rb20 wont run at 14psi?

[dwhe009]

i cant be my fuel pump as i can see it still holds 60psi while on boost.

fuel ratios good.

im quite a poor bugger so i might look at replacing the airflow meter if this is the problem, ( i cant afford z32+ retune)

although, it must have something to do with the knock sensors as the cut does not appen at 14psi, with the timing turned right down. ( wouldnt this be same airflow?) i.e. @ 14psi, cuts with normal timing, @ 14psi does not cut with very retarded timing. The same airflow is going through the motor, its just firing at different times.

Does this not eliminate air flow meter problem?

[Cubes]

Its definately an interesting one..

I would really like to know why the fuel cut occurs. If it is really a knock sensor that causes it.

[The Alchemist]

as far as I'm aware the knock sensor retards timing when it detects knock...it does not cause the engine to "cut" out.

A "cut" could be caused by an ignition missfire from a bad coil(s) , very likely, or an AFM voltage drop out which happens when they age and the power regulator that holds the voltage constant across the AFM sensor drops out. This causes a 0 (zero) voltage reading and an instant engine cut out. Can easily be seen happening with a scope on the signal return for your AFM.

Worth checking anyways..

Mike

[Col-GTSX]

Ok.... exact same problem with my old car RB20 silver top fitted...

Was a boost cut cause by 2 things...

1. AFM was maxed out.... Ecu resets the hot wire causing no power for about 4 seconds

This was sorted by going a Z32 AFM and adapter....

2. Once this was fixed the engine would shutter and be all like go,stop,go,stop... this was caused by low fuel pressure. I bought a rising rate and this solved that problem...

[Mr GTS4]

well i tested this.. i bled my boost to 14psi last night and i had no cut at all. zip, nutin... don't know what the go is.

i think you should reset your ecu, check the plugs on your knock senors, clean out your AFM and filter, check plugs and test coil packs and this should fix your problem and make your car run alot smoother.

[Cubes]

The cut has absolutely nothing to do with the coils.

It isn't a miss-fire it is a total fuel airflow related cut.

The slight detonation could be caused by the fuel cut as it may cause a lean out at the last second when fuel is cut. Hence why the PowerFC pro doesn't just cut fuel but cuts ignition also. If you run NOS you do not want a fuel cut.

I tried 2 AFM's and it made no difference. Its the limitations of the stock ECU.

dwhe009,

If you are getting a cut lower than most people (14psi compared to my 17-18psi) then think of it as a blessing. The same amount of air is getting in to your motor a few psi easier than the rest of us on the stock turbo.

I would also get your car on the dyno and make sure it isn't leaning out.

Unless you are running a Wideband O2 sensor then the Jaycar AFR meter is ok for general checking of the afr's BUT it won't show real time afr's as the std O2 sensor is too slow to do so.

It may very well be shooting up in to the 14's in a fraction of a second as mine did on 17-18psi and now on the rb30det when running 8-9psi.

I set my boost to just under the cut at 16psi (on cold nights I had to set boost to ~14psi as it would cut in the higher gears, normal days nights 16psi was fine)

With a wideband O2 sensor on the dyno its hard to catch the afr's visually as the afr's go lean very quickly.

12-13:1 is too lean for a stock setup. It should be running well in to the 10's on 14psi like mine used to.

16psi was in the 11's then 17-18psi would start to lean out hence I think the reason for the fuel cut?

I would be looking at your turbo, maybe it isn't a stocker but a rb25 turbo?

Or maybe it is a stocker that has been rebuilt with a new slightly larger core as the old one may have hacked the housing a little that required a slight machine out.

While you are playing around replace your fuel filter (if older than 6months) and & the fuel line hose (especially the one under the fuel filter). Be sure to get Fuel injection fuel line not just std. stuff. Shop around some places sell it for $20 a metre others $10 a metre.

I think your barking up the wrong tree with regards to playing with ignition timing. Leave it at 15degree's.

If I retard the RB30DET to anything less than 15degree's I get detonation in the mid range. Advance it slightly and the flat spot dissapears.

The same used to occur to the rb20det.

