Causes Of Lean Running

[roccorich 16]

Sorry its under cover now.

 

But yes it is black and sooty around the edges.

 

Is that a good or bad sign?

[DamirGTI 325]

Really need to get a lambda probe or gas analyser of some sort on it now to see how it is all through the revs.

 

I think its a bit rich at idle but Id rather the car be richer than lean for now.

 

Defiantly ! an cheap DIY measuring aid can be maid as per that last article which i posted .

 

Needs just an 4 wire zirconia narrow band lambda sensor and multimeter . Drill the exhaust just before the middle silencer (drill upwards cos if drilled hole downwards the moisture inside the exh. system will shorten the life of the sensor and it's ability to read correctly) weld in an boss for the sensor , fit the senor in , connect heater element to the live power source with the engine running (two white wires , connect one on a 12v other one on ground) , the rest two are sensor signal wires - connect these on the multimeter probes and go for a spin , after roughly 10-15min. when the sensor heats up you'll get correct readings :

 

0.63V - 14.7:1 (stoichmetric)

0.78V - 13.5:1

0.82V - 13:1

0.85V - 12.7:1 (best for full load)

 

http://www.buckeyetriumphs.org/technical/Carbs/AFMonitor/AFMonitor.htm

 

.. so just transfer voltage readings into lambda values , or buy an AFR gauge for use in conjunction with narrow band sensor .

 

I've been doing this before when i didn't have an proper wideband sensor along with the gauge/meter with zirconia narrow band sensor and multimeter , and it really works and it's cheap ! narrow band zirconia sensor as particular is very precise in pinpointing lean mixtures .

 

D

[DamirGTI 325]

Sorry its under cover now.

 

But yes it is black and sooty around the edges.

 

Is that a good or bad sign?

 

Rich ! tight back the AFM spring a bit till the sooty deposits disappears .

 

You'll really have to measure mixture somehow . It may be rich just @ idle/low throttle opening and going lean at full load .

But better still if it's a tad on the rich side rather than on the lean , however neither one aren't good for the engine if over excessive rich/lean .

 

D

[roccorich 16]

Any tighter and it starts going white again.

[roccorich 16]

White on the tip and the insulator that is.

[DamirGTI 325]

Odd .. if you can't tweak it to the spot between rich/sooty and lean/white , maybe the AFM is faulty so try an known good spare AFM .

 

But once again - you really need something to measure the mixture in order that you can see actual lambda values across the rmp. range . Personally i wouldn't trust spark plug color tune up .

 

D

[roccorich 16]

Ive got a 200 mile round trip to do tomorrow.

 

So may take the 205 and see how it is after that.

 

I did go up to 18 teeth richer before going down to 13 then up to 15 then 16.

 

So maybe its still soot from then that may burn off after a bit...

 

Im quite friendly with the Mot bloke by my parents where Im going tomorrow so may see if I can stick it on his analyser and see what its doing through the rev range.

[roccorich 16]

Ok. Stopped a couple of times yesterday to check plugs abd nake adjustments but wasnt happy with how it was going so today I had another play by watching the RPM while moving the needle.

 

Ive now got it set with the idle screw 11 turns out and the spring 8 teeth richer than it was before I started fiddling.

 

 

Ive ordered a Lambda sensor from Eurocarparts that was on sale for £8.25 from £45!!

Its a 3 wire one zirconia one.

 

Then ive ordered a clamp on section with a boss in it so I can clamp it onto the tail pipe as I cant weld and it means I can use it on other cars too.

[sickomotorsport 4 2 Cars]

Timing out?

[roccorich 16]

The timing is around TDC at the moment, possible a couple of degrees advanced.

 

Once ive got the mixture somewhere close I'll try advancing the timing somemore then recheck mixture.

[DamirGTI 325]

That'll do nicely !

