Hi, I have found something very interesting in solving my maf code 33 error and i feel this could help many of you guys with this code.I thought i had found my code 33 or by moving msd box wires away from the maf but i was wrong.It came back.

Recently i purchased a 85 corvette tpi for a great price.I figured sense the flow chart pointed to the maf i would swap the one off the vette to the gta.I have tried several maf (6-7) new from the parts store all with the same code 33 issue.When i used my corvettes the code 33 was instantly gone.

I then immediately compared resistance values between my brand new *bad* maf and the good working vettes.Pin D and E on the new maf ohm at 3.53! On the good working maf i found the values to be at .035!!!

Long story short i ordered a BWD maf for a 85 vette and it works like a charm on my 87 gta! Odd thing is a buddys 89 irocz maf gave me a code 33 as well but worked great for him.
In the parts stores (advance,oreilly,autozone) some of the MAF sensors say they should work on both an 85 vette and a 87 gta.... Thats is incorrect!!

If you have a MAF code 33 (MAF too high) and cant find a single thing wrong with your system anywhere and have a 87 year car. Try a maf off of a 85 corvette or try to check the new meters ohm across pins d and e! Some cars will work with 3.5 ohms but in my case i needed .035 ohms

My everlasting question to all the pros here is: How can two identical cars use two different MAF meters when the ecm and prom are the same??
Logically i would think that the limp home resistors have something to do with this. Or is this is from a variance of the relays that power the MAF and burnoff?

87 is an odd year as there are some differences from early and late model 87's

So there it is, I hope i solved many peoples impossible MAF code 33 nightmares with this thread!
If you anyone has knowledge on this matter please let me know!!

 

Hi again, After further research I have discovered that there are 3 different MAF sensors for 85-89 tpi engines.

1985 is only one year (corvette)? tpi bwd number is 27850

1986-1987 BWD reman part number is 27854

1987-89 has a different MAF than the 86-87 There is i believe a difference from early to late 1987 MAF sensors (not 100% sure on this)

So if your having a untraceable MAF code 33 make sure when you buy the new MAF sensor that the parts store is giving you the right one.They should show 3 different part numbers for these years.If they don't then i would recommend going though a MAF manufacturer that does.

I am staying away from microtech personally.I called them up and what it came down to for them was a part number consolidation issue.

This may be your issue if your engine is mostly stock getting the code 33 after following this flow chart.If the chart points to the MAF and it is known to be good.

http://www.chevythunder.com/myweb/maf_code_33.htm

The flow chart don't lie for stock applications.

Again i really hope this helps someone and would love it if anyone that this has helped would post to this thread and let me know.

 

FIXED!!!!!!!!!!

After two years of working on her and a lot of head scratching she is finally fixed!

Order the 85 MAF for my 88 and instantly no more issues! You are a true life saver!

 

This is an interesting situation. From my viewpoint, I would of course have to caution anyone planning on using this fix to be sure that they have thoroughly completed the flow chart. The flowchart you have linked is a copy of the flowchart from the GM factory service manual. These flowcharts are meant to eliminate mistakes but they do not account for in range or some intermittent failures. I have seen several cases where the sensor and or ECM seem to pass the test, yet under certain conditions, the sensor voltage will go above the code set limit.

In cases like these, I end up with a lab scope back probing the signal circuit, while also watching sensor voltage on datastream, both while driving the vehicle. This type of in range or intermittent failure can be difficult to pinpoint. But if there is either a logic center failure in the ECM or a poor internal or harness connection, this is about the only way to find it.

It is interesting to note that pin D is the MAF burnoff circuit, while pin E is the 12v MAF power circuit. It makes since that a cross circuit between these two could cause MAF voltage to read very high. As far as why vehicles with the same basic MAF circuit and ECM would use different sensors, you would have to ask the engineers who designed and programmed the system. Variations in MAF data and actual MAF voltage would be due to variations in programming of the PROM and MemCal.

 

all the memcals I have seen have the same gram per second threshold for the code 33.

 

Hi again its been awhile since ive been around but anyhow i don't want to let this thread die i think there may be some significance in the info here that can help.

I completely agree with you ase doc flow charts should always be followed. Am i correct in believing that from the variance of resistance across the few different MAF that we have available to us that the ecm can wrongly interpret the voltages it sees from the MAF due to this "resistance variation" in effect triggering low and high codes when all other parts of the system are correctly in spec?

 

In post-1985 and pre-1993 cars, the resistance of the D terminal to ground may be less relevant than one might expect. The D terminal is the input from the MAF burnoff relay to signal the MAF to light off at full voltage (BURN-OFF MODE). The resultant analog MAF output voltage to the ECM via the C terminal is what the ECM required to confirm a successful burn-off cycle. Some of the aftermarket MAFs which use a thick-film sensor and output transistor instead of a current monitor on the hot wire and output transistor simply shunt some of the D terminal input signal to the output to simulate the correct threshold for a good burn-off, since the thick film sensor doesn't actually perform a burn-off. This may explain the difference measured from the D terminal to ground, or it may be coincidental.

In either case, the proper method for diagnosis is to measure the MAF output voltage during burn-off to verify a minimum of 3.5V.

This should not have any effect on the 33 error (MAF flow high) unless the burnoff relay is unintentionally applying power to the D terminal during normal engine operation, or there is some MAF output problem. Since the sensor is mostly surface mount devices potted in poly, diagnosis of the electronics other than externally is difficult, and repair is nearly impossible.

 

This thread is amazing! I'm having the same issue after putting a motor together. Maf was fine before

 

My 88 firebird has been dieng very randonly. But never throwing any codes. After weeks of getting stranded from it randomly dieing, this morning I fired it up and it gave code 33. Wonder if this is just an added problem to the random dieing? Or could it be the source? One time when it wouldn't start I put a wire from injector to negative terminal on battery and repeatedly touched it very fast and it made the injector pulse....so I have been trying to track down the source of no pulse. To no avail. Code 33 wouldn't have anything to do with injector pulse???

 

Might have more than one issue , use the charts to diagnose code 33

https://www.thirdgen.org/forums/tpi/...code-33-a.html