Fuel Pressure Priming

[xanatos]

Please forgive a n00b if this has been covered, but I didn't see anyone using this as a solution and wanted to run it by all the guru's on here. I'm wanting to have my car start as soon as I turn the key when cold instead of having to crank for the 4 to 5 seconds before the fuel system is fully primed. Because I'm on an aeromotive afpr, the system only stays primed for about half an hour before it goes back to atmospheric level. I was thinking about permanently or at least creating a clip to be placed under normal driving conditions on the B+ to Fp terminals in the diagnostic interface. I'm putting in a 255 LPH pump this weekend, so maybe I'm being premature in wanting to do this.

By doing this, I assume the pump will not be on with the key in the accessory or off position, but when I turn the vehicle to on, the fuel system will prime to which I can then start the vehicle and drive. Will there be any negatives or possible issues in driving like this. In essence I'd be removing the ECU control of the fuel pump I believe.

If this is not a good idea, short of running a short switch to place in the cab to prime my fuel system prior to cold starting my vehicle, is there another solution to prime the fuel system before starting?

Thanks a million guys.

 

[The Reaper]

the fuel system primes itself when you turn the key on

i think you need to check yur CSI its prolly dirty or not working properly

 

[MKIIINA]

the fuel system primes itself when you turn the key on

i think you need to check yur CSI its prolly dirty or not working properly

exactly. as soon as you turn the key to the acc/on position the fuel pump kicks on. this provides pressure to the rail and injectors but there is a small lag. just give it a sec and you should be good to go.

did you pull the efi fuse previously to reset the ecu.

 

[spipedong]

Most cars prime for a few seconds when the key is turned on, but in my experience the Supra's fuel pump doesn't start until you crank the car (ie, the ECU sees pulses from the CPS). I have a walbro, so it's very obvious when it's running.

 

[xanatos]

I believe that is incorrect that the fuel pump primes when the system is turned to on in my car. I don't see pressure until I actually turn the key to ignition nor do I hear the fuel pump if I just turn the key to the on position.

I don't think I have a problem with the CSI as I don't show any fuel pressure till the system attempts to start. (iginition) It's not a huge deal as it only takes about 3 seconds, but that seems like an extrodinary amount of time when your turning the car over compared to many other vehicles.

I know when I start my Rodeo, I hear the fuel pump kick in for a second when I first switch the car to on before proceeding to ignition thus priming the system. Perhaps I have something faulty if mine does not prime when the key hits the on?

Can someone verify that their fuel pump kicks in to prime the system when switched to on (not ignition) to kick the fuel pressure up in prep for starting? I just don't like having to turn the car over for more than a second when starting as that's a lot of wear on the starting system.

 

[xanatos]

Most cars prime for a few seconds when the key is turned on, but in my experience the Supra's fuel pump doesn't start until you crank the car (ie, the ECU sees pulses from the CPS). I have a walbro, so it's very obvious when it's running.

Yeah, what he said. LOL.

 

[spipedong]

Can someone verify that their fuel pump kicks in to prime the system when switched to on (not ignition) to kick the fuel pressure up in prep for starting? I just don't like having to turn the car over for more than a second when starting as that's a lot of wear on the starting system.

I can verify that it /does not/ do this on my car.

 

[shaeff]

snipedong is correct, it switches the pump on when cranking.

try jumping +B and FP in the diagnostic block to see if that helps. (this will turn the fuel pump on)

-shaeff

 

[johnathan1]

I was thinking the same thing, xanatos...

My fuel pump doesn't turn on with the the key in the on position, and my car takes a few seconds of cranking to start when cold...

When the car was cold, I jumpered the fuel pump, and instantly heard the fuel rail fill with gas...my car was no easier to start with the fuel system pressurized than it was under normal circumstances.

I'm thinking I have issues with my cold start circuit, either CSI, or something with the time switch, or wiring (which is very likely the problem).

