Airflow Meter

[Bogsye 22]

I can't get a low enough CO level for the MOT, and it seems that it relates to the idle mixture.

 

In the Haynes manual the idle mixture setting screw is described as an allen type. It also looks like it's accessible from th top of the AFM. However on my 1.9 (8v) it's accessed from the side and has a slotted head type screw. Twiddling this has absolutely no effect on the idle, so I'm assuming that there's something up with it.

 

I guess my main question is what is th correct AFM for the car, and what other makes/models of car could I get a suitable unit off, from a breakers?

 

I've had a good rake around on the search, but can't find the answer.

 

Any ideas would be appreciated.

 

Thanks,

 

Brian

Edited June 20, 2009 by Bogsye

[welshpug 1,626]

got a part number?

 

should be;

 

205 GTi 1.9 litre (XU9JA)

 

Bosch LE Jetronic

 

0 280 202 109

 

 

on the usual 128 bhp 1.9, or on the 122 bhp cat equipped one;

 

 

205 GTi 1.9 litre (XU9JAZ)

 

Bosch ML4/M1.3

 

0 280 202 202

Edited June 20, 2009 by welshpug

[Bogsye 22]

Thanks for the info.

 

Unfortunately not got a part number - will have a look tomorrow for it.

 

The car's a bit of an oddball, as it's cat equiped, but has had a D6B engine dropped in. I'm guessing the AFM for the cat version is the way to go so it all matches. Main problem is that I need to get it back to the MOT place by a week on Monday other wise I'll be down another test fee

 

It's going to be a busy week!!

 

Thanks,

 

Brian

[welshpug 1,626]

depends which ecu its running, but if its just the engine itself that's been changed and ALL the Motronic components are there then yeah, just find a 205 1.9 cat afm, can't imagine that'd be too easy

[Miles 331 1 Cars]

Same as all the Mi16's

[welshpug 1,626]

easy then

[Bogsye 22]

That sounds good!

 

The hunt begins!

[Bogsye 22]

It's definitely the correct unit, so I decided to open the lid of the AFM to see if the lack of idle mixture control was a mechanical issue.

 

It's a little potentiometer that the adjustment screw connects to, so it seems the potentiometer is possibly the fault. Looked on RS Components and they stock the exact same model of "Trimpot" so I'm tempted to have a go and fit a new one. They are £1.01 each. I contacted a place that can repair the unit but they want £120.00. I'm thinking it's worth the risk for a bit of soldering.

 

Looks like I don't need to disturb the rotor, so no worries about spring tension. The PCD that the rotor works on looks in decent condition too, so it's probably worth it.

 

Just need to swiftly decide what to do!!!

[Bogsye 22]

Well, I got the new trimpot/potentiometer that adjusts the idle mixture and soldered it into the AFM.

 

Then spotted the next glitch. The thermistor that monitors inlet air temperature is shot. So I'll be needing one of them too. I got some resistance & temperature figures from the 944 article about AFMs so I think it will be fairly easy to get a new thermistor from RS.

 

As a temporary fix, I've soldered a 2k ohm resistor across it, so the ECU will think the air temperature is in the region of 20degC (I think)

Fitted it all back together and it runs pretty well - so I've not completely farked it with my amateur electronics for beginners.

 

Just need to see what CO I'm getting now. If nothing else it's been quite good fun.

 

I can see a twin carbs setup on the horizon.

Edited June 27, 2009 by Bogsye

[powermandan 0]

Please let me know if your solder job does the job with emissions as my AFM is slightly out of spec

[Bogsye 22]

The result:

 

Hooked a Gunson test meter onto the exhaust to see what happened, and I can now alter the CO at idle using the screw on the side of the air flow meter that operates the new trim pot.

 

Although the Gunson test meter isn't a perfectly calibrated instrument it does show how adjustment varies the CO level, which is good to see. Interstingly when the fault described below manifests the CO rises up to 6% which is what the MOT guy was finding.

 

The next fault:

So, having brought the engine up to temperature I was getting nice low CO values - about 1% - 1.8%. It was looking good. Then suddenly the engine note changes slightly and the CO heads off up to 6%. This happened about 20 seconds before the cooling fan cut in.

