GavinP

Hi

I think the Lambda sensor on my car is not working properly (94 WRX Auto).

It's coming up to MOT time and I have removed the Link ECU (Lambda OFF) and replaced the OE ECU and the AFM/wiring - the car starts for about a second and then gives a CEL.

If I hook up the diagnostic plugs (black), I don't get any error codes - although I understand the CEL for the oxygen sensor is 32.

The LambdaLink shows full rich on starting although the car is cold.

The car runs fine with the Link ECU fitted.

The last time Bob did some mapping on my car, he said the Lambda was on it's way out - is there anything else it could be so I can make sure I have all the options covered ?

Second opinions ? Good places to source a new one ? Easy to replace ?

Thanks

Gavin

Jan Shim

Hello Gavin,

I had a very similar incident with my 98 WRX. When i was running the Link ecu, my LambdaLink monitor showed A/F ratio getting leaner and leaner until it was only showing amber at best on full throttle. Obviously this was a worry and I thought it's time to fit another sensor (third piece) as Link ecu is notorious for killing O2 sensors due to its extremely rich idle.

So, I decided to fit the stock ecu just to see what would happen since i wasn't going to get a new sensor till a week later. Oh man, the LambdaLink showed all signs of a healthy sensor. Took the car for a spin and there was absolutey nothing wrong with it. Plug the Link ecu back and again it started to lean out (nothing wrong with MAP either).

The difference between your situation and mine is I never got a CEL after fitting back the stock ecu. And,the Link ECU never went back. I decided I was much happier running the JECS ecu and seeing the car idle perfectly (nice leanish AFR) and running smoothly than it ever did before.

Bob Rawle

Gavin, if you havn't got round to replacing it the=n you should, also the maf could probbaly do with a good clean, you have the hot wire variety so a good blast with brake cleaner and a gentle rub of the wire with a soaked cotton bud should sort it.

Jan just cos you couldn't map your link to idle at a decent afr doen't mean its a Link problem ... it only uses the numbers that the tuner puts in it. The jecs idles as rich as they come when the engine is cold.

Since the main difference is the Jecs uses the maf then thats where the problem is likely to be, had this with my Sti 2 wagon when I re-fitted Jecs, cleaning the maf sorted it.

GavinP

Jan / Bob,

Thanks for the replies.

The Link ECU works well - I just swap the ECU once a year (normally for about two hours!) to pass our annual motoring "roadworthiness" test (MOT) which has a comprehensive gas emissions test. I wouldn't want the OE ECU in place for any length of time!

Bob said the last time I saw him that the Lambda sensor was on it's way out so I'm certain it needs replacing - I just wanted to know if there was anything else I should check as well.

The MAF should be OK as it has sat in a box for the last year but I'll give it a clean to be on the safe side.

Thanks again,

Gavin

Jan Shim

Bob,

I mean no disrespect to your tuning abilities with the Link ecu. If anything, I thank you for sharing and coaching me to overcome the teething problems I had as a Link newbie and so forth. Fact remains, I have personally seen cars that were tuned by a few 'qualified' tuners including one from PossumBourne and let's just put it this way, it made me feel real good that I too was capable to tuning rich AFRs for idle (essentially anyone can). The rich phenomenon on earlier Link boards was a pest and I dont know if there has ever been a new chip to replace this 'flaw'.

The JECs ecu idles rich simple because it's programmed that way. This is explained in the Workshop Manual under Temperature Coefficient. The lower the ambient temps resulting in a low coolant temp triggers the ecu to idle longer (and richer) that normally until temp has normalised. I have had two difference experience with the Link-JECs swap in the past, one where the oxygen sensor was genuinely defective (so had to be replaced) and the other pretend defective. The last one was really odd and there is still no answer. I checked and checked and could found no problem with the MAP yet it shows lean on WOT. Plug in the JECs and everything was ok.

Gavin, I have also seen cars where the oxygen sensor was faulty but never threw a CEL, and there was another where it threw a CEL only after the car had been trashed for a while causing the sensor to overheat. Once the engine cool down, no CEL. Your situation could be any of this.

Jan

GavinP

I just called RCM who look after my car and a new Lambda sensor is £234.43 + VAT !

Bob said that the UK part is identical apart from the wiring loom and I have also heard Halfords produce a generic part which works as well - if anyone has any details/part numbers, it would be appreciated.

Is changing the sensor a difficult job ?

Thanks

Gavin

ozzy

Gavin,

On a MY99/MY00 UK car (haven't seen inside a 94 WRX), the lambda is in clear view on top of the downpipe (just behind the heatshield).

Andy.F (Scotland forum) has fitted the Halfords one without any problems. He did have to mod the wiring adapter though.

I think it's 22mm (memory?), so an open-neck or even round-neck spanner would do the job,

One word of warning though, my dealer told me that it's VERY easy to strip the threads on the downpipe when changing the sensor. Their advice is too use a pressure washer to cool down the downpipe and apply tons of lubricant before trying to remove it.

If the DP isn't cooled down, then they guarantee that the thread will strip.

Stefan

[Edited by ozzy - 6/17/2002 11:17:31 AM]

Jan Shim

Gavin,

Here are photos of the Oxygen sensor and location of where the sensor is fitted. On mine, I run a BPM twin dump that has the sensor bung at an angle so it was very easy for me to change out whenever i wanted. I think on the stock downpipe and most other designs for that matter, the sensor sits parallel to the engine and makes tool movement virtually impossible.

As for choice of sensor I would not mess around with third party parts. Stick to genuine BOSCH sensor for your Subaru. There is a difference in wiring between earlier models WRX eg 1996 and 1997, the version 2 sensor I bought came with longer wires than what you see pictured below. Either way, remove your sensor and pay attention to the wire configuration. You would need to worry about this ONLY if, say, you bought a Ver 2 sensor to fit into a Ver 3/4 car otherwise it's a plug-n-go affair.

ozzy

Just to say, the pictures look identical to MY99/MY00 cars too.

Jan,

When you changed your sensor, was the car cooled down i.e. not driven for a good few hours?

Stefan

Jan Shim

Stefan,

My car is a 98, everything looks the same in that area from a '97 to '00. I did the work first thing in the morning before the car was started. I did use some penetrating PTFE-based lube around the thread before attempting the work. If you have the right tool (and I do mean the RIGHT tool) that allows you to move in such confined space, it's a relatively painless job.


Jan

Ken E

The sensor on a 94 WRX is usually in the header, not the downpipe as the later cars, unless it has been moved.

Jan Shim

You are right (recalling a friend's ver 2 STi Type RA). Get an aftermarket downpipe and re-locate the Oxygen sensor to the downpipe.

Marc R

BTTT

GavinP

I ordered an OE one in the end - while sitting down...

My rationale was that if the sensor doesn't work properly, the consequences to the engine could be VERY expensive....

Although the Link doesn't use it (although the Lambdalink does) - I decided it was better to be safe than sorry IMHO.

I got a starter motor from a breakers when my one failed for a third of the price of a new one but this is a "it either works or it doesn't" sort of item and if it failed, there is very little risk of damage to the engine.

I'll keep repeating these comments while crying over my bank statement....

Thanks

Gavin