Sigma 150 - balancing throttles and TPS

[Bone Rat]

Hi,

Not a frequent poster as most things bumble along but thought I may need some help this time.

I've got a 150 Sigma Roadsport - factory built and owned from new since 2011, at the moment it's running OK. When I picked it up it had the usual problem with the throttle bodies being out of balance and drove like a kangaroo. Eventually this was adressed at the Midland branch after some denial there was an issue. Had the latest map applied at that time & now drives well.

Started servicing & looking after it myself this year, it appears to be straight forwards at least as the mechanical side goes. But I'm concerned that the throttles will eventually go out of balance again and need resetting. I'd like to be able to do this if push came to shove. I've got access to a synchrometer and Easimap 6. Every account I see talks about resetting the TPS as part of the process, however long I search I can't see any description of how to do this on the Sigma 150. The car has the original MBE ECU which I know is locked down. Easimap does read it OK.

Can anyone tell me if balancing is a viable proposition for DIY and point me to any directions to do so especially around the TPS and resetting. Or is it a case of 'getting a man in'?

Many thanks

Andy

[Domus]

On the Easimap the TPS setting is shown.  It needs to be 1.04v at idle.  The TPS is a black plastic unit on the back of the throttle spindle near the ECU.  Two small Allen headed screws need to be slackened and the unit turned.  Be warned it can be frustrating as it moves when doing up the screws again.

[martyn]

Hi Andy,

This is dead easy.  Especially as you already have all the necessary tools.  Defiantly don’t 'get a man in' it takes 5 minutes and needs to be done often.  I find the adjustment screws on my throttle bodies don’t stay in place for any more than a couple of months!

I have ChrisC to thank for all the information here, he has helped me so much and taught me well!

Refer to this image to understand the adjustment screws:

https://www.dropbox.com/s/t3dmi1trizsccd1/Throttle%20Body%20Adjustment.jpg?dl=0

1) With the engine running and nicely up to temp, use your synchrometer to gauge the air flow into each of the cylinders at idle. The balance screw will adjust the airflow into the left two cylinders (1 & 2).  Use this screw to match the airflow going into the right pair of cylinders (3 & 4).  It is not possible to balance cylinder 1 with cylinder 2, this is fixed and won’t be far off at all.  Same with cylinders 3 & 4.

2) Now you need to set your idle and TPS.  When the engine was originally mapped, they used an idle of 950rpm and the throttle position sensor was reading 1.04v at idle.  So, you need to match these values (as much as is possible) to get the optimum fuelling across the rev range.  Plug into Easimap and call up "Throttle angle 1" to see the TPS voltage.  The idle adjustment screw controls the idle stop of the throttle.  The TPS is adjusted by loosening the sensor on the end of the throttle bodies, rotating by hand to the desired voltage, then tightening again.  Adjust these until you get ~950rpm and 1.04v. One effects the other so you may need to adjust each several times as you zero in on the correct settings.

3) Re-check the balance of the cylinder banks again, and adjust if necessary.  With everything adjusted correctly as above you should find that you're pulling between 4 and 5 kg/hour

4) Switch engine off then switch ignition back on (but don’t start).  In Easimap, call up "Throttle Site 1".  The TPS voltage is converted into a "site" and it is this site that is used in the maps.  site 0.0 is idle and site 15.0 is WOT.  Check that the slightest touch of the throttle pedal moves you off site 0.0 (it should if you're set to 1.04v).  Check that pressing the pedal to the stop achieves at least site 15.0.  Also check that this fully opens the throttle butterfly plates (will probably need an assistant to operate the pedal for you).  If either of these checks fail then you probably have some slack in your throttle cable, or the pedal stop is too high (most likely slack as the pedal stop shouldn't ever need adjusting once set).  You'll need to adjust accordingly.  If you find the revs don’t die back quickly after a blip then you probably have too much tension in the cable.

Some Tips..    

• Check and write down all your settings before you adjust anything.  From Easimap write down your rough idle RPM, and idle TPS voltage.  With your synchrometer make a note of the kg/hour into each cylinder.
• Take your time and adjust one thing at a time.

I've made this seem more complicated than it is.  It's really not, I just wanted to get all the detail in so you understand why you're doing something and not just how.

[ChrisC]

Well said martyn 

[Domus]

Many thanks for that very comprehensive answer. 

