sophomore

My 94’ 400 went limp mode and started throwing only code 52, knock sensor in bank 1. i wanted the wiring harness, connectors, and knock sensors replaced quickly and i didn’t feel like doing it myself. Two weeks later the shop is saying my ecu is to blame and it will have to be repaired along with the knock sensor replacement. They said the voltage reading was way out of spec. It looks like I have three options, have them repair the ecu, buy one off ebay, or say ***** it and just have them do what i originally wanted done. Any advice is appreciated i just want my car back 😪

also the ecu was rebuilt last year by relentless motorsports before i owned the car, has anybody worked with them in the past?

t2d2

iTrader: (8)

Did they verify that the knock sensor is actually bad, or are they just relying on the ECU's knock sensor code?

On my first SC (also a '94 SC400), I had knock sensor and limp mode issues that turned out to be entirely due to the ECU. The capacitors had leaked bad enough that the trace for the knock sensor pin was barely hanging on by a thread, resulting in intermittent signals.

All of the ECUs are long past due for servicing, with a ~14 year shelf life on the capacitors. so it's always wise to do that (if it hasn't been done) before chasing down other potential problem sources.

sophomore

see i read about how common the capacitor leak on these cars are. that’s something that can be repaired on my current ecu? the shop made it sounds like relentless ruined the ecu.

t2d2

iTrader: (8)

Mine was in pretty bad shape and the guy I took it to was able to repair it, but he had to create a new "bypass" trace, so a regular business might have called it a lost cause.

sophomore

bruhh 😂😂 that’s what relentless did! they created a bypass and the shop was ******* on it. alright i’m about to pick up my car and replace the ecu. i’ll keep mine and try to work on it. they said the ecu burned the knock sensor but i can’t find any information on it. if i replace my ecu should i be worried about the knock sensors still having to be replaced? you didn’t change yours did you, just the ecu?

Duck05

I have to enforce what t2d2 is suggesting. Last year I experienced all kinds of weird issues with low idle and not sustaining a running engine. After a lot of troubleshooting and replacing several parts in the fuel system, I requested the shop to swap in my rebuilt/spare ECU and the main issue went away and fixed other weird behavior as well. Car is running better than it has been in a long time.

Sent out the failed ECU to SIA to be rebuilt and they reported 4 bad capacitors and 6 damaged traces. Now that repaired/tested ECU is the spare.

Just completed the required CA smog test for registration and all measures improved from 2 years ago.

Can’t stress enough when weird conditions and check engine codes start to appear, at least start with the ECU to check that box before diving too deep into expensive and time consuming troubleshooting actions (especially if you do not know the ECUs history).

sophomore

I finally got my ecu and opened it up. I’ve been lucky enough to have help and there does appear to be damage on some capacitors. I still have more research to do but have another ecu on the way. might see if there’s someone local willing to plug theirs into mine, but I’m very hopeful.