 

[xanatos]

So all that being said, a semi-perminant jumper placement of B+ to Fp on the Diag Panel isn't such a bad idea? Anyone know if another member has rigged their system to turn the fuel pump on like this? If I really want to get fancy, I may add a momentary relay circuit that flips the fuel pump on for 10-15 seconds when the key is placed in the on position to prime the pump and then disconnects the jumper afterwards, thus placing the pump back under ECU control.

I'm gonna give it a spin as soon as I get out of work and I'll let everyone know how it turns out. I'm hoping it will be a much more immediate startup.

 

[johnathan1]

It shouldn't make a difference, Xanatos. It isn't starting right away like it should, because something isn't working right. You should try and figure out what it is, and fix it before you start making modifications, that aren't really necessary.

 

[xanatos]

News flash. Big difference. With the jumper installed, when I turned the key to the on position, my fuel shot up to the correct level, then by the time I turned the key, normal start time. I'm a bit uncomfortable leaving it jumpered all the time as I believe this bypasses the ECU's control of the fuel pump. I'll look into building a momentary on switch and wire it in so that I get a 10 second bridge on those contacts which should be ample time as I really only need about 2-3 seconds of priming time.

I don't believe there is any other issue with the vehicle, unless the fuel pump is getting old or with the new afpr, it's just slower to prime the engine. If I get a chance to install my 255 lph pump this weekend, I'll see if that makes a difference too.

 

[johnathan1]

Yea, please update the thread once you install the new pump...I'm curious to see what effect it will have.

 

[suprashy]

It shouldn't make a difference, Xanatos. It isn't starting right away like it should, because something isn't working right. You should try and figure out what it is, and fix it before you start making modifications, that aren't really necessary.

The answer doesnt get any better than the response above. Plain and simple. I think its your CSI. Did you clean yours? Many times, that is the culprit. It would take my car a few attempts to start, then I cleaned mine last fall, and now the car starts right up despite our current freezing temps.

Secondly, I imagine Toyota designed the fuel pump to come on with the car on, and not when the key is in the ACC position for safety purposes. Do you really want your fuel pumping if your car is not running? There's a reason why Toyota created the B+ fp jumper solution to test fp. I'm no expert, but these are my thoughts. Either way - good luck!

 

[mkiiSupraMan18]

seems kinda silly to me, leave for work/school 5 seconds early. :icon_bigg

Besides, that's 5 seconds of cranking getting the oil moving.

 

[jetjock]

What the last two posters said.

However if you want it to come on with the key and still allow ECU control over the pump simply jumper (if you have a GTE) the Circuit Opening Relay. It's job, as stated above, is to stop the fuel pump whenever the engine stops.

All vehicles utilize some method for this because it's mandated by federal law. In the GTE it's done by ECU control of the COR, in the N/A it's done by a switch in the AFM. Other cars use an RPM relay and still others use a G switch. In those cases you get automatic priming and still retain the safety feature. Since G switches and RPM relays are cheap and easily installed that's the best route to go if you're determined to do this.

 

[Dirgle]

^^^
Yes, as JetJock is hinting at it's there in case you get into an accident. Once the engine stalls it stops pumping fuel. This is important so that you don't continue to pump fuel to a broken line possibly creating a sever fire hazard. And if a fire does start it's easier for fire crews to put out since fuel is not being continuously pumped into it. I'm sure that’s important if you’re stuck inside the car. It's a very important safety feature.

If you get into an accident I guarantee one of the last things on your mind is turning the key all the way off. Not worth it for the convenience of starting a few second earlier.

 

[xanatos]

The answer doesnt get any better than the response above. Plain and simple. I think its your CSI. Did you clean yours? Many times, that is the culprit. It would take my car a few attempts to start, then I cleaned mine last fall, and now the car starts right up despite our current freezing temps.

Secondly, I imagine Toyota designed the fuel pump to come on with the car on, and not when the key is in the ACC position for safety purposes. Do you really want your fuel pumping if your car is not running? There's a reason why Toyota created the B+ fp jumper solution to test fp. I'm no expert, but these are my thoughts. Either way - good luck!

