Passenger cylinders not firing correctly, right cat glowing after 2 mins

[davidbr]

Hallo from Germany,

my 1997 Viper GTS gives me some headaches. I have it in an auto workshop right now to get a new exhaust installed with legal catalysts. After they installed everything, the Viper turned out to not run correctly on the passenger side cylinders. The cat on the passenger side glows after idling for just 2-3 min, so we think there is fuel burning in the catalyst. The driver side cat stays cold. The ignition works fine according to the workshop. They already changed both ignition coils, all spark plugs and cables. Compression is okay too, on all cylinders, they also checked rocker arms, valves and springs, and these parts seem to be okay too. As they're out of ideas right now, I will have the car delivered back to me in a few days to look for the problem myself. Apparently it is multiple cylinders not running correctly, so I guess there could be some kind of gas leak or the PCM is fried badly. Does anyone here have an advice for me where to look first?

Thank you very much

David

 

[Viper Specialty]

Check for fuel leaking into manifold, exhaust leaks, O2 sensor issues, plug wire incorrect routing. If nothing found, replace PCM. We do stock controllers if needed.

 

[kblake905]

Hallo from Germany,

my 1997 Viper GTS gives me some headaches. I have it in an auto workshop right now to get a new exhaust installed with legal catalysts. After they installed everything, the Viper turned out to not run correctly on the passenger side cylinders. The cat on the passenger side glows after idling for just 2-3 min, so we think there is fuel burning in the catalyst. The driver side cat stays cold. The ignition works fine according to the workshop. They already changed both ignition coils, all spark plugs and cables. Compression is okay too, on all cylinders, they also checked rocker arms, valves and springs, and these parts seem to be okay too. As they're out of ideas right now, I will have the car delivered back to me in a few days to look for the problem myself. Apparently it is multiple cylinders not running correctly, so I guess there could be some kind of gas leak or the PCM is fried badly. Does anyone here have an advice for me where to look first?

Thank you very much

David

Seems more like a plugged cat?

 

[davidbr]

Seems more like a plugged cat?

The cat is completely new, so that would be really surprising. It was parked in a collector's storage for eight years until I bought it in last winter, and I couldn't drive it so far either (it was straight piped with empty cats, just way too loud and everything but street-legal), so maybe there is some damage from just being unused.

Check for fuel leaking into manifold, exhaust leaks, O2 sensor issues, plug wire incorrect routing. If nothing found, replace PCM. We do stock controllers if needed.

I will do plug wires first and look for leaks, then maybe interchange the O2 sensors (or run it without?). With "manifold", do you mean the exhaust or the intake manifold? I know that the fuel lines are part of the intake manifold, is there any chance to reliably check them without taking the manifold out?
I hope that the PCM is okay, if not I'll get in touch, thank you.

 

[daveg]

My first thought was Plugged Cat. Did the car run normal before bringing it there? Did they re-use O2's?

 

[davidbr]

I cannot really say whether or not it ran normal before. I only drove the Viper about 20 km after I bought it, and as it was completely straight piped, it was just so loud that I didn't notice anything. They reused the O2's.

 

[daveg]

Same same amount of Exhaust exiting the Passengers side VS drivers side?

 

[davidbr]

No, it seems to be less on the passenger side or more specifically, it is not the same "regular" flow on the passenger side as on the drivers side.

 

[daveg]

Factory Cats?

 

[davidbr]

Aftermarket HJS cats.

 

[Viper Specialty]

The cat is completely new, so that would be really surprising. It was parked in a collector's storage for eight years until I bought it in last winter, and I couldn't drive it so far either (it was straight piped with empty cats, just way too loud and everything but street-legal), so maybe there is some damage from just being unused.


I will do plug wires first and look for leaks, then maybe interchange the O2 sensors (or run it without?). With "manifold", do you mean the exhaust or the intake manifold? I know that the fuel lines are part of the intake manifold, is there any chance to reliably check them without taking the manifold out?
I hope that the PCM is okay, if not I'll get in touch, thank you.

Fuel leaks into Intake manifold. Exhaust leaks in exhaust manifold. Either of them can cause this.

Note: Once a converter overheats, its usually near instantly dead. Dont think just because its new it cannot be bad. Once the core melts, backpressure increases, O2's dump fuel, and the condition runs away.

Head/Cam cars w/cats are notorious for this.

 

[davidbr]

First of all thanks to all of you for your ideas.

Note: Once a converter overheats, its usually near instantly dead. Dont think just because its new it cannot be bad. Once the core melts, backpressure increases, O2's dump fuel, and the condition runs away.

Head/Cam cars w/cats are notorious for this.

