I bought a BF412 and some hose tonight and hooked it back up, reset my PCM, and went out for a cruise. No noticeable difference in driving (PCM compensates for it, so I didn't expect one), but the slight surge I had during idle went away. The IAC is more stable too.

 

This has to be one of the most misunderstood sytems on the LT1. I have seen Fred explain this so many times and in so many ways, I gave up counting. Fred, you really need to write this up one time and stick it ony your web page somewhere. Your fingers must be getting tired.

 

This thread got me thinking, so I went to check and see if I had oil going into the line connected to the TB, and I do. I then checked the PCV valve, and it rattled when I shook it. So , this means that I'm having excessive blowby, correct? How would I go about fixing this? I don't really have any drivability problems, or a big loss of power, but I remember doing a compression check on one of the cylinders, and while it was within spec, it was on the low side.

 

There is so much erroneous info in this post that it would take days to correct all the errors you made. Ryaskovic went a long way toward explaining where you are wrong. A complete misunderstanding of how the control system works, how the PCV system works and its purpose, and the concept of "holding the rings stable with vacuum"... all dead wrong.

NO. The MAF measures the "mass" (pounds) of air entering the engine. It does not tell the PCM whether "WOT exists or part throttle"..... the PCM relies totally on the TPS sensor and the MAP sensor for that info.

The PCM uses closed loop info from the O2 sensors to regulate A/F ratio (rich or lean). It does does not use info from the IAC to set A/F ratio. It can't do anything with the IAC except alter the idle speed. And TPS is used for a variety of purposes, including a determination of when to enter power enrichment mode and what the target A/F ratio should be, but all of this is totally unrelated to the PCV system, or the MAF sensor. All you have done is throw around a lot of terms to confuse people, and it has nothing to do with the subject we are discussing.

Now you are babbling.

The MAF measures (meters) the airflow entering the combustion process. It tells the PCM what the mass (pounds) of airflow is. The PCM uses this to determine the amount of fuel added to the combustion process. If the air for the PCV system passes through the TB, the MAF sensor has metered it, and the PCM added the fuel to burn it. If the air for the PCV system snuck in through a breather, or a leak in the intake manifold, the MAF doesn't know about it, the PCM doesn't know about it, and no fuel will be added to consume that air until the O2 sensors see it.

Trust me... just because the LT1 has 10.4-10.5:1 compression doesn't mean it needs vacuum to hold the rings in place. That is required on mega-motors, running low tension rings. And, if you spent enough time in the garage, you would understand that when the engine goes WOT, THERE IS NO VACUUM IN the intake system, so there is no vacuum in the PCV system. That is the point where you do need vacuum to hold down the rings in a racing motor with low tension rings, but not in a stocker.

The vacuum levels use in racing engine crankcases is on the order of 10-15"Hg. You can not generate that level of vacuum at WOT with a PCV system. You need a $600 vacuum pump. Do a little more research on the subject.... maybe even do a "search" and review a couple of the threads posted on "Advanced Tech" on this subject. The general consensus is that vacuum pumps are for racing motors, and of little value in a street engine, or even something of the magnitude I am running.

My description of how the PCV system works on an LT1 is right out of the manual... I didn't make it up, I didn't invent, I just looked at the pictures and read the description in the shop manual.


And your point is? Yes, you will develop a pressure in the crankcase if you seal up the outlets, but who would be stupid enough to do that?

This isn't rocket science, and doesn't deserve the huge volume of rhetoric that has been posted. Normally, I would just ignore a post like this, but it has so much bad info in it, I had to reply.

 

I just check my hose and it had oil in it. I went and got a Purolator
breather filter part #b23165 fit perfect in the valve cover and attaches right to the hose going to the TB. Cost $3.99


ps:while I was at it removed the TB and throughly cleaned all the varnish from inside of the Intake. It idles better and I think has better throttle response.

 

So, we have a choice of either the Deutsch BF412 breather filter listed on the first page, or the Purolator unit you pickied up? How does the Purolater look compared to the Deutsch one? There is a link to a pic on the first page.

 

you guys need to stop using your brain and just read the facts

the only way you could run a breather and not have an open system is if you blocked off the PCV valve too. this would close the vacuum leak that you opened up by adding the breather. the only problem with this however is that you dont really get any crankcase venting with just a breather unless your rings are shot.

 

They are identical , probably the same manufacture.

 

Alright..since it seems like someone here may know the answer to this.. .the tube that connects to the TB allows oil to drip into the TB. Taking off the black top piece (Throttle body cover that is on the top held on with hex headed screws) I discovered there is a rubber gasket material. How important is it? whats its function? Mine was in poor condition and I believe its ripped in a few places. This would probably affect the way the car runs in a minor way correct? Especially if the seal around the top was allowing any amount of air to seep in. Thanks in advance.

I may need to clarify ..so just ask if that was confusing..

 

the function of any gasket is to prevent fluids from leaking... this includes air. but w/o the gasket i dont see how you would notice any change in the way the car runs. now that doesnt mean you can take the black tb plate off but the gasket if its in bad enough shape then you could toss that.. even if it seals a little bit though is better than no seal at all.

 

OK taken STRAIGHT from the gm service manual


The MAF sensor which is located between the air cleaner and the intake duct measures the amount of air ENTERING the system. A large quantity of air entering the engine indicates an acceleration or high load situation, while a small amount of air indicates deceleration or idle. The ECM/PCM uses this information to control fuel delivery.

 

Yes the gasket is important . I replaced mine about a year ago .I forgot the part # but got it at the dealer for around $3.
It seals the tb plate.Alos when you have it apart clean it out and clean out the hose.

 

Your post did nothing but support the statements that Injuneer and Roadie have made. For some reason, you're just reading the explanations incorrectly. Yes, the MAF tells the PCM how much total air is going into the system, and thus, the amount of fuel needed for the appropriate A/F ratio under closed loop. Maybe what you're not understanding is just the air path for the PCV system. Let's go over it again.

The air enters through the air filter , and then passes through the MAF. Then the air goes through BOTH the the TB blades, and through the little outlet on the side of the TB just before the blades. This hose connects to the pass-side valve cover. The air then travels through the engine picking up some gunk along the way to the PCV valve doing it's emissions thing. The air then goes through the PCV, and renters the engine, wear it gets ignited in the combustion process. So, as you can see, even though all the air that went through the MAF didn't go directly into the TB, it still made it to the combustion chamber to be ignited, along with the rest of the air. So, the air WAS metered by the MAF, as it is the only point of entry for air with the PCV system intact.

A couple things may not be exact in my explanation, but the basic concept is correct. Got it now?

 

Yes, and thats consistant with what Fred said. He used the word 'meter' to mean measure. THe word meter can also mean regulate, but in this case he just meant it measures the overall intake of air. maybe that helps somehow? After the total airflow enters through the MAF a small percentage goes to iac and the pcv system while the rest goes through the TB into the engine where the rest eventually ends up as well.

I'm not really sure why you posted that.

-brent

edit* maybe your still back on the WOT thing? WOT is determined by the TPS as previously stated and then the fuel delivery is switched to being determined by table values.

 

One more and I will drop it the MAF says for an example I have 30 pounds of air coming in it does not say ok I have 30 pounds of air coming in MINUS the pcv MINUS the IAC MINUS the tps e.t.c so that is the only thing I was trying to explain I wasn't going into a pissing contest over a stupid pcv system I merely meant the MAF does not CARE if you plug the pcv as far as it's concerned it doesn't exist in it's formulas calculated for total air entering the intake