Club 80-90 Forums

Hi all

Took my bus for it's first UK MOT today and it failed on emissions. CO too high. Max 3.5 result 3.68. I'm no expert on such things, anyone got any advice on how to get this down? Seems so close it's mean to fail it!

Cheers

By the way I really did try searching this before posting, surprised it's not been asked before...

My mv has been running rough for a while, I fitted a new temp. sender no.2 and last week it passed at 0.6 c.o.

Sounds like a good place to start looking. If your's read 0.6 then mine is certainly too far out!

First adjust the CO screw on the air flow meter (allen key vertically down at back next to air flow exit/elephant trunk). Screw out acw to lean off mixture.
Also check idle switch is working on throttle body.

Do you have a Bentley ??? Pricey but invaluable imho !!

There's a CO screw... Amazing.

Thanks for that, will check both things tomorrow before taking it down for a retest.

Personally I wouldn't touch the mixture pot just yet.
Just start at the beginning, gap and clean or replace the plugs.
Check resistances of the HT leads.
Inspect cap and rotor.
Check/set ignition timing.
Check temp2 with ohmmeter.
Make sure the idle/full throttle switch is doing what it's meant to [continuity at idle and full throttle]
Check the throttle body for wear [highly likely]
Pull the injectors out and check the spray pattern [likely]
Check the vacuum hoses to the fuel pressure regulator are intact.
Check the vac advance and retard diaphragms are in good order [a leak here will upset the fuel pressure regulator and think it's at a higher throttle position that it's at so fuel pressure will increase and as it does so with the idle amount of air going in it will result in a richer mixture.]
Check the fuel pressure.
It is very very rare that you have to adjust the mixture pot, it's usually something else that's failed.

That lot is going to take 30 mins or so, you'll need a multimeter [which any T3 owner should have really] a timing light and a cheap £5 gauge off e-bay for the fuel pressure.

Timing on a DJ is 10° BTDC if you run it on super, back it off a bit for unleaded, the book says 5 but we tend to go to about 7 or so.
Fuel pressure is 2 bar with vacuum, 2.5 bar without and is checked by removing the small blanking plug on the T-piece by the dizzy.

92Syncro wrote:Took my bus for it's first UK MOT today and it failed on emissions. CO too high. Max 3.5 result 3.68.
Seems so close it's mean to fail it!

It's not that close... CO on a non-catted engine should normally be around 1.0-1.6%. 3.5% is the absolute worst possible allowed...

Don't forget to beat out & vac the air filter (if you can't get a fresh one locally)

Any ex-SA bus will be full of fine orange dust

That is some fantastic advice Simon! Thanks for all that.

I did adjust the mixture, and took it for it's MOT, and it has passed! I know how much adjustment I put on it, with a plan to back it off, but it looks like the tester adjusted it to get it to pass too.

Now I've got a good decent checklist of everything to check, I can go through it carefully without the pressure of the MOT. (needed to get it quick to register with the DVLA before my VIN insurance expires).

The air filter was replaced just before it left SA and I reckon it's the only single part of that bus that doesn't have a layer of orange dust!

Thanks all!

Like I said, we hardly ever adjust the "mixture", there is always another problem that causes it.
Last resort for us to adjust one, that or unless sticky fingers have been at it!

Simon Baxter wrote:Like I said, we hardly ever adjust the "mixture", there is always another problem that causes it.
Last resort for us to adjust one, that or unless sticky fingers have been at it!

That's just the point, once upon a time they were fitted with tamper proof caps. Never had one in yet that was still intact, so they've all had sticky fingers in!
Also, I thought it so obvious that all else should be/would have been checked first that it didn't need saying. My mistake, soz.

ajsimmo wrote:I thought it so obvious that all else should be/would have been checked first that it didn't need saying.

Ha, never underestimate the lack of knowledge some people have with engines! It's what keeps you traders in business and me scratching my head when someone tells me my carbon monoxide emissions are to high

To be fair I should have checked all that, but didn't know what of all that would effect emissions, now I know all of it!