dirtyd6669

I have an 87 trans am 305. I was getting code 34 so i bought a used mass air flow sensor. Now im getting code 33. the problem before i changed anything was when i would give it gas it would rev up or want to accelerate and it was like it wanted to just die on me. i switched the mass air flow sensor and it seemed to run fin for a day and then it started to do the same thing but not as bad. When i first noticed the problem i saw that a few wires from the sensor had rubbed up against the belt and were worn through the insulation so i clipped them and then hooked them back up to a new plug i had gotten. Can anyone help me out with the problem and give me there input on it and could the wires have messed up the ecm when they touched a metal bracket on the engine

cIaRmOaCrZo

ahhhhh mannnn, i have the same freakin problem lol. (86' 305 tpi) but mine is intermittent, which in my opinion SUCKS more because its hard to tell when i actually fixed it. the check engine light comes on when its acting up, then not on when its fine, so thats an intermitient b i t c h lol. when the check engine lights on, if i dont give it throttle at 1,500 rpms, it will start surging and stuff. iv actually wiggled the connector at the MAS and it go away. but the actual problems on fixing it, was like changing to the upgraded burn off relay. theres more, ill try to post them for you

cIaRmOaCrZo

Subject:MASS AIR FLOW (MAF) SENSOR SYSTEM
DIAGNOSIS CODES 33, 34 AND 36
Model and Year:1986-87 CAMARO AND CORVETTE EQUIPPED
WITH 5.0L OR 5.7L PFI ENGINESTO:ALL CHEVROLET DEALERS

Some vehicles equipped with 5.0L or 5.7L port fuel injected engines may experience "Service Engine Soon" light with some combination of codes 33, 34 and/or 36 stored. This bulletin summarizes diagnostic procedures to be used in trouble shooting these codes.
All 1986 model year vehicles should be updated to the latest service PROM per bulletins: 86-162, section 6E Corvette or 86-194, section 6E, Camaro and checked for "Service Engine Soon" light reset prior to further diagnosis. In the case of 1986-87 Camaro or 1986 Corvette the MAF power relay should be checked to assure that it is part number 10067925. If it is not, then it should be replaced with part number 10067925. Please do not substitute.
Diagnosis
CODE 33 (MAF SENSOR VOLTAGE HIGH)
1.Inspect to determine that part number 10067925 relay has not inadvertently been installed as a burnoff relay or incorrectly connected as a burnoff relay. (reference bulletin 86-152, section 6E).
NOTICE:SOME SERVICE PARTS BOOKS REFLECT THIS INCORRECT USAGE.
For proper relay parts usages, please refer to the relay usage chart provided at the end of this bulletin. No substitutions should be made. 2.With the engine fully warmed up and operating in closed loop, check the airflow at 2000 RPM in neutral using a Tech 1 or equivalent scanner capable of testing air flow. If it is below 16.0 gm/sec for a 5.0L or below 10.0 gm/sec for a 5.7L engine and the block learn value is greater than 130, replace the MAF sensor.

If code 33 still resets, refer to section 6E of the appropriate service manual for further diagnostics.
CODE 34 (MAF SENSOR VOLTAGE LOW)
1.Inspect the plenum side of the throttle blades for deposits. If even a small amount of deposits are present, clean the throttle body per bulletin 87-100, section 6E.
2.Thoroughly inspect the vehicle for sources of air entering the engine without passing through the MAF sensor. Specifically, look for a cracked, cut or loose duct between the air meter and the throttle body, poor inlet runner to plenum or manifold sealing, a split PCV hose or any type of vacuum leak. A large quantity of air does not necessarily have to be involved. If any leaks are found, repair the condition, clear the codes and check if the code resets.
3.Check resistance of the MAF power relay contacts per bulletin 87-99, section 6E. The resistance should be less than 1 ohm across closed contacts. If the resistance is greater than 1 ohm replace the relay.
4.Check the minimum air rate and compare to specifications found in bulletin 87-100, section 6E. If the air rate is below specifications, please reset by connecting a vacuum gauge to port A on the throttle body, increasing the air rate by turning the minimum air screw until one inch of vacuum appears on the gauge and then reducing the minimum air setting by one half turn of the screw.

If code 34 still resets, refer to section 6E of the appropriate service manual for further diagnostics.
CODE 36 (MAF BURNOFF)
1.Inspect to verify that the MAF power and burnoff relays currently on the vehicle agree with the usage chart provided at the end of this bulletin.
2.Check the relays for proper function per bulletin 87-99, section 6E. Also check for PCV plugged condition per the same bulletin.
3.Check all electrical connections carefully.If code 36 still resets, refer to section 6E of the appropriate service manual for further diagnostics.

RELAY USAGE CHART
YEAR MODEL POWER RELAY BURNOFF RELAY
86 Corvette 10067925 10094701
86-87 Camaro 10067925 10094701
87 Corvette 14089936 14089936

cIaRmOaCrZo

Model and Year:1986-87 CAMARO, CORVETTE WITH 5.0L OR 5.7L
(VIN CODE F, 8) ENGINETO:ALL CHEVROLET DEALERS

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 Dealer Service Bulletins:86-162 (Sec. 6E) and 86-194 (Sec. 6E).

Mass Air Flow (MAF) power and burnoff relay part numbers should be checked to assure that they agree with those listed in Dealer Service Bulletin 87-270-6E.
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 cannot 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 B1 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 intended to provide supplemental code 33 diagnostic information and is not intended to replace the Code 33 diagnostic chart in the Service Manual.

dirtyd6669

were you ever able to get your problem fixed

WileECoyoteSr

Man I'd love to find out how your fix went. Of course mine is different. I have the L98 with MAP. I've been getting the hesitation off of a stop, surging, and now a check engine light with NO CODE! Any thoughts?

dirtyd6669

still trying to fix it
cant find the problem yet

WileECoyoteSr

For a lot of good hints on NO START problems you might go to
https://www.thirdgen.org/forums/tech...art-story.html
It's a thread I started to diagnose my 91 Z L98 problem and it helped me. You have to skim through each post because the amount of knowledge shared there is amazing. And it covers every conceivable "failure to launch" situation as I called it.

dirtyd6669

okay lost my internet for a few days but im back heres an update to what ive done so far. I bought a factory service manual for my car to see what it had to offer me for help. I pulled all of the plastic coverings off the wire harness that i could and followed the wires from my maf sensor and relays and found no problems under the hood with the wires that i was able to get my hands on. i pulled out the back seat and followed the wires from the fuel pump all the way to the dash and found no problems on those wires either.

update to the problem to help make it clearer for people is i am getting code 33 which is maf sensor voltage high. but dont know if that is causing the problem i am having. the problem is when i push the gas down past 1500 rpms it doesnt want to accelerate like it should

Haz

That is the most helpfull post I have found here regarding MAF issues. Are the checks for code 34 much the same? I have been trying for some time and following resetting TPS and IAC positions I changed from a code 33 to code 34.

I do not have access to a scanner so have been checking voltages. Have >12 volts on red wire.from MAF power relay. With ignition on/ motor off have 5.0volt from ECU when MAF unplugged (across green and black wires), drops to 2.7v when MAF plugged in (no air flow as motor off). Does this seem right. What resistance should be across MAF pins. I have A-B 60k,A-C 22.4k, A-D 1.7k, A-E 19.9k & B-C 82.5k.