Misfire (SES light, codes included)

Hello Riv Fans,

Hope you can point me in the right direction with my rough-running, misfiring SC '95.

The other day, as I was motoring happily along, it suddenly started running really rough, like I was down a cylinder. I limped home, and I thought maybe something had gotten wet (it was raining) so I let it set overnight. The next morning I started her up and everything was fine. I started off and got about a mile and a half before the misfiring started again so I turned back. Same thing happened the next day, so it seems like it has to warm up before the problem occurs.

I read the codes, and here's what I got:

P0300 Misfire Signal Misfire Detected
P0131 Oxygen Sensor Signal Is Too Low
P0171 Fuel Trim Sensor Signal Lean
P0257 Turbo Boost Sensor Signal Circuit Problem
P0300 Misfire Signal Misfire Detected
P0401 OBD1 Delta RPM Linear EGR Flow Failure

It seems unlikely that three different sensors could all be bad, so I guess my question is whether one failure could be producing the other codes, or whether there's some other component common to these sensors (ICM?) that I should be checking? I don't want to assume for example that the O2 sensor is actually bad and then start throwing money at it.

If there's nothing obvious, I hope someone reading this might at least have some insight so I have a direction to go before I take it to the shop and start dropping cubic dollars on it while they fish around.

Thanks in advance!

I am guessing the first thing to do is look around under the hood, I'd be looking for a loose / damaged plug wire, Hopefully you find it before you kill a coil. Which might have happened already the SC coils are very hi energy and will self destruct without a load (spark plug and wire).

albertj wrote:

I am guessing the first thing to do is look around under the hood, I'd be looking for a loose / damaged plug wire, Hopefully you find it before you kill a coil. Which might have happened already the SC coils are very hi energy and will self destruct without a load (spark plug and wire).

Actually, I should have mentioned that. The first thing I considered was a bad or loose plug wire, so I checked them out visually. Nothing was loose and they seemed in good shape, although there could be a problem under the boot. But they aren't old, maybe 18 months, and they're Belden Max Protect 8mm wires.

Figured it could also be a bad plug, but I wondered about the P0300 code - if it was a particular plug or wire, wouldn't the code indicate the misfiring cylinder? As in P0301 would indicate cylinder 1?

I hadn't considered the coil going bad as a result of this until your reply. I was going to ask you the best way to determine if a coil had gone bad, or how to diagnose which wire/plug could be the issue. Then I decided to try the old school method. I started the car and pulled an replaced the plug wires one at a time. Sure enough, when I pulled either of the top wires (6/3), the engine ran no differently.

So I guess now I'm wondering if the bad coil is the source of my problems or a result of something else?

Also, what are the chances the plugs on that coil are still intact? Time for new plugs after the coil?

Well, I answered my own question. I figured a coil was a cheap and easy enough fix to try, and I had an AZ credit burning a hole through my pocket, so I popped a new one on along with new plugs. Got a better look at the plug wires, they looked good.

But no change, still misfiring. And now I may have bricked the new coil as well, but that was a risk I was willing to take. Any other ideas anyone?

I am still thinking wires.

Riv ignition is very high energy and you would not be the first on RivPerformance to come across a set of wires that our coils banged into whimpering defeat. (I am also thinking about pointing out that the 95 has 3 coils not one and you just talk about one. Do you have the single coil module with 3 coils? If so your car was modified. I have never seen one of those on a Riv, just the module with 3 coils bolted on top. )

Lets try this: Do you know which plugs are misfiring?

A word to the wise: The approach of trying various new parts will frustrate you, most folks that I've seen do that turn around and sell or scrap their Rivs pretty quickly actually. It gets old and real expensive, real fast.

There is a thread on here on checking coils and I think there may also be some info on checking the ignition module. You might want to think about getting a good used ignition module from a junkyard, or at least tracking one down. You need to be checking the grounds on yours.

The coil guidance will tell how to use an ohmmeter to measure resistance across each of the coils, and how to check coils for shorts. The ig module guidance IIRC basically says to remove, clean the ground plane, coat with dielectric grease and reinstall with good coils and good wires. You also need an ohmmeter to check the wires.

Sounds like somebody with this car had a bad wire or 2, and popped on a new set after the bad wire fried one or more coils. I could be wrong. Only way out of this hole is diagnostics. Part swapping on guesses probably wont' work well.

then it will be back to the car's OBD> First thing to do - clear all the codes and see which come back (repeat the condition).

albertj wrote:

I am still thinking wires.

Riv ignition is very high energy and you would not be the first on RivPerformance to come across a set of wires that our coils banged into whimpering defeat. (I am also thinking about pointing out that the 95 has 3 coils not one and you just talk about one. Do you have the single coil module with 3 coils? If so your car was modified. I have never seen one of those on a Riv, just the module with 3 coils bolted on top. )

Yes, sorry if I was unclear - I have 3 coils. What I did was unplug the wires at the coils while the car was running, and unplugging either wire from the top coil (plugs 6 and 3) made no difference. It continued to misfire. When I pulled any of the other four, there was a noticeable change in the engine, so from this I deduced that the top coil was bad, and that 6 and 3 were not firing. When I pulled the plugs themselves this was confirmed, since 6 and 3 looked different. Not bad, but they looked darker and dirtier than the other four, which were whiter and sort of ashy.

albertj wrote:

Lets try this: Do you know which plugs are misfiring?

So I'm thinking 6 and 3, but I still don't know if this started with 6 or started with 3 and then it killed the coil so now both 6 AND 3 aren't firing, or did it start with the coil and 6 and 3 were both not firing from the start.

albertj wrote:

A word to the wise: The approach of trying various new parts will frustrate you, most folks that I've seen do that turn around and sell or scrap their Rivs pretty quickly actually. It gets old and real expensive, real fast.

Point taken. I've owned this Riv for about 12 years, so I've had my share of horror stories. It spent three months at two different garages a year or two ago until someone diagnosed some sort of problem in a weird, poorly documented ignition circuit.

albertj wrote:

There is a thread on here on checking coils and I think there may also be some info on checking the ignition module. You might want to think about getting a good used ignition module from a junkyard, or at least tracking one down. You need to be checking the grounds on yours.

The coil guidance will tell how to use an ohmmeter to measure resistance across each of the coils, and how to check coils for shorts. The ig module guidance IIRC basically says to remove, clean the ground plane, coat with dielectric grease and reinstall with good coils and good wires. You also need an ohmmeter to check the wires.

Sounds like somebody with this car had a bad wire or 2, and popped on a new set after the bad wire fried one or more coils. I could be wrong. Only way out of this hole is diagnostics. Part swapping on guesses probably wont' work well.

then it will be back to the car's OBD> First thing to do - clear all the codes and see which come back (repeat the condition).

Looks like I've got some work ahead of me. And the plug wires were replaced in the process of fixing the ignition problem, so they aren't too old and everything was running well since then until the misfire started.