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Random Leaning @ Idle And Coasting

StealthX

By StealthX,
in Engines & Forced Induction

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StealthX Veteran

StealthX

Posted
Posted

Hey guys.

My car was doing something strange yesterday.

It started going lean and popping at idle, at normal operating temp, so I grabbed out my hand controller and my LC1 was telling me it was running about 18-20AFR!

Everywhere else was fine, under boost, cruising above 2000rpm etc, all fine, but as soon as the revs dropped below 2000rpm, coasting with no throttle and idle conditions caused the pop. Coasting down in gear under 2000rpm made it pop like mad. It's as if anything below 3mS of fuel became unstable, like I was running 1000cc injectors lol

It usually takes about 2.0mS of injector to get 12-14AFR at idle depending on ambient temp, but yesterday I needed 20% more fuel, 2.4mS gave me 14-15AFR with the occasional pop and 16-17.

Does anyone know what this sounds like? Keep in mind I havn't changed anything before, all I've done was install some LED angel lights, which weren't even on at the time.

dying fuel pump - unlikely, the pump is only 18 months old

blocked fuel filter - possibly

dirty injectors - maybe

bad batch of fuel - maybe, I filled up at Gull using their 98, which I had never done before!

Any ideas?

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Lithium Grand Master

Lithium

Posted
Posted

Whats your setup - do you have an AFM?

What kind of voltage is the ECU reading?

Does the car do it consistantly since you first spotted this issue, or was it a once off?

And to clarify, do you mean specifically coasting down - or if it is actually sitting there at idle, will it stay at 18-20afr consistantly?

StealthX Veteran

StealthX

Posted
  • Author
Posted

Whats your setup - do you have an AFM?

What kind of voltage is the ECU reading?

Does the car do it consistantly since you first spotted this issue, or was it a once off?

And to clarify, do you mean specifically coasting down - or if it is actually sitting there at idle, will it stay at 18-20afr consistantly?

Sorry not much info... haha

EMS Stinger - map sensored, no TPS.

Engine is a QR25DE+T

returnless fuel system, walbro pump, 440cc WRX injectors, stock everything else.

I'm not sure if it's a one off, I havn't started the car up today, just been sitting here studying all day - ill report back when I go for a drive later.

There's two situations that it does it, at idle, and coasting down in gear at low revs, both occur at low throttle, below 2000rpm.

it's odd because it's never done this before!

Does it sound like anything common?

Rolls Grand Master

Rolls

Posted
Posted

I had this sample problem and couldn't fix it, would backfire badly when coming back onto the throttle and would pop at idle idling around 17:1 then would go back to 12:1

even had pete from nistune look at it and he wasn't sure of the cause

StealthX Veteran

StealthX

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  • Author
Posted

I had this sample problem and couldn't fix it, would backfire badly when coming back onto the throttle and would pop at idle idling around 17:1 then would go back to 12:1

even had pete from nistune look at it and he wasn't sure of the cause

That's exactly what my car is doing!

Aside from the current leaning problem, my car has always had an issue at around 1700rpm, you have to apply load very smoothly, otherwise it'll buck down and die, I've tried adding up to 40% more fuel at these points and it does nothing. As long as the car's had the EMS there, its had a problem at 1700rpm, but now since this new tank of fuel, it's developed this weird leaning condition.

Actually thinking of it now, the servo that I filled up at was a United. Up until last week I've avoided them because I didn't know they sold 98. But last week I filled up with their "98" for the first time. I'm leaning (pardon the pun) towards bad fuel...

blind_elk Grand Master

blind_elk

Posted
Posted

Frankly, I wouldn't be worrying about running so lean at idle. It will not damage the engine at all, because there is virtually no load on the engine.

As for the popping, have to set up the EMS to shut off the injectors when the throttle closes (such as when you coast down, or change gears)?

StealthX Veteran

StealthX

Posted
  • Author
Posted

Doesn't have an idle map as such, it's got a separate function for idle control, then I've just tuned the points around idle for 12-14 ish, then air temp and water temp correction values take over from there too, none of which I had changed before it started going wierd. Has no TPS.

Dont know what fuel pressure is doing, I dont have a fuel pressure gauge, if it starts going wierd again I'll look into it further...

Went fir a drive yesterday and it's all fine again...

StealthX Veteran

StealthX

Posted
  • Author
Posted

Loose wires somewhere?

I cleaned up all the mess behind the head unit yesterday, coincidentally it stopped being wierd, but all I was doing was cable tieing things up, besides there's nothing behind there to alter fuel control...

Anyway thanks for your help bros!

StealthX Veteran

StealthX

Posted
  • Author
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Okay so the problem surfaced again today, and today was the same type of day. It's got something to do with overcast humid days. Not necessarily hot vs. cold, cos it runs fine at night and during a hot day. Maybe humidity plays a part?

i'm gonna do a fuel filter, run some injector cleaner through and install an air temp sensor and tune some air temp comp maps, see what that does.

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