Sunday, 2 October 2016

Stut-tut-tut-tering Throttle - Arcing on Airflow Connector

I bet you're all dying to know what happens when you get some arcing on the connectors on your airflow sensor?!?  Well, you can rest easy, as you're about to find out!

On literally my first few laps at the Llandow Track Day last weekend, the car felt like it was hesitating a little in fourth gear... I noticed it once or twice, thought it was odd, and then came into the pits thinking it was just me being overly 'sensitive' having not been on track for a few months.  After all I'd just driven some two hundred miles to the circuit without a glitch...

...I had a quick chat with Alex Graham, and agreeing it was probably an airflow issue, we decided it best to unplug the Lambda sensor and see what effect that would have.
I'm not dead - just unplugging the lambda sensor
I'm not dead - just unplugging the lambda sensor
I then went out for a few laps, and initially all seemed ok, but after two or three faster laps the problem re-appeared which meant removing the lambda sensor didn't do anything to help the situation - in fact the stuttering was worse!

Car with stuttering throttle - The accelerator was planted to the floor when the car was stuttering and slowing down in the video below:-

So back into the pits it was, and some more head scratching... The lambda sensor was plugged back in again, and this time a group turned up to lend a hand... We removed the bonnet, started the car and everyone started gently pulling and prodding the visible cables and connections on the loom.
Plenty of help - pulling and prodding cables and connectors
Plenty of help - pulling and prodding cables and connectors
With a bit of pulling and prodding - Craig Harding seemed to locate the problem by wiggling one of the wires on the back of the airflow sensor connector.  We removed the connector and it was clearly evident where the issue was.
Signs of arcing on the connectors of the airflow sensor connection block
Signs of arcing on the connectors of the airflow sensor connection block
A 'quick fix' was to slightly twist the male pin on the airflow sensor - which seemed to fix the issue for the rest of the day.

The next day on the drive home the car started stuttering again, sometimes worse than others, so knowing what the problem was, I drove carefully back.  When I got home I took a picture of the sensor and connector block and emailed it to Tony at the Caterham Parts department.  He said that the sensor was easy to get hold of, but the connector block was a special order from the company that makes the looms.
Caterham R500 Airflow Pressure Sensor and Connector Block
Caterham R500 Airflow Pressure Sensor and Connector Block
The connector came into stock in a day or two, and towards the end of the week the new parts were on my desk.  I had a bit of spare time this afternoon, so thought I'd use my time wisely and fix the problem.

THE FIX
It's a pretty easy fix really (approx 30 minute job), but here are the steps I went through.

First, I removed the connector block - a 'top tip' when working with electrics - take a picture of the wiring BEFORE you take it all apart - it makes things a lot easier when you're putting it back together!
Picture of wiring of rear of airflow sensor connection block
Picture of wiring of rear of airflow sensor connection block
With the connector block detached, I replaced the airflow sensor (mounted on the rear of the carbon housing of the throttle bodies / trumpets).  This is just one bolt and nut, and self explanatory to change.

Next up, get the connectors out of the block.  Seemed a bit fiddly at first, but once you know how to do it, it's dead easy.  The white block in the image below is used to lock the connectors into place, and is removable, by pulling forward with a screwdriver.  With the lock removed you can then place a small flat-head screwdriver into the connectors and then pull them out, gently, from the reverse.
Connector 'lock' with visible signs of arcing
Connector 'lock' with visible signs of arcing
With all the connectors now removed, I replaced the connector on the green wire - which was the one that seemed to be causing the arcing.
Connector replaced, all ready for crimping and the refitting.
Connector replaced, all ready for crimping and the refitting.
To refit the connectors, it's just a case of pushing them into the right holes - but note, they only go in one way, so make sure you don't force them, as there's no need.  The connectors make a satisfying click when they are seated properly and with all the connectors in, refit the white lock and then plug the whole block back into the airflow sensor.
Connector, connection block and airflow sensor replaced - now time to test it!
Connector, connection block and airflow sensor replaced - now time to test it!
With the new airflow sensor fitted it was time to start the car and see how it would run:-

As you can see from the video it started and ran perfectly.  I took the car for a half hour (or so) blat with Karl who was over from Ireland for the weekend, and no problems surfaced - so with that, it seems like the problem is fixed.

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