Zimba

Hi, I have a 1991 LS400 with 474000km's. It's a one owner and was always serviced at the same Lexus dealer. Recently it was given to me and the engine wouldn't start for a month and now it runs really rough, black exhaust smoke, wont rev over 2500rpm and prefers light throttle applications.
Initially there were no OBD codes but then it threw a code 31 so I replaced the MAF sensor. It now makes no difference to the engine if itsconnected or disconnected or if I swap back the original MAF.
Then I tried the igniters and coils. Disconnecting these made the car run even worse so I gather they seem OK.
Next step was swapping an ECU and then I resorted to replacing the capacitors with the Yamae approved Digikey caps - it made no difference.
With the new ECU it throws code 14, 15,24 and 31.
I'm just not sure what to try next?
The forum's assistance would be greatly appreciated.
Regards
Jason - Melbourne, Australia.

CLLEXUSS

Hi Jason, black exhaust smoke is commonly caused by running too rich.

I might take a look at the fuel pressure regulator in your 1991 as it might be failing causing it to run rich.

There may be a way to test it first ( check videos on youtube on how to test fuel pressure regulators ) to see if it's bad before you buy another ( just in case that's not the problem ) but that's what I'd be looking at.

Gcuarino

I replaced the whole mass air flow assembly. Tried just the sensor that didn't work so the whole assembly! Runs great, no limp mode no black smoke, no more 7 mpg. Got it on Ebay for about 100$ new.