Does a full decat cause running rich

[blaze_away]

Over on faceache I had a reply post from Steve Bowden which I thought folks over here might have thoughts on......regarding running rich.

Full decat 4.6

Quote
I did wonder if the decat could be causing this as it seems a common comment on different decatted cars online. Although in theory the decat shouldn’t change things, the lack of precats means the o2 sensor is seeing more oxygen than it expects , with the std map, and would normally get when the precats burn off the last unburt fuel and oxygen. I wonder if that means it thinks it’s too lean and adds more fuel causing your issues. Once the plugs are sooted, the problem gets worse as the combustion is poorer. Just a theory....
Unquote

Whats your thoughts ?

[Classic Chim]

Hi Frank.
That’s an interesting theory.
I went pre cats out leaving Catted Y in place on CUX. .
Noticed more fumes but assumed it’s because more escaped out the exhaust.
Plugs very sooted but then always were.
Eventually decided it always smelt rich, new rebuilt engine,,,,,, so went for a mapped ECU as washing your bores isn’t the best idea.
Maybe it was this all along but suffice to say it’s been mapped with pre cats removed and no smell, great economy and no over fuelling.

That’s maybe one reason cars going to Joolz come out in better shape as he corrects all this I’d imagine.

[bobfather]

With full decat ACT manifolds and CliveF Y piece my plugs look great and the O2 sensors are clean. I had considered changing the tune resistor to set it up like the early precast V8s but was advised that it would be better to leave it alone.

[blaze_away]

bobfather said:

With full decat ACT manifolds and CliveF Y piece my plugs look great and the O2 sensors are clean. I had considered changing the tune resistor to set it up like the early precast V8s but was advised that it would be better to leave it alone.

Bob thats really interesting. Would you mind if I ask some more detailed questions I think we could help a lot of those suffering poor fuel economy ?

If thats ok....

Is it on 14CUX ?

If yes what fuel map is it ?

Do you have RoverGauge ?

Have you done any daya logging ?

[bobfather]

blaze_away said:

Bob thats really interesting. Would you mind if I ask some more detailed questions I think we could help a lot of those suffering poor fuel economy ?

If thats ok....

Is it on 14CUX ?

If yes what fuel map is it ?

Do you have RoverGauge ?

Have you done any daya logging ?

Yes it's running 14CUX. I don't know which map, it's a '99 4.0l on the factory map. I do have Rovergauge and see nothing out of the ordinary when using it. I know someone with a 5.0l running the same exhaust who suffered from lumpy running. During the investigation it was discovered that someone had fitted a decat tune resistor. While that appeared to be a reasonable change to align with the lack of cats, refitting the standard resistor solved the lumpy running. It's not absolute proof but it was enough for me to choose to leave the tune resistor alone

[blaze_away]

bobfather said:

blaze_away said:

Bob thats really interesting. Would you mind if I ask some more detailed questions I think we could help a lot of those suffering poor fuel economy ?

If thats ok....

Is it on 14CUX ?

If yes what fuel map is it ?

Do you have RoverGauge ?

Have you done any daya logging ?

Yes it's running 14CUX. I don't know which map, it's a '99 4.0l on the factory map. I do have Rovergauge and see nothing out of the ordinary when using it. I know someone with a 5.0l running the same exhaust who suffered from lumpy running. During the investigation it was discovered that someone had fitted a decat tune resistor. While that appeared to be a reasonable change to align with the lack of cats, refitting the standard resistor solved the lumpy running. It's not absolute proof but it was enough for me to choose to leave the tune resistor alone

Hi Bob
Thays useful to know. Could we speak on phone ?

[bobfather]

blaze_away said:

Hi Bob
Thays useful to know. Could we speak on phone ?

I don't mind but I'm not sure what more info I could contribute. I'm not the font of knowledge on this subject, I just read these pages do what works for others or experiment when knowledge is lacking. My Chim is mothballed currently so I'm not able to plug RG in to check anything

[blitzracing]

The TVR set up is not ideal by any means, it would have been better to have the probes upwind of the cats for sure. I think the pre-cat position may be the reason for the stalled lambda switching I see on the TVRs at idle. and also you are delaying the response at higher RPM. Im terms of running richer, the basic lambda cycle is simply cycled around the mid point of too rich / too lean all the time. This is because the Cats remove 3 nasties from the exhaust, by adding oxygen to unburnt hydrocarbons to allow them to ignite and I think the carbon monoxide to make CO2. On the otherside when there is less oxygen it removes an oxygen atom or molecule from the NOX component. So if you think about it, you will have spare O2 on the lean part of the cycle, but less on the rich part as you cant break down the NOX. TBH Id be very surprised if this would shift the overall mixture significantly, as the lambda is pretty crude at, if you look at an AFR gauge on the Cat map, its all over the place anyway. Dont forget the ECU is designed to run Range Rover with no precats anyway.I think for most parts black TVR plugs are because the fitted plugs are too cold, and if you run the 6 grade BP6ES as per the Range Rover, they run fine.

This plot shows the output of a wideband lambda in yellow against TPS and AFM outputs without any catalyst- you can see at the steady load the lambda switching is pretty tight ( the dotted line is 14.7), but the moment to move the throttle it takes a while to reestablish that leads to big swings in AFR. I dont have a plot like this for a something with precats Im afraid.

