fuel pressure weirdness

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samnlou
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fuel pressure weirdness

#1 Post by samnlou » Wed Feb 22, 2017 6:15 pm

hey all

as always I have a zed with weird behaviour (yeah ok that seems to be the norm right!)

anyhoo...


the current weirdness in the Aus Zed is this - driving along no probs, but if you just take your foot off accelerator the motor cuts out.

Normally one would suspect a fueling issue - and they would be correct. I have replaced :
fuel pump (walbro 255)
fuel filter (repco)
all the rubber fuel line (except the one joining the two rail sides together - to be replaced when the engine comes out)
removed factory fuel damper
removed factory fuel pressure regulator
added sard regulator - 50mm (I think)
attached guage to regulator so I can monitor pressure when testing
TPS - just was not working correctly with crazy varying readings
plenum vac lines - all have been replaced with new line cos mostly old and brittle and yucky is not gonna work so well.

so fuel pressure under operating conditions is now working just fine, but if you run revs then just let accelerator go the fuel pressure falls to nothing. This leads to stalling, but if by some miracle it stays working then pressure slowly builds up.

One time last week the car had been running for a few hours when it did this (just round towning as ya do) and had to let the engine cool off before it would restart. Fuel lines and filter were crazy hot and it really was behaving like fuel vapor lock in a 70's car (I think it was one of the 36 degree days we were enjoying).

HUH!?!?!

Other issues I know about, but should not be related:
the AIC valve is stuck at 70 and is one of the remove the engine and sort it out tasks.
both O2 sensors have given up and are reading 0.4.


Anyway if anyone has a good suggestion I am all ears :) Well maybe just 2 ears but ya knows what I mean.
I don't have too many cars...
I just need a bigger driveway ;)

Lurker
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#2 Post by Lurker » Wed Feb 22, 2017 7:05 pm

Try checking all the vacuum/boost lines. Leaks in these often show up under deceleration

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TT_ZX
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#3 Post by TT_ZX » Thu Feb 23, 2017 11:22 am

Do you mean the IACV (Idle Air Control Valve) is stuck?

This sounds like a classic case of the idle being setup wrong. If the base idle screw is wound in the revs drop but the idle control valve will open to compensate for this. However when you lift off the throttle the revs will drop too low before the idle control valve can compensate and can often cause a stall.

Find a procedure to setup the idle correctly (workshop manual) and follow it. From memory this involves disabling the idle air control valve and setting the base idle to 650 rpm when warm. The idle air control valve when then lift the rpm to 750 when it is enable again.

Of course you want to check for vacuum leaks first because this can cause similar issue.
When in doubt................C4!

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lil-vulky
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#4 Post by lil-vulky » Sat Feb 25, 2017 2:15 pm

TT_ZX wrote:Do you mean the IACV (Idle Air Control Valve) is stuck?

This sounds like a classic case of the idle being setup wrong. If the base idle screw is wound in the revs drop but the idle control valve will open to compensate for this. However when you lift off the throttle the revs will drop too low before the idle control valve can compensate and can often cause a stall.

Find a procedure to setup the idle correctly (workshop manual) and follow it. From memory this involves disabling the idle air control valve and setting the base idle to 650 rpm when warm. The idle air control valve when then lift the rpm to 750 when it is enable again.

Of course you want to check for vacuum leaks first because this can cause similar issue.
I agree with this, I had the exact same issue after i pulled the plenum and done a few things, just had to reset the idle control valve and slight tweek of the base idle screw. I done a pcv delete which would explain the slight difference in air flow.

That's also the correct way to set it, pull the plug adjust base idle to around 650-700rpm then plug iacv back in and the idle should raise to about 850-950

http://z32.wikispaces.com/Idle+Control

samnlou
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#5 Post by samnlou » Thu Mar 02, 2017 1:04 pm

Thanks team :)

Yeah I had gone through all of this already (including replacing the faulty TPS) - been driving me buggy!

I have managed to make an interim (until I get the garage up and the motor comes out and everything in sight is deleted) solution.

Pulled the plug on EGR (slight improvement)
Pulled the plug on FIC/AAC (slight improvement)
Pulled the plug on PRVR (slight improvement)

reset butterfly at throttle body (when warm - effectively a warm idle adjustment) and re-adjusted the TPS to suit.

Now the car starts, even when it is baking hot (we been getting 35 degrees plus for a couple of weeks). Idles smooth, doesn't stall, acceleration is far better, halved fuel consumption. Woohoo!

For the interim I have left fuel pressure a little higher than it should be (4k/cm instead of 3.2k/cm).

Now to deal with the surging caused by ECU trying to compensate for no reading from O2 sensors :/

Not one problem at a time so not so much trouble shooting as trouble shotgunning. Fun huh ;)
I don't have too many cars...
I just need a bigger driveway ;)

samnlou
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hahahaha cry

#6 Post by samnlou » Sun Mar 05, 2017 1:14 pm

well it serves me right for praising the car a little...

setting the scene:

we had a thunder storm Wednesday night. very windy.

At some point someone has relocated the ptu, had not bothered tracing the wiring to locate it.

Wednesday I reversed the car in the driveway instead of forward like usual.

consequence:

I had one smell trip to do Thursday and the car was awful. guess where the PTU is - you guessed it right under the vent in the nose panel! rain, wind, electrical component = truck ride for the last 3km home. sigh it never pours but it thunders as well ;)


Ah well I have ordered an S2 PTU conversion which I will locate a little bit more sensibly. Shake of head...
I don't have too many cars...
I just need a bigger driveway ;)

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#7 Post by Hayd3n » Sun Mar 05, 2017 5:49 pm

ohh buggetr , but glad you found it

samnlou
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#8 Post by samnlou » Sun Apr 30, 2017 1:28 pm

so, with the replacement PTU is the car went better, but still not great.

Found myself with a day not involving helping other people so I devoted it to problem solving. After unplugging all the extraneous junk that will be removed later and cleaning the AAIC/FIC valves, but was still playing up.

The last thing in the manual to check is the MAF. Unplugged it, turned the kay and off it went. Bah should have known that would be a problem as well!

Anyways ordered a replacement (Which arrived faulty as well), so bought another one locally and off we go. Since then have done about 1500km on three tanks of fuel. Woohoo!

Have the new O2 sensors as well, but they are 12mm and the ones installed are 18mm. unghh. So it is still running with no O2 feedback so I am considering the k/l to be not so bad :)

Whoever gets this car from me will be getting a good deal methinks!
I don't have too many cars...
I just need a bigger driveway ;)

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