Hilton

Hi all,

The attached dyno graph is of my '89 5-speed S4 - stock except I replaced the mid muffler with an X-pipe.

Power is a good result, especially on a Dyno Dynamics dyno in shootout mode.

But.. AFR is all over the place - dropping as low as 10 ! You can see it's hitting the power curve too.

Background:

• The car has NO CATS and NO O2 sensor, from factory - its UK spec
• Idle mixture has been adjusted to factory recommended 1% CO using an exhaust gas analyser
• Tried with two different '89 S4 LH brains - same power, same fuelling issue, so faulty LH isn't the cause
• Checked pins for MAF signal potentiometer at LH plug - same reading as on the pot's pins
• Actuator test with JDS Spanner says WOT switch on throttle sensor works (as does idle switch)
• LH Coding plug unplugged and re-plugged to make sure its seated
• MAF is JDS rebuild thats about a year old

So.. what can cause rich running like this?

I thought it might be the TPS, but a test a few mins ago says its fine, using JDS Spanner to read the signal.

Two separate pulls graphed below in case it tells anything - first was 278.3 rwhp max, the one after was 275.1 rwhp.

Lizard928

Hilton, this is how a lot of S4 are. Adding an O2 won't help as the O2 isn't used at WOT.
What you need is to get your car sharktuned.
And maybe a good italian tuneup. But word has it that is pretty dangerous over there

mark kibort

still have stock mufflers, right? as was said, cats are only restrictive and dont change much as well as the 02 sensor not doing anything at all at WOT. i the coding plug set up for no cat or O2 sensor?

loosecannon

Just a thought: if the engine temperature sensor isn't plugged in or not working, the computer thinks the engine is cold and richens the mixture. I had a simlilar problem with a 911.

Hilton

Colin, getting sharktuned is in my future - just not until I've got more of the bits in my garage bolted on/in Not all engine related, but I need to focus on getting the car sorted for track days.

Having said that, I have a hard time believing that the AFR of 10 is just conservative tuning from Porsche of the S4 map - its *way* off.

Interesting idea - I woke up a half hour ago, and the intake temp. sensor was what sprang to mind after a sleep on it. Need to do some reading to see how to test and what effect it would have - still only 5:40am here tho so coffee must happen first.

Mark K - coding plug is definitely non-cat manual gearbox - pulled and checked the pins and inside of it to make sure the loop of wire was intact. The O2 sensor connector exists in the harness, but there's a bridge joining one of the white wires to the signal pin plugged into it, from factory. You're right about WOT using open-loop anyway - which is why I initially thought TPS was the culprit. But a test of it last night says its fine.

Keep 'em coming.. I want to get these dyno's done so I can bolt more stuff on. My '87 arrives in a week and a half and needs some work, so I'm racing to get this car to a known-good state

Hilton

One thing from peering at the graphs over coffee..

The later of these two runs is noticeably richer across the range. Still bottoms out at 10, but is there longer, and elsewhere the grpah is pretty consistently lower. Given the engine is warmer, it may well be temperature related?