 

On 3 wire sensor , two wires will be for the heater element one on 12v other on ground (usually you'll get the wiring identification/instructions along with the sensor) and third one will be sensor signal - connect multimeter positive probe on this wire , and negative probe either on the chassis ground or the sensor body (as the sensor signal grounds via sensor body)

 

Stick an pipe with the sensor inside the tailpipe , secure it , set the multimeter on voltage readings place it somwhere where you can see it while driving (or get someone to drive while you look at the multimeter readings) .

Like so (mind you , this one is running rich !!) :

 

In order to retrieve correct readings from the sensor , need to wait/drive around at least 10-15min for the sensor to heat up .

 

D

[roccorich 16]

Cheers

 

Ill let you know how I get on with it when it all turns up.

 

Rich

[roccorich 16]

Had a little play with it last night but was gdtging confused by the readings.

 

Gonna try again tonight.

 

What sort of voltage readings am I aiming for across the rev range?

 

I was getting about 0.8.

 

And does it matter what I get on over run with the throttle closed?

 

Cheers

 

Rich

[DamirGTI 325]

At idle , ideally would be switching from 0.63V to 0.75V

Cruise , this'll be hard to get the right number cos the value will bounce quite a bit up and down , switching voltage from 0.65V to 0.78V will be fine at light throttle openings/load .

Full load is most important , here you'll need between 0.85V and 0.9V .. any reading below 0.8V at full load will be bad for the engine ie. lean

Overrun , the system shuts down the injectors during the overrun (providing that the TP sensor is working and is adjusted properly) so here the value will drop and will be fluctuating down the 0.6V value .

 

Do not bother with the precise number at idle/cruise , check/adjust full load range as even a slightly leaner mixture here is not acceptable (lower than 0.8V)

 

 

D

Edited November 6, 2013 by DamirGTI

[roccorich 16]

Cool.

 

When you say full load do you mean full throttle or over 3000rpm or something else?

 

On the overrun it was dropping right down to 0.3 and a bit less I think.

[DamirGTI 325]

When ever you floor it (despite the actual rev range) you must see increase reaction/switch over of the volt readings up to the 0.85V - 0.9V, so say you're cruising at low/mid throttle openings with the voltage switching from 0.65V to 0.78V - as soon as you press the acc. pedal all the way down the voltage must switch sharpish up to the 0.85V - 0.9V keeping that value until you release the pedal .

 

With moderate acceleration , when going from low/mid to high revs the values must rise linearly and with the voltage increase as the revs build up . Expect to see no less than 0.8V from 4000 up to the 6250 (limiter) with the highest voltage being 0.9V @ 5000-6250 rmp . If the voltage increases slowly or worst starts to decrease at certain point as the engine builds up the revs that needs to be rectified .

 

D

Edited November 6, 2013 by DamirGTI

[roccorich 16]

Cheers that all makes sense now.

 

Went out to test it tonight and the sensor seems to have gone.

 

I started getting readings over 2 volts.

 

As soon as I unplugged the heater feed it dropped below a volt.

 

I removed all the sensor connections and tested the resistances

 

I got about 7 ohms across the heater coil and infinite resistance across everything else.

 

Yet if I put 12v down either of the heater wires I suddendly get 12v across the sensor.

 

So the heater must be shorting somewhere...

 

Luckily Eurocarparts accidently sent me 2 so after I complained about it taking so long to arrive so I will try again tomorrow when Its not raining.

Edited November 6, 2013 by roccorich

[roccorich 16]

Ok so got the spare sensor working and had a play with it tonight.

I set the spring tension back to how it was when I got the car to see how it behaved.

It was about 0.78 0.8 at idle. Managed to get it fluctuating around 0.5, 0.6, 0.7 with the mixture screw.

 

Took it for a drive and the mixture went up with the revs but around 3000RPM it switched and went very lean, this was over about a 200 RPM range and came back over to 0.8 after 3000 RPM.

 

So I kept adjusting the AFM spring tension until the switching around 3000 RPM stopped. This was 4 teeth richer.

 

However now its not possible to get the voltage down to 0.7 at idle. Its 0.8 ish at idle.

 

Its a pretty steady value while driving around but does go up to 0.9 at the top end of the rev range and with WOT.

