1.9 8V S.a.d - Do I Actually Need It?

[Lukespeed 10]

As the title suggests I suspect my sad valve is playing up due to extremely high tick over etc..

 

Is this vital? Or can I simply unplug, unbolt, and just block the pipes? Or will this cause it to run like a bag of spanners?

 

I have a tick over of about 1800rpm, and a misfire under load but it isn't a constant misfire just intermittent. So far I have changed..

Plugs

Leads

Dizzy cap and rotor arm

Coil

Ignition amp

Tachy relay

 

So I'm thinking it's either sad valve or afm?

 

Any help appreciated! Cheers!

[welshpug 1,661]

It's not the sad causing this, its poor setup of t-b afm, tps ignition etc.

[Tom Fenton 1,542]

I don't know why everyone always wants to blame the SAD! No wonder its sad!!!!!!

Its a very simple thing, a bi metallic strip that moves a disc to close off the airflow. When cold the aperture is open to allow extra air through to raise the idle speed. Inside it there is a heater coil, this is what is supplied electrically. A combination of conducted heat from the engine/thermostat housing and the electric heater coil makes the aperture close up to fully closed as the engine warms up.

Easy way to test, with the engine fully warmed up and idling, get hold of either pipe to/from the SAD and crimp it closed either with your fingers or a pair of grips. If the idle speed then drops, the SAD is not closing and needs looking at. Sometimes a good clean out of gunk can help. If the idle speed DOES NOT drop, then your issue is somewhere else.

As for misfire under load, the SAD cannot cause this.

[scbond 15 1 Cars]

As above, set eveything along the air intake up properly. Might be worth checking the adjustment if the SAD to make sure it isn't open too much.

[Anthony 1,003]

Echoing what Tom said - the SAD is a very simple device and generally speaking very reliable.

 

Indeed, I can't remember last time I saw one that was faulty or needed adjustment.

 

Remember that all the SAD does is allow a small amount of extra air to bypass the throttle when the engine is cold, with that extra air still being metered by the AFM and hence additional fuel injected to keep the mixture correct. It's little different to you just keeping your foot gently on the accelerator pedal. Once you understand that, you'll see that there's absolutely no way that it could possibly cause a misfire under load for example.

[Lukespeed 10]

Cheers for the responses! I shall leave my s.a.d as it is!

 

Any advice on setting up tps etc?

 

My engine has a Vernier pulley on it, and I suspect at some point someone has been playing with the inside's of my AFM as it has insulation tape around the black cap on it.

 

Cheers

[dcc 855]

A quick search will reveal all the answers you need

[Lukespeed 10]

Last night I went outside and played with my electrics abit.. After altering the throttle position sensor, tickover screw abit, and realising that my sad wiring had a break in it, I know have a respectable tick over! Hooray!

 

But I still get a miss under heavy load.. I have a friend with a 2 mile long tarmac drive to his farm so we tested down there, first and second gear no issues, but when it started pulling hard in third at about 5 grand it started missing, shift into fourth and get it up to 100 gt misses heavily again, but if you back off the throttle slightly it clears and pulls again, but if you put throttle back down again it misses?

 

Any ideas?

[Lukespeed 10]

And I also used 1980's technology in the way of 'Colortune' to get the fuel/air right on the afm allen bolt

[welshpug 1,661]

were the ignition parts all new and o.e quality?

[Lukespeed 10]

Everything is new except for the coil, which was bought on the understanding it was in good working order. could a dodgy coil create these symptoms?

[Anthony 1,003]

Coil failing can cause misfiring under load, so yes, could well be at fault.

 

Might be worth trying another (original Bosch) ignition amp too, as aftermarket ones can cause issues if you've replaced that with new also.

[murtaghp 3]

When I had similar symptoms on my last 205, it turned out to be a faulty dizzy.

 

The misfires that it was producing at the time were quite violent and would also affect the rev counter though.

[Lukespeed 10]

Last night I borrowed a coil off a friends running car, and it partially cleared up the misfire! it has now started missing from 6000rpm+ rather than 5000rpm+ which is an improvement, but something is still wrong somewhere.

 

Anthony I tried another Bosch Ignition amp, and it made no difference, but it had an extra pin due to it being off a MI16, will that make any difference?

[welshpug 1,661]

no, 1.9 mi had the same part number.

[jackherer 543]

Are you fitting known good ignition amps already fitted to heatsink plates? If not are you using thermal transfer paste?

[Lukespeed 10]

Yep off a well running car and just fitting the full plate with it so I don't have to reapply thermal paste. Starting to fall out with this car now, supposed to be at Croft on 30th but there's no point booking it till its running right!