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Code 33


Tay Jay

Anyone ever have this?
I get it everyone and a while, and the Vette loses complete power.
It will accel if I push down 1/8th on the accel, but if I go any further it will just rev the motor and put.

Also I think I have been having some backfire/pressure.
At start up I will wait a while, then rev to 2k then get off, and I will hear this Gun Shotish noise from the exhaust.
Hummmm! Never had those things happen, yet.
Sounds like cats. Mine wore out and when they did, if it was making noise (a rattling sound, like a bad rod), it would run fine, but if it was quiet, the car wouldn't get out of it's own way! No power what-so-ever. All three of mine went at once.

Hope this helps.
I believe that Code 33 is the Manifold Absolute Pressure (MAP) Sensor Circuit.

First of all, if you intend on doing work on your Corvette, I highly recommend that you pick up a service manual for your model year. Although your Corvette is a 1988, this is out of the 1990 Service Manual for the Vin 8 engine code which is the L98 engine:

"The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4.0-4.8 volts at Wide Open Throttle (WOT).

Code 33 will set when either the signal is too high for a time greater than 1 second, or the TPS (Throttle Position Sensor which helps control fule delivery is less than 2%.

An Engine misfire or a low unstable idle may set Code 33. Disconnect the MAP sensor and system will go into backup mode. If the misfire or idle conditions remains, see "Symptoms," Section 6E3-B. If the ECM recognizes the low MAP signal, the ECM and wiring are OK.

An open in CKT 476 will result in a Code 33.
With the ignition "ON", and the engine "OFF", the manifold pressure is equal to atmospheric pressure and teh signal voltage will be high. This information is used by the ECM as an indication of vehicle altitude and is referred to as BARO. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Reading should be the same, +/- 0.4 volt."

There is also a flow chart included for diagnosing the MAP sensor, but obviously, I can't post that here. Again, if you don't have a service manual and you plan on doing your own work, I highly suggest you get one.

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