Mark P

car will not start the first time I try after it's been sitting for a long time (~8hrs). Then when I try again, it will start but it will run lean (about 18:1 A/F) while the car is in "warm up". Then EXACTLY when the RPMs drop (~1200 -> ~800), the A/F goes right to the expected 14.7:1. This occurs with two different sofware tuners software in my car, so it's not the ECU/tune. It, however, has to be something that is only operating (or not operating) during warm up conditions. What could that be?

I am completely unaware of what secondary air injection does and if it may or may not be a possible cause of my issue.

I don't have any engine fault codes for SAI. The only code I had was for a coolant fault (temp sensor or thermostat) which I assume I fixed recently when I did a timing belt service.

I don't even know if this car has SAI??? I have seen a black plastic horn looking thing which I am guessing is this? anyone have a photo?

This is for my AWW 1.8T Golf, btw.

ModifiedA4

if you dont have SAI codes, its unlikely it is the issue.

basically SAI injects fresh air into the exhaust stream. this will cause unburnt fuel in the exhaust to burn in the cat. the cat then warmed up quicker. the reason for SAI is for reducing cold start emissions.

on the 1.8t the combi valve on the head opens via VAC from the N112 solenoid. meanwhiel the SAI pump forces fresh air into one of the exhaust ports in the head.

you reading lean on startup is probably exactly what it should read given SAI.

on my 2000 1.8t the combi valve is a silver cannister on the back of the head:
<img src="http://www.modifieda4.com/images/thread-repair/DSC00336.sized.jpg">

By the way, TIP B5 S4s have the SAI system.

Mark P

Otherwise, I'm not sure how it could be the culprit. It would seem that my issue has to be something that is only used during warm-up. Tell me more about this check valve - is there just one, etc?

Btw, I'm reading lean from my wideband and the car stumbles if I try to drive it. I just let it complete it's warm up, then all is fine. It's not a matter of just the ecu reporting something being lean - it's actually running lean.

block 31 (I think, or 32) is reporting that the Actual A/F is pegged at 1.00 during warm-up. I believe this to be a fake reading to safeguard the fact that the O2s are not up to operating temp yet and wouldn't read correctly if their value was used. The Desired A/F is specifying a rich condition (I think I've seen as rich as 0.87). This is all as I would expect for a warm-up conditions. As time passes, then the Actual readings become real and I can see the expected fluctuations. Likewise, after warmup, the Desired A/F goes to 1.0. All, as I would expect.

What's not expected is that while the car is reporting that it's desiring a rich condition, the car is actually running lean. And I'd like to solve this.

Thanks for the info on SAI. I've been reading some archives and I think I now understand it better. I did find a pic too, and it looks as I thought, which I do believe I have:
<img src="http://pictureposter.audiworld.com/97664/img_3728.jpg">

<img src="http://pictureposter.audiworld.com/97664/img_3734.jpg">

Silver Streakin'

I believe 13 is the brake fluid resv and 12 is going to the brake assist.

ModifiedA4

if you are having problems after start/driving then its not the fuel pump check valve.

you could just have a generic lean issue (like a vac leak) which is exacerbated by the cold start.

if it treuly is a SAI/cold start issue, a 3rd gear WOT log should show perfect numbers? no?

Mark P

As soon as the rpms drop down to ~800, the car runs perfect.

I'll take some vids/data logging to show the following....

1.) let car sit ~8 hours
2.) try to start car
3.) it may or may not start
3b.) try again if needed - always starts 2nd time
4.) car operates in "warm up" mode. RPMs are higher (~1200) and Desired A/F requests rich (0.90 lambda). Wideband showes A/F is lean (up to 21:1 - max reading of gauge).
5.) wait 2 mins (during which time, Desired A/F slowly becomes less lean, approaching stoich 1.0)
5b.) if I try to drive car now, it will stumble in it's overly lean state.
6.) warm up ends, and exactly when RPMs drop to normal idle (~800), the wideband shows that A/F goes right to stoich (14.7)
7.) All is great

If the car has been driven more recently (say 3 hours or less), go directly to step 7 and enjoy. No problems then at all.