 

What I need is a decent system description for the system to help figure out what is happenning. It's basically identical to what the MOT guy discovered. It behaves brilliantly, then it goes rich all of a sudden.

 

The one certainty is that this is a very definite change over from running lean, to going very rich.

 

Any ideas?

[welshpug 1,626]

sounds like the ecu coolant temperature sender breaking down?

[Bogsye 22]

I've just been reading this article, and certainly the CTS is the sensor that makes the biggest difference to the fueling, so you may well be right!

 

Motronic 1.3

 

Probably worth my while to pop a new one in anyway and see what happens. Now that I can use my friend's emissions meter it's at least possible to see changes in output.

 

The only fly in the ointment is the paragraph that indicates that if the ECU detects a faulty sensor it defaults to a "hot running" substitute value, but I suppose if the sensor is actually giving readings within range, but just spurious, then maybe it explains this.

[shalmaneser 26]

I found my car was definitely running too rich with a busted temp sensor, the reason i thought it was shot was due to the fuel consumption it was so bad! pop a new one in, can be had from GSF for about £4 from memory. lots of posts about changing them, do a quick search.

 

Might well help.

[munster 0]

Maybe i misunderstood, but can someone confirm 8v and 16v AFMs are the same?

[Tom Fenton 1,526]

They are similar looking, but different.

[welshpug 1,626]

Maybe i misunderstood, but can someone confirm 8v and 16v AFMs are the same?

 

 

only the 8 valve CAT equipped engines are the same

[munster 0]

ahh CAT only. I saw what Miles wrote, and thought it was too good to be true..

[Bogsye 22]

Yep, for the cost it's worthwhile - I'll get one tomorrow.

 

The weird thing is that document about Motronic suggests a Cat equipped car can't be adjusted for CO via the potentiometer, but I definitely observed a change up and down. Strange.

 

Munster,

If I have the correct end of the stick, the AFM on Mi's is the same as a cat equipped 1.9.

Mine for sure is a Bosch 0280202202 and mine is Cat equipped. It's a Dec 1991 1.9.

 

Brian

[munster 0]

thanks Bogsye. Its sounds like you have got the correct end of the stick, going by what Anthony says in this thread http://forum.205gtidrivers.com/index.php?showtopic=95755

 

Gives another option for anyone looking for Mi AFMs, such as myself (although i imagine 1.9 Cat AFMs are probably even rarer lol)

 

Drop me a PM if anyone reading this has an Mi AFM they can sell me..

[Bogsye 22]

Hmmmmh. Still knackered.

 

Well, the temperature probe for the coolant wasn't the issue. Popped in a new one, and checked the old one out of interest, and it behaves just as it should.

 

The only consolation is that the fault is very repeatable. With the engine idling the cooling fan comes on as it should, and then shortly after the engine note changes and the CO heads from about 1.8 up to 6%.

 

I'm going to have to simply work through each component systematically and check resistances etc.. otherwise I will have a predominatly new 205 if I just keep replacing bits randomly.

 

One think that did strike me is the engine/ECU fault light. This doesn't come on with the ignition. So, I'm wondering if it's working, or been tampered with. If it came on it would suggest the oxygen sensor is having problems.

Will start there I think.

 

Does anyone know if this light comes on with the ignition??

 

So, that's another MOT fee due if this thing will be back on the road.

 

Deep breaths............. and exhale.

 

 

 

EDIT: Just discovered that I can possibly get the fault codes via the check light - maybe.

Edited July 1, 2009 by Bogsye

[Bogsye 22]

Hah! Some fool has removed the engine management warning light!

Swapped over the temperature one & unsurprisingly it lights up at around the same time that the CO goes mental.

 

One step forwards!!

 

Time to check out the oxygen sensor.

[pug_ham 241 3 Cars]

You can check your oxygen sensor with a multimeter.

 

Depending on the plug colour (red or black) you should have resistance across the heater plug pins of approx 2.5ohms if its good.

 

I tested the lambda sensor on my mums 205 auto when it wouldn't pass the emissions & it ws dead but the EML ws on almost constantly on her car.

 

Graham.

[AndyJ 1]

If the fault light is now working, read the fault codes! Saves you spending wads on a new lambda sensor etc if the ecu indicates something else is knackered.

[Bogsye 22]

Thanks chaps.

That'll be this afternoon's task