1800 rpm tickover

[davelittlewood]

Hi all,

Had a weird one today.

Drivng down a steep hill in 5th on overrun. The car suddenly decided that we weren't going fast enough so it speeds up by itself!

Hit the brake but then the car stars surging so I dump the clutch in and the engine revs up to 1800 rpm???

Reangaged the clutch a few times but just the same until we get to the bottom of the hill.
On the flat the car does not respond to light throttle until mid throttle when it suddenly takes off but it really lumpy.

Pulled over and the motor is still at 1800......

I let it cool down and had a look round the engine bay. No loose wires, no split hoses.

Pulled the ecu and left it for 5 mins and then reassembled.

Car runs fine now but some what worried that something nasty is about to happen (I'd always told myself that I wouldn't pull the pin on an MBE system unless the current dizzy or ecu packed up, might be time to phone Dom).

I guess it could be the throttle pot going?
The ecu thinks that I've got the throttle part open and so over fuels but then as I increase throttle nothing happens until the throttle actually goes past where the ecu thinks it is??

I dunno but we've got a 300 mile journey home tomorrow and I don't want to do it on the back on an AA truck!

Any ideas?

Got no tools here so I'll only be able to have a good poke at it tomorrow afternoon.

Dave

[ianwayne]

OK, I'll say it. Stepper motor??

[blitzracing]

Odd combination for the throttle pot- it would be having to give a voltage reading to say the throttle was open when it was not- the only way this will happen is if the ground wire in the throttle pot goes open circuit and they can break where the wires enter the TP, so its worth close inspection in this area and the connector. A worn out TP / open circuit does the opposite and will cut the fuel when the car is running normally as it reads that the car is on the over run. Mind you 1800 rpm sounds a bit high for a running setting- it think its nearer 1200 so it might be something mechanical like something holding the throttle plate open a tad.

Edited by blitzracing on Saturday 6th September 09:00

[MADMAX2]

blitzracing said:

Odd combination for the throttle pot- it would be having to give a voltage reading to say the throttle was open when it was not- the only way this will happen is if the ground wire in the throttle pot goes open circuit and they can break where the wires enter the TP, so its worth close inspection in this area and the connector. A worn out TP / open circuit does the opposite and will cut the fuel when the car is running normally as it reads that the car is on the over run. Mind you 1800 rpm sounds a bit high for a running setting- it think its nearer 1200 so it might be something mechanical like something holding the throttle plate open a tad.

Edited by blitzracing on Saturday 6th September 09:00

Mark you are a legend !!

[davelittlewood]

Mark,

Correct as usual!

It was only a guess on my part.

Well 250 miles later and not anther problem.

Ah well, have to spend the money on the chassis instead ('hello, is that R T Racing.....')

Dave