Strange boost issue

[threedogs]

Bumped any update yet,??

[docp1980]

Still trying to sort it out. Just realised I can check the boost on my scan gauge so that will tell me whether it's happening at the manual gauge on in the intercooler/MAP sensor as the scan gauge reads from that.

[docp1980]

Looks like the gauge is the problem as my scan gauge is still showing full boost at the MAP sensor, even when the gauge drops to 0 and i'm also seeing differences in boost level between the MAP reading on the scan gauge and the gauge (taking into account the 14.9 PSI atmospheric pressure reading). Will check the O-ring under the MAP boost line adaptor and also pull apart the Dawes to look for any obstructions this weekend.

[threedogs]

Very rare but sometimes the ball in the Dawes doesn't seat properly.
but do one fix at a time till you find it

[docp1980]

Very rare but sometimes the ball in the Dawes doesn't seat properly.
but do one fix at a time till you find it

So it's been over a month now and I still can't find the problem... Pulled apart the Dawes valve, it was clean as a whistle. Reassembled, problem still there. Took the boost valve adaptor off the intercooler, o-rings look fine and were seated correctly. Checked the intercooler, no sign of oil on the underside, catch can seems to be doing its job very well.

What I can't understand is how the issue corrects itself after say 15-30 mins of driving. So especially from a cold start i'll accelerate and the boost on the gauge will not spool up at the normal rate, hit about 15 PSI (Dawes set to 20) and then just fall away to 0. The turbo is still working though as the power doesn't drop off but the induction noise and the delivery of power just isn't the same (sounds a lot rougher) as it is when the boost gauge shows everything working nicely. In addition, I have noticed that my EGT's seem to be lower when accelerating with the boost gauge showing 0, which sounds like the turbo is working harder? What then happens, is if I get on the freeway and tap the throttle on and off and few times, the gauge will then return to normal and everything goes back to being fine. Another thing I have noticed is that comparing the MAP sensor reading to the boost gauge, the readings are pretty close when the boost gauge is functioning, but when the boost gauge reads 0, the MAP just goes straight to 22 PSI boost (taking into account the atmospheric reading) and doesn't deviate until you stop accelerating.

All hoses appear to be fine and if it was a hose leak, you wouldn't expect the problem to correct itself or for the strange rough acceleration to occur. Same with the gauge, if that was the problem, then it should be dodgy all the time. Once it corrects itself I can drive for hours without it reoccurring.

Any help would be greatly appreciated as it's driving me nuts and i'm at the point where I think i'll need to take it to United Fuel Injection to see if they can solve it.......

Cheers,

Matt

[threedogs]

Cheapest option IMO would be to maybe get it Dynoed, just a thought

[4bye4]

Can you disconnect the boost gauge at the motor end and block the hole where the sensor screws in. Then just drive it for a while and see if the fault goes away or no. At least you will have eliminated the gauge from the issue.

[mudski]

Have you tried a new maf?

[boots]

Tested your intercooler for leaks ?

[the godfather]

So it only happens when it is cold right?
I would be looking for a fracture somewhere, maybe in the little plastic vacuum tank under the IC.
They also have a one way valve in them that can play up occasionally.
I will try and post a picture of the unit.
They are $95.00 from Nissan. I just replaced mine because it was perished.