Okay, I did not know this. I hope it is still okay. The engine should be stock (at least it was sold to me as stock lol).

Once I got it back in my garage, I will start with checking all the ignition wiring and contacts and have a look at the seats of the injectors. Before I start the car again.
If I do not find an error there, then I guess it would be best to take off the right cat, put on some pipe or something, and see what happens when it runs. Probably should also use an OBD scanner or an oscilloscope to see what happens with fuel and O2 sensors with and without cat. I will post an update here once I had time to check things.

That will cost a few nerves.

 

[Viper Specialty]

First of all thanks to all of you for your ideas.



Okay, I did not know this. I hope it is still okay. The engine should be stock (at least it was sold to me as stock lol).

Once I got it back in my garage, I will start with checking all the ignition wiring and contacts and have a look at the seats of the injectors. Before I start the car again.
If I do not find an error there, then I guess it would be best to take off the right cat, put on some pipe or something, and see what happens when it runs. Probably should also use an OBD scanner or an oscilloscope to see what happens with fuel and O2 sensors with and without cat. I will post an update here once I had time to check things.

That will cost a few nerves.

Correct.

Best to troubleshoot this without the cat installed.

in a stock application, this can nearly always be tracked to a few simple things:

1. Misfire due to ignition fault.

2. Fuel leak into cylinder. via cracked manifold or bad injector.

3. Exhaust leak / cracked manifold. O2 introduction causes fuel trims to go wild, and mix of oxygen/extra fuel melts down converter.

4. Bad O2 sensor/wiring issue on fuel/sensor/ignition.

On an otherwise healthy stock engine, I doubt its going to be related to internal damage, tuning issues, or otherwise.

 

[Goggles Pizano]

If cat is not hot, then it is not working.

Fuel trims should have been looked at first.

Start first with checking all the cables and connectors to O2s, spark wires are in correct locations and any wires/connectors they removed to do whatever they tried to do to fix it.

 

[GTS Dean]

Be sure your plug wires are installed on the correct coil terminals. Many manuals are wrong.

 

[yzf1999]

Does anyone know if the factory 1997 manual is wrong?..I plan on changing plug wires eventually and was gonna use the manuals routing.

 

[Viper Specialty]

Does anyone know if the factory 1997 manual is wrong?..I plan on changing plug wires eventually and was gonna use the manuals routing.

I believe it is. Go by what the coils say, not the manual.

 

[Steve-Indy]

As Dan says, go by the numbers marked on the coil packs...period.
Use a mechanic's mirror when making the connections of the plug wires to the couple packs.

The diagrams printed in the Viper Service Manuals have been a source of misinterpretation since the very beginning.

 

[davidbr]

So, today I got the Viper back at my place and had a first chance to have a look at the engine.

- The new coils and spark plug wires were installed correctly, just like in the photos from GTS Dean (thanks!).
- The injector wiring seems to be correct too, same colors as in the manual.

I am still waiting for the OBD diagnosis tool that I ordered, couldn't look at actual ignition/fuel/O2 values so far. The workshop looked into the cylinders and said that all look the same on both banks, so I think the error is more likely to be in the exhaust manifold (but I could be completely wrong about that).

As I wanted to go on, I took off the heat shielding from the right exhaust manifold to have a first look. It's a bit burnt in the lower middle, looks a little weird to me, but could be absolutely normal too. It's a cast exhaust manifold. I'll test wiring connections tomorrow and see if I can spot any cracks or leaks on the exhaust manifold.

 

[Goggles Pizano]

Get a IR thermometer. That way you can hit each cylinder exhaust pipe and the cat too to get temperature reading.

 

[davidbr]

Get a IR thermometer. That way you can hit each cylinder exhaust pipe and the cat too to get temperature reading.

I decided to already pull the manifold because it looked odd to me. The pipes of cylinders 6 and 8 are in a dark grey (like annealing colors?), different to the others.
The manifold seems to be okay, I have to check for straightness, maybe have it grinded and then put it back in with new gaskets and a new O2 sensor.

 

[davidbr]

The exhaust manifold is pretty much straight. I couldn't find cracks by looking. I closed all openings and put it under some pressure with a bicycle pump (lol), couldn't find any leaks. I'm now waiting for gaskets to put it back in.
The injection valves and the Schrader(?) valve were still under pressure, even though the car did not run for about two weeks now. So I guess the gas distribution in the intake manifold is also okay.