Not to come off as a know it all (cause I certainly don't know tons about cars...yet) I know it is not my CSI. I've already cleaned this, did it when I changed my headgasket. It starts fine when it's cold, as long as there is fuel pressure. If I pre-prime the line by jumpering prior to attempting to start the engine when cold, it starts up just fine. This has nothing to do with cold starts other than lack of fuel pressure. No fuel, no start.

BTW, please don't take my tone as anything other than a response to your concern. I see a lot of people who get defensive when someone responds and I don't want you to think that I'm getting this way. Just merely trying to clear up that I don't have a concern about the CSI or the circuitry surrounding that.

The purpose of my question here was primarily aimed at those people who have installed afpm's in their vehicles as it is commond for them not to hold fuel pressure where as the factory system, I believe, does. If you drop the pressure on any other vehicle to the fuel system, you'd have the exact same problem of the car not starting until adequate fuel pressure has built up in the system. The CSI is useless just like the regular fuel injectors without fuel in the system.

And to state on record, I did not have this issue till the afpr went in, thus leading me to believe that the inability of the afpr to maintain fuel pressure in the system for long periods of time after the pump has shut down is the cause. It even states so in the instructions IIRC. I'm just curious as to what other Supra owners with similar instances have done. I believe a couple of posts up, one of the members here is indicating that he has done exactly what I'm refering to wherein the FP primes the system from a momentary circuit which is activated when the car is switched to on. I stress that I'm not trying to get the FP to run constantly or in the accessory key position, only when switched to on and only for long enough to build pressure. My experiment last night shows that it does exactly what I thought it would. Make the car start normally since my problem is definately lack of fuel pressure.

 

[xanatos]

What the last two posters said.

However if you want it to come on with the key and still allow ECU control over the pump simply jumper (if you have a GTE) the Circuit Opening Relay. It's job, as stated above, is to stop the fuel pump whenever the engine stops.

All vehicles utilize some method for this because it's mandated by federal law. In the GTE it's done by ECU control of the COR, in the N/A it's done by a switch in the AFM. Other cars use an RPM relay and still others use a G switch. In those cases you get automatic priming and still retain the safety feature. Since G switches and RPM relays are cheap and easily installed that's the best route to go if you're determined to do this.

That's exactly what I was thinking about doing. Just a momentary (maybe as short as 5 seconds) circuit open relay that is triggered when the system is switched to on. Regardless, as I was planning on putting a larger fuel pump in anyway, I want to see what impact this has on how quickly the system is primed with the existing circuit.

 

[jetjock]

It's your car. Just want you to be informed is all.

There are several things that can effect starting depending on whether it's cold or hot. My car pretty much starts at the touch of the key either way but several times in the past I've mentioned priming using the methods stated. I even tried it on my car for a while but since it made zero difference I yanked it off. These days I only jumper the FP for troubleshooting reasons.

Although I don't have that afpr I'm puzzled why it won't hold rest pressure. I find it difficult to believe it'd be designed with such a basic flaw but as I said I'm not familiar. That'd certainly cause hard hot starts though. If I were you I'd check with aeromotive as to why it doesn't hold pressure and also check the fuel pressure up system to see if it's working.

An rpm relay will provide the pulse you're looking for while the G switch will turn on the pump with the key yet turn it off in a collision. Either can be easily installed in several locations. Best to put the rpm relay right at the diag block. The G switch goes in series with the pump anywhere convenient. If you get one with both NO and NC contacts simply use the NC contact to jumper the diag block or COR. There are lots of ways to skin this cat. Get one that can handle the pump current or use a relay to pilot it. You could also use the G switch to control the stock FP relay. It'd work fine but from a safety standpoint isn't optimum. However the odds are millions to one it'd cause a problem.

All that said put the new pump in and see what happens but I'd still resolve the loss of rest pressure if I were you.