Too new to repair this sc400.Engine problem.

[rextech]

Hi guys, I´m new here and new with Lexus too. I need your help, please.
I just bought a sc400 with 60k miles -1 month ago-, it is a nice car, I really like it.
Yesterday morning I started it up -cold start- and I noticed that the engine has no power, it started but has a big power loss. The idle is very low and it seems that there are some pistons that are not working properly. There is no check engine light on and i don´t know what is bad with it. There is no bad sound in the engine bay, no overheating, i really don´t know how to diagnose it.

what can i do? what is your advice?

Thanks for your help.

rt

 

[Peewee]

Sounds like a coil or an ignitor has died.

Is it idling rough?

 

[qca]

peewee's on the money .use the self diagnostics too see if a fault code is stored
it could also be a failing fuel pump or blocked filter

 

[rextech]

Thanks guys, I will check for stored fault codes, ignitors and coils.
Now I know where to start.

I will do the job this weekend and then write back to inform you.

Thanks,
rt

 

[stukid]

Common failure is the coil on the #1 bank (above AC compressor).
They go bad, car will run on one coil, but only on 4 cyls!

 

[rextech]

Guys, I checked the coils using the service manual -Volume 1- intructions. First I checked the easy one -the LH coil-, it has to be checked for resistance on two points. The value for the first point -high tension cord and positive (+) terminal- should read from 0.40 to 0.50 ohms, that one reads 1.2 ohms in that coil, so there is a difference. The second point - positive (+) terminal to negative (-) terminal - should read from 10 to 14 Kohms, that point reads 12.5 Kohms so it is fine.

To be sure I took out the another ignition coil -the RH coil- and did the readings, it has the same values of the LH coil on both points. Both coils should not be bad, I don´t think so. Maybe the value from 0.4 to 0.5 ohms is a service manual error or do not match with my 1992 sc400 because the manual I´m using is from a 1993 sc400.

Now, it will be harder, I´m going to check for stored error codes like QCA says. Then the rest.

thanks,
rt

 

[stukid]

I reread your original post, you stated pistons not working properly.
Are you describing a misfire?
Is the Check Engine light on?
If the spark plug wires are Toyota (lexus) they will have a date code on them.
If they are original, they can cause miss, as can bad distributor caps, rotors or spark plugs.
Don't rule out moisture in the plug wells.
With spark plug covers off - you can run the engine and pull plug wires(from the dist caps) one at a time to attempt to locate cylinders. . .

 

[rextech]

Thanks for your posts.

There is no misfire, the engine sounds a little just like a broken exhaust pipe. The Check Engine light is off and the date on the plug wires are 92, plus some other codes (5Z-16 ES-X). It seems like the plug wire brand is Yazaki.

Well, I discover something very interesting, i visually check the engine under the car and notice that the RH pre-cat was red heat, it was glowing (the engine was just idling for ten minutes) and the LH pre-cat had the regular color (like rusted brown) so i called a more experinced friend and he told me that is posible that the pre-cat is clogged so i`m going to "disconnect" it.

It makes sense, let me check and then post back.

thanks,

rt

 

[rextech]

well guys, I replace the cats with 2 1/2 inch pipes, The RH cat was very clogged. The fail continued so i get mad and pull out all that plastic that cover the spark plugs and wires. After check each ignition wire -pulling them out with the engine started-, I noticed that two pistons from the engine RH side and both of the LH side were not working. All that four pistons are feed with the LH ignition coil so I disconnect the ignition coil high tension cord to ground it, result: no spark. Now I don`t know. Could be a broken ECU to igniter wire or a fail in the ECU or the ignition coil failing. I proved both of them and the measures were right. Anyway I`m bored so i`m going to buy a new coil to see what happen.

BTW, i check the high tension coil for continuity and was ok, i checked the ignition relays too and there were fine.

i could interchange the coils to check them too.

just to keep you inform and to feed this knowledge data base that help us a lot.

thanks,

RT

 

[Peewee]

Sounds like a coil or an ignitor has died.

Is it idling rough?

I suggested this a few weeks back.

Unplug one ignitor at a time, unplugging one will make no difference to the engine, unplugging the other will cause the motor to stall.
Mark the one that makes no difference.

Then turn the car off, swap the two plugs over on the ignitors, and start the car again.

Now unplug the one you marked.
If that makes no difference, then that ignitor is dead.
If the motor now stalls, then one of the coils is dead.

 

[stukid]

I hope replacing the left hand coil fixed your problem-
I have seen them cause this and other problems-just like the car is running on 4 cylinders.
The cats glow because the injectors are still dumping fuel, and there is enough heat from the other cyliders to 'start the oven!!"

 

[rextech]

It is ready, it was the LH ignition coil. As you know i checked both coils and the measures seems to be right -see a previous reply from me-.

Without the cats the engine is smoother and the car is faster. Some more horses were released with this mod. It is true that each sc400 cat costs like $8000?

I don´t like the new engine sound so much and it "drinks" more fuel than before but i like the new car feeling, it is more responsive too at the gas pedal.

I still have a minor problem with the exhaust, i need an exhaust gasket, that one that is like a ring and goes at the exhaust manifold and cat joint . Here in my country there is no any lexus dealer but Toyota. Do you know if that gasket is used by another toyota? maybe the 6 cylinder camry? or the land cruiser?


conclusions:
*Do not believe so much at the coils resistance readings.
*With a fail like this -engine with no power- check each cylinder first -wires, spark plugs- as stukid said.
*If the engine is failing but it is shaking the possibility that an ignition coil is failing is like 0.9. The ignition coils feeds the engine symmetrically, i mean that each coil is used for 2 pistons in each side of the engine so the balance is 50% and 50%. -my english is not so good so i don´t know if my explanation is clear-

For example: If two pistons from the same engine side are "out of service" the engine will shake because one side will have 4 piston working and the other side will have just two pistons working.


Well thanks to all of you for help to fix my car.

RT