But now I think I found something:
I measured electrical resistance on all injection valves. All have about 11.9 ohms, so okay.
I measured electrical resistance between general ground and all ground wires on the injection valves, all ten ground wires have about 6 ohms to general ground.
Then I went on and measured electrical resistances between ground wire and control wire on all injection valve plugs. On the left bank all five electrical resistances are infinite. On the right bank all five electrical resistances are at about 8.5 Megaohms. So there could be something off with either the wiring or the ECU.

 

[GTS Dean]

I can't say whether those are normal readings on the coil packs, but remember - one pole of each coil has a different spark energy because of a longer ground path than the other and that imbalance follows the firing order, not top or bottom of the coil. I think Dan Lesser put together a nice diagram to illustrate the issue.

 

[davidbr]

I did the electrical resistance measurements on the injection wiring, not on the ignition wiring. Sorry if my posts aren't correct or easy to understand, English is my second language and I sometimes struggle with grammar and misuse words, especially when it is for the technical terms.

So on the injection wiring, injectors (is it "injector" or "injection valve"?) 1, 3, 5, 7 and 9 had infinite electrical resistance between their respective wires, and injectors 2, 4, 6, 8, 10 had 8.5 Megaohm each. I disconnected the three plugs from the PCM are did the same measurements directly on the 10 pins, and there all 10 pins each have about 8.3 Megaohm against ground. Leaves me a bit head-scratching why I didn't get the same values when I tried to measure the resistances right at the electrical plugs for the injectors. I'll go on with livedata once I have the gaskets and the exhaust manifold reinstalled.

 

[davidbr]

Wanted to give an update and say thanks again for the help everybody gave. The Viper is healthy again.

It took me quite a while to get gaskets for the exhaust manifold. Then turned out the workshop had damaged the seals on multiple injection valves as well as the threading of the fuel pressure measurement valve on the intake manifold ... took me some more weeks to repair that all.

Live data did not help me much at first. There was no O2 data available on the reader for the car, but fuel and ignition were a little off on the right side. No errors, even after multiple starts.

Then I measured resistance on the o2 sensor, and noticed that the heating circuit (white cables) basically was no circuit anymore, infinite resistance. I was unable to get an original o2 sensor in time here, so I bought a universal one from Bosch and put it in place instead. I was skeptical about that fixing the overall problem at first, because I would have thought that a damaged heating circuit on the sensor would lead to an error in the ECU immediately, but seems like I was wrong. Now the cat does not overheat anymore. Fuel data is still a little bit different from left to right, which probably is due to different sensors and different ages, but little. Temperature diff +15 °C from left (old sensor) to right (right sensor) at idle (basically 200 on the right, 185 on the left). Will watch it, perhaps add some temp sensors.

I wonder if somebody has done work on the ECU at some point, as no error code ever showed up. But I am unsure. Last two owners in Germany denied doing anything to the car. Who knows ...

Only problem left right now is winter. Looking forward to post an Autobahn video here in 2-3 months. Thanks again to everybody, great community!

 

[daveg]

Glad you got it sorted out. Last time I was on the Autobahn in Germany I was stuck in Traffic..
True Story.

 

[serafins]

Wanted to give an update and say thanks again for the help everybody gave. The Viper is healthy again.

It took me quite a while to get gaskets for the exhaust manifold. Then turned out the workshop had damaged the seals on multiple injection valves as well as the threading of the fuel pressure measurement valve on the intake manifold ... took me some more weeks to repair that all.

Live data did not help me much at first. There was no O2 data available on the reader for the car, but fuel and ignition were a little off on the right side. No errors, even after multiple starts.

Then I measured resistance on the o2 sensor, and noticed that the heating circuit (white cables) basically was no circuit anymore, infinite resistance. I was unable to get an original o2 sensor in time here, so I bought a universal one from Bosch and put it in place instead. I was skeptical about that fixing the overall problem at first, because I would have thought that a damaged heating circuit on the sensor would lead to an error in the ECU immediately, but seems like I was wrong. Now the cat does not overheat anymore. Fuel data is still a little bit different from left to right, which probably is due to different sensors and different ages, but little. Temperature diff +15 °C from left (old sensor) to right (right sensor) at idle (basically 200 on the right, 185 on the left). Will watch it, perhaps add some temp sensors.

I wonder if somebody has done work on the ECU at some point, as no error code ever showed up. But I am unsure. Last two owners in Germany denied doing anything to the car. Who knows ...

Only problem left right now is winter. Looking forward to post an Autobahn video here in 2-3 months. Thanks again to everybody, great community!

The cars run a pretty primitive malfunction detection system but being emissions related I'd think it should have registered. Maybe the export cars got a different program or computer.

They do recommend replacing O2 sensors in pairs for this very reason. I'd swap in 2 oem sensors when you have a chance or at least get another universal sensor and do the other side.