Fuel Pressure drop at high RPM(Honda Fit)

[Skelly]

Has anyone had a problem with there Honda Fit dropping fuel pressure at high RPM? we have changed fuel pump, filter, injectors, engine harness and still having the problem. Any advice would be great.
Thanks
Sean

[chrisw52]

fuel pressure sensor?

[Messenger Racing]

PM sent

[Lotus7]

Maybe I'm overlooking something, but does the electric pump even know or care what engine rpm is?
Short of a massive over-demand by the injectors, which would be obvious via bad engine response, what could starve the fuel rail and result in a low P reading?

Or, is the engine+car demanding so much electric power at high rpm from a weak battery for some reason that the electric pump is an innocent victim and cant maintain pressure?

[Jon Jeffords]

Is the engine power dropping off with the fuel pressure? If not, it may be a bad fuel pressure sensor.

My Honda fuel pump was fine when it was cold, then would intermittently starting having pressure dropouts near the end of the sessions, with a noticeable corresponding drop in performance.

[Skelly]

Hi John
That is exactly what is happening, It starts out fine when its cold, but by the end of the session or day it starts having issues. The only problem is we have changed the fuel pump already along with the in tank filter and still having a problem. We are going to change the in tank regulator and try this again. thanks for all the advice.

Sean

[Jon Jeffords]

If you are logging battery voltage, check to see if your battery voltage is stable during the fuel pressure drops.

Do you have a switch on the dash to manually turn the fuel pump on and off? Could the problem be an intermittent internal issue with the switch, or the switch wires?

[David Ferguson]

Is the fuel cell venting properly?

[problemchild]

Is the fuel cell venting properly?

That was one of my thoughts.
You are not giving values which makes it more difficult to help. Does it fall from 45 to 38 or 10 psi?

Considering "in tank" issues, if you are losing pressure over time, then you are either sucking air because you have an issue with the internal hoses (which become exposed as fuel drops) or overheating something. Externally, I would take the regulator apart and look for broken parts or debris.

What happens when you boost the pressure?

When I was trying to use an external pump, the return needed to be specifically located so as not to dump air back near the pickup. I would have this same symptoms. The internal pump should not have this issue.

It is a pretty basic system, so if you maintain voltage, and have changed the pump, then it only can be the regulator, internal lines, or the vent.

Good luck!

[Skelly]

Car will be running fine, but later on in the day as it gets hotter is when the pressure would go from like 48PSI down to below 30PSI above 6000RPM for a brief second then go back up to 48 PSI.tried downloading screenshot. Hope everyone can see this.

[Messenger Racing]

I had multiple in tank HPD regulators give me trouble over the years - not sure why but I suspect sitting dry hurts them as they run many miles with modern fuel in street applications. I converted all of my Honda FF to external Aeromotive regulators and have not had a problem since but if I do I can diagnose and fix much easier. Good luck and thanks for sharing what you learn.

Jay

[Raceworks]

All the high RPM problems I've had have either been coils going bad or wiring issues.

Bad fuel pumps usually don't affect the pressure. The flow decreases and you have a lean running condition (light gray or white tailpipe). Bad regulators usually have low pressure all the time. Clogged fuel filters may or may not show up on the pressure sensor depending on where the sensor is in relation to the filter, and the "tailpipe test" works for them too. If you're only running the "sock filter" on the pump you really should run an external one as well.

I wasted a whole weekend chasing a high RPM miss that turned out to be a relay that rattled loose and was shutting off the ignition.

Another time we thought we had a fuel pickup problem (it only lost pressure in turns), which actually turned out to be a loose ground wire the driver's leg kept leaning into.

Check all the connection points for the fuel pump, plus any areas where the wiring might be making contact. You could have an intermittent short or broken contact issue.

The only other thing I can think of is if you have extremely high under-hood temperatures or badly-routed fuel lines / external filters you might be having some sort of "vapor lock" issue.

[fkennette]

My Mygale F2000 used to do this, and it turned out that the fitting on bottom of the fuel pump was sucking in the the bottom of the fuel cell, then releasing, then again, etc. Easy fix was to remove fitting and mill two small slots across it so some fuel could be sucked in from the side and this stopped the problem.

Hope this helps,
Francis