Exhaust Restriction ?

[RageCage]

Hi,

I just did a vacuum test on my 85 Chevy Caprice V8 305. At idle I get a reading of 20, when I rev the engine, it drops right down to 15 or 10, and builds back up gradually to 20 in a couple seconds, but never over 20, until I let go of the throttle, at which time it pops up to 25, then settles back to 20.

Exhaust restriction ? Could it be something else ?

When I had a new tailpipe put on, they took it down from a 2 1/4 inch to a 2 inch. Would that have caused it ?

The car runs OK, but on hills, it isn't too strong. Even before the new smaller tailpipe, it was not very strong on hills. Once in a while I have gotten the rotten egg smell on long steep hills. At first I thought the engine was just getting old, but maybe it's a clogged cat or something ?

Thanks

[94-9c1-lt1]

Its not the cats. when you smell that rotten egg smell, it means you car isn't burning the gas right. The cats burn gas that your engine doesn't, so you need to check all filters and spark and timing. Having a smaller tailpipe will take 10-20 horspower away from the top of the rpms, otherwise it shouldn't effect climbing a hill, steep or not.

[RageCage]

Thanks, 94-9c1-lt1. It has new plugs, timing is right ( 6 deg btdc), air filter is not clogged, wires, cap and rotor are pretty new. Could be the O2 sensor needs replacing, though. I've heard that when they get old they send a false "lean" message which makes the computer enrich the mixture.

The O2 sensor is the original, and has 368K miles on it. I just recently started hearing about the O2 sensor needing to be replaced regularly. What do you think ?

RC

[PeteA216]

Yeah, give the O2 sensor a try, it wouldn't hurt to change it. If you really have trouble climbing hills, then try downshifting manually (depending how fast your going) Also, if you going steady at about 45 -50 mph and you begin going up a hill, and you give it some gas to help it out, be sure it kicks out of overdrive. If not, then that could be why your car is having trouble climbing.

[CD Smalley]

Is that timing spec right? I think my 86 is supposed to be 0* BTDC, wit the EST unhooked....

[Morley]

Originally Posted by RageCage

The O2 sensor is the original, and has 368K miles on it.
RC

Heh, yeah replace it. GM used to reccommend changing them every 35k miles...so you are a tad over due.

[jogoff69]

I had the same rotten egg smell, I replaced the o2 sencor, and it went away.