Hard To Idle After Turbo Install

[FordyR31]

Hi,

Had my GT3076 installed yesterday and the car wont idle after driving. Drove fine before the switch. Could it be tune related? Previously had a PFC tuned for a FMIC 3" exhaust, stock afm and R34 NEO turbo. only things to change are some of the plumbing from turbo to cooler, intake pipe and obviously the turbo. If I start it cold it idles fine. Once i drive it and pull up in traffic it just stalls and takes about a minute of me trying to gently feather the throttle til it idles. Any help please?

[75coupe]

hmmm put a much larger turbo, stock afm and no tuning done, and motor has problems with it...

nope sorry it all sounds fine to me...

[wolverine]

Vacuum hose not reconnected??

[The Mafia]

I'd say you're a complete fool for driving it without a tune but double check all hoses etc.

[FordyR31]

I had to get it home..... its tuned just not for this turbo which is running 7psi gate pressure. have checked hoses and cant find anything

[75coupe]

if its not tuned for the new turbo then its simply not tuned...

release the gate completely so it gets no boost until its tuned...

what bov is installed?

[GTSBoy]

I hate to say it, but what the hell has the tune (or lack thereof) got to do with hot idle?

We're talking about no revs and no load and so the turbo has no effect on the idle. Things like changing the BOV configuration and so on might contribute, but he could have strapped a T88 on there and you'd still expect it to hot idle.

And he could nurse the car along with little or no boost to drive it home and again the turbo would have no impact on the way the car drives, and even if he made a little boost here and there, the bloody car has an AFM so it's quite likely that it could handle it just fine without turning the plugs into charcoal crayons.

My vote is also on hoses or similar installation whoopsies.

[FordyR31]

Its a GFB bov and its been on there for years. it drove fine to get it home in the fact it was smooth and could change gears etc but as soon as the clutch went in it and the revs dropped at a set of lights will stall. The gear changes dont see the revs drop enough so thats why it seemed to drive if that makes sense. Even sometimes on decel it can get a bit shuddery. I dont intend on driving it anymore until it is tuned I just dont want an already expensive tune to turn into an expensive fix and tune so was just looking for an answer in case it was something I could do and then get it tuned.

Edited April 5, 2012 by FordyR31

[75coupe]

is that an ATMO bov?

[badhairdave]

Do you guys do a risk analysis before you take a dump? Sorry, should go back a step; Do you guys do a risk analysis before you eat something spicy?

Nah, sorry mate, can't put it on the dyno, not safe to drive it onto the rollers....

Idle issues; check vac lines, afm may be a bit touchy if you have a short metal intake pipe or an atmo BOV so the tune it may need a touch up in that area possibly combined with adjusting the idle screw.

[FordyR31]

The bov is plumbed back permantly on one side and i have tried with both the atmo attachment and the plug in so it was completely recirculating. Again this is no change to how its been for the past 5 years. yes it now has a steel 3" intake pipe but all the plugs are the same for the bov and breather etc. its just a metal copy of it pretty much to retain the stock airbox until i get another one made and afm position.

[The Mafia]

Is the IAC valve plugged in?

We need more information on what has been done.

For all we know, you could have bolted a bigger turbo, cams, injectors, blow through super charger, and hooked up a bottle of NOS.

More information please, not just dribble it in as we need it.

[FordyR31]

I have already mentioned whats been changed.

before issues:

S2 RB25DET

Power FC tuned

R34 NEO turbo

Splitfires

3" exhaust

FMIC

Recirculating GFB bov

Stock intake and airbox

They are all the mods that were done and it was running perfectly.

Changed the turbo

Modded the intercooler pipe to suit

steel intake pipe with all hoses attached as if it were the factory one.

[32vspec2gtr]

The tune could be the issue for the fact that the turbo could be a bigger restriction on the intake side hence snuffing the engine because the turbo is trying to effectively stall and the engine can't breath enough through the intake hence why it stalls. Would be unlikely but possible.

As said before, it sounds more like vac lines of some sort allowing it to gain air that it doesn't relise it has hence leaning out and stalling. Check ALL piping (before turbo, after turbo and even manifold, even if you haven't been there as you could have bumped it off) as even a leak from a clamp not been done up can suck air through which the engine doesn't know it has. It will idle when cold due to the engine automatically enriching the engine till it gets to temp. Effectively counter acting the air in the system it doesn't even know about. When it gets to temp it leans back out and stalls for been too lean.

You could have gotten oil from the filter if its an oil based filter onto the air flow meter even, or simply it could have gotten dirty while installing the turbo as you only need to get a little bit of crap on it to make dramas. For this one, get some contact cleaner (yes contact cleaner not brake clean or anything else) from super cheap/ autobarn/ etc for a couple of bucks and clean the fine wire in the center of the airflow meter where the air passes over.

Give that ago to start with.

Matt

[GTScotT]

Youve stuffed the plugs because your driving a car tuned for a 1hp turbo which now has a 500hp turbo.

The ecu measures load by AFM voltage, I imagine that the AFM voltage would be a little higher when your cruising around (using some throttle) than when using the tiny turbo.

Get it to a tuner ASAP as the extra fuel would be washing down the bores and potentially FK'ing the motor.

[FordyR31]

Thanks for the feedback. I won't be driving it til its tuned.

[32vspec2gtr]

Youve stuffed the plugs because your driving a car tuned for a 1hp turbo which now has a 500hp turbo.