[Bone Rat]

Hi,

A big thank you to everyone especially Martyn, this has been bugging me for months. It does sound fiddly but straight forward and I think it'll will provide many happy hours over the summer.

Brings back memories of the step father trying to sort out his clapped out MGB with a Gunsons Carbalancer or something back in the 70's.

Got to admit I initially thought the 150 a right pain when I first had it - CC used to insist the kangarooing was

1. Normal for the car
2. because I hadn't stuck my foot against the footwell to prevent sudden movement
3. was because it had a cable not 'drive by wire'

It was only when it was balanced that the engine really showed what it was capable of, really nice revving engine. I decided it was time to look after it myself.

Once again thanks, made someone very happy

Andy

[martyn]

The best part for me when checking was finding out that the left bank of throttle bodies were only pulling around 3 kg/hour and effectively restricting air into those cylinders.  A quick tweak of the balance screw and the idle revs immediately picked up, confirming the free power upgrade!  Also, I had considerable slack in the cable, meaning that I could only achieve throttle site 14.7 with the pedal pinned.  Adjusting that got me to site 15 and the throttle body rotating all the way to its WOT stop.  Driving the car afterwards, it felt like it had an extra 15bhp.  Which to be fair it probably did have!

Getting the throttle cable tension right is an important step in my opinion.  It improves response and precision as you transition from zero to a small input (as you do in traffic) and vice versa.  It also helps to prevent kangarooing as there is no jerk on the throttle as the slack is suddenly taken up.

[RedCat7]

Handy thread to keep bookmarked :)

I've been balancing the TBs for a few years but only got the Easimap cable this year.  Since theyn I've been through the process a few time now and I'd say it not as easy as the guys above suggest. Patience is required until you get the knack! 

My additional tips:

It is possible to balance throttle 1 vs 2 and 3 vs 4.  You use the little air bleed grub screws on the top of each body.  Loosen the 10mm locknut and tweek the screw as required to allow air to bleed in.

I would suggest setting the TPS as close as possible to the tipping point between 1.03 and 1.04v because the setting does seem to wander a little (maybe 0.005v) over time or with temperature.  I found that if set bang on 1.04, occasionally the engine would idle at the first load site (triggered by 1.05v) causing it to hunt.

The TPS will move if the bolts are not tightened enough.  Mine moved so that the idle was 1.00v, resulting in hesitation at low revs.  The TPS body is plastic so there is also a risk of damage due to over tightening.  I tightened as much as possible using the wrong end of an allen key and so far so good.

When re-fitting the Air Filter,  make sure the dipstick still fully engaged in the sump, otherwise you will end up with a oil leak.  Luckily mine was only a minor leak and I spotted it before loosing enough to even require a top-up.

[martyn]

Hey RedCat,  thanks for the info about balancing the individual banks of cylinders.  I've just had a look at my car and I think I can see the locknuts and screws that you refer to.  The problem is that they're completely obscured by the fuel rail.

If these are indeed the correct adjustment screws, how do you adjust them without taking the car apart?

 

[RedCat7]

I use a natty low profile ring spanner that was supplied with some flat pack furniture:

[martyn]

Ah,  as I suspected there seems to be two slightly different TB designs used.  My adjustment screws emerge vertically making them pretty much impossible to adjust.  The TB looks identical in every other way though.

[mantioras]

Hello everyone. Reviving an old thread, as it seems to be one of the most informative on how to balance the Sigma 150.

I believe I have an opposite problem regarding the air flow. I connected the Easimap 6, adjusted TPS position to 1.03-1.04v (it was 1.1 or 1.2 initially, throttle site 5...), and then tried to balance the idle at 950±50rpm, and that was tough, as the engine was hunting quite a lot, between 800-1100 rpm. Then removed the air filter to measure the air flow, and it looks it's pulling in around 7-8kg/hour. Probably even a bit over 8, as the synchrometer is mechanical, its scale is not very precise, and the engine was hunting for revs. The good thing is that both banks (cyl 1-2 and 3-4) are pulling similar flows each.

