Desperately need HELP!!! Code 33 MAF
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Melting Slicks
Joined: Oct 2000
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From: Na
Desperately need HELP!!! Code 33 MAF
Ok here's the scoop. I need to have my car tested for emissions ASAP. My plates have already been suspended and I have before the 13th to get it my car to pass or I face a HUGE fine.
Anyway, after driving for about a minute the check engine light comes on. It comes up as code 33 mass air flow sensor. The MAF I have currently intalled is brand new as well as the power and burnoff relays. I also reset the TPS and IAC according to tech tips. Also, there are no vacuum leaks that I can tell. Can a bad vehicle speed sensor cause this by any chance? The one I have in there does not work and I don't get a mph reading on the dash.
I really need help quick! Is there anybody in the Chicago area that can look at the car for me??? Thanks everyone.
Anyway, after driving for about a minute the check engine light comes on. It comes up as code 33 mass air flow sensor. The MAF I have currently intalled is brand new as well as the power and burnoff relays. I also reset the TPS and IAC according to tech tips. Also, there are no vacuum leaks that I can tell. Can a bad vehicle speed sensor cause this by any chance? The one I have in there does not work and I don't get a mph reading on the dash.
I really need help quick! Is there anybody in the Chicago area that can look at the car for me??? Thanks everyone.
Team Owner
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From: Summerland B.C. Canada
http://members.shaw.ca/corvette86/Code%2033.pdf
There is some diagnostics here.
Did you get my email reguarding digi dash ?
There is some diagnostics here.
Did you get my email reguarding digi dash ?
Le Mans Master
Joined: Feb 2000
Posts: 9,715
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From: Kempner Texas
Originally Posted by NUckINg FuTS
Ok here's the scoop. I need to have my car tested for emissions ASAP. My plates have already been suspended and I have before the 13th to get it my car to pass or I face a HUGE fine.
Anyway, after driving for about a minute the check engine light comes on. It comes up as code 33 mass air flow sensor. The MAF I have currently intalled is brand new as well as the power and burnoff relays. I also reset the TPS and IAC according to tech tips. Also, there are no vacuum leaks that I can tell. Can a bad vehicle speed sensor cause this by any chance? The one I have in there does not work and I don't get a mph reading on the dash.
I really need help quick! Is there anybody in the Chicago area that can look at the car for me??? Thanks everyone.
Anyway, after driving for about a minute the check engine light comes on. It comes up as code 33 mass air flow sensor. The MAF I have currently intalled is brand new as well as the power and burnoff relays. I also reset the TPS and IAC according to tech tips. Also, there are no vacuum leaks that I can tell. Can a bad vehicle speed sensor cause this by any chance? The one I have in there does not work and I don't get a mph reading on the dash.
I really need help quick! Is there anybody in the Chicago area that can look at the car for me??? Thanks everyone.
The oil pressure switch or the ECM, through control of the fuel pump relay, provides the voltage for the MAF. The MAF then gets 12 V for it's power relay which then provides 12 V to the MAF sensor.
So the MAF may not be getting powered up so it won't see the voltage it needs, the ECM then sets Code 33.
Circuit 998 has a pull up resistor but if it's open, the ECM will see high voltage as set Code 33.
Also, if the MAF sees the Burn-Off signal while the engine is running, a Code 33 will set.
Apply 12 V to the pump terminal on the ALDL ("G"). You should see 12 V at the MAF; if no voltage check to see that the fuel pump is running, if not repair the fuel pump circuit - could be a bad fuel pump relay not keeping the MAF powered up. Applying 12 V to the MAF ("G") will insure the MAF remains powered up.
There's a very long trouble-shooting procedure in the Shop Manual using a volt meter and test light to test all the circuits.
Hope this helps.
Jake
Melting Slicks
Joined: Jan 2002
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From: Lecanto Florida
I was getting that code and came here for advice. Cleaned the filter and the MAF but the thing that I think cured the code was replacing the two relays that are attached to the firewall behind the battery. Sorry, I don't know the name of the parts off hand but they both work in conjunction with the MAF and aren't expensive. They both have the same part number = #14089936
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Originally Posted by CREWZIN
I was getting that code and came here for advice. Cleaned the filter and the MAF but the thing that I think cured the code was replacing the two relays that are attached to the firewall behind the battery. Sorry, I don't know the name of the parts off hand but they both work in conjunction with the MAF and aren't expensive. They both have the same part number = #14089936
This is a cheap fix and may solve his problem
Jack
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From: The Top of Utah
I'm no L98 or MAF system expert, but the ECM MAY need the VSS input to keep things straight. Check the trouble shooting charts for a code 33, in your Helms. One thing I DO know, is if there are any air leaks between the MAF and the TB (not a vacuum leak) or a vacuum leak, it will cause the MAF to send erroneous readings to the ECM, because it isn't monitoring all the air getting to the engine. Just because a sensor sends bad reading and the code points to the sensor, doesn't mean that the sensor is at fault.
RACE ON!!!
RACE ON!!!
