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TBI with really sluggish acceleration

Old 11-24-2018, 07:47 PM
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Car: Firebird
Engine: LG4
Transmission: Auto
TBI with really sluggish acceleration

I have a 1992 305 TBI and its really sluggish and seems to be getting worse. According to my GPS gtech, my 0-60 time is 11.5 seconds. I dont have any hesitation when stepping on the throttle, no SES light lit. Engine does not burn any oil. The fuel pump was replaced along with a new screen and filter. Didnt seem to make any difference. My autoxray shows when at operating temp, the integrator will go up to 130-132, then slowly step down to around 122-124, then quickly goes back up again. TPS and CTS seem to be functioning properly, along with IAC. Everything is stock, no aftermarket parts.

Every year it just barely passes emissions for HC. Timing set to 0, new mobile1 oil, air filter and denso O2 sensor produced these results:
Idle:
219/max220 ppm HC 0.20/max1.20% CO
33mph dyno:
106/max220 ppm HC 0.28/max1.20% CO

I have since advanced timing 4, but no change noticed in acceleration. What else can I look for? Thanks

Last edited by firestorm; 11-24-2018 at 08:10 PM.
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Old 11-25-2018, 11:05 PM
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Re: TBI with really sluggish acceleration

Any car that barely passes emissions testing for HC that has a catalytic converter has a defective catalyst.and/or tremendous misfire. If it has tremendous misfire...the catalyst is toast anyway.

First guess: Your catalyst is plugging. Excess back pressure is killing power, faulty catalyst is allowing too much HC emission.

Of course, you'd do well to check all the usual "tune-up" issues--cranking compression pressure, fuel pressure, cap, rotor, plug wires, plugs. Brakes dragging?
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Old 11-26-2018, 01:30 AM
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Car: Firebird
Engine: LG4
Transmission: Auto
Re: TBI with really sluggish acceleration

Never gave the cat a thought. It is original. The cap, wires, plugs and coil were replaced when I failed once a while back.

One more thing i forgot, When I'm coasting off the highway offramp, the RPMS will bog down and the car will feel like the brakes are dragging, but around 45mph, the rpms will come back up and the drag feel will go away.
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Old 11-26-2018, 02:12 AM
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Re: TBI with really sluggish acceleration

"Around 45mph" sounds like the torque converter clutch has a problem. That's typical engagement speed for a TCC.

Could be something else...but the speed is about right for the TCC.
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