K Series potentiometer - Helpful technical advice from prangerman (1 in a very short series of 1!)

[prangerman]

My R300 K series recently developed a rather scary hesitation at low revs in low gears, which almost led to it being rear ended when pulling away from traffic lights when the engine coughed and spluttered and died. I didn't even have time to drop the clutch. A quick restart and a good dose of revs and a gentle right foot when accelerating from first to second got me home.

 

I reset and rebalanced the roller barrels and with a Minister "how to" guide which I had the foresight or luck to print off some years ago, I also decided to check the resistance across the potentiometer. The Minister guide suggests the resistance across pins 1 and 2 should be 0.45ohms. Mine read 0.32ohms. There is very little adjustment on the potentiometer but I managed to get the resistance up to 0.43ohms.

 

Together with the rebalancing of the RBs the hesitation seems to be cured although I need a good long blat to be sure. A recent short proving blat suggests that it's running like an R300 should 😬 (if only I could cure the reluctance to fire up from cold ☹️ - despite newish battery, HT leads and new spark plugs, water temp sender to ECU, and air inlet temp sender on the RB backplate).

 

If you have a K series and a spare few minutes it may be a worth checking the resistance across pins 1 and 2 as I presume the resistance on mine was right at some point in the car's earlier life.

 

Peter

 

Peter

[bluespeed]

Peter,

Good to hear of another R300 K series owner that has struggled to get his car to start. I have been through the same experience and finally have got her setup so she starts on no throttle input with a very healthy battery. As soon as the battery starts to fade, the problems started with mine. I also had the THBs balanced which improved things.

 

Chris at the seven workshop had all my injectors cleaned (the car not me personally 😬) which has also aided starting a little.

Have sent you a message as I have a question about your R300.

 

Mine now starts well, oh and sealing up the exhaust has also helped recently.

 

Simon N

 

[prangerman]

Simon

 

Thanks for that. Did you or Chris manage to identify the root cause of the problem? I guess mine could be a fuelling issue or a mapping issue or of course both.

 

Peter

 

[Slipper man]

Is there any way I could get a copy of the Minister guide? It would be very useful

[prangerman]

Slipper man

 

BM me your details and I'll scan and send you a copy. (You may have to wait until the weekend when I can look for the guide having recently cleared out the study and not put it back together yet )

 

Peter

[Ian B]

You need a few filing cabinets, then you'd know where things are!

 

[prangerman]

Ian

 

I would be fine if I'd ordered the right sized suspension folders. I blame SWMBO...

 

I have 50 unused new A4 sized suspension folders for sale.

 

Peter

[Jerry Auton]

I could do with some.

[Paul Deslandes]

are you sure its 0.43 Ohms as this is an incredibly low value and comparable with the wiring resistance? I wonder if you mean kilohms, i.e 430 Ohms, or even 4,300 Ohms. 5kOhms (5,000 Ohms) is the normal total resistance value for a TPS potentiometer. If the resistance you're measuring is between the pot wiper and ground then 430 Ohms would make sense as, assuming the voltage across the TPS is 5 Volts, 430 Ohms between these points would result in a sensor voltage of 430millivolts which would be about right. e.g. an MBE is normally set to between about 360 and 380mV.

 

Apologies for being pedantic 😬

[prangerman]

Paul

 

I will happily admit to automotive electrical numptiness (although I have in the past changed batteries and the occasional fuse - wow 😬).

 

My references were to the advice in the Minister guide. I should have made clear that the reading on the pot is using the 20k scale.

 

That is now my auto-electrical knowledge completely exhausted.

 

Thanks to Simon (bluespeed) for the phone call yesterday advising me to look at the exhaust system for leaks/gaps as another possible reason for my cold start issues.

 

Peter