Yesterday my car started running super rich at idle. It shows as low as 9.06:1 on my wideband, and I have to even hold the gas pedal to keep it running. Before it has always idled at about 14.7:1.

Vacuum is good at 22 in w.g. at idle
Boost is fine at 10 psi on the road.
Car runs very well under full power, goes like stink (about 300 WHP) with an AFR of about 12.5:1
Rich idle sometimes clears up and goes back to 14.7:1, but when I came home from a test run it started to idle super rich and stumble at low speed.
I checked for exhaust leaks and could find none.
Car was dyno tuned many times including last fall and has always run perfectly at idle and under boost for 3 years now.
Hondata S200 with OBD1 ECM, RC 750 injectors, Walbro pump, stock FPR and rail, Full-Race road-race turbo kit.

So what could have gone wrong to cause this sudden change as of yesterday only after years of no issues?

Intermittent bad O2 sensor? (I don't have a CAT)
IAT sensor?
vacuum leaks?
Any other sensor?

Need help quick as I'm paid up to be on track tomorrow

 

did you check vaccum hoses....

 

No I didn't check vacuum hoses since I assumed they would be OK if it pulls 22" of vacuum at idle. Only vacuum hoses are line to BOV which is working fine, line to boost gauge, line to brake booster, and a couple more I will check for leaks, all coming off my Victor-X mani.

Does a vacuum leak cause rich idling?

 

Are you running open or closed loop? If your running closed it could be your O2 sensor. Are your water temps normal?

-platinum

 

stock fuel pressure regulator?

sometimes regulator diaphrams can go back, aftermarket or stock, or you could have a slight blockage in your return line

 

stock o2 sensor could be going bad

 

wait, do you have a wideband O2 or a stock O2 sensor? cause iirc most widebands are good for about 60hours on gasoline and about 20hours on race fuel. at least thats what AEM says.

 

Yup, O2 sensor went bad.

 

How about the most simple of things - clean your valves/injectors? Its a good idea to run a good cleaner like the tecron stuff once in a while through your tank. You could have excess carbon deposites on the valves/chaimber/pistons since you are running richer than 14:1 fairly often. A good beating can usually remove exhaust and chaimber deposites, but intake is harder to deal with. I'm also assuming you don't recirculate your blowby, which can further block your setup intake to exhaust valves.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blinx9900 &raquo;</TD></TR><TR><TD CLASS="quote">wait, do you have a wideband O2 or a stock O2 sensor? cause iirc most widebands are good for about 60hours on gasoline and about 20hours on race fuel. at least thats what AEM says.</TD></TR></TABLE>

We install several AEM W/B's a week and never have them go bad that fast, but it is always a possibility.

You might want to switch out the sensor just in case.

Ian

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by qksl2 &raquo;</TD></TR><TR><TD CLASS="quote">

We install several AEM W/B's a week and never have them go bad that fast, but it is always a possibility. </TD></TR></TABLE>

agreed, but thats what aem says.

 

To everyone who said the stock OEM O2 sensor was bad, thanks. That was it. Car was running pig rich at idle in closed loop. Track buddy brought over a spare used OEM sensor. I put it in and 5 minutes later everything was back to normal, idling when warm at around 14.7:1. My wideband (Tech-Edge with Bosch sensor) is not in any way connected to the ECM. It just reads the values in the exhaust.

That is my second OEM O2 sensor that goes bad in about 3 years since I have been running this turbo, and car is pretty much only driven on road racing tracks, and only on street to get to the tracks. First one that went bad threw a CEL because the heater in it went open circuit, but this second one had no CEL error and it's heater measured fine at 14 ohms. I do not use race gas, just Sunoco 94. Does anything cause these Honda OEM senors to go bad?

Anyhow car ran fantastic all day yesterday on track, with zero issues, which is a first for me. Turbo smiling all the way up the back straight!

I have another quick question. Wideband reads pretty steady between 11.5 to 11.7:1 under full power down the straight for about 25 seconds going from 3rd to 4th to 5th gear. Is that a good value for AFR? Car is getting all black on the rear bumper are from the rich mixture. Is it too rich?

 

Id say thats a pretty safe a/f to run under full boost. And it should read around 14.7 at idle. With a straight threw exhaust your gonna get some soot on that bumper.

 

i read 12.5 AFR is the best for optimal power, but 11.5 AFR is a nice medium that keeps things cool too.

 

All-right, I'll keep the AFR where it is at 11.5:1.

But is there some kind of magic cleaner to get that black soot off the rear of my "used to be white" ITR? When you drive on road racing tracks, you burn a ton of fuel at full throttle, unlike anything you would ever do on the street. I've tried a lot of things but nothing seems to work very well. It makes me a kind of a visual magnet for the police on the way to the track so I'd like the rear of the car to look a little more normal.