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Another What Is Wrong With My Car Thread.

Abo Bob

By Abo Bob,
in Engines & Forced Induction

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Abo Bob Grand Master

Abo Bob

Posted
Posted

Ok here goes, deep breath.

Car is R34 GTT, was auto running a ROM tune. Ran fine, 255rwkw.

Got manual conversion. Was supposed to get z32 AFM fitted and pfc tuned but dyno broke so took Z32 and pfc back out and back in ROM tune and stock AFM.

Car ran fine, some hesitation and very rich but went ok at all boost levels.

Got Z32 refitted and PFC fitted and tuned. 11.8:1 AFR. Ran nice for a couple of days.

Started getting high knock levels.

Took to a dyno where it ran 225rwkw and pinged and was rich off the scale.

Suspected AFM was faulty as voltages seemed high for any given rpm/boost level.

Seemed to get gradually worse. Day by day dropped the boost a little until it was 7 psi. No pinging there.

Changed z32 for another - no fix.

Found dodgy looking wiring to new afm. PFC was getting some voltage even with engine off. Told that PFC had been shorted by dodgy wiring. PFC sent to be fixed. Wiring fixed.

Put old ROM tune (stock chipped ecu) and stock AFM back in thinking it would run fine as it did before but it didn't. Pinged and rich as hell at 12psi.

Tried swapping CAS for a known good one. No change.

Checked base timing at various stages, fine.

So we have audible pinging at anything over 7psi. It's not leaning out, in fact it's very rich. It does it with PFC or ROM tune. Does it with 3 difference AFM's. Does it with 2 different CAS'.

What am I missing here?

SECURITY Grand Master

SECURITY

Posted
Posted

ive got no experience with the pfc so if its that someone else will have to help you out.

it could be your timing.

base timing on an auto is 20btdc, base timing on a manual is 15btdc. has that been sorted?

is the person that checking the timing leaving the clip that goes on the trigger wire open and not clipped?

my timing was off by 10 when i had the clip clipped.

blind_elk Grand Master

blind_elk

Posted
Posted

There was something (on here?) in the last week or so that V RICH mixtures can also cause pinging. Have you checked all the PFC maps? Fuel pressure?

The safest way to check timing is to insert a lead between #1 coil and #1 spark plug.

Abo Bob Grand Master

Abo Bob

Posted
  • Author
Posted

Yeah I've gotta get a lead to use for that. Do you think Repco or whoever would sell them?

I've been told less than 9:1 AFR can cause pinging. Haven't checked fuel pressure yet.

Didn't bother with pfc maps as it happens with both the pfc and the rom tune.

Sydneykid Grand Master

Sydneykid

Posted
Posted

Wow, this is going to be a guessing competition. Rich running is either too much fuel or not enough air.

My first guess would be the AFM/wiring, check the linearity of the AFM voltage at the ECU. It should be smooth/progressive as you increase the engine load.

My second guess would be to agree with Dunk, check the linearity of the TPS voltage. It should be smooth/progressive as you open the throttle.

Third guess, air leak somewhere after the AFM and before the inlet valves. More air is being measured (by the AFM) than is actually getting into the engine

Last guess is excessive fuel pressure, maybe the return line is blocked or the FPR failed. A quick check of the fuel pressure should reveal all.

Please let us know what you find

:rolleyes: cheers ;)

Abo Bob Grand Master

Abo Bob

Posted
  • Author
Posted

No the AFM output does not look ok. The Z32 was showing 1.3 volts at idle and I'm told it should be between 0.8 and 1.1 but I didn't check the RB25 AFM to see what it was reading nor do I know what it should be reading.

Also the z32 seemed to shoot up fairly quickly to 4.x volts but then take a while to go any higher. It was doing this even at 7psi of boost.

I'll check the things mentioned there tonight thanks guys.

paulr33 Grand Master

paulr33

Posted
Posted

yeah 1.3 at idle does sound high

im not sure the stock afm is that high at idle

yeah can u confirm vg30 is selected in AFM

also what are the % corrections on the airflow table

what does a map tracer look like for a dyno run ?

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