[dfinney]

Okay, think I've narrowed it down after reading threads, but needing opinions please. 97 Monte Carlo 3100 started hesitating about a year ago, but quit after a couple times. So I kept driving it. Couple months later, started doing it again but really bad. So I parked it. (Too cold to work on it) Started looking at it yesterday. Here is the story. I bought the car, and next day fuel pump went out. So it got a new pump and filter. Ran good for 10,000 miles, then this. I can still drive it but hesitates with a little throttle, and falls on its face at highway speeds going up hill or when it is throttled (Under a load). Sometimes it seems like it starts running good for a little bit during a trip, but when I put my foot in it, its back to falling on its face. Sometimes it will set an SES light, but goes away after a bit. Only code it throws is misfire codes, but I think it has to do with starving it for fuel when throttling it. Its got new plugs and fuel filter now, but fuel pressure reads 38-39 psi on a cheap gauge, and bounces up a bit when throttled. Vacuum reads low at 16 in/hg and not steady. When throttling it drops to 5 in/hg and as it rev's up it goes to 19 in/hg, but never steady. The drop in vacuum is pretty much the same as it acts when driving. I checked vacuum hoses and sprayed starter fluid around to check for leaks, but nothing. Here is when I found out it might be intake gasket. I take the oil cap off and idle drops and vacuum drops to around 15 in/hg, then back up to 16 in/hg. I can take my hand and cover and uncover the oil fill hole and the vacuum changes accordingly, along with the Idle. So I'm figuring intake gaskets, but wanted to run it by you guys. Thinking the fuel pressure being low is only because of the low vacuum to fuel regulator, cause I'm checking it at the valve stem. I appreciate any comments or advice.

[dfinney]

Now I've got the first O2 sensor stuck in the manifold. Was wanting to try a new one before I did anything, due to a few threads I read, but couldn't get a wrench on it. Sooo I broke it off to get a socket on it, and then broke a socket, and probably ruined a 100$ torque wrench. Ha ha it was the longest ratchet I had. Any suggestions??????

[nitehawkjcb]

Spray PB Blaster on the O2 area of the manifold, I'm sure it's rusty. I think you need a 1" wrench to loosen/tighten?

It could be your intake gaskets, might as well do a compression test while you're at it...

[dfinney]

nitehawkjcb, on 10 April 2011 - 11:42 PM, said:

Spray PB Blaster on the O2 area of the manifold, I'm sure it's rusty. I think you need a 1" wrench to loosen/tighten?

It could be your intake gaskets, might as well do a compression test while you're at it...

Ok got the O2 swapped with a little spray, finesse, and a two foot 1/2 in drive ratchet. Car runs lots better, but still sluggish on take off, accelerations, and uphills. Still confused by the slight idle change when removing the oil fill cap and putting it back. It doesn't completely fall on its face anymore though.

nitehawkjcb: What would the compression check tell me. Valves not seating maybe, or do you think the vacuum loss may be from a head gasket. Theres not any blow-by in oil chamber so I'd think the rings are okay.

Also what would you think the cat being clogged up might cause. It seems to be more like a loss of power now.

Thanks for the help.

[Batman96LS]

i would replace the fuel pressure regulator first. yeah it's $60...but it's easy to get to and since you've already had some fuel system issues i would start there. and while you're at it toss on a pcv valve. under $3 and usually is forgotten about but could be the source of some MINOR vacuum issues.