TBI Code 33 help!!!

[elks]

So I am running into TBI code 33. MAP Sensor Voltage Too High. I had an extra new one in the shop swapped the sensor and still had the code so I look up the Flow chart. So in the chart I got from CK5.

The engine starts and idles fine. Elevation is 5100 feet.

The flow chart I have asks if the map sensor displays a voltage reading over 4 volts. When Idling I get a voltage reader on the scanner of 3.92 volts. Since that is not over 4.00 volts it says the code is intermittent, If not additional codes are present then refer to Diagnostic Aids. Under Diagnostic Aids Section It suggest to find a similar vehicle and see if the baro is close +- .4 volts. I do not have another system on hand to check, but the map sensor voltage vs. Altitude shows I should read between 3-4.6v. With the engine off and key on I am reading 3.96v.

So what do I do to check? Should I be checking voltage to the Gray and Purple Wires?

Is it because there is not much difference between idle and engine off? Should that number be greater? If I rev the engine the map sensor voltage drops as expected all the way down around 1 volt.

Any ideas? I feel like I am missing part of a chart for what to do when code 33 sets but sensor voltage is below 4.0 volts.

 

[elks]

Also this is on a non-egr system.

 

[4xcrazy]

Why is it tripping that code, is it not driving right? Running right during throttle?

 

[black dawg]

map voltage at idle should be near 1 volt. Seems like key on engine off map voltage will be 4.5 ish depending on altitude.

 

[elks]

map voltage at idle should be near 1 volt. Seems like key on engine off map voltage will be 4.5 ish depending on altitude.

The engine light is on and giving code 33 map voltage too high. I just barely installed the motor and the TBI system. I have cleared the code 2 times and it almost always comes back on as soon as it starts up. With my scanner hooked up I never see a voltage higher than 3.96. This last time I did the check it read same voltage for engine off as it did at idle. could that be the problem that at idle I am not getting enough vacuum? Engine is not built other than an rv cam and intake exhaust. When I check with Howell they said the computer I have would be fine for ending specs.

What else might cause it if my voltage does not seem to be spiking high?

I test drove it in the lot, and it accelerates well, etc. Other than the light performance does not seem to be an issue unless the motor has a bunch of power that is missing...

 

[black dawg]

with the light on, it is ignoring map input, so it would run fine without it.

I would check for vac at the sensor, then voltage to and from the sensor.

 

[dyeager535]

You sure you've got everything hooked up right? I'd really check to make sure your MAP sensor is getting manifold vacuum, and that the ground is actually grounded. Pin A is ground, B is the signal, C is the 5V reference. A is grounded through the ECM, no idea if that is switched or what, may have to have truck in run for that to ground.

I'd then run a vacuum test, that is the first step to troubleshooting this code, before you look for sensor voltage. If it's below 15", you have another problem. Seems unlikely since it idles ok and you haven't changed anything that should cause a massive drop in vacuum (except I'm guessing an EGR delete, which could), but it's not something you know, it has to be over 15", and it's a new install that isn't working right.