I need new ideas. Constant, not intermittent, code 33. I have changed both relays behind the battery. Still no change.
Checked all connections, and visually inspected the MAF unit. All looks good.
If it's the ECM, is there a way to test, before I go through all the trouble to change that? It still gives me the code 12, before it gives me the code 33.
Any way to test the MAF before I buy one of those as well?
Where's the best source for those parts ?
I have a factory service manual as well as the Haynes and Chiltons. :smash: :smash: :smash: :smash: :smash:

 

What happens when you get on the gas?

 

The car runs fine otherwise. I notice a slight decrease in mpg; and with cruise control set at 65, once in awhile there is a hesitation.
But nail it from a stop and it will burn the tires, run smooth right up to the redline, and not miss a beat anywhere.
This whole thing is really frustrating.
SOMEONE out there must have had the same problem at one time. :confused: :mad

 

I had the same code on my 86. Changed the relays and the MAF- still got the code. I found a service bulletin which addressed the issue. There was a problem with the original "PROM" chip. The service bulletin stated which chip to replace the original with. I contacted Jeff at Superior Chevrolet (great guy). He shipped me the new prom. It took care of everything. It also increased the shifting rpm so she would not lock into OD before 41mph, that is if you have an auto trans. The car runs great now. I will get you the service bulletin if you want. Just email me and I will send it back as an attachment. Hope this helps- it sure solved my problems.

 

Here are all the service bulletins I found on error code 33. Not sure if these will help, but at least you have them.

Service Bulletin Number: 86-152
Bulletin Sequence Number: 110
Date of Bulletin: 8609
NHTSA Item Number: 86552
Make: CHEVROLET
Model: CORVETTE
Year: 1986
Component: FUEL:FUEL SYSTEM OTHER PARTS
Summary: SERVICE ENGINE SOON LIGHT CODE "33" MAF SENSOR VOLTAGE HIGH-PERFORM DIAGNOSTIC C HECK FOR CODE 33 FOUND IN 1986 SHOP MANUAL-CHANGE MAF POWER RELAY-MAF POWER RELA Y NEW P/N IS 10067925-ALL 1986 CHEVROLET CAMERO MODELS WITH LB9 ENGINE (ENG. COD E F), AND 1986 CORVETTE WITH L98 ENGINE (ENG. CODE 8)

Service Bulletin Number: 87-270-6E
Bulletin Sequence Number: 031
Date of Bulletin: 8801
NHTSA Item Number: 98253
Make: CHEVROLET
Model: CORVETTE
Year: 1986
Component: ELECTRICAL SYSTEM:IGNITION:ELECTRONIC CONTROL UNIT
Summary: MASS AIR FLOW (MAF) SENSOR SYSTEM DIAGNOSIS CODES 33/34 AND 36-MAF POWER RELAY S HOULD BE P/N 10067925-IF NOT REPLACED WITH P/N 10067925-ALL 1986 TO 1987 CHEVROL ET CAMARO AND CORVETTE MODELS WITH 5.0L OR 5.7L PFI ENGINES

Service Bulletin Number: 87-298-6E
Bulletin Sequence Number: 129
Date of Bulletin: 8809
NHTSA Item Number: SB002811
Make: CHEVROLET
Model: CORVETTE
Year: 1986
Component: ELECTRICAL SYSTEM:IGNITION:ELECTRONIC CONTROL UNIT
Summary: CODE 33 MASS AIR FLOW (MAF)SENSOR VOLTAGE HIGH DIAGNOSIS-CONDITION WHEREBY MAF S ENSOR CIRCUIT CAN NOT ACCOMPLISH CAUSED IN-OPEN OR INTERMITTENT IN CIRCUIT 998-S HORT TO GROUND IN CIRCUIT 900 FAULTY OR INCORRECT BURNOFF RELAY-CONNECTIONS SHOU LD BEINSPECTED FOR CORROSION AND/OR BENT PINS-ALL 1986/1987 CHEVROLET CAMARO AND CORVETTE MODELS WITH 5.0L OR 5.7L (VIN F, 8) ENGINE TLH

 

This is the revised Service Bulletin I was making reference to. #86-1626E. The PROM replacement takes about 15 minutes.

Number: Reissue 86-162

Section: 6E

Date: MAY, 1987
Subject: ENGINE CALIBRATION CHANGE: TO
IMPROVE DRIVEABILITY AND ELIMINATE FALSE "SERVICE ENGINE SOON" LIGHTS

Model and Year: 1986 CORVETTE
TO: ALL CHEVROLET DEALERS


Chevrolet Dealer Service Bulletin 86-162 is being reissued to provide a revised calibrator for use on the 1986 corvette with aluminum heads and manual transmission. All copies of Dealer Service Bulletin 86-162 (Section 6E) dated Oct., 1986 should be destroyed.

