pmihaltian

I'm having a terrible time with the local Chevrolet dealer. I'm getting a Code-33 error message which, as you know, is a mass air flow sensor problem. To date we have replaced the MAS, and several MAS relays all to no avail. We are now getting ready to change out the pre-cats and the catalytic converter. Their technician really doesn't know what is wrong with it and is just changing out very expensive parts with no success at all to date. He is looking for a broken wire (needle in the haystack) now which will cost a small fortune and may take forever.
I remember a couple of years ago Vette Magazine ran an article on how to solve problematic and phantom Code-33 errors, but I can't for the life of me find the article nor anyone who seems to be able to tackle this problem.
Can you help me? Please drop me a note and let me know if you can or can possible recommend someone who might be able to help.
:chevy

PeteL

Here is a start:
http://forums.corvetteforum.com/zerothread?id=187775

Do a search on the forum, try different areas for code 33. Think your dealer is guessing and you should take the car away before you spend the family inheritance on this job.

Factory shop manual will do wonders. http://www.helminc.com

Good Luck,

Pete

Marcho Polo

I got your email, and was going to reply, but I'll just post here so it can be saved!


First, does the check engine light come on right away and stay on the entire time you're driving? Or is it intermittent?

If it's on all the time, check your 'guages' fuse. If this fuse is blown, you'll get a code 33. The MAF circuit is tied in with that fuse.


Also, do you have a Helms Factory Service Manual? if not, I can scan the code 33 diagnostic flow chart and email it to you or post it. That would help alot.


Next, other things on the same circuit as the MAF that if they short out can cause code 33 but are not documented well in the manual:

If you get a wiring diagram, circuit 39 is the main wire for the MAF. It also feeds power to the Torque Converter Clutch Switch inside the tranny. If the connector on the tranny gets messed up, it could cause the guages fuse to blow. The wiring also routes through a switch near the brake pedal to disengage the TCC when you hit the brakes. Check the wiring at the pedal and the tranny on the drivers side.

Circuit 39 also feed the EGR switch near the back of the motor by the distributor on the passenger side. It also feeds an air switch (Never did figure out exactly what this was, but it's in the vicinity of the EGR switch and TPS on the top of the motor somewhere!).


Circuit 39 also controls the Canister Purge Solenoid near the front of the drivers side, by the headlight.

Wait, I'm not done!!!!


Circuit 39 also feed the seatbelt buzzer. Also feed the courtesy lamp delay timer. Also the key buzzer/dinger and seatbelt buzzer.

If you have a rear defogger, it feeds power to that as well. It feeds the check engine light bulb in the dic.

I think that covers it. Circuit 39 is a pink wire with a black stripe. If any of these items fails and shorts that wire out, you'll get a MAF code.... code 33.


It can be a tough one to track down. I spent a month on this with my '85 a couple years ago. I had a new tranny put in and the tranny shop messed up the TCC connector which shorted out.... you got it.... circuit 39!


Does your TCC lockup on the highway? If not, check the wire to that.

About 6 months after the tranny shop fixed that connector, I started getting a code 33 again. This time the connector to the MAF was worn out. I crimped the female side of the connector to make better contact with the male MAF side and it solved it. Might want to check that.


Hope this helps you out!

Aggravated4life

Code 33 is a pain in the butt to troubleshoot and requires sometimes expensive guessing at fixing the problem.
It can be falsely triggered by many items at times.
It takes a very skilled tech sometimes,like David F on the forum to troubleshoot and check the wiring before attempting repairs in a process of elimination and it seems the tech at the dealer doesnt know how to do this for your car.
But this can trouble the best techs too.

Do you have a larger throttle body on the car?if so,let us know.I would bet the TPS and minimum air speed screw is off.it will set a code 33 and run like crap until properly adjusted.
Or if someone toyed with the stock settings,or your TPS or TB blades are binding and not putting out the proper signals.

With the 86 cars,the green wire on the MAF connector needs to be checked.Check the connector and be sure it isnt broken.
Make sure there isnt a short in that wire.

Heres a list of things to check the tech should do before diangosing the fix ahead of time.I got this out of a book I have.

Clear codes and run the car...does code come back?
If YES,connect a digital voltmeter to the dark green wire at the MAF sensor.
Turn the ignition switch to "on" not start the car and note the voltage.
If near 0 volts,check the voltage at the termninal B12 at the ECM.

If theres 5 volts there,the ECM is good and you have a break or short in the dark green wire somewhere.If no 5 volts,and the connection is good there at the ECM,have them install a new or try a new ECM to see that fixes the problem.
(dont pay for it or take it if it doesnt)

Going back to the MAF test on the green wire,if there IS 5 volts on that wire,check the purple wire for 12 volts at the MAF with the engine running.
If theres 12 volts, the sensor is BAD.

