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Question: 1987 Mass Air Flow Sensor - Code 33 Diagnosis and Replacement Options

VetteLee

Member
Joined
Aug 10, 2008
Messages
24
Location
Dana Point, CA
Corvette
1987 Callaway Twin Turbo
I had my 1987 Callaway serviced recently: transmission rebuild, new clutch and replacement of the thermistor used to measure water temp for cold starting. On the drive home from the shop, I got a check engine light and found it was a code 33. After clearing the code, it will usually reappear after driving the car, but not always. I've replaced the related relays.

The Corvette shop said the Mass Air Flow Sensor could be bad, but it might be the ECM. They can swap in a test Mass Air Flow sensor.
Is it likely the problem is something else? I'm suspicious that I didn't have the problem until the work was done.

I'll run the checks as outlined by the service manual next to see if there are any obvious problems. Are the test harnesses offered by Mid America Motorworks useful?

If I decide to replace the MAF myself, can you make a recommendation for source/brand/model? I see there are various replacements and rebuilt units.

Thanks,
Lee
 
No experience with this but have seen post about a relay for the Mass Air Flow Sensor.

Glenn
:w
 
No experience with this but have seen post about a relay for the Mass Air Flow Sensor.

Glenn
:w

Thanks Glenn,

As I recall, I've replaced four relays; I think there were two behind the battery and two up on the firewall:
(1) MAF burn off
(2) fuel pump
(3) MAF power
(4) I don't remember the function of this one :confused.

Lee
 
it is a little suspecious that this appears as it leaves a shop...but, knowing that these wiring harness's are a wreck after 20 yrs makes me think that your problem could be anything from a dirty plug connector to a wire working its way loose in the MAF plug.
I have had to change the MAF plug 3 times because the thing is so cheesy that wires break at the plug and vibration finishes them off. '

How did the eng perform when the code appeared? seem normal or was there some poor performance? Usually when a MAF failure appears, it'll set the code, shift into limp home mode in the ecm and there will be issues applying gas or accellerating.

Go for the MAF swap,. and if that makes no difference take a look at the ECM plugs and prom . Sometimes its as simple as unplugging, and plugging in again. Contacts get corroded especially living near salt water...Dana Pt? ( nice community btw, I miss OC)

Grounds on the harness are also critical. I'm fighting an intermittant condition that cuts several injectors in half while enrichening others. This comes/goes at will. Its electrical, somehow related to grounds or connectors, your problem is probably similar. These harnesses seem fine until disturbed somehow then they cause all type of problem.
 
Thanks for the info boomdriver - sounds like you've been having a lot of fun chasing down your problems.

It's definitely going into limp mode when the code comes on - very poor performance, low rough idle, etc.

When did you live in OC? I'm about a mile or two from the beach here and the car is garaged.

Lee
 
Thanks for the info boomdriver - sounds like you've been having a lot of fun chasing down your problems.

It's definitely going into limp mode when the code comes on - very poor performance, low rough idle, etc.

When did you live in OC? I'm about a mile or two from the beach here and the car is garaged.

Lee
I guess it was around 2001....I was in Newport then moved up to Ventura Harbor. I miss Ca lots..
I eventually left the state...I thought the cost of living had gotten out of control so I went looking for greener pastures....
Biggest mistake of my life. I can;t put a price tag on a drive up PCH.
Life just got better when I did that...:beer Driving thru Huntington or Dana Pt...or Malibu in a friggin Corvette? Thats as good as it gets !

Now I'm stuck with a drive around beltway 8 (houston) for entertainment.
 
Here's another option that would be well suited for a Callaway (or any other high hp 86-89 L98 with MAF):

Instead of just buying a replacement MAF sensor, you could convert to a modern slot-style MAF sensor and housing that offers increased measurement range. With an accompanying ecm tune and injector upgrade to either 42 lb. or 63 lb. injectors, you could eliminate the superfueler if desired, and have the advantage of fully integrated and tuneable fuel and spark control capable of supporting up to 800-900 hp.

These products and support are all available from Blowerworks.
 
I guess it was around 2001....I was in Newport then moved up to Ventura Harbor. I miss Ca lots..
I eventually left the state...I thought the cost of living had gotten out of control so I went looking for greener pastures....
Biggest mistake of my life. I can;t put a price tag on a drive up PCH.
Life just got better when I did that...:beer Driving thru Huntington or Dana Pt...or Malibu in a friggin Corvette? Thats as good as it gets !

Now I'm stuck with a drive around beltway 8 (houston) for entertainment.

Maybe you can figure out a way to get back here. I think the economy is stronger in Houston that it is here right now, though.

Take care,

Lee
 
Here's another option that would be well suited for a Callaway (or any other high hp 86-89 L98 with MAF):

Instead of just buying a replacement MAF sensor, you could convert to a modern slot-style MAF sensor and housing that offers increased measurement range. With an accompanying ecm tune and injector upgrade to either 42 lb. or 63 lb. injectors, you could eliminate the superfueler if desired, and have the advantage of fully integrated and tuneable fuel and spark control capable of supporting up to 800-900 hp.

