Code 33 troubleshooting

[mmarriott2]

1979 Chief 360 with TH400.
Previous owner installed the Howell fuel injection, MSD ignition and distributer. He had the engine rebuilt and balanced. He says it ran great for a couple thousand miles before it started having problems. He states it started while driving down the highway one day, and it hasn't idled or ran right since. He gave up on it back in 2005. I just purchased this beauty and started going through it.
What Ive done so far, drained fuel tank, replaced in tank sock, inline filter, and all fuel lines. Checked fuel pressure, its at 12 psi. Removed the smoked MSD ignition box and distributer and replaced them with new stock pieces. Set the timing to 10*. Replaced numerous vacuum lines, and cannot find any leaks.

Problem: Hard to start, I have to apply gas pedal to start. When it does start it doesn't want to idle and it sounds horrible. Then after a minute or so the check engine light comes on and suddenly the engine wants to idle. And will even rev up fine. Shut it off and I have to start the process all over again. Grounded out the ALDL plug and it throws a code 33. From what Ive found that is for the MAP, unless the vehicle idles poorly, if so you are supposed to fix that prior to working the MAP. And yes, the MAP sensor is mounted directly above the vacuum line. I called howell they instructed me to check the MAP sensor itself, which has checked fine, or the vacuum line. The line is brand new and not clogged.

I would love to hear from the gurus on where you would go with this.

[mmarriott2]

Quick update:
Just found a little trick where I unplugged the MAP sensor and ran it for a minute and to check for a code. I got a code 34 now. That is an open in ground circuit or sensor?


Just replaced MAP sensor, no go.

[Bill usn-1]

Code 33 means you have high map( a low vacuum ) condition for 5 sec while idling.
So the first question would be...where is the map connected?
Should be on the port between the 2 fuel lines on the back of the throttle body.
Nothing else should be connected to this hose.

The next thing to check is the actual vacuum at idle at this port vs your engine vacuum at idle.

Then I would check you local baro pressure and check the actual voltage out of the map sensor to see if it's correct.

Pins
A=gnd
B=signal
C=5v

From the parts required FAQ on the BinderPlanet.

11. MAP-manifold absolute pressure sensor- this senses the change in manifold pressure. it usually is mounted on a plate, bolted to the intake manifold. You can modify the plate and remount it on the IH manifold or make a plate and mount it on the firewall.

A 1 BAR MAP sensor reports barometric pressure times one, which is approximately 14.7 psi or 30in/Hg (inches of mercury). As an example, a typical three wire MAP sensor has 5 volts and ground to power the circuit. The signal circuit, or return voltage to the computer, is about 4.5 volts at barometric pressure of 14.7 psi; this measurement is taken at key on engine off. The sensor can withstand about 1.5 BAR of pressure, but the return voltage will peak out at about 4.8 volts. This type of sensor is designed for a normally aspirated engine to read a negative pressure, or vacuum, at a typical barometric pressure.

Testing
http://www.autozone.com/az/cds/en_us...rInfoPages.htm

This is the voltage to pressure table for a standard 1-bar MAP...
Volts, kPa
0.00, 00
0.30, 10
0.60, 20
1.10, 30 (approx 20 Inch mercury vacuum)
1.70, 40
2.70, 50
3.30, 60
3.80, 70 (approx 10 Inch mercury vacuum)
4.40, 80,
4.90, 100 (no vacuum; full atmosphere)

[mmarriott2]

Thank you for the reply. I will check the two vacuum when I get the ECM back from Howell. After talking to them I decided to send it in for a reprogram. Although I know it has some vacuum at this switch because when I disconnect it and start the Jeep I can hear the vacuum from the drivers seat.

Where do you get the local barometric pressure? Doesn't that change pretty regularly?

[Bill usn-1]

http://www.weather.com/
put in your zip code and then open the weather details and it will have your baro pressure listed. Normally 29.XX