too much fuel pressure

**KIRCHNER** · 11-26-2024, 03:53 PM

trying to stop surging on my 2.4 efi, rigged a remote gauge. slowly crept up from 36lb to 60 wot. has new regulator, return line no obstructions, idles great normal pressure. at speed pedal seems to have dead spots,engine goes flat, except for w o t. when i back down, pressure stays high, engine sounds good. i was expecting low f pressure! any ideas?

**donmac** · 11-26-2024, 07:36 PM

sounds like tps issue with dead spots in throttle! have you checked voltage @wot . , you running weldon pump?

**KIRCHNER** · 11-26-2024, 09:01 PM

YES, does sound like tps@ part throttle, 7.48v wot. Whats with the high f pressure. i have 2 regs, if i apply vacuum[my mouth] with a short hose, i cant budge either. at idle if i pull off the vacuum line, its nothing like automotive vacuum, much weaker, maybe 16'' not enough to move that diaphragm, i m o.. running stock pump,vst, new float 2.4,220.

**skialot2** · 11-26-2024, 10:03 PM

Sound like a defective regulator. Max pressure should be max pressure. It shouldn't matter what the TPS is doing. Max pressure should still be whatever it is set at. High pressure will make it run rich, causing flooding. If the pressure is varying, it could cause surging.

**David - WI** · 11-26-2024, 11:22 PM

Assuming the fuel pump doesn't flow more than the regulator can get rid of.
What's the battery voltage st WOT? You may just be pumping way too much fuel once the battery is fully charged.

**skialot2** · 11-27-2024, 12:53 AM

Originally Posted by David - WI

Assuming the fuel pump doesn't flow more than the regulator can get rid of.

If the fuel pump can flow more than the regulator can get rid of, he would need a better regulator.

**David - WI** · 11-27-2024, 03:16 AM

Originally Posted by skialot2

If the fuel pump can flow more than the regulator can get rid of, he would need a better regulator.

No kidding?

Or, possibly a better voltage regulator... depends what the problem actually is.

**KIRCHNER** · 11-27-2024, 08:03 AM

ibought a second reg, both act the same. 12.6v wot. why would voltage affect f pressure? my scharader v is at the bttom of fuel rail, pump is external, stock early 2.4 laser.

**LakeFever** · 11-27-2024, 08:41 AM

It’s hard to know what’s going on by reading this but it looks like your actual fuel pressure setting on the regulator is 60psi. For whatever reason when the motor is at idle the vst pump is only putting out 36psi. Maybe low voltage or amperage at the vst pump until the motor winds up?

**KIRCHNER** · 11-27-2024, 06:17 PM

i spoke with 2 of the best merc mechanics out there, there stumped. should be high at idle n loose pressure as rpm goes up. the reg is non-adjustable. put a vacuum pump on 1 today, wouldnt budge. im ready to cut 1 open & see whats goin on. did the tps also voltage nice smooth full travel. btw why is there a in-line filter on a vacuum line?? my 2.5 has one too. maybe its not vacuum at all??

**David - WI** · 11-27-2024, 07:09 PM

If the fuel pump spins faster at higher voltage... and the fuel pressure regulator can only divert so much fuel, it would be the same as a restriction in the return line.

Look at the difference in flow between 12.0v and 13.5v...

Click image for larger version.

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**FORBESAUTO** · 11-27-2024, 08:06 PM

If pressure isn’t rising when removing the vacuum line or dropping when applying vacuum, sounds like there is an issue with return side not allowing fuel to enter back into VST like blocked passages excessive low fuel pressure etc. Try pinching off the line from pulse pump temporarily to allow fuel level in vst to drop and see if it helps. If not I would trace out the return circuit from the regulator back into vst. Being it’s rising with rpm makes me wonder if low side pressure isn’t rising with rpm making it impossible to return? Just a thought

**KIRCHNER** · 11-27-2024, 09:04 PM

tha,nk you for the input. could the mech pump overpump? on the hose everything seems normal. only we i get on plane the pressure climbs. i traced the return passage, took the top off the vst, all clear/clean. seems the regulator[s] original and new dont function. the vacuum pump test said 25'', the reg didnt open, why didnt the hose collapse? from the suction? dont know what to believe anymore, ArtK,

**FORBESAUTO** · 11-27-2024, 09:41 PM

Wouldn’t think it could over pressure, but who knows. Just another thought, the vacuum line for regulator is on the intake side of the reeds and not somehow got crossed up and hooked up to the crankcase side causing pressure to be applied to regulator raising pressure with rpm?

**KIRCHNER** · 11-28-2024, 08:44 AM

Originally Posted by FORBESAUTO

Wouldn’t think it could over pressure, but who knows. Just another thought, the vacuum line for regulator is on the intake side of the reeds and not somehow got crossed up and hooked up to the crankcase side causing pressure to be applied to regulator raising pressure with rpm?

i will check that, a possibility for sure,, thks