FLex

93SC 400 with 107,000 miles: After filling up with gas, car started running rough (coincidense?). New timing belt, acc. belt, and sparkplugs were done. Still having rough idle and slow to rev. Checked sparkplugs and half were clean and half were black. All the black ones are connected to the left rotor. I changed out left and right new caps and rotors, crank angle sensor and new left ignition coil. Still having same symptoms. Any thing else to check or ideas? It is still running on 4 cylinders.

Carpe Diem

Have you done a compression test on any of the left bank cylinders?

George

SupraCoup3

this post is gonna get moved to the engine section any time now, but I'll chime in.


Did you happen to degrease/clean your engine bay? The spark plug wells for the SC400 are quite deep. I know because before I joined CL (heh, about 3 years ago now) I cleaned out the engine bay, and got water into the wells.

You did have the timing belt changed, right?

I07k, that engine is just getting going. It shouldn't be anything major.


John

Edit:
(Tbelt won't make the engine run rough... it wouldn't run at all. It's possible you've got some bad gas)

mmarshall

You mentioned that you got this after a fillup. There are several ways you can mess up your fuel system during fillup. (assuming you're using the right octane). One is by filling your tank while or shortly after the tanker truck is pumping its gas load down into the tanks. The tanker truck has high-pressure hoses that pump thousands of gallons into the underground tanks...and that pressure stirs up any dirt, water, and sediment that is lying on the bottom of the tanks. If you are filling your car up while that is happening, where does that dirt go?...yep, right into your tank, into the fuel pump, clogging up the filter, and plugging up fuel injectors. The only solution is to have a thorough fuel system cleaning. Another source of fillup problems is letting the gas level in your tank get too low. If this happens, when you fill up, you do basically what the tanker truck does.....the fuel nozzle pressure stirs up ay sediment in the bottom of the tank and.... bingo....same thing....right into the fuel system. Your car may have dirt in the tank.....it has over 100K on it. That is why fuel-injected cars should be kept at least one quarter-to-one-half tank full at all times. This will also help prevent moisture condensing in the tank. Third, all brands of gas are NOT alike....cheap cut-rate brands don't have good detergent packages, and may contain sediment as well. I recommend Chevron, Amoco/BP, or Mobil.
Anyhow, of course, this doesn't prove you got the problem from gas, but clogged injectors do give the symptoms you describe. Give it a can of BG44K or another good injector cleaner and see if it doesn't run better in a couple of tankfuls. If not, it may need a professional cleaning.

FLex

Thanks for all the replies but it still doesn't explain why 4 plugs are black and 4 are clean.

Lexiss_sc430

iTrader: (2)

I would check your distributor becasue this sounds like it can be caused by that, since on sc4's we have 2 distributors one on each bank, one could have gone bad while the other still works fine. That is what I would think is going wrong.

Tommy

TxLexus

Since all the black ones are connected to the left ignition coil. I say you should check the left coil cap and rotor and wire connection. Sounds to me like the wire to the left coil might have slipped off the coil or the cap. Since your left ignition is new, make sure the connection is good and proper. after checkin all this and it still does it, your ignition coil may be defected

I do agree with MMarshall about what dirt in gas tank would do. But in this case, if it was bad gas or dirt in the tank, then all the plugs would be fouled, not just one side.

Just my opinion, Good luck

TxLexus

The black plug is due to not getting any sparks to burn gas. The ignition coil produce sparks.

Again this is just my opinion.

FLex

At least I am thinking along the same lines: I have replaced new caps, new rotors, new ignition coil, new crank angle sensor and checked all the connections. Any other ideas?

TxLexus

you checked all that and it still does it?? Are you sure you are getting sparks?