Decats, Lambdas, And Chips

[StreetDragster]

Hi All,

My Chim has all three cats removed. The car came with the old cats, which i notice has lambda sensors in, were the decats do not.
The car also has a Mark Adams chip.

I've noticed a slight hesitation on slight throttle, nothing major, but the plugs also soot up quite a bit, and its heavier on juice than the rest of the pack from what i've seen (About 160miles to about £40, but thats mainly 30-40 mph pottering). All symptoms of overfueling.

Is the current setup ok, or is the ECU currently on its open loop fueling mode which would explain the overfuelling symptoms. Should i try and get the lambda sensor boss's mounting in the decatted pipes?

Thanks

Matt

Edited by StreetDragster on Thursday 18th October 11:45

[blitzracing]

Your best bet is to reinstall the lambda probes, and make sure you are running the catalyst map (white resistor wires). There is NO advantage what so ever in running the non cat map, as you loose the accurate fuel control at low to mid RPM. The cat fuel map goes open loop towards full power so you still get the advantage of richer fueling when you need it. If you are running the cat resistor without the probes, Im not certain what will happen, but it might drop into get you home mode / map. The non cat resistor has green wires on it if you want to check, but its a backward step fueling wise.

[RumbleBee]

That sounds like the symptoms that I am experiencing, slight hesitation, black plugs etc. What sort of voltage should I be getting from the lambda sensors at idle? Is this a good way to check that they are working?

Thanks

Ben

[StreetDragster]

blitzracing said:

Your best bet is to reinstall the lambda probes, and make sure you are running the catalyst map (white resistor wires). There is NO advantage what so ever in running the non cat map, as you loose the accurate fuel control at low to mid RPM. The cat fuel map goes open loop towards full power so you still get the advantage of richer fueling when you need it. If you are running the cat resistor without the probes, Im not certain what will happen, but it might drop into get you home mode / map. The non cat resistor has green wires on it if you want to check, but its a backward step fueling wise.

Cheers, it has got the green resistor in, just checked. So if i install the lambdas and the white tune resistor the Mark Adams chip will still work correctly and i should then gain closed loop control at lower engine revs?

Thanks

Matt

[blitzracing]

You can check them with an analogue voltmeter across the probe output. You should see a constantly fluctuating voltage between about .3 and .7 volts on tickover after about 30 second or so of running. The wire colours are blue (screened) for sensor output and black for ground. The third wire is for the heater and carrys 12 volts when the fuel pump runs. If the sensor output sticks at a higher or lower voltage you gave a problem with fueling or lambda control. You could try a digital voltmeter, but the readings may be hard to decipher as the voltages constantly change. If the plugs are black, the fueling is miles out, and Id expect the lambda probe output to be at the .7 volt plus range and not changing. This is assuming its running rich at tickover, not just higher up the RPM band.

[blitzracing]

Cheers, it has got the green resistor in, just checked. So if i install the lambdas and the white tune resistor the Mark Adams chip will still work correctly and i should then gain closed loop control at lower engine revs?

Thanks

Matt
[/quote]

Spot on. You need around a 3.7k resistor for the non cat map, or I have seen some cars running no resistor at all, and its seems to default to the cat map. Mr Adams modifies both cat and non cat map in his chips so you wont loose his specialist mapping.

[StreetDragster]

Excellent, thanks, thats my job for the winter. Y-Pipe off, boss's welded in, lambdas installed and a white tune resistor. Hopefully get into the 20's for MPG on low throttle driving

Just one more question, with the lambdas installed into catless pipes, it will still adjust the fuelling properly wont it, and not adjust wronging because its expecting a certain type of mixture from the cats (which arn't there, if you follow me?)

Thanks again

Matt

Edited by StreetDragster on Friday 19th October 08:16

[blitzracing]

The lambda control is set for around 14.1 AF, which is just fine for general use and it wont get upset because it has no physical catalyst.

[StreetDragster]

Nice one, thankyou!

Matt

[RumbleBee]

Thanks from me also, will give it a try.

Cheers

Ben

[RumbleBee]

Connected a multimeter accross each lambda probe and the blue wire gives a nice fluctuating voltage and the red wire gives a healthy 13.5 volts. One thing I did notice is that the voltage occasionally flicked to 1.2v on the blue wire. However, I think this is a symptom of using a DMM and not an analogue one or an oscilloscope. Checked a spark plug on each bank and both look sooty, but not too bad on the electrode itself. Going to try new plugs and leads and give it a good back-road blast to see if it just needs the soot to be burned off to remove the hesitation a low rpms.

