i have been trying to figure out why my 2000 Bonneville is running so poorly. I have had several different codes, all have to do with misfire and running lean. Some of the symtoms are rough idle ( not always). Blinking SES light under acceleration and also not really accelerating, this smoothes out after acceleration stops. My wife had the car stop on the interstate with temp rising and warnings about disabeling the AC. first code was misfires so I changed plugs and wires and got good results for a short while, then got lean left bank, this is when the car stopped on my wife. Changed the O2 sensor and runs mush better but now code shows lean on right bank and misses that come and go for cyl 3, 2, 6,4, Mostly cyl 3. I thought maybe conveter is stopped up but why would that cause leans. Had smoke test run and found no vacuum or intake leaks, changed fuel filter and tested fuel pressure it is about 45psi it jumps around when engine is revved but never drops below 40 psi, cleaned Mass air sensor (fairly new one) still runs poorly. Do you think fuel pump or converter or is there some way to test for either. Coils checked good at garage.

tape up your pressure gauge and drive it, if the pressure falls under the recommended pressure while accelerating it could be filter or pump

How'* your coolant level doing?

And do you know when the last time your lower/upper intake gaskets have been replaced?

My fuel pressure gauge is too short to get to a place I can watch it while driving and I am confused as to what the pressure should be, On line i saw that it was supposed to be between 41-47 psi which mine is but a replacement pump at the auto parts store says 80 psi. My coolant level is good as are all other fluids and the engine has run at normal temp since I changed the O2 sensor.

Sounds for sure to me like an injector....

80 is likely what it will put out with no load. its hard to tell what the fuel is doing unless you figure a way to watch the gauge when its having the issue. is it still while accelerating? you still get misfires or just lean code?

I guess that I can take off the hood and check the fuel pressure under load while accelerating. If it is injectors, it would be multiple ones, the worst is 3 but have seen misfires on 2, 4, 6 as well. I have not changed the intake gaskets but the smoke test revealed no leaks and I tried an old trick of spraying carb cleaner around the manifold while running to see if I could get a reaction and got nothing. Right now it misfires at idle, seems to smooth out driving unless under either hard acceleration or pulling a very steep hill.

you can put injector three on the other side and see if the mis moves. i guess now that i think about it the other bank might be compensating or something.

EGR stove pipe can cause a lean condition on whatever bank it feels like if its cracked.

Your fuel pressure is fine. Never heard of a stock car with 80 psi.

If you can, post up all of your codes please.

Thanks, I would not have made that connection, Is there a way to test for the EGR stovepipe being cracked? I looked it up and it looks like there would be some coolant leaks. I do have a small amount of coolant sitting at the edge of the manifold. But it must be a tiny leak as my levels are good. I don't know the code numbers but i will find out when I get a chance to work on the car again. Probably on Saturday.