New service calibrators (Ref: called Mem-Cal in Shop Manual)
have been released for the 1986 Corvette with the 5.7L TPI
engine. These calibrators will address the following
customer comments:

1. "Rough Idle" on both hot and cold engine. The idle speed is raised to 625 plus or minus 25 RPM with automatic transmission and 750 plus or minus 50 with manual
transmission vehicles.

2. "Chuggle or Shudder" at low speeds - Torque converter clutch (TCC) engagement speed is raised to 41 MPH with automatic transmission vehicles.

3. "Surge" at road load - This improvement is for automatic transmission vehicles only.

4. "Engine Overspeed" in 1st gear - This improvement is for manual transmission vehicle only.

5. "Hesitation" on light acceleration with a hot engine.
6. "Service Engine Soon" lights - eliminates the following false codes:

A. Code 33 - Mass Airflow Sensor Voltage Low
B. Code 34 - Mass Airflow Sensor Voltage High
C. Code 43 - Electronic Spark Control (ESC) this correction is for cast iron head Corvettes only (VIN #119016 or earlier).



If normal engine diagnostics and repair do not correct the
above conditions, it will be necessary to replace the
calibrator in the ECM. Below is a listing of the new
calibrators and their usages.

I. On Iron-head Corvettes (VIN #119016 or earlier)

A. Manual Transmission use 1227943
B. Automatic Transmission with 2.59 (GM1) Axle use 1227942
with 3.07 (G44) Axle use 1227944



II. On Aluminum Head Corvettes (VIN #119016 or later) and all convertible models

A. Manual Transmission use 1228473

B. Automatic Transmission with 2.59 (GM1) Axle use 1228107
with 2.73 (GU2)/3.07 (G44) use 1228109

Use applicable Labor Time and Operation Numbers.

 

Thank you for that information. I'll work the problem from that angle. I'm wondering how they can say the PROM replacement only takes 15 minutes. Last time I got to the ECM unit, it was a long time under the dash to get it out, probably an hour or so.
Maybe while I'm there I should put an aftermarket PROM in it. Anyone know if there's a difference in price between a stock GM, and aftermarket PROM?

 

Are the relays you using for the MAF the same relay? On have you up dated to the revised power relay? I would start with that first, you may already have the updated PROM you would have to go by the code on the back of the PROM when I get my TIS2000 up and working I'll check to see if I can find the codes for you.

David Fulcher

 

FYI, the stock MAF relays on my 88 GTA has the number "8081" on top. I believe they are SPDT relays. I was throwing a code 36 and 34. I replaced the battery, the MAF, the MAF relay and the burnoff relay. Now I've got a code 33. :mad

EDIT: On the 86 it uses the older rectangular relays instead of the oval ones like my GTA uses. They're still SPDT though.


[Modified by Jim85IROC, 9:05 AM 3/4/2002]

 

Here is a link to the codes for your 86. Hope this helps.

http://www.angelfire.com/biz2/PROTECH/c4codes.html

 

Let me just say here that either one of you have a 1227165 ECM then there is a good chance that the ECM could be the problem. I think the 350TPI F bodies also use a 1227165 ECM so you need to check the GM replacement is 16198259 you can no longer get a 1227165 from GM(thank goodness) also only 86 used the two different relays they started out with the same part number relay but because of code 33 problems went to another relay for the power that had a shock rubber mount but there is also something else different between the two because if you install they incorrectly it will set a code 33 that is why I have ask if they are the same relay if so I would first replace the power relay with the revised relay and start from there because if this does not fix it you will probably need an ECM. But here is something else to look at:CODE 33 MASS AIR FLOW (MAF) SENSOR VOLTAGE HIGH DIAGNOSTIC #87-657-118
VEHICLES AFFECTED: 1987-86 F AND Y CARS W/5.OL AND 5.7L ENGINE

Some vehicles may experience a check engine light with a Code 33 stored which cannot be easily diagnosed. To promote better diagnosis of this condition, a brief explanation of the criteria for setting a Code 33 and an explanation of the possible causes follows.

Before beginning diagnosis, all 1986 models should be updated to the appropriate service PROM listed in bulletins: 86-657-106 and 86-650-109.

Mass Air Flow (MAF) power and burnoff relay part numbers should be checked to assure that they agree with those listed in bulletin 87-650-119 and 87-657-113.

Code 33 is set when the voltage at Pin B12 of the ECM exceeds 2.2 volts for 1 second or more either at startup or when the Throttle Position Sensor (TPS) is less than 20% and the RPM is less than 2000 RPM.

The ECM provides a 5 volt signal at pin B12 through a pull up resistor. This voltage must be brought below 2.2 volts by the MAF sensor circuitry during the conditions mentioned in the above paragraph or a Code 33 will set.

A condition whereby the MAf sensor circuit can not accomplish this can be caused in the following manners:

- An open or intermittent in Circuit 998 (dark green wire from ECM pin B12 to MAF sensor pin C)

- A condition causing voltage at MAF sensor pin D during crank or run such as:

- A short to ground in Circuit 900 (black wire from ECM pin D12 to MAF burnoff relay pin F).

