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Another journey you can follow advise me on if you like
Since buying the car it has gone from running too rich (P0172) to running too lean (P0171). It seemed to stop being too rich after filters + oil change.
Now the engine light comes and goes with P0172 - running too lean.
Soo... where to start? You might have noted, that I have another thread where I am chasing down a leak. Some of the questionable items in that thread are related to oil breather/separator/pipe components.
Basically.. the components in the picture below, I think I will need to replace... And these are all involved in creating "vacuum", right?
Also, the second picture is from my car, and the pipe (as shown in pic 1 also) is wrapped with some kind of tape.. This is suspect I think and needs replacing.
What do people think.. how does one go about detecting a vacuum leak?
The new parts shown in the first picture do not create the vacuum - they just route the vacuum from the source to the destination in the engine.
If you have a scan tool (presumably you do not), you can check the short term fuel trim at idle and at a higher RPM to see if there is a marked difference. If the short term fuel trim doesn't change much, there is likely no vacuum leak.Using a spray of carb cleaner, WD40, propane, (most any flammable fluid) on the intake side of the engine along one of the vacuum paths will detect the leak point. When the RPM goes up, you have found the leak. . Or you can smoke (with an auto smoke creating and pumping machine) the intake to see where the smoke leaks out. Probably other options also. Check out Youtube for videos of checking for vacuum leaks.
The new parts shown in the first picture do not create the vacuum - they just route the vacuum from the source to the destination in the engine.
If you have a scan tool (presumably you do not), you can check the short term fuel trim at idle and at a higher RPM to see if there is a marked difference. If the short term fuel trim doesn't change much, there is likely no vacuum leak.Using a spray of carb cleaner, WD40, propane, (most any flammable fluid) on the intake side of the engine along one of the vacuum paths will detect the leak point. When the RPM goes up, you have found the leak. . Or you can smoke (with an auto smoke creating and pumping machine) the intake to see where the smoke leaks out. Probably other options also. Check out Youtube for videos of checking for vacuum leaks.
Yea, I know it doesn't create the vacuum, but I believed that some of those parts are involved in the vacuum - and I plan on possibly replacing anyway, due an oil leak I have.
Ok, thanks for the update. I do have the iCarSoft MB V2.0 Scanner and have had a look this evening at the short trims etc.
From the scanner I was viewing some real time values - at idle the values were kinda jumping around -10 to -8% at first. Then when I rev the engine they jump to 0%.. then when I bring back to idle, the start jumping around again, down to -10% and sometimes up to +5%
I was also doing some other scanning and came across cylinder bank 1 running lean and cylinder bank 2 running rich - wtf lol.
Also, when I was idling at the traffic lights a bit after I had a rough idle, which happens some times.
To finish up - I cleared the codes using the scanner, now the light is gone. I don't expect that to fix the problem but at least I can see when it comes back and get updated codes. How bad is it to drive around like this? -- I do very few miles anyway (3500 miles per year)
Thanks a lot for your help so far on this
Conor
You will be able to see the fuel trims jumping around in this video I made:
Looks like a vacuum leak to me. I've seen STFT jump around like that on many different engines and engine types. Usually comes down to a vacuum leak of one form or another.
Yep, replace all of the PCV parts you have in your first picture. In fact, I'd recommend all of the pieces in this set. Two words of warning: the space behind the passenger head is very limited, so scope out access and make sure you have tools that'll fit. Second, I believe the previously mentioned oil separator is mounted with a reverse-threaded screw. I'm not positive, so look before you leap.
I replaced the same pieces you're looking at and I'm glad I did. There was a fair amount of dust in the engine where they mounted as well as the in the intake ducting. Very uncool. I also replaced the seal on the air cleaner assembly, part number 2720940080. It's upstream of where vacuum is maintained, but they shrink over time and will let unfiltered air in. I also replaced the 90° pipe going from the air cleaner to the throttle body since its seals were looking pretty suspect as well.
Beyond that, post back with any other vacuum leaks you find. My engine doesn't idle as smoothly as I like either (despite new engine mounts), so a minor vacuum leak somewhere is a possibility. I'll keep an eye on your other thread too.
Looks like a vacuum leak to me. I've seen STFT jump around like that on many different engines and engine types. Usually comes down to a vacuum leak of one form or another.
