LT1 gas mileage

[deja]

Good points. The thing that bothers me about his system is he says his engine is not drawing anything from where the breather hose would hook up on the throttle body.

 

 

Not having the stock PCV system shouldn't do this to your mileage. The point of a PCV system is to evacuate fumes from the crankcase. Breathers will do the job, but the stock PCV system will work a little better. The downside to the stock system, however, is that it routes those fumes (along with oil vapor) back into your intake, which isn't exactly a plus for performance applications.

[lgoodson@pacbell.net]

Ok. There are some great posts here while we all try to figure this out so let me answer some questions.

The pump I am now useing is off a 94 BMW 633. It is rated at 100 to 110 PSI and 50 GPH. The reason for switching to this pump is that it is Quiiiiet! Unlike the 280ZXT pump. I picked up a couple of different pumps at the local Pick A Part just to see if I could find a quieter one.

The stock fuel pump for the LT1 is rated at 90 to 95 psi and 55 gph so I don't see much difference, I get theses numbers from AutoZone's web site where they list the specs for the different pumps.

The fuel pressure indicated by the gage I have on the Pressure line is reading right at the required pressure that my shop manual states that it should be. 47 Psi before start and 39/40 after start up. So the excess presure is bled off through the return line. I wouldn't think that this would be over powering the fuel injectors but I am getting poor mileage and the injector noise is loud when I put a listening device on the fuel lines and regulator. I even can here them while sitting in the car.

 

As far as the PVC line is concerned, I have been running the breather on one valve cover as the othe cover does not have a hole. My shop manual states that the engine is suppose to be a sealed unit and I should have vacum at the dip stick if everything is in place. They say that with out the sealed system, engine damage could occur. I have since installed a hose and PVC valve off a camarro I found at the salvage yard just to see if there is any difference. While I was doing that I noticed that I do NOT have any vacum at the throttle body connection point. The manual says, in that event, check for leaks: valve covers, oil pan etc. I have no leaks so I don't know about the lack of vacum? I do notice that the idle is not real consistant. Some times it idles down to 500 or so and I think that could be as a result of a vacum leak so I am still checking.

 

What is causing thr noise from the lifters at the fuel lines. The lifters themselves seem to be normal.

Larry

[Inferno 08]

Having a breather won't cause damage to the engine. The only way damage could occur was if the system was somehow sealed and pressure built up in the crankcase, which would most likely end up just blowing past the rings.

 

From what you're describing, it sounds like you have a vacuum leak somewhere. A good way to test for that is to spray something flammable like starting fluid or carb cleaner on vacuum lines or anywhere that you suspect a leak. If that causes the car to rev a bit, you've found your leak.

[lgoodson@pacbell.net]

Yea, I'll try that test, I just put a new intake gasket on the engine because I had a oil leak at the rear. I don't have the leak any more and there arn't very many vacum lines in fact I believe there is only 2. Brake assist and fuel regulator which seems to be working normally.But I will also check around the throttle body.

 

That's an old trick. I learned it back in the 60's

 

Re-Reading what GM says about the crankcase ventilation, You are correct. It says that operating the engine without any ventilation it could be damaged so they say to be sure to replace the valve and hoses as needed.

 

Yea, I get nothing in the way of vacum at the throttle body at Idle.

[wheelman]

Which PCV port are you checking for vacuum?

I have a 95 LT1 with a MAF so it may be different from yours.

My throttle body has 2 PCV ports, one on the right next to the TPS and one on the lower left under the main intake.

The one on the right connects to the hole in the valve cover and will not have a vacuum, but instead is fed from the intake tract downstream of the air filter, in front of the throttle blades. This feeds air into the engine block and on a MAF car must pull air from the intake tract.

The other PCV port connects to the left side of the intake manifold via a hose and contains the PCV valve, this port will have a vacuum.

 

The system applies a vacuum to a passage in the intake manifold that connects to the engine block, pulls air from the block through the PCV valve into the throttle body. This creates a slight vacuum in the block which is pulls fresh air in through the hole in the valve cover.

 

So if you have a breather in the hole and the hose connecting the PCV to the left side of the throttle body you should be fine. If you don't have the hose from the PCV to the throttle body thats where the leak is.

 

From the sounds of it this wouldn't cause bad fuel mileage though. A speed density car is much less affected by vacuum leaks than a MAF car.

[lgoodson@pacbell.net]

I had the PVc hose from the pasenger side valve cove hooked to the top port on the throttle body but have sense removed it. Couldn't see a difference so I have put the breather back in and pluged the port. I had no vacum at this port.. Haven't checked the other port yet. I thought that it was the head vent passage so no vacum would be there.

 

As far as the fuel problem, I just insatlled another set of O2 sensors, GM/Delphi ES10966 purchase from http://store.getgmparts.com/. I can't be sure that they are the right ones though because that site does not provide any way to search various models to determiine what they might take so I took the guys word for it on the phone when I ordered. Today I ran the engine for a while and after a while the "check engine" light came on. It has never done that before but I thought that it might be because I changed something and the computer needed to be updated or cleared which I understand that all that is required is to diconnect the power to the car and the memery will get cleared. I did that and so far, no check engine light. We shall see and we shall see if the milage improves.

