TPS and IDLE - 310r (2020)

[Andrew P]

I've found a lot of threads on this topic, and they've been great info so far, thanks to all! However, I wanted to create a new thread to clear a couple of things up - hope that's ok!

My 310 is my first Caterham and I have had it a couple of months now and love it!

However, it has been reluctant to start and the idle is a bit volatile, almost throbbing where it seems to dive to a low rev and then tries to recover over revving and then repeating for a bit till it settles.

I have Easimap up and running, so can see the throttle site and angle increasing, and it was at  0.3v at site 0.0 and from what I understand my car should be around 0.4v at site 0.0. Is that correct? 

I have adjusted to 0.4v (having reset ecu with battery disconnect), but it still wasn't quite right, but better. 

I understand that the idle screw has a part to play, and I am not quite clear how to balance the two, and was wondering if there's any trade secrets to share? I can tune the idle, which changes the voltage, reposition TPS and reset ecu, but I don't seem to get a steady idle and the throbbing when idling remains. 

Another aspect could be the lambda sensor (from my readings), which I haven't explored yet, but given the age of the car I'd be surprised if it was faulty. 

Thank you for your patience and help!
 

 

[Roger Ford]

I don't know the answers to your questions (sorry) but may I ask where you got the EasyMap software from and what connector you needed for the OBD2 port?  I've been searching for the info, but a lot of it seems to be based on older cars which I understand need a serial port, whereas I don't think more recent cars do (mine's a 310R as well).

 

[ChrisC]

In my experience (I have not worked on a 310R, but plenty of 150, and Duratecs), the TPS voltage seems low, but the actual voltage isn't important, what's important is your idle is set to the transition point. I.e. at idle the throttle site is 0.0, but just 0.01v increase sees the throttle site increased from 0.0 to 0.1 (at least, or could be more)

I liken it to 'standing on the edge of a cliff', the closer you are to the edge, the less hesitation you get.

The lambda sensor should give you a messages depending on its state. It will be inactive when the coolant is below 60C, and 30 seconds after the engine has started.  Then you should see lambda sensor doing its thing, maintaining the correct ratio.  They do fail, so I wouldn't rule it out based on the age, but feel you would be unlucky if it has failed.

Don't be afraid to open the throttle stop a little, the idle speed is controlled by the ECU advancing and retardant the ignition. It sounds to me like your throttle stop is a little to closed, caused the reluctance to start and low revs, but this is only guessing based on the description.

I know this exact task is on my winter service task list for my 420, which since the decat, and as the miles have increased has started to hunt a little when the coolant is lower than 20C, so I will be opening the throttle stop a little, and readjusting the TPS back to the cliff edge.

[ChrisC]

It's a MBE specific lead, but the software is free.  
 

https://www.sbdmotorsport.co.uk/MBE-MAP-KIT-3-CAN-basic-can-mapping-kit-for-mbe-can-based-ecus.html
 

It's expensive, and you can't make any changes, only read live data, so diagnosis is based on observation and logging not codes.

That said there was some great work carried out my members to make a Raspberry Pi version, if that's your thing.

[Andrew P]

This is the cable and the software - https://www.sbdmotorsport.co.uk/MBE-MAP-KIT-3-CAN-basic-can-mapping-kit-for-mbe-can-based-ecus.html / https://www.sbdmotorsport.co.uk/easimap%206%20pc%20software-easimap-6-pc-software---download-for-free.html

[Andrew P]

Thank you, Chris (your blog and posts helped me get this far!!!) - I getcha on the cliff edge thing... makes sense. Is there a method to try to hone that? How do you know you've gone too far, etc.?

I think the older sigmas have a higher voltage on the TPS, from my internet learnings. I originally set it to 1.04v whilst exploring, and it was idling at 2.6k rpm, which was a surprise, but sounded good!

Will dig into the lambda sensor outputs, didn't get that far!

[aerobod - near CYYC]

If the panels are available, display the target idle speed and fuel trim. As ChrisC said, also ensure your TPS voltage is as high as possible while still staying within throttle site 0.0 when the engine is warm. Confirm you have some slack in the throttle cable if you adjust the idle stop, too.

If you can see the target idle speed and fuel trim, the aim is to minimise the amount of variation around the idle speed and have minimal fuel trim adjustment. If the fuel trim is always positive, close the throttle by adjusting the stop, if it is negative open the throttle more.

