MicroSquirt.com read only forum (Jan.15,2018)

Has anyone used the PWM feature to limit the current to hi impedance injectors to quiet them down? Are there any issues with running the PWM duty cycle up around 75%-90% with hi impedance injectors?

I'm running Delphi/Lucas injectors rated at 24lbs and 12.2 Ohms. At a specific range of injector pulse width/duty cycle they create a really loud squeal that sounds almost like a fan belt slipping. (no it's not my fan belt, I checked). I was thinking of trying to reduce the PWM duty cycle by 10% to 20% to see if that helps but before I do I wanted to see if there are any known issues with trying this.

I have all the injector control features populated on my V3 board including the flyback circuit.

shauer wrote:... At a specific range of injector pulse width/duty cycle they create a really loud squeal that sounds almost like a fan belt slipping. (no it's not my fan belt, I checked). ...

It sounds like your fuel pressure regulator may be 'singing' or squealing. It happens at certain flows and pressures. If you are using a FPR with a manifold pressure reference vacuum line, try pinching or pulling the line off momentarily when it's noisy to see if that changes or stops the sound. If so, it's definately the FPR. There are other ways to test and there are various fixes.

I would not mess with PWM in any case as it shouldn't affect the sound they make when operating properly, i.e. - opening and closing at full velocity.

HTH,
David

PSIG -

Thanks for the info. I'm using a TWM FPR that is regulating my kjet fuel pump (about 70psi) down to about 43psi. I do not have a manifold reference line so nothing to pull.

What are some other ways to diagnose a noisy FPR?

This happens between about 2000 and 4500 RPM and a MAP range of about 80 to 90 so it's kind of tough to troubleshoot at idle.

Thanks!

Your 70 to 43 psig regulation is in the standard range - and although I don't know your setup - MS is primarily designed for manifold pressure referenced fuel regulation. Be that as it may, a high kpa whine can also be identified by wrapping the FPR in dense foam or other stuff. Gets quieter? That's it.

The whine is somewhat common on aftermarket FPR's and can cause early failure. It's the oscillations with the valve banging shut so rapidly it sings. One fix or diagnostic is to give the rail and FPR some pulse-damping by installing an EFI filter as close to the FPR as possible BUT place it on a T-fitting with the other end plugged to trap air inside as a pressure buffer. Or add some length of R9 (EFI) fuel line to absorb pulses (not my favorite but can be diagnostic). Or switch your injections to alternating if already simultaneous, etc.

If it is the FPR I wouldn't work too hard at a fix before getting factory assistance, warranty or replacement (maybe with a MAP referenced model). Sometimes a spring or diaphragm change will do it.

HTH,
David