If theres no 12 volts,apply 12 volts to the ALDL connector to terminal "G" on the purple wire to the MAF.
IS there now 12 volts at the MAF purpe wire?

If Yes,check the fuel pump fuse.If the fuse is OK,replace the oil pressure sending unit.

If No voltage,then check the wiring to the MAF power relay.If the wiring is good,replace the MAF power relay or recheck the connections there.

Whew eh? Look at Craig M's reply...theres more there of possibilities and Im adding some tests there from a book.
Hopefully, your tech will follow the repair manual to the letter and spot the fix easy.

Keep us posted on the repairs.I also wish David F was here to help us out too.
:)

drive it

Ditto to all the above! And could you give us a little more info-is your engine stock? mods? any other codes? code 33 only after light cruise or immed?

pmihaltian

The engine is stock with only bolt on stuff like K&N filter, performance PROM (which has been in for 6-7 years and has always worked fine), TB airfoil and beefed up Acell ignition. It has a Doug Nash 4+3 transmission. The car was tuned up a couple of months ago with new plugs, wires, TPS, IAC & distributor parts. Up until a couple of weeks ago its been running very strong and without any problems. Then one evening coming home I rounded the corner onto my street and it just died...like it was running out of gas. It will idle just fine but if you give it gas it just bogs down and wants to die. You can press the accelerator down very slowly and the engine speeds up just fine, but it you press gingerly it bogs down and wants to quit. Now, when its cold it starts and runs good until it gets up to about 100 degrees and then it dies again. No check engine light when we startup, but comes on after slight warm up and stays on with engine running badly. No other codes have been registered.
The local Chevrolet dealer's technician is now stumped. So far we have changed out the MAS and both MAS relays. He claims that he has checked and replaced every wire connector in question (I think this is all of them actually) and traced down the wires from the ECM to the MAS all with no identified problems. Also, we took the performance PROM out and replaced it with the original chip because we were having difficulty getting code readings out of the ECM with the performance PROM. All of these changes have had no improving effect. Recently, he says that he has had the car out on the road and it worked fine one day and the next day its acting up again with code 33s and the same symptoms I mentioned above.
Today he told me that they ordered a new ECM, put it in and had no change in condition so they took it out and sent it back.
STILL STUMPED !
:confused: :nonod:


[Modified by pmihaltian, 10:59 AM 12/5/2001]

pmihaltian

Craig:

Thanks for sending me this information. I really appreciate your ideas and help. We are tracking down circuit 39 and any associated problems.
I know I have a bad solinoid or a bad connection on the 4+3 transmission OD unit and I think the OD unit may be on circuit 39, If so, maybe this is the root of the problem. I'll let you know what we discover.
STILL LOOKING...

:boxing

pmihaltian

I finally got the code 33 problem solved on my '86 Pace Car. After 6 weeks in the shop and $1400 in repair bills it finally boiled down to the ECM unit. However, there were many other minor problems which, while not the root cause, may have been contributors to some of the error data we were getting along the way.
In the final analysis we replaced the MAS and both relays twice. We repaired all the grounding problems you guys led us to, replaced many relay and wiring connectors and swapped out the ECM twice. And, oh yes, replaced the front pipes and converter which, of course, had nothing to do with the Code 33 problem.
What it finally came down to was the ECM falsely recording low voltage input from the TPS which thru off the MAS and generated the code 33 and caused the engine bogging performance.
When it was all said and done, the guidance you guys provided was instrumental in helping us track down the problem. Your suggestions were accurate and on target. Again, I sincerely thank you for taking the time out of your busy schedules to help a fellow Corvette lover who you don't even know. A special thanks to Dave Fulchner and Craig Marcho who were spectacularily helpful - THANKS GUYS !

PeteL

Yeah! A code 33 fixed, sorry it cost so much money.

I am confused why it took two ECM's to find a bad ECM? Did a fault in the system somewhere cause the replacement ECM to fail in some manner?

Marcho Polo

Glad you got it working! I know that 33 is a tough one. Sorry you went through so much to track it down, but hopefully it's in tip-top shape now and will give you a few more smiles as you drive!

vader86

i was just about to say to replace the ECM, after relays, wires goin out, and MAF that is usually the problem.

1127mrvt

the 33 and 36 were maf and 22 is throttle position sensor i replaced distributor and all relays the tps the mass air flow the fuel pump the prom the ecm now the only code is the 33 still the 33 the car use to bog down when i gave it gas going down the road as long as i didnt give it too much gas it was ok but now my only problem is when i crank it up i have to give it gas for a few seconds to get the missing out of it then it will drive like a champ any idea what could cause it i have a brand new raceing wires new plugs new injectors and any more ideas on the code 33

JrRifleCoach

If only others would take the time to work out their problems BEFORE sending the car to the shop.

Many $$$$ can be saved.

pmihaltian

THIS THREAD IS ALMOST 12 YEARS OLD !!!

pmihaltian

See attached code 33 write-up.