- A faulty or incorrect burnoff relay

- A short to voltage in Circuit 994 (dark blue wire from pin A of the burnoff relay to pin D of the MAF sensor)

- A condition causing reduced voltage supply to pin E at the MAF sensor such as:

- An open, intermittent, or short to ground in Circuit 993 (red wire between pin E on the power relay and pin E on the MAF sensor)

- A faulty or incorrect power relay

- A faulty fuel pump relay

- Poor or intermittent ground on Circuit 450 (blk/white ground)

- Circuits 340 or 120 intermittent, grounded, open or spliced into with anything which draws enough current to lower the voltage by 2 volts or more for a 1 second period. This includes but is not limited to CB radios and alarm systems. (Circuit 340 orange extends from ECM pin Bl to MAF power relay pin A and fuel pump relay pin E; Circuit 120 tan/white extends from fuel pump relay pin A to MAF power relay pin D).

- An intermittent or low TPS switch causing the ECM to run a Code 33 check at a higher throttle angle (and therefore higher airflow rate) than specified.

- A faulty or poorly connected MAF sensor.

As evidenced by the above list of possible causes of Code 33, this circuitry is very sensitive to minor wiring discrepancies and poor or loose connections. All connections should be checked carefully. One method is to wiggle the connections while meeting the conditions for running a Code 33 test as listed earlier in this bulletin. In addition, they should be inspected for corrosion and/or bent pins.

This bulletin is extended to provide supplemental Code 33 diagnostic information and is not intended to replace the Code 33 diagnostic chart in the Service manual


And here is the part number of the revised relay, don't be confused about the part about it being intermitten I would still have the revised relay installed just incase.

2. If Code 33 is intermittent it will be necessary to change the MAF power relay. The MAF power relay new P/N is 10067925.

David Fulcher

 

Thank you guys for all that info.
Yes, the 2 relays I changed are not identical to each other, but are the correct numbers. In fact, I got the numbers from one of you guy's archived posts to someone else who was having code 33 problems, last year..
One is rubber mounted, and both are a square shaped. The shipping tags on them showed one to be a maf relay and the other to be a power relay.
With the occasional blip of hesitation I get going down the freeway, I wonder if the fuel pump relay could be at fault. I know that when the car was under warranty, something to do with the fuel pump failed. Maybe the pump itself, I don't know.
Where is the fuel pump relay ?
I checked the TPS setting and it shows to be where it has been for the past 8 years. So I've ruled that out.
And, is there a quick way to get the ECM out ? I have replaced the stock pad on the front of the dash with the flat piece from MAD. Do I have to take that back out ?
Maybe someone near this area wants to take this car off my hands like it is. I'm open to that.
Until then, I'll keep looking for help here. Thank you all.
:) :seeya

 

Thank you guys for those numbers. I have verified the correct relays were installed.
I dropped the ECM out, and found a light green wire skinned, possibly broken. Its next to a blue wire, and they're kind of by themselves.
What do I use to clean the pins and plugs on the ECM ?
Number of the ECM....."remanufactured by GM" Service # 1227165
The number on the side of the EPROM is 68767 8724
I'm thinking I will repair the bad wire, stick it back together and try it.
From your post, it sounds like the best fix would be to just go ahead and replace the ECM anyway. But what about the EPROM ? Does it need to be updated.
Would you check your bulletins on that ?
I'll keep checking back here for info.


[Modified by DI2FLY, 6:29 AM 3/12/2002]

 

DI2FLY,
>>Number of the ECM....."remanufactured by GM" Service # 1227165
That is the old GM ECM. As David F said, you need the updated GM replacement ECM # 16198259. Call NAPA. I bought a replacement ECM for my 88 from Riebes NAPA in Roseville for $117. That is about half the cost of one from GM. It is the same unit as GM, rebuilt by NAPA. The only difference is GM warrants their unit for 90 days and NAPA warrants theirs for life.

The EPROM probably is old also. Since it doesn't come with a new ECM, as suggested I would upgrade to a new EPROM from Jeff at Superior Chevrolet. Jeff offers great prices and is good to do business with.

If you need any additional help feel free to email or call me at 331-6554. I live in North Sacramento and will be glad to help. I can hook up my scan tool to your ECM and we can test it that way too if you are interested.

For a good HONEST and reliable corvette shop, contact Corvette Care in Rancho Cordova. Keith Becky is part owner and the Shop Manager. Great guy. 916-638-1911

Mike

 

Thanks, Mike. I tried to call you at 3pm, but you were still at work.
I had already picked up the new ECM from Performance Chevy, and installed it. It is the upgraded one. Still have to use my old PROM since no one has one, and I'm told it would be a week before one could get here. I'm going to try it , thinking the problem was the ECM, not the chip.. Still working on the broken wire, though.
I agree with you on Corvette Care in Rancho. Keith is a credit to this hobby. But I have seen other references to Superior Chevy. Where is that, and how do you contact them ? :chevy