Fair enough.. i'm not that well versed in the trim values and values that come back through the reader in general (or well versed in anything really, for that matter!! - but i'm learning )
Originally Posted by atraudes
Yep, replace all of the PCV parts you have in your first picture. In fact, I'd recommend all of the pieces in this set. Two words of warning: the space behind the passenger head is very limited, so scope out access and make sure you have tools that'll fit. Second, I believe the previously mentioned oil separator is mounted with a reverse-threaded screw. I'm not positive, so look before you leap.
I replaced the same pieces you're looking at and I'm glad I did. There was a fair amount of dust in the engine where they mounted as well as the in the intake ducting. Very uncool. I also replaced the seal on the air cleaner assembly, part number 2720940080. It's upstream of where vacuum is maintained, but they shrink over time and will let unfiltered air in. I also replaced the 90° pipe going from the air cleaner to the throttle body since its seals were looking pretty suspect as well.
Beyond that, post back with any other vacuum leaks you find. My engine doesn't idle as smoothly as I like either (despite new engine mounts), so a minor vacuum leak somewhere is a possibility. I'll keep an eye on your other thread too.
Ok, i'm onto all that stuff now and i'll be sure to have a look at the air box stuff too, thanks.
Thanks for the heads on up the space limitations.. i've just been snagged on that while trying to replace the plugs (CGI engine) so postponed as they aren't really required right now.
Thanks for your advice and offer to keep an eye on the other thread too.
Do you have the CGI engine in yours or just a regular M272?
Engine vacuum is at it's highest when engine is idling. So that's short term trim check check #1. The raise engine RPM to say 2500 RPM steady for 30 seconds or so, enough time for the short term trim to adjust, that's check #2. Don't just rev up the engine for this test. If the trims correct substantially, that means you very likely have a vacuum leak. Personally, I would use WD40 and spray along the suspected fitting tubing, gaskets, covers, etc and see if you can find the place where the engine runs smoother, that's where the vacuum leak is. You may THINK the leak is in a certain area, but keep an open mind and keep going until you really find the right spot. Could be anywhere there is vacuum.
Lots of You tube videos on how to do this. My favorite is by South Main Auto.
Engine vacuum is at it's highest when engine is idling. So that's short term trim check check #1. The raise engine RPM to say 2500 RPM steady for 30 seconds or so, enough time for the short term trim to adjust, that's check #2. Don't just rev up the engine for this test. If the trims correct substantially, that means you very likely have a vacuum leak. Personally, I would use WD40 and spray along the suspected fitting tubing, gaskets, covers, etc and see if you can find the place where the engine runs smoother, that's where the vacuum leak is. You may THINK the leak is in a certain area, but keep an open mind and keep going until you really find the right spot. Could be anywhere there is vacuum.
Lots of You tube videos on how to do this. My favorite is by South Main Auto.
Thank you!
Just to be clear, once the flammable engine is pulled in and hits the combustion chambers the engine will run smoother? i.e. Rev a bit higher? I read elsewhere that the flammable liquid gives a jump in RPM due to extra combustion. I'm just double checking.
Yes. Vacuum leak means too much air is pulled in compared to amount of fuel. The extra fuel (WD40, etc) sprayed on the leak makes the engine smooth out (air/fuel mixture closer to shat it's supposed to be) and RPM will rise because of that.
I'm going to by some "cold start" starting fluid.. as I am trying to narrow down some oil leaks in the engine also, and don't want adding any further oil, just right now.
That said, when everything is back rosy, I will be giving the car a good clean over and spray with WD-40.. it's just timing
Do you have the CGI engine in yours or just a regular M272?
The regular M272.
Fair word of warning: be careful when spraying anything flammable around a running (or even just hot) engine. There are a number of ways that it could light up in your face, like hitting hot exhaust headers. Keep the can at arm's length as much as possible and be mindful about how much you're spraying. Keep things like a blanket and/or fire extinguisher nearby.
Fair word of warning: be careful when spraying anything flammable around a running (or even just hot) engine. There are a number of ways that it could light up in your face, like hitting hot exhaust headers. Keep the can at arm's length as much as possible and be mindful about how much you're spraying. Keep things like a blanket and/or fire extinguisher nearby.
Good warning. I think when I go at this, I will do it in stages. I won't empty the can within five minutes. I'll start at one section and give a break before moving on.. that should allow for evaporation/dispersion of fluid.
Good warning. I think when I go at this, I will do it in stages. I won't empty the can within five minutes. I'll start at one section and give a break before moving on.. that should allow for evaporation/dispersion of fluid.
Excellent idea.