Edited by blitzracing on Saturday 18th January 11:07

[blitzracing]

In terms of getting the best from a decat map- you do need the correct green map for the engine capacity. I did see a big improvement MPG wise on my 3.9 switching from white to a bespoke green map, but I did spend a lot of time leaning off the mixture under light load to around 15.5 :1 and considering the weights of the car, thats 90% of its running time. If you are running a green map its also very important to set the CO trim on the AFM as you can make the car run horribly rich or lean if you dont. Dont run green on a TVR chip, its completely the wrong map.

Edited by blitzracing on Saturday 18th January 11:09

[HarryW]

My confused brain seems to recall something about the standard cat map, as selected by the tune resistor being much richer than the non cat map. The richer map helps keep the cats cooler too?

[blitzracing]

The cat map clamps the mixture at 14.7 up to 3400 rpm. Above that it goes open loop for max power. The non cat map will do whatever the map data is, and by default the TVR chip will be whatever the Range Rover needed if you just switch it across, NOT for the TVR, its completely wrong so you need a remap / bespoke chip. If you remove the cats, best bet is stick to white tune, as although it wont be optimised for MPG, it will have enough fuel for the TVR cam at higher RPM. The Range Rover white and green map run horribly lean.

[blaze_away]

bobfather said:

blaze_away said:

Hi Bob
Thays useful to know. Could we speak on phone ?

I don't mind but I'm not sure what more info I could contribute. I'm not the font of knowledge on this subject, I just read these pages do what works for others or experiment when knowledge is lacking. My Chim is mothballed currently so I'm not able to plug RG in to check anything

OK. Once you are up and running ideally would you be able to run RG and log the data for a short run out then 10 mins on idle. Then let me have the log file and the static.txt file. I can then analyse the data for differences with my data. Hopefully we can then see whats the same and whats different.

[blaze_away]

blitzracing said:

In terms of getting the best from a decat map- you do need the correct green map for the engine capacity. I did see a big improvement MPG wise on my 3.9 switching from white to a bespoke green map, but I did spend a lot of time leaning off the mixture under light load to around 15.5 :1 and considering the weights of the car, thats 90% of its running time. If you are running a green map its also very important to set the CO trim on the AFM as you can make the car run horribly rich or lean if you dont. Dont run green on a TVR chip, its completely the wrong map.

Edited by blitzracing on Saturday 18th January 11:09

blitzracing said:

The cat map clamps the mixture at 14.7 up to 3400 rpm. Above that it goes open loop for max power. The non cat map will do whatever the map data is, and by default the TVR chip will be whatever the Range Rover needed if you just switch it across, NOT for the TVR, its completely wrong so you need a remap / bespoke chip. If you remove the cats, best bet is stick to white tune, as although it wont be optimised for MPG, it will have enough fuel for the TVR cam at higher RPM. The Range Rover white and green map run horribly lean.

Thanks for both those posts, have now had sometime to study them.

I would now like to at least try a Green Tune map ( even if its not perfect) so could you advise how I best do that. (FYI I do have stevesprints maps and can burn chips) Once I make a bit of progress I can then plan a proper custom remap.

What I am trying to avoid is a wasted long round trip and the remapping costs only to discover I have a fundamental fault that's preventing sensible fuel economy. I'd be happy to just prove it will run leaner than its does right now. If that makes sense ? Everything I've tried thus far seems to return 14-17 mpg and black plugs

[blitzracing]

Best thing to do is make the switchable tune resistor and then unplug the ECU between switching maps or it will throw a fault code. If you cant get a suitable non cat map, you can copy the basic white map into the green map location with tuner pro as a starting point, it wont harm you engine at least, but you really do need an air / fuel ratio gauge to see whats going on. You can mess around with the mixture up to 2400 rpm with the CO trim on the side of the AFM on green without doing harm. You can set the basic mixture by ear at idle on the CO trim- one way the engine runs rich like its on choke, the other the engine will rock and the idle becomes unstable as it leans out. The best thing to do is run it too lean, then slowly richen the mixture until the idle is smooth and stable.

Here are the two tables of Steve sprints 430 /450 maps in 3d, you can see the differences. The green tune here is a 4.3 map white 4.5 cat

Edited by blitzracing on Sunday 19th January 18:27

[blaze_away]

Brilliant Mark. Thank you will get into action....

[blitzracing]

Thinking about it one of Steves maps would be a good place to start, got to be a load better then whatever TVR had in green.

[blaze_away]

Thanks again Mark. Have gotten hold of original TVR 430 precat map off there but it looks a little odd ?

Fueling drops off a cliff rows 75-88-100 in maps 2 and 5 (green and white)

(btw I have also got a problem with tunerpro in that its now decided it won't let me close a bin file with changes)

[blitzracing]

I've seen this in Tuner pro- whatever that is its not the map. I'm still confused about the fact that the map can be in a 128k eeprom or a 256k, and sometimes you need to use the 14CUX toolkit to replicate the map in the larger Eproms to get a sensible view. Another possibility is the XDF file is wrong, there are various versions out there that changed as various new bits of relevant data where found in the Eprom.

[spitfire4v8]

It's looking at the wrong address , it's an early chip so you need to be using the old map table addresses and make sure that if you've read the 16k file through rovergauge you look at the correct offset otherwise use the toolkit to double it up .. Steve I think has an xdf with all the updates he's done including the 16k and 32k offsets done for you.. I've "done a TVR" and spurred my xdfs off from the steve versions so use steves.

Edited by spitfire4v8 on Tuesday 21st January 10:23

[blaze_away]

Thanks Mark, Joolz

Looks like I've discovered my level of incompetemce.....need to do some more learning.