Having a pretty weird issue with my SC400 running extremely rich. Black smoke and backfiring from exhaust

I Have:

Replaced coils and wires, spark plugs are ok Replaced injectors and fuel pressure regulator

• replaced MAF
• blocked off fuel to the cold start injector
• Rebuilt Ecu, had leaking caps
• unplugged TPS for both cruise control and regular, seen no changes.
• made sure there are no vacuum leaks.

Anyone know much about these SC's? I'm pretty well stumped. Only things I can think of are



-SIA electronics didn't do a good job rebuilding ECU

-ignition module is bad

ANY help appreciated!!

Hello,

Does the car run stably aside from black smoke?
How did the issue first begin, before or after all the listed parts were replaced?
What parts did you use? Unless it is an OEM MAF, Regulator and Injectors that you got, I would put the old ones back in.

Make sure the parts you got are OEM or very good quality, as it is quite common to see people go with shotgun approach replacing all the parts they reach, making a relatively small issue a lot worse with so many added variables.

If that's good, I doubt the issue is related to Spark, usually when you have Black Smoke from the exhaust, it means that the fuel is burning, but not fully, with Spark, fuel either ignites and burns to the fullest extent it could, or doesn't burn at all and flies out of the exhaust, so I would check everything fuel-related first.

There aren't too many causes for Rich mixture, it could be the Fuel Pressure, Injector Issue, or the Sensor Malfunction. An indirect way to check Fuel Pressure, try putting the old Regulator in and taking the Return line off, see how much fuel comes out, but it would be a lot better to get a proper Pressure Gauge. Sensor Malfunction, OBD1 cars are tricky without proper tools, so the easiest way may be to disconnect them one-by-one and see if that helps at all. Injectors are even trickier, they are hard to test without a stand if they are not leaking, at that point it all depends on what kind of parts you got.

Hope this helps and best of luck!

the car sputters at idle. Runs better warm than cold, but despite temperature I can’t rev over 2k rpm, as it backfires and nearly stalls. I bought the car recently, had a no-start condition. Previous owner had the battery cables hooked backwards, and the rotor button was upside down. Fixed that, now the car runs but runs stupid rich. I used all OEM parts. Remanufacturer DENSO injectors, FPR, and an OEM maf. I’ve had a feeling that the issue had nothing to do with spark, but with all i’ e replaced it’s the only other variable. Most people online that I’ve talked to point out that the ECU is likely still bad. I had mine serviced at SIA Electronics out of Illinois and they have mixed reviews. I cracked open the Ecu just to see and they did, in fact replace the leaking capacitors I told them about. I don’t currently have a fuel pressure gauge, but I will report when I get one.

Remanufactured Denso Injectors? I honestly never heard of it before, unless it's Diesel injectors, can you provide a link to a place where you got them, even for the future reference if nothing else, as here is just about the only link I found on the subject.

If you have a spare Manifold laying around, or you can take yours off, you can make a rudimentary stand to check the Injector spray pattern using the Manifold and Rails as a stand, and a 6V AC Transformer as the power to injectors. It won't be pretty, but at least it's simple to do. Other than that, if you still have old injectors for that engine you can try swapping them back in, they rarely go bad, at least as far as I can tell, and even if they do, not all at once.

Hope this helps and best of luck!

No offense to Arsenii do not do all of that work yet start with simple things and double check simple things First let the car warm up then unplug the maf and see if you get your revs back if you do take it for a drive and see if it runs normal. if not check your timing before doing anything else and triple check that you didn't put a pair of ignition wires in the wrong place. Next although they are new i would unplug one coil at a time and see if the car can start with only one. let me know what happened. Do you have a check engine light on?

i’ve unplugged the MAF, both TPS, and no changes. Timing is correct, and the plug wires are in the right spots. I haven’t gotten a check engine light. I just replaced both ignition coils and the ignition module. I will check and see if it can start with only one coil.

have you checked the ignition cap and rotor? They may be bad or could be installed 180 degrees out

yeah, when I first bought the car it wouldn’t start at all because the driver’s side rotor button was upside down. Checked both when I did, and it was just that one.

I may be wrong but have you checked any vacuum lines collapsing?? I would place the rear on jack stands and remove the wheels and have a friend accelerate to the 2k mark and observe if any vacuum lines are collapsing on themselves. Additionally have your cats checked. Maybe they're clogged? Maybe replace the EFI relay that round one on the left-hand side of the fuse box.

This was going to be my suggestion also after checking the coil. Remove the pre O2 sensors and see if you can rev past 2k if each coils can start the car on its own. If you can rev it is clogged cats