1996 SC Riviera Misfire #6 Cylinder

which book?

Albertj

Key word there is "can". I don't believe that TC can't work if a single misfire occurs. It seems your TC light has been coming on a long time before this misfire, right?

Nope - never came on once until the Service Engine light came on.

Okay, I guess if we hunt down the source of this miss-fire, the TC light might go away then. Would be interesting to remove both codes, then see which shows up again first.

The weird thing is that there is no code for the TC unit. Just misfires. And now there are misfires all over, not just on the 6th cyl. I was focused on the wire/plug... because it was just listing one cyl.

Now, with multiple misfires, I'm going to check MAF. I have replaced wires and plugs already - maybe that alone will clear it out.

I'm also going to check the connectors to the TC on the front wheels.. I just had tires put on and maybe they knocked something.

although the TC and PCM work together, codes from ABS and TC have to be read with an ABS scanner. WSS info cannot be pulled from the PCM. It's a different computer.

But still you need to figure out what is going on. Can you read your O2 sensor voltage? If the O2 is wonking out you could be running into an endless lean situation.

Well, apparently, changing the plugs and wires have done away with the SES light, which apparently has the TC working, and the engine is starting and running much better.

The car had over 100k on the original plugs and wires, I can't believe that is all it was.

I'm gonna keep my eye on this stuff though - it seemed too easy!

Did you change the wires again? Or was it the plugs that fixed the problem?

The wires were done first (because they were easier!)

After those, the light cleared but came back on. Then I put the plugs in... and there is now a noticable smoothness to the idle and it starts much easier.

Not sure if you've noticed this but the 3.8L SC engine is one of the quickest, easiest starting engines I've ever seen. The car was not so smooth on start up, taking more than a revolution. Sometimes, taking a bit of gas to make it smoother when warm.

Its now firing right up, smartly. And the idle is back to rock solid at 750 to 800.

I'm sure both plugs and wires helped, I'm not sure which one put it over the top: but the code is out now... and it wasn't cleared manually, so it went off itself.

If you look closely at the old plugs, maybe one looks different?

Glad you got this fixed, and glad it only cost you $1.50 for a bad plug (you needed the wires/plugs anyway).

Well, the old plugs were definitely worn. Far from the worst I've seen though.

I hope this is the problem and not just an intermittent SES light! But the driving speaks for itself.

Wonder if the bad plug was carbon fouled and arcing, or had developed an open center electrode.

Those old plugs weren't OEM (ACDelco), were they? Bosch Platinums? How long had they been in? Please let us know - thanks

Albertj

They were stock - the whole car is... one of the reasons I bought it. It was about 107k miles.

Might not be worth the forensics, if only because the stock plugs are 'scheduled' to be changed out at 100K miles anyway - actually that's the first scheduled change.

But if you have time on your hands check for a DC short betwen the center electrode and the case of each old plug. One probe on the top of the plug and the other on the screw threads. Resistance should be >10M ohms. Some meters may read OC for open circuit. If you are getting any conductivity that's a likely cause of the problem you observed.

All the best

Albertj

Thanks Albert, I chucked the old ones... I shouldn't have but I was in a hurry to clean my bench. I'm pleased with 100k miles from the originals as it is - not sure but if there was a failure, it was only one out of six!

And it was time. I do have to say that I'm really happy with the Iridium plugs - as of right now I can recommend them.

I use Iridium plugs also. Have 78K miles on my second set of them. I did not have any misfire problems with the first set, I just changed them out when they reached the 100K service interval. Also changed the oxy sensors around 150K - I was using CarCode to check another issue and found the sensor output voltage was lower than it should be.

Albertj

I think at 107k I'm going to be replacing the O2 sensors here soon also. Thanks for the info.

Did your mileage change when you put new O2 sensors in?

Yes, mileage improved back to new levels, had gone to ~24 on hwy before changing oxy sensors. Mileage had worsened slowly over time - only way I could tell is I had spot-checked it when I got the car and checked it from time to time. I keep a journal in the glove box with every repair listed, and various observations. So I remember oil changes and such. Anyway, mileage went back to ~28 on highway after changing sensors.

The issue for you, I think, is that you ought to have a definite reading from the oxy sensors befoe you change them. Bosch says change 'em every 50K. Hmmm... maybe if they are abused. If you've been running premium, and/or a gas such as Chevron with Techron, 50K would be kind of soon. Also, there was a factory TSB - the dealer can flash the ECU ROM to compensate for lower voltage levels from a functioning but old oxy sensor. Bottom line is I would not just go change yours because I changed mine. I would try to measure the levels somehow. I used CarCose from Alex Peper, running on my laptop, with a cable I bought from Alex. Have a look at the site sometime, http://www.carcode.com/, for more info.

Albertj

I'm thinking at 107k with the original it is time!

i've got 140k still on original, and i dont think i would benefit from a new one. most guys here are still running stock 02, it is one of those "if it aint broke...". also some cars are more prone to 02 failure, the OEM delco sensor seems to be very good on the l67 engine.
but on the flip side a new one is only like $50
so will +1mpg more mileage offset the cost? probably if you drive alot.

I drive a lot! And with a heavy foot!

Yes the OEM Delco sensors seem fine. When I replaced mine I installed a pair from gmpartsdirect.com.

Albert

AA wrote:

I've never heard of a misfire condition that would turn the TC light on. Even if it "could" happen, doesn't mean that's the cause for certain.

This actually just happened to me last night. SES light, solid then flashing....TC light on and off. Code P0300 (engine misfire). When I checked the misfire, I saw Cylinder#6 had 112 misfires. New plugs fixed this. So it appears that there is some correlation to the misfires and TC light.

The PCM can't calculate load and what-not to control the TCS if misfires are occuring.

7901mark wrote:

AA wrote:

I've never heard of a misfire condition that would turn the TC light on. Even if it "could" happen, doesn't mean that's the cause for certain.

This actually just happened to me last night. SES light, solid then flashing....TC light on and off. Code P0300 (engine misfire). When I checked the misfire, I saw Cylinder#6 had 112 misfires. New plugs fixed this. So it appears that there is some correlation to the misfires and TC light.

Hey, the flashing SES light actually did what it's supposed to do!