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Hi all, I have a 3.9 efi classic 1992, hard to start seems to be flooding either no spark or to much fuel tested air flow meter and showing 5 volts on red/black and blue/green wires think it should only be.3 to. 34 is there any way of adjusting these volts, I can adjust the Co's with Allen key on the back of meter, also been browsing through bay for parts and noticed a plenum which had a ball like object on top of throttle body mine has not got one, what is it and would it stop my over fueling,  don't suppose anyone in this area to help for couple of hours for some beer tokens I'm running out of ideas, thks dd

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If it's over fuelling it would either be coolant temperature sensor (NOT the one for the gauge) or the airflow meter.

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The ball object sounds like a cruise control bellow, so nothing to do with what you think.

Make sure your spark is strong, and make sure your collant temp sender is showing the right resistance, figures in tech archive.

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sorry for late update, got classic running steady but ticks over at 1000 revs can't seem to get idle right, still getting fuel in sump, downloaded rovergauge soft ware, comes up on laptop it was showing fault code on air control valve and i cleared it and has'nt come back, the fuel pressure gauge on laptop starts off 25 and after creeps up to near 50, but i don't know or if i should ajust it, i'm not computer minded, really need this sorted all welding done for mot need it running to get to garage, its also runs on gas but its empty had to remove for welding, was thinking of meggasquirt but have'nt got a clue where to start lol, dd

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I'm curious how your laptop knows the fuel pressure when the 3.9 EFI doesn't have a fuel pressure sensor :huh:

There's not much to the 3.9 system, if it's idling high it's either the stepper valve is letting air in by demand of the ECU, or it's stuck, or there's an air leak.

If it's putting too much fuel in it's either because the ECU thinks it should (airflow meter or coolant temp sensor), or because of a fault such as a stuck injector or fuel pressure regulator.

 

Megasquirt is great but won't fix a mechanical problem with the engine so you need to have it running OK before even looking at something like that.

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Posted (edited)

Check the fuel return pipe, the flexible parts have a habit of delaminating and blocking the return, results in excessive fuel pressure at the manifold (fuel rail) .

Easy way to check is to disconnect the return pipe at the regulator and put a piece of pipe from that into a jerry can or similar, if it fixes the problem, you have a blockage in the return line.

Edited by Dave W

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Make sure the diaphram in the fuel pressure regulator has not split. I have dealt with this problem before,it literally floods the inlet manifold with fuel and will quickly ruin the bores,pistons and rings of the cylinders which suck it in.

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thks for advice ally v8, how do i check fuel pressure regulator it looks like a sealed unit, fuel inlet and outlet little hose on the back, would it be ok take hose off and start it fuel should'nt come out correct?, dd

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