Failed MOT on emissions - TVR AJP V8

[Tanguero]

Failed with persistently high lambda reading. CO and HC were a bit on the high side but passed.

Test 1

Test	Value	Limit
CO	0.143	0.3
HC	105	200
Lambda	1.044	0.97-1.03

Test 2

Test	Value	Limit
CO	0.292	0.3
HC	191	200
Lambda	1.037	0.97-1.03

Standard exhaust with cats, there don't seem to be any obvious exhaust leaks.
According to the ECU software both lambda sensors are switching between 02. and 1.0 volts so I assume are working ok.

I would be really grateful for any ideas as to what I can do to get it through?

[Pumaracing]

Check for an exhaust leak. A high lambda reading indicates a lean mixture i.e. excess oxygen but the CO and HC readings contradict this. What is therefore happening (probably) is there's an exhaust leak which is letting air in, confusing the ecu which is then injecting more fuel to compensate but still leading to an overall weak reading from the MOT lambda probe in the tailpipe.

Do you get any crackles and pops on the overrun? That's a sure sign of a cracked or leaking exhaust manifold but the leak could be downstream from that.

Blocking the tailpipe(s) with a rag is a good way to find exhaust leaks.

[Tanguero]

Thanks for the suggestions! Much appreciated.

Crackles and bangs (and flames when the cats are not in) on the overrun go with the territory on the AJP but I will have a thorough check of the manifolds as well as the rest of the system.

[Tanguero]

Now passed!!! Looks like it was an air leak in the exhaust where the back box joins, cured that and the lambda dropped within limits. Thanks for your advise!

[Pumaracing]

Thanks for the update. Another satisfied customer

[Steve_D]

Pumaracing said:

Thanks for the update. Another satisfied customer

Your getting good at this. Chalk up another win.
Pity you can't charge.

Steve

[Poledriver]

Pumaracing said:

Thanks for the update. Another satisfied customer

OK, for your bonus question:-
My 4.5AJP8 is very lumpy and hesitant below 2,500RPM. From 3,000RPM it pulls like a train, only faster.

It had whirlwind intakes, ATC sports exhausts, is de-catted with Jules suggested cross piece in the link pipes. It has been re-mapped by Jules.
I've had the TB's, throttle pots and adaptives checked and set up by Andy at APM.

Is this low-end poor running normal, or do I have a problem?

[Pumaracing]

Poledriver said:

OK, for your bonus question:-
My 4.5AJP8 is very lumpy and hesitant below 2,500RPM. From 3,000RPM it pulls like a train, only faster.

It had whirlwind intakes, ATC sports exhausts, is de-catted with Jules suggested cross piece in the link pipes. It has been re-mapped by Jules.
I've had the TB's, throttle pots and adaptives checked and set up by Andy at APM.

Is this low-end poor running normal, or do I have a problem?

I have no idea what any of the bits you've fitted are being as they're car specific and I have nowt to do with TVRs, however, if the cams are stock then there's no reason why tractability should change greatly. You'd have to do something pretty radical with either exhaust or intakes to really hurt low rpm running. Very short intakes obviously tend to hurt the bottom end on most engines but it should still run clean.

If I knew what duration the cams were it would help because long cams in conjunction with mismatched other bits aren't going to be happy at low rpm.

If the fueling and ignition are correct below 2500 then clearly the package isn't working but I'd still check the basics first. Compression test, cam timing etc.

[Incorrigible]

If it's possible, take it back to Jules. I'm sure he'll want you to be satisfied with the map

[Poledriver]

Incorrigible said:

If it's possible, take it back to Jules. I'm sure he'll want you to be satisfied with the map

Unfotunately time and distance are working against me on this one!
I think I'll try and find a rolling road where I can get a plot of RPM/power/torque/fuelling from 1,000 RPM upwards then work on from there!

[itiejim]

I had similar symptoms with my AJP when the lambda sensors went down. Plugging it into the diagnostics should show them bouncing up and down between 0.1-1.1 volts (+/-).

Once you are over 3000 rpm (and/or a certain throttle opening which I think is about 50%) the ECU ignores the lambda readings and just goes with the map.