vacuum leak on a '96 lumina

[ilLUMINAteddriver]

Alright, some basic information on my Lumina - 1996 model year, 4T60E automatic tranny, 3.1L engine, VIN M (which they all were, but what the heck), 209,700 miles on the engine. I have replaced all six injectors, the fuel rails, the Cat, the EGR valve, and all the plugs were swapped last winter.

Here's the problem - I have a vacuum leak and a misfire in the #1 cylinder (last time the code was run, at least, I don't see why it'd have moved around). I have flushed the engine (the problem with the sticking valve seems to have gone away but I still have the misfire and the SES/CEL light keeps coming on, but it's flashing a lot less when it does) and replaced all six injectors (after 209K, it's about time), complete with the gasket and O-rings I was supposed to have put on. I farmed that one out to the local occupational education place because I didn't have the tools or the experience to do it myself and whenever I wanted help nobody was willing to help me.

So, I've eliminated the valve (at least enough to say so, I know it'll need replacing and come fall when the OcEd place opens up again they'll be seeing my baby again), and the injectors as faults. Fuel injector cleaner seemed to help when the misfire first showed up, so that's why I went for the swap out. My understanding is that the injectors on this particular model of engine from GM had a slight fault that could crop up, especially after high mileage.

The vacuum leak was diagnosed about sixty thousand miles ago but wasn't really a concern till recently. Having eliminated the other faults (again, at least enough to say so), I'm forced to say it's the leak causing the misfire. Further evidence to back me up goes as follows -

There's a major vacuum hose running from the plenum to the brake system to provide the boost, and I've inspected that line and found it to be visually solid. However, when I step on the brake at idle, the engine slows, lopes, and sounds like it's going to stall. I pulled another vacuum hose off and ran the engine without it and had the same problem without stepping on the brake, only more so. So, by process of elimination (and the fact that after pumping the brakes heavily night before last before I took off and had more problems than I've had since I replaced the injectors and cat), I'm forced to conclude that the problem lays with the brakes.

So, any suggestions about fixing it? Anything further I could check? When the misfire isn't happening constantly, the power and pep is great, but I can't get that light to go out anymore and I'd really like to fix this problem if I could, or at least have it fixed since my mechanical skills are pretty basic. I change my own oil, changed the EGR valve and the tranny fluid, and can do very minor work myself at present. The mileage isn't bad when the SES/CEL light is off (about 26mpg), but when it's on I'm getting closer to 20, sometimes as little as 18, and I can't afford to sink much money into the car let alone feed her right now. I'd like to get another winter out of her so I can retire her gracefully and then let the Taurus I just bought take over for a few years. I may have to sell my Taurs, however, because CARDONE won't get back to me about the defective water pump they sold me that I dropped $100 on having installed and refuse to pay to have the work done again after only 46 days, so this baby is my only transportation right now. Any and all help would be and is gratefully appreciated. Thanks!

[jeffcoslacker]

Cap the line at the booster and see what happens when you step on the brakes.

If nothing, the booster is leaking.

[ilLUMINAteddriver]

Electrical tape works wonders - I couldn't pull the cap out so I pulled the hose off and taped the end up so no air could get through. The idle cleared up quite a bit and when I stepped on the brake, no engine response, just a steady idle. In addition, the brake pedal firmed up almost instantly and stayed that way. Sounds like the booster or reservoir (if there is one, I don't know on this model) is leaking like a sieve.

Is this fixable?

[cadgear]

Next step is to check the hose itself, the check valve, and the booster. The booster is an easy replacement, but I wouldn't repair one - cheaper and easier to replace as a unit.

[ilLUMINAteddriver]

The hose is in great shape, quite flexible, no deterioration, solid, no leaks I can tell, etc. How would I go about checking the booster and the check valve? I have a Haynes repair manual, would it be covered in that? I ask because I'm not sure where the book is at present so I can't check it. Thanks!