Ok, saturday I start the car up for the first time in about 2 weeks. It idles really rough and is rough when i rev it up a bit. SES light then comes on, code 33 MAP sensor voltage too high. I check the voltage for the MAP sensor according to the instructions in the manual (ignition on/engine off) and it reads within acceptable parimeters. We checked for vaccum leaks and found none. The car ran perfectly fine 2 weeks ago, I changed nothing. Any advice on where to go from here?

This is a 1991 RS with a 355 TBI BTW

 

Genopsyde

Code 33 hmmm. Check the reference voltage supply at pin C of the MAP sensor (gray wire typically). Measure voltage between pin A (ground) and Pin C (+5 V ref) with a DVM. It should be right around 5 Vdc. With Key on engine off the MAP voltage (Pin B, light green wire typically) should read around 4.8 to 4.9 volts. If it reads the same as pin C the sensor is probably is history. Also check ground reference pin A. With everything off, measure resistance between Pin A and electrical ground (stud next thermostat). It should be fractional ohms. I hope this helps

Another functional check – with engine idling MAP output voltage (depending on idle vacuum) should be in the neighborhood of 1.2 to 2.0 volts. If it is stuck at 5 volts check grounds and most likely MAP sensor is history.

//RF

 

Who did the chip tuning?

RBob.

 

RFmaster,

Thanks for the input first off, when I read the MAP voltage via the aldl scanner, it read 4.45-5+ while the engine was at idle.

 

Genopsyde

With engine idling check and see if you have vacuum at the MAP sensor - disconnect vacuum hose right at the MAP sensor. If there is no vacuum you have a hose problem, but if you do have vacuum then most likely MAP sensor is history – replace it. BTW, MAP sensors are susceptible to moister damage and should always be mounted with inlet port pointing down.

 

Now that you mention it, moisture may have been what did it. I didn't think so at first because this car has been in the garage since 2004, but a few weeks back I took it out and hosed off the dust. I didn't have a hood on it at the time either, just covered up the distributor and most of the engine with a piece of sheet plastic.

 

RBob, I got a chip from pcmforless right now for startup and engine break-in period. afterward, depending on how lazy I am or not, I'll either get a dyno tune, or tune myself.


Edit... I just clicked the link to your site and I'm wowed. That's some great stuff you got going there, I just might be doing some business with you instead.

 

The reason I asked about the chip tuning is that a high MAP malfunction code is common on modified engines. They idle with a higher then normal MAP value (less vacuum at idle). Then if they don't run perfect they can easily trip the code. Normally only need to increase the trip point and all is well.

Glad to hear you like the EBL setup. It really will make a difference.

RBob.

 

Genopsyde

I agree with Rbob about modified engines setting of High MAP flags due to lower vacuum levels at idle. Can you measure vacuum at idle with the vacuum gauge?? Depending on MAP sensor part number a voltage level that ECM should see can be estimated. I assume that your MAP sensor has red connector insert.
Another way to check MAP sensor is to connect vacuum hand held pump (Minivac) and see if the MAP voltage changes. If there is no change - MAP is most likey shot.

//RF

 

How it must be done?

 

Increase the code 33 max limit value.

RBob.

 

Sorry to bring this thread back to life, but I am having this problem. I upgraded to a way bigger than stock cam. My manifold vacuum is around 10 inches now. I am not sure what the stock vacuum was in a 1991 camaro rs tbi 305. I am getting the code 33 and i believe this is because it thinks the engine is under load because of the new low vacuum due to my new cam. Because of the low vacuum, my map sensor is sending a high signal to the computer which is in turn causing my engine to run very rich. I believe I need a modified MAP sensor to send a signal to the computer saying the low vacuum is ok. Is it possible to purchase a modified map? or upgrade my computer? What exactly are my options?

Thanks,
Wyatt

 

How big is the cam? specs?

Is issue only at idle? You may be running off only about 50% of the VE table(>50 MAP).

 

It is an edelbrock performer rpm cam. Part number is 2204. It runs very rich no matter what rpm, just not as noticable at higher ones. I believe my map sensor table needs modified so it knows the lower vacuum is the way its suppose to be and that the engine isn't undetermined loss like it normally would be when the vacuum drops signalling you stepped on the pedal.

 

234/238 @.50 112 LSA. Pretty big for a 305 cid.

I would consider idle in OL and maybe keep OL <25 mph. You will need to datalog and work on the VE tables for sure. Dont think tampering with MAP sensor will work. I have never seen that done. There may be the option to uncheck that MALF flag so it dont throw a code.

 

Im working on getting the equipment to burn chips. I am looking for a cable to hook the aldl connector to my laptop

 

I have an '89 formula TBI car, i put in a 355 with a ZZ4 cam and 350 injectors and am haveing problems with it running right, and also throws the 33 code. Ive purchased new Map sensor, ignition coil, and module. No vaccum leaks to be found.
When i first put the motor in it ran well, and stalled sometimes, now its stalling more often. It will idle for maybe three minutes and stall.
I was hoping on a custom burned chip would solve it, but pcmforless isn't dyno tuning or burning chips for cars older than 98 now!
Im nervous to order a mail order chip.
Any ideas,??? Im in N Carolina

 

Best value is to do it yourself aka DIY. check "free tune' on this board sticky. then check DIY board for stickies to learn more.