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Catalytic converter overtemp protection

6K views 12 replies 5 participants last post by  Redtruck-VA 
#1 ·
I'm hearing that there are some tuning issues associated with Catalytic converter over temp protection routine being adjusted in CMR tunes. I'm curious as to what can be done to control WOT AFR. What I understand is that when the cat heats to a predetermined point held in a table that the Catalytic converter is identified as being overtemp and then fuel is added in an attempt to cool the cat. This added fuel may/will cause the WOT AFR to richen to a point that hurts engine power. My questions are: 1. What is actually measuring the catalytic temperature to determine overheating condition. 2. Can the predetermined point in the Catalytic converter overtemp protection routine be modified by the CMR tune?

Thanks,
 
#2 ·
Ok here goes the Catt temp is an est of the load vs what the throttle is and the fuel table calculations (its complicated)

As for tuning it out late 2004-up you set it way higher than can ever be reached ever under any conditions. 2003-early 04 there is no real way to up the temp I believe the pid is there but does nothing tune wise. Now I believe it can be tricked a little bit but its tricky. "White lightning" I believe can do it for you I have no idea as o yet how to do it with cmr yet. (Soon hopefully)
 
#3 ·
Very much appreciate the information. I'm trying to do some research and better understand how it works.
Thanks,
 
#5 ·
Hey guys, Im the owner of the truck in question. I have attached two data logs one where you can see the AFR drop down to 10's, and one with the cat temp.

The truck is a 2003, 392 stroker. I have recently upgraded to true dual exhaust, vararam intake and efan and am ready for a new session of tuning to get all the parts working together. Any and all advice on who should do my tuning would be great!!

Truck is currently down to do a SRT 10 brake caliper conversion but when I'm up and running again, getting the tuning spot on will be my main focus. First thing I'll do when I'm up and running again is a AFR/EGT/LOAD datalog.

To give you guys an idea as to (lack of) performance, (no drag racing tracks) I'm using an iphone app and my 0-60 is around 7 seconds, wich I personally find slow for the mods I have. I am at about 6600 pounds, i'm also running a propane system (for cruising, WOT I switch to gas) wich adds weigth to my truck.

cat temp:



AFR:

 
#6 ·
what are you using to log the AFR. In order to tune it better a data log from the predator would be best if you have one also a video showing AFR on a guage and rpm from dash if possible helps put 2/2 together then a pretty good tune can be done.

also what injectors are you running and have they been scalled into your pcm so they spray correctly.
 
#7 ·
I'm tuning using a PLX device OBDII tuner linked to an external PLX afr gauge. So all the PID's are from the pcm (same like diablo) only the afr is a seperate PID.

I've edited the afr log so it starts just as the WOT pull starts, you can clearly see the AFR slowly dropping down to and probably going even richer than 10 (10 is the max afr the wideband can pick up). When I come off the throttle the AFR leans out at 20 wich is apparantly normal?

I am using srt4 injectors. They are rated at 55lb at 58psi, so with the weaker 2003 fuel pump is 46lb at 43.5psi. (got this info from Stu @ Inertia). They have been scaled by hemifever, if the scaling is correct I don't know, any way of checking? Quick question, what is the fitting called on the fuel rail where you can release the pressure? Maybe a mechanical fuel gauge that connects to this fitting exist and can be a cheap way to verify fuel pressure?

Thanks for the help, open to all tips/suggestions.

Edited AFR vid

 
#10 ·
I'm tuning using a PLX device OBDII tuner linked to an external PLX afr gauge. So all the PID's are from the pcm (same like diablo) only the afr is a seperate PID.

I've edited the afr log so it starts just as the WOT pull starts, you can clearly see the AFR slowly dropping down to and probably going even richer than 10 (10 is the max afr the wideband can pick up). When I come off the throttle the AFR leans out at 20 wich is apparantly normal?

I am using srt4 injectors. They are rated at 55lb at 58psi, so with the weaker 2003 fuel pump is 46lb at 43.5psi. (got this info from Stu @ Inertia). They have been scaled by hemifever, if the scaling is correct I don't know, any way of checking? Quick question, what is the fitting called on the fuel rail where you can release the pressure? Maybe a mechanical fuel gauge that connects to this fitting exist and can be a cheap way to verify fuel pressure?

Thanks for the help, open to all tips/suggestions.

Edited AFR vid

If the 03 pump is really 43 psi, the injector scaling could be off a little, I am not sure if Sean is aware of that difference or not. Would be worth mentioning to him.
I think hes on vacation, if you want to send me the file I'll see if there is any COT that can be disabled, but I do recall the 03s being limited in this regard.

Thanks
 
#9 ·
Christoff, the valve on the fuel rail is called a Schrader Valve, same as on a tire.
 
#11 ·
I believe most injectors are "flow rated" at 43psi. Don't know why.
The 03 fuel pressure is 48+/-2 psi. The 04+ is 58+/-2 psi.
My notes show the 03 injectors flow 28# at 43psi and 31# at 58psi.
As for the OEM O2s sensor, it is a narrow band, I wouldn't trust it to read correctly when the AFR is other than 14.7. I would install a wideband to see what you are truly getting at wot. My 2 cents.... Note: I have a 05 pump in my 03 so of course it is different... lol
 
#12 ·
Thanks for all the help guys, I have a fuel pressure gauge ordered, that way I'll be able to give you a definitive answer on what pressure the 03 pump actually has!

I also have a wideband installed so correct AFR is no problem. So the AFR data in the previously posted datalog is from a PLX wideband, all the rest are pcm PID's obtained through a PLX obdII gauge.

As said before I'm offshore now for 4 weeks, so it will be a while before I can test stuff.

Christof.
 
#13 ·
Sounds good. Have a safe trip..
 
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