Wife comes home today to announce that her engine lights been on for awhile and now its idling rough. 2000 Seville SLS with about 73,000 miles on it. If it had plug wires I would say it sounds like a bad plug wire or a plug.

Before I go someplace to pull the codes and start tearing into this any suggestions.

Could the Oxygen Sensor be causing this, cam sensor, etc... Any suggestions would be greatly appreciated.

Also is it necessary to replace the plugs with the Denso's it has in it our can I go with the ACDelco 41987's. The part number on the Denso matches up to the Owners Manual GM number.

Plugs and wires would be my first guess.

Ok, I pulled the Codes and this is what I got.

P0304: Cylinder 4 misfire

P0741 Torque Convertor ckt performance or Stuck off.

Since I have not gotten an service manual for this vehicle yet where is the #4 cylinder located.

What would be the most likely cause. Plug, coil pak, wire insert that goes down the plug hole and connects to the coil pack or injector. If its an injector would'nt it show up on the codes. Are the rubber plug inserts that connect the plug to the coil pak are they only a GM item?

Alright Pulled all the plugs and they all look pretty good. I'm going to replace them, however I still need the engine diagram for cylinder placement. Any help would be greatly appreciated guys. Thanks

Not sure I am understanding you as they should be numbered on the cam cover if that's what you are talking about.

........................................ rear of car ..................................


. passenger side ...................1 3 5 7 ..............drivers side

. ........................................2 4 6 8 ............................................

. ........................................front of car ..........................................

Not sure I am understanding you as they should be numbered on the cam cover if that's what you are talking about.

........................................ rear of car ..................................


. passenger side ...................1 3 5 7 ..............drivers side

. ........................................2 4 6 8 ............................................

. ........................................front of car ..........................................

This particular model Caddy does not have the cam covers numbered for some reason, unless Im missing something I could not find them.

Replaced the Plugs and the fuel filter tonight and its still mis-firing. Flashing service engine light during excelleration, steady on during idle.

Its sounding more and more like a faulty injector. Anyone have the run down on how to check them?

check the coil for cyl 4 it may be dead/weak
easy way to check is to put an old plug into the wire and ground it whith the engine running.
search for northstar fuel rail or something similar it has been discussed before

This is a COP engine there are no plug wires.

This is a COP engine there are no plug wires.
sorry, bad use of terminology. I would still test the coil.

sorry, bad use of terminology. I would still test the coil.

OK, so how does one test this particular type of coil?

I would switch the coil with one from another cylender. Run the engine for awhile. Then check the codes to see if the misfire has moved with the coil.

P0741 - TCC (Torque Converter Clutch) System Stuck Off
This code sounds serious, get it checked out. I don't know much about transmissions so I can't help you here.

I would switch the coil with one from another cylender. Run the engine for awhile. Then check the codes to see if the misfire has moved with the coil.
.

Unfortunately its one giant coil unit that bolts into the valve cover head. All the coils are molded into the unit.

Cylinder #4 is the front cylinder bank, 2nd from the left as you face your car from the front. My '98 STS doesn't have COP so I'm not sure if you can test the #4 coil by lifting off the coils and inserting spare plugs to check for an obvious blue spark at each coil while cranking. Be sure not to crank for long while testing this way or you'll pump fuel into the front bank and this may fowl your plugs and later overheat the front manifold cat converter.

I've had injector sticking problems with my '98 STS at around 50K miles. On both cases, I got the misfire to go away with a heavy application of throttle. Two GM techs told me injector sticking is unfortunately common; a result of insufficient cleaning ingredients in many fuels. Many of the threads in this forum (at the very bottom) note a Kansas newspaper article confirming this. Your dealer can try a cleaning process for your injectors, about $130, where they apply injector cleaner at the fuel rail, under pressure.

My car got two new injectors under warranty and they suggested I should run Amoco Ultimate or Shell V-power (5 times the mandated cleaning ingredients), if not all the time, every 2nd or 3rd tank-full.

After the cleaning process, two new injectors, and occasional tanks of Amoco Ultimate or Shell V-Power, I've had no more problems with misfire.

Follow up.

Well I switched the front and back COP and my Error code went from #4 to #5 which would indicate a bad coil.

I do have a question. On the right side of the COP unit were the wire harness plugs into there is an electronic box with heat sinks that snaps into the unit. What the heck is this?

I initially just switched the COP units without changing this electronic box and when I went to fire up the car I had battery problems, almost like the system shut down all power. Wierd. I figured maybe these units were propiratary to each side of the engine so I switched them and then jumped the car and discovered the #5 problem.

Anyways any input on these little electronic boxes would be helpful and info on whether they are propriatary to the right and left side. The code numbers under the box are the same except for a couple of secondary numbers.

On another note I hate dealerships that don't have parts departments open on the weekend.

Follow Up.

Got a new front COP and the Caddy runs like new again.

Very easy change out, about an hour total time.

On the fly dealer cost was about 226.00. They honored there internet price. Normal price was $248.00. If I could have waited Rockauto.com was around 180.00.

Talked too my buddy who is a service writer for the local Caddy dealer and he said the cost to diagnos and replace the COP would have been around $990-$1200.00.

Local Autozones have the latest OBD II reader so that was a free borrow. Reset all the engine codes and everything checked out great.

Hope this thread helps somebody else out in the future.

OMG! $990-$1200 to diagnose and replace a coil?

Man, helps to have someone on the "inside". What a money maker from the STEALER.

Sorry for those of you with sensitive ears. but the STEALER is fool of SHIT sometimes..