Loss Of Boost, Yet Otherwise Running Fine?

[Lolrick]

Hi SAU,

I have an R34 GT-T with a high flowed turbo and Greddy profec spec b boost controller. Normally, both my stock boost gauge (part of the centre tri-cluster) and the greddy boost controller correctly read my boost, which the previous owner informed me was set to approximately 14 psi. He also told me that the vehicle had been tuned by toshi (If you're reading this, thanks!)

However, I've noticed that just recently the Greddy unit and my stock boost gauge both sit at 0, and won't budge no matter how hard I'm flooring it and at what gear. I feel that i also have lost my significant boost, as normally it comes on quite hard. I can still hear my blow off valve working, and the car still revs freely and drives nicely, but there just isn't the same amount of boost power.

I'm usually right into my vehicle DIYs, but honestly this has gone somewhat over my head. I had a cursory look under the bonnet to check that the boost gauge was not obviously disconnected, and i had a flick through the settings to make sure it wasn't just in the wrong mode.

I will investigate the sender unit, as per M35 Factory Boost Gauge Repair

However, this only made reference to the stock boost gauge, and not to actually controlling the boost pressure.

Would love to hear if anyone has any solutions from similar experiences where the boost pressure just dropped off and stopped reading overnight.

Thanks!

Mick

Edited March 12, 2014 by Lolrick

[Badgaz]

this could be a split in your hose that goes to your boost gauge and/or controller

Edited March 12, 2014 by Badgaz

[Badgaz]

this could be a split in your hose that goes to your boost gauge and/or controller

[Lolrick]

this could be a split in your hose that goes to your boost gauge and/or controller

Thanks, will get a mechanic mate to check for me at work tomorrow. I hoping that would be a relatively cheap and easy fix, to replace the hose?

[Got a Pulsar]

Cuppla Bucks.

[Lolrick]

Cuppla Bucks.

Music to my ears

So like I mentioned, the stock boost gauge sits at 0 (so it hasn't dropped to -1, but sits halfway at 0) and the Greddy boost control shows only 0, no matter what i do with the throttle. Can a split hose lead to showing no reading at all? Which hose would it be (i.e. where does it come from and where does it lead) As i mentioned, I still can hear the blow off valve, I just can't feel any boost

Cheers for the speedy replies, guys!

[RBrennan25]

Sounds to me like a split hose, either from the manifold to the boost gauge or on the greddy solenoid itself, or one of the hoses has simply come off the nipple. Both of these problems are extremely common. Happened to me and from memory it cost me $4 for the hose. Could be free if the split is right at the end of the hose and you just cut that bit off

[Guilt-Toy]

and use cable ties. on every place possible.

[Lolrick]

I've had someone mention that perhaps it's a fuse that's gone? Will investigate that as well - has anyone had any fuse related problems (and possibly a solution why it blew in the first place)

Additionally, I've noticed that so far the fuel gauge has not moved from above the full position - is this related?

Edited March 12, 2014 by Lolrick

[Lolrick]

Alright, so I had some guys at work investigate (work at a fleet leasing office, lots of qualified mechanics around). Turns out it was a tiny vacuum hose that had popped off, which comes off very easily (pictured, on and off. Wasn't near the boost controller, but near the manifold). Will check out autobarn and grab some silicon hose and clamps and update all of those hoses there. Both gauges working properly - I'm quite relieved!

However, the guys also pointed out some uncovered wires (pictured) - their suggestion was to shrink tube it. From the photos can anyone offer any advice, and tell me what that particular unit does? Should I crimp it as well?

Further, the fuel gauge still is not budging from 'full', which is kinda concerning as it has now been 5 days and nearly 200kms since i filled up. Anyone have any ideas for this?

Edited March 13, 2014 by Lolrick

[GTSBoy]

If that plug is the wires for the power steering level sensor, then yes, insulate it. You won't be able to put heat shrink on it unless you get the pin pulled out of the plug first (heat shrink has to slide over the wire from one end) but you could always give it a good clean with some spray cleaner (to get all the power steering fluid wetness off it - bound to be there, never seen a dry one) and just use good electrical tape.

As to your fuel gauge......either gauge is broken, sender is broken or wiring is broken. Would have thought that would be obvious.

You will almost certainly have 1/2 tank or less in it now.

[Got a Pulsar]

That's the wiring for the Stock Boost solenoid.

It's been cut and Earthed (in a previous life) for the High Boost Mod. (7psi fulltime)

Shrink wrap or electrical tape will be fine. It's only an earth wire so no biggy.

Fuel gauge sounds like like sender or wiring... perhaps the previous owner also tried to Earth the fuel pump and got the wrong wire.

(earthed the sender instead?)

[Lolrick]

That's the wiring for the Stock Boost solenoid.

It's been cut and Earthed (in a previous life) for the High Boost Mod. (7psi fulltime)

Shrink wrap or electrical tape will be fine. It's only an earth wire so no biggy.

Fuel gauge sounds like like sender or wiring... perhaps the previous owner also tried to Earth the fuel pump and got the wrong wire.

(earthed the sender instead?)

I'll probably ask around on the forums a little more before i rip out the sender and have a look - most people with sender issues have their gauge drop to zero once it gets halfway, whereas mine is stuck on full. I'm hoping there's an easier fix!

also with that high boost mod, that would have been before the boost controller was installed, correct? Boost mod just means there's no 5-7 variable psi?

Thanks!

[Blackkers]

yep. If that boost hose has popped off then I'd be clamping it or at least using a cable tie. If your boost gauge doesn't read vacuum off throttle as well as no boost under load then its definitely not a turbo boost problem. Shouldn't have felt much slower though.

Just make sure your wastegate line is attached properly, if that pops off you can do some more serious damage

[Got a Pulsar]

I'll probably ask around on the forums a little more before i rip out the sender and have a look - most people with sender issues have their gauge drop to zero once it gets halfway, whereas mine is stuck on full. I'm hoping there's an easier fix!

also with that high boost mod, that would have been before the boost controller was installed, correct? Boost mod just means there's no 5-7 variable psi?

Thanks!

I wouldn't pull out the sender yet (even though it's good fun! ) but just have a look around the tank lid area for any "Extra" wiring.

Boost mod eliminates the 5-7 psi yes. Likely prior to the Boost controller.

[Lolrick]

I wouldn't pull out the sender yet (even though it's good fun! ) but just have a look around the tank lid area for any "Extra" wiring.

Do you mean the part where i open the fuel cap to fill the tank at the servo, or the part near the spare tyre where i access the sender?

Will post more photos later on when I've replaced the hoses, let the noobies like me see what the issues are. This forum is enormously helpful, but I find those without much prior experience benefit greatly from seeing a few photos along with guides/solutions!

[Got a Pulsar]

Yeah the tank access in the boot.

[Lolrick]

Quick question, so the guy at Autobarn reckons it would be easier to cable tie the end, as the width of the hose is different at each end. I tried to cable tie it, but it still feels loose. Am i better of getting a clamp and replacing the zip tie?

[scotty nm35]

Sounds like the hose is old and loose, or you have replaced it with a hose that is too large. A cable tie is usually more than enough to hold a vac hose tight.

If you replace any hoses, make sure it isn't the hose with the restrictor in it leading to the stock solenoid (if you are still using it), as otherwise your boost will skyrocket.

[KiwiRS4T]

If you have any slack in the hose cut the end off to lose the worn part.