Large amount of white smoke coming from bottom of cat converter VR Caprice 5.0 V8

[vr84]

Hi guys,

I've had a small misfire for awhile and the car recently decided to only run smooth on LPG, I initially thought it was the airbox as it had a crack in it from a backfire, but today I built a new airbox with backfire valve and petrol running did not improve. I drove it around for about 30 minutes then came back, and popped the bonnet to find a huge amount of white smoke coming from under the car. I got under the car and seen it was coming directly from the bottom of the cat converter.

Now I am wondering would a broken cat cause running issues? Could it be the cat converter all along that made the car run rough? If so I guess I will need to take it to an exhaust shop first to get that sorted out, but if this isn't likely to cause rough engine running conditions, should I be looking elsewhere, such as the injectors to see if any are blocked.

Just to note as well, the white smoke was coming out regardless of whether the car was running on petrol or LPG, but there is considerably more smoke when running petrol, I guess that is to be expected with the nature of both fuels.

Any suggestions as to where I should begin, I had the injectors changed 10 months ago, so if it could be them I would be inclined to take the car back to them first before warranty runs out, otherwise if rough running is a symptom from a cracked / burnt out / damaged cat converter, then I will take the car direct to an exhaust shop for a stock replacement.

If anyone has recommendations as to where a good exhaust shop is in the western suburbs, I'm all ears too, I only know of one local to me called St Albans Exhaust, but have not been there in over 10 years. I'm not looking to upgrade the cat, just need a 100% stock replacement. Maybe a mechanic is better than an exhaust shop for stock replacement exhausts?

 

[BlackVXGTS]

I wouldn't have thought a leaking catalytic converter (as distinct from a blocked converter) would cause running issues since the cats are placed in the exhaust after the oxygen sensor. However, maybe the leakage is caused because the cat became blocked. Your best bet for a stock cat would be a used one from a wrecker.

 

[vr84]

Thanks, does seem most likely the cat became blocked, i don't see what else would cause so much smoke to emit from it. For the stock cat though I'd rather try and find a new or new replacement for it, unless it's a part that can't be sourced aftermarket, I prefer to stick to new parts, lasts longer and less chance of needing to do the job again twice.

 

[Not_An_Abba_Fan]

LPG runs hotter at the engine than petrol, cats have a tendency to melt the front and block up when running on gas. The back fire could have split the case so that's where the white smoke is coming from. If it's only running rough on petrol, then it would have to be an issue with the injectors or the supply line. Injectors don't take long to block up when running on LPG.

 

[vr84]

Cat was replaced for $350, couldn't visually see where the smoke was coming from or if anything was blocked, but the smoke has stopped since having a high flow cat installed. The exhaust guy said exactly what you said NAAF, except the backfire he believes probably pushed the heat in the cat beyond melt point, he thinks it is likely melted somewhere in the center and partially blocked. He said the stock cats are ceramic and prone to issues with non injected LPG systems, the new one is entirely metal based which can handle the extra heat.

Engine running rough on petrol is indeed unfortunately another issue, I've had ignition module, dizzy, coil, leads, plugs and injectors done recently, mechanic checked the ECU code and it was showing up as a failed right bank oxygen sensor, but the car cleared that status after logging it, I had noticed the check engine light coming on and off again randomly a few times, but it disappeared within about 5 - 10 seconds and only did it once a week, so didn't take much notice until now.

Mechanic has told me to keep using the car until the light comes on again, if it doesn't appear again within a week he will need to manually check the sensors, extra $$$ so hopefully the car logs the issue soon

 

[vr84]

Just to clarify for any future reference, there were a few issues on the car. The engine had a few burnt valves from which at least 1 of the cylinders wasn't firing, the injectors had started to block because the fuel filter wasn't replaced at the same time the ignition and fuel system was repaired two years earlier. I had the heads rebuilt and the fuel system flushed along with the injectors cleaned, new fuel lines and a new fuel filter.

Issue was likely the amount of LPG or Petrol being pushed through the exhaust due to the burnt valves, which then burnt out the cat converter. This also destroyed the right bank o2 sensor.

Everything has been sorted now, so hopefully now more issues