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How A Little Thing Can Change The Car So Much

Wacky Dee

By Wacky Dee,
in Engines & Forced Induction

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Wacky Dee Veteran

Wacky Dee

Posted
Posted (edited)

I'll try to keep this as short as possible ...

I have an R34 GTT with a turbo back exhaust. At some point (after getting an aftermarket turbo-back exhaust from JustJap) I took it to a place for a dyno. On the dyno run the 'actuator flap' got stuck open (according to the mechanic) which meant it couldn't make boost past 5psi or so so he 'fixed it' (what he did, i was never told).

Anyway, I recently had the car tuned and ECU remapped by Toshi and it made a significant increase in performance.

However, for the past few weeks, ever since that dyno, the car's been making a rattling noise as I took the foot the off the accelerator. A few people thought it's the cat and they recommended I get rid off the xforce cat.

So I went to justjap today (where I bought my exhaust from) to get the cat replaced with a Catco one and hopefully fix the annoying rattle. They changed the cat and still same rattle.

So the mechanic then took down the dump/front pipe and all the brackets and tried a few things ... 2 hours later, everything's back on. Fingers crossed. Nope, still rattling.

Now at this point I'm thinking, f**k he's probably gonna just say "sorry mate, don't know what it is". Nope, he opens the wastegate cover again and starts looking around and notices the actuator isn't sitting correctly and thinks could be the reason for the rattle.

So he pushes the actuator back a little bit and BINGO. Rattle is gone.

I ask him why he reckons the actuator wasn't sitting correctly - he goes, looks like there's a mark there ..like someone pushed it the wrong way. Immediately I remember the original dyno where the actuator flap got open and got 'fixed' by that shop's mechanic.

So I'm happy. The rattle is gone. The mechanic reckons it should actually make boost a bit sooner now.

A BIT SOONER? It feels like a DIFFERENT CAR. It runs SOOOO much better it's not believable. The boost is coming on crazy quickly and the car feels about 3 more responsive in low to mid range (haven't had a chance to flog it yet). First, 2nd and 3rd gear are unbelievable. Response is so much better and the car feels twice as fast as before. I can hear the turbo spool up all the time, unlike before. To put into context, it feels 3x better than it did prior to and after the ecu remap (which was quite a significant increase in power/response too).

All this only after initially going after a stupid rattle. Turned out the rattle was just a symtop of a far more serious problem.

I still cannot believe how good the car feels - seriously, it's like a brand new car completely. Well, to be fair I did get a new cat (although it's highflow jut like the previous one) and a new airfilter, but I'm sure it's mostly the actuator issue that explains the change in response/boost/power.

So big thanks to the boys at JustJap (Kirrawee) for taking the time to find and fix an issue created by another incompetent shop. Most guys would have given up after 2 hours of trying to fix what was no more than an annoying rattle. They went all the way and it paid off bigtime.

CHEERSSSSS!

Edit: now I just gotta pray this fix doesn't affect my ecu remap which was done using a road tune while I still had that 'rattle' ie. the car wasn't really making boost early enough or as much.

Edited by Delta Force
R31Nismoid Grand Master

R31Nismoid

Posted
Posted

If you gate flap was loose when tuning, you will indeed need to go back for a retune.

You would have been making some boost, but not in the right places due to the gate flap being open earlier than it should.

Guilt-Toy Grand Master

Guilt-Toy

Posted
Posted

its a standard ecu... it won't damage his engine just cause him to lose power because it will go to a low octane map due to pinging.

If its going hard at balls just take it to a dyno shop for a dyno run to test the AFR's $110 and if the afrs are ok then your right :P

Wacky Dee Veteran

Wacky Dee

Posted
  • Author
Posted
If you gate flap was loose when tuning, you will indeed need to go back for a retune.

You would have been making some boost, but not in the right places due to the gate flap being open earlier than it should.

I had my AFRs tuned by Toshi and I did do a dyno after the remap (while the actuator was still farked) ..according to the dyno graph I was making boost just fine but it feels so much better now.. here's the graph http://www.skylinesaustralia.com/forums/in...t&id=165600

I'm gonna go to Toshi's see if he can have a listen to the engine for pinging while we drive... hopefully this wont screw up the remap

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