# The sensitivity of the modern vehicle



## Drachenfire (Jun 6, 2017)

One of the headlight bulbs on my '15 Silverado blew this morning.

To change them requires removing the airbox to get to the lamp. As I was putting everything back together my neighbor came by to chat.

I finished putting everything back together and did a final checked of the lights to make sure they both worked properly. I started up the truck to park it in it's customary. As soon as I press the accelerator, the engine hesitated badly. I tries again and the same thing happened. 

I figured something came loose.

I shut it down, popped the hood and re-seated the plug to the MAF sensor as aside from the light sockets, that was the only thing I unplugged. It was at this point I realized that in my distraction with the neighbor, I missed connecting the air hose between the airbox and the throttle body. Reconnected the hose, cranked up the engine and it was again purring like a kitten.

It is incredible how just a simple disconnected air hose can cause such a detriment to the engine's operation.

Just an FYI in case anyone was wondering, the bulbs I had in were Sylvania H11 XtraVision and have had them in three and a half years.


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## Windows on Wash (Aug 30, 2011)

Not sure a small vacuum leak would create that level of hesitation, but perhaps. If it wasn't throwing and SES light, that must have been it, but we don't see them stumble that hard over a vacuum leak not under load. Once you mash the gas, the car is under zero vacuum and depending on the size of the hose, there isn't that much air flowing through it.


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## SeniorSitizen (Sep 10, 2012)

That's been a test for mechanics shortly after the steam engine was being set aside and the internal combustion was developed. It seems these modern engines are real sensitive to the air/fuel ratio.:biggrin2:


The test was to drill a small hole in the bottom of the intake manifold ( out of site ) at a location it would affect a cylinder or sometimes 2 cylinders and the mechanic was required to find the culprit. Pass the test -- you're hired -- fail the test, next application please.:vs_laugh: Ole Henry had um standing in line a 1/4 mile long applying.


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## Brainbucket (Mar 30, 2015)

The MAF wasn't registering the air that wasn't moving through the hose when the hose was off.:vs_cool:


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## BigJim (Sep 2, 2008)

SeniorSitizen said:


> That's been a test for mechanics shortly after the steam engine was being set aside and the internal combustion was developed. It seems these modern engines are real sensitive to the air/fuel ratio.:biggrin2:
> 
> 
> The test was to drill a small hole in the bottom of the intake manifold ( out of site ) at a location it would affect a cylinder or sometimes 2 cylinders and the mechanic was required to find the culprit. Pass the test -- you're hired -- fail the test, next application please.:vs_laugh: Ole Henry had um standing in line a 1/4 mile long applying.


Sensitive is right, an extremely small pin hole of a vacuum leak will reek havoc on some of these cars now days, it sure did on our 2008 SE R Spec V Nissan. I like to have never found that leak. A very small exhaust leak will really mess these new cars up big time also.

Right now I have a code of a single misfire on one cylinder. I know it is a single misfire because the code will clear itself, then later it will do it again.

Finding an exhaust leak is pretty easy, but an extremely small pin hole vacuum leak is pretty tough.


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## raylo32 (Nov 25, 2006)

Similar thing happened to me after I swapped the cam in my old Camaro. I started it up the first time and it stumbled badly ran very very rough. I thought I messed something up. Turned out it was just that the edge of the air intake boot that connected up to the throttle body rolled over and was leaking. That thing was a bear to get on properly and I missed the fact that I hadn't gotten it on fully. So there was a disconnect between the air the MAF was seeing and the full amount of air getting into the engine. The ECU didn't like that. Not at all. I straightened that out and I was off to the races.


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## chandler48 (Jun 5, 2017)

Diesels aren't that picky, but you leave off the turbo hose, it won't pull your hat off in a strong wind. Turbo is passive energy, but it does most of the work of air flow.


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## Drachenfire (Jun 6, 2017)

Makes you wonder how many people have gotten taken to the cleaners by an unscrupulous mechanic over a simple air leak.


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## chandler48 (Jun 5, 2017)

You're right. I usually attempt to find small pinhole vacuum leaks using short spurts of ether near hoses to try and locate them. The engine will rev slightly when it sucks ether in.

Edit: That's for gassers. Diesels are positive pressure engines.


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