Running too lean - suggestions please

[TV8]

Despite having good power for a 400, I was not happy with how my car run following a change of exhaust. To be fair, it hasnt liked cold starts since last winter and it is running lean on the MOT, passing without the main-cat for the last two years!

Looking at the two rolling road print-outs, has got noticeably leaner accross the rev range in the last 6 months!

Since the first run in March (ACT decat y-piece already fitted), I have sorted a dodgy HT lead, fitted a smooth bore elbow and an ACT sports exhaust, so not that many changes for a the ECU to try and work-out I would have hoped!

To get to the bottom of the poor running (particularly from cold and in the cold) I booked it into Austec for rolling run run and testing. They tested timing, base idle, throtle pot and fuel presurre, plus all the codes on the ECU connector type thing. Apart from the fuel ratio, everything was fine according and they suggested a re-map or maybe a change of injectors, new plenum trumpets and re-map (if I wanted to maximise the remap)

If it has to be remaped, then so be it but I strugle to think that the smoothbore and ACT system (pre-cats still in) should require one if everything else is ok?

The only think I havent checked is plugs for even colour but not sure that would affect fueling that much in 2000 miles?

I have booked the car in with Dan Taylor for the 14th, just not sure what for!!!

Suggestions appreciated please.

MArch afr

[TV8]

afr now. Similar shape but noticeably leaner.

[lestershaw]

i had a similar problem, it turned out to be an air leak behind the plenum, so maybe look for air leaks. the mechanic sprayed something around the plenum and the afm and pipes in between and when the revs rose he knew he had found the problem, :-)

[Goaty Bill]

lestershaw said:

i had a similar problem, it turned out to be an air leak behind the plenum, so maybe look for air leaks. the mechanic sprayed something around the plenum and the afm and pipes in between and when the revs rose he knew he had found the problem, :-)

I never did see what your problem was in the end on that posting lester.
I expect the thread got too long and (like this one already - sorry) hijacked too often.
Glad you found it.

[TV8]

Thanks for the tip about the air leak. Will have a look at the weekend. Any idea what was sprayed please?

[Chimpafrolic]

TV8 said:

Thanks for the tip about the air leak. Will have a look at the weekend. Any idea what was sprayed please?

EasyStart

http://www.halfords.com/webapp/wcs/stores/servlet/...

Drawn in at the induction leak it finds it's way into the combustion chambers and the revs rise accordingly.

EasyStart is just ethanol and it's not good for your engine, using it to detect an induction leak is not an issue but continuous use should be avoided.

Please don't smoke when using it unless you want to remove your eyebrows.

[TV8]

Thanks - any other suggestions please?

Looking through the search engine, based on the price of getting the injectors cleaned, some of these seem like a reasonable investment - Opel/Vauxhall X18XE/X20XEV injectors. Are they ok with the standard map please?

[TV8]

No apparant leaks found with easystart. Plus the car started perfectly and instantly found idle from cold. After reversing out of the drive, it wasnt so clean at idle. Once warmed up, pulled cleanly and ran well but it was warm.

[blitzracing]

Assuming you are running the catalyst fuel map and the correct chip in the ECU (Not some old Range Rover one- these will run lean) the AF Ratio should hold around 14.5:1 up to 3400 rpm, at less than 2/3 throttle, but then become richer under full load and power at around 12.5:1. If you think the modifications you have made to the exhaust are to blame, a variable fuel pressure regulator can be used to put an extra 2-3 psi on the fuel rail to richen the mixture without a remap- a decent one was about £90, plus you need a fuel rail adaptor to plug in place of the stock regulator. The £30 ebay regulators ones are too course for acurate use. Dont consider new injectors, its way over the top for a fairly simple issue, although you can always run some injector cleaner in the tank.

[TV8]

Thanks Mark. It wasnt at 14:1 before, so maybe need to check the resistor and the ECU as the fueling looks the same shape as before, just further up the scale!

[haircutmike]

TV8 said:

Thanks Mark. It wasnt at 14:1 before, so maybe need to check the resistor and the ECU as the fueling looks the same shape as before, just further up the scale!

I would be tempted for another run at Charlies as Austecs readings may be out, then you could have a second run with my ecu and compare.

[blitzracing]

That looks like it could be non catalyst fuel map, and if this is the case it will have been needed to be rechipped to run like this. If by chance someone has thought, Ill remove the cat' and simply switch the tune resistor, its very likely you are running a Range Rover map. As far as I can tell TVR only ever modified the map the car left the factory with. If you open up the ECU there should be a label on the chip like 3.9 cat if its the TVR origional. Mind you the Ginetta's where around 20 bhp down from optimum on the 3.9 when they left the factory running a Range Rover map, and your power output is good.

Edited by blitzracing on Friday 4th November 12:55

[TV8]

Assuming this is the tune resistor, on the meter it is showing 3860 ohms - so close enough to be 3900 for the cat map?

[TV8]

This is the ECU. 4 C is marked on it, assuming the main chip is the relevant one. There is also a little red/orange blob. Not sure if that is to mark a corner for connecting or means something else.

[TV8]

haircutmike said:

I would be tempted for another run at Charlies as Austecs readings may be out, then you could have a second run with my ecu and compare.

I am thinking about that Pete. Shame they dont do Sunday trading!

[blitzracing]

Thats a catalys tune resistor. This means the ecu should be holding the AF ratio at around 14.5:1 in closed loop. The ECU should flag up a fault code if it cant be maintained (after a while- its not very sensitive), but yet you say its had a full ECU diagnostic done? The ECU wont throw a fault code if the lambda probes fail how ever(or are not connected), as it does realise it should be running in closed loop. It needs a voltage from the probes before it turns the lambda control circuitry on, so if its never there, it never throws a fault code. You need to check the lambda voltages as if these are cycling as they should, there is a mismatch between what the probes are recording, and the rolling road results. The problem with the rolling road results is you never quite know when the ECU goes from closed to open loop use, as after all you would not hold the throttle to the floor at say 2000 rpm to force it into open loop. Assumming the throttle and power is fed in gently, I would expect to see the change at 3400 rpm. This is a slight red herring however as you are worried about full power fuelling, not closed loop. At full power you should see about 1.2 to 1.3 volts on the lambda probes, as they are on their range limit as the mixture richens. A genuine lean running situation the voltages will drop below this or even 0 volts.

[MKnight702]

Swap to a Weber 500 4 barrel carb, you'll never run lean again!!!

[TV8]

Ok, thanks. Sort of get that, but where and how do you measure the voltages please?

[blitzracing]

Its difficult under load, but basically you need to extend the lambda cable (the black and white wires) into the cabin so you can get a voltmeter onto them, and then get a passanger to read the voltages as you hold the car flat out for as long as you can to try and repicate full power and load. Thats the interesting bit, trying to hold it flat out for long enough to get a decent reading without going into warp drive or crashing in the process. I do have various bits of test gear that makes its easier that I could loan I guess.

[TV8]

Thanks Mark. I have sent you a mail.

All other suggestions, bar carb conversions, appreciated