WHEN I hit 4000 rpm engine pulsates up and down
 

I have a 2002 Saturn SC1 when I rev up the engine now it hits 4000 and a pulsates up and down up and down before anytime I drive it and put a load on it it bogs down.
I've replaced Coolant Temp Sensor, Fuel Filter, cleaned EGR, checked fuel pressure...Pulled top OS sensor above CAT and had same problem....???? Any and all suggestions will be helpful..ty

4000 rpm is the rev limiter rpm built into the PCM programming for when the car is NOT moving. It restricts the fuel as you hit 4k, the rpm drops, the fuel flow returns, back up to 4K, same thing. That is where the pulsation comes from.

The problem stems from the pcm getting incorrect speed information. The car is moving but the sensor feeding the PCM to determine the speed is either disconnected or faulty.

Is your service engine soon light on?
If so, please get the codes read for free at AutoZone or similar.

If your speedometer does not work check the vehicle speed sensor VSS. I think that controls the dash signal.

I Believe the transmission output shaft sensor feeds the PCM info which it converts into speed. Yours seems to indicate the vehicle speed is 0 when it is not.

I'm trying to confirm this. I'll be back.

The S cars had both sensors.


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Thanks but hold on....I'm still in the driveway...the speed is 0..
sorry I didn't metion that

100% agreement with derf here. Is this when you're just sitting still and revving it up or when you're actually traveling and kick it up when changing gears or what? You COULD have a cat con that's starting to come apart with that many miles on it. We need to know more about what the circumstances are before you notice the fluctuation.

Thanks I apologize I meant to say that as I'm idling in driveway ...when I rev up to 4000 it pulsates...well I took it out this morning starts great...idles great ..start off then get on road...shift to second... floor a little..jerks and pulsates...idle down to 5 mph...accelerate...jerks and pulsates????

Your clutch is cold. Keep driving.
Daily occurrence for me

And stop punishing your engine at 4,000 RPM standing still. Unless you want to accelerate your oil consumption.

Just curious. If you let it idle for 5 minutes or so before taking off, does it still do that? Jerk and pulsate?

Well Zi drilled 2 holes in the CAT I MN the back and now I have power to drive around...yeah...but it still lurches and jerks on acceleration until I Rev High and hold down accelerator then feather off and switch up gear

Because you're warming up the clutch.
keep driving.