chevy1963

Well I have been getting this very bad poping from the driver side exhaust. Friends have said they see flames come out the pipe when I get on it. It VERY LOUD all most like a gun going off, My dad said he heard it 1/4 mile away I thought it was a bad plug, So i changed the plugs to Auto lite 104's.Still does it.NEXT I thought maybe the PRO mags are to tight on a exhaust valve and keeping it open, I readjust them last night still didn't fix it, Sounds worse then before. So I'm going to try adjust them again.

Plus to make things worse Bryan (pcmforless) read my data file and told me My MAP kpa's are to high around 65 during idle bad vaccum leak. I have checked every thing can't it. Bryan said that a bad adjustment of the lifters could cause a vaccum leak.

madwolf

For what it's worth, 65 KPA is not unusual for a cam that big at idle.

chevy1963

I aksed bryan that, and he said it was to high. Can I send you my data master file for you to look at? He told that theres no way for him tune my car with these problems.

madwolf

The reason I said that is because my car has almost the same size cam as yours and it can get 65 KPA at idle. Most big cams idle in that range.

I'd have to agree though, it doesn't sound like a tuning problem.

jpolz

Sounds like your valves might be mis-adjusted or your plugs are firing in the wrong order?

chevy1963

What I did last night I brought # 1 up and adjusted it the bumped the motor over to bring # 3 up and so on, I finshed the drivers side then did the same thing for the passenger side. i try'd method one of shoebox's and that didn't work either.

ktg

I tried all 3 of shoebox's methods. The last one gave me the most accurate adjustment. I pulled all the plugs and cranked the motor over by hand, adjusting the intake as the exhaust started to open and adjusting the exhaust as the intake was nearly closed.

slopokrodrigez

If the exhaust valve staying open later (as in mis-adjusted) where the problem, you would have glowing header tubes. So do you?

The very next thing to do is a leak down test followed by a compression test.

chevy1963

Not that I have noticed, because I drive the car up the street and down the street and it starts poping, I just go put it away

How do you do each of these?

slopokrodrigez

By the way, another cause of back firing is running too lean. I noticed that you recently posted ELSEWHERE that your plugs are indicating a hot condition. Read the reply to the post.

AS far as a leak down test is done using a gage block with a valve and 2 gages. This is hooked to compressed air at 100psi. Each cylinder is tested at TDC and pressurized. The second gage indicates the pressure in the cylinder and tells if the cylinder is leaking by indicating a percent. If the cylinder(s) is leaking, it's then a simple matter of finding the noise of leakage. If the intake valve is leaking, you will hear a rush out the intake. If the exhaust is leaking, you will hear the air at the muffler or tail pipe. If the rings are leaking you will hear air at the oil fill cap. Get it?

Here's one for example but they are available from others at a much lower price.
http://buy1.snapon.com/products/diag...JPG&email=true

The compression test is done by hooking up the gage and disconnecting the coil wire and cranking the engine over with the throttle held open and in the same position for each cylinder. With both tests, it's not only important to get good readings on each cylinder, but also to be consistant between all the cylinders.

Oh yeah, look under the hood while the engine is running at night and see if you notice anything out of the ordinary.