These products and support are all available from Blowerworks.
Thanks for the idea, tequilaboy. I'll check it out.

Lee
 
I checked with Greg Carroll at BlowerWorks, asking for some info and if they had any Callaway Twin Turbo customers. Here is the response I got:

"Hi Lee - no Callaway customers yet. You'd be the first but I'm sure not the last. The old Bosch sensor wears out and the calibration goes south. Additionally with the new sensor you can eliminate the burn off relays.

The new sensor is far superior to the old and will fly thru emissions.
The new BIN simply directs the MAF output to a new ECM input (U can download the IG from my website). If you are to keep the engine exactly as is I'd copy your BIN with the redirected input. We stay with the Bosch 254 gms/sec.

However if U want to we can go with bigger injectors and a new tune (600 gms/sec) where you now eliminate the MicroFueler. I suspect with a good dyno tune you could safely squeak out more ponies since there would be no fuel distribution problems from the wet manifold.
VTY
greg"
 
MAF Sensor Code

Had it on my 87. Dealer wanted to replace MAF for several hundred $. I pulled out the battery and replaced the 2 MAF relays at NAPA for about $20 each and it fixed the code problem. Hope yours is that easy.
 
Dont have a Vette but have a tpi.The burn off relay is a very common issue with them.Dont replace the maf before you do the relays first.I made that mistake and still had to do the relays.
 
I've already replaced the relays. I'm hoping to do some more checks this week using the test harness I just got that plugs into the MAF connector.

I spoke to my Corvette mechanic and he had some suggestions for testing.

Lee
 
I've already replaced the relays. I'm hoping to do some more checks this week using the test harness I just got that plugs into the MAF connector.

I spoke to my Corvette mechanic and he had some suggestions for testing.

Lee

I assume you've already visually checked the thin MAF wires inside the MAF tube, right?

Jake
 
Thanks for the info boomdriver - sounds like you've been having a lot of fun chasing down your problems.

It's definitely going into limp mode when the code comes on - very poor performance, low rough idle, etc.

When did you live in OC? I'm about a mile or two from the beach here and the car is garaged.

Lee

lee,
After some effort, I discovered that my problems were the result of failed wiring in the driver side injection harness section. Wires were so degraded inside the insulation, that the signal was faulty and inconsistant. The injectors were getting portions of the signal, and the resistance was slowing the signal down or making each pulse out of phase or less than adequate. The cure was to chop out these bad sections and solder in new pieces. About 10 or 12 wires around 6" to 12" in length.
The MAF section of harness is in the same bundle that comes from the firewall behind the distributer. I had problems with the purple wire (2nd wire in the plug) breaking off internally right at the plug so I had replaced the MAF plug a couploe times in the past. I question one replacement now and suspect that it was the injectors that were acting up and not the MAF.

Point being, I have been told for years that GM had some issues with wiring harness insulation back in the 80's. So, if you can prove that the MAF is ok, then it might be to your benefit to start checking continuity in the harness to the MAF. It ain't fun, but it can be enlightening. Normally, if the ECM is setting a code, that means there is faulty input going TO the ECM....bad wiring or connections to control devices like injectors may not set a code because that fault is FROM or AFTER the ECM...so the ECM does not know there is a problem.

I have yet to find a single other wire thats defective in this harness, just the driver side injector section.

Good luck with it.
 
My former 86; broken wire inside MAF. Replacement for $50 taken from a wrecked 'F' Body and my local wrecking emporium. Tested on site.

Ran fine for years and was still going strong when I sold the car.

Jake
 
My former 86; broken wire inside MAF. Replacement for $50 taken from a wrecked 'F' Body and my local wrecking emporium. Tested on site.

Ran fine for years and was still going strong when I sold the car.

Jake


$50 ?

musta been the military discount.... The civilian discount is only $2
 
If you need

I have a Stock MAF if you need one for cheep.
 
I have a Stock MAF if you need one for cheep.


speaking of MAFs...

does anybody have any experience with the Granetelli adjustable MAF ??

its an expensive lil piece of hardware....wanted some feedback before the investment.
 
Grounds

On the bell housing is a grounding post with several wires attached to it one of the grounds is a flat strap ground wire that goes to the ecm. I would check to be sure that all the ground points are clean and tight with all the wires on it. Also you might remove the stud and use a tap to clean out the threads for this ground post. They will get a white corrosion on them causing the stud to not make a good ground in the bell housing. Also clean the grounds behind the battery and on the frame rails on each side of the engine. The ecm in many cases uses the ground to contact a sensor for information. The grounds for the sensors in effect are used as switches by the ecm to contact them it closes the open ground to the sensor and reads the sensor output.
 

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