MOT emissions failure

[Rpm]

Yesterday I took my G reg mk1b for its first MOT since 1996. It's been in my garage for 17 years and me and my son have spent the last year, on and off, getting it running again. I was expecting a few failure points but it sailed through on everything except emissions.

It registered 8.46% CO against a limit of 3.50%. HC was 515ppm against a limit of 1200ppm. Idle speed and smoke tests both passed.

The guy who did the MOT said the results indicate that it's running too rich so I should check air filter and plug gaps as a starting point.

The filter's a bit dirty but doesn't look that bad to me. Then again, since its been standing for so long, maybe it's deteriorated in some way and isn't letting enough air through. I'm going to get a new one. Plugs are a nice brown colour so, according the standard photos in my Haynes manual, no obvious signs of excess fuel there I didn't check the gaps because I couldn't find my feeler gauge but I'll get some new plugs regardless.

I had the injectors cleaned last year, so they should be ok.

Not sure if this is relevant, but one of the exhaust tailpipes had fallen off so I repaired it by using some jubilee clips to fix it to its neighbour and then used gun gum to seal the joint with the back box. If that seal's not tight, could that affect the emissions reading? But if it was that bad, I guess it would have been an MOT failure.

Apologies for the rambling post Any suggestions on what else I should check?

Thanks

Rob

[jimi]

Put in a new air filter and a set of plugs (you can get a set of NGK's on ebay for under a tenner)
Check that the rotor arm and distributor contacts are clean and in good condition.
Check for a vacuum leak on the intake, it's only needs one of the small vacuum hoses to be drawing a little air to mess up the emissions.
The only time my car has failed in the last 5 years was a couple of years ago on emissions and the problem ? .......... slack vacuum hose

[elbon50]

Welcome to IMOC Rob

It would be helpful if you fill in more details in your profile

Peter

[phaeton]

Also make sure it is good & warm before they do the test, there is a 5th injector on the inlet manifold which acts like an automatic choke, if the car is still not up to temperature this will still be injecting fuel.

Alan...

[Rpm]

Thanks for the comments guys.

jimi: I forgot to say that I've already changed the distributor cap and rotor arm. Any suggestions on part numbers for new plugs? I'll have a look at the hoses tonight.

elbon50: I've added my location to my profile. I'm just down the road from you in Cannock!

phaeton: I'm pretty sure it was warmed up enough. Certainly the temperature gauge was around halfway on the drive to the garage and the tester had it running for good while on the lift. But when I get the retest, I'll be sure to check.

Thanks again

Rob

[SuperRedMR2]

Turn the idle screw down

[jimi]

Any suggestions on part numbers for new plugs?

I use NGK BCPR6EY11 (same as Mr T recommends)

[Tiamat]

If you know someone with a Halfords Trade Card you can get new plugs from Halfords at about £5. Think last time I did it I paid £4.96.

I also run the MK1 using MK2 plugs and it has gone through the MOT every time, only use these plugs because they're always on the shelf and the MK1 ones aren't always there.

Might also be worth putting some redex or something through it too, give it a damn good clean. I know the jury is always out on 10K Boost, but I have used this before MOTs and it has made a difference.

[un1eash]

I'm not convinced the cold start injector does anything, I've had mine disconnected for years.

Have you checked the timing also?

[JMR_AW11]

Have you tried adjusting the idle/light running mixture screw?

[elbon50]

I think a new air filter element will do most to cure the problem Rob

We should meet up sometime since we are such near neighbours

Ian08 is another one. He's at Bednall

[JMR_AW11]

The air filter shouldn't really affect the mixture because the ECU uses a speed density EFI system.
I think the mixture screw will give the most control over fuel ratio.

[PW@Woodsport]

Jeremy is right, i'd be adjusting the idle mixture screw, effective up to around 3500rpm if i remember right Jeremy?

Also make sure your ignition timing is correct, if the timing is showing as 30* at idle instead of 10* (bridged) or 16*(unbridged) then it's highly likely your TPS is out of adjustment and causing the ECU to switch from its idle maps, obviously this will throw your emissions way off.

[JMR_AW11]

Hi Paul
Yes I recall that on the later mk1B ECU the mixture screw gradually loses its influence with increasing rpm and it has no effect over 3500rpm.

I vaguely remember that the screw on the early mk1b has a constant effect on the mixture up to 3500rpm. A few years ago I posted up an HTML page about all this on my BT webpage but BT closed down their free website space a while back.

Mine scraped through the emissions test last week after being off the road for two years. It hit 3.0% CO. Sometimes my MOT tester plays with the mixture screw to pass this test so it's definitely worth a play with it.

[Rpm]

Guys

Thanks again to all of you for your advice.

Following Jimi's suggestion, I was checking the small diameter vacuum hoses on top of the engine. It turns out that one was disconnected. The one that I think, having looked at the Toyota workshop manual, goes to the fuel pressure regulator.

I guess I removed it when taking the injectors out then forgot to reattach it. Stupid

Could that explain what I'm seeing?

I'll be putting new plugs and air filter in tomorrow regardless then I think i'll take it back for a retest.

I'll make sure that I know where that idle mixture screw is so we can adjust it during the test if necessary.

I'll let you know how it goes.....

Cheers

Rob

[mrdb]

That would be your overfueling then. Regulator pressure would be to high at idle as it wouldnt see the vacum.

[jimi]

Mixture Screw (courtesy of Jeremy Ross)

[tottacrolla]

I'm not convinced the cold start injector does anything, I've had mine disconnected for years.

Have you checked the timing also?

and this is wrong:

"Also make sure it is good & warm before they do the test, there is a 5th injector on the inlet manifold which acts like an automatic choke, if the car is still not up to temperature this will still be injecting fuel."

The cold start injector only works when the engine is cranking and not actually running.

[pk_090]

Id say give it a good hoon to the test station too. My failed on emissions last year and the tester just took it out the back in neutral and redlined it a couple of times. He says it cleans all the crap out. This is mandatory on a diesel, IIRC its at least 10 seconds of full throttle in neutral before it goes on the ramps. My old work had a huge soot trail where the testers would nail it and the crap came out.
Alex

[Rpm]

Result!!!!!!

The old girl passed the MOT this afternoon. CO down from 8.46% to 1.5%. Seems that replacing that vacuum pipe made quite a difference!

I'll be looking to get her taxed tomorrow and then the next round of expense starts: wheel refurb, new tyres, cam belt. And turning a pink bonnet back to red

It's strange, but even after owning the car for 23 years, I still look at it and think: Wow!

Thanks to everyone who suggested things for me to try.

Cheers

Rob