420R Running rough

[Tony Leigh]

Today I took my 2019 420R out for a short blat and after about 40 miles whilst heading back home I thought I could smell burning and then the car started to run roughly. It was only a few miles back home and during that time the engine would stall at junctions when idling, although it did re-start, and was down on power. The water temp. and oil pressure looked fine. When I got home I had a quick look at the engine but couldn't see anything obvious although the rear section of the side exhaust silencer/cat (I have a rear exit exhaust so the cat isn't separate) was very hot, and after several minutes when the front part of the silencer/cat was cool to touch the rear part of it was too hot to touch. This may be normal as it's not something I've paid attention to before and the rear part has shown more discolouration (I assume due to high temperature) for some time.

The car has done around 4000 miles from new. I've searched the forum and can see posts about failed sensors such as the lambda sensor or TPS, which have caused running problems. So my guess is that the engine started to run rich due to a failed sensor, probably lambda (?), resulting in unburnt fuel passing through to the exhaust and burning there. 

I may be wrong in my assessment but would appreciate the thoughts of those who have more experience/knowledge than me with suggestions for fault finding/resolution. I don't have the cable or software to interrogate the ECU but I do have a multimeter.

[aerobod - near CYYC]

The best way to do a quick test on the Lambda sensor is to unplug the connector and see if the car runs better (although not perfectly), as the ECU will default to open-loop only operation.

You can't really get a meaningful result with a voltmeter, although back-probing the signal lead while connected to an oscilloscope with a high impedance probe will show the 0.5Hz or so oscillation of a correctly functioning narrow band sensor.

[Benton]

I'd put money on the lambda sensor failing. Sorry I only know how to check lambda/TPS using Easimap plus cable
What part of the world are you in? How about contacting your local area rep for finding someone local with the software?

[KnifeySpoony]

Definitely check the lambda and TPS. From my understanding lambda sensor failure is more rare, but it's easy to check. My 420R is on roller barrels, so it simply won't run without the TPS (different mapping strategy), but my TPS recently started failing after about 3000mi. Replaced and all is well again.

[Benton]

Another check would be to take a look at the state of the spark plugs for anything obvious.

[SamC]

I had similar a while back and it was the TPS. 
 

As suggested above, disconnect the lambda to rule that out, if it isn't that then the TPS is the next most likely suspect I reckon.

You can get them dirt cheap on eBay (link to similar, check to make sure it is the right one for you first!!!) and then you can decide whether to replace with a pukka one or not if it is successful.

[John Vine]

I would also check the wires going into the TPS connector.  These are prone to fracture (especially the brown), although I would imagine that a 2019 car might well have the upgraded TPS subloom (or a better quality loom) as standard.

JV

[Tony Leigh]

Thanks for all your comments. I checked plugs this morning and they don't look too bad maybe a bit more sooty than I would expect. I disconnected lambda sensor and went for a short run, no better unfortunately. Exhaust note has changed (I noticed this when the problem occurred but re-confirmed it this morning). Best way I can describe it is that is more boomy and the car just doesn't want to go, occasional stall when coming to junction off throttle and, may be my imagination, but seems to maintain same speed (60 mph in 4th) at lower revs than before. I guess symptoms are a function of incorrect fuel/air ratio. So looks like it's the TPS that isn't working. I live near Kings Lynn and it is our area meeting (Carrotland) next Monday so will see if anyone there can help further with diagnosis.

[Tony Leigh]

Thanks SamC and JV. Cables to TPS look fine, so I have invested in a cheap replacement to start with as suggested by Sam. One further question - when replacing TPS are there any things to watch out for or is it just a simple case of unbolting and inserting new one - I just recall from other bits I've read that setting up TPS is quite an art but have never done this myself (yet). 

[SamC]

The TPS is just a straight swap mechanically. There is a flat on the sensor shaft to ensure it goes in correctly. Just make sure you align the body in a broadly similar position to the one you removed.

Mine re zeroed when power cycled (which I believe all duratecs do), but I know some have to have a software reset. I'm sure someone will be able to confirm that for you though.

