Fuel and spark, but won't start. (HEI, MSII, V3)

[turbo-brooks]

This is on a typical SBC with HEI ignition.MSII V3 board, relay board etc.

I don't doubt that I've done something wrong, but for the life of me, I can't find the problem. It sounds as if it's trying to start, cranks stumbles, and just won't fire off..it won't even back fire. Even in if you crank the timing WAY advanced or retarded. It won't slow the engine down when cranking like it should if you really crank the timing up. It's for sure getting spark to the plugs.

At first, I had the 12V for the injectors (the 4 wires on the end of the relay board hooked up to 12V, not to the injectors) - thought for sure this was the problem. Fixed that, went to kick it off MANY times, no luck. Even in clear flood (now you can smell fuel, and it acted flooded)

If you probe the injectors with the key on, BOTH wires are getting power (tested with a test light). I thought MS supplied ground to the injectors to trigger them? (so one of them should be a ground, or pulsing ground when cranking?)

Ignition capture set to rising edge
cranking trigger set to trigger rise
charging scheme set to standard coil charge
spark output set to going high

(This is using a 7 pin module)

I've gone over the wiring over and over, and don't see anything wrong, or nothing seems wrong to ME - but, again,it's entirely possible that I have something wrong.

The only other oddity is the 5V from Vref - I wasn't sure how to setup/wire it so the TPS is getting it's 5V from Vref as does the 5V to the HEI module (PinB across the relay to Vref)....

Any suggestions!?!?

[turbo-brooks]

...continued.

I finally got the thing to have spark and fuel - but still won't start. For whatever reason, I had it wired/jumpered as if it were using a hall sensor instead of the standard VR sensor used in my HEI. Mine is wired like this diagram -



I've checked, checked and checked the board again - and it's passing all the stim test that I could think of, like it should. Now, the injectors are pulsing a ground on crank, and it's getting spark - but the spark seems to be weak looking. It'll studder and stumble, but just won't fully kick off. I thought I had fouled the plugs again, but even after putting another new set in - it still won't start. Sounds exactly the same. I just ohm'd out the coil/cap - and it's getting 1.0 ohms across the primaries and 7,000 across the coil/ground.

The only thing I can think of - I have a smallish wire powering the coil (it's a temporary wire). Is there anyway the wire is not passing enough voltage to satisfy the coil? It's a 16Ga I believe.. Seems I remember the factory uses a 12ga?

...or.. Is there possibly a setting I'm missing out on that could possibly be the cuplrit? (I'm using tuner studio fwiw)

-Brooks

[Matt Cramer]

How much dwell are you using? A weak spark may mean not enough dwell. Also, put a timing light on it and see if your timing is somewhere reasonable.

[turbo-brooks]

Matt -

As I lay in bed last night thinking about this problem - I thought of the same thing you just mentioned. The dwell..I can't remember what it's set at, other than I think it's the default. (I'm at work and forgot my laptop.)


Also, Since it's using a VR sensor - I noticed that I had forgot to adjust the POTs. The R52 POT is fully CCW. The R56 is 6 CW from full CCW.

Timing, I can't be sure of - but, I have adjusted it from WAY up to WAY down with no changes. However, all of that was done before I found the mistake in the VR sensor jumper (I didn't ahve VROUT jumpered right)

[Matt Cramer]

Also, Since it's using a VR sensor - I noticed that I had forgot to adjust the POTs. The R52 POT is fully CCW. The R56 is 6 CW from full CCW.

Timing, I can't be sure of - but, I have adjusted it from WAY up to WAY down with no changes. However, all of that was done before I found the mistake in the VR sensor jumper (I didn't ahve VROUT jumpered right)

Do you have the VR sensor actually wired directly to the MS? If you have the MS getting RPM from the HEI module, you do not need the VR conditioner as the HEI module conditions it for you.

[turbo-brooks]

you'll have to forgive me - I'm a MS newb and not totally electronically savvy - Not sure what you mean by conditioner. It's wired just like that diagram above.

