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MAP / fuel pressure typical delay times

Murray_Calavera
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Murray_Calavera Mentor

Murray_Calavera

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Hello my tuning friends 

Just wanted to bounce some thoughts around here. What would you consider a normal time for fuel pressure to catch up to boost pressure?

Say your cruising at 4000 rpm at around 10% throttle, then you pin the throttle, how far behind the MAP pressure would you expect the fuel pressure to trail / how long would you expect it to take for the fuel pressure to catch up? Would you expect it to be linear, say the fuel pressure trails perfectly behind MAP by 2 psi and then when boost stabilises at the max setting, fuel pressure also stabilises?  

Reason I ask, very recently the fun police inside my ECU said no no to this happening (see attached picture) 

I've got the sad's looking at the data. Looks like my fuel pump isn't keeping up :(. Will have to think about long term solutions...

The silver lining is, the car drives fine. If you didn't look at any data you wouldn't know anything is wrong. 

FP lagging.jpg

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Murray_Calavera Mentor

Murray_Calavera

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I installed this pump just over a year ago -

https://aeroflowperformance.com/af49-1057-525lph-e85-hi-flow-fuel-pump

Do we think the pump is starting to fail, or should I be looking at anything else in the fuel system?

When it was originally installed, everything was fine. I checked the 98 and e85 tunes, all good. 

For quite a while now, maybe 8+ months I've been on 98 only and the pump has been keeping up. But now that I've put e85 in it (the tank is currently about 50% ethanol) the pump suddenly can't keep up. No idea what's changed in the past year to upset the pump. 

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robbo_rb180 Veteran

robbo_rb180

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1 hour ago, Murray_Calavera said:

I installed this pump just over a year ago -

https://aeroflowperformance.com/af49-1057-525lph-e85-hi-flow-fuel-pump

Do we think the pump is starting to fail, or should I be looking at anything else in the fuel system?

When it was originally installed, everything was fine. I checked the 98 and e85 tunes, all good. 

For quite a while now, maybe 8+ months I've been on 98 only and the pump has been keeping up. But now that I've put e85 in it (the tank is currently about 50% ethanol) the pump suddenly can't keep up. No idea what's changed in the past year to upset the pump. 

I would not recommend using any of the aeroflow pumps. Very prone to failure.

*I use and recommend a lot of their products. Fuel pumps are still best to stay with the big player's TI, Bosch, Pierburg

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GTSBoy Grand Master

GTSBoy

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3 hours ago, Murray_Calavera said:

It's the same age, just over a year old. I'd be surprised if it was an issue.

It's less about the sock and more about what might have been shaken loose from the tank walls/floor maybe by E85 or summat.

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Murray_Calavera Mentor

Murray_Calavera

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22 minutes ago, GTSBoy said:

It's less about the sock and more about what might have been shaken loose from the tank walls/floor maybe by E85 or summat.

Yep a thing for sure, in this case though I've been on e85 for many years. Maybe 6 or 7 years? Can't remember, but a long time now.

But yeah, looks like I'm going to have to swap out the pump for the 3rd time now, so we'll get to see what the sock looks like anyways. 

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Murray_Calavera Mentor

Murray_Calavera

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23 minutes ago, Dose Pipe Sutututu said:

Nek minnit PRP mechanical fuel pump and in bay surge/prime tank 

https://www.platinumracingproducts.com/products/platinum-racing-products-intermediate-mechanical-fuel-pump-kit-to-suit-nissan-rb-twin-cam

 

lol they are sexy. 

My imaginary car would run a big boy electric fuel pump though. Maybe 2 of something like these in tank - 

https://fuelab.com/91901-1000hp-in-tank-power-module-fuel-pump/p327

But knowing my luck, I'd find out fuel lab can't make pumps and I'd be pulling them out again anyway lol. 

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Murray_Calavera Mentor

Murray_Calavera

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I haven't logged any data yet, but I wanted to bounce this off everyone while I'm waiting to take the car out for a proper run. 

So the car was very hard to start this morning, finally fired and I took it to Supercheap to test the battery. Turns out the battery was low on voltage (can't remember the exact figure) and down about 250cca from where it should have been. Even though their simple battery tester said the battery was "fine, just needs a charge" they replaced it under warranty, pretty happy with that. 

Could a failing battery be the cause of the pump failing to keep up? The pump is pretty hungry, it pulls something like 20 amps from memory but I don't know how much this all matters when the car is actually up and running and the alternator is doing its thing. 

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GTSBoy Grand Master

GTSBoy

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1 hour ago, Murray_Calavera said:

Could a failing battery be the cause of the pump failing to keep up?

Yeah, but maybe not. Maybe yeah. Maybe not. You know how it is. I mean, if the volts are low and the pump has reduced capacity, then it will maybe not be able to supply enough fuel to keep up with your peak demand, but it really shouldn't make it go lean as you're ramping up, then catch up again. The pump dynamics are (should be) a pretty instant trade off between flow rate and pressure, and even that shouldn't matter because it is actually the job of the fuel pressure regulator to take care of that dynamic, leaving the pump to see pretty much the same pressure and flow conditions any time the engine is running.

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Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

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1 hour ago, Murray_Calavera said:

Could a failing battery be the cause of the pump failing to keep up?

Maybe go log your voltage vs. RPM as you doodling around town. The issue could be your alternator is cactus which has been supplying fluctuating voltage to the rest of your car thus killing your pump early.

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Murray_Calavera Mentor

Murray_Calavera

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15 minutes ago, Dose Pipe Sutututu said:

Maybe go log your voltage vs. RPM as you doodling around town. The issue could be your alternator is cactus which has been supplying fluctuating voltage to the rest of your car thus killing your pump early.

Should I be logging ecu voltage or battery?

Edited by Murray_Calavera
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