Help needed please. Duratec R400 jumpy and stalls on idle

[kristianbs]

Hi, firstly apologies for my lack of technical knowledge, my first Caterham and I have the feeling it'll be a steep learning curve!

I drove it for the first time yesterday and it was perfectly fine. This afternoon it started first time, I left it idling and warming up for 10mins, and the first mile it drove like any other car.

Then the car started lurching even under constant throttle position, I smoothed with the clutch but didn't go away. Pulled over and it stalled under idle (I assumed was set too low, but from what I have read on a previous thread 950 is optimal and my rev gauge shows 1250! How reliable these are I don't know)

turned off and back on. Stalled after about 10-15secs of idling. Turned ignition off and on, applied a little throttle (constant), was on fine for 20secs and then it decided to have a bit of a rev party - 1000, 2000, 1000, 2000 about ten times over before settling back to "normal". 

I managed to limp home, the car was perfect for 2 miles and then started its random rev jumping but less severe for the last 2.

any ideas what's causing please and how to fix?

**Note: I have a master battery cut off on the door jam, it is very damp out there today so perhaps electrics? Also pressure reads 2 under idling, Higher under throttle. Under acceleration there is no issue at all. Temp gauge in middle at 80-85degs

​When I got home I turned off and on and recorded from the bonnet vents (apologies for random pic, YouTube doesn't allow audio only!). Nobody is in the car or touching throttle throughout: 

thank you in advance!! Kristian 

 

[Jonathan Kay]

Welcome.

Did it go lumpy when the engine speed became unstable?

Check the throttle position sensor wiring and connections.

Does your cut-off switch isolate everything? Did you see any signs of problems with the electrics, such as erratic instruments?

I'd also check that your pedal, cable and throttle are all operating smoothly before you move on to more complex possibilities.

Jonathan

[kristianbs]

Hi Jonathan,

it became lumpy at low speeds (but I was in gear 1 or 2 of a 6spd box) - a bit like the rattle judder you get in a normal manual if you were to go into 5th @ 25mph or something

the isolated switch literally turns off everything, including immobiliser. All instruments were operating as normal, The only odd thing was the rev counter going up and down quickly. (I assume the oil pressure gauge should increase with revs - as mentioned in new to all this!)

thanks I'll take the bonnet off tomorrow in the sun and investigate a little further - take a look at the contacts and cables. I hope it's just weather related as it did spend the night outside in the rain!

 

[SM25T]

Rev counter rising and falling. Sounds like a poor earth under dashboard. Main earth point is on a stud by wiper motor above passenger knees

[kristianbs]

Thanks, the rev counter was matching the revs of the engine at all times as far as I could tell. So the instruments seem accurate, just the throttle response is not corresponding to the pedal 

[JNC]

Sounds like the TPS !, You say  the car is new to you, did you buy it from a dealer ?, if so take it back.

[John Vine]

To start with, try looking here:

1. Throttle Position Sensor (TPS)
2. Lambda sensor
3. Wiring connections (corrosion, poor earths)

Re 1: The TPS wiring on the R400D is very susceptible to vibration-induced fractures.  Check each of the three wires where they enter the TPS, especially inside the connector.  Note also that the TPS itself may be failing. 

Re 2:  This sensor only operates when the engine reaches about 60C, and only then on part throttle, but a faulty one could give the symptoms you describe.  The best way to test it is to connect your ECU to Easimap software (requires a bespoke lead).  For info, try this in the search field: "Easimap AND MBE AND lambda".  The lead itself is available for loan (see here -- although I'm afraid mine is already out!).  Whereabouts are you?

Re 3: Especially the ECU earth and TPS connector.

 

What year is your R400 and does it have rollerbarrels?

JV

 

  

[kristianbs]

Thanks John,

the more I think about it the more I think it's probably moisture related. Unfortunately it never made it home (in the dry!) last night as I hit a piece of metal on the A3 and had a blow out ... so the car spent the night in the rain without a full body cover on the bonnet until I could go back and get a new one fitted to the rim. Tomorrow is due to be dry so I'll take the bonnet off and have a tinker or use an airline to dry it all 100%

Im based in Wandsworth SW London, and it's a 2008 model without roller barrels 

cheers kristian

[SM25T]

Remove plug leads from engine end and blow air into plug recesses in engine with plugs still fitted. Unplug each electrical connector in engine bay one at a time and dribble a little WD40 into each female half before plugging back together.

[John Vine]

the more I think about it the more I think it's probably moisture related.

That could well be the problem.  A few years ago, my R400D was (without my knowledge) subjected to a severe power-wash following a service.  It ran like a three-legged toad all 90 miles home.  Once I'd dried things out the next day, all was fine.

Give the ECU connectors a specially good blast with your airline.

JV

[ScottR400D]

My R400D before I had roller barrels fitted never idled that smoothly, it hunted between 1000 and about 1250 from new. Since fitting the RBs it idles perfectly steadily at 950. I'm not sure that a standard set up will idle that well but others may have more experience.

As an aside, it's never a good idea to start a car and leave it idling to warm up. Just about the worst running conditions for the engine. Not that this would be responsible for your current issues. 

[aerobod - near CYYC]

A standard R400D setup will idle very well if the mapping is modified, I have a perfect idle at 1000RPM, but had to swap to the unlocked 9A4 ECU to get there.

[JNC]

I must have been lucky with my Roadsport 175 D it always started hot and cold ticked over faultless , I upgraded to RBTB's via CC the 220 bhp upgrade had it mapped with the two Steves and it still runs faultless.  

[John Vine]

...had to swap to the unlocked 9A4 ECU to get there.

Was that to accommodate your elevated altitude?

For info, my R400D with RBs starts and idles perfectly on the standard CC-supplied MBE and map.  But then I live at 70m rather than 1260!

JV

[aerobod - near CYYC]

Yes, elevated altitude was the main reason, the standard 992 ECU defaults the air pressure to 1040 millibars, as I found out when adding the SBD pressure sensor. The 992 can see the air pressure and is wired to accept the sensor, but the maps don't use it.

i also found that the standard maps didn't correctly use the full range of the TPS, perhaps due to the tolerances in either the throttle body or TPS manufacture, but I couldn't have both the minimum throttle site below 0.5 and the maximum above 14.5 when the throttle stop was set to allow the engine to idle. I also found inaccurate mapping around the temperature sensor curve and decided to use a wideband oxygen sensor that required mapping adjustments to get the best out of it.

Overall the encryption and locking of the original ECU was too limiting for what I needed to do with the car. I do have the 992 ECU as a backup, which I did use I 2015 after I did a map update on the 9A4 and had Windows crash on me during the write to the ECU, causing it to be "bricked" and having to be sent back to SBD for a factory reset. Supposedly the crash happened during re-write of the communications block in the ECU, so I couldn't communicate with it anymore, just bad luck according to SBD.

[kristianbs]

Thanks for everyone's help, use of my girlfriends hairdryer and a battery charger seems to have cleared any gremlins! 120 miles of problem free motoring this morning!

[Jonathan Kay]

Well done.

That lumpiness as one or two cylinders dropped out, rather than erratic speed without lumpiness, might be  a useful clue for the next victim.

Jonathan