TPS incongruity

[BrianG]

OK.. this is my first shot at setting the MG TPS but still.... the instructions I have found posted on this forum don't make sense to me.

 

Mostly what I've found is a recommendation to set the baseline "with the throttle closed - to 150 mv".

 

THEN there is a reference to the idle speed value of any where from 485 - 515 mv (depending on whose numbers you like.

 

Well, this doesn't make sense to me.

 

If you set the baseline a 150 with the throttle closed, the idle value is going to be what it is...... dependent upon your individual choice of idle speed, amongst all of the other things that affect throttle opening.

 

SO...

 

Which is the critical value??

 

closed throttle at 150 mv

 

OR

 

idle(at whatever RPM) at 485-515 mv?

[Guest ratchethack]

Which is the critical value??

This, my friend, will depend on who you ask.

 

The 500-525 mV linked at 1100-1200 RPM as read on the Vague-Liar tach method works for me.

 

THEORETICALLY, they should both yield THE SAME RESULTS!

 

Pick your procedure, and give 'er your best shot.

 

If it works well for you first time, well now you've more'n likely joined sides f'er life.

[dlaing]

The closed throttle reading of 150mv is done with linkage disconnected, set screws backed out and choke fully withdrawn, so it is not the same as at idle.

 

 

Which is the critical value??

 

closed throttle at 150 mv

 

OR

 

idle(at whatever RPM) at 485-515 mv?

IMHO the TPS should be set to 150mv FULLY closed.

At idle I don't think the TPS should be adjusted, but the idle should be set so that the TPS falls into the 485-550mv range. One can tweak the TPS a little and probably get a better result, but too much and you may be asking for trouble. Higher numbers generally run richer, so people are drawn to them like flies to manure.

The range being 485-515 or 500-550 is also not a settled issue as it appears to vary by bike.

 

 

 

THEORETICALLY, they should both yield THE SAME RESULTS!

 

 

There is much more room for variation at idle.

At 150mv the butterfly is simply closed.

At idle valve rocker adjustment, engine condition, throttle body condition, exhaust design, ECU trim, veglia reading, and more add up to a lot of possible variation.

But it is quicker to set at idle.

I think once you set to 150 disconnected and then find an ideal at idle setting, you can repeat it.

[pasotibbs]

OK.. this is my first shot at setting the MG TPS but still.... the instructions I have found posted on this forum don't make sense to me.

 

Mostly what I've found is a recommendation to set the baseline "with the throttle closed - to 150 mv".

 

THEN there is a reference to the idle speed value of any where from 485 - 515 mv (depending on whose numbers you like.

 

Well, this doesn't make sense to me.

 

If you set the baseline a 150 with the throttle closed, the idle value is going to be what it is...... dependent upon your individual choice of idle speed, amongst all of the other things that affect throttle opening.

 

SO...

 

Which is the critical value??

 

closed throttle at 150 mv

 

OR

 

idle(at whatever RPM) at 485-515 mv?

 

I agree this is a little confusing, if I understand correctly the FI system is based on a fixed predetermined map,TPS position,engine temp,air temp and RPM are used by the ECU to determine how much fuel should be injected at that given point.As others have said throttle closed is completely closed ie fast idle linkage removed (don't lose the little c clip) and idle screws backed out fully, you then set the TPS itself to 150mv(this gives the baseline from which the map is calculated), then you adjust the idle screw until the TPS reads 525mv( the value can change when the engine is running due to output from the alternator so you may want to set it to 500 with the engine off then tweak later while balancing the throttles), the ECU should now be in the correct area of the map for a good idle (the actual RPM can be fine tuned by the air bleed screws if required)

 

As I understand it some fuel injection systems can determine how much air is flowing into the engine and from that determine the amount of fuel to inject, but ours can't, so if you set the idle TPS wrong the entire map is potentially off.

[BrianG]

Ok... as far as I'm concerned, a baseline or datum point is the design reference point from which everything else flows and from which individual variation and error grows.

 

SO...

 

I chose the "TPS from the closed throttle" parameter as the sensible baseline parameter.... mostly because it's pretty much a useless number for anything else.... and that in itself is enough to make an engineer pick it. Given this assumption I manipulated the mechanical issues to get the throttle place on the bore wall (closed).

 

Initial reading was 106 mv......... final adjusted reading was 156..... (crap that thing is position sensitive!)

 

Then I set Idle to somewhere between 1000 - 1100 Vague-alia RPM...... so it sounded right, ticking over nicely but not quite doing the Harley "potato - potato - potato" thing.

 

Then I balanced the TB's at 2200 RPM and then at idle I adjusted balance with the air-bleed screws that started at 1/2 turn out (we are at 3500' MSL)

 

Then I checked idle TPS output and I see 485 at that nice slow tick-over with no apparent desire to change directions.

 

ROAD TEST

 

No real change in power.

 

VERY real change in drivability...... NO hickups at idle..... NO chuffing at part throttle.... Positively Honda-like throttle response, and immediate starting when hot (which was a minor concern before this event)

 

So... A cigar is really a cigar......... and resolving the problem is, for some, simply a matter of normal procedure. I'll count myself lucky in that regard......

 

Thanks guys...... I'm off riding!!

 

 

 

 

 

 

(Just for yucks I checked cranking compression and show 110/105 rt/lt -- is this close?)

[docc]

 

 

Then I set Idle to somewhere between 1000 - 1100 Vague-alia RPM...... so it sounded right, ticking over nicely but not quite doing the Harley "potato - potato - potato" thing.

 

 

Setting the idle screw to show the correct mV is the best procedure. Using the Veglia will likely set your idle 300 rpm below the indication.

 

Greta news to see another finicky runner cured with a good tune-up!

[Tom M]

(Just for yucks I checked cranking compression and show 110/105 rt/lt -- is this close?)

 

Sounds like you didn't open the throttle WFO when you took that reading. I know my old Honda was down around there with the throttle closed but when I opened it like the procedure in the manual said all 4 cylinders were well within spec at around 170 - 180 psi.

 

Congrat's on getting your tuning issues sorted out