 

Another problem I have been asking for help with is the Injector noise that could be plainly heard sitting in the car. Today I replaced the braided steel line running from the chassis fuel line to the fuel rail steel lines. I replaced it with a rubber hose -6 fuel line and the noise in the cabin went away. I can still hear it but I have to listen hard to hear it. Just Insulating the engine fuel line on the engine from the chassis line helped a big amount.

 

I also notice today that my intake gasket at the rear is leaking again. After only a 150 miles or so it is leaking. I took pains when I replaced it before making sure that all bolts were torqed to spec and still I get a leak. I used the strongest RTV I could find but still it leaks.

Any Ideas???

 

One more thing. I went around the car with a can of starter fluid spaying everything and listening for increases in RPM. Couldn't find any but I did see the intake leaking, Could this be also a vacum leak. I would think that the oil would keep it pretty sealed as far as the vacum is concerned

[lgoodson@pacbell.net]

Ok, I installed the new Delphi 02 sensors. Today I had the car out for about 20 miles. As I was driving it I noticed that the fuel gage was sinking like a rock so I don't believe I solved the mileage problem. I also noticed that I now have backfire through the exhaust. Loud poping when I let off the gas at a high RPM to slow down. It never poped and backfired before with the other 02 sensors. What is causing this, Too rich or too poor?? or is this normal with no back pressure. Remember I have a 2 1/2" exhaust to the Y pipe and 3" out to a 3" magnaflow.

Do I have the correct sensors now or what??

[Z48LT-1]

Larry,

 

I'm wondering whether your PCV system and intake oil leak problem may be related. It strikes me that the PCV system ought to create a partial vacuum in the oil-wet spaces in the engine and putting a breather in place of the PCV system might create enough of a pressure blockage to drive the oil to the easiest gap.

 

I continue to wonder whether datalogging might help you diagnose your mileage problem. The fact that the new O2 sensors changed the engine's behavior (popping on throttle-off) suggests to me that the computer is having some issues somewhere. I'm sure the ecm tuning process has a pretty steep learning curve but I'm thinking that might be the quickest approach to solving your problems. Alas.

 

Wish I had some experience to back up my hunches on this. I suspect someone here has been through it and I hope he chimes in.

 

Best -- Gary

 

The day is committed to error and floundering; success and achievement are matters of long range.-- Goethe

[lgoodson@pacbell.net]

I plan to find someone who can do the Data logging for me to see exactly what is going on. I am looking around here when I have time to find someone. Don't really know what type of person or service that I should be looking for.

And yes. I an going to pull the intake again and re seal it one more time. I hope!

[lgoodson@pacbell.net]

Z48LT-1. Almost everyone I talk says that they use the breather instead of the PVC valve without any problems. These LT1s leak at the rear intake. I have been told that it is a common problem. Pulling it again tomorrow.

 

deja. Put the original O2 sensors back in. No more poping out the exhaust. With the Delphi sensors I went 102 miles on 10.2 gallons. That's 10 MPG. Worse yet.

 

What I am thinking is that I have a 3.90 rear end and therefore I have the poor milage. Would a 3.90 do that? I am going to spin the tire and count the drive line rotations and get a clue as to the ratio.

[RTz]

Would a 3.90 do that?

 

Read post #2.

[deja]

I wonder if the exhaust leak was causing the popping. Either way I'm glad that is gone. But I doubt the 3.90 is the main cause of your poor mileage. But if the exhaust leak was affecting the readings of the O2 sensor that could cause the PCM to get confused and force it to add fuel.

 

Z48LT-1. Almost everyone I talk says that they use the breather instead of the PVC valve without any problems. These LT1s leak at the rear intake. I have been told that it is a common problem. Pulling it again tomorrow.

 

deja. Put the original O2 sensors back in. No more poping out the exhaust. With the Delphi sensors I went 102 miles on 10.2 gallons. That's 10 MPG. Worse yet.

 

What I am thinking is that I have a 3.90 rear end and therefore I have the poor milage. Would a 3.90 do that? I am going to spin the tire and count the drive line rotations and get a clue as to the ratio.

[lgoodson@pacbell.net]

After I fixed the exhaust leak I still had the poping until I changed back to the NGK sensors.

At 70 MPH the tach reads 2000 RPM. Does that sound like a 3.90 or 3.36?

 

Replaced my intake gasket today following everyone's instructions leaving it sit for a hour before torqueing the bolts. Change the TB gasket as well and a couple of the injector "O" rings. Leaving it sit a couple of days before starting it up to make sure the RTV is good and cured but a fuel pressure check revealed no leaks so it shold be ready to run.

 

Looking into the TB, it looked really dirty and I know I cleaned it a couple of hundred miles ago so I wonder why this is. It was dirt and what felt like oil mixed in. Where could all this be coming from? The air cleaner I have is one I bought at Kragen or Autozone for $30 bucks but it should work better that this. 200 miles????

 

My fan belt is starting to look worn. On both edges I can see the cords in the belt showing in places. This, I can't seem to get a handle on. Every thing looks fine and the pulleys look all lined up so I don't know.

 

Thanks to everyone

Larry