11hhrlt

So I wasn't sure where this inquiry should go...

I hooked up a vacuum gauge to my 2.2 (2011, 45k, auto) and it's acting funny. Vacuum needle stays steady and at the proper range until warm-up. Once I hit @ 170
degrees or so the needle starts jumping. It moves in a fairly steady rhythm within a few inches (of mercury) from center. The needle steadies under a load. The gauge is
hooked up straight from the intake manifold close to the engine. According to the charts I've read this could mean (possibly) a bad valve guide and/or some other valve
problem.

It's also possible this could be normal. I haven't noticed any strange noises or performance problems except lower than average gas mileage I seem to be getting.

Has anyone here done a read with a vacuum gauge on a later model 2.2? What year and what were the results? I'm thinking maybe the VVT may have something to do with
the jumpy needle.

Thanks in advance for any info you can provide.

843de

What is the reading you're getting, a "healthy" normally aspirated Ecotec 2.2/2.4 should be pulling between 17 and 18 inches of Mercury at idle. Although GM considers a range of 17-20 inches to be acceptable.

If it's pulling something like 15 inches at idle, then you'd begin to suspect a vacuum leak. Or in the worst case, valve guides or rings.

You'll have to refresh my memory here, but your HHR hasn't presented with any stored codes, is that correct?

The instability in the vacuum readings may be due to the ECM shifting from "Open Loop" to "Closed Loop" operation, but I need to dig into the FSM for my 2011 to be sure.

11hhrlt

843, thanks for responding. I'm perplexed. No codes showing but I'm not sure if there is anything "stored". I'll do that the next time I pass an Autozone.

The gauge needle is steady and right where it's supposed to be at idle, between 18 and 19 inches. But when the motor gets to operating temperature the needle starts to fluctuate wildly but in a rhythmic way. Again, maybe 2 inches of fluctuation both over and under the average (18/19).

I'm not aware of "open loop/closed loop" you mentioned. Can you explain?

Lucky

I maybe wrong but I seem to recall that vacuum gauge readings on newer engines are not as accurate as they use to be.

The newer engine in the effort to get better emissions and power out of a small package has the valve timing advanced where some valve overlap is normal.

Which would give you a slight bounce of the gauge.

Anyone else want to back me up on this one or am I just over thinking this.

843de

When the engine is first started, and rpm is above 600 rpm(approx), the system goes into 'Open Loop' operation. In 'Open Loop', the ECM will ignore the signal from the Oxygen (O2) sensor(s) and calculate the air/fuel ratio based on inputs from the coolant and MAF sensors, but mostly from a pre-programmed table contained in the ECM/PCM.

The system will stay in 'Open Loop' until the following conditions are met:

1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)

2. The coolant sensor is above a specified temperature (Approx 155-180 degrees Fahrenheit)

3. A specific amount of time has elapsed after starting the engine.

The specific values for the above conditions vary with different engines and are stored in the ECM/PCM. When these conditions are met, the system goes into 'Closed Loop' operation. In 'Closed Loop', the ECM will calculate the air/fuel ratio (injector on-time) based on the various sensors but mainly the O2 sensor(s). This allows the air/fuel ratio to stay very close to 14.7:1.

donbrew

It goes to closed loop within a few minutes of start up on my 2011 2.2L.

11hhrlt

Not sure how that relates to the gauge reading (needle fluctuation). Here's an example of what I'm seeing. Scroll to the bottom of the page to view.
Click on "scenario 8":

http://www.secondchancegarage.com/public/186.cfm

It would be most helpful if there was something I could compare my 2011 2.2 with. Has anyone put theirs on a vacuum gauge?

843de

If you can stand a few days wait, I'll be game and hook up my 2011 to a vacuum gauge this coming weekend.

Sad to say, but the vacuum gauge is going the way of bias ply tires, old tech in a high tech world.

11hhrlt

Sure! If you don't mind, that would be great. No rush. I can wait.

Yes, ye old vacuum gauge. A fine tool for the mechanical components - what's left of them.

843de

Almost consigned to the toolbox drawer of history, like dwell meters, point files, and carb synchronizers.