idle rpm and AFRS ??

[ranj]

New poster! (less than 10 posts)

Its been over a year now but my car is nearly ready to go back on the road , i was setting up the idle and also checking the afr.

Was just wondering what idle speed your 5 runs at and at what afr with the lights off and no fan running ???

The fan seems to take about 200/300 rpm off the idle speed when it kicks in and also weakens the afrs , i assume this is ok.

At the moment im running a idle speed of 1200rpm and a afr of around 14.0 thats with no fan running and no lights on. I cant really go any lower as when the fan kicks in the idle drops and the car begings to shudder .

Do you think this idle speed is too high ?????

[Mart]

My old raider ran 1k rpm idle with a lumpy rt200 cam.

Unless your cam is hotter, you shouldn't need to run any higher than 1k.

AFR's are pretty much spot on - That equates to around 1.3/1.4% CO, which is fine.

Might be worth oiling up the fan motor, or if it's peeing you off that much/doesn't make any difference, you could out the o.e unit & fit something like a Spal fan.

[ranj]

New poster! (less than 10 posts)

My cam is a rt150 so not lumpy at all , could a tight engine affect the rpm drop as its just been freshly rebuilt , not even done 10 miles yet ......... will try oiling up the fan and see if that helps reduce the rpm drop ....can get it to idle at 1000rpm mart but if i put my lights on then even that starts to make the car shudder ......

Mart how did you calculate the co% from the afr reading ????

[5teve L]

Are you taking the dash RPM counter as gospel??
I just did mine so the AFR's were right & the engine sounded right, the rev counter is sometimes (more often than not) ....wrong...

Also if you get a power drop can that not be down to battery or alternator or earths ??

[ranj]

New poster! (less than 10 posts)

nah not takin as gospel , but saying what it reads , just been to get MOT done and it passed but only just ....... beacuse of the CO reading , i messed about with it before i went ......then had to mess again with it ... but it all worked out OK.

Just interested to know how to work CO from the afr readings on the gauge ......

[Mart]

It's just a mathematic formula.

Something is wrong if you only just passed the emissions test, as an afr of 14:1 is circa 1.3/1.4% as I mentioned previously. Given that the Renault & Haynes manual quote 1.5% +/- a wee bit, you're well in, so assuming the mot station's sniffer is calibrated, either your probe/gauge is giving you inconsistent inaccurate readings, or the idle fuelling is fluctuating badly.

[ranj]

New poster! (less than 10 posts)

always the possibility of my gauge not being accurate .......

[Mart]

Given that the Renault & Haynes manual quote 1.5% +/- a wee bit

In fact, if I remember rightly, I think the MOT c.o pass rate for a gtt is 5%, which equates to an afr of circa 12.6 - That's miles too rich for an idle afr though.

[Brigsy]

3.5% c.o is the max for a gtt. I always set the c.o to 1-1.5% with ease, no idle probs