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R33 30/25 Misfiring Under Load No Boost

Caelen

By Caelen,
in General Maintenance

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Caelen Contributor

Caelen

Posted
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Sorry to start a new thread but from what I can find is evey1 elses issues seem to vary...

R33 running

RB30/25 combo, z32 afm, chipped ecu, bosch pump, Twin turbos, Greddy EBC, Built manualised auto box.

So as it goes.. drove car home from gearbox shop (after new box fitment) parked in driveway (car drove beautifully and was pretty much nursed home), came out next morning to check on dash wiring as cluster is not working, not knowing the the fuel pump switch is on the dash, long story short crossed fuel pump wiring as it was dodgy as shit (EEk), found the blown fuse replaced and re-assembled went to start it and the following

really hesitant in starting needs a bit of throttle to coax it into running then idles ok but wants to die every 30secs if not given a squirt on idle, wont boost under load but will rev freely on a single squirt but if pumped to rev up will cough and splutter. Under load wont boost can hold the throttle open 1/10th and seems to go ok but the second it goes down further dies out and feels like its on 2 cylinders but if accelerator pumped under load seems to want to go a little better but don't want to push it to detonation as still coughs and farts!!!

So this resulted in the following

New spitfire coils

New plugs (0.8mm gapped)

replacement (tested ok) ignition module

New z32 afm (and computer reset will stall when afm unplugged)

Pressure reg reading steady @ 45psi

Tried a known good Ecu (worse result and doesn't want to idle at all...)

Replaced CAS

Checked timing hasn't slipped (from top view seems ok, wound the motor over a good 8 times to see that marks lined up (didn't want to pull balancer to get cover off so viewed from top cam marks)

Hooked up Ecu talk software and no faults and read outs seem ok, pic attached of car on idle.

I'm desperate for an answer! About ready for it to go to the shop... Was thinking Racesolutions as im in the Penrith NSW area?

post-124075-0-59845600-1390429270_thumb.jpg

Ben C34 Grand Master

Ben C34

Posted
Posted

As it seems pump related I would check you are getting full voltage to the pump with car running.

Someone else's dodgy wiring is a nightmare, why is the a fuel pump switch on the dash?

Caelen Contributor

Caelen

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It is running standard in tank pump to push fuel to surge tank in boot,

then a Bosch pump under the bonnet, no idea why it is on a switch I was scratching my head at the same thing (stupid idea! considering it's just spliced into the standard wiring for the pump so remote power/ecu controls the unit switching on via relay as standard).

Regulator gauge reads a constant 45psi if it was a fuel pump voltage issue would I be correct in saying if it was to lean out under load the regulator pressure would drop to show this happening?

I get what your saying in that as the car requires more fuel the pump has to work harder to get it there with the same pressure (hence draws more power). So if it was a voltage issue I would see the gauge drop as it needed more fuel as it wouldn't supply the power. Correct?

Ben C34 Grand Master

Ben C34

Posted
Posted

Yeah that's true about the pressure, missed that bit, but we are just assuming that's the base pressure its tuned at. As you didn't do it is hard to tell. I would pull off the pressure reg vac line and prime pump, see what the pressure goes to, it should be higher than with engine vac applied. I would still check pump voltage.

Caelen Contributor

Caelen

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Ok, will throw a volt meter on when I get home and post up what it's getting on idle and under load.

I am relatively sure I have ruled out the possibility of a sensor fault and really does feel like it's not getting the fuel it needs.

I have held the fuel return line with a set of pliers and the motor on idle sounds stronger and more full if that makes sense but no difference in the rev range, with the bogging issue still the same, it is as if it's getting fuel as when in gear and the accelerator pressed past that point it wont die but will sit for a bit sounding like its on 2 cyl without stalling until I let off again if I pump the accelerator under load it will rev a little more but will start to pop and miss.

I'm thinking if the wires to the fuel pump crossed and shorted (and the fuse blew) could this still have caused damage to the pump that may only be evident under load??

Ben C34 Grand Master

Ben C34

Posted
Posted

Voltage is a constant 14.8, no difference when the vacuum line is taken off in regards to pressure reading.

with the car running? The fuel pressure should raise when you disconnect the line with the car ruining.
Caelen Contributor

Caelen

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Posted (edited)

So that issue sorted, car runs 3 pumps, 1 for nos and 2 for general supply one external one internal. Got that issue sorted and have the 2 pumps running that should. I now get a reading of 20psi but with other switch hits 100psi? Reacts and drops like it should but no fuel pressure with the 2 pumps, getting the voltage it needs? Now revs as it should (bit rich) but will break down on boost and i dont want to push it with such low readings

Edited by Caelen
Caelen Contributor

Caelen

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So car went to MRC at castle hill, got it back all running A1, was rich as hell and miss firing like crazy, got a false reading from fpr due to it only been in use for the NOS, guys did a really good job and car runs beautifully now! The best shop I have been to for guys who know skylines!

Caelen Contributor

Caelen

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Didn't have much time to leave it with them due to working hours and being able to pick it up. They had it a few hours did a safe tune on 10psi @241kw/atw has a bucket load more potential just needs an aftermarket ecu, tried running it on 18psi but cant get the niztune ecu to feed more fuel under high boost even with the software Mark was using just wouldn't let any more through. So no power run on high boost until I work out what to do.

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