Fuel pump pwm setup

My fuel tank is getting super hot.. Aeromotive say heat is coming from the rail. Others say the intank pump is heating the fuel.

I've decided to close loop pwm the pump with a high output from my megasquirt 3 pro.

Are these relays ok to use?

Can I just disconnect the boost ref from the FPR and wind it up to say 75psi (base pressure+total boost+10psi headroom) with pump at 100% duty then reduce duty to get base pressure. ?

Or should i be utilizing the boost ref on the FPR?

That relay looks like it's designed to switch A/C - some of them have trouble when used with DC.

I'd leave the regulator in the system and just use open loop to back down the pump duty cycle, if it's already plumbed for a regulator and you don't want to remove it.

Are you going to closed loop PWM and control fuel pressure with pump speed, or are you still going to rely on the regulator to control fuel pressure?

Yes, AC SSRs do not do DC.  You'll need something similar but for DC.    That being said I'm not familiar enough on PWM use with SSR.  A look at the data sheet  may help.

You'll need a MOSFET with a heat sink. Sometimes people call them a DC-DC SSR. Getting them with a high frequency won't be cheap. A 50-100 Hz one can be had for $10.

AwesomeAuto said:

Are you going to closed loop PWM and control fuel pressure with pump speed, or are you still going to rely on the regulator to control fuel pressure?

Yea adjusting pump speed and I was intending dead heading against the regulator with boost ref disconnected.. But hoping the regulator set at 75psi will bleed enough to prevent the pump from stalling. Apparently these pumps need a small relief hole drilled if going true returnless...  Does that make sense? Would it work? 

MadScientistMatt said:

That relay looks like it's designed to switch A/C - some of them have trouble when used with DC.

I'd leave the regulator in the system and just use open loop to back down the pump duty cycle, if it's already plumbed for a regulator and you don't want to remove it.

Dont want to remove it thats for sure. I need to work out how the megasquirt actually controls it in open or closed loop. I have pressure sensor in the rail so can use that or have it reference an rpm/load table for open loop... 

I found this relay... Its actually suggested in the ms3 manual for this purpose.. Ss fan relay from a jeep

Closed loop will only work with some types of pumps. This uses a fuel pressure sensor and no regulator - the ECU pulses the pump based on measured fuel pressure.

Open loop is just "Use X duty cycle at Y RPM and Z load". It works well if you have a regulator already in use and just want to back down the pump speed at low RPM and load.

I would run the regulator as normal and pulse the pump. Allow the regulator the final say in fuel pressure. Do open loop pump control to slow the pump down. That'll be the easiest way to get started. If it doesn't solve your issue, look into going further. 

School me please... Would using the regulator in open loop mode whilst pwm the pump not result in having fuel pressures all over the show?? 

A FPR is usually getting a fixed pressure so regulates to a certain pressure that rises with boost if needed

If the supply pressure  to FPR is changed surely idle pressure will be way below what's happening up the rev range? Or is that normal and you just tune to that? 

As long as the pump is still supplying somewhat more fuel than needed to maintain target pressure, the regulator will still regulate to its target pressure (it'll just be dumping less back to the tank to get there than if the pump were running flat out). 

rslifkin said:

As long as the pump is still supplying somewhat more fuel than needed to maintain target pressure, the regulator will still regulate to its target pressure (it'll just be dumping less back to the tank to get there than if the pump were running flat out). 

Oh ok. I really thought that wouldn't be the case. I'm heating fuel and notice my base pressure dropping off as the pump becomes more inefficient... Basing my assumption from that. 

Open the open loop pump control table and lower the duty cycle down to the lowest amount you can get it without fuel pressure falling below what the regulator is set for. You'll be able to slow the pump down and still let the regulator take care of maintaining pressure.

If its a Racetronix pump, they're known for pressure falling off when they get hot. 

In reply to AwesomeAuto :

Thats a plan then... 

Thnks all..