Glowing Main Cat / removal
Discussion
Your thoughts please. I returned from a recent run to find my main Cat glowing red - a 2 inch band of red glowing at the top. The "Y" piece was OK, just glowing inside the main canister. The car is a Griff 500 running MSII Extra and I have already removed the Pre-Cats. It may have been this way for a while, but noticed the glow in the dark of the garage. Three questions someone may be able to help answer:-
1. What might be the cause of the Cat failure a) mixture, b) mechanical failure, c) other? (Note that I run a wide band lambda and the mixture is controlled and would tend to be rich rather than lean.)
2. Has anyone done a DIY Cat removal? Any advice welcome - presume you cut off lower end, remove Cat and re-weld?
3. Can anybody advise on any type of cone design to insert to maintain some sort of back pressure (Do not like the idea of an empty cavity - apart from the excess noise, etc.) Any exhaust specialist out there?
Thanks.
1. What might be the cause of the Cat failure a) mixture, b) mechanical failure, c) other? (Note that I run a wide band lambda and the mixture is controlled and would tend to be rich rather than lean.)
2. Has anyone done a DIY Cat removal? Any advice welcome - presume you cut off lower end, remove Cat and re-weld?
3. Can anybody advise on any type of cone design to insert to maintain some sort of back pressure (Do not like the idea of an empty cavity - apart from the excess noise, etc.) Any exhaust specialist out there?
Thanks.
Excess uncombusted fuel can burn in the cat. Or the cat may be damaged/blocked (not unheard of)... easiest way to remove is to use an ACT or Clive F de-cat Y piece (not sure if Clive is still producing but he's on here and they do come up occasionally in the ads if not). These are appropriately sized, but people have cut and shut the oem dustbin as you describe although that seems a load of hassle unless you like fabricating and have the kit
DaveG said:
Your thoughts please. I returned from a recent run to find my main Cat glowing red - a 2 inch band of red glowing at the top. The "Y" piece was OK, just glowing inside the main canister. The car is a Griff 500 running MSII Extra and I have already removed the Pre-Cats. It may have been this way for a while, but noticed the glow in the dark of the garage. Three questions someone may be able to help answer:-
1. What might be the cause of the Cat failure a) mixture, b) mechanical failure, c) other? (Note that I run a wide band lambda and the mixture is controlled and would tend to be rich rather than lean.)
2. Has anyone done a DIY Cat removal? Any advice welcome - presume you cut off lower end, remove Cat and re-weld?
3. Can anybody advise on any type of cone design to insert to maintain some sort of back pressure (Do not like the idea of an empty cavity - apart from the excess noise, etc.) Any exhaust specialist out there?
Thanks.
Get one of Clive's Y pieces,you won't regret it..perfect balance of quiet and noise when you want it...1. What might be the cause of the Cat failure a) mixture, b) mechanical failure, c) other? (Note that I run a wide band lambda and the mixture is controlled and would tend to be rich rather than lean.)
2. Has anyone done a DIY Cat removal? Any advice welcome - presume you cut off lower end, remove Cat and re-weld?
3. Can anybody advise on any type of cone design to insert to maintain some sort of back pressure (Do not like the idea of an empty cavity - apart from the excess noise, etc.) Any exhaust specialist out there?
Thanks.
Thanks for the input suggestions. Injectors were cleaned after rebuild and pre MegaSquirt about 3000kms ago. Will measure each header pipe temperature today and see if that thorws up anything. (I know one bank runs hotter than the other).
I will email Clive, but I am in Australia and I think cost plus delivery may force a DIY solution.
I am concerned about the possible noise and resonance issues of having and "empty" Cat box. Would very much like to hear about possible "cone / baffle" design I could use in there?
I will email Clive, but I am in Australia and I think cost plus delivery may force a DIY solution.
I am concerned about the possible noise and resonance issues of having and "empty" Cat box. Would very much like to hear about possible "cone / baffle" design I could use in there?
I'd be more concerned about why this happened in the first place - fixing the exhaust is the least of your worries. Firstly it is important to know exactly where the glow occurs - either in the exhaust system immediately before the catalyst, or in the area of the catalyst itself.
An exhaust system will glow immediately before a blockage, and this is the easiest way to find them. If the glow is immediately before the catalyst, then it is blocked.
If the glow is in the area of the catalyst, then excess fuel is being burnt in it although it has not yet failed (but soon will). This excess fuel can reach the catalyst for many reasons including engine mechanical problems, faulty injectors, failed Oxygen sensor, retarded ignition timing, or poor mixture control by the management system (which can be an installation issue).
In all the years I've been doing TVRs I have very rarely ever seen a blocked main catalyst.
Since you say one bank runs hotter than the other, it implies that you have a mechanical problem brewing. There is no reason why your setup should require you to run a mixture richer than AFR 14.6:1 when cruising. As soon as you go above this value the catalyst is in danger of burning out. Between 2/3 and full load you should be aiming for 12.5:1 AFR.
An exhaust system will glow immediately before a blockage, and this is the easiest way to find them. If the glow is immediately before the catalyst, then it is blocked.