Originally Posted by conor1n
The next thing is to figure out the vacuum components.. where does the vacuum begin and end?
Vacuum will be present anywhere between the throttle body's butterfly valve and the intake valves. So, inside of the intake manifold, primarily. Anything that connects to the intake manifold is a potential leak point. Anything upstream of the throttle body (intake ducting, air filters, MAF sensor, etc. won't have vacuum.
Vacuum is generated by the suck stage of the 4-stroke engine, where the piston is receding and drawing an air/fuel mixture into the combustion chamber. Because the butterfly valve on the throttle body is closed, the piston is unable to freely suck in air, creating a vacuum. When the throttle body is wide open, the vacuum is very slight since air is moving freely. The reason vacuum leaks are a problem is that the only air that's supposed to enter the combustion chamber has gone through the air filters and has been measured by the mass airflow sensor. If you have a leak allowing unmetered (unfiltered) air in, then too much air will be present in the combustion chamber, resulting in a lean burn (not enough fuel). The O2 sensors detect that the ratio is off consistently and throw the code you're seeing.
Maybe more info than you were looking for, but it's better to have too much.
Vacuum will be present anywhere between the throttle body's butterfly valve and the intake valves. So, inside of the intake manifold, primarily. Anything that connects to the intake manifold is a potential leak point. Anything upstream of the throttle body (intake ducting, air filters, MAF sensor, etc. won't have vacuum.
Vacuum is generated by the suck stage of the 4-stroke engine, where the piston is receding and drawing an air/fuel mixture into the combustion chamber. Because the butterfly valve on the throttle body is closed, the piston is unable to freely suck in air, creating a vacuum. When the throttle body is wide open, the vacuum is very slight since air is moving freely. The reason vacuum leaks are a problem is that the only air that's supposed to enter the combustion chamber has gone through the air filters and has been measured by the mass airflow sensor. If you have a leak allowing unmetered (unfiltered) air in, then too much air will be present in the combustion chamber, resulting in a lean burn (not enough fuel). The O2 sensors detect that the ratio is off consistently and throw the code you're seeing.
Maybe more info than you were looking for, but it's better to have too much.
That's perfect! The more information the better. I have just ordered The Automotive Handbook from Bosch, to get a full detail of how it all works. For me the theory is just as important as DIY'ing to just get stuff done.
It is normal for fuel trims to bounce around a bit. -10 is too far though. One would expect -5% to +5%. Simply refers to how much fuel it needs to add or remove from the base fuel map in order to stay at the desired ratio. 14.7:1 in the case of gasoline/petrol. Pay attention to the system status for each bank. CL (closed loop) means the computer is actively adjusting fuel from base fuel map to reach optimum ratio. OL (open loop) is when it is not adjusting from the base fuel map so the trims going to 0% is by design. Open loop is generally used during med-heavy acceleration (or in your case blipping the throttle in park.) Fuel trims are really only useful when the data is taken while driving. Running lean but the car idles around -10% is odd. It is removing 10% fuel, the opposite of compensating for a lean condition.
I'd be more interested in what the temp sensors say. Engine coolant, and intake air temp. Make sure the air intake tubes from the radiator support to the air filter box are still connected. Also the back side of the filter box/housing is well seated and sealed to the throttle body. I have seen these motors get upset when they start sucking in hot air from the engine compartment instead of the outer ambient air. They run on a speed density system and as such are quite sensitive to temp deviations. (actual vs measured)
The PCV is a good place to start for vacuum leaks. Also the front side of the intake manifold has several vacuum actuators. They can either rupture the diaphragm or the lines leak. The actuators control tumble valves and adjustable intake runners. Look to see if the links are broken or popped off. They can also cause wonky behavior. I will attach a picture of the front side of the manifold.
I have found the "spray it down with something flammable" is the most reliable method. When you hit the leak the RPMs will perk up.
PS: how do i make it smaller? I tried to reduce the size by 50% in MS editor but appears to just resize back up when attached.
Last edited by Spazm.Xylam; Nov 10, 2019 at 02:46 PM.
Reason: add additional info
I will check all those items. In the mean time you can see that I think I have found the vacuum leak. It looks like it was the area which was bandaged up. I also thought I could hear a hissing sound. The peculiar thing is that when the engine consumed the fuel, I didn't notice the RPM increase.. it was more like the engine got bogged down and thus decreased the RPM. Perhaps that is because I was spraying too much, or because the liquid is highly flammable. Who knows?
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