Rb20det Afr Issues

[nicksamaniac]

So im at a loss on what wrong, time to ask?

Bought an 89 r32 gtst m-type rb20det.

Had it about 2 months now, and slowly been starting to run worse and worse.

Was running well when I got it, been using it as a daily (my other cars are a 260rs stagea and a rb30det patrol) so was after a stockish type car, lower fuel use etc, but lately has been randomly playing silly buggers on me.....

1st time, got in it to go to work at 5am, started it up and only 3 or 4 cylinders running?

Took my other car, that arvo I pull the plugs, completely sooted and fouled, put some new bcp6res set to 0.8mm, all good for a while, 2 days later starts missing and coughing, randomly not a solid fault so I assume ignition problem so I Swapped the ignitor for my other cars, problem goes away.

Then a Week later, while on the highway it randomly starts missing again, but goes away?

Happens every so often for a few kms,

Then nothing for a few days, but develops this hectic hunting, like 200rpm up to 1600 back and forth, till it eventually stalls.

So I begin fault finding, changed the fuel filter, no difference, decided to go all out, put my wideband o2 gauge in from my patrol, find its running 10:1 @ idle, so this is my hunting/stall/fouled plug issue,

But!

Anything over 2000 rpm its 17+ afrs.

(Dont know how long its been doing this for?!?!)

Light throttle it has no fuel, I dare not boost it!

So then I think, ah ha! Fuel reg is stuffed, change the reg, install t piece to test pressure,

All good, 43.5 at idle no vac, 36 with vac, take it for a drive and pressure rises with boost but still I have bad afrs?

The hunting problem is fixed,

Afrs are 14-15 at idle, but if I hold rpm at 1500, it drops to 18:1?

So then I checked the fuel pump, thinking its not keeping up with rpm/load,

Pulled it out, put my spare Walbro 255 in, gave it the 12v power mod to eliminate the dropping resistor.

Drove again with the gauge to check pressure, still in spec.

Sooo, then I think well it must be afm related?

Its obviously reading the wrong load.

So swap to a known working afm, same issue, I test the afm wiring back to ecu, found some high resistance on earths, fix it, tests up all good, but still the same issue with lean afrs!

I removed the fuel rail, checked everything is clean, baskets are clean, put it back together, same issue.

So then I put my pfc out of my patrol in, load a stock rb20 tune, start it up, everything is reading correctly......

But same issue!

Here's whats been tested.

-fuel pressure is 100% in spec.

-pressure tested inlet/cooler pipes to 15psi.

-tested for vac leaks on inlet with aerostart.

-tested all earths, to ecu and sensors,

-12v checked at injectors, afm, ignitor, ecu

-no faults at ecu logged.

-tested/swapped afm

-tested/swapped cas

-tested ecu wiring inputs and outputs

-

Mods list.

-fmic

-3" turboback exhaust

-pod with enclosed box

-rb25det turbo (45v3)

-Walbro 255l intank, wiring mod done,

Stock 10psi boost, gate only.

Stock fuel system, injectors, rail, reg, (except pump)

When I drove it with the pfc, I logged a run to see if I could find probles during playback

Using fc datalogit but nothing out of place via what I saw, except the lean afrs.

PLEASE HELP ME!

Im out of ideas, and getting general unhappy with it!

[KiwiRS4T]

Get injectors cleaned and tested?

[XGTRX]

What's the timing like?

Check the pfc advance and the check it with a light.

[nicksamaniac]

Yeah checked timing is set at 15' base, and tried the cas from my patrol, no change.

[XGTRX]

Did you check various rev ranges to see if there weren't any variances?

If no check it as I have had this problem before with similar symptoms.

[nicksamaniac]

All the way to 8000rpm is 17:1 or higher, it will spike richer if stabbing the throttle but i assume thats due to acceleration enrichment. If i hold any rpm steady (while parked) its just lean.

[nicksamaniac]

What ended up being your issue xgtrx?

Ive run out of things to check?

Ive done every test that the workshop manual says, everything checks out as per the book, im out of ideas?

Its running exactly like the injectors are only opening 50% of what they should, like its faulted at an exact value, not intermittent at all if that makes sense?

[thewayweroll]

We have had several RB20s that do similar things when you put a pod on and move the AFM and filter closer to the turbo .Extending it back out usually fixes it straight up

[nicksamaniac]

I might try that?, don't think its my issue as it was running fine before.

Its still the stock turbo inlet pipe, afm is still in the corner stock airbox position but ill try anyway.

[XGTRX]

Mine was the timing fluctuating. Cas issue. intermittent advancement. Thats why I said to check the timing at different rpms cause it costs nothing and easy to do. I have heard of that afm issue also with the pod and modded position.

See how u go.

[Dose Pipe Sutututu]

2x things that come to mind.. especially with our aging old cars.

1. That rubber hose that goes to the aux air control unit, it comes off the cross over/J-pipe.. those tend to break with age

2. PCV playing silly buggers

try blocking both of them and see what is going on.

[nicksamaniac]

The iac valve has a new pipe, as i deleted the air regulator when i removed the rail to inspect the injectors,

I tried blocking the pcv pipe but made no difference, i also made sure the valve is checking correctly and free moving.

[nicksamaniac]

Have spoken to previous owner (we keep in contact as he owns my old stagea!)

He told me last big service it had, it got timing belt, plugs, splitfire coils (#5 had failed/was failing)

Filters, oils, injectors serviced,

Few other no engine related jobs.

All this was backed up by me actually having a read of the recipts he gave me with it!

Im really at a loss for ideas of what's left to check?

[KiwiRS4T]

Borrow a fuel pressure gauge - there may be a blockage or a leak somewhere. You are not getting enough fuel for some reason so check the physical flow.

[Dose Pipe Sutututu]

or somehow you're introducing foreign air somehow

[nicksamaniac]

Like this, done this on the first day of fault finding, thinking it was my problem to start with

[XGTRX]

Ha ha I think you are right.

[nicksamaniac]

Ok, update, tested every circuit from sensor or actuator bact to the ecu, all continuity checks are spot on excellent condition.

Tested fuel pressure again while driving, all 100% correct.

Pressure tested the whole inlet circuit to 25psi, only leak point was the pvc, so i disconnected it and am running crank case to atmo (for the purpose of fault finding)

The pcv is now fully separate from the engine, check timing is set, tried 15' base and 20' base, proved no different while running.

so it has zero intake leaks, Injector bases started to leak air Slightly at 30psi.

All electrical is 100%, ecu code is 55 no malfunction.

Fuel pressure is 100% in spec.

Still idles at 10:1 off scale rich, afrs are all over the place while driving?

Wtf its got me stumped?

[Dose Pipe Sutututu]

hrms.. sticky injector?

[nicksamaniac]

It has now got my old injectors from my rb25de (engine was the head donor for my 30det) still running the same?

I seriously cant fault anything, ive even started again from scratch thinking i probably missed something.

But have come up empty, i even dud all the process flow chart checks from the wshop manual.

Im about to buy a 25 and harness to drop in and just replace this pos!

Id read heaps of threads on 20 issues, and thought id never own 1 cos there obviously no good.

But decided id give this one the benefit of doubt cos i liked the car.

So here i am with 1 and it has issues!

What do ya know!