I've been battling code 33 for several months. I,ve replaced MAF, ECM, Power & Burnoff Relays nothing has helped. By checkng gms/sec with auto X-ray I've noticed that it is always setting the code @ 1800rpms with @ 46-51gms/sec. If I accelerate hard I can cheat the code, but in traffic when I gradually accelerate it sets the code. I've put about 70,000 mile on this combo and have just recently started having this problem. Anybody have any ideas?

Dennis

 

Code 33 is set when the signal from the MAF (or MAP in newer cars) is too high for over 6 seconds. I would first check that the TPS is set correctly - if 1/4 throttle is sensed incorrectly from the TPS, the computer will interpert that as MAF signal too high for a low throttle condition, and set code 33.
I hope it is that easy!

George

 

No, I've tried to bump the tps up @.64 with no luck. If I could reprogram the gms/sec from 45 to 75 for setting code 33 it would be fine.

Dennis

 

OK. That was my best quess. How about a vacuum leak on the engine side of the throttle valve? That forces an incorrect throttle position at light loads, but has little effect later. But at the transition, where the leak is being overcome, you could get a code 33 condition. At least it's easy to check for, with a little ether sprayed around.

George

 

No, I have'nt been able to find any vacuum leaks.
I sent my prom back to TPIS so they could check if they could find anything there. I asked them if they were able to change the gms /sec in the diagnostic code 33 and raise the threshold from 45 to 75. I have'nt heard back from them yet.


Dennis

 

Dennis,

Wouldn't it bother you not knowing what was going on? Changing the alarm limit is kinda desperate.

Of course, "Desperate times call for desperate measures"

George

 

I have spent a lot of time and money chasing this down. I just cant find anything wrong. I dont know if this is a common problem for a 383 mini ram setup but I think the motor is calling for that much air. The window for setting the code is so small that a couple of gms/sec or 100 rpms it would never set the code. Plus it's not intermittent, it happens everytime the car is on a load between 1800-2000 rpms with <1/4 throttle. Any other time the car runs great.

Dennis

 

I have had the same problem for a long time and it drives me nuts. I drive with the car in 3 and the TC disconnected to keep the rpms up.

 

I've been doing the same thing, I unlock the converter on the freeway it flashes enough rpms not to set the code. Still does not help leaving a light in traffic.

Dennis

 

Here are a few of the links from my attempt to correct this code 33. I am into the corvette shop for $1100. I have spent about that much on my own troubleshooting. The latest attempt will be swapping the high stall converter for a stock one. I don't see how but the rumor is that it might be able to cause this?????????
http://forums.corvetteforum.com/zerothread?id=444702
http://forums.corvetteforum.com/zerothread?id=439472
http://forums.corvetteforum.com/zerothread?id=443562
http://forums.corvetteforum.com/zerothread?id=465255 :mad

 

What happens if you try to adjust the TPS down to .45 vollts? Throttle response might suffer, this is just a test. But it could be very enlightening if the code 33 goes away. For sure setting the TPS too much on the high side of the stock .54 volt spec can cause the code to appear.

Do you have the stock throttle valve assembly? That can make more of a difference in air flow VS throttle plate angle than dropping in a different motor.

Even a very large cam and motor can only draw a certain amount of air through a certain throttle opening.

George

 

I have tried a high tps setting, low setting, and a right-on setting. I have tried several different TB and presently have a 52mm in there. I have re-wired the relays, replaced the relays, along with just about everything else.

 

Excellent. What were the results of your testing with different TPS settings? Earlier you mentioned that:

"checking gms/sec with auto X-ray I've noticed that it is always setting the code @ 1800rpms with @ 46-51gms/sec"

That was at some TPS setting. If you got the exact same report at different TPS settings, the error cannot be ignored, IMO.

Conversely, if the Gms/sec error varies proportionately with TPS settings, you could very easily justify changing the alarm limits, or installing an aftermarket MAF scaling device. You could then be assured that:
1. the MAF frequency varies proportionately with air flow
2. the TPS is sensitive to small angular changes
3. both signals arrive at the computer

I would still try to locate the problem, just on principle. But I would not throw any more money at it. But if the error report is the same at different base TPS settings, I would be concerned.

