87 chevy got some codes

[bigbubba87]

hey guys
got a promblem with my 87 tbi.
it will run fine when cold but as soon as it warms up or go to start it up warm,it runs very rough and is very  rich.
i checked the codes,i had a 33 and a 45.i think the 33 is a map signal and the 45 is a 02 sensor.
i found the egr valve,an with it running if i pull up on the diaghram the engine will try to stall.

so were do i go from here,what should i check?any ideas?
thanks bubba 

[VileZambonie]

If you open the EGR it will stall the engine. Pull the vacuum hose off of the EGR valve and see if it makes a difference. Often the EGR solenoid will stick open and you'll have a horrible idle. This will also set a MAP DTC. Try that 1st assuming it's tuned up correctly.

[bigbubba87]

yeah it's got new cap,rotor and spark plugs,i've also change the fuel filter.

i did disconnect the vacum line to the black box from the egr,i think that is the map sensor.

the eng did not do anything differnent.if i disconnect the water sensor the engine revs up and seems to run fine at a high idle.

[VileZambonie]

Ok everytime you unplug one of those sensors you set a DTC. Just pull the vacuum hose off of the EGR valve and plug it with a screw. Clear your codes by disconnecting the battery for 30 seconds. then reconnect and see what happens.

[bigbubba87]

i'll try that thanks

[chevy754x4]

the 33 is a MAP code....the 45 is Rich Exhaust code

good luck finding the the culprit

[bigbubba87]

ok
so i caped off the egr,i disconnected the battery for 30 seconds.

i started truck, it was cold,it ran just fine,had a little rich condition nothing major.

i let it get to around 150*f than turned it off,i have a mechaincal gauge on it.

when i started it back up it stalled right out,started it again an it stayed running just reel ruff,if ya step on gas it's real rich,an just won't come up in speed,once i did get the speed up it never stop puting out black smoke.but it didn't even out either,when ya step off gas it dies.

check engine light comes on,i checked it   12 code an 33 code.

any thoughs?
bubba

[VileZambonie]

Sounds like a bad MAP signal. Check the vacuum hose to the MAP. Do you have a digital meter? If not just replace the MAP sensor.

[bigbubba87]

yes i have a meter,
what sure the voltage be?

also please info me what does the map do?

[Captkaos]

MAP is manifold Absolute Pressure.  It determines air mass flowing in the motor.  Should be around 1.25V.

[VileZambonie]

Speed Density

Speed = RPM

Density = MAP (Manifold Absolute Pressure)

Absolute pressure is a Negative pressure or as we call it a vacuum. As engine load increases Manifold vacuum drops. The map sensor senses changes in manifold pressure and compares it to Throttle position (driver demand), Engine speed and other factors (Engine Coolant Temp, O2 in closed loop,...The ECM then goes to it's look up tables and determines the correct injector pulse width. A typical input value to the ECM from the MAP at idle would be about 1.25V and at WOT about 4.25V.

To test the sensor -Key on engine off with your meter hooked up in parallel to ground and backprobe...

Probe cavity A (PPL wire) Should read nearly zero volts (ground ckt)
Probe Cavity C (GRY wire) Should see close to 5V
Probe Cavity B (LT GRN) Signal wire you should see close to 4.5V...with engine idling voltage should drop to less than 2 volts... ideally close to 1.25V if the engine is running good.

[bigbubba87]

i will check that.
i should also check to see if i have vacum to that sensor correct?

[VileZambonie]

Yes and check the condition of the hose and make sure the sensor is mounted higher than the hose so no moisture can freeze in the hose.

[bigbubba87]

hey guys,
found the vacum hose was off the back of the tpi.
don't understahd how that happen,but glad it's fixed,runs like a champ,
that voltage would be in dc volts?
thanks for help.
bubba