[Andrew P]

Thank you, Aerodbod!

I see 'TPS Fuel + Trim' panel already, which shows a value in milliseconds, is this what I need?

... and try to get it to 0.00ms whilst maintaining TPS voltage as high as possible and site 0.0?

[David_Long]

Good advice in posts above, but you maybe over complicating things. The behavior you describe is typical anti-stall and probably due to a mismatch of throttle opening and throttle site. Personally from experience, I would forget voltages and set the TPS for zero site when the throttle is fully closed (i.e. the idle backed off until it is fully closed) then adjust idle up for best idle running - which maybe at the quoted voltages. 

[ChrisC]

As above, just keep increasing the throttle opening until you find the happy point where it will idle, then get the TPS to throttle site 0.0, but on the edge, so as soon as you touch the throttle it's in a higher site.  With the Duratecs the TPS doesn't officially have any adjustment, but actually a little rats tail file can open out the mounting holes just a little bit enough to get the setting needed.  It's only a tiny bit that's needed most of the time.  With all the battery disconnects it's a tedious process, but worth the effort.  Much easier if you have an isolator.
 

I am soon going over to a mates 310R which is running well (as far as I know) to look at a rear suspension clonk. If I get time I will see what TPS voltage, and manifold vacuum it's pulling at idle.  The vacuum should vary depending how closed the throttle flap is at idle, if your running a higher vacuum at the same idle speed your throttle flap is more closed.  (Assuming no manifold leaks)

[aerobod - near CYYC]

You may get idle hunting if the throttle butterfly opening and fuel injector timing is such that the engine wants to idle at a speed other than the target idle, as the engine mapping is such that it will add fuel if the idle speed is lower than target and remove if higher than target. The idle speed is only really adjustable by remapping the engine with the MBE ECU, as opposed to trying to adjust it by changing the throttle stop, there is only one speed it will idle properly at.

If you have the Adaptive Map Output value displayed, it should be close to 0% during steady idle when all Lambda conditions are in an "OK" state, typically moving either side of zero by less than 5% (i.e. from -5.0% to 5.0%). A continuously negative value would imply too much fuel and too little air, so open up the throttle blade. If continuously positive, close down the throttle blade.

Besides the Adaptive Map Output you can estimate the fuel trim by comparing the Final Injection Time to the adjusted TPS Fuel + Trim. The adjusted time is calculated by multiplying by the compensation factors for air and coolant (for example 4% air plus -1% coolant would be 4% for a compensation factor of 1.04) and adding the Battery Voltage Comp time. If the TPS Fuel + Trim is 3.21ms, compensation is 1.04 and Battery Voltage Comp is 0.42ms, then adjusted time is 3.21 * 1.04 + 0.42 = 3.76ms. If the final time is 3.50, then the fuel trim is -0.26ms (i.e. fuel is being removed due to running too rich, so more air is needed).

You may have to play around a bit if the mapping is continuously providing too little or too much fuel for the target idle speed. Variation between engines or just a poor map could cause this.

[ChrisC]

Are yes good point, hunting can also occur with to much throttle stop. I find stalling and starting problems are normally throttle stop to closed, hence I only mentioned opening but the adjustment can be either way.

love the maths 

[Andrew P]

Mega info! Thank you all.

I couldn't find the Adaptive Map panel (I have Map Pot 1 and Map Pot 2...?), I also couldn't get anywhere near the maths...

I got it running best as per the cliff edge method, which shows idle around 850 rpm. The TPS Fuel + Trim is always around 2.6ms, the voltage is on the cliff edge at 0.41v, this results in a Final Injection Time of 4.85 ms/cycle.

2.6 x 1.04 + 0.41 = 3.11 ... meaning I am +1.7 and potentially running lean (based on your explanation above)?

Am I reading from the correct panels? The car sounds alright and throttle response is good (cliff edge) showing site 0.4 at the slightest of movement. It does still hunt just a little when returning to idle, but it does seem a better.

Thanks again, chaps.

[Andrew P]

For clarity, this throttle body has the same construction (and may be the same) as mine: https://caterhamparts.co.uk/other/1982-throttle-body-sigma-125-including-tps.html

The first picture shows the TPS (as i understand it) this rotates, which changes the voltage positively and negatively (opening and closing the throttle?).

