Solving Automotive Performance Issues
Using a Vacuum Gauge to Check Engine Performance
This is defiantly old school but as I’ve stated over and over in this article modern engines function in the same way they always have. Your engine is an air compressor. When it’s working correctly, it’s smooth and wonderful. If it’s not working correctly it can cause performance issues. A vacuum gauge is an inexpensive tool that can tell you quite a bit about how your engine is performing. If you hook a vacuum gauge up to an intake vacuum source, it can tell you a lot about your engine’s health. On a good running engine you should see engine vacuum between 17-21inhg at idle. The needle should hold steady and not shake about. If it’s low or shakes, then you have a performance issue somewhere. I don’t want to get into all the specifics of what problems are indicated by the vacuum readings you get, but I do want to make you aware of this tool and it’s capabilities. Even if you just hooked up the gauge and observed the reading you would have a pretty good idea of how your engine is performing. At some point I may do an article just on using a vacuum gauge. For now you can use this next test to see if you have and exhaust restriction. It’s a pretty cool test, I think you’ll like it.
Using a Vacuum Gauge to Find Exhaust Restrictions
As long as we’re on the topic of engine mechanicals, let’s talk about the effects of a restricted exhaust. Imagine being able to breathe in but not out. It wouldn’t be long before you pass out cold. The same thing can happen to your engine. If you have a restricted exhaust due to a catalytic converter failure, damage to the pipes themselves, or a restricted muffler, your engine will be sluggish and underpowered. Surprisingly, testing for this isn’t that difficult. All you need is a trusty vacuum gauge. To use a vacuum gauge to find an exhaust restriction, you first need to find a place on your intake where you can hook the gauge up. You’re looking for an intake vacuum source. This would be a source that has high vacuum at idle. Look for a line connecting somewhere after the throttle body. Pull it off while the engine is running. If you feel vacuum there, that’s where you want to hook up. On a good-running engine, intake vacuum should be between 17 to 21 INHG. (That’s inches of mercury for those of you who are curious.) Vacuum is also measured in Bar, but for this article we’re going to use INHG.
The needle on the gauges should also hold steady and not bounce around. If it does, this might indicate a mechanical issue with the engine. Also, intake vacuum is highest at idle and drops off to zero the closer you get to wide open throttle (WOT). With the engine running, take your first reading. Raise the RPM to about 2000 or 2500 and watch the gauge. If you have an exhaust restriction, you’ll begin to notice that vacuum will slowly drop off over time, and it might be harder to maintain the RPM. If the vacuum remains the same, then you don’t have a restriction and you can move on to other tests. Here’s a video showing the test in action.
Catalytic Converter Problems
If you suspect your catalytic converter is bad, or you have a P0420, there is an easy test to check your catalytic converter’s operation. You first need to get your hands on an infrared thermometer or a thermocouple. Basically, you need something that can accurately measure temperatures up to 1,200º F.
When a catalytic converter is working properly, it will be 100º F hotter at the outlet than it is at the inlet. First, make sure the engine is up to operating temperature. Then run the engine at about 2,000 to 2,500 RPM. Take the temperature readings at the front and rear of the catalytic converter. You should see an outlet temp that’s 100º F hotter than the inlet temp. If you don’t, the catalytic converter is bad and should be replaced.
I’ve heard that you can sometimes repair a bad converter, but I have yet to try any of those methods. Jury’s still out on that one. I mention this because catalytic converters are often quite expensive. That’s because they contain platinum, and platinum in their substrate. These are precious metals and are expensive. The expense of a new converter often holds people back from repairing the issue. If you live in a place where there is emissions testing, you will have to deal with it at some point.
I’m going to once again touch on aftermarket parts here. There are some universal catalytic converters out there that you can use as a replacement. Know that sometimes these won’t work and will still set a P0420 right out of the box. So if you’re faced with having to replace your catalytic converter, be sure to use a quality part for best results, OE (Original Equipment) if you can afford it. Here’s a video demonstrating the converter test.
Video Title: Solving Automotive Idle Problems – EricTheCarGuy Video Description: In this Article, Solving Automotive Performance Issues, Eric looks at what can be the cause of Solving Automotive Performance Issues with your vehicle .Thumbnail: http://www.ericthecarguy.com/images/faq_buttons/Large_FAQ_Images/Performance-and-Driveability-icon-large.png
13 thoughts on “Solving Automotive Performance Issues”
Giovanni Alfonso
November 3, 2022 at 1:19 pm
Good afternoon Eric , I have a 2007 ford expedition EL Eddie Baur. I have codes P0172,P0175. I have spent a lot of money changing parts. I have changes everything that I can think of when coming to a car running rich. And the car is still running rich i don’t know what else to do. I have changes o2 sensors all of them, fuel filter, fuel pump, spark plugs, injectors, purge valve, MAF sensor ECT sensor both Catalytic converters. Can you please help me. Oh and also took my computer to get looked at and they told me is fine.
