Query re Throttle Cable and TPS??

[CtrMint]

Guys,

A quick query to help me better understand the throttle and possibly avoid needless work.

Off the back of my post regarding emergency tools and the subsequent focus on throttle cables I went and checked mine today.  I removed the pedal box cover etc to check for any signs of wear from the fixing around the pedal, and of course, checked the throttle body side too.

All looked good however I added some heatshrink to the end where it meets the pedal to help reduce any unwanted play and abrasion.

While working I noticed I'd not set the throttle pedal to ensure maximum throw or rather horizontal opening of the throttle body valve.   As a result, I've adjusted the pedal stopper to increase the throw on the pedal and adjusted the adjustment screw on the throttle body.  Doing so has increased the throw of the butterfly valve, but there is still more potential movement in arm/valve.  I'd say the cable has another 5mm of travel left, but it's blocked by the stopper which is at its max.

The remaining travel doesn't make a massive difference in the butterfly value, but I would assume the TPS needs full travel to achieve 100% open throttle in the ECU and thus maximum acceleration?

Ideally, I'd put a standard OBDII reader on the ECU and check the TPS reading, but CC tells me unless I have there required cable and software all data is incorrect.

I guess my question, to those that know far more than me, do I need to achieve 100% throw to achieve 100% open throttle or does a 100% throttle occur with less than a 100% throw on the cable/TPS, hence it's fine as is?

If it's important I have the cable set so the butterfly is permanently closed, with the slightest of tension in the cable, once you put any pressure on the throttle cable it starts to open up the valve.

Hope that makes sense.

Thanks

Mark

PS weather has been foul this evening so haven't been able to test drive or experiment with the changes so far.

[ChrisC]

So you want full open butterfly at full throttle and a butterfly closed enough to pull a good vacuum at idle, but open enough for the idle to be smooth.  The stop on the butterfly adjusts the idle, and the combination of bending the throttle pedal and the adjustment of the pedal stop permits the full throttle.  Since you don’t have a battery isolator disconnect your battery during the adjust, because the ECU is permanently powered and gets confused if the TPS idle setting changes.  Apart from that your good to go.

To read settings from the ECU you need Easymap and the appropriate lead but that’s only to read not change.  Only people with the Caterham unlocked software can change the ECU, but that’s a different discussion.

[Tom_Arundel]

photos

I got so fed up with the fiddling that I made this. It extends the top of the pedal, gives a quicker throttle action, avoids the cable bending and fretting and is easy to access.

Don`t forget that there is a pedal UP stop as well as a WOT stop and a choice of pivot positions

Closed throttle must be set on the throttle body stop not with the throttle pedal stop. Cable should be just slack at closed throttle

 

[CtrMint]

Thanks guys.

I think I need to build a little more understanding before I make too many changes, hope you don't mind if I ask a couple of further questions.

• If I remove the cable from the throttle body, will the butterfly fully close, or does the idle stop still control how far it will close?  I'm assuming the idle stop is something on the spring and not the threaded tube which the cable runs through.  I ask as I believe the idle might be a little high at present, it tends to idle at about 900rpm, I would have expected about 500. If so I might need to lower the idle.
•  
• Naturally, what is the typical ideal idle for a 420?

If the idle is too high then I would expect a reduction will increase the clockwise rotation of the butterfly and thus take up further cable, which I can then compensate for in the adjustment on top.  This will then help achieve full open throttle.

Sorry but chance of a pic or confirmation of the idle adjustment and direction for increase/decrease, thanks

[John Vine]

The butterfly position at idle is controlled by the stop, not the cable.  The stop adjustment is via the screw set into the side of the throttle body (from page 125 of the Duratec Assembly Guide):

 

Turning the screw anticlockwise will increase idle speed (and vice versa).  Note that there will probably be a nyloc underneath the screw mount.

I'd say an idle speed of 900 was pretty well bang on for a 420.  My R400D idles at around 850 when first started, and gradually creeps up to 900-925 when warm.

JV

[ChrisC]

So picture stolen from the internet, but I have highlighted where the idle screw and locking nut is.    Providing the throttle cable isn't pulling on the butterfly for some reason the idle will be set by that screw.   If the throttle cable was unattached the spring will close the throttle to the idle screw stop.   The threaded block holding the throttle cable is for fine adjustment of the throttle cable tension. 

Don't believe the instruments, mine always displayed a steady 1100 rpm, but actually the ECU reported 850 - 900 rpm, so your 900 is fine.   Making the idle lower made my cars ECU hunt making the idle very erratic.    A 420 has a modified cam, so a 500 rpm smooth idle is probably to much to ask, couple that with the lightened flywheel and I bet it would almost be undriveable at slow speed.       I can see why you think that way, after all its how all modern production cars get their CO2 emissions on tests.

Don't forget to make any adjustment with the battery disconnected. 

Bending the throttle pedal and adjusting the throttle pedal stop is the way to get fully wide open throttle (or that lovely solution above)

[John Vine]

Don't believe the instruments...

Indeed.  My figures were taken from Easimap as the tacho won't go much below 1200.

