Cold Pressure

[Joss]

Something I've noticed is that when cold, my R34's ECU seems to back off a bit when oil pressure goes over 6.4 (ish). I guess to protect the engine from you flooring it when cold!

Once it's hot, the pressure never gets this high (maybe 5.5)

So would the higher pressure (7) which Motul gives at cold exacabate this?

Cheers

[gary]

joss,
I am quoting oil pressure from my car only dont forget i have the HKS high capacity pump and nismo bearings my comments were from a test i have done on oil i have used the results were very positive,
if you have a lack of power when cold it would suggest to me you are overfulled and has nothing to do with oil pressure at all in fact the higher pressure will only help the situation.
In all the engines i have taken apart the one thing that is common to all of them is the fact that the big end bearings are through the white metal and the oil control rings are carboned up
and 9 times out of 10 the valve guides are on the limit the oil people are using aint up to the skyline but MOTUL is.
I will be posting the price stucture that i will offer the owners club
for a bulk purchase of engine diff gearbox transfer power steering
and coolant soon and for those who have allready contacted me that can see the advantage straight away your liquid gold is on the way.
Gary
GTART.CO.UK

THE FUTURETIVE

[DCD]

Joss, what oil do you use?
I'm currently on 15W-50 (300v)...but I can't report any similar things as its still quite warm here.
Next time I start up from cold I'll check the pressure

[Joss]

I think it's black oil

It's always done this ... from stone cold, when the pressue hits about 6.6 there's hesitancy from the engine (sort of like a missfire) I presumed it was a safty warm up mode feature.

It only lasts for about 5 mins of driving.

Mind you, my car does also have a backpressure problem which I need to get sorted so it could be this.

- Joss

[wroestar]

Joss,
I get that in the R32. You start the engine, give it a minute to settle itself, then pull away. The idle is at about 1200RPM and as you drive it seems to be holding back. Once I've gone a few miles all of a sudden (as the water is now up to working temp) she smooths out and away we go. (idle is now at 800 to 900RPM).......its a little like a 2 stroke Kart engine that's "fourstroking". You lean it off and suddenly it stops fourstroking and becomes a 2 stroke again. I know with the kart the fourstroking was caused by the 2 stroke mixture being too rich. I would guess that in a roadgoing 4 stroke car engine this is effectively the "choke" thats controlled by the chip which in turn moniters engine water temp. Once the temp gets high enough it reduces the amount of fuel.
Well thats my explanation....and I'm sticking to it!!!!
Its probably a load of Holyhocks
If it is please correct me I'm interested
Anyway Joss I hope it helps
Regards
Technical wroestar

[RobGalley]

Hi

My gtr33 does this as well - from cold very hesitant - 2 miles down the road, clears itself....I am sure when I got the car it never did it and it has since got worse....

Cheers
Rob

[Garry Keevash]

Likewise my GTR33 does this as well. When cold i.e. first thing in the morning it hold back and is hesitant - 2 or 3 minutes or a mile down the road is seem to correct itself and is fine. This has always been the case since I've had the car.

I have also noticed that on occasions my boost will be lower than normal say .5-7 bar if I stop and switch off and then start my journey again the boost often returns to 1bar. Also whan I am experiencing low boost when I throttle down and ease of several times is seem to rectify the low boost returning top the correct boost pressure is this a coincedence? This problem is intermitent and does not happen all the time. The car has stage 1 chip and has only covered 34,000 miles so I don't expect the turbos to be at fault.

Is the explination of the choke affecting cold start performance correct? This does stack up when remembering back some 20 years to my machanic days

Moreover, is there any explination for the boost to behave in this way

Thanks in anticipation od any advice

Cheers
Gazza

[tim at svs]

Morning all. Well my R33 does this too. I could be completely wrong (this is not unknown) but I reckon the ECU runs the engine so rich on cold start that the fuel is making the engine stumble so thats why it doesnt pick up. It only takes a couple of minutes for the cylinders to get hot enough to change the way the engine runs and all is being burnt properly. The over-rich condition is backed up by Garys findings on carbonised piston rings, and all of us running more boost than stock will have a higher fuel delivery too. Many of the Japanese tuners use an excess fuel delivery to cool down the combustion temperatures, so often there is too much fuel present, albeit better than having a hole in your piston, and more fun when toasting all the tailgaters with flames !

Lets face it we shouldnt be running much boost at all when the thing is cold (80 percent of cylinder bore wear occurs when the engine is below operating temp, good oil helps this condition but the fact is it still happens). So in my case, I poodle around like an old fart until I see my oil temp gauge has at least moved onto its base line, then vroomvroom away we go. Probably completely wrong but it works for me. Because of all the 'blow-by' (past the rings) that turbo engines suffer from, combined with all that extra fuel, it re-inforces the need for some high quality oil and a regular change in our cars, especially when thinking about how small the oil capacity is (a 911 for example has about 3 times the volume of oil than an RB26)Anyway I must stop rambling. Tim

[RobGalley]

Nice to know other peoples cars perform the same - I had assumed that it was due to mine being an import, and not having the ECU changed....

Also (maybe my imagination) but it seems less hesistant cold when running super unleaded....

Rob

[jamie m]

1) The holding back when cold is a function of the ECU. It is present as a base line parameter on Jap and UK ECU's simply to protect the engine during initial warm up, it occurs up to 3000rpm. When tuners re-map the ecu it is not something they remove as it is in every owners interest.

2) The boost suddenly capping itself to say, 0.7 bar is also a safety feature of most ecu's. It does this as a safety measure when it detects detonation. Simply, turn the car off wait a few seconds then turn it back on again (this re-sets the ecu) and you'll be back to full power. If this happens alot then I would get a specialist to look at the car.


Jamie Martin.

[Peter]

As Tim says, I always keep off boost until the oil temperature gets to 70C so couldn't comment on cold performance. The Apexi Power FC does give a little opportunity to look at some of the functions that the ecu has one of which is water temperature correction. This applies factors to the fuel map, low load and high load. So, for example, at -10C, it more or less doubles the fuelling. At +30C, it adds 14% under low load and 29% under high load. It's only when the water temp gets to 80C that it leaves everything to the base map.

As Jamie says, the anti knock function comes in and knocks boost and ignition back if it detects excessive det. If this keeps happening, as it did with mine when I first bought her, you need to seek expert advice. Having said that, SUL and Octane booster sorted mine out.

Peter.

[Joss]

That makes sense and seems consistent with the car's cold behaviour .. I thought it was the ECU being careful

Oh, and I'm being very carefuly woth the right foot, this is all <3,000 rpm boost <0.20 ish.

BTW ... is anyone else using Optimax ... it does seem better so far (and cheaper )

[jamie m]

I'm Using Joss wherever possible, it probably is better but I can't really tell whilst the 34 is standard as the UK chip tails the power out dramatically after 6,800 rpm.

Jamie M

[jamie m]

correction:

I'm using "it" Joss!!!!

[Alan]

Hi Joss
Yes I am using it as the garage at the end of my road has now been converted.
Yes I think the car runs smoother
I thought it was my imagination.
Best regards