Alright, I REALLY need help...

[BruceJ30]

I can't figure it out. But i think it's a vacuum hose leak or a sensor.But after my car warms up, i have a dramatic loss of power.It's really bad, so bad that I'm getting around 8 MPG.

Car has the power it used to once it's cold, but once it warms up, i lose almost all power.

Please help, the gas issue is eating into my wallet.

[alex61089]

have you tried cleaning the mass air flow sensor?

[BruceJ30]

Yeah, i know for a fact that's not it.

But we think the catylitic converter is blocked.We're going to run the temperature of both of them todayand see which is running really hot and then switch it out.

[alex61089]

crapping out oxygen sensors could be the cause too.. Do you have have codes stored on the ECU?

[BruceJ30]

34

[yodawill2000]

34 is Knock Sensor.But that alone shouldn't cause 8 MPG.

[BruceJ30]

Would it cause the loss of power?

[yodawill2000]

Below 3K rpm.After that its ignored by the ECU.But cracks in the plastic housing are common.When cold all is well then when it heats up the cracks expand and the timing is retarded because the ECU thinks you have pinging going on.Easy way to see if that's the issue is the resistor in the wiring harness maneuver.Way easy to do.Do a search here for knock sensor bypass.But please note that its a diagnostic trick , not permanent. And only use the Highest octane fuel you can get.If it really is pinging it will take a toll on the crank bearing.They used a knock sensor for a GOOD reason.

[SteveTheTech]

crapping out oxygen sensors could be the cause too

Exactly my first thought. The old Js have the ability to use the LED on the back of the ecm to monitor O2 sensor cycling rate although it is extremely rudimentary and the results would be more accurate using a standard multimeter.

Cam adjustment could cause a miss as well as a faulty reading from the coolant temp sensor or resistance in a signal wire that is subject to heat saturation could cause a mixed signal but by far the easiest thing to check is the O2 sensors. I would be surprised if your cat was clogged as they usually break up and don't clog unless you have run something awful through the engine. The cats are pretty close to the engine and run warm and reach operating temperature much faster than other old cars so catalyst degradation is not as common.

[GerryO]

Failing O2 sensors should trigger the CEL light and register codes, but when one of mine was failing, it only triggered the CEL near the ends of 100+ mile trips. Replacing them both improved freeway mpg by a couple.

[BruceJ30]

Well before i did the transmission swap, i pressure washed the undersideof the car so all the dirt and dried mud wouldn't get in my eyes. So i thinkwater got up into one of the catalytic converters and rusted it and whenit gets hot whatever it is expands and restricts the flow. Because afteri drove a little bit with the loss of power, an exhaust leak started.

And most of the time an exhaust leak starts slowly and progressivelygets worse, but this one just started out really bad. So i think all theback pressure caused by the converter busted the gasket and startedthat leak. But i'm looking closer at that tonight, and if that's not it, i'llbypass that knock sensor.

Are there any links someone can send me about bypassing that knocksensor?
Modified by BruceJ30 at 7:58 AM 8/27/2009

[BruceJ30]

GerryO

I know that they would trigger the CEL light, but mine isn't on and doesn'tcome on after long trips or anything like that.
Modified by BruceJ30 at 7:46 AM 8/27/2009

[alex61089]

right a completely BAD oxygen sensor would throw a CEL but one that works on and off could possibly be ignored by the ECM or not recognized. They get bad as they age... So they might not be completely bad but replacing them could improve the fuel economy.