PI MU, not always a bad thing to adjust!

[Tim D.]

Hi Chaps,

Since I bought my car (6 months ago) i have had to run it at all time with a little choke..

Finally got round to fitting my wideband Air:fuel meter and took the car for a spin..

As I expected, without the choke the car was running VV lean (AFR >20:1 at part throttle).

Adding the choke bought this into a reasonable range (12:1 -14:1) although at higher revs and WOT (wide open throttle) the mixture richened out to around 9:1.

So, bit the bullet and richened the mixture using largest of the MU screws. 2 1/4 turns brought the mixture to near 14:1 at idle without the choke (wouldn't idle happily before with choke in!).

Took the car for a spin and now the mixture stays between 12:1 and 14:1 in pretty much all situations. 12:1- 13:1 at cruise (70 mph) in overdrive top. Only times it moves out of the 12:1 -14:1 range is on overrun when it leans out to 20:1 (anyone know whether I should adjust this if yes, how)

 

"Seat of the pants" dynometer is very positive, more responsive throughout all conditions, more urge!

 

So, with the caveat that your using an AFR meter it seems quite reasonable to adjust the MU..

I should add that this is way easier than getting Webber DCOEs to run nicely under all conditions!

Cheers

Tim

[Peter Cobbold]

Most normal engines will cruise happily at AFRs 15-17. But the 6 lacks vacuum advance - which is needed to give longer for the weaker mixture to burn. Also the PI has no way of overcoming the 'lean spike' upon wot'ing ( no Weber throttle pump, no SU piston damper etc), so it has to be set rich just to avoid that stumble.

But the AFR meter will allow you to set it up optimally

[bluetr6reborn]

very interested in this, would like to find out more

[Tim D.]

Happy to help. What do you want to know?

Tim

[TIMS]

Tim

 

What is an Air Fuel Meter, where do you get one, where do you fit it, so you can see it when you are driving?

 

As you will tell an absolute novice to this technical stuff!! Give me electrics / hydraulic systems every time.

 

Regards

 

Tim

[Tim D.]

Was trying to set up so the transient weak spike on acceleation was partially masked by setting on the rich side of 14:1 without going too rich.

Ideally want to do some runs with a MAP sensor temporarily wire in. Then should be able to get to the optimum. Although it seems pretty good at the mo!

Tim

[TIMS]

Tim

 

Now that's a new piece of kit to confuse me a "MAP" sensor!

 

Can I please add that into my earlier query.

 

Regards

 

Tim

[Tim D.]

Hi tim

Sorry.

An air fuel ratio meter is a sensor you put in the exhaust which gives an indication of the efficiency of the fuel burn. Modern cars with electronic fuel injection us them to monitor and hence adjust fueling.

In most modern cars the sensors are simple (narrow band) and tell the electronics whether the mixture has moved from the optimum

For tuning a wideband sensor is used which gives a response proportional to the mixture.

There are a number of companies that offer these, Innovate, Webcon etc. I use one from a company based in Australia WBO2 which provides a signal for a simple dash mounted dial, or more usefully provides a data stream which can be recorded by a laptop and analysed later. The same system can also log rpm so you have idea of the mixture over different rev ranges. The MAP. Sensor us an air pressure sensor that measures the pressure in the inlet manifold. Given that the PI in the TR6 uses manifold pressure to determine the fueling if you collect data on mixture (AFR) and the manifold pressure you should theroetically be able to adjust the MU (metering unit) to give the best settings for an engine. In theory a rolling road helps with this as you can check a range of engine loads, but the software for the AFR meter help with this if you give it data from some driving.

 

Does this help? Happy to help more.

The AFR meter is very helpful in this situation. Otherwise you have to rely on spark plug colour, exhaust sniffing, colour tunes and all sorts of other black arts.

 

Cheers

Tim

[TIMS]

Tim

 

Thanks.

 

So two practical questions on a TR6.

 

1) How and where do I fit the sensor into the exhaust.

 

2) is this the sort of setup you are talking about? Not cheap!

 

http://www.ebay.co.uk/itm/INNOVATE-MTX-L-AFR-Wideband-Air-Fuel-Ratio-Gauge-3844-/300506017816?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item45f78df018

 

I am starting to understand, I think.