[turbo-brooks]

OK, I did a bunch more research based on what you said above -

It appears you don't have to use the 7pin module with the V3 mainboard? (do you still get timing control?)

The diagram above came from here - http://www.megamanual.com/ms2/GM_7pinHEI.htm

For using the HEI with a relay board:

Pin R goes to 'tach' on the 20-position terminal block (which in turn connects to DB37 #24).
Pin E goes to 'S5' on the 20-position terminal block (which in turn connects to DB37 #36).
Pin B goes to dedicated wiring to a relay (as shown in the diagram), or to 'fidle' if you are using the spare port settings and have modified the relay board's "GV" jumper to supply 5 Volts by connecting the middle terminal of the GV jumper to 'Vref' on the 20-position terminal block)
Pin C goes to the coil's negative terminal,
Pin + goes to the coil's positive terminal (and switched 12 V supply),
Pins P & N go to the VR sensor.

but on this page it implies you can run the V3 (what I have) main board without the 7pin module - http://www.megamanual.com/ms2/pickups.htm

In general, the most suitable option for controlling ignition timing advance on a distributor with a VR sensor on MegaSquirt-II is using the VR sensor circuit built into the V3 main board (see step #51 and #52 here) and the high current ignition driver circuit on the V3 main board to control the coil. With the V2.2 main board, you can use a GM 7 or 8-pin HEI module to convert the signal AND control the coil. There is much more on this on the GM HEI page.

I guess, assuming this has complete timing control (This is a turbocharged 383). I'd need to know how to hook up the VR sensor and direct coil control....I'll keep digging, but if you should happen to see this before I find it.. post up!

Thanks Matt!

[turbo-brooks]

Ok, I'm filling in the blanks slowly but surely -

65. It is choice time again. In this case, you will decide whether to populate the high-current ignition driver circuit. This circuit can be used to drive a single coil in a distributor application. In conjunction with an appropriate input signal (from a VR, Hall, or optical sensor, or even points), it allows you to eliminate a separate ignition module, such as a GM HEI 7 or 8 pin module, and run the coil directly from MegaSquirt

[Matt Cramer]

I personally wouldn't bother using the VR conditioner / direct coil control option if you already have the HEI module. There's normally not much to gain from it. I'd recommend figuring out why the HEI isn't working, first.

[turbo-brooks]

What's the gain/loss in functionality from one to the other?

My thing is, I'd like to lose one component that may not be needed - particularly the made in china HEI module. lol.

[turbo-brooks]

I did a bunch more reading and never saw a distinct definition of what you gain with the module and without.

Having said that, I changed over to the high current circuit and deleted the module and it briefly started and runs super rich - so rich that it dies easily. It floods super easy, mainly due to the fact that the injectors pulse after the key is turned off for some reason.

Once this happens, it won't start a second time at all... ideas?

[Matt Cramer]

I did a bunch more reading and never saw a distinct definition of what you gain with the module and without.

Having said that, I changed over to the high current circuit and deleted the module and it briefly started and runs super rich - so rich that it dies easily. It floods super easy, mainly due to the fact that the injectors pulse after the key is turned off for some reason.

Once this happens, it won't start a second time at all... ideas?

Check to make sure the injectors do not receive power when the key is off. The MegaSquirt injector drivers can stick on after the unit is powered down.

[turbo-brooks]

I did a bunch more reading and never saw a distinct definition of what you gain with the module and without.

Having said that, I changed over to the high current circuit and deleted the module and it briefly started and runs super rich - so rich that it dies easily. It floods super easy, mainly due to the fact that the injectors pulse after the key is turned off for some reason.

Once this happens, it won't start a second time at all... ideas?

Check to make sure the injectors do not receive power when the key is off. The MegaSquirt injector drivers can stick on after the unit is powered down.

I did test that - it's dead. The wierd thing - when you kill power, and the pump continues to run, you can hear it slow down.. once it gets to a certain point, the fuel pressure appears to take over (?) and the pump gets pushed backwards, or at least that's what it sounds like it's doing. There's no other electrical devices in the truck running - like fans, waterpumps etc.

