loss of power at certain speeds

[Drovers Hill]

I recently had the EGR blocked on my 2002 3 L and a Dawes valve fitted. The work was done by a reputable workshop. The first time I took the car for a country trip it kept losing power at 110 km/h. A short off/on with the accelerator reset it and all was good for the next few minutes. If I didn't vary the position of the accelerator it would do it over and over. It appeared that the computer was detecting an over boost and putting it into limp mode; easy off the accelerator was enough to reset it. This is weird because the Dawes valve is designed to prevent boost spikes, not cause them. I took it back and they guy said it was set to a maximum of 13 PSI boost. They fiddled with the engine and went for drives - experienced the problem. The bloke said there were codes for a faulty MAF sensor and over-boost. They swapped my MAF sensor for one that they knew worked. But still no fix. I am taking it back again next week. I did some more testing. The problem only occurs at steady speeds and only between 2,500 RPM and 3,000 RPM. Travelling everywhere at 120 km/h doesn't appeal to me. Nor does below 90. Any ideas?

[Clunk]

sorry mate, I know nothing of diesels, hopefully one of the guys who knows will be able to give some pointers...................... have you checked the throttle position sensor (stab in the dark).

Have a good search mate, I'm sure this has come up a few times

[threedogs]

You'll need to fit a boost Gauge and EGT for sure seems you are spiking and going into limp mode.
How can you adjust boost with no gauges?.
As for your MAF you can clean them with spray from SCA, hope you never paid for a MAF sensor'
ChecK search engine on Chaz yellowfoot You need to fit a provent 200 catch can as well to help keep your MAF clean.
Most here use a pillar pod with boost/EGT fitted
Removing EGR plate may help for the time being.
The term to search is NADS Nissan Anti Detonation System ,Highly recommend fitting
Have you fitted a larger exhaust lately???
This will also cause over boosting/limp mode

[Drovers Hill]

Yep. I have been cleaning the MAF sensor - it has never been oily. They assumed mine was faulty and swapped it for one they had in the workshop - I will be asking to have mine back because it made no diofference. I have read a lot about the NADs stuff - and the catch can is next. I am trying to find one that can fit 'neatly' without having to use hose adaptors etc. The provent seems popular but there's a lot of stuffing around with hose diametres. Exhaust is stock and Iplan to leave it that way for now. The guys who installed the Dawes valve - they do lots of them - did the calibration. I presume they used a temporary boost gauge. I will be having more 'discussions' with them - until this is fixed. The weird thing is that it is OK at 120 km/h; wouldn't overboosting be happeningf then too? There's a graph somewhere that shows recommended boost pressures through the rev range - i might take that to them. Or I might fit a boost gauge and do it myself. Are Dawes valves easy to adjust? Is it the gnurled wheel that you turn?

[threedogs]

@100kph you should be on 10 psi give or take 1psi
spike could be 15 psi to 20psi,
What condition is your intercooler in?? oily ??if its oily its leaking I'd say

[Drovers Hill]

I took it off the motor a few weeks ago and it was very clean and no signs of oil or leaks. The guy who fitted the Dawes valve said they limited it to 13 PSI. But at 90 (2,500) I am getting power loss - presumably limp mode. MAybe its a faulty Dawes valve; I doubt that they did a test with the car moving at highway speeds. Sounds like I will be installing a boost gauge soon.

[mudski]

TLDR....
Fit a needle valve along with the Dawes your issues will more than likely disappear. Doubt the Dawes is faulty. Nothing in them really to be faulty like your issues you have. If a Dawes is faulty, it just would work at all.
Unless their boost gauge they use is faulty its quite hard to tell whats wrong. Adding a needle valve lets you control the mid range boost. A dawes is for max boost.
I had a similar issue, but my max boost was at 16psi, that I would see limp mode only at a certain rev range IF I got the revs to that range slowly, if I floored it, it would do it. My boost at 100k's was at around 12psi which I liked but I had to open the needle valve up just a little to lower the 100kph boost level which also solved this limp mode issue I was getting.

[mudski]

What condition is your intercooler in?? oily ??if its oily on the outside its leaking I'd say
Fixed that for ya Johnny...

[Drovers Hill]

BAck to the workshop. Problem continues even when they take the Dawes valve out (leaving EGR block in). Boost pressures are all over the place. And lots of pressure in the valve cover - maybe a bloocked PCV valve?

[mudski]

BAck to the workshop. Problem continues even when they take the Dawes valve out (leaving EGR block in). Boost pressures are all over the place. And lots of pressure in the valve cover - maybe a bloocked PCV valve?

Check the ic for leaks mate. A leaking ic will play havoc with boost. As for the pcv. Take the hose off the intake pipe and take her for a spin and then see if there is any vapours coimng out of the hose while idle.

[Drovers Hill]

All fixed. Turns out that the Dawes valve was faulty. They put a different one in and everything is back to normal now.

[mudski]

Would love to know how the dawes was faulty. There basically nothing in them to be faulty. A spring and a ball. And thats it.

[dukesta83]

I have had a faulty Dawes valve where the spring was not stiff enough and was compressing under normal boost pressures.

[mudski]

Thats not a faulty valve. Its just some engines require a stiffer spring to work the same as another of the same engine. That issue had been resolved now with a stiffer spring in all valves.