Fuel pressure down, about to start stripping, any wagers on the culprit?

[Mike B]

Car has been laid up since Ryan mapped it in Jan, I've had a lot of jobs to get her tip top again and not a lot of spare time to do it in, so progress has been slow. That said, now I am on a mission...

 

The Svyecs is putting in a rev limiter at 4500rpm, so I logged it to see why, and after I trawled through the logs I found the culprit..

I have to say that once I got my head round the softwear and manuals the Syvecs is an exceptional bit of kit. Only a few session poking around but I'm appreciating it more and more.. Anyway, enclosed is the log pulled..

 

I have hardly any fuel pressure :-( 8.5 psi dropping to virtually nothing on boost. Thankfully the ecu is going into protection, I do think this is an essential thing to have on any tuned car..

 

So I started to play..

- Vacuum line is attached and I have logged sucking blowing on it and fuel pressure remains completely unchanged.

- Pressure regulator adjustment makes no difference. I logged winding it in and out and there is no change in fuel pressure.

- I felt and squeezed the inlet hose to the regulator, it's under hardly any pressure. I could nip it and stop the engine.

 

So,

Fuel pump...

- be surprised if it was this, as ryan fitted a new one when mapping, and mapped it at 620hp

- Fuel pump wiring is solid - direct from the battery with two relays, all checks out.

- Fuel hoses in tank, possibility of a split.

 

Fuel Filter...

- Replaced with a new unit in January, so I would also be surprised if it was this.

 

To be honest I am at a bit of a loss, and I think it may well be down to a bad fuel pump. Aside buying and trying a new one, Im not sure if there is any way i can test the pump. Makes noise and pumps fuel, but I suspect not enough...

 

any bets?

any suggestions?

 

and incase I want to do some reading, anyone suggest a high pressure, high volume fuel pump? I'm pushing my luck with 650's at 620 hp.. need good pressure and flow. Used to run 2x walbros and now running one pump (the pumps that ryan used in his race car).

[Ian C]

My money is on the pump

[dr_jekyll]

chek the voltage the pump is running at. i had low fuel pressure and it was because the old wire was breaking down. i was only seeing 4,1v at the pump. i ran a12v to test it and the pressure soared

[Andy Blyth]

- Fuel hoses in tank, possibility of a split.

 

50p on this option! Especially if the hose in the tank is not qualified to SAE J30R10.

[Mike B]

My money is on the pump

So was mine...

 

chek the voltage the pump is running at. i had low fuel pressure and it was because the old wire was breaking down. i was only seeing 4,1v at the pump. i ran a12v to test it and the pressure soared

I thought this too, but the cable that connects this pump to the battery (via 2 relays) is a super thick amplifier cable. It's very heavy duty. I also tested voltage running and ign, and was not seeing anything anything unusual.. 13v running, 12.2 idle..

 

50p on this option! Especially if the hose in the tank is not qualified to SAE J30R10.

me too..

[Mike B]

update...

 

Ryan looked at the logs.

The FP feed I am looking at / logging is relfp (relative fuel pressure) ie the difference between fuel pressure and manifold pressure,

FP1 which is further up the data feeds is zero, meaning that the sensor is not wired into the correct syvecs port.

 

The odd thing is that when I re-wired it I had thought I had wired it into the correct port.. enough to make the warning light extinguish, but I must have done something else.. so the focus has shifter back to the ecu and sensor interface. It's the only thing I had changed since ryan's install came home, so logically it's bound to be right...

I will chase later this morning :-)

[Mike B]

Fixed!

 

I WAS looking at the relative fuel pressure which was showing an inverse reading of the fuel pressure because...

The FPR was both wired incorrectly and sending no signal to the ECU, so the ecu was only showing the outcome of an equation where one half of it was zero..

Interestingly I had the sensor wired in such a way that it fed .85v to the ecu on 5v, but did not function properly. This was enough to extinguish the warning light, but also did not register in the softwear...

 

After quite a bit of faff I found the correct wiring instructions for the FP sensor from SP. Then, after I rewired, I could still barely get a reading from the thing. I was mulling over whether to order a new one, when I looked closer at the specs I found it was a 12v feed not a 5v feed like everything else... so I rigged the feed to 12v and....

 

Ta da!

 

47psi logged in the ecu.

 

 

Road test below. (blue is fuel pressure)

She's back to her normal savage self :-)

 

All this thanks to the new ECU, logging ability and knowledge in the form of Ryan and Wez (thanks guys) to stop me wasting time chasing dead ends. If you have a choice, get one, this and the CW susp and geo set are the two best things I have done to the car so far.

 

[dandan]

Well done Mike

[Ian C]

So not the pump then

[Wez]

Glad it's all sorted, added bonus that nothing needed replacing

[mellonman]

that is good news mate so ryan fixed it without even seeing the car , speaks volumes for the ecu, and your poor wiring skills

[Chris Wilson]

You can't beat a mechanical pressure guage on the feed to the rail for diagnostics. Just squeeze off the return (with engine off) and see what the pump makes dead ended, and what it makes return flowing, then measure flow volume in 60 seconds into a bucket. Diagnoses 90% of fuel pump issues in a few minutes. For sure electronic measurement with fail safe is great for normal usage, but i always trust a quality mechanical gauge over a sender and electronic gauge. It does help to RTFM / F1 when viewing logging though

[Mike B]

that is good news mate so ryan fixed it without even seeing the car , speaks volumes for the ecu, and your poor wiring skills

Guilty!! in my defense it was Ryan that told me it was a 5v feed... Problem started when when I retired the gauge, I also retired the sensor's power supply that the ecu was using...

 

You can't beat a mechanical pressure guage

It's true...

before stripping it would have been an easy test to save a lot of faff. I'm glad I sat and read more before picking up the spanner. Saved me a good few hours of scratting around on my back.

[mellonman]

You can't beat a mechanical pressure guage on the feed to the rail for diagnostics. Just squeeze off the return (with engine off) and see what the pump makes dead ended, and what it makes return flowing, then measure flow volume in 60 seconds into a bucket. Diagnoses 90% of fuel pump issues in a few minutes. For sure electronic measurement with fail safe is great for normal usage, but i always trust a quality mechanical gauge over a sender and electronic gauge. It does help to RTFM / F1 when viewing logging though

 

very true keep things simple less to go wrong,my mechanical pressure guage did help me pin point my fuel pump/ecu issue