Also think it may have got worse since I removed the pre-cats, any possible truth in this?

Thanks all.

Edited by RumbleBee on Tuesday 23 October 08:37

[blitzracing]

Ive got a Ginetta set up like this with no precat, no main cat and TVR Chimaera chip, and I dont have any hesitation problems at all. Obviosly this has a different exhaust system than yours, but from my experments with this ECU so far, fueling only causes it to hesitate under acceleration when it significatly overfuels (I could only replicate this on the fixed map), and the system does seem to cope well once switched to lambda control. Its possible the glitch is caused by the time it takes for the ECU to correct the mixture if it is rich, and its possible another sensor is not functioning correctly. ( The water temp sensor makes a big difference to the mixture.) Have a search on this and the Griff' forum for posts by Mark Adams, lots more info. Of course it may not be fueling, things like a failing coil can cause simular symptoms.

[RumbleBee]

Interesting. Sounds like if I replace the leads and splug parks it may help. The leads were definately breaking down. But would that cause the plugs to be black?

Thanks again.

[blitzracing]

Er no- forgot about that bit. I assume your lamda readings are with the new cat resistor?.

[RumbleBee]

I havent checked, but pretty sure they will be as it was running fine with full cats in place, only started to give me problems after I removed the pre-cats. The hesistation is very subtle and mainly occurs when driving round town at low rpms. Im beginning to think that the soot was caused by town driving and is the cause of the problem and not the result. Going to try new plugs and leads at the weekend and see if it helps. Thanks blitz for your very informative comments.

[StreetDragster]

Also worth checking your lead/shroud combo.

I had magnecor leads with the resisted shrouds, and i found out that they are designed to be used with un-resisted shoruds, so i changed them and pickup seems to be immproved.

Whether its all in my head or not i don't know, but worth checking all the same. I now have 8 resisted shrouds spare if you want to borrow them to fault isolate your car if you think yours are suspect

Thanks

Matt

[RumbleBee]

Thanks for that offer, will bear in mind. The leads I have look like new (only had the car 6 months). But when I lift the bonnet at night its a little lightening storm in there. They are Unipart leads, so clearly not up to the job. And they were fitted by a TVR authorised service centre. The new leads I have are Bosch, £33 from Halfrauds, they are resisted. Not sure whether the shrouds are resisted or not. Can I check with a multimeter? So if I have resisted leads, I want unresisted shrouds? (castle race engines have em). The shrouds are in good condition but not sure what type they are.

Thanks again.

[StreetDragster]

You could probably check with a multimeter, but mine had/have it written on the side-

Resisted
BERU 0 300 372 304 (5K Ohm)

UnResisted
BERU 0 300 302 303

EDIT- Forgot to say, that i think your only supposed to have one set of resisters on the ignition system (can someone correct/confirm?) So of the plugs/leads/shrouds you only need one set of resistors.
For example, i have the Magnecor Leads (Resisted), Unresisted BERU Shrouds, and NGK B7ECS Plugs (Unresisted)

Hope that helps

Matt

Edited by StreetDragster on Wednesday 24th October 11:07

[blitzracing]

Its all a matter of reducing radio interferance vs spark intensity. At a minimum Id recommend at least one resistive path between the coil and plug, to keep the back emf's and spikes to a reasonable level. So resistive leads can be used with non resistive shrouds and plugs. If you are running non resistive magnacors then use at least resistive plugs etc. Its not an exact science, as the longer the plug lead the higher the resistance becomes (resistve ones), so it will never be the same across all 8 cylinders anyway. You want to avoid making everything resistive, as the spark just gets too weedy. In terms of testing, you can use a multimeter, set to ohms to measure the conductive path across whatever. Resitive items would be 5k ohms or over (more like 20k from memory). If its a matter of a few ohms its non resistive.

[StreetDragster]

Hi all, a quick update...

With the lambdas in and the ECU on the cat map part throttle and hesitation were much improved, but not perfect. Turned out that the vacuum advance module was duff, with that replaced now part throttle is silky smooth when combined with the lambdas.

Thanks

Matt