Running lean how to solve?

[chris52]

At last years growl RR I was told that the car was running lean but due to having a slight exhaust leak I was told not to worry . Anyway now the leak is fixed new plugs, leads, air filter, ACT smooth bore pipes and Act carbon trumpets. Timing is 28deg BTDC at 3.5k rpm.

The car has done about a 1000miles since and seems to be running fine temps never go over 90 even in the 26deg weather we had this weekend while stuck in traffic. But fuel consumption is crap, and after removing the plugs today I find the electrode part is a very light grey almost white which as far as I know indicates a lean mixture.

So where do I start, I dont want to start replacing things just for the sake of it.
Any help would be great

Chris

[TVR Beaver]

Hi Chris.. my car run's a bit leaner in the hot weather.. It's the thinner air that does it.. and it can exagurate the hesitance bit at very light throttle.....
Anyway... if you are running way out the only thing to do is get a chip.... you can get the tornado chips on e-bay or book a RR secion with Mark Adams and get it set up 100% for all the mod's you've done.... Not sure what other options you have... how far out is your air screw... try it in another 1/2 turn (it shouldn't make any differance but I've found it does on my car??).. or aftermarket ECU?

[DarkMatter]

Chris,

The first thing that I would do is, using guidance from the Steve Heath book, carefully check the voltages/resistances of all the sensors etc which feed back to the ECU - I discovered that my lean running above 3000 rpm was due to a faulty voltage feed to the throttle pot. Have you used a fault code reader to see if the ECU has registered any faults? It may be worth buying one of 'blitzracing's lambda voltage readers to assist you?

[daxtojeiro]

Hi Chris,
Id invest in a wideband lambda sensor or borrow one and figure out exactly where you are lean, reading the plugs is only a general indication and means very little to be honest.

Once you know where your issues occure it will be easier to diagnose,
Phil

[TVR Beaver]

daxtojeiro said:

Hi Chris,
Id invest in a wideband lambda sensor or borrow one and figure out exactly where you are lean, reading the plugs is only a general indication and means very little to be honest.

Once you know where your issues occure it will be easier to diagnose,
Phil

That sounds like a great plan.. then you can lend it to me!!... Any idea how much they are and where do you get them?..

[chris52]

Thanks for the info guys. I will be getting out my multimeter and checking everything this weekend. To be fair I may be hunting for nothing and everything is probably ok. But With the Le-Mans trip looming only a couple of weeks away I would just like to make sure.

daxtojeiro said:

Hi Chris,
Id invest in a wideband lambda sensor or borrow one and figure out exactly where you are lean, reading the plugs is only a general indication and means very little to be honest.

Once you know where your issues occure it will be easier to diagnose,
Phil

This may be going a little to far for me but thanks for the sugestion.

Chris

[daxtojeiro]

If you live near Norwich I can soon lend you one. I do sell them but Im no the cheapest about, expect to pay £150 to £200 for a wideband lambda and controller,
Phil

[chris52]

daxtojeiro said:

If you live near Norwich I can soon lend you one. I do sell them but Im no the cheapest about, expect to pay £150 to £200 for a wideband lambda and controller,
Phil

Thanks for the offer but unfortunatley not near you. I am going to have a check through the sensors and then get it on a RR to see whats happening.

Chris

[Argent]

TVR Beaver said:

Hi Chris.. my car run's a bit leaner in the hot weather.. It's the thinner air that does it.. and it can exagurate the hesitance bit at very light throttle.....
Anyway... if you are running way out the only thing to do is get a chip.... you can get the tornado chips on e-bay or book a RR secion with Mark Adams and get it set up 100% for all the mod's you've done.... Not sure what other options you have... how far out is your air screw... try it in another 1/2 turn (it shouldn't make any differance but I've found it does on my car??).. or aftermarket ECU?

I was talking to Mark Adams the other day and he told me that the TVR generic set up for 500's is on the lean side particularly when it goes open loop, over 3400rpm I think.

A.

[chris52]

I have booked it in for a RR session tomorrow to see what the air/fuel mix is like across the rev range, so will post results when I get them.

Chris

[blitzracing]

Although the stock narrow band sensors are limited in range, you still get a signal as the mixture gets richer outside the lambda 1 range. Lambda one typically switches from 0 - 1 volt, and a good Lambda probe will generate nearer 1.3 volts at around 12.5:1 AF ratio. The problem here is the probes are used as switches to control the mixture, not linear devices to give an acurate voltage reading for any given AF ratio, so the output cant be taken as gospel, as it seems to drop as the probe ages. Having said that if you can get anything over 1 volt, it wont be running dangerously lean. In terms of getting it richer, check the Throttle pot at full throttle. You need at least 4.6 volts to get all the nessasary fuel, although the ECU is supposed to self calibrate, I dont believe it works that well and you may need to open up the mounting holes to get the required voltage. It will also alter the point the fuel enrichment occurs, and the fuel shut of point on the overun. You can end up with a nice burble on the overun if you wind the voltage up as it wont shut the fuel off quite so readily as you close the thottle. If you already have 4.6 to 4.8 volts there is nothing to be gained. Dont forget the plug temperature rating will alter the colour of the burn on the tip, so are you running the correct plugs?

