Jump to content
SAU Community

Recommended Posts

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?

Link to comment
https://www.sau.com.au/forums/topic/365739-random-leaning-idle-and-coasting/
Share on other sites

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?

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?

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

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...

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)?

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...

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!

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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • I know why it happened and I’m embarrassed to say but I was testing the polarity of one of the led bulb to see which side was positive with a 12v battery and that’s when it decided to fry hoping I didn’t damage anything else
    • I came here to note that is a zener diode too base on the info there. Based on that, I'd also be suspicious that replacing it, and it's likely to do the same. A lot of use cases will see it used as either voltage protection, or to create a cheap but relatively stable fixed voltage supply. That would mean it has seen more voltage than it should, and has gone into voltage melt down. If there is something else in the circuit dumping out higher than it should voltages, that needs to be found too. It's quite likely they're trying to use the Zener to limit the voltage that is hitting through to the transistor beside it, so what ever goes to the zener is likely a signal, and they're using the transistor in that circuit to amplify it. Especially as it seems they've also got a capacitor across the zener. Looks like there is meant to be something "noisy" to that zener, and what ever it was, had a melt down. Looking at that picture, it also looks like there's some solder joints that really need redoing, and it might be worth having the whole board properly inspected.  Unfortunately, without being able to stick a multimeter on it, and start tracing it all out, I'm pretty much at a loss now to help. I don't even believe I have a climate control board from an R33 around here to pull apart and see if any of the circuit appears similar to give some ideas.
    • Nah - but you won't find anything on dismantling the seats in any such thing anyway.
    • Could be. Could also be that they sit around broken more. To be fair, you almost never see one driving around. I see more R chassis GTRs than the Renault ones.
    • Yeah. Nah. This is why I said My bold for my double emphasis. We're not talking about cars tuned to the edge of det here. We're talking about normal cars. Flame propagation speed and the amount of energy required to ignite the fuel are not significant factors when running at 1500-4000 rpm, and medium to light loads, like nearly every car on the road (except twin cab utes which are driven at 6k and 100% load all the time). There is no shortage of ignition energy available in any petrol engine. If there was, we'd all be in deep shit. The calorific value, on a volume basis, is significantly different, between 98 and 91, and that turns up immediately in consumption numbers. You can see the signal easily if you control for the other variables well enough, and/or collect enough stats. As to not seeing any benefit - we had a couple of EF and EL Falcons in the company fleet back in the late 90s and early 2000s. The EEC IV ECU in those things was particularly good at adding in timing as soon as knock headroom improved, which typically came from putting in some 95 or 98. The responsiveness and power improved noticeably, and the fuel consumption dropped considerably, just from going to 95. Less delta from there to 98 - almost not noticeable, compared to the big differences seen between 91 and 95. Way back in the day, when supermarkets first started selling fuel from their own stations, I did thousands of km in FNQ in a small Toyota. I can't remember if it was a Starlet or an early Yaris. Anyway - the supermarket servos were bringing in cheap fuel from Indonesia, and the other servos were still using locally refined gear. The fuel consumption was typically at least 5%, often as much as 8% worse on the Indo shit, presumably because they had a lot more oxygenated component in the brew, and were probably barely meeting the octane spec. Around the same time or maybe a bit later (like 25 years ago), I could tell the difference between Shell 98 and BP 98, and typically preferred to only use Shell then because the Skyline ran so much better on it. Years later I found the realtionship between them had swapped, as a consequence of yet more refinery closures. So I've only used BP 98 since. Although, I must say that I could not fault the odd tank of United 98 that I've run. It's probably the same stuff. It is also very important to remember that these findings are often dependent on region. With most of the refineries in Oz now dead, there's less variability in local stuff, and he majority of our fuels are not even refined here any more anyway. It probably depends more on which SE Asian refinery is currently cheapest to operate.
×
×
  • Create New...