CO Level, fuelling problems

[Alexdaredevilz]

Ive trying to set my CO level to 2-2.5%

I pugged it all up to the machine etc

Ive tried to adjust the AFM the best i can, but the readings keep jumping from 1.5% to 3.8%

The car will idle high then settle down after 15 secs?

I got minor shunting

Also it will drive it self sometimes, as in I can do 50 mph with out touching the pedal

Is there a sensor that's staring me in the face that's busted?

Thanks alot

Alex

[blitzracing]

The CO trim on the side of the AFM only works on the non catalyst fuel map, otherwise the lambda probes are used to set the mixture. C0 should be around .5 to 1% if alls well, although the engine will idle quite nicely at 2.5%. It should not however go as high as 2.5% if both lambda probes are working and the ECU is running in emission compliant mode as it should. NOTE theses are values before a catalyst, so tail pipe readings should be much lower if the cat' is hot and working. You need to get a test meter on the output of the lambda probes across the black and white wires and check for a 0 - 1 to 1.2 volt signal switching at around 3/4 second intervals on both sides of the V8 to show the probes are working. Access to the lambda connectors is awkward, you either have to dig around at the front of the chassis by the top wishbones below the exhaust down tubes, or there is a similar extension plug and socket poked away behind the fuel rails on each side of the V8. If you cut enough cable clips, and can pull the connector up to get at it.

A high idle is caused by either a sticky stepper motor, a false speed sensor signal being present at the ECU, the throttle pot is out of adjustment, or possibly an air leak around the plenum somewhere.

[Alexdaredevilz]

Its full decat ran on green tune, with best guess MA chip

Do you think I could have a faulty AFM?

As for the idle,

Today I adjusted the throttle pot, was 0.22 now 0.33 as been told by the MA guide I was sent

I also set the base idle using the instructed method

I clean the stepper motor out this morning, and my idle has got worse, now it sticks at 2K rpm and now wont settle back down,

How would I go about checking my ECU is receiving the right signal? could my stepper still be the cause of this?

Many Thanks

Alex

[debaron]

Try disconnecting the stepper cable when the car is idling nicely.

If the revs still play around then you can rule out stepper problems.

Many people cut out stepper entirely and fit a 'constant flow' device. Even heard of plumbing fittings being used. Plenty of info around on it.
If you discard the stepper you'll need to give it a bit extra throttle from cold but after 15 secs or so it's fine and will give nice steady idle at all times (providing everything else is working properly!!)
I haven't done it myself but someone who has (beastmaster) said it also made a real difference to the smoothness and power delivery of his 500.

Good luck!


Ryan

[blitzracing]

Ive covered quite a bit here:

http://www.g33.co.uk/fuel_injection.htm

Although In you case id be looking for an air leak around the plenum pipework, plenum base, or possibly the trumpet base as both the idle and CO are unstable to start with. The CO setting is tricky at best of times as there is a noticeable time delay between setting the CO trim, and what appears at the tail pipe, so you can end up chasing your own tail. Also small air leaks play havoc with the idle mixture, as with the throttle shut the plenum pressure is at its lowest so air leaks have a bigger effect than when the throttle is part open.

As suggested, the idle should always return to the same setting with the stepper being disconnected, or block the stepper feed pipe, and ensure the base idle is constant. You can spray easy start around anywhere that might leak, and if the idle changes as the easy start is drawn in, then you have found the leak, but please be careful around a hot engine!! If you are tempted to visit B&Q's plumbing dept to fix the issue, something else is wrong, its a bodge that masks the issue, not fix it.

Other things that makes the idle remain high are a speed signal reaching the ECU when the car is not moving, as this is generated by a slightly suspect bit of TVR electronics under the dash, but I dont know if this signal will show on a test meter as such. It should be near 0 volts with the car stopped. Also check that the area around the throttle plate is clean, so its seating as it should.

I dont mind having a look at for you if you can bring it over (Junc 14 M4) if you cant trace the fault.

Edited by blitzracing on Sunday 6th March 10:28

[Alexdaredevilz]

You hit the nail on the head Blitz

I think I have found the problem

Do you think a crack this size could cause my idle and CO issues?

Thanks

Alex

[Alexdaredevilz]

Crack sorted out, with liquid metal stuff

Resealed trumpets and base,

Started up, WOOHOOO idling great,

Went for a test drive and the buggers idling high again and shunting :-(

Ive done some searching and im going to test my speed sensor (where ever that is)

Would this method work? - Park car on hill, start car up (idling nicely at this point) then release brakes and in theory when I pick speed up the revs will rise then come to a stop to reveal buggered sensor? and at no point in this test touch the throttle

Thanks

Alex

[blitzracing]

Wow, how do you get a fracture like that?. As for the speed sensor, start the car and drive it normally to get moving, ( 20 mph is plently ) then depress the clutch to disengage the engine, and throttle off, and keep the clutch depressed. The idle should stay higher than normal idle at this point, and let the car coast to a stop, and after a few seconds the idle should step down to its normal 800 or so rpm. The speed sensor circuit becomes active at about 3mph, so the car has to be stationary to get the idle to drop.

[Alexdaredevilz]

The wall was very thin where I milled it out, and im guessing after a few heat cycles it cracked,

Will test tomorrow,

Thanks

Alex

[Alexdaredevilz]

I didn't get round to touching the Chim today, as I managed to fall down a hole and chip my shin bone :-(

But as I lie in A&E bleeding to death, I thought to myself

If I were to disconnect the speedo from under the arm rest and the problem went, wouldn't that be a better way to confirm weather or not its that playing up?

Thanks

[blitzracing]

The "speedo calibration box" appears to have more than one function, in so much it simply produces a fixed pulse to the ECU once the car is moving above 3mph, but it may also produce a the correct pulse stream for the speedo from the speed sensor. (Assumming its electronic- I dont know). I would think the best thing would be to unplug the speed sensor (Its around the diff somewhere I think but its not the same on a Ginetta) and see what happens. The speedo calibration box is a poor design because it can reach a "floating" state where it produces a speed pulse even when the car is not moving as the inputs are not tied well to the ground plain and can rise far enough to produce a trigger pulse (Thanks to TVR mike for this diagnosis). Problem is unplugging the sensor may just make the floating voltages worse, but unplugging the speedo wont do what you want it to. Otherwise I think you could measure the speed signal pulse where it enters the ECU, but Im not sure how a DVM would read it but you could try it on the AC or DC setting, as any voltage indication would show a pulse was present.

[Alexdaredevilz]

I just tried disconnecting the speedo, and tested it, and its fixed!!

But it appears some one else has been there before me, and stuck a alarm system in wiring that comes off it

Where to go from here? As im clueless now