How To Diagnose Exhaust Restrictions -EricTheCarGuy

If you're experiencing poor performance, overheating, pinging, or having trouble getting up hills you might want to check to see if you have a restricted exhaust. An engine needs to breath which means that not only does it need to take in air but it also needs to get rid of the spent air, much like we do when we exhale. If it's not able to do that properly you'll experience all kinds of performance issues including lack of power. This video shows an easy non obtrusive way to check to see if you have an exhaust restriction using a vacuum gauge. A vacuum gauge can tell you a lot about how your engine is running including if you have a restricted exhaust. If you do find that you have a restriction you can confirm it by either dropping the exhaust at the manifold or removing an O2 sensor and taking it for a drive. If it runs better you likely have an exhaust restriction. Don't assume it's the catalytic converter though as I've seen mufflers and exhaust pipes cause restrictions as well. Here's a video on how to check your Catalytic Converter should you suspect it's bad.

Stay dirty

ETCG

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[RadiantFreeEnergyResearch]

I learn from every single one of your videos. I've never met a master mechanic that seeming effortlessly explain in simple non technical words- the complexities of the individual automobile parts- parts function and purpose- and diagnostic possibilities. As always- great video. Thank you Eric.

[thomasgoodman]

Eric, YOU ARE THE MAN!!!! 50 years experience and I learned something today. Had a Caravan with no power above idle. Idle vacuum was 22, dropped to 19-18 after a few seconds at 2000 rpm.

Also gotta say you are articulate and easy to understand.

[tommason]

This is just the tip I needed to find out whether catalytic converter is clogged up or not. Everybody else said I have to disassemble it to see it. This tip is a lifesaver. I have a manometer to measure the vacuum. Thanks a lot for the video!!!

[thecke]

I'd love to see more diagnostics videos like this. I really hate throwing parts and knowing stuff like this helps me and my wallet prevent that.

[TheBattlestorm]

Good video. I have even seen exhausts so restricted that the vac dropped down to almost zero at easy accel. Vac gauges are still one of my number one goto tools for performance issues.

[brianday]

I think you solved the problem with my CJ. I'll check it in the morning to be sure. I got an Error Code of "High Manifold Pressure". Makes sense now! Thanks Eric!

[AlexformerVWowner]

I wish I had watched this video so many sensors and hundreds of dollars ago. I had a lose in power, very rough idle at cold start up. I disconnected the o2 sensor and the problem went away. So off to the muffler shop I go. Thanks Eric.

[stevelopez]

Thanks man, i work at a shop and had a car with no check engine light on but would lose power up big hills only, no acceleration at 60 at 4000rpm,
Did this vacuum test and the vacuum doesn't drop to down at full throttle.
Removed b1s1 o2 sensor and the power returned. Sold the cat and rusted o2 sensors.
Completed monitors and the car passed smog. All is good now
:-)

[mechguy]

I hope he does a full video on how useful a vac gauge is and all the different things it can tell you about your engines health...

[southerner]

Great video for those of us with older, pre-computerized cars. A lot of videos about catalytic converters talk about throwing codes, which is no help on a carbureted engine with no ECM.

[ColdWarVet]

FYI Eric, on my sons 2001 Mazda 626, just did my test. I used a Vacuum brake bleeder from Harbor Freight and out it on an evap tube, it read ~20 inches but it was chattering back and forth at a rate like a bobble head on steroids. I was by myself so I reached over to the throttle body and turned the plate manually to give me about 2K, the vacuum dropped to under 15!!!! Wow took me a few minutes to watch your video and 1 minute to do this test and drink a beer while doing it. So no I'm so happy, I'll have another beer. BTY my problem is a rough idle that gets better once I get to higher revs, its my sons car so I don't know if its losing power as I don't drive it. I had done a few other things that improved the idle greatly but this is certainly the last problem...If you're wondering of you really help the average Joe out there, you do my friend, you do.

[Jayson]

Old video I know.. but this is the only video out there that explains exactly what you should be looking for on that vacuum meter! Thanks Eric!

And I'm not falling for no banana in the tailpipe trick. 😉

[knurlgnar]

yup. The multiple flame fronts causing pinging usually start from a hot point that gets hot enough from the compression and flame pressure rise to spontaneously ignite and start its own secondary flame front - maybe the spark plug, maybe a piece of carbon buildup. Retarding the ignition lowers peak pressures in the cylinder which reduces the chances that the pressure from spark or burning fuel will produce pressures high enough for the remaining unburnt fuel-air mix to 'detonate' all at once.

[FrancisMaxino]

Does that mean removing the oxygen sensor will fix the performance problem of a restricted exhaust rather than fix exhaust?

[dmoten]

Thanks eric!..this helped me with my sons 01 civic... unpluged the bank 1 o2 sensor..took it down the road..ran pefect..before it wouldnt go pass 20mph...Thanks again!

[lisab]

O lawd that banana poke was jus soo funni! Ok so here I am trying to figure out why I don't have any manifold vacuum. I found a PDF article that detailed the various symptoms found while using a vacuum gauge. A restricted/plugged exhaust just stood right out!

Just weeks before I encountered a stall and then a crank but no start, I had a new catalytic converter installed. Hooking up the vacuum gauge and fuel gauge after confirming spark, etc, I found a really good high fuel pressure but with a leak down and thus indicating a bad regulator. The vacuum gauge kind of ticked off of zero but nothing more. So at this point I isolate the PCV and the A/C-heating vac hoses and do a direct vac test. Still no vacuum!

Now I'm going nuts, scratching my balls and pulling my hair out!, I go online and find that great and simple PDF that after led me to watch your video.

Tomorrow, I will check the If I find a bloody banana or anything else in the tail pipe, I will surely do a war dance!

[dungeonhack]

Nice to see you back with a new video. You make the best auto repair vids out there. Was sad to see that you haven't be making any videos then went to ETCG1 and finally found out why. Be safe, Have fun and Stay dirty.

[knurlgnar]

Pinging is generally the result of multiple flame fronts colliding inside the combustion chamber and is not by itself a highly damaging condition. The knock sensors detect this and try to prevent the next stage which is highly damaging detonation, where the entire fuel charge ignites all at once without flame front propagation.

[TrueBlueEG]

Fecking great video, this demonstrates the value of simple hands on experience, scan tools will get you so far, but only if you understand the principles, a multimeter, compression gauge, vacuum gauge and some thinking can take you a long way.

[mikelehmen]

You make everything so simple to follow ! can't thank you enough Eric ! Keep up the great vids !