[CtrMint]

So it sounds like my idle is actually about right, assuming the gauge is accurate, but you're suggesting it might not be, and without Easymap I can't tell.  I could try and lower it, see if the car runs OK and doesn't hunt etc.

I suspect then I need to bend the throttle pedal further as there is no more play left in the pedal stopper.   I hated doing this the first time, as I felt I was putting a lot of stress on the pedal box floor.

I might be being dumb here, but the pedal starts from the same position and essentially has the same throw regardless.  If I bend the pedal further forward the throw is still the same, that won't give me full throttle still, so will I make an additional adjustment on the cable adjuster as well?  Or do I also need to look at the pedal up stop mentioned by Tom?

[ChrisC]

I bend mine out of the car, in a workmate bench, covered in ducted tape to protect the paint.  I also use the position level with the pedals.  It means I have to bend it so far the bolt can’t be removed, and I have to make sure it lines up with a slot pre cut in the pedal box. 

[7 wonders of the world]

Interesting comments about the poor accuracy of the instruments CC supply, thought mine old ones were pretty rough, the tacho was up and down like a tarts knickers - had hoped the newer ones would have been much better.

I checked my Digidash 2 when I installed it against the Emerald live data and there just a nats pinkle between them 

[ChrisC]

The rev counter in the R is the problem, 6 o’clock is 1100 rpm, hence I think it’s all to do with the angle of the dangle. 

[CtrMint]

I am starting to think it would be easier to cut the cable end off, feed it through and clamp it as required.  I'm sure someone mentioned that during my build.

[ChrisC]

Reading some build blogs, if you do that before PBC, CC bend the pedal, replace the throttle cable, and charge you for the pleasure.

[aerobod - near CYYC]

The idle speed is set by the tune in the ECU, I can’t remember the exact value for my R400D ECU tune as I have a custom map now, but it was close to 900RPM, Easimap will display the set value. Any attempt to mechanically adjust it away from the value set in the ECU will cause idle hunting or driveability issues as the ECU will try to attain the set value with fuel adjustments. With my custom tune that is a bit more track than road orientated, I find it best at 1000RPM, where it stays within 20RPM or so of the set value, pulls cleanly from idle and returns smoothly with abrupt throttle release.

At idle the throttle stop should be adjusted so that the throttle map value is in the range of 0.0 to 0.4 to ensure Map 0 is used instead of Map 1, picking the value that gives the smoothest idle. The throttle pedal should then be adjusted to reach at least throttle map value 14.5 at wide open throttle by a combination of stop adjustment, pedal bending and cable length adjustment. The cable should have very slight slack at idle to make sure the throttle is against the idle stop and not be forced into excessive tension when the throttle hits the stop when fully open (ensuring the throttle stop prevents that from happening).

 

 

[ChrisC]

Thanks James,  That’s why it hunts if you close the butterfly to far at idle, it can’t maintain the ECU set idle speed.   I have seen it the over way as well, where the idle speed is higher because the butterfly was to far open at idle, but it didn’t hunt.

[CtrMint]

Thanks guys.  

I've not changed my idle and it's always seemed fine, apart from being high, but that's now confirmed as expected, so I guess it's to do with the travel available when the pedal is depressed. Given I've got the pedal stop full out I would assume it's to do with pedal length and the pedal bend.  Though I still can't picture how it helps.

Think I'll leave that until I get back from the Taffia fish n chip run.  It's not like I'll need 100% throttle on the road  

[John Vine]

Thanks for that.  But there are a few things I don't understand...

The OP's car has a plenum and, as standard, has a map based on the Manifold Absolute Pressure (MAP).  On the other hand, a car fitted with rollerbarrels (like mine) has no plenum and instead has a TPS-based map.

I can see how, on a TPS-based car, the throttle site is defined by the TPS voltage.  But on a MAP-based car, how does the MAP signal translate to the required throttle site?  Presumably the ECU does the trick, but how?  And why would a MAP-based car need a TPS at all if the MAP sensor provides data on engine load etc?

JV

[ChrisC]

I can answer why a MAP based car needs a TPS, The TPS acts a bit like a accelerator pump on carbs.  It tells the ECU whats required before the MAP sensor.  Obviously in the electronic world it also acts in the opposite direction (unlike an accelerator pump) identifying over run.   

I have never seen my 420 at throttle site 0 during idle, worst was 6 (before disconnecting the battery) and more normally 1.   This is the exact opposite to my Sigma 150 where 0 was the target for the idle. 

I have said before a good vacuum in the plenum seems to create a better idle to on throttle transition, and this has been my focus on improving the drivability of my 420, BUT take it to far and the 900 rpm idle can't be maintained.

[John Vine]

Thanks, Chris, that explains a lot.  At idle, my R400D sits squarely at Site 0, with the TPS showing 4.63v.  WOT gets Site 15,  although I don't have a note of the TPS voltage for that (something like 1.45v, I think).

When I took the car (pre RBs) to the Two Steves some years ago, Steve G recommended junking the MAP map and going for a TPS one instead.  IIRC, he said it would be much easier to map, and would be needed anyway should I opt for RBs in the future. 

JV