 

I am feeling your pain. I too have an 86 vette with a code 33 problem. When it lights it runs like garbage. When its off it run unbeleivable. Mine is a 420 cube 11.3 :1 ported miniram motor that has had only 250 miles on the combo. This problem started shortly after changing my wiper motor. I am not sure if I disturbed crappy wiring. Now it seems to light the code as soon as it starts (95 % of the time). When code 33 is lit it barely wants to run at part throttle (esp. when cold). Seems to be running really rich and breaking up. When the code is off it runs mint minute one and has crisp throttle response. I have changed tps steeings up and down, min. air rate a few times, MAF sensor itself, tried 2 different computers with no real differences. I am not sure where the relays are on a late 86 for the MAF or I would have changed them too. I need to figure this problem out asap ( I almost got beat by a 03 lighning pickup from a 20 mph roll) My car should run easy 11's. As for another problem I have an auto xray and it wont communicate with any of the ecms I have at least not properly. I have a 86 , 87, and an 88 '165 computer. If I configure it for anything other than 85' the data is screwed up and worthless.
When code 33 is lit I have no power down low and the O 2 sensor is realling 0 mv. when at any high rpm under load. 5500 and up in first, 4600 and up in second, and anything above 3500 in third.
any ideas?

 

George,

I,m not following what your saying about maf gms/sec v.s. different tps base settings. I,ve tried various base tps setting but it still sets the code @ 1800 rpms @ 46-51 gms/sec. To my knowledge the tps setting has nothing to do with gms/sec? The throttle blade opening allowing air to pass over the wire element in the maf is what changes the amount of gms/sec.
I have made up a wire harness to backprobe the maf and connect it to a multimeter as I drive down the road. I dont see any voltage fluctuation at the power wire. I dont get any voltage at the burnoff wire except for @1 sec when I shut the car off. I get a 5 volt reference siginal from the ecm. The ground is good. The voltage back to the ecm varies with throttle opening and load with it setting the code 33 at 2.2volts @ 1800 rpms. The only problem I know is the motor is calling for more than the(2.2volts) 45 gms/sec @ less 2000 rpms, which is what the diagnostics code 33 for a stock vette is set up for.


Dennis

 

Dennis,

The error "code @ 1800 rpms @ 46-51 gms/sec" means that your MAF signal is too high for a particular throttle setting. In the fore-mentioned case, the alarm occurred at 1800 rpms, with the MAF reading 46-51. If the TPS position is changed, and everything is working OK, the alarm might then occur at 2000 rpm, or at 1800 but with 40-46 gms/sec. If the TPS position has no effect on the alarm, that indicates that something more serious than high airflow is occurring. If the alarm changes, at least the reading of TPS and the comparing to MAF frequency is working. So perhaps it is only a little too much air.

That is my reason for asking you to check the alarm at various TPS base settings.

George

 

George,

According to my GM service manual code 33 will set when: when maf sees more than 45 gms/sec for 1 sec at less than 2000 rpms with less than 1/4 throttle. I know that I meet these conditions when it sets the code. Do you know what tps voltage it takes to be considerd 1/4 throttle? It would be interesting to see how high I could run the tps voltage to make it think its at 1/4 throttle.

 

There is no set voltage for 1/4 throttle. It will depend on the min and max voltage for a particular TPS setting. The computer then scales the voltage range and figures out volts per degree of movement. I do not know about the scan tools, but you might be able to query the computer as to what the current table is.

The best test I could come up with was my suggestion of moving the TPS and collecting the errors. Even though the 1/4 throttle voltage remains unknown, for sure a large movement of the base TPS position has altered it.

George

Of course a TPS that has a bad spot can give you a code 33, but I am sure that you said that you tried a new TPS? Right?


[Modified by George West, 6:38 PM 11/10/2003]

 

My 420 cube 86 sets a code 33 the moment I start it. It never waits for me to drive or anything. Using a auto xray (after idleing for 10 minutes in closed loop) I have derived the following.

Engine Rpm between 1000 and 1100
TPS at .60 volts
Mass Air meter at 10 grams
Injector pulse 1.4 - 1.5 ms
Oxygen sensor between 450 and 650 mVolts
Knock sensor even
Block learn 118
O2 cross counts about 15 a second
Idle air motor position between 29 and 37
coolant even at 170.6

seems to idle smooth when warmed up.
thottle response is not nearly as good as when code 33 is not lit.
Car cannot be driven at slow speeds at part throttle without it feeling like someone turned off the ignition for about 2 seconds every minute or so. Wont rev past 5700 in 1st (0 mv on the O2)
wont rev past 4500 in second (0 mv on O2)
wont rev past 3500 in third (0 mv on O2)

Peak reading in the MAF sensor with Code 33 lit is only 165.
Peak without code 33 is 253.

Any ideas?

 

Gold86vette,

I think it would be safe to say since you set your code on start up you probably have an electrical problem. Do you have a GM service manual? You can use the code 33 diagnostic flow chart diagram to verify what components are or are not working. Also, when the SES light comes on it is going to a limp mode even though the scanner is still showing air flow thru the maf it is not using the information for engine management. It goes to default programming and limits the engine to a get me home safe mode. It is not a good idea to make full throttle runs, you are risking damage to your engine.