Setting up the throttle pot on roller barrels

[Richard Price]

I've been looking at a car with a VHPD on roller barrels with an MBE ECU.

The drivability at low throttle openings was quite shocking!

 

I've had a look at it with Easimap, and diagnosed very erratic feedback from the throttle pot. I swapped it with my own pot, and the VHPD instantly runs much sweeter.

 

However, its possible to twist the pot on the mountings before tightenin, and go from load site zero to site three.

 

When we have a new pot, how should the pot be set.

 

If it has any bearing, the car has been tweeked a few months ago by the two Steves.

 

(yes, I've seached the archive, but can only find a link to a site that no longer exists....)

 

Edited by - richard price on 5 Mar 2013 21:28:34

[SLR No.77]

Richard, not sure about setting it up with an MBE .... but with an Emerald it's simply a case of ensuring the TP is mounted solidly then performing the "throttle reset procedure" to enable the ECU to know the start and finish positions of the TP movement. Everything else is then established around these points.

 

Stu.

[NoLimits]

Richard YHM

[Richard Price]

🤔

[Mark Durrant]

Richard

 

At idle the TPS should be set to load site zero.

[NoLimits]

Going further and to be a little more clear than Mark.

 

Look at the throttle index map. Lets say site 0 is .48 then the pot should be set to 0.47

 

This is the "general" method SBD would use if they do not have the info available as to what it would actually be.

[PizzaOvenKing]

Hi,

 

I apologies for hijacking this thread... I am having a similar issue with my roller barrel K series with MBE ECU...

I'm not as clever as you are with being able to dive in and investigate the issue/cause and wonder if you can recommend someone in the south (Oxford but will travel) that could look at this as a possible reason for my car not idling very well.

 

It also runs really rich and bangs and pops, this could of course be to do with the lack of Cat... the previous owner removed it!

 

Any pointers appreciated.

 

Best Regards

 

 

[Markiebabes]

Hi lestyn

I had issues with mine (R400 k ) with a lumpy idle and a local member John (bio) helped by setting the idle and throttle pot with a syncronometer

Made the idle smoother and car seems to go better once done I now do this on a regular basis 😬

 

If your about on the last Saturday of the month,pop over to the Penn7's meet,I'm sure John ( sorry for volunteering your services ) will be able to help 😬

 

Edited by - markiebabes on 9 Mar 2013 06:20:16

[Bio]

Hi Lestyn and Mark 😶‍🌫️

Would be willing to help at home (Kings Langley) or at the Penn meet, just give me a call on 07780860875

 

John

 

[MartinH]

Another for John (BIO) who set up my TPS, idle and balanced the flow on my Coswoth roller barrels recently. Top man

[Bottrill]

Evening, All

Is there a general reason why 0.47 seems to be the default value? I Swapped over to a new potentiometer this afternoon after a slightly fluctuating throttle on fast idle and a high CO on the emissions at last weeks MOT. The car is an EU2 R300 K.

On installing the new potentiometer I got an idle reading of 0.33 with the multimeter. The car idled very smoothly on the cold start map and once it was warm. When the throttle was blipped however the revs would drop and then bounce back to a stable 1000rpm. I've reverted back to the old potentiometer to be on the safe side without fear the engine would be running lean and adjusted the idle. The idle value is now back to 0.46. I did notice however that the holes had been modified to cater for more adjustment on the old potentiometer, something I had read about previously to try and get to this reading.

apologies to bring back a topic discussed many times over.

Lee

[Paul Deslandes]

The ECU looks at the TPS voltage to determine the throttle's position which is defined by a number of sites, 16 in the case of MBE, site 0 to 15

Each site is recognised by the TPS voltage falling within a certain band for each site over the range 0 to 5V.  At idle it's at site zero, which is the lowest voltage, so any voltage lower than the 'site 0 to site 1 transition voltage' will be read as site zero.  Hence, when your TPS was at 0.33V rather than 0.47V it still read it as site zero.  However when you blipped throttle the voltage didn't increase sufficiently to transition to site 1 and above, hence the bogging as the timing and fuelling didn't change according to the maps.

