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Pre-IVA emissions fail - any pointers please?


andyismilesaway

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andyismilesaway

Good evening all,

 

I had the Westfield trailered to the local garage today for a check of brakes, headlight alignment and emissions - the good news is all 4 corners were braking as expected and headlight are now pointing in the right direction - however no matter what we did we couldn't get the emissions to pass...

 

The car is a 1.8 1997 mx5 engine with k&n filter, hoses to accommodate, WF 4-1 manifold with normal mx5 lambda sensor and a WF cat exhaust, standard ECU and stock engine. I've followed the coolant reroute with ECU temp sensor (where the thermostat once was) in the front of the block and temp gauge sender at the rear in the thermostat moulding. Engine was running for a good 20+mins and water was well up to temp of 100deg with fan kicking in and out as I'd hope.

 

Now the numbers:

Fast idle run 1: CO 0.544, HC 41, Lambda 1.013

Fast idle run 2: CO 0.477, HC 60, Lambda 1.009

Idle: CO 0.176

 

So it was the CO that was a FAIL and only at fast idle.

 

The car build has been a steep learning curve, and I've loved every second (even the wiring?...) - but I'm really not sure what the numbers are telling me. The garage suggested using checking all air hoses after the MAF sensor and using brake cleaner sprayed on all the joins to see any changes in revs to highlight any leaks.

 

Other than that, and checking, tightening connections has anyone anything more scientific or systematic I can do?

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KugaWestie

Good advice from the garage, check for vacuum leaks. All round the manifold, make sure all the dead ends are capped off.

Does it run without the MAF plug connected?

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KugaWestie

Have you run a diagnostics check?

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KugaWestie

Have you got the EGR sender connected onto the loom to eradicate any errors?

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andyismilesaway

Not tried without MAF, will give that a go.

Il give diag a go and yes, I've got all the egr kit attached to hope to not generate any diag errors. Thanks, all good thoughts

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Mark (smokey mow)

Andy looking through your build pics, have you connected the Idle control valve (ISC) which is below the throttle body to the inlet ducting? This would normally be a piece of 15mm hose, its hard to tell with the angle of the photos but I can't see one.

https://andyswestfieldbuild.wordpress.com

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andyismilesaway

Evening, yes all connected up with a small piece of L shape hose from the isc to a spur I added into the main big intake pipe.

Good call though. Next job is to try and spray some of the fittings and hope to note a change in revs/behavior - realistically reckon seeing any change is likely if there is a small leak?

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Kit Car Electronics

You wanted science...

 

Look at it this way - the test is supposed to be a cat test. If you didn't have a cat, you'd likely meet 3.5% CO and 1200ppm HC at 1.0 lambda. A functioning cat shouldn't have any problem getting to >85% conversion efficiency, which would be 0.5% CO and 180ppm HC, hence the 0.3/0.5% and 200ppm limit.

 

But you made it to 40-60ppm HC which would be >90% HC efficiency, yet failed the CO. It suggests that your engine-out gas might be richer than 3.5% CO, but the lambda probe (and presumably the engine sensor) read lambda 1. That normally happens when:

 

(a) an exhaust leak lets air in near the sensor so the engine runs richer than the sensor indicates.

(b) a poor fuel distribution across cylinders makes some richer than others (dirty injectors or intake leak)

© ignition is retarded to cause incomplete combustion

 

I'd be looking for leaks first, particularly on the exhaust joints 

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andyismilesaway

Thanks, appreciate the info! Okay, intake checking and exhaust side leaks - Il give all the above a bash

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KugaWestie

I am looking forward to you reporting back already

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andyismilesaway

Okay, quick update: a few mins in the garage show one of the inlet manifold takeoffs capped end was a bit loose and i suspect not a great seal. Also the heated oxygen sensor was only a bit beyond finger tight in the manifold - argh!

I've just ordered a new washer for the headed oxygen sensor so I can tighten it up properly.

I guess either (or both...) of the above could have caused the emissions results I saw:(

Annoyed with myself I didn't check everything in advance but you don't know until you know!

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KugaWestie

Hopefully it's as easy as that!

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