need help please, here's my symptoms Options

[Akimbo]

okay...i dont know what it is...i initially thought catalytic converter or exhaust. But here's my symptoms, just throw me some ideas

- Car smells like exhaust fumes
- Bad gas mileage
- Loud hissing sound when throttling
- Between 3k-4k RPM's the car shudders and lurches a lot and I either have to keep the RPM's a little higher or a little lower.
- Loss of power/torque

GO!

[crankyelbow]

okay...i dont know what it is...i initially thought catalytic converter or exhaust. But here's my symptoms, just throw me some ideas

- Car smells like exhaust fumes
- Bad gas mileage
- Loud hissing sound when throttling
- Between 3k-4k RPM's the car shudders and lurches a lot and I either have to keep the RPM's a little higher or a little lower.
- Loss of power/torque

GO!

I'm on the same boat, except my RPM shudder range is 2-3k.

Perhaps this can offer you some insight:
I bought the car with the issue, so I don't know what it was like before. The problem seems somehow linked to how much the car backfires when I shift - sometimes it'll backfire with most shifts, sometimes with few... the shudders hasten and slowen respectively.

Running lower octane gas (87) seems to help the issue - but the car runs stronger otherwise on 93.

Changed my plugs/wires and it helped but didn't cure.

When I bought the car it had NO exhaust after the flex pipe AND the flex pipe was broken. Back then it backfired like all hell and shuddered way more. Now it has a straight pipe because at the time I couldn't afford to do a muffler/resonator or fix the flex pipe.

A good seafoaming of the intake really smoothed the car out at idle and higher RPM's and helped some with bringing in power, but didn't help at all with the shudders.

The cat doesn't seem out of the question but the car doesn't feel now like it has excessive backpressure.

First, I think I'll gut the cat and see what happens.. but before that I HAVE to get at least a resonator - this thing is way too loud already

If not cat it'll have to be a vacuum leak or distributor/coil. The whistle inclines me to belive its a vacuum leak... that coupled with my inability to turn the car off with pouring sea foam into the brake booster line makes me think it was sucking air in somewhere else just enough to not get completely choked by the liquid I was literally dumping in there.

I have a 94 GT manual, btw.