The third picture shows the idle screw as I've been calling it (idle stop in real money?), this also adjusts the voltage positively and negatively.

So I increase the voltage via the idle stop, I have to back off the TPS to reduce the voltage and bring the site back in line - which seems to be 0.41v @ site 0.0 for the 310.

It's these two things that I have been adjusting, just saying this out loud in case I am missing another aspect, given my relatively noob status!

[aerobod - near CYYC]

Hi Andrew, the Adaptive Map Output value is under "Lambda Control" "Long Term Lambda Control" when you add a panel by right clicking on the dashboard page and select the realtime channels. It is also worth bringing up the Idle Speed Target panel which is under "Idle Speed" "Idle Speed Target" to see if the adjustments are such that you are actually idling close to the set target. There are also other panels that may be useful to display under the "Idle Speed" folder.

Your adjustment of the TPS to 0.40-0.41V after any throttle stop (idle screw) change is a good strategy for keeping the throttle site just in the 0.0 range.

If Adaptive Map Output is not available there or Lambda is not in "Conditions OK" state, I would say your current calculation points towards the throttle blade being a bit too much open, so more fuel is being added to compensate for the lack of fuel in the map. As I mentioned, the map may just not be very optimum and you may not be able to get to the optimum fuel and throttle opening values, but as a reference point at 1000RPM idle on my R400D, my Final Injection Time is typically around 3.95ms for a fully warmed up engine and Lambda between 0.97 and 1.00.

[David_Long]

I think the issue that rightly are trying to get your head around is how to match the mechanical throttle body butterfly position to the 0.4 volts that is quoted. It is the relationship between these two that you are trying to get right. The actual figures are less important. From a practical point of view the only reference point that is fixed is when the throttle is closed. So I would use that as the reference point for throttle site zero (your 0.4v). Then open the idle screw to allow it to run smoothly. I doubt this will have much effect on the voltage or throttle site  - maybe up slightly. But at least the relationship between the two will be very near to correct and a good stating point. A second check you can make is to see where the full throttle position maps to - it should be throttle site 16 when the butterfly is fully open IIRC.  

[Andrew P]

Ah! Just worked out you need to change Easimap into Advanced mode... check me out, advanced indeed...

[Andrew P]

Thank you, David - it is somewhat baffling!

The idle screw can change the voltage and site quite significantly, which I can correct by resetting the TPS. I think the metrics to measure for "run smoothly" is the bit I am trying to understand, because, as you point out, I can get to 0.4v in a million and one different ways... I think i was getting full throttle at just over site 15, 15.1 maybe @ 4.7v, I don't believe this figure changes no matter what I have tried.

I think I have a couple more things to review and try.

[aerobod - near CYYC]

Hi Andrew,

In terms of full throttle, the adjustments of the idle position of the TPS will affect the full throttle voltage a bit, but the mapping is such that you have to accept the highest value achievable if the throttle is fully open. After getting idle right, I would check cable adjustment to ensure a small amount of slack, then adjust the pedal stops to ensure a fully open throttle with no significant load on the cable (i.e. pedal hits stop as opposed to cable is stretched at full throttle, leading to potential breakage).

I've found the Caterham mapping on my car originally only got to about 15.3, when I put in my own map on an unlocked ECU I remapped the full throttle voltage to be throttle site 15.9.

[Andrew P]

So, I got easimap back up and with the two new panels, it all seemed ok. The Adaptive map didn't really move and stayed at 0.0%. The target Idle came down to around 820 rpm when the coolant was above 60c and the actual idle was floating around that number and sounds like it's running good, to me...

I didn't make any adjustments based on where I got to earlier, so it is still perhaps slightly over-fueling / compensating... not sure I have the expertise to whittle it down further!

Will take it out for a drive tomorrow, to see how the throttle and idle behave on the road vs. the drive.

Thank you to everyone for all your help!

[GulfSeven]

I just had an issue with my 2020 310R fixed under warranty - I was getting hesitation between 5k and 6k rpm. That turned out to be the immobiliser relays vibrating, but at the same time as fixing that they said the TPS was way out of calibration. Since being fixed, in addition to not hesitating between 5k and 6k rpm anymore, the drivability at low revs has been much improved. I think my TPS might have been out of calibration from new.