420R Kangarooing (but only sometimes.....)

[7 Minder]

Our 420R spec car running RBTBs and an MBE 992 locked ECU is prone to part throttle kangarooing.  I've only run the car a few times this year (all in the last couple of weeks or so) and sometimes it's really bad and other times virtually non-existent.  

At least a couple of the recent runs have been after starting the car and letting it warm up at idle before driving.  Yesterday I drove away immediately after starting and it was hugely improved.  Pops and bangs on the overrun were much reduced too.

I'm wondering if the ECU does anything different in the idling warm up vs drive away scenarios that might account for the difference?

[AristoCat]

I had something similar happening on my new 420R, my issue was the TPS (throttle position sensor) - I ended changing it out twice, the last time for a genuine part.

[Jonathan Kay]

https://duckduckgo.com/?q=site:caterhamlotus7.club+420+kangaroo

!

Jonathan

[John Vine]

#1:  I'm wondering if the ECU does anything different in the idling warm up vs drive away scenarios that might account for the difference?

One basic difference is that, during warm-up, the ECU runs in open loop and uses a pre-determined setting for fuelling.  When the coolant reaches 60C, the ECU moves to closed loop, and adjusts the fuelling based on feedback from the lambda sensor (and others). 

I think the general consensus is that it's better to warm up the engine quickly -- that is, by driving rather than idling.

JV

[Geoff Brown]

Now if it had been a car running the standard plenum I would say that the problem was possibly normal but not with RBTBs. Got to be something basic like the TPS.

[7 Minder]

Thanks all.  I was wondering if the ECU might store any temporary settings as the car was fine yesterday after driving away immediately after start up, even when properly warmed up.  But a few days before it was almost undriveable.  Wedging my foot against the side of the footwell helps marginally.

TPS is worth looking at again.  I set it up meticulously last year with Easimap but another issue I occasionally have which I think might be TPS related is the idle sticking around 1800 rpm.  Is it a standard Ford TPS?

 

[John Vine]

#6:  Yes, it's a standard Ford TPS.

... the idle sticking around 1800 rpm. 

That could be caused by a binding throttle cable preventing the RBs returning to their rest position.  It could also contribute to the kangarooing behaviour.

JV