420R Hesitation at part throttle when hot

[KnifeySpoony]

My 420R on roller barrel throttle bodies has developed an issue. When the car is hot, ie only after driving for 20-30min, well after the engine is up to temp, I'm getting hesitation at partial throttle - basically from 0-5% throttle, tip in feels normal, however it's like from 5-20% throttle, no fuel is being added, and the car hesitates severely/will not accelerate at all. If I keep gradually opening the throttle, once its gets past about 20% or so, then it's like it catches, I get a surge, then the rest of the throttle travel is normal. Car pulls hard and smooth to redline at larger throttle openings. When I get the hesitation, it's interesting in that if I keep the throttle depressed at that position, and press in the clutch, the revs do not climb at all as they normally would when the load is removed- this initially led me to believe it was a TPS issue. No popping from exhaust. No smoke that I can tell. 

 

I checked the TPS with easimap - idle voltage is correct, and it seems to be sweeping/responding normal with throttle. Barrels are adjusted properly. I replaced the TPS and initially thought it was solved on a long drive, but it now it's behaving the same again. Seems impossible a second TPS could fail so quick and exactly the same manner. I swapped out the sparkplugs and no change. I have read that there can be an issue with the wiring to the TPS failing, but I can't see how it would cause the behavior I'm seeing.

Any thoughts? I know that CC sells the silicone TPS setup:

https://caterhamparts.co.uk/looms/5817-tps-duratec-race-flexi-silicone.html

[Angus]

I have an R400D on RB's so same engine setup.  I get a very similar problem:  When starting from warm / hot, typically after stopping for fuel, then after 30-seconds to 1 min after startup, I get a huge flat spot, similar symptoms to what you are describing.  The engine stutters along, regardless of throttle position, then suddenly picks up and all is OK.  From then on during the drive the problem doesnt re-occur and everything is OK, until I switch off and restart when hot.  Cold start no problem - on the button every time.

I have had this problem for years and I live with it.  Car has been mapped (twice), lambda sensor and TPS changed, no change.  I am running the upgraded coil-pack sub-loom and TPS wiring.

Someone once said that it was the ECU getting confused because there are two temperature inputs, but I have no evidence to support this.

 

 

 

[KnifeySpoony]

I should clarify that my symptom does not go away after one episode- it is persistent once it starts acting up.

[aerobod - near CYYC]

I've had a similar problem in the past which was due to over fuelling causing the plugs to foul, but would be cleared when the engine was in Lambda open-loop mode.

If the problem is repeatable I would first check for misfires by checking the primary temperatures with an infrared thermometer to see if they are all even and stable. If they are, I would confirm Lambda values are correct if possible. The standard narrow band sensor is not very good for this but at least Lambda should be oscillating between lean and rich from a couple of times a second to every couple of seconds. If you have access to a wide band sensor system, diagnosis of incorrect fuelling is much easier, I have an Innovate LC-2 wide band system replacing the standard Caterham narrow band system for this purpose.

In terms of temperature sensors on the car, there are 3, but they are explicit in the function and should not cause any issues with the ECU if they are reporting the correct values:

- IAT sensor for the ECU, which is likely in or near the airbox for RBTBs and in the plenum for plenum systems

- Coolant temp sensor for the ECU

- Coolant temp sensor for the dash gauge.

[John Vine]

Have you tried a new lambda sensor?  Your symptoms are not unlike what I was suffering here.

I would suggest you run an Easimap in-flight logging session, and examine the lambda trace for regular oscillations (as James mentioned in #4).

JV

[Chris SSR400]

I get exactly the same quirk Angus. Good to hear im not the only one. I've always made the (slightly) educated guess that the engine is in some mid state of cold & hot start up. as its only ever when i restart after its partly cooled. If i turn off the engine and start straight back up its fine equally if i let it cool completely its runs great. As it never lasts long i also just live with it. 