 

Mu's have always been the dark art to me, but I can see how this meter could help.

 

Perhaps an article for TR Action? Basic setting an MU with a wideband sensor - how to buy, fit and use.

 

Regards

 

Tim

[Tim D.]

Hi Tim,

It is a little expensive.

The one I would go for is http://www.wbo2.com/2j/default.htm which is cheaper and more flexible. It can be used to log AFR, revs + 2 extra inputs (e.g MAP).

With regards the sensor there are 3 options.

1) buy one of these http://www.innovatem...&cat=271&page=1 which just clamps the sensor onto the end of the exhaust

2) weld a boss into the exhaust and then you screw the sensor in when you need it (you can get a blanking plug when you dont

3) put a short extension on the exhaust with the sensor fitted to a boss in the extension (DIY version of option 1)

 

Regarding TR action, could do, but am by no means an expert on the Lucas PI (I have only made two changes and both were successful, beginners luck!)

 

Could do something on installation and use of wideband AFR for tuning engines as a whole..

 

Cheers

Tim

[Rien]

Hi Tim,

It is a little expensive.

The one I would go for is http://www.wbo2.com/2j/default.htm which is cheaper and more flexible. It can be used to log AFR, revs + 2 extra inputs (e.g MAP).

With regards the sensor there are 3 options.

1) buy one of these http://www.innovatem...&cat=271&page=1 which just clamps the sensor onto the end of the exhaust

2) weld a boss into the exhaust and then you screw the sensor in when you need it (you can get a blanking plug when you dont

3) put a short extension on the exhaust with the sensor fitted to a boss in the extension (DIY version of option 1)

 

Regarding TR action, could do, but am by no means an expert on the Lucas PI (I have only made two changes and both were successful, beginners luck!)

 

Could do something on installation and use of wideband AFR for tuning engines as a whole..

 

Cheers

Tim

 

Hi Tim,

You see the AFR meter are a very good investment, but the exhaust clamp are not! they are to far away specially when you will compare or/and logging the readings with a MAP, MAF, trottle & RPM signal.

 

I will start a forum (for everyone of course) that only discuss LUCAS PI related experiences, do you interested?

 

Regards,

 

Rien

[Tim D.]

Yes.

Agree the clamp is some way from the engine so some delay. But best I can do at the moment, and equivalent to many rolling road setups.

Perhaps when the exhaust is off next time I'll weld in a boss.

Tim

[Peter Cobbold]

Yes.

Agree the clamp is some way from the engine so some delay. But best I can do at the moment, and equivalent to many rolling road setups.

Perhaps when the exhaust is off next time I'll weld in a boss.

Tim

 

Tim,

Do you see the 'lean spike' on the meter? is it about 1 AFR ratio ( eg 14 to 15) for perhaps 1 to 2 secs?

Peter

[Rien]

Tim,

Do you see the 'lean spike' on the meter? is it about 1 AFR ratio ( eg 14 to 15) for perhaps 1 to 2 secs?

Peter

 

Hi Peter,

 

I have logged many PI's with the most exciting faults but never seen the 'lean spike' you see, I think the metering unit that you show that spike have a worn sticking control stop, dry (and early haevy) follower or/and bad linkage rollers, dirty air filter or a combination of this all.

When all parts are in a good condition, correct fuel pressure, the Mu enrich the mixture as fast as whatever acceleration pump to.

Most problems are a to rich mixture!

 

Cheers,

 

Rien

[Peter Cobbold]

Hi Peter,

 

I have logged many PI's with the most exciting faults but never seen the 'lean spike' you see, I think the metering unit that you show that spike have a worn sticking control stop, dry (and early haevy) follower or/and bad linkage rollers, dirty air filter or a combination of this all.

When all parts are in a good condition, correct fuel pressure, the Mu enrich the mixture as fast as whatever acceleration pump to.

Most problems are a to rich mixture!

 

Cheers,

 

Rien

 

Rien

Lean spikes are not peculiar to Lucas PI but are the result of fuel pooling as liquid on the manifold walls. When the throttle is opened from cruise the greater fuel per squirt results in more liquid fuel depositing on the walls. It takes typically 1-2 seconds to reach a new equilibrium in evaporation rate from the liquid, but is dependent upon manifold design. The rich setting of the Lucas MU is probably needed to ensure enough liquid is present on the manifold wall at cruise such that the spike AFR is still rather rich.

