Back pressure guage anyone?
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Back pressure guage anyone?
For the life of me I can't remember or find what engine vacumn should be. While I was looking in the FSM I saw where they recommend using a Back Pressure guage on the 02 bung to check for restricted exhaust,
anyone have one of these things, I would have thought it could be checked with a regulator vac. guage?
anyone have one of these things, I would have thought it could be checked with a regulator vac. guage?
Drifting
Joined: Jan 2002
Posts: 1,663
Likes: 139
From: Vail AZ
I'd be tempted to fire it up for a few seconds without an O2 sensor installed just to see what it was doing. I'd think that if the exhaust was flowing properly you'd have a bit of pulsing at the bung, but if it were restricted you'd be blowing exhaust out the opening like crazy. A little Bubba, for sure, but it'll give you a clue.
Drifting
Joined: Jan 2002
Posts: 1,663
Likes: 139
From: Vail AZ
Never used one, but here's one if you haven't already found a source.
http://www.amazon.com/gp/product/B00...lance&n=228013
http://www.amazon.com/gp/product/B00...lance&n=228013
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
holy poop, that puppies expensive, but thanks for the post. I just thought it would be an easy way to eliminate or confirm a possible clogged cat. I'm not having any problems now, but the cat is always in the back of my head.Heck, if it were 30-40 bucks, I'd have one.
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
i have used a Sears vac/fuel pressure gauge,,,,,had engine warm ,hooked it onto the fitting went to full throttle then a quick power brake then the heat started on the rubber hose,,,, if i had a foot of braided line on it i could have drove it
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Be a nice tool for a vette club to have...few guys could chip in a few bucks and pass it around if someone thought they might have a clogged cat.Sure would be easier than dropping the exhaust.
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Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Ye olde timey vacuum gauge had a 10 or 15 pound pressure reading on the other side of zero, for checking the fuel pressure of mechanical fuel pumps. I'm sure these must still be available. Look where cheaper gages are sold, like J.C Whitney (where I bought mine, a hundred years ago) or Harbor Freight.
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Pro
Joined: Apr 2005
Posts: 590
Likes: 0
From: Boynton Beach, FL
I think I still have the gauge I made in my tool box. All you need is an old fuel pressure gauge that reads up to 5 psi. To prevent the gauge from cooking I plumbed the gauge with a coil of copper pipe into the O2 sensor bung. Anything over 2 psi through the cats at idle and its time for a replacement. Good luck.
Larry
Larry
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by rick lambert
I guess you and I are the only one old enough to remember JC Whitney
CFI-EFI
but that is interesting, I'll look.
CFI-EFI
but that is interesting, I'll look.
Originally Posted by rick lambert
Guess I'll take a look for an old fuel pressure guage..I just thought it had to show a negative like CFI-EFI said.
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PS. HERE you go!
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
To check my exhaust back pressure I just use a sears vacuum/fuel pressure gauge. I tap the exhaust with a 1/8 pipe plug and then use a brake line compression fitting for 3/16 line and screw it into the exhaust pipe and then attach a 2 foot length of steel brake line to the compression fitting. The two foot piece of brake line eliminates the heat in the brake line and then I attach the rubber hose to the brake line and route it through the window to my gauge in the car. Take the car for a spin and see what the backpressure is at WOT at all RPM ranges. After testing is complete I put a 1/8 pipe plug in the exhaust.
Safety Car
Joined: Apr 2001
Posts: 3,525
Likes: 2
From: Houston TX
Originally Posted by bjankuski
To check my exhaust back pressure I just use a sears vacuum/fuel pressure gauge. I tap the exhaust with a 1/8 pipe plug and then use a brake line compression fitting for 3/16 line and screw it into the exhaust pipe and then attach a 2 foot length of steel brake line to the compression fitting. The two foot piece of brake line eliminates the heat in the brake line and then I attach the rubber hose to the brake line and route it through the window to my gauge in the car. Take the car for a spin and see what the backpressure is at WOT at all RPM ranges. After testing is complete I put a 1/8 pipe plug in the exhaust.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
Originally Posted by AKS Racing
What kind of psi are you seeing at 5K RPM and up at WOT?
Safety Car
Joined: Apr 2001
Posts: 3,525
Likes: 2
From: Houston TX
Originally Posted by bjankuski
The lower the better, my current car has 1-1/4 PSI at WOT. The same car used to have 3 PSI at WOT and when I redid the exhaust to the current configuration that gave me 1-1/4 PSI the car picked up 32 RWHP with no other changes.
This reading was at 6K in 2nd Gear WOT. I have no cats, but full exhaust with mufflers. I have known this to be a problem for some time, but have not attempted to resolve.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by rick lambert
I'll be damned CFI-EFI, you remember the monthly catalogs?
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