Testing for a plugged, clogged, restricted exhaust, converter

2003 Impala 3400 V-6. Using scan data to verify proper fuel delivery. How to perform an exhaust backpressure test.

Category:

Autos & Vehicles

Tags:

• plugged exhaust
• catalytic converter test
• how-to
• low power
• restricted exhaust
• clogged exhaust
• backpressure testing

[CHIBA280CRV]

OKAY was the test after the cat replaced and were there any findings?

[ScannerDanner]

@CHIBA280CRV I was not involved in this car other than the diagnosis. The owner took the car elsewhere for the repair.

[spelunkerd]

Can you tell us the main things you look for when examining an engine that comes in with a clogged cat? Does alcohol in gas cause that problem? If the engine is running fine with no misfires, is there anything else that you need to check for?

[ScannerDanner]

@spelunkerd Not sure about the alcohol content, but after a repair, I make sure fuel trim #s look normal under different loads, also that there is no misfire. Truthfully on the Impala and Monte Carlo, I have seen so many melted cats. and found no cause when I am done. I think it may be in the programming of the fuel curve?. Here in the aftermarket, we just put a new cat in it (factory cat of course) and if everything looks good we let it go.

[altlandf]

Would it hurt to run the vehicle with the 2 front O2 sensors removed? I have a OBD II code reader will this find a problem with the fuel trim? What should I look for? Would too much ethanol in the fuel melt the cats? In Pa right now there should be no more than 10% of that garbage in the gas. The 97 Explorer is NOT a flex fuel vehicle. The more ethanol the hotter the combustion gets. Anyway excellant video. Could you not use a regular psi guage?

[ScannerDanner]

@altlandf Not for a short test drive and I have done that before to test for a plugged exhaust.

Your OBDII code reader should have some data PIDS you can look at, so if it does, then yes fuel trim can be seen with it. You are not using fuel trim to ID a plugged exhaust.

Yes you can use a regular psi gauge, in fact I made my own adapter with an old O2 sensor and I use my cheep vacuum /psi gauge

[CHIBA280CRV]

Well the guy who took it somewhere was not to bright ,having a great tech like you right there!! his mistake.....thanks S.D..

[spelunkerd]

Nice diagnostic walk through.

[ScannerDanner]

@buddiiee The restrictions in an exhaust system come from a melted and broken apart catalyst. The pieces of the cat can become trapped in the muffler too so at times the exhaust must be replaced from the cat. all the way back to the muffler. (including the cat. too of course).

After the repairs the system should also be checked for a cause of the cat. failure. Its never good to just replace the cat. without checking for a cause.

[ScannerDanner]

I didn't look at fuel trim closely for this one, but I know at idle and low speed they were in the normal range. Well at least normal enough for me to not look to closely. Also at WOT fuel trim is not relevant due to the O2 sensor being ignored and the system operating in open loop.