1 is it possible to change change to rising edge? I can't find that option in the settings.
Six_Shooter
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Re: GM 350 V8, TBI, HEI with 8 tooth VR

Post by Six_Shooter »

I realize you're likely beyond this point, but I would recommend using the HEI module, it really does make it easier, by allowing the module to do most of the spark control, and only turn timing control over to the MS when above a set RPM. IMO it makes it easier for a novice to get an MS system up and running than trying to have the MS do everything.
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RonnieBe
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Re: GM 350 V8, TBI, HEI with 8 tooth VR

Post by RonnieBe »

We did as suggested and reinstalled the HEI module then the ignition became steady.

We also rebuilt the stepper motor Idle Air Control-valve to a three wire Bosch IAC so its running very smoothly, the idle speed is really steady.

But, there is always a but, the engine won’t start without giving some very very little gas.

When cranking the motor starts, but dies, starts and dies.

It’s in the overlapping between cranking and idling it dies. But if I just gives little gas then it will start and the idle is perfect even if I release the gas.

I just have no clue what setting can be adjusted for this, I tried a lot but nothing helps.

Any suggestions will be very much appreciated.


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Re: GM 350 V8, TBI, HEI with 8 tooth VR

Post by jsmcortina »

Set the idle valve to be more open during cranking and increase the crank-to-run idle time. You may need more ASE also.

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