[Matt Cramer]

I did test that - it's dead. The wierd thing - when you kill power, and the pump continues to run, you can hear it slow down.. once it gets to a certain point, the fuel pressure appears to take over (?) and the pump gets pushed backwards, or at least that's what it sounds like it's doing. There's no other electrical devices in the truck running - like fans, waterpumps etc.

Whoa... the fuel pump is still running when you kill power? That is another thing that shouldn't be happening. Something is very wrong with the way you have this wired up. Maybe you should draw up a diagram showing how your particular wiring is set up, as it appears you have wired it in a nonstandard way.

[turbo-brooks]

I did test that - it's dead. The wierd thing - when you kill power, and the pump continues to run, you can hear it slow down.. once it gets to a certain point, the fuel pressure appears to take over (?) and the pump gets pushed backwards, or at least that's what it sounds like it's doing. There's no other electrical devices in the truck running - like fans, waterpumps etc.

Whoa... the fuel pump is still running when you kill power? That is another thing that shouldn't be happening. Something is very wrong with the way you have this wired up. Maybe you should draw up a diagram showing how your particular wiring is set up, as it appears you have wired it in a nonstandard way.

It's just like one of the many instructions said to do it - the VR sensor wires use the TPS return, and tach input. The coil uses 12V and S5 on the relay board. Nothing else has been changed since I removed the 7pin module.

It's getting feedback from somewhere, I just have no idea where.

Is it possible that the coil's input power to the primary side is feeding back through the junction block or something?

[turbo-brooks]

I've created a different thread - maybe this topic isn't relevant to the original post, but the .msq is posted over there too for anyone who wants to see it. Now, that I've ditched the HEI 7 pin module and the MSII is getting signal direct from the VR sensor, I'm getting some wierd problems. As noted in this thread viewtopic.php?f=89&t=39512 the engine tries to start, but floods easily (could be any number of things), but the problem is that when you kill the key there's some sort of feedback/noise in the line that causes the pump to continue to run and the injectors to pulse, which REALLY floods it, and after that, it won't attempt to start again. This thing has pretty big injectors, and takes about a nano-second to fully RUIN the plugs. lol.

The ONLY things that have changed are the VR sensor wires are directly connected to the relay board (tps return and tach), and the ground to the coil goes to S5. The positive wire of the coil goes to a junction block temporarily, and I manually unplug it to kill the power to the coil (temporary, but always been like this).

The one thing that sticks out is that I'm not using a shielded wire anymore, but that shouldn't matter after the key's off - right?

[Matt Cramer]

Please draw up a COMPLETE wiring diagram for the MS system, one that shows where EVERYTHING is getting power. This does not sound like a VR sensor input issue - it's something totally different.

[turbo-brooks]

Please draw up a COMPLETE wiring diagram for the MS system, one that shows where EVERYTHING is getting power. This does not sound like a VR sensor input issue - it's something totally different.

I don't have a way to draw complete schematic - but I promise, it's exactly like what' shown in the relay board schematic. I even bought the premade cable between the MSII and the relay board.

The two power wires into the relay board are coming from switched 12V and one from the battery direct.

The only thing different from this direct coil drive schematic http://www.bgsoflex.com/mspower/mspower_ShemV1.2.pdf is the 12V to the coil is spade connected to a junction box.. temporarily.

Now, I will say this - above when I was saying "when i turned the key off" - I meant to say "when the key returns to run". Since the engine didn't crank, the fuel pump primes for a split second after the key returns to run. Now, I've figured it out I think - the truck is VERY low on fuel. I think what is happening is that when the key returns to run, the pump stops - and the pressure in the line is backflowing through the pump and spinning it backwards. THIS is the feedback into the relay board, and since the key is still in the run position - it's pulsing the injectors for whatever reason. It might be happening because of cavitation, or because the check valve in the pump (if there is one) is failing - not sure... but, as of right now, I'm 99% sure it's the fuel backflowing through the pump and spinning it backwards thus causing the feedback

[Matt Cramer]

Ok. The MS is supposed to pulse the injectors at the key on - this is called the priming pulse. And in your case, you have too much of it.