I will be replacing my catalytic convertor soon with a known good, low mileage one, as my car has the infamous SCR Efficiency code present. Since I’m going to have the whole pipe assy down and off the car, requiring me to remove the urea injector, egt, and two NOX sensors, it would sure be nice to see that urea injector actually squirt the urea. I have a Foxwell NT520 and am hoping that one of you can tell me if that tool can be used to actuate the urea system and let me see it work. I just want to make damn sure that crap is working before I put the cat assy back in place.
Q: Why are you replacing your SCR? Or to rephrase, how do you know it’s a culprit, as it rarely is.
A: Well, here’s the story. I have had both NOX sensors recently replaced by the dealer under that special extended BMW warranty and the dealer called me to say that they couldn’t figure out why the car was still setting the SCR Efficiency code so they had to submit a case to BMW. A couple days later, BMW comes back and says to replace the SCR to fix the problem. Since I didn’t want to spend $2700 on a new SCR at the dealer, I declined the service and set about finding a good used one to replace it with.
In the meantime, I read about the thermostat possibly being a root cause for SCR efficiency code being set. So, using my foxwell tool, I measured the one that I had and it was 5-6 degrees Celsius lower than it should have been. It was probably ok, but I changed it anyhow and the new (88C factory spec) thermostat corrected temperature back to factory spec.
Reset all the codes when I changed the thermostat, and still, the stinking SCR efficiency code still comes on.
I really think that there is a possibility that the SCR got clogged up when I tried to cheese-by and use the Liqui-Moly diesel intake cleaner. That crap ruined one of my EGT sensors (the one that is right by the Urea injector), and it also caked up my Urea injector with a hunk of soot/sludge looking crap that I had to chisel out with a pick (it wasn’t urea crystals either).
Anyhow, I’m at the final stages of trying to get this thing to work like the factory intended. If the SCR replacement doesn’t solve the issue, I guess I will have to do the alphabet deletes and tune the car. Does create a problem here in California when it comes time to ‘smog’ the car. Might have to take it to my in-laws in Texas and leave it there? Not sure….
Q: There should be a procedure to test your SCR efficiency in ISTA. I’m not sure if Foxwell will do it. Most probably have not played with it because of the deletes. Other thing you may wish to consider is TestO to monitor parameters. There are a whole bunch for the urea system.
I know the Foxwell NT520 will monitor when the urea is injected and some other stuff. I haven’t played around with it enough just yet. My hope is that when I weld in the other Cat that the problem just goes away. I have another cat that is like new sitting in my garage, I just have to get off my butt and get it done. Perhaps I’ll find my ’round to-it’ this coming weekend… Hoping for the best.
I intend to cut open the existing cat and do a post-mortem on it. I want to see its clogged, or caked with crap, just need some kind of evidence that its shot. I’ll gut it after that and weld it shut so that if I ever want to do the ABC delete, I’ll at least have it laying around.
I don’t think its the age of the urea, the dealer changed out the urea tank under that extended warranty too. Interestingly enough, the car hasn’t asked for any urea in quite some time. Not sure if its even using any anymore, that’s why I wanted to check and see if the urea was squirting since I was going to have all of the components out when changing the SCR.
Here are a few parameters I found for Urea and SCR:
Oxygen linear NOx sensor 1 or 2;
Determined NOx concentration sensor 1 or 2;
Oxigen binary NOx sensor 1or 2;
Number of SCR adaptations;
Weighted untreated NOx emissions per km;
Average SCR efficiency;
Mileage last successful SCR cumulative NOx emissions;
Active state duration SCR;
Signal from NOX sensor 1or 2;
Various NOx offset values;
Lambda signal from NOx sensor1 or 2;
Diagnostic status of NOx sensors;
Raw NOx emissions;
Aging factor of an SCR cat;
Dosage for the engine test;
Urea consumption since last start;
Urea consumption since last fill;
Desired value for urea nozzle duty cycle;
Output duty of the urea nozzle;
Urea feed pump duty cycle;
Desired feed pump duty cycle.
And a whole bunch more.
You can monitor some of these to understand what is going on.