Code 33
 

1998 502 MPI, code tool flashes code 33. Engine stalls on occasion. It there a simple way to verify that there is something wrong with the MAP sensor?

Re: Code 33
 

here you go hope this helps

Re: Code 33
 

Thanks GOODT. the procdure points to the sensor being faulty. Can that be verified without a scan tool. How do I measure output voltage with the MAP sensor in operation. Do I pierce the insulation on the output wire with the DVOM ?

Re: Code 33
 

The ignition on/ engine off voltage is 4.9 and the idle voltage is 2.70. Sounds very high to me. Could that be the problem?

Re: Code 33
 

Cleared the codes and put in another MAP sensor. Engine still stalls after some 5 minutes of driving. Checked for codes, it flashes 33. Checked voltage, ignition on/ engine off 5.12 Volts, engine idle 2.84 Volts. Followed the trouble shooting procedure measuring voltage A to C (5.03 V), B to C (4.75 V)and with ignition off probing B with a test light (No light). The procedure says; replace MAP sensor. ?!

I am at loss. Could it be a vacuum leak? Where to put a vacuum guage on a 502 MPI?

Re: Code 33
 

I would put it on a spx or diacom laptop and check whats going on and what kind of readings it getting in the long run if you have to pay someone to check it out its still cheaper then the time and parts youll be putting out if not

Re: Code 33
 

A laptop would be terriffic but I don´t think I can get hold of one in my neighborhood. I found a vacuum guage and hooked it up. It reads 14 inch hg and steady at idle. So back to the facts;

1. Engine stalls on occation in the mid range. Especially when the engine is warmed up
2. The ECM throws code 33 repeatedly. If I clear the codes and start and stop the engine it will throw 33 again.
3. Engine vacuum at idle is from what I can understand normal, 14 inch hg.
4. MAP output at idle is with both MAPs that I have tried 2.7-2.8 V which is from what I can understand way too high. Even at sea level.
5. The troubleshooting procedure points at the MAP.

Should I get hold of another MAP? I am not 100% sure that the second MAP was OK.

GOODT, do you know what the MAP output should be for 14 inch hg?

Is it possible to get a small leak at the MAP mounting hole that messes up the MAP reading?

Re: Code 33
 

If the volts are high it means low vacuum signal, check for a leak or clog to the MAP sensor, possibly a clogged port in the manifold.

Re: Code 33
 

I have now made some investigations and calculations. The GM 1 bar MAP sensor is a linear device 0-1 bar. 13.7 inch hg vacuum should give a MAP reading of 2.68 Volts for the old MAP. It reads 2.67 so there is nothing wrong with the sensor output.

Is 13.7 inch hg vacuum at idle good enough?
Why does it throw code 33?
Why does the engine stall?

Re: Code 33
 

Okay, I like your thinking, so let's look at this a different way. The MAP is reading right but setting a code when the engine stalls because vacuum goes too low. So what else could cause stalling? If you are not loosing fuel pressure it should start right back up. If you are losing spark you should see the tach drop out quickly. You may have a sticking idle air valve if it only stalls at idle. Have you checked the basics-cap, rotor, wires, fuel sep?
What is base timing and full advance?