[KnifeySpoony]

Thank you all for the input- you've given me a lot to look into. Interesting about possible vapor lock - I didn't think that was a thing with fuel injected engines. The roller barrels, having a lot of thermal mass and being right under the injectors and fuel rail, seems to make sense as a possible heat source to boil fuel. Here in California, all we have is E10.

[John Vine]

Vapour lock was suggested as a possible cause for my woes (see #5), but generally discounted in the end.  Personally, I think it's very unlikely on an R400D/420 as the fuel rail is capacious and there's so much moving air under the bonnet.

JV

[Geoff Brown]

#7 - Statement about E10 only being available may be the cause of the troubles. When visiting the continent after E10 was first launched my R400 (with RBTB) would not behave when up to running temperature.

Tick over was lumpy & low with the engine stalling itself. Re starting was a little problematic catching ignition with a little throttle then revving the engine to 'clear its throat'. Pulling away after this episode required a boot full of throttle after which the engine appeared to settle down but a slight lumpiness or throttle hesitation was always detected when accelerating or cruising. The next junction or traffic jam was met with intrepidation.

On return to blighty E5 sorted out all the problems. Now I run on Shell V-Power E5 98 & the engine has never run better. 

Avoiding E10 fill ups as much as possible is the mission! Unless 'sur la continent'.

Getting the ECU re programmed to take into account E10 may be the solution. But if you have a stock ECU unlocking it may be another problem.

[KnifeySpoony]

New lambda sensor and problem seems to be solved. I had the no name sensor that others have mentioned recently. Replaced with proper Bosch part. 

[John Vine]

#10. Thanks for the feedback.

JV

[John Vine]

#10  Out of interest, did you record an in-flight Easimap log (see #5), or did you simply replace the sensor anyway?

JV

[KnifeySpoony]

Well..  It's kinda solved but now there's a new symptom. Now the 5-20% throttle range is smooth, but from 0-3%, ie initial tip-in there is hesitation/sputtering/misfire. And it does it immediately after starting even when cold. Car starts instantly and idles fine. Giving it verrry slight throttle will cause it to sputter/miss. More throttle and it revs fine. Interesting the drastic change in behavior with the new 02 sensor but not sure how to interpret. I'm thinking the 02 sensor isn't even active when the car is freshly started so I don't understand why the new sensor would cause this behavior. I'm going to triple check the TPS voltage, roller idle spacing, sparkplugs, etc.

[Nigel Riches]

O2 sensors are generally not active until a certain engine temp is reached, and a time has elapsed for the heater in the sensor to stabilize, so as you say, shouldn't be this at start from cold. Bashon, 

Nigel.

[aerobod - near CYYC]

The typical ready state for Lambda sensor closed-loop operation is:

- 90 seconds after start (to allow Lambda sensor heater to reach operating temperature)

- Coolant temp above 60C

- Throttle less than about 50% (for example throttle site 8.0 and below on Caterham MBE ECUs)

- Throttle site not changing rapidly

- Engine revs less than about 2/3 of maximum

[KnifeySpoony]

 I tried unplugging the new sensor and the car runs exactly the same. So clearly my new 02 sensor is not doing anything. So it seems to me that either it's 1: sensor is DOA, 2: it's incompatible (it's a Bosch sensor that used to be included with r400/420R not the no-name sensor my kit came with), 3: the wiring from the sensor to the ECU has gone bad, or 4: the ECU has gone bad. 

 

Seems like sensor logging wouldn't be that valuable at this point. I suppose I should check wiring continuity; how to do this? Multimeter at sensor plug and at ECU plug? What pins go where? I could also put the OEM sensor back in and see if the behavior reverts or stays the same.