Iliya
July 18, 2022 at 6:57 am
Love your videos Eric 🙂 I have a Suzuki alto 2011, and in the last
3 years ,sometime, randomly, especially (but not only) in the first 5 -10 minutes of its operation, the viechle stalls when I press the clutch pedal during ride. I start the engine immediately back on without any problem. It might occur
1 to 4 times during those 10 minutes, and then mostly it keeps driving without any problem after that (it might not stall at all in the first place). A side note is that it happens more often during winter. The OBD scanner reveals nothing and no other obvious sign appears (a very rare ESP light might appears but I don’t think it relates to the mentioned problem), but I suspect that its about a dirty throttle body, and maybe a simple clean up will hopefully solve the problem. But before I do that (its a little complicated in my car) I would like to hear your thoughts about it… again, I really appreciate your work and hope to hear your answer or somebody’s else in the audience 🙂
ישראל נוישטט
August 3, 2022 at 4:51 pm
hi how did you rezolve the cars problem
I have it too in my suzuki car
Ralph Bowes
February 21, 2022 at 3:37 pm
Hi Eric,
I love your channel. I have a 2007 Ford F150 with a 5.4l. It will barely move. Max speed maybe 5 mph. It runs good in park and you can rev the engine but as soon as you put it in gear you have no power. The rpms do not go up past 1500. I ran codes and I got p0300, p0305, p0306, p0308, p0316 and p0420. Could you please give me an idea about what is going on or possibly where to start? Thank you have a great day!
Northshore
March 31, 2022 at 5:02 pm
Plugged cat
Eli
January 24, 2022 at 5:33 am
Hi Eric,
I own a 2003 Acura CL Type-S with a 6-speed manual(195k miles). I have a a random misfire on an assortment of cylinders for some time now. I have replaced/serviced the following: the spark plugs, coils, valve adjustment, valve cover gaskets, plenum gasket, EGR port cleaning, EGR Gasket replacement, and throttle body gasket, and checked for vacuum leaks. I was wondering where the next step would be to try to resolve this issue. There is a little electrical whine when I accelerate (maybe bad ground(?)) and I was curious if you think that could trigger that many misfires. Any direction or advice is much appreciated. Thank you and have a good day
Eddie
April 25, 2022 at 11:47 pm
Hi Eric I in need if help if u would please contact me back i have a 98 honda civic runs good motor warms uo the. It hesitates an bearly moves let it set an cool down works fine
Gabe
March 31, 2021 at 5:29 am
Hi Eric. I have a 2011 Dodge Caliber Mainstreet. I have code p0301. It seems that my misfire is turning out to be a serious issue and I need some insight. I’m currently checking all the small things that I know of before replacing parts for cylinder 1. All spark plugs and coils are good. Fuel injector is not clogged, it is working properly and ohms match the manual. I looked at the intake valves through fuel injector port, they are clean. I do have carbon build up in the combustion chamber. Compression test performed on all cylinders shows high readings of 200 to 219 psi (Are high readings due to carbon build up?). Another thing I read is that sticky valves or bent valves could be an issue and I could check doing a paper test. The exhaust is making the paper pulsate rapidly and is being sucked into the pipe. Also I took the oil cap off while the engine was running and there is a loud chopper like sound with a lot of air being forced out of the oil port. I couldn’t find anything that explained what that means. I did find articles talking about blowby gasses but all said I should see white smoke. There is no white smoke coming out. Is my issue still classified as blowby gasses or do I have a different issue?
Jessica Gregory
November 20, 2020 at 3:59 pm
Dear Eric the car guy, I have a 2004 Toyota camry 4 cylinder so my spark plug blew out of my engine it was replaced 4 months prior to these. Should I try to fix it or do you think I should get a new engine? If thats the case ill sell it can’t afford a new engine.
Roberto
March 30, 2022 at 7:57 pm
Erick i have a 2008 Honda Accord that won’t go past 3000 rpms. Sometimes when cold it will trow misfire codes p301,!p302 and p302 or p0300 i eease them and codes won’t come back.
Jared
October 18, 2020 at 11:51 am
Hello @EricTheCarGuy,I am Jared from Kenya,I changed the Engine for my Subaru Lagacy,from then I got a real big problem…whenever I step on the gas,the car strain and just goes off,but as I disconnect the MAP sensor it pick to it’s maximum power.What might be the problem?.
Kelvin Exum
June 10, 2020 at 10:14 am
I have a 98 Lexus gs400. On the most part, my car runs quiet and smooth. Other times, it will have a bad idle. So bad at times that the check light will flash but later stay steady. I have gotten it checked to find out it is misfiring on one side of the engine.
Jim srack
July 16, 2020 at 5:22 pm
Hello Eric, your the Man. Ok here’s the situation Honda Element 2003 replaced Vetec solenoid, screen was clean in old part. Thought it was resolved, however the surge came back even at a lesser rpm before the surge than previously. What I don’t get is if the screen is clean whats causing the surging. Thank you in advance for your response