[Andy135]

Possibly a dumb suggestion, but have you checked that your exhaust/silencer isn't partially blocked with something? Or maybe the internal silencer baffles are breaking up and have obstructed the exhaust flow?

[Tony Leigh]

Thanks Sam and Andy. I will try the new TPS when it arrives in a couple of days and see what that does and then investigate other possibilities if not successful. Not too sure how easy it is to inspect silencer internals without endoscope as only have smallish (relative to overall diameter) inlet/outlet although I guess a major obstruction may well be pretty visible, but hoping new TPS solves problem.

[aerobod - near CYYC]

Hi Tony,

With the exhaust note change you may be getting a misfire, but this could be a symptom as much as a cause. With the sooty plugs you obviously have a rich mixture which could be caused by the TPS if the plugs are evenly sooty. Any variation in sootiness could point to a coil pack, coil pack wiring or plug issue (or less likely an injector). Using an infrared thermometer to check that the exhaust primaries/headers have an even or uneven temperature can point to a misfire in a specific cylinder while the engine is running.

Cylinder #1 has a common coil pack wiring failure mode (fracture at the connector or plug pin loose / showing signs or arcing), especially if the upgraded silicone wiring loom is not in place

[SamC]

Hi Tony, did you get anywhere with this?

[GulfSeven]

TPS and idle needs to be set up with Easimap doesn't it? Or is the Duratec different to the Sigma in that regard?

[Tony Leigh]

Reply to SamC #14.

The new TPS has arrived but I haven't fitted it yet. I did run the car up yesterday and measured the exhaust primary temperatures with an infra-red thermometer. No.1 primary (nearest the front of car) was running significantly lower at circa 60C, with no.'s 2 & 3 at circa 130C and no. 4 slightly lower at circa 110C. That made me think there is a problem with the coil pack, I removed the spark plugs from 1 & 2 and no.1 seemed to have liquid on it which I presume is petrol, no.2 was dry but a bit sooty.

I carefully checked the wiring loom around the coil packs and TPS and can't see anything obvious but most of the wiring isn't really visible as it's covered with insulation type tape (I am sure there is a specific word for this tape but I'm sure you will know what I mean). A lot of our area members use Luke Stevens at Team Leo's as he is a very knowledgeable specialist (I have used him myself in the past too), so I am thinking I may resort to taking it to him to have a look.

I could change the TPS but I can't see how this is adjusted as the screws look they just bolt in a fixed position so unless I am missing something the only option seems to be to change the throttle stop which doesn't seem the right thing to do, or as others have suggested changing settings within Easimap software which I cannot do. 

Changing different items may be the only way forward for me which feels a bit too much like random trial and error with the added jeopardy of generating other problems along the way if I get something wrong, hence why I am leaning towards asking Luke to have a look, but I do appreciate everyone's comments.

[aerobod - near CYYC]

Hi Tony,

It is worth swapping the coil packs between cylinders 1 and 2 to see if the cold primary stays with #1. If the problem goes away, look carefully with a magnifying glass at the coil pack pins and connector sockets for signs of arcing. If the cold primary / misfire stays with #1, try moving the wiring around to see if it gets any better due to a possible fracture in a connector wire. Cylinder #1 seems to be more prone to wire vibration that can cause wire fracture or opening up of the connector socket (with subsequent witness arcing).

[SamC]

Re the TPS...

I was under the impression that the ECU re learns the zero once it is power cycled. So as long as the sensor isn't on its end stop at either extreme of travel, it should be ok.

I may be wrong on that, so it would be good if anyone could clarify?

[aerobod - near CYYC]

I can't say what the exact Caterham 9A4 locked config has for TPS calibration as it is not visible or adjustable using Easimap, but my unlocked 9A4 ECU has a voltage setting for minimum TPS (1.30V - Throttle Voltage Lower Limit) and maximum TPS (4.70V - Throttle Voltage Upper Limit) positions. The only other config item is TPS direction (clockwise or anticlockwise) and Voltage Default on TPS failure, which is set to the same as the Lower Limit in my ECU. The locked Caterham ECU features are likely to be the same as the unlocked ECU at a given firmware level.