Retarding the timing gets slightly better boost response BUT you don't make the power. This is what I noticed anyway. It sounds like the turbo spools really early.

Similiar to cold morning starts how the ecu pulls ignition timing out as to warm the car up quicker creating a slight flat spot that makes boost really easy feeling or if the TPS is incorrectly adjust a really bad flat spot feeling.

EDIT: Have you got the origional mesh on your afm or have you removed it?

[dwhe009]

cubes,

the air flow meter has the oringinal mesh. Why, what does this do by removing it.

It is definately the oringinal turbo.

The Alchemist,

I will try to watch the signal from airflow meter today. Cant use my oscilliscope cos it runs on 240V, ha. I hope multi meter will be fast enough to see what is happening.

[Cubes]

Removing the mesh for myself caused the car to run slightly richer & also have a bit of an idle hunt with a nasty jerk when I would back off boost quickly. Its like the air would try to go back through the afm and dump some fuel in I am unsure.

I put the mesh back on and the car and it was nicer to drive. BUT the only down side was the mesh does make a bit of a difference to spool. I swear it spooled earlier.

But this could be due to the slightly richer mixture through the mid range making more power (Nissan RB20DET's tend to run fairly lean in the low to mid range when making or coming on to boost, richening up the mixture picks up a little power here).

[dwhe009]

ok, heres a update on my problem.

have been driving up and down motorway at 14psi today. Had a multimeter hooked up to air flow meter output. It showed correct values of 1V at idle and 1.5V at 2500rpm with no load.

Was doing runs in 3rd gear from about 80kms and the cut only happened once.

The air flow meter voltage goes right up to 4.8V at full throttle at around 5000rpm, but the fuel is not looking to good. I am seeing 50psi fuel pressure here and not good 14:1 ratios ( keep in mind i only have a jarcar meter hooked up to standard oxy sensor, not very accurate) . This must be leaning out due to fuel pump running out?

It was starting to ping......

Am i right in saying the fuel pressure should be 45psi + boost (15psi)= 60psi?

[The Dan]

3LIT3 FORS3,

                     how can a r32 have a boost cut, it has no map sensor. Cant it only have a airflow cut?

If a coil pack was dodgy, then one cylinder would just miss, not cut. wouldn't it?

When you say 90% of all R32 sylines have error 34 come up, this is bull, that would mean 90 % of all r32s are running like crap.  any error code makes the engine run with much less timing and richer fuel. Plus this error code has only been happening since i upped the boost over 11psi.

Would you like me to take a photo of my Map sensor and post it to ya.

And no the error code doesn't make it run like crap either.

I ran 18 PSI through mine for 2 years with code 34. replaced them and still get it, replaced harness and still get it. replaced computer and still get it.

I know 20 other skyline owners with error code 34 and they all know people with it also.

Maybe your intake pipe before the turbo is sucking closed or something. The 32's are renowned for it. Fork out 75 bucks and get a run on a dyno where the guy can watch what it's doing, then you will have a better idea of what's going on.

[The Dan]

ok, heres a update on my problem.

have been driving up and down motorway at 14psi today. Had a multimeter hooked up to air flow meter output.  It showed correct values of 1V at idle and 1.5V at 2500rpm with no load.  

Was doing runs in 3rd gear from about 80kms and the cut only happened once.  

The air flow meter voltage goes right up to 4.8V at full throttle at around 5000rpm, but the fuel is not looking to good. I am seeing 50psi fuel pressure here and not good 14:1 ratios ( keep in mind i only have a jarcar meter hooked up to standard oxy sensor, not very accurate) . This must be leaning out due to fuel pump running out?  

It was starting to ping......

Am i right in saying the fuel pressure should be 45psi + boost (15psi)= 60psi?

There is no way you are going to get 14:1 ratios at 5000 rpm. Try something like 10:1. you'll only get 14:1 when you are cruising and even then it goes up and down constantly as the computer monitors sensors.

[The Dan]

ok, heres a update on my problem.

have been driving up and down motorway at 14psi today. Had a multimeter hooked up to air flow meter output.  It showed correct values of 1V at idle and 1.5V at 2500rpm with no load.  

