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A New Exhaust - And Some Problems

Grungle

By Grungle,
in Four Door Family & Wagoneers

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Grungle Enthusiast

Grungle

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So i got a new exhaust for my M35 today. 3 inch stainless with 2 mufflers. It's not as quiet as i would have liked, but i'll see how i feel once i've done a few km in it.

Problem 1: the exhaust shop couldn't get the dump pipe off "without removing the engine" :( . So they fitted a cat-back, and i'll do the dump later. a pain the arse, but no problem.

Problem 2: The car runs TERRIBLY. it has always had problems under high boost (missing, possibly pinging) and after changing the spark plugs it seemed to get a bit better, but after changing the exhaust today it's absolutely terrible. has anyone else experienced this? what could it be? and most importantly, how can i stop it?

how much "tuning" can be done with the factory computer? i'm not chasing more power, i'm more interested in getting it to run cleanly. As I said, it has never been quite right, it's just that the problem is more apparent with the exhaust.

Fuel economy is ok (i have squeezed 600km+ out of a tank a couple of times), i have good power and i've done about 12,000km in it so far. no other mods.

any recommendations for someone to take a look at it in Adelaide (Northern suburbs if possible)?

i'm just about stuck. it's fine at low loads and there is no problem getting around town, but get it out on the highway to overtake someone and it coughs and splutters and carrys on... any ideas?

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andy65b Veteran

andy65b

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There is not much room around the back of the turbo. It is mean to be very hard to get in there but you should be able to get the dump off without removing the engine.

I have done roughly the same with my exhaust, dump pipe back 3 inch exhaust with high flow cat and 2 mufflers. My car got a little quieter in the 2 weeks after the exhaust was fited (or I got used to the noise). I have not had anything like you have explained in the higher rpm.

Is the car idling correctly (ie, between 600-700rpm), do you know what your max boost is?

Have you got an oiled air filter? Sometimes the oil from the filter can get on the MAF sensor and give a bad reading.

So many things it could be.

Good luck sorting it out

Cheers

Andy

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Grungle Enthusiast

Grungle

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hmmm...

standard filter (not oiled) and it idles perfectly.

it's not neccessarily happening at high rpm, but at high boost. if i bring the revs up slowly without boosting too much it's fine. haven't checked boost pressure (no guage) but i would be surprised if it's been changed from stock - nothing else on the car has been.

may be a fueling issue...might just have to book it in somewhere and see what "the professionals" can come up with.

as for the dump - I told them it was going to be difficult, and i guess they took that as meaning if it's too hard don't do it. I'll just change it when (if?) the turbo goes.

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scotty nm35 Grand Master

scotty nm35

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hmmm...

standard filter (not oiled) and it idles perfectly.

it's not neccessarily happening at high rpm, but at high boost. if i bring the revs up slowly without boosting too much it's fine. haven't checked boost pressure (no guage) but i would be surprised if it's been changed from stock - nothing else on the car has been.

may be a fueling issue...might just have to book it in somewhere and see what "the professionals" can come up with.

as for the dump - I told them it was going to be difficult, and i guess they took that as meaning if it's too hard don't do it. I'll just change it when (if?) the turbo goes.

Sounds like a blocked injector or like you say, fuel issue.

Dump comes off just fine, I had mine off just the other day. I removed one of the studs from the turbo though, to make it easier, as the oxy sensor was in the way.

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zei20l Grand Master

zei20l

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run an injector flush through it. i got a little more kms from a tank afterwards. but my car has been running fine *touch wood* and will continue to do so

also, clean the AFM, do an oil change and filter, make sure the airfilter is clean, replace if necessary. also, check to make sure you have the two silver 'dots' on the plate in your engine bay to make sure its been 'fixed'. there was a recall on a few things...... if they havent been done, the compliance place should be responsible for it

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iamhe77 Grand Master

iamhe77

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Hate to ask an obvious question, but are you using a decent quality 98 fuel?

These cars NEED to run on 98 as a minimum and if you are not already using them, I would suggest that you stick to BP Ultimate, Mobil Synergy 8000 or Shell Vpower.

and yes, the dump can certainly come off without removing the engine... so can the turbo for that matter.

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scotty nm35 Grand Master

scotty nm35

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Hate to ask an obvious question, but are you using a decent quality 98 fuel?

These cars NEED to run on 98 as a minimum and if you are not already using them, I would suggest that you stick to BP Ultimate, Mobil Synergy 8000 or Shell Vpower.

and yes, the dump can certainly come off without removing the engine... so can the turbo for that matter.

And the turbo doesnt take 4 days to remove and refit. :)

Moral of the story, do the work yourself! :)

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iamhe77 Grand Master

iamhe77

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And the turbo doesnt take 4 days to remove and refit. :)

Moral of the story, do the work yourself! ;)

Oi! Cheeky.

So where were you in June last year?

I would do the work myself, but since I am mechanically semi-retarded, it is probably best that I don't :)

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KiwiRS4T Grand Master

KiwiRS4T

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The computer is not currently tunable although people are working on it! If your engine is pinging you could be damaging it. Have you changed your fuel filter? Maybe you need a fuel pump. Try to get your fuel pressure tested or ideally stick it on a dyno and get your air/fuel ratios checked to make sure it isn't running too lean anywhere.

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scotty nm35 Grand Master

scotty nm35

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oh btw hows the emanage going scotty

and the G box

better?

Theres a lot of misinformation floating about, especially from the professionals. :)

Everythings an easy job if you have a hoist, Just wish I had the room.

Emanage is great, I just wish it controlled the throttle directly. Let me just say the power curve isnt linear anymore, the ecu only gives 1/4 throttle max to 3000 revs then all hell breaks loose. The stall is 2800, and the turbo comes on at 3000 as the throttle opens fully. Makes for interesting tuning not to mention driving it.

And harden up Cam, or I wont make you any more hot up bits. :)

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scotty nm35 Grand Master

scotty nm35

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So if the emanage is not controlling the throttle and you are only getting 1/4 throttle to 3000rpm, would an aftermarket throttle controller make a difference?

Cheers

Andy

Funny enough, thats what I just asked Cam via PM.

Does anyone know if this TREC controls the throttle directly? Thats what is implied on this page.

http://www.jdmstyle-usa.com/trec/index.html

If so this is the answer. Speaking with the 350z guys, the ECU craps itself if you run manual throttle body.

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zei20l Grand Master

zei20l

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its that exact project im working on with a mate. he has my spare TB and now the wiring diagram of the entire car. im not sure how long it will take, but i asked for +X% on the current voltage to open the throttle. but now with that information, he may need to look at the RPM as well!

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scotty nm35 Grand Master

scotty nm35

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its that exact project im working on with a mate. he has my spare TB and now the wiring diagram of the entire car. im not sure how long it will take, but i asked for +X% on the current voltage to open the throttle. but now with that information, he may need to look at the RPM as well!

The power to the throttle probably wont be a straight voltage, but a pulse width modulated signal, like a stepper motor. It could be controlled cheaply with a modern 12v model train controller. (Digital command controller) It just worries me if something shorts and I get full throttle while waiting at the lights, which is why nobody sells it as a product. I think the controller has some smart protection inbuilt though.

Perhaps the best option is to run cable and new TPS, but leave the original there, plugged in.

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