EFI University

Scheizty · Joined: 16 Mar 2009 Posts: 3

Hey guys, here's my dilemma.

I am running a FSAE team and we have an R6S motor from yamaha. We are running a cop wasted spark using the stock crank trigger with one tooth missing (4-1). During cranking, we are getting spark and she will turn over if we use starting fluid. If we do not use starting fluid, the injectors will not open. If we do use starting fluid, the engine will turn over and fire but it won't sustain, it instead dies almost immediately. So far, we have spark and air.

Notes: the motor ran before we received it; the timing has not been messed with since then. stock airbox, injectors, tbs, exhaust. We are just trying to get it to run on the stand. The injectors are set on two channels and the polarity was changed to utilize a common positive for the injectors.

Is there are reason why the injectors are only firing when the engine has sped up? Is there a way to crank the motor faster or is there a setting so that the injectors will open at a slower crank speed? I was thinking that maybe there isn't enough current at this speed to open the injectors. I could really use the help. Thanks.

Gadgeroonie · Joined: 24 Aug 2004 Posts: 1723 Location: UK

this may not be the best forum to get megasquirt advice

have you tried any of the dedicated megasquirt forums ?

gunnar · Posted: Mon Mar 16, 2009 4:25 pm Post subject:

Are you using any kind of priming pulse on it?

How high of an rpm are you getting while cranking without any fuel being added?

baldur · Joined: 12 Oct 2007 Posts: 430

The injectors will open if the engine turns fast enough for the ECU to pick up the speed signal, in other words if you get ignition you should get fuel also.
Is the fuel pump running? Also, do the realtime variables in megatune indicate that the TPS is working?
If the TPS doesn't work it may read as if the throttle is fully open and that triggers flood clear mode.

Check for fuel pressure and +12V at the injectors, then check that the throttle position sensor works in Megatune.

Scheizty · Joined: 16 Mar 2009 Posts: 3

tps is fully functional from 0 to 100%

fuel pump primes during startup. We aren't running a fuel pressure gauge, but when we cut the fuel line to put in a filter it sprayed everywhere. When the ECU is turned on, it shows the priming pulse for a second while the pump is priming, but then shows no signal. I only get a pulse reading when the starting fluid is used.

The cranking rpm is set for 300rpm. I changed this to 25 and there was no change.

Also, when cranking, it takes a few turn overs before the engine speed begins to show in megatune. I forgot what speed it reached.

Btw, could changing the polarity of the injectors have anything to do with it?

Thanks for the replies and your concern.

baldur · Joined: 12 Oct 2007 Posts: 430

What do you mean changing injector polarity? By default the ECU can only supply negative to the injectors, they must be connected to a fixed +12V source unless you've changed the injector driver circuitry for your own.

Matt Cramer · Joined: 25 Sep 2007 Posts: 275

Scheizty · Joined: 16 Mar 2009 Posts: 3

The stock crank trigger is a 4 tooth wheel using a hall sensor. We shaved a tooth off for the ecu to recognize tdc.

From what my guy was saying is that the original ecu was using a common ground with a switched positive. It was necessary to switch the polarity to utilize a common +12v source. He is the electrical guy, I guess I should look at it, but I'm not the greatest with these kind of things.

Matt Cramer · Joined: 25 Sep 2007 Posts: 275

Switched positive is a bit unusual. I've seen it on only a couple systems like the '70s era Bendix system.

As this is a FSAE team, do you have access to an oscilloscope? Would you be able to scope the sensor signal and post a picture of the trace?
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Matt at DIY Autotune