Got it. Thanks.
I couldn't find any wiring diagram for the BMW-s having thermocouples to monitor exhaust temperatures (no wiring diagrams specific to Japan specs) but I found a document describing the operation of the EGT system on Porsche 928. This car had rather similar concept to the 348's - two separate ignition modules (one for each bank) and a thermocouple and a blue "950C relay" for each side. In the case of too high EGT on one of the banks, its "950C relay" shuts the injection for the bank down. In the case of BMW-s, 4 or 6 cylinder engines, it probably just completely shuts the engine down. The blue 950C relay I showed is what I removed from my BMW E30 M3 (originally a Japan spec car) but now significantly modified for racing. Instead, I installed an EGT gauge which I monitor. I believe the Japan specs BMW-s had to have this system because of very strict emissions regulations in Japan.
In my personal experience with my 348 = old wives tale. 1) I have a few old stock cats that have been hollowed out because of the ceramic monolith burning up over time = my car did not catch fire. And that is with the cat tcu's working and no slow down lights. 2) I have literally burned up the insides of a metal core cat while driving, as in flames spitting out the exhaust tips = my car did not catch fire. Before you ask, I was on the highway when a crank sensor gave up the ghost, which resulted in the spark plugs not firing properly causing raw fuel to get pumped out the exhaust. I immediately pulled off the highway and shut the engine off. The only thing that took damage was the insides of the cat, but man what a light show was coming out the back. LOL! Yes I was running with the idiotic cat tcu's unplugged. "But it would have saved your cat." NOT! I have run my 348 with the stupid things plugged IN and I STILL ended up with hollowed out stock cats, and burned up ceramic cat cores. The cat tcu's are nothing but a pain in the ass, and useless. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Ernie is correct. The metallic core cats go fast. In my case, 355, I lost spark in 2 cylinders due to an intermittent coil failure. Started the car, drove a little. Car started running on 6. No SDL. Kept going a little and flashing SDL came on then went solid. I immediately stopped. Cat temp never got to the fuel cut off limit. Let ti cool down and started again. SLD again went to flash, solid then spark came back and engine ran fine from there on. Never reached fuel cut off (limp mode). When I checked the cats the 1-4 cat looked like Ernie's picture. Back 1/3 of the core was shot. The ceramic cats can probably handle higher temps but they break up due to vibration. Image Unavailable, Please Login Image Unavailable, Please Login
