i've been suspecting a manifold gasket leak for a little while now, but i've recently noticed what appears to be a leak under acceleration when it's cold....it goes away when it warms up though......I just pulled up a few of my data logs from a month or so ago and the left bank is usually 4-10 counts higher on the long term fuel trim........ Does it sound pretty possible?.....I cant hear or see anything when it's cold and i look under the hood but all signs seem to be pointing towards it.......What do u guys think?

 

oh and i forgot to mention that it will backfire in between shifts.....It use to only do it when it was cold, now it does it all the time

 

If you suspect a vacuum leak, there are several different ways to find out.

First, check all the vaccum hoses and connections. Over time, being exposed to heat can cause the rubber vacuum hoses to become brittle and leak.

Some even tend to expand from constant heat exposure making for a leaking connection. You can try using hose clamps on those, but it would be better just to replace them.

If it's the intake manifold gasket, you can first attach a vacuum gauge to one of the intake manifold ports and see if the reading holds steady, without any sudden dips and recovery. If the reasing doesn't remain steady I'd suspect a gasket vacuum leak.

So then I'd use some kind of fluid t pin point the location. Some use an UNLIT propane torch, others use spray carb cleaner or some other such spray. I've always use water. When the are is found, the idle will change and, in the case of using water, white smoke will exit the muffler(s). Just be careful with the water around the Opti.

Last vacuum leak I had was due to the "O" ring on one of the injectors leaking. I had to point my garden hose at that specific area for it to show up. Turned out that when I'd changed injectors I mistakenly left one of the old "O" rings in the intake and when I installed the new injectors I ended up having TWO in that spot. You'd think that 2 "O" rings would seal better than 1, but that wasn't the case.

If you decide you have to pull the intake, let me know and I'll send you a write up of mine on how I do it which will eliminate any future leak.

Hope this helps.

Jake

West Point ROCKS!

 

Exhaust leaks and misfires can also cause the long term fuel trims on one bank to be different than the others. So could a problem with a fuel injector.

 

I forgot to mention this: You should also check the intake manifold bolt torque. Over time they can lessen resulting in a vacuum leak.

Jake

West Point ROCKS!