Also I do still have a couple of lambda display boxes left for sale , under accessories in the TVR section of PH.

[chris52]

blitzracing said:

Although the stock narrow band sensors are limited in range, you still get a signal as the mixture gets richer outside the lambda 1 range. Lambda one typically switches from 0 - 1 volt, and a good Lambda probe will generate nearer 1.3 volts at around 12.5:1 AF ratio. The problem here is the probes are used as switches to control the mixture, not linear devices to give an acurate voltage reading for any given AF ratio, so the output cant be taken as gospel, as it seems to drop as the probe ages. Having said that if you can get anything over 1 volt, it wont be running dangerously lean. In terms of getting it richer, check the Throttle pot at full throttle. You need at least 4.6 volts to get all the nessasary fuel, although the ECU is supposed to self calibrate, I dont believe it works that well and you may need to open up the mounting holes to get the required voltage. It will also alter the point the fuel enrichment occurs, and the fuel shut of point on the overun. You can end up with a nice burble on the overun if you wind the voltage up as it wont shut the fuel off quite so readily as you close the thottle. If you already have 4.6 to 4.8 volts there is nothing to be gained. Dont forget the plug temperature rating will alter the colour of the burn on the tip, so are you running the correct plugs?

Also I do still have a couple of lambda display boxes left for sale , under accessories in the TVR section of PH.

Cheers for the info. I did email you about the display boxes a couple of days ago, but with not hearing from thought they must be sold out. The throttle pot test does the car need to be running at WOT or can it be tested with just the ignition on and WOT. I do get a reasonable burble/poping on overrun if that suggests anything.
Cheers Chris

[chris52]

Throttle pot readings are 0.36v to 4.98v and a nice steady increase inbetween.
Ignition on engine not running. Pretty sure these at the top end of the values but are still within tolerance yes?

Chris

[TVR Beaver]

Looks okay to me.. where did you check it?.. you should do it at the ECU plug.. that is where the ECU sees the voltage so includes any resistance in the loom wire etc.... also take the earth from the ECU ground... it can (will) change the readings!!

Edited by TVR Beaver on Tuesday 25th May 20:37

[chris52]

TVR Beaver said:

Looks okay to me.. where did you check it?.. you should do it at the ECU plug.. that is where the ECU sees the voltage so includes any resistance in the loom wire etc.... also take the earth from the ECU ground... it can (will) change the readings!!

Edited by TVR Beaver on Tuesday 25th May 20:37

Cheers John
Yes checked from the ecu plug and used the ecu earth. Going to see what the RR session comes up with tomorrow.

Chris

[blitzracing]

Apart from chipping, if its lean, you can increase the fuel pressure a tad, but it can lead to overfuelling when cold.

[TVR Beaver]

blitzracing said:

Apart from chipping, if its lean, you can increase the fuel pressure a tad, but it can lead to overfuelling when cold.

May have a go with that one on my car.... what's a good and cheap adjustable regulator??

[chris52]

Ok had the RR session today and yes it is running lean at higher revs. As you can see (the pink line) at 3000rpm it starts at 12.2:1 and gradualy keeps getting leaner until you hit 6350rpm when its 13.8:1. Is this a problem? I know that idealy its supposed to be 12.5:1
The RR session was done in 4th gear max power was 281bhp max torque was 292 lbf ft.


Here is the graph from the Growl this was done in 3rd gear BHP 269 torque 330 lbft


Now I know its difficult to compare two different graphs from different dynos, since the growl the only things I have done to the engine are smoothbore pipes, carbon trumpets, replaced a none working vacume advance, set the preloads (were slightlty out),fitted new Magnacore 85kv leads and timed up the cam. could I have realy gained 12 bhp and lost 38 lbft torque.
Any help would be great

Chris

Edited by chris52 on Wednesday 26th May 18:39

[TVR Beaver]

Chris.. how much did you move you cam by?...
Also 3rd gear v 4th gear.. 3rd good for torque... 4th good for BHP I'd of said... I have similar results with the RR graphs I have... all you can compare is the curves.. and they do look okay...

What you going to do about the running lean bit?... My car was running leaner than this at the top.. and probably had been for years?... I think mine was 14!

[chris52]

TVR Beaver said:

Chris.. how much did you move you cam by?...
Also 3rd gear v 4th gear.. 3rd good for torque... 4th good for BHP I'd of said... I have similar results with the RR graphs I have... all you can compare is the curves.. and they do look okay...

What you going to do about the running lean bit?... My car was running leaner than this at the top.. and probably had been for years?... I think mine was 14!

I had to advance the cam about 1deg I needed 110 ATDC closest I could get was 110.5 so I guess at the moment its 0.5deg advanced.
I will try to measure the fuel pressure at full power some how, other than that it could also be the AFM reading incorectly (info thanks to greenv8s)

Chris