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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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thanks for your help guys.

yep, i only use BP Ultimate 98, tried a few others and that seemed to work the best/get the best milage.

i thought the fuel filter was changed when the car arrived in Oz, but i'll have to look at the paperwork again and change it if it wasn't. I recently changed the oil, oil filter and spark plugs.

I think it needs to go on a dyno and get checked out. until i can get a look at A/F ratios and actually find out what's going on i shouldn't just keep randomly changing things...

I know my way around a toolbox so i'll do the rest of the work myself i think - and i've got this exhaust set up so i can run one of your dumps Angus (when they're ready).

when it comes to imports local mechanics seem to be making most of it up as they go anyway. i'll book it in for a dyno run and see what the deal is.

nickcorr Proficient

nickcorr

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Really does sound like you need to get it on a dyno sooner rather than later.... Need to check the A/F ratios as the new exhaust has made an existing problem worse with the increased flow.. Are you running JDM cats and pipes or some buggered compliance set up?

Any high end misfire could be a whole heap of things but also could be the engine leaning out.. If this happens too much then there is a good chance of the engine going pop with holes in pistons etc.. It might also have killed some of the cats and maybe the O2 sensors if neat fuel is getting though the system during a misfire.

You're getting good fuel consumption so you know that it's not overfueling like most Nissan turbos.

Edited by nickcorr
zei20l Grand Master

zei20l

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chances are your fuel filter wasnt done, its locate in the tank and attached to the fuel pump. BUT, if it was done, they may hace stuffed something up re-installing the filter/pump

pixel8r Mentor

pixel8r

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Posted (edited)

When you reach max boost, is it a misfire or does it completely cut ignition for a split-second?

In the earlier stageas (I know this because it happened with my previous s2), just putting an exhaust on was enough for it to hit whats known as "boost cut" or R&R. There are two triggers, one seems to be that the ecu either has a boost limit or an airflow limit (basically when your AFM signal reads too high) and will cut ignition, and it almost sends you through the windscreen its so sudden. The other trigger is when the A/F ratios get say below or near 9.0. In this case it will switch to R&R (Rich & Retard) fuel mapping which is like a "failsafe" mode to protect the engine. Basically it just dumps loads of fuel in at this point. This only continues while the AFR's are low. Once you lift your foot and things return to normal, the ecu switches back to your usual fuel map.

Either of the above scenarios may be happening in your case. I doubt very much that Nissan removed the "boost cut" from the M35. And as with the C34's, it will happen in some cases but not others. It was a bit of hit or miss. Essentially the way around it was either tune the AFR's or fiddle with the Air Flow meter signal so that it didn't read so high. Most interceptor/piggyback ecus do both.

Dont be tempted by the Fuel Cut Defender - all that one does is limit the AFM signal once it reaches a certain figure - yet it doesn't restrict the actual airflow in any way - so there is the possibility of running lean. Not a risk I'd want to take. Its essentially just bypassing your ecu's built-in protection.

Edited by pixel8r
Grungle Enthusiast

Grungle

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The other trigger is when the A/F ratios get say below or near 9.0. In this case it will switch to R&R (Rich & Retard) fuel mapping which is like a "failsafe" mode to protect the engine. Basically it just dumps loads of fuel in at this point. This only continues while the AFR's are low. Once you lift your foot and things return to normal, the ecu switches back to your usual fuel map.

This certaily sounds possible - i have hit the ignition boost cut in my old cordia, and it's not an enjoyable experience - the stagea is definitely not that violent, and it does get better when you lift slightly. As I said, if you slowly bring the revs/boost up it's not a problem and revs smoothly all the way to redline...it's just when you flatten it that it seems to get a gutful of fuel and goes nowhere.

to the dyno...!

  • 4 weeks later...
Grungle Enthusiast

Grungle

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Update:

Took the car into Sinergy in Adelaide to get looked at while i was away (getting married :ermm: ).

They took it for a drive, agreed something was wrong and reduced the gap on the spark plugs. Things improved, but not by much.

After approval from me, they ordered a new set of coilpacks and installed them today - they say it's all fixed and can be picked up tomorow.

I'll leave an update after I've been for a drive and let you you all know how it goes. :P

Grungle Enthusiast

Grungle

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fixed!

they replaced the coilpacks and it's all good - no miss and pulls strong all the way to redline.

They said they hadn't ever seen it in a VQ engine before...but as most of you probably know it happens frequently (?) in the RBs.

Oh well, it's fixed now. :ermm:

SHIZNT Collaborator

SHIZNT

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Posted

Was gonna say sounds like coilpacks to me... had exactly the same issue with my C34 Stagea... Ran nicely on factory boost but as soon as I raised the boost to 10-11psi is starting missing and running like crap... changed spark plugs, gapped them smaller ect but only slight improvments... Finally put it on the Dyno at RE Customs and was advised it was the coilpacks and as soon as they put the Spitfires in problem was fixed!! :thumbsup:

SHIZNT Collaborator

SHIZNT

Posted
Posted
that is VERY weird. maybe its the additional heat from our turbo engine that make them stuff up faster?

glad you got it fixed and it wasnt TOO expensive

Common problem with most engines running coilpacks that are covered... after awhile the heat causes them to burn and then you start loseing spark... this is why you see alot of rb25's without the engine covers...

At the end of the day these cars are 7-12yrs old and probably have never had them changed befor which sounds not so bad to me..

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