[KnifeySpoony]

Did a trackday at Laguna yesterday - Once again the car was fine on track (new PR actually), however the part throttle issues have deteriorated significantly. It's extremely unpleasant/challenging to drive on the street at this point. It does it even when cold, and doesn't like to rev at all on light throttle in neutral; sputters and coughs bad. I checked the plugs again - they all look fine and all look the same- don't see anything obviously wet - does this mean it's NOT a misfire then? The most rearward cylinder exhaust primary is a little cooler than the other 3 but not cold. While idling (which is smooth, btw), I unplugged each coil plug one by one: the front three cylinders this produces an immediately rougher idle. Unplugging the rear cylinder created no change in idle, however revving is even worse. I swapped coil harness and no change. Swapped coils between 2 cylinders - same behavior. The picture is confusing me more and more... One thing that I noticed is that immediately coming off track with the car very hot, it runs fine around the paddock - However in stop and go traffic on the way home with equivalent water and oil temps, the car was almost undriveable. 

 

Any thoughts?

[ChrisC]

Yes, a friends 420R did exactly the same.  It was a faulty coil driver in the ECU, proved with the use of my ECU (our cars were of a similar age).  It happened at a track day.  That said wiring loom faults are also no that uncommon, so check everything if you haven't got access to a spare ECU.  MBE repaired the ECU for a modest price.

[aerobod - near CYYC]

The fact that the problem goes away when the engine is hot and under load may point more to a wiring or connector problem than a failed ECU driver. I had a similar intermittent problem on #1 cylinder caused by a faulty connector on the coil. A loupe was needed to see slight arcing on the connector contacts, but I used a cheap recording oscilloscope to see the voltage spikes on that cylinder differ from the other cylinders when the engine misfired. Vibration over time seemed to be the cause of connector failure in my case, I added some foam tape on the coil cover that contacts the connectors to hopefully alleviate the problem in the future.

[John Vine]

I've just re-read this thread but I'm still not clear what has (and hasn't) been tried. So, some questions:

Did you record an Easimap log from cold (static and in-flight)?

Have you checked the wiring and connectors to the lambda sensor?

Have you checked, in microscopic detail, the plug loom and connectors? (Ditto for the TPS and injectors.)

JV

 

[KnifeySpoony]

In my mind, it would be odd if it was a connector or some other wiring fault to the coil, as I had exactly that issue last year, which created the exact opposite symptom from what I am having now- ie the car was fine at part throttle and low RPM/load, but then misfired only at WOT at high RPM. My first order of business is to check wire continuity from the coil to the ECU. Will also check for the 02 sensor, as the behavior seems to fit with a toggle between open loop/closed loop operation to me. Another thing that I am considering is the MAP sensor - I have seen threads saying failure there could cause similar issues, but I'm not sure. In the RBTB setup, it's just acting as a temp/barometric pressure sensor. 

[aerobod - near CYYC]

A sensor input problem (such as failed Lambda) will show up with Easimap logging, an electrical continuity problem will show up with an oscilloscope trace. It is difficult to home in on the definitive problem area without these diagnosis solutions in place.

If you don't have an MBE cable to use Easimap, it is definitely a worthwhile investment. You can also get a USB 2-channel oscilloscope for about $60. Both can be hooked up to a Windows laptop.

[KnifeySpoony]

I do have the easimap setup. I will try to decipher the lambda readings. Also i need to confirm 100% that it's a misfire on #4. I will run it then pull the plugs hot to see if #4 is wet. If it is a misfire only on one cylinder, that would seem to eliminate a sensor issue i would think. And tonight i have just checked my wiring continuity on the #4 coil and injector, as well as lambda and MAP sensors. So if #4 is really misfiring then perhaps the ECU coil driver could indeed be the culprit. All this is new to me. Fun times. 

[KnifeySpoony]

So it seems that the idle voltage being off by just a few hundredths is enough to cause such behavior. I guess 4.62V really means 4.62V. Live and learn...

[Geoff Brown]

Anecdotally it appears that the ECU driver can come under suspicion. A member in my area had the same symptoms which after chasing all sorts of possible causes, lambda sensor, spark plug, TPS, ignition sub loom, fueling, earthing etc it turned out to be the ECU driver for number one cylinder.

It was a new car barely one year old !