Was doing runs in 3rd gear from about 80kms and the cut only happened once.  

The air flow meter voltage goes right up to 4.8V at full throttle at around 5000rpm, but the fuel is not looking to good. I am seeing 50psi fuel pressure here and not good 14:1 ratios ( keep in mind i only have a jarcar meter hooked up to standard oxy sensor, not very accurate) . This must be leaning out due to fuel pump running out?  

It was starting to ping......

Am i right in saying the fuel pressure should be 45psi + boost (15psi)= 60psi?

Do a fuel flow test. Hook 12 volts directly up to your fuel pump fuse and get someone to hold a line into a milk bottle (2ltr). Time it and see how much you get after 30 seconds, then double it and that's what it's doing per minute. You should be getting around 2-2.5 litres per minute from memory.

[tomj]

dyno run will tell you all you need to know

dont risk popping an engine for the sake of 70 bucks

[Cubes]

The air flow meter voltage goes right up to 4.8V at full throttle at around 5000rpm, but the fuel is not looking to good. I am seeing 50psi fuel pressure here and not good 14:1 ratios ( keep in mind i only have a jarcar meter hooked up to standard oxy sensor, not very accurate) . This must be leaning out due to fuel pump running out?

This is exactly what happens to mine as the cut occurs. Fuel AFR's go extremely lean then cuts.

I really don't know what it is, the only explaniation is the airfow value has ran off the ecu's map. hence it uses the last value from the map which will eventually cause the motor to run leaner and leaner until a point where the ecu decides enough is enough.

Maybe its a safety feature that takes samples from the O2 sensor where if the car is under load and it gets anywhere near 14:1 it will cut fuel to prevent major damage.

[BHDave]

Fuel pressure is 2.5bar base (unless you have an aftermarket reg and have set it higher) so around 37psi (2.5*14.7psi). so 50psi at 14psi boost is pretty much spot on.

What this means is your fuel pump is fine and your reg are fine.

The 2 things to check at this stage are your base timing and your a/f ratio

for an accurate a/f reading get it on a dyno. Before you do that get yourself a timing light and a 1 foot plug lead that you can connect to number 1 spark plug and jam the other end in the coil, take your reading off this as it gives a much better result than using the loop at the back of the head.

Forget about the knock sensor at this stage, disconnect it when the car is on the dyno, theres a 2 pin plug near the ignitor that plugs into the 2 sensors that you can trace.

If it is running lean then it may be the injectors, or a possibly a single injector. I have seen a good dyno operator diagnose this problem with one power run and he even pointed to the cylinder that was running lean and causing the car to ping.

[grigor]

Would you like me to take a photo of my Map sensor and post it to ya.

Hi,

I'd like to see that photo.

The only presure sensor on a standard R32 is for the in dash boost gauge, doesn't do anything for engine management. Sorry.

[dwhe009]

3LIT3 FORS3,

Cheers for your great help

BHDave,

Are you sure about this fuel pressure, in the manual it says 2.5bar (37.5psi) at idle, and 3bar (45psi) with vaccum line on regulator off. ( i.e. 45psi base +/- manifold pressure) therefore at about 15psi boost, fuel pressure should be 45+15=60psi ?not 50psi?

Cubes,

cheers mate. Its just funny cos everyone goes on about the standard computer just going real rich at higher boost and i would be happy with that cos all i want is it to run safely at 14-15psi.

[dwhe009]

to everybody who says put it on dyno,

I know this would be the best way to slove the problem but im the kind of guy that loves to solve problems myself and not just watch someone else do it. I would rather blow up the motor than have someone fix everything and not knowing exactly what was happening and what he did.

The most fun about having a quick car is playing with it.

Thanks for all your help though

[Cubes]

lol.

Well, head out and buy that wideband O2 sensor, rip the injectors out and give them a clean and expect to spend big $$.

grigor is right about the ecu not sensing boost. It only sees air flow/density values.

[dwhe009]

Cubes,

am i right about the fuel pressure values?

If so then i will clean out all the lines and injectors, then put in another pump in paralell to the VL one i already have. That should stop it leaning out.