So do I adjust the air flow down to the recommended 4-5 kg/hour? Should I go through the "nipple" of each cylinder, or is there a way to tune down all four TBs at once? [Adjustment screws are at an angle, not immediately below the fuel rail, so at least it is a more user-friendly version than for martyn] I suspect the engine would hunt even more, and I should be ready to adjust the idle screw again, at the same time as tweaking the throttle bodies? Or quite the opposite, as now presumably the fuel mixture is too lean and idling should actually improve with less air? On the other hand, is there something else forcing more air to go in? I'm a bit reluctant to go all-in with these adjustments and don't want to mess up everything completely, as previously it was working: not ideal, but at least driveable... :)

BTW, the fully depressed throttle reaches only site 12, so I presume this is fixed by adjusting the engine stop nut?

New-to-me Caterham Sigma 150 (2009), ECU still not with the newest remap (ie. MAP sensor still connected to the manifold via a hose).

[Bone Rat]

Hi, 

Only just come across this, I was the OP! Must admit I've had great results following the detailed information I was given. I use a mechanical synchrometer (a barrel shaped thing with a rubber cone you stuff in the body) & easimap.

I must admit mine only pulls an indicated 3.5 to 4 - BUT the important bit is that each bank is equal. It doesn't hunt, only get some idling issues if the stop is set too low. Tend to keep it at about 850 to 900 rpm. 

The fully depressed throttle should be more than 12,so that may need adjustment. Also I'd get the map updated. There is quite a detailed thread on ere about the issues with the importance of the latest /final map. It doesn't need the small hose connected. I found this made a significant difference to it's running. Trouble was trying to get CC to do it in the first place. Bit of advice is to leave the disconnected tiny hose attached to the bulkhead mounted unit. If you get water in the unit it's not good.

Hope it works out 

Andy 

[ChrisC]

All the instructions on setup are based on the last map released by Caterham, without that everything is best guess because the TPS is not being used for the mapping strategy.  With the MAP sensor connected it's driving the decisions, but MAP on ITBs don't tend to work very well.   Your best option is to get the last (latest) map installed and setup according to the instructions at the beginning of this thread.  

[mantioras]

Andy, Chris, thanks for the responses. I am planing to send the ECU to the factory for a remap in late autumn, when the car is stored for winter. Still want to enjoy a few sunny autumn days:) So another round of fiddling with the TPS, air flow screw and the synchrometer will be after the remap.

However, I'm out of ideas on how to achieve the full range of 0-15 for the throttle site :/ I opened the pedal box, and the throttle pedal does not have any links/bolts/adjustment-things to play with it. The end of the throttle cable is secured to the pedal with no possible adjustment, the pedal itself does not have any "pedal stop" that could be adjusted or removed to increase the pedal's throw. I haven't touched the end of the cable which is secured to the TB axle, but right now TBs are closed with the pedal in the topmost position, and if it can be pressed to the full bottom, I do not see how I could achieve more range fiddling with the cable. I presume the TPS itself cannot be adjusted or calibrated in a way that it starts "seeing" the throttle site range of 0-15, instead of current 1-12, can it? I had disconnected the battery for several times, hoping that TPS might "reset" in that direction, but it did not make any effect.

[ChrisC]

I think for now forget the TPS range and just look down the ITBs and ensure full throttle opens the ITBs fully.  
 

There should be a throttle stop under the throttle pedal, which should be adjusted so you don't push to far, and put the ITBs under strain once wide open throttle is achieved.  As for pedal adjustment it's done by bending the pedal as needed, but this is normally done during build.

[Bone Rat]

I agree with Chris, the main thing will be checking with the mk 1 eyeball that the butterfly flaps go from closed to full open. 

Hopefully the remap over the winter will help considerably, CC weren't very helpful with my teething problems all those years ago. But, once the map was sorted and it was balanced it runs really well. The 150 seems to be regarded by CC as the problem child and was dumped for the 140, but once it's running well it's worth it. 

Good luck keep us informed of progress! 

Andy 

[Kingsley Young]

#15 I have the 150 Roadsport and I would forget sending the ECU to the factory and try to get to either Team Leos Motorsport or the two Steve's in Raynham they will be able to sort the problem!

Kingsley. 

[mantioras]

Kingsley, thanks for the recommendations. Already sent an email to Team Leos. Could you please include the exact contact of the two Steve's? I have trouble googling them out :/

Factory quoted 80 gbp for the remap, plus shipping, so I thought that's a low cost option and keeping still stock. Programmable ECU and a custom map is way more expensive, so at least now I'm not in the mood for that route. At least not when I haven't got the latest factory map. If that does not work, then of course aftermarket options might be the way.