The ecu measures load by AFM voltage, I imagine that the AFM voltage would be a little higher when your cruising around (using some throttle) than when using the tiny turbo.

Get it to a tuner ASAP as the extra fuel would be washing down the bores and potentially FK'ing the motor.

I don't understand this???

AFM does have an effect but it only measures the amount of air passing over it.

The amount of air passing over it effectively cools the wire causing the wire to have more resistance in which alters the voltage giving you a reading.

The input voltage never changes. It is set to 5 volts from memory and is so that even if there is low power, spikes, etc it will still read effectively.

Engine load on the other hand is measured by a number of factors. These include tps, road speed, boost/vac, inlet temps,O2 sensor readings, etc.

In my opinion, by changing the turbo it has done nothing to the lower part of the map. This is because the AFM is still reading the amount of air coming in as nothing has changed that fact that it is still cooled by the amount of air coming in. Therefore if the turbo was changed and the air increased or decreased it should in theory measure that anyway and adjust to compensate. If it was adding too much fuel it would be picking up that it is doing so via the O2 sensor and still it would adjust to suit.

I do however agree that the engine should be tuned for the new turbo asap as the amount of air the turbo would flow at higher rpm compared to the older turbo could effectively have the afm run out of room to measure therefore leaning the engine out causing detonation or depending on the safety setups in place on the power fc could richen the A/F mixture causing it to wash bores.

If this is incorrect please explain to me as more info can never hurt

Another thing to check is to make sure you haven't damaged the O2 sensor as well, as this is used under cruise and no load situations (idle) as a closed loop system and is also disregarded during warm up.

[GTScotT]

I don't understand this???

AFM does have an effect but it only measures the amount of air passing over it.

The amount of air passing over it effectively cools the wire causing the wire to have more resistance in which alters the voltage giving you a reading.

The input voltage never changes. It is set to 5 volts from memory and is so that even if there is low power, spikes, etc it will still read effectively.

Engine load on the other hand is measured by a number of factors. These include tps, road speed, boost/vac, inlet temps,O2 sensor readings, etc.

In my opinion, by changing the turbo it has done nothing to the lower part of the map. This is because the AFM is still reading the amount of air coming in as nothing has changed that fact that it is still cooled by the amount of air coming in. Therefore if the turbo was changed and the air increased or decreased it should in theory measure that anyway and adjust to compensate. If it was adding too much fuel it would be picking up that it is doing so via the O2 sensor and still it would adjust to suit.

I do however agree that the engine should be tuned for the new turbo asap as the amount of air the turbo would flow at higher rpm compared to the older turbo could effectively have the afm run out of room to measure therefore leaning the engine out causing detonation or depending on the safety setups in place on the power fc could richen the A/F mixture causing it to wash bores.

If this is incorrect please explain to me as more info can never hurt

Another thing to check is to make sure you haven't damaged the O2 sensor as well, as this is used under cruise and no load situations (idle) as a closed loop system and is also disregarded during warm up.

Yes, the AFM has 5v in and the element measures flow by vibrations in the passing air and outputs a voltage. The ECU reads that as airflow and plots a certain point on its mapping with that data along with other data.

To say it would little impact on mixtures is ridiculous. Thats like saying boosting a stock R33 cant possibly make it hit R&R................... Wrong right? Yeap.

The points that are likely to be screwing his mixtures badly are the cruise areas of the map like I said. Between 3000 and 4000 rpm where the turbo IS pumping a fair volume but is not yet 'boosting'. You have to agree that the stock turbo would not suck an identical volume to a 3076R at that level, and its doing a little more than idling along (consider your in 3rd gear at 40kmh and start trying to chuff along to 60kmh). Thats going to be a big difference in flow from the compressor between the two, and subsequently a big difference in the resultant map trace.

I hope Ive explained it clearly enough for you. My theory is that his plugs are fouled. Remember that his comments were, it ran like shit after I drove it a while. Not, my car ran like shit ever since I installed the new turbo.

[GTSBoy]

Wrong wrong wrong.

Nissan AFM is a hot wire type, not a vortex counting type (like Mitsu). AFM is THE thing that determines engine load. What the AFM says the load is, that's the load. Doesn't matter how you get that load - by hanging the AFM off a big motor, or hanging it off a small motor with a little turbo working hard or a big turbo hardly working. The load is the measured air quantity.

THE SIZE OF THE TURBO WILL HAVE NO SERIOUS EFFECT ON THE MEASURED LOAD OF AN ENGINE THAT IS JUST BEING DRIVEN AROUND GENTLY. It's only when you get serious revs and boost happening that the differences in exactly what revs which airflows happen at start to affect a tune.

As I said previously, he could have bolted a T88 to the engine and it should not affect how it idles, and it should not affect low load driveability either. In fact, you could try to drive it quite hard, and as long as the previous tune covered the low load (ie, no boost) high rev portions of the map properly, it would probably be quite fine then as well.

[JonnoHR31]

Drive it around all you want, under light loads your not going to wash down the bores and destroy your engine, what a joke! Whilst i wouldnt reccomend it, 90% of the time it'll be fine to thrash on low boost too, aslong as the previous tune isnt miles out.

It sounds like a leak somewhere, check every bit of the intake piping for leaks and if you cant find any you could try pressurising the intake and using some soapy water on the joins. Otherwise if your certain its not leaking, try cleaning the afm.