tworottiedogs

I thought I got rid of the codes by cleaning contacts and replacing the O2 sensor. I went for a ride and after about 5 minutes the service light came on and the car ran like crap. It sounds like it's skipping and has no power. Code 33 is the only one to come up. Haynes says it's MAF related. It also states that missing can cause the same fault. Can a MAF cause the crappy idle and missing or do you think I should concentrate on ignition problems. I pulled the plug wires, cap/coil and rotor and will be replacing them tomorrow. The way this problem keeps coming back makes me wonder. I wouyld think that the ignition would cause problems all the time.

I hate intermittant gripes.

Update:

This seems strange. I set the TPS votage a few days ago but now it is high and fluctuates. It reads about .65 and stays steady for a few seconds and then drops. It kicks back up to .65 and then repeats the drop. Does that mean ECM problems??

thanks, :mad


[Modified by tworottiedogs, 6:37 PM 11/23/2002]


[Modified by tworottiedogs, 1:40 PM 11/29/2002]

Bluevette85

Unplug the maf and see if it idles better or tap the maf and see it the idle changes. You could start with replacing the two maf relays.


[Modified by Bluevette85, 9:47 PM 11/23/2002]

Cooter

When I first bought my '86, it ran like crap and had codes 33 and 34. I swapped MAF's and nothing changed, I changed the relays and got rid of the 34, but the 33 kept coming back. I noticed on the scan tool that the O2 reading was really off and constant, so I replaced the sensor, but it did not change anything. So, after checking wiring and finding no faults anywhere, I replaced the ECM and the problem magically went away.

drive it

First you need to follow the above....go ahead and change the relays-they're cheap. Tap the maf, make sure the tps is good, etc.
If everything checks out OK-did this only start after mods? Your sig says you've got a bigger cam...how much duration,lsa?
Also adjust the throttle blades so your iac is about 20 to 30 at idle....
then if it still keeps throwing the code 33-(real common with mods) you need to reprogram the parameters for that $#*&^ code 33! It's under ecm constants-maf high diag. error-code 33. The stock program is 45gps. Just increase it to 100 or so; it'll still set the 33 if you have a real problem then.

tworottiedogs

I replaced the ECM and that didn't help. I am going to swap the TB back and see if that may be the culprit. I did unplug the maf and the idle did change. I haven't swapped the relays. Where are they? They are not listed in the haynes manual.

Now I have codes 33, 36 and 44

I replaced the o2 sensor already. Does this look like a vacuum leak problem? Wouldn't a vacuum leak cause MAF and O2 sensor faults???


I just swapped the TB back and it didn't change. Same codes and same symptoms. Bad idle, stumbling accelleration.

I am going to put the other TB back on and the old ECM back in. I might have to get professional help on this one!

[Modified by tworottiedogs, 6:07 PM 11/26/2002] :mad


[Modified by tworottiedogs, 6:57 PM 11/26/2002]

Goody

No experience on this engine, but MAF relays seem to repair this malfunction more often then not. Page Scorp508 for assist.

tworottiedogs

Any idea on where these relays are? Thanks. I just called auto zone and they have them but I can't find them???

scorp508

The MAF power and burnoff relays are located behind your battery. If you take the battery panel off (the gill panel) and look to the right of your battery you will see the two of them mounted to the firewall kind of near the door jamb.

Now.... be careful as there are different part numbers for different years of C4s. Here are two service bulletins. The 2nd one has the part numbers in it.

Mass Air Flow Sensor - MIL ON/Code 33 Set

Number: 87-298-6E
Section: 6E
Date: SEPT., 1988
Subject: CODE 33 MASS AIR FLOW (MAF) SENSOR VOLTAGE HIGH DIAGNOSTICS

Model and Year: 1986-87 CAMARO, CORVETTE WITH 5.0L OR 5.7L
(VIN CODE F, 8) ENGINE
TO: 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 DealerService 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.


MAF Sensor - MIL ON/Codes 33/34/36 Stored


Number: 87-270-6E
Section: 6E
Date: Jan., 1988
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 ENGINES
TO: 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
87 Corvette 14089936 14089936


[Modified by scorp508, 7:26 PM 11/26/2002]

tworottiedogs

I am not trying to sound retarded (it just happens that way) but the two relays are not in the same place?? One behind the battery (power relay) and one behind the breadbox (burnoff relay)??

86 Corvette 10067925 10094701

scorp508

85 is the only year you will find one behind the breadbox. In 86 they will both be behind the battery. :yesnod:

tworottiedogs

The TSB has two different part numbers but all of the history posts say they are the same. Does it matter?

scorp508

As far as I konw '86 does in fact use the different P/Ns as you see. My 87 and I think all after that have two of the same.

tworottiedogs

thanks for all the help. I'll post the results.

Bluevette85

The power relay has 5 contacts and the burn-off relay has 4 contacts. You can use the power relay for both but not the other way around.

tworottiedogs

First problem was found thanks to everyones help. It had two 701 relays installed. More to do before I can see if it's fixed.

tworottiedogs

Still no luck in fixing this. I replaced both relays. It started up fine and idled smooth. I made it about 100 yards from the driveway when it set code 33 again and fell on its face. I wouldn't idle anymore and I limped home.

This is what I have done:

Replaced:
iac
ecm
burnoff relay
MAF power up relay

Swapped out:

throttle body
IAC

I swapped them with the old units to see what would happen and it did the same exact thing.

Any clues or is it time for professional help and more
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$

vettedreams

Hey Mike, sorry to here about all the prob. I wonder if my modifying the MAF has something to do with it? I did gut it with a sawzall, I bet if you go to Rowe"s auto sales in N.B actually Bridgeton, go in parts and ask him if you could try a used MAF, they gutted an "87 this summer the parts are still there, thought about it myself awhile back just never did it.

tworottiedogs

Thanks Rich,

I thought about looking for a MAF to swap in there. I'll try to find that place this weekend. I miss the simplicity of the '71.

tworottiedogs

I swapped the MAF and it didn't help. Nothing else is left that I can find. I swapped:
MAF
ECM
IAC
MAF relays
TB
EGR

scorp508

I forget, did you replace or at least investigate the TPS?