If the glow is in the area of the catalyst, then excess fuel is being burnt in it although it has not yet failed (but soon will). This excess fuel can reach the catalyst for many reasons including engine mechanical problems, faulty injectors, failed Oxygen sensor, retarded ignition timing, or poor mixture control by the management system (which can be an installation issue).
In all the years I've been doing TVRs I have very rarely ever seen a blocked main catalyst.
Since you say one bank runs hotter than the other, it implies that you have a mechanical problem brewing. There is no reason why your setup should require you to run a mixture richer than AFR 14.6:1 when cruising. As soon as you go above this value the catalyst is in danger of burning out. Between 2/3 and full load you should be aiming for 12.5:1 AFR.
Thanks for your comments Mark.
As you suggest I am investigating prior to removing the Cat. I have no Pre-Cats and the glow is in the Cat itself, at the top inlet end of the main Cat - a 2 inch cylindrical band around the Cat and it then extends down the front of the Cat, gradually disappearing. (Colour = cherry red at the band). This seems to imply the possible source is from the left bank (Cyl - 2468) which feeds the front side of the Cat and and that the first 2 inches are blocked or burning unburnt fuel?
My WB sensor is unfortunately located after the Cat (hence my intention/thoughts of moving closer to "Y" when Cat removed.)
The sensor datalog shows it is working fine. Mixture control logs Ok - rich idle (13.8), cruise (mid 14's), hard accel (12's)
Injectors may be a problem, but cleaned some 2-3000kms ago after engine re-build. I have removed each connector and cleaned with fluid. Now considering replacing with Chev LS1's.
Not sure what mechanical problems you envisage - I did do a re-build, new cam, rings, head, and bottom end a short while back.
I am still playing with the Spark Map and have just retarded a little in the 1500-2000 cruise zone. (Shunt zone. 10 deg at idle and around 24-5 deg at 2000rpm).
Header temperatures are reasonably consistent:-
250 230 195 255
230 200 230 190
Cat= 400 (probably high due this problem)
Interestingly the right bank (top line above) runs hotter than the left bank which is the suspect one from the glowing problem?
I will continue checking this wk-end (Need to drive at night to see if it is glowing.)
Can post maps if anyone is interested.
As you suggest I am investigating prior to removing the Cat. I have no Pre-Cats and the glow is in the Cat itself, at the top inlet end of the main Cat - a 2 inch cylindrical band around the Cat and it then extends down the front of the Cat, gradually disappearing. (Colour = cherry red at the band). This seems to imply the possible source is from the left bank (Cyl - 2468) which feeds the front side of the Cat and and that the first 2 inches are blocked or burning unburnt fuel?
My WB sensor is unfortunately located after the Cat (hence my intention/thoughts of moving closer to "Y" when Cat removed.)
The sensor datalog shows it is working fine. Mixture control logs Ok - rich idle (13.8), cruise (mid 14's), hard accel (12's)
Injectors may be a problem, but cleaned some 2-3000kms ago after engine re-build. I have removed each connector and cleaned with fluid. Now considering replacing with Chev LS1's.
Not sure what mechanical problems you envisage - I did do a re-build, new cam, rings, head, and bottom end a short while back.
I am still playing with the Spark Map and have just retarded a little in the 1500-2000 cruise zone. (Shunt zone. 10 deg at idle and around 24-5 deg at 2000rpm).
Header temperatures are reasonably consistent:-
250 230 195 255
230 200 230 190
Cat= 400 (probably high due this problem)
Interestingly the right bank (top line above) runs hotter than the left bank which is the suspect one from the glowing problem?
I will continue checking this wk-end (Need to drive at night to see if it is glowing.)
Can post maps if anyone is interested.
Just to partially close this post, here are my inconclusive results so far.
I have reduced the Cat glow on the last test. Why inconclusive - too many variables changed in my haste to improve and inadequate time to individually test results of each change(but still testing).
Changes
- coil pack connectors cleaned and reset alternating the "connector pairs"
- ignition map modified a little (rate of change from idle to 3000 - thanks Lindsay [Cinquento]
- IAT compensation map altered (it can get pretty hot down here)
- MAPdot Threshold increased in Acceleration Enrichment
- spikes appearing on the log for Pulse Width and Duty Cycle have now disappeared under hard acceleration.
- running a bit smoother generally.
I plan to continue the investigation into the header temp variance, coil packs and possible injector replacement. I will also remove the Main Cat at some convenient time.
I have reduced the Cat glow on the last test. Why inconclusive - too many variables changed in my haste to improve and inadequate time to individually test results of each change(but still testing).
Changes
- coil pack connectors cleaned and reset alternating the "connector pairs"
- ignition map modified a little (rate of change from idle to 3000 - thanks Lindsay [Cinquento]
- IAT compensation map altered (it can get pretty hot down here)
- MAPdot Threshold increased in Acceleration Enrichment
- spikes appearing on the log for Pulse Width and Duty Cycle have now disappeared under hard acceleration.
- running a bit smoother generally.
I plan to continue the investigation into the header temp variance, coil packs and possible injector replacement. I will also remove the Main Cat at some convenient time.
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