MBE ECUs have been supplied set up with different TPS voltage curves, e.g. mine have always been 0.36V at idle but I have seen several with 0.47V like yours. The best way to find out what yours is, although from your report I would guess it's 0.47V, is to look at the ECU with Easimap which will allow you to see both the TPS voltage and the site number that it is going to.  If your ECU is unlocked/unencrypted, you'll also be able to see the TPS throttle angle/voltage curve which will give you the same insight.

Paul

[Bottrill]

Paul,

that's great, many thanks. Is there any harm in fitting it and leaving it at the lower voltage on idle or would it be best to modify the holes to allow further adjustment to get near 0.47v as with the current TPS?

Lee

[Paul Deslandes]

I'm a bit surprised that you can't adjust to the correct voltage without modifying it.  However, as that seems to be what was done before, I would definitely try to get it to 0.46V as otherwise you'll have a very badly tuned engine almost certainly running lean and with incorrect timing - not good!

Hopefully it's just a case of carefully elongating the screw slots a bit more. I'm not sure how easy it is to get at the TPS but try leaving the screws out and adjusting the pot with the ignition on and engine not running so you can see how much fettling you have to do.  Just do it a bit at a time.

Paul

[Bottrill]

Excellent, I will give it a go. I read a number of times about elongating the holes for the screws a while back. I've came to have a look at mine and someone had beaten me to it. Whether it's because of the Roller Barrel design and the TPS part in question is used primarily on regular single inlet manifolds across various manufacturers, I'm not sure. 

Thanks, anyway,

Lee

[Bottrill]

Paul,

I've elongated the holes and managed to fit and set at 0.45V. The car was warm, so a quick run round the block where it seems to give a smoother throttle at low revs. The car still smelt rich on idle though. I will try it in the morning from a cold start. 

I don't suppose you know whether the 0.36V or the 0.47V settings were linked directly to the the 956 or 967 MBE ECU's? Out of interest it's an early 2003 R300. 

 

http://www.bikerhouse.com/testsite/minister2011/support/roller_barrel_setup_k-seriesr.php# 

The Minister Power guide which I've used in the past says 0.45V. 

Thanks

[Paul Deslandes]

It all depends on who mapped the ECU in the first place and their preferred TPS throttle position/voltage map. Over the years I've had 912, 956, 967 and 9A4 ECUs that all had their idle setting as 360mV (0.36V) but I know that others, presumably from other 'mappers', were set at 460mV.

The only way to see what's really going on is to connect up a laptop with Easimap and identify the voltage at which it transitions from site 0 (idle) to site 1 and set it just below that by about 20mV.

It sounds as though you're on the right track though

Paul

[rj]

Mine is set to 0.2V (!)

But... this was done by someone ignorant. (Myself, that is..)

I guess the important bit is the alignment. I also have moved the load sites to match, which means that the car us remarkably drivable even at low throttle or low RPM.

What I'm trying to say is; With a little patience it can be done.

[Paul Deslandes]

The TPS gives a voltage in the range of roughly zero to +5Volts which is linearly related to the throttle angle and the ECU uses that voltage to 'look-up' the load site in the range zero to 15.  Although the voltage related to angle is linear, the lookup table is not. 

So at small throttle openings the sites progress relatively quickly from one to the next as the throttle is opened as this is when the engine's increasing demand for fuel and ignition timing change is greatest.  As the throttle opening increases the rate of change decreases. Provided the shape of the TPS voltage/load site curve is correct and the start and finish voltage are towards the bottom and top of the voltage range respectively, the absolute values don't matter. 

As RJ says, although 0.2V is quite low there's nothing wrong with it so long as the ECU is mapped accordingly.  From memory most SBD supplied MBE maps set idle to 0.36V and Caterham supplied, which I believe were mapped by Cosworth, are set to 0.47V.

Paul