Gen 3 misfiring/stumbling.

[Chorn]

My Gen 3 has had an intermittent problem for a while with misfiring/stumbling. The dealer took a look at it twice, and replaced all the spark plugs one time and the driver's side front O2 sensor the second time. Over the winter, I replaced the ignition wires with AB Wires, and the coils with Screaming Demon. The problem persists. It is hard to nail down precise conditions that cause it, but it does seem to get worse the hotter the engine gets. It was particularly bad today, and on one occasion when it was doing it while idling, I could smell rotten eggs, so I presume I was getting fuel but no spark.

The car judders badly when it happens, but then smooths out for a few minutes before it happens again. It happens in all gears, at any speed. The car just appears to run out of power when it happens; you can't accelerate.

At this point it has new wires and coils, recent (1,000 miles) plugs, and a new O2 sensor. I checked the plugs and injectors when changing the wires, and they appeared ok. I've cleaned the throttle body. No check engine light is being thrown. The car is totally stock aside from the new wires and coils.

I don't want to take it back to the dealer, they've already had two cracks at it, and it feels like throwing money away to take it back again. I'd appreciate any hints as to the next place to look, or if people solved similar problems. I searched the forum but didn't find anything yet.

Thanks,
Paul.

[98intrigue]

Hi Paul,

What's your exhaust setup? What sticks out like a sore thumb to me is if your plugs look good and your injectors are firing, have you checked your cats? The OEM cats are known to fail.

[bluesrt]

sounds to me like a fuel injector dropping in and out

[Rocket]

No codes are being thrown? Any mods to your Viper?

[kirkinsb]

I had a passenger side upper cat fall apart on the inside and plug the secondary cat. My car stumbled and simply ran like crap. Mostly when trying to accelerate. Removed my cats and all was immediately better than ever. I bet your cat/cats are failed. Rotten egg smell would make me think a failed cat as well. Only way to really tell is to remove the Cats and inspect. My secondary cat was about 85% plugged from debris from the first Cat failing.

[Resident Alien]

Another vote on plugged cat.

[bluesrt]

also, the longer this car runs bad, if the cats arnt already done for, they will be soon

[Chorn]

Thanks everyone! I appreciate the replies, and ideas. I'm not getting any codes at all. The only mods on the car are AB Wires and Screaming Demon coils, absolutely everything else is stock. Exhaust is totally stock. I put a multi-meter on the injectors when they were cold, and got relatively consistent readings between 12.0-12.7ohms. I'll try driving it for a bit to warm things up, and seeing how the injectors' resistance reads then. I was really hoping it was an injector or two, because they are easy to change. I don't think I can do cats at home, without a lift, but I haven't researched that yet. I wasn't thinking it could be cats, so thanks for that idea! I'll go do some reading about how to check/change those.

Paul.

[pony23]

I had the same problem and it was coil pack, but you weeded that out. I also vote for cats with that egg smell. You can do the exhaust without a lift. I did mine with a set of race ramps (front and rear) and it's not bad. The ramps get you 12" off the ground and that is plenty of room.

[Roddy]

Thanks everyone! I appreciate the replies, and ideas. I'm not getting any codes at all. The only mods on the car are AB Wires and Screaming Demon coils, absolutely everything else is stock. Exhaust is totally stock. I put a multi-meter on the injectors when they were cold, and got relatively consistent readings between 12.0-12.7ohms. I'll try driving it for a bit to warm things up, and seeing how the injectors' resistance reads then. I was really hoping it was an injector or two, because they are easy to change. I don't think I can do cats at home, without a lift, but I haven't researched that yet. I wasn't thinking it could be cats, so thanks for that idea! I'll go do some reading about how to check/change those.

Paul.

You can do the cats at home. Its not super hard, just jack up the entire side of the car and support with an axle stand front and rear, you can get some pretty good clearance. Then just take your time, I ordered replacement clamps for the exhaust too before I got into it.

May sound dumb, but check that your spark plug wires are seated and nicely connected on both ends. I know I had one that didn't want to "pop" into place.

[98intrigue]

If it's a blown cat, the temperature on that cat should be hotter than the good cat. You can always buy a cheap infrared thermometer gun and check the temps of the 2 cats and compare.

[AZTVR]

And if you need an experienced Viper tech to solve the issue, there is always Tator's Garage; although it might be a hassle getting the car there.

[Chorn]

Thanks again! Good idea on the infrared thermometer, I do have one of those. I'll try pulling the bodywork and driving the car to warm it up, that'll let me check the injectors while hot too, while I check the cat temps. Then I'll know my path forwards. I'll investigate some performance cats to replace the stock ones if needed, maybe even an exhaust, to at least make all of this worth it!

Paul.

[Chorn]

I've been out of town, but finally I am making progress. I pulled the injectors and had them cleaned, no problems there. The worst one was at 75.5cc, now all are back to 78cc, no spray pattern problems.

I pulled the sills off and took the car for a run. When I got back, the passenger side front cat was running about 200F warmer than the driver side. Both rear cats were the same, running at about 410F. So I think that is an indication that the front passenger cat is knackered.

A blind sniff test of both pipes from the wife resulted in a judgement that the driver's side exhaust exit smells worse than the passenger side. So it all seems to be pointing to that passenger side cat.

I put it up on the ramps and once it's cooled off I will start pulling the cats out. Hopefully a new set of cats will cure the problem, although I can't help thinking that something else must have caused the cat to fail. I didn't think cats spontaneously fail too often, but maybe I'm naive.

[AZTVR]

Hopefully a new set of cats will cure the problem, although I can't help thinking that something else must have caused the cat to fail. I didn't think cats spontaneously fail too often, but maybe I'm naive.

I'd agree with you. The OE cats are supposed to last 100000 miles. However, with all of the other things that were changed before you identified that cat issue, perhaps you also fixed the cause.

Anyway, a good time to consider Hi-flow cats. I'd recommend talking to JonB about the options for the way you use the car.

[jvm728]

You can do the cats at home. Its not super hard, just jack up the entire side of the car and support with an axle stand front and rear, you can get some pretty good clearance. Then just take your time, I ordered replacement clamps for the exhaust too before I got into it.

May sound dumb, but check that your spark plug wires are seated and nicely connected on both ends. I know I had one that didn't want to "pop" into place.

My installer that did my headers thought I had a bad cylinder because I had misfires. Turned out to be this. Easy fix. I moved coil packs around and the problem followed. Ended up being the wire not seated all the way. Took me into limp mode often

[speedtactics]

Cats for sure, incase no one thought of that yet.