Thread Starter
Melting Slicks
Joined: Oct 2000
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From: Na
I'm so frustrated right now!!! I went through all the diagnostics and everthing checks out. With terminal G on the ALCL jumped, the MAF is getting 12V on terminal E. A and B on the MAF are getting good ground aso. With the ignition on MAF terminal D has 0 volt as should be and CKT 998 is getting 5.7V with the ingition on which is within range. Is there anything else to check? Is it possible my brand new MAF is faulty (it is a reman Bosch from autozone) I already exchanged the MAF once at Autozone. 
I forgot to mention I also had my PROM reprogrammed. Is it possible there is something screwy in the programming???
I forgot to mention I also had my PROM reprogrammed. Is it possible there is something screwy in the programming???
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Have you changed the relays yet? Many posts have indicated that this action will clear MAF codes. My 86 was throwing 33/34's until the relays were replaced. Not that I'm suggesting to start throwing new parts (money) at the problem, but this is a cheap fix that has proven results. BTW my 86 uses two different P/N relays.
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Drifting
Joined: Feb 2003
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From: Davis CA
May I ask the obvious question? Why don't you go ahead and have it tested? I don't believe that the presence of codes is a problem is it? So get past inspection then worry with the codes. Maybe you have a wacky computer.
Or was a test failure what started this thread?
Steve
Or was a test failure what started this thread?
Steve
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From: The Top of Utah
Originally Posted by NUckINg FuTS
I need to mention that no mater what I do the code 33 will not display when the car is in park. It will ONLY come on when the car is being driven 
Originally Posted by Chatman
May I ask the obvious question? Why don't you go ahead and have it tested? I don't believe that the presence of codes is a problem is it? So get past inspection then worry with the codes.
NUckINg FuTS,
I'd be spending some time on that VSS. I think your symptoms merit it. Does the book address this? Good luck, and...
RACE ON!!!
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,019
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From: Na
Chatman,
The car starts farting and spitting as soon as that code comes on. There is no way it will pass in that condition.
I will try swapping out the VSS and see what happens. If not, then I will try a new computer. Desperate times = desperate measures $$$
The car starts farting and spitting as soon as that code comes on. There is no way it will pass in that condition.
I will try swapping out the VSS and see what happens. If not, then I will try a new computer. Desperate times = desperate measures $$$
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by NUckINg FuTS
I will try swapping out the VSS and see what happens. If not, then I will try a new computer. Desperate times = desperate measures $$$
Originally Posted by CFI-EFI
Just because a sensor sends bad reading and the code points to the sensor, doesn't mean that the sensor is at fault.
RACE ON!!!
Le Mans Master
Joined: Feb 2000
Posts: 9,715
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From: Kempner Texas
Since you made all the trouble-shooting checks (which I hope included the checks at the ECM itself), I see only two options without having to resort to taking it to a dealer/shop.
One is to borrow known good parts, like the ECM, PROM, MAF, relays. Install them on your engine and see if the problem is corrected. If the problem is corrected, then swap in your parts one at a time until the problem recurs; you'll then know which one is causing it.
There's got to be someone in your area that has the parts you need. I did if for a friend last year to help him sort out a problem he was having.
The second is to buy/borrow a ScanTool, Diacom, etc., to get real time data on what's going on.
Wish I could help more.
Jake
One is to borrow known good parts, like the ECM, PROM, MAF, relays. Install them on your engine and see if the problem is corrected. If the problem is corrected, then swap in your parts one at a time until the problem recurs; you'll then know which one is causing it.
There's got to be someone in your area that has the parts you need. I did if for a friend last year to help him sort out a problem he was having.
The second is to buy/borrow a ScanTool, Diacom, etc., to get real time data on what's going on.
Wish I could help more.
Jake
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,019
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From: Na
Jake,
The only test I did on the ECM was at CKT 998. It was getting 5.7V with the ignition on. Also, I have access to a snap-on scan tool. What kind of data should I be looking for???
The only test I did on the ECM was at CKT 998. It was getting 5.7V with the ignition on. Also, I have access to a snap-on scan tool. What kind of data should I be looking for???
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Originally Posted by NUckINg FuTS
Jake,
The only test I did on the ECM was at CKT 998. It was getting 5.7V with the ignition on. Also, I have access to a snap-on scan tool. What kind of data should I be looking for???
The only test I did on the ECM was at CKT 998. It was getting 5.7V with the ignition on. Also, I have access to a snap-on scan tool. What kind of data should I be looking for???
Start out by disconnecting the battery to clear the stored code.
With Diacom running on my laptop, I can monitor most of the critical sensor functions to see if any of them is out of range. There are about 27 different readings that I look at. I know from experience which readings I should be getting, but in the beginning I referred to my service manuals to see in what range the readings should be.
For your code 33 problem, you should look primarily at airflow and fuel readings.
According to the diagram someone else already posted (which is directly from the GM Corvette Shop Manual), here are the circuits to check when trying to find the cause of a Code 33:
120, 340, 450, 900, 993, 994, and 998. Ckt 465 (Fuel Pump Relay Drive)is also shown in the loop, but the manual doesn't show a checking procedure.
Do you know somone with a MAF you can borrow just to try? Even one from an 'F' body will work.
If you check everything there is to check, then it has to be the ECM that's bad.
Jake
Last edited by JAKE; Sep 9, 2004 at 01:25 PM.