Boost Control for ZD30 DI

[PaulvdMerwe]

From spending quite some time under the hood of my recently purchased Patrol, struggling to get the EGT's down to an acceptable level it would seam that if I can get the turbo to boost "higher" (0.9 - 1.2) or more constant, the EGT's are fine. So I would like to post the following and get your opinions on it.

The turbo boost is controlled by the valve on the intake which is in turn controlled by the ECU. If one connects the vacuum line from the pump directly to the turbo, (bypassing the control valve ) every thing works well and the ECU has no control over the turbo. Except that the vacuum is a bit high and therefor boost is to much.
So why can I not run a vacuum line directly from the pump to the turbo, but with a control valve in to restrict the vacuum? Would this not give me a constant boost witch is then adjustable to say 0.9 - 1.2 bar?
This is pretty much what the Dawes valve does, isn't it? but what is all the other bits in the kit for?

I look forward to hearing your opinions on this.

Thanks

[Michael]

I dont know much about the system and how exactly the Dawes valve work.

The ECU controls the vacuum through that box on the intake and it actually works pretty well usually.

I had this same problem on a ZD30 before, just change that box and your troubles will be over

[DaleB]

The dawes controls max boost by leaking boost into vacuum so dropping vacuum. The needle valve is to bleed off the vacuum to control the speed at which it increases, I. E. Turbo spool up.

Without the needle valve the spool up is too aggressive! Also fuel consumption becomes hectic.

[DaleB]

If you connect you vacuum direct to turbo you will go into Limp mode. Boost will way over shoot and she will be a bugger to drive!

Most standard setups run around 1 bar boost (15psi) max on dawes with a slight bleed on vacuum via needle valve. This should give you around 350 deg on flat road at 100 kmph.

I get around 300 deg. I have a limp problem caused most likely by a stuffed flow meter so restrict boost at 12psi currently. I run around 9 psi in above conditions.

[JoshJ]

Thanx for explaining the dawes valve fuction Dale. I have always wondered about it.

With the new CRD a good tuner can adjust the boost spikes, curbing it electronically and smoothing out the boost increase. In Aus some guys run dawes and needle on their CRD's and some dont. Mine was not ruff but could be smoother. All thow I had spikes when pushing it and doing quick gear changes.

Mine was set very nicely by the new Guy at SAC boksburg when they re-map my chip after the exhaust. So its very smooth now and runs on 1bar only spiking to 1.2 between quick gear changes. He made it so that when i am in 5th gear and get over exited and pushing the throttle to the floor, It increases the boost to 1.2 bar, running leaner and causing EGT's to cool down. This is great when running up long heals, cause you tend to over commit and before you know it the throttle is to the floor and EGT's are sky hi. So all I do know is when I realize I am to the floor ( aspecially when overtaking on up hills) i just ease off the throttle to about 3/4. And then imidiatly feel the car pulling again and the EGT's start climbing again. So it a nice protection.
I like it.

[ricster]

silly question.... but if the mass air flow sensor/meter thing is stuffed or dirty, would this not send incorrect readings to the ecu causing the boost to be erratic.

[juice]

I had a similar issue with mine , turned out to be the maf sensor, it all had the correct voltage but until there was air flowing over it for a while it would tell the ecu there was a problem (old and must have been damage) it would then drop the boost away and the egt would go sky high , I also changed the boost control valve ,but it was not the problem
put the old one back , the vvnt turbo is always adjusting itself to optimize for fuel consumption , you should get 350-400 deg at 120km and boost should be around 1bar , but as you add juice the boost drops away to around 0,6 and egt climb
I tried the dawes valve and needle control what a different car (thanks dale) but then you land up with overboost and car goes to limp mode
I was not in the mood to fiddle with the turbo vnt screw so I put it back to original and use the dawes for spikes
in the ref doc they say that once you change the exhaust you need to adjust the vnt screw to stop the overboost and slow the spoolup
which put the car into limp ,also try what they say about coasting along and the twitch for the overboost
you can get a new maf for around R1650
regards
juice

[JoshJ]

Thats another thing thats iterresting. I also got boost spike befor of up to 1.7bar when I was at the coast. It never through me in limp mode. It only caused the MIL light to come on. I have adjusted my VNT screw way in the begining as per ref. Doc. It realy does help and work. But you must do it very carefully and small adjustments at a time. The car was much smoother. But when I went to chip the Patrol I put it back o normal. So they can adjust the car with OE settings. The boost spikes was after the first chip tune. Before that it would only spike to around 1.3bar. And was boosting 0.9bar. After the VNT adjustmet it spooled up slower and never went over 1.1bar.

I agree with the other guys. If your MAF is failty the rest of the system cant work correctly.

[DaleB]

The way I understand it the ecu controls the fueling. So if the maf is faulty the ecu sees too much or too little air for a given fuel requirement and throws a limp mode. I.e. Running higher boost the ecu sees that you are pulling more air than you should with potentially too fast a ramp, it got there too fast, so thinks you are under fuelling and throws Limp or other way around.

Alternate workaround is a bigger intake diameter, lower intake speed lower maf reading or fool maf feedback to ecu via resistors or chip or whatever.

[DaleB]

Juice, what did you set max boost to? To get around Limp I have mine currently at 12psi.