 

Im hoping to be able to borrow an exhaust gas analyser next week like this. http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_188065_langId_-1_categoryId_255216

 

So I can get a better idea of the CO level at idle.

 

Will that sort of tester be of any use to test the fuel mix whilst revving?

[welshpug 1,622]

are you using the screw on the afm to adjust idle mixture?

 

that type of gas tester doesn't react quick enough, you need a wideband lambda and display for a quicker reading of what is happening.

[roccorich 16]

Yes. Had it fully wound out.

 

Ill just use it for the idle CO then, hopefully my Lambda readings are slightly off and thats why its showing so rich. As from what I understand narrowbands are more about the switching than the actual values.

[welshpug 1,622]

I would back the spring tension off and wind that screw in about half way, you might have some hope of getting it closer.

[roccorich 16]

But what about the leaning out at 3000 RPM?

[welshpug 1,622]

check the resistance of the afm as you move the flap with a screwdriver, you might have a dead spot.

[DamirGTI 325]

Never had an CO gas analyzer so i dunno how to work with one .

 

Anyways , if the mixture across the rev range is now good with the added 4 teeth's of the spring tension , i wouldn't be too worried about the idle being at 0.8V ..

Yes it is a bit "rich" , or it may sound rich , but no one of such old cars with 8v engines and without CAT can actually run stoichiometric mixtures ie. 14.7 @ idle (0.6V) , mainly CAT equipped and newer multivalve engine powered cars with sophisticated engine managements (usually sequential injection) and with variable adjusting cams are capable to run stoichiometric at idle .

Others usually run around 13-13.5 (0.7/0.78V) range , and even 12-12.3 (0.9V) @ idle for cars/engines with wild cams richer mixture is needed to make them idling smoothly .

It's mainly down to the engine management system which utilize one or multi CAT emission control , engine combustion efficiency and camshaft profile which determines needed idle mixture , CAT equipped systems will for sure need as closest to the stoichiometric as possible at idle and even off idle they tend to run on a bit lean mixtures .

 

For 1.9 8v engine with an old analogue Jetronic engine management , without CAT/lambda mixture control , and hence it has quite hot cam as standard 0.7V switching to 0.8V should be fine tbh . Also when checking , the engine needs to be fully warmed up .

I got mine to run very close to stoichiometric at idle , but that was only after the engine mods (heavy head job , high CR and better squish band which enhances engine burn efficiency , reworked mixture control and spark) .. dunno if i would've been able to adjust it so on yet a standard engine , haven't tried that .

 

If the wiper track has "dead spots" , that'll still be the issue even with adding spring tension and will be seen/spotted via multimeter values monitoring , so i doubt that theres something wrong there .. but can check and see if theres any issues with the wiper track .

 

To lower it a bit more from 0.8V try like this : tight the idle air screw (brass one on the TB) so that it's just slightly opened allowing min. air bypassing so that the engine doesn't loose revs up to the point that it'll cut off . Even if so , compensate with the small screw at the back of the TB ie. the throttle butterfly stop screw , add a few turns to crack open the throttle butterfly a little bit more to allow more air passing by .. and readjust the TP sensor afterwards .

When done that - then try adjusting the AFM mixture screw , and see if you can lower it down below 0.8V .

 

As for the CO reading , buying an gas analyzer doesn't make much sense to me if you're gonna use it just one/two times , i'd go to the local MOT station and ask them if they'll allow you access to they're gas analyzer so that you just check the idle mixture and adjust as needed .. leave some beer money for the MOT man and job done .

 

D

[roccorich 16]

http://static.photobucket.com/player.swf?file=http://vid783.photobucket.com/albums/yy111/dozzum/20131116_161716.mp4

 

The plugs are very white again.

Heres a video of the AFM resistance check aswell. What do you think?

 

http://i783.photobucket.com/albums/yy111/dozzum/20131116_160829.jpg

 

http://i783.photobucket.com/albums/yy111/dozzum/20131116_160805.jpg

Edited November 17, 2013 by roccorich