The Throttle Index Map then uses the Lower Limit for throttle site 0.0 and Upper Limit for throttle site 15.0, with a curve applied to map the sites between 0.0 and 15.0.

When viewing the Easimap TPS Voltage and Throttle Site panels, the voltage and throttle site maintain the same relationship with no apparent calibration to reset the Lower or Upper limits through engine restart or ECU complete power cycles. The only adjustment I have found is about 0.02V of tweaking possible due to movement within the TPS mounting holes, typically only enough to change the throttle site from 0.0 to 0.4 against the idle stop.

Normally it is worth having the TPS resolve to about throttle site 0.2 at idle, so that any thermal changes in the engine compartment don't put it above 0.4 or keep it pinned at 0.0 if the Voltage Default is the same as the Lower Limit (otherwise it will show TPS errors if the voltage falls below the Lower Limit). Any throttle site below 0.5 will resolve to closed / idle throttle.

[SamC]

Ok, thanks James.

I guess that must mean the calibration of the sensor is fairly well controlled then.

I replaced mine with a sensor from a motor factors and it has worked flawlessly, although I imagine when viewed with Easyview etc it may not be entirely the same.

[Tony Leigh]

James/Sam,

Thanks for your comments, the suggestion about swapping coil packs is a good one and fairly obvious but not one I had thought of (I had a stressful day yesterday so wasn't thinking very clearly - that's what I'll blame it on, anyway). Will give that a go before swapping TPS as I can't see how a faulty TPS would cause a problem with one cylinder and unless there is something amiss with my temperature gun or measurement it does seem to point to a problem with that cylinder.

[John Vine]

Re #17:

Just to add that I had exactly the same problem on my 2008 R400D.  One of the wires to #1 COP connector fractured, but it was very difficult to spot as the actual break was inside the sleeve of the connector, right up against the terminal pin.

If that proves to be your problem too, the permanent fix is to fit CC's upgraded coil sub-loom.  This has fatter, silicone-sheathed wiring, and is much beefier.  I fitted 3AL080A, which completely solved the problem.

JV

 

[Tony Leigh]

Thanks John,

I had another quick look today, swapped coil packs between 1 & 2 and carefully checked wires, terminals, etc. There is still a temperature offset of circa 50C between no.1 and rest. But it does increase consistently, i.e. just after starting temps maybe 100 for 2-4 and 50 for no.1 then after a few minutes temps rise to 140 for 2-4 and 80 for no.1. Tried moving wires but no obvious change. Checked temp at different points on primaries and as expected they do vary but no.1 seems consistently cooler. Once up to temp (coolant) the engine idled fine, so I really need to take car out for a drive to see what it's like under load, hopefully will get a chance to do that sometime this weekend.

[MTW]

Did you manage to resolve this issue? I'm having the same issue with my 420r at the moment.

[aerobod - near CYYC]

My R400D had this or a similar issue some years ago. The wire to #1 coil can vibrate a lot. Sometimes the wire fractures, but in my case the connector pins had opened up a bit and there were signs of arcing when looked at with a jewellers loupe.

Easimap would not show anything wrong, I eventually had to drive around with a USB oscilliscope attached and recording to see the spikes in supply voltage to the coil that lasted a couple of milliseconds. I also could see the temperature of the primary drop with an infrared thermometer if the car did it's occasional misfire while at idle.

After replacing the coil subloom, I put foam tape on top of the coil connectors to allow them to contact the coil cover and try to damp out any connector vibration. Haven't had any issues since.

If you only have misfires at high revs, though, don't assume it could be just a coil or wiring problem. A lean high rev misfire due to a faulty injector could be a problem that is more dangerous to the engine health. This may show up with Easimap as a Lambda value that is too lean, but may be difficult to diagnose without a wideband sensor compared with the fitted narrowband one.