Air Fuel Ratio Queries

[chipstick 382 1 Cars]

For a while now my car has appeared to run rich. (2.0 GTi6 with Satchel bodies and DTA S40)

 

Initially I changed the coolant temperature sensor but that hasn't improved it.

 

I've hardly used it this year mostly due to that fact and the rough running. It's put me off using it.

 

I recently bought an AEM AFR sensor and gauge so I could measure severity of the fueling and potentially see what could be causing the rich running over varying conditions.

 

Throttle position sensor faults appear to cause rich running from doing some googling. When I have connected the ECU to a laptop it shows 0 when closed and 100% when full throttle is applied so I believe I can rule that out.

 

I've given the car a quick run this afternoon since fitting the gauge and it fluctuates all over the place. From low 11's up off the scale to ---- for a split second depending how it's driven. After about 10 mins when the car was up to temp it stuck at 14.6 then 14.7 without moving. Restarted the car a couple of times and it wouldnt move from that so I'm unsure whether a connection has loosened or it's packed up.

 

If anyone can recommend some specific testing or things to look at on the laptop I'm willing to give anything a go.

 

Worth noting - the gauge gets it's power from one plug and there's another plug which goes directly into the S40. If I source another junior power timer plug and fit it to the gauge lead, will the S40 be able to make live adjustments based on the readings it is given?

[Sandy 189]

Your best bet really is to come back down so I can check it over, otherwise you really are guessing and any suggestions from here are going to be generic at best. If something has changed then I'll be able to identify it and restore everything to the way it should be, you'll get further and further away otherwise! Running closed loop lambda control on aftermarket ECUs isn't as easy as it sounds to get right and can often spoil the smoothness of a good map.

[chipstick 382 1 Cars]

Yeah you're right that's the best thing to do - get it sorted once and for all otherwise I could be changing umpteen things and it's likely I'd get fed up before I resolved it no doubt.

 

The tax is up at the end of December and it won't be renewed until April as it will be stored away until the spring. Would you be able to fit me in one day this month at all Sandy? I'm quite flexible on a day so if you fire some dates at me I'll take a day off work and whip down

[Sandy 189]

Message me know when suits and I'll fit you in

[Anthony 1,000]

As said, given your proximity it's probably best popping back to Sandy if you've checked the basics.

 

Plugging the laptop in and making sure that the various sensors are reading correctly and that the TPS is calibrated with smoothly increasing values as the throttle opens is the main check to do, which it sounds like you have.

 

If you've got a synchrometer, it's worth checking that the 'bodies are still in balance, as if they've gone out both fueling and driveability - particularly on light throttle - suffer badly in my experience. You need to be a bit careful though, as if you adjust them to a different initial setting than they were mapped at then it won't run right.

 

Don't try and use the wideband lambda to get the ECU to adjust the fuelling and mask the underlying problem, and certainly don't blindly start adjusting the map - if Sandy did it then it will be right for the engine setup and there will be something that's changed elsewhere causing the problem.

 

With the wideband lambda NOT connected to the ECU (ie reading it on a gauge) I would expect to see something in the ballpark of low-mid 13's on WOT and mid-14's to low-15's on cruise. It'll be richer on startup and when the engine is warming up, it will go lean on overrun, and it will fluctuate quite noticeably with inclines and different loads/throttle. If it's widely different then something's amiss.

 

I'd pop along to Sandy personally though if the basics look alright and he can fit you in, as some issues can be a complete pain to find and you can make finding the original fault difficult if you've been changing/adjusting things trying to find the cause.