The lean spike will be worst after the manifold has cooled during high-load running. On other hand manifold heating from the exhaust will reduce pooling.

 

If the cruise mixture is set to say 15-17 to optimise fuel consumption then I think the lean spike will be a problem, the engine will stumble. But it might be possible to reduce that stumble by advancing the spark at cruise ( using the vacadv capsule and throttle edge take-off) and keeping it advanced during the spike.

If I had the Pi fitted thats what I'd be trying.

Peter

[Rien]

Rien

Lean spikes are not peculiar to Lucas PI but are the result of fuel pooling as liquid on the manifold walls. When the throttle is opened from cruise the greater fuel per squirt results in more liquid fuel depositing on the walls. It takes typically 1-2 seconds to reach a new equilibrium in evaporation rate from the liquid, but is dependent upon manifold design. The rich setting of the Lucas MU is probably needed to ensure enough liquid is present on the manifold wall at cruise such that the spike AFR is still rather rich.

The lean spike will be worst after the manifold has cooled during high-load running. On other hand manifold heating from the exhaust will reduce pooling.

 

If the cruise mixture is set to say 15-17 to optimise fuel consumption then I think the lean spike will be a problem, the engine will stumble. But it might be possible to reduce that stumble by advancing the spark at cruise ( using the vacadv capsule and throttle edge take-off) and keeping it advanced during the spike.

If I had the Pi fitted thats what I'd be trying.

Peter

 

I think I have never notish this becouse I adjust them never leaner than AFR 14-14.5 to for smooth running.

Maybe that are the reasen that Maserati injected upstream.

Advancing the spark and hold them advanced during WOT with only the adv capsule are not possible I think, that will go with a TR 250 and early TR6 distributor with both vacuum advance and retard capsules.

Too bad I do not live in your neighborhood, I would like to try my electronically controlled metering unit on your boosted TR , he can now handle overpressure.

 

Cheers,

 

Rien

[Tim D.]

Haven't specifically looked for the spike ( need to do some runs with the AFR testing certain conditions). When the car was running lean (before I tuned it ) the was a clear hesitation when you snapped open the throttle. Can't feel this now.

Would be good to collect some datasets on a range of tr6's in a range of conditions.

Cheers

Tim

[Peter Cobbold]

Haven't specifically looked for the spike ( need to do some runs with the AFR testing certain conditions). When the car was running lean (before I tuned it ) the was a clear hesitation when you snapped open the throttle. Can't feel this now.

Would be good to collect some datasets on a range of tr6's in a range of conditions.

Cheers

Tim

 

Tim

The hesitation when you snapped open the throttle is due to the lean spike at the AFR you were running at cruise. By richening the cruise AFR the lean spike has been moved to an AFR at which the transiently lean wide-open-throttle mixture is still rich enough to burn OK at that spark timing.

If you want to get the engine to run lean at cruise - for economy - there's no easy way to get the MU to give an over-rich mixture for a second or two. But it should be possible to play with the spark timing to achieve the same effect and get rid of that stumble. Thus:

Connect the advance retard capsule to a new drilling at the butterfly edge. This need only be say 1mm bore, and in same relationship to the butterfly as on SU carbs of similar bore. In this position 'vacuum' will only occur at cruise ( butterfly slighly open) as it is created by the venturi effect of fast moving air. The 'vacuum' at butterfly-edge vacuum goes away at tickover and at wider throttle openings because the air velocity by the take-off drops.So it wont change wot sparking, the curve stays standard. The lean AFRs needed for economic cruising need more advance - because the mixture burns slower. Now we floor the throttle and would get a lean spike and a removal of the vacuum almost instantly, so it would stumble. But if we keep the vacuum a second or so longer, keeping the spark advanced we can cope with the lean spike. Easy to do - fit a 'ballast bottle' in the small bore hose to the va capsule. Plastic will do, testing different volume until the stumble goes. Once sized you can make it prettier.

I'd try setting the AR to say 17 and see if the va capsule does the job. AFR 20 is very lean - nor surprised it stumbled, and without fancy sparking kit it probably could not be made economical either!

Peter

 

 

 

.

Edited July 15, 2012 by Peter Cobbold

[Tim D.]

All makes sense.

With the lean mixture was noticing a very transient pinging when snapping open the throttle when cruising. I wondered whether this was caused by the lean spike.

Car is running pretty well now. Getting the motifs leaner on cruise would be good though. Has anyone tried the changes you mention?

Tim

[Peter Cobbold]

All makes sense.

With the lean mixture was noticing a very transient pinging when snapping open the throttle when cruising. I wondered whether this was caused by the lean spike

.

Car is running pretty well now. Getting the motifs leaner on cruise would be good though. Has anyone tried the changes you mention?

Tim

 

Tim

AFR20 is too lean, so could be the cause of the pinking. At that AFR the burn rate will be very slow until shortly before TDC when it will speed up, but because most of the mixture has yet to ignite it detonates - hence pinking. It might be possible to use the va capsule to give the mixture more time to burn by advancing the spark, but 20:1 is pretty extreme.

Connecting the vac advance capsule from the carb butterfly edge is standard on many engines. Its nothing to do with engine design , the common factor is the way the mixture burns that demands cruise advance. The PI cant give a transiently over-rich fuelling to kill the lean spike, so presumably had to be run rich at cruise to avoid customer complaints about pinking upon wot. I have no idea why the factory did not connect up the va capsule as i've suggested. But a flame is a flame, and the PI TRs should be capable of getting close to the earlier carb'd engines in fuel consumption at cruise. There's an EFI 6 that does that - try searching thr TR6 forum for 'lean spike' for his data on spark and AFR on that car and replicate that, you'll be close.

Peter

Edited July 15, 2012 by Peter Cobbold

[kiwican]

Too bad I do not live in your neighborhood, I would like to try my electronically controlled metering unit on your boosted TR , he can now handle overpressure.

 

Cheers,

 

Rien

 

 

Hi Rien,

 

I was following your thread on your electronically controlled metering unit with interest, can you give us an update if things have progressed?

 

Thanks

 

Simon

[Rien]

Too bad I do not live in your neighborhood, I would like to try my electronically controlled metering unit on your boosted TR , he can now handle overpressure.

 

Cheers,

 

Rien

 

 

Hi Rien,

 

I was following your thread on your electronically controlled metering unit with interest, can you give us an update if things have progressed?

 

Thanks

 

Simon

 

Hi Simon,

 

Sorry but no realy progres, it is a finalcial question, I have three choices:

1. I can wait for my frients car to use them for try the mod.

2. I build a car for myself again ( I have parts for 2-3 )

3. I build only a engine and buy the eddy current engine brake, this is what i like most.

 

I think the first option are most realistic, if the results of this are promised then I go option 2 or 3.

 

I thought not many people were interested, so I will also not have made much effort lately.

 

Thanks,

 

Rien

[kiwican]

Hi Simon,

 

Sorry but no realy progres, it is a finalcial question, I have three choices:

1. I can wait for my frients car to use them for try the mod.

    

2. I build a car for myself again ( I have parts for 2-3 )

    

3. I build only a engine and buy the eddy current engine brake, this is what i like most.

 

I think the first option are most realistic, if the results of this are promised then I go option 2 or 3.

 

I thought not many people were interested, so I will also not have made much effort lately.

 

Thanks,

 

Rien

 

 

I understand about the financies side of things. If you continue on with it please do post updates. I thought it was a great idea and good compromise between the mechanical system and going full EFI.

 

Regards

 

Simon

[Tim D.]

Hi Chaps,

below is the data from my AFR run (about 30 minutes of varied driving).

It would be better to have data on the AFR and MAP and/or throttle position and/or RPM.

I should be able to get the RPM sorted, but need to find a MAP sensor that works on 5v and has a known pinout..

 

 

http://i491.photobucket.com/albums/rr278/shynsy/AFRdataTR.jpg

 

Overall the MU is delivering in the correct range with very little rich running. The lean tail on the data is from overun when the mixture goes pretty lean

 

Cheers

Tim

[Davidw]

Rien, can I just add my voice to Simon's above? I found your previous thread on the electronic enriching device fascinating and would love to hear more, when time & finances permit. I'd certainly be in the market for such a device at reasonable cost.