I smacked the MAF sensor a bit harder than I have ever before trying to get that wire to rattle around before I even started the car today. Then I decided to unhook the MAF before I started messing with it this morning and it didn't start the black smoke and surging, but it was idling rough and at about 1000RPMs with fluctutations of about 25 RPMs (much improved from the videos.) Since it didn't start the black smoke and surging I plugged the MAF in and it started the surging and black smoke after only maybe 5 seconds, so I unplugged it right away and after about five seconds it cleared up alotand returned to the 1000RPM idle. When it is at 1000 it acts like a carbed car with a minor vacuum leak.
Secondly, I pulled plug wires off one at a time and found that #7 makes no difference....so I am checking compression again on this cylinder. Plug wire resistance was 900ohms. Sparking good out of the rotor when I held the wire close to the post with insulated channel locks.
EDIT: Compression same 120 and 135 @WOT with plugs in all other cylinders.
Ohm tested injectors at 14.7 across the board.
Intake or runner leak on number 7 ? could be a bad injector, make sure you don't have a broken wire to that injector older TPI s are noted for that. In case you don't know the system is set up to bank fire the injectors. One injector not working can cause the O2 sensor to tell the ecm that more fuel is needed. When I had a couple of dead injectors on my 90 Corvette I had a little of your problem, not this extreme though.
Originally Posted by scavanger
I am beginning to wonder about this MAF sensor.
Maybe number 7 was fouled from yesterday's testing. I think I will leave the MAF disconnected. I have an original TB for it. I am like you I keep all my stuff in boxes...just in case!
OH, I also got some cigars and lit it up pretty good and didn't observe any vacuum leaks. Spotted some more with the leftover MAF cleaner and no luck there either. It was quite evident that it was burning MAF cleaner if I gave a slight shot to the air filter. It was a more viable test this time as the idle is no longer surging like it was.
Maybe the maf ..check voltages...probably will idle a little high when disconnected ..ecm perimeter setting?
I think the maf is pretty expensive item for this...check all good ..read ..read ..chevy thunder.
I went through the flow chart for diagnosing a code 33 (MAF high signal) and found that ckt 998 (dark green wire at MAF; Terminal C) has 3.73 volts. This should be somewhere between 4-6 volts according to the chart. The diagnosis is faulty ECM. I probed this circuit at the MAF connector and directly at the ECM pigtail and both readings were 3.73 volts. I am confident I had a good ground on the car when I got this reading. I checked calibration on my relatively new digital voltmeter and found that my new car battery has 12.48 volts and two C batteries (1.5v) have 1.635 and another 1.64 volts. So, this begs the question..is this sufficient evidence to buy a new ECM? I look forward to buying one if it will solve the problem.
Check voltages first on other sensors for 5 volts reference with key on this tpi is about same as a tbi...usually if ecm is bad will be bad all over the board...no good voltages at either sensor.Best ground ..right off the battery.Usually ecm will smell burned if bad..from leaky capacitors ect.
Hey rat man..i,am going to do some thorough reading on this tpi..thing ...see what all could cause this code.
Will report back tomorrow evening.You read also see what we come up with? Maybe someone else will read also?
One thing i know if tps off will cause this code also..check voltage sweep on the tps?
Should be a steady rise in voltage no glitches.Also how about maf burn off relay and power ..should be how to check in thunder.
CC! I think we are on to something! The first other 5v that I checked MAT was also low.
Originally Posted by chevychase
Took a good sniff of ECM no smells.
I found the '88 Pontiac Firebird Service Manual (my car is '89) and it states the same 4-6 volt requirement for the '88. I probed around and here is what I found:
Take a look at these figures:
Battery: 12.38 At Terminals
B1: 12.30 MAF Burnoff Relay
A6 11.99 Ign. 12v
D12: 11.87 VSS
C14: 5.00 TPS
C10: 1.28 CTS
C16: 12.06 Battery 12v
B1: 12.05 Battery 12 v
C12: 3.72 MAT
B12: 3.73 MAF
These last two really concern me. The MAT in the video reports about what I would expect given the TB coolant bypass was done by PO...maybe a little low. One thing that did show correct was the TPS and that was exactly 5.0v.
I will ponder this a few more days while I consider an ECM for it. In the back of my head I am thinking this car is not capable of running correctly...geesh. It has to come to an end soon! lol
CC Thanks a ton for all the help. I will run TPS sweep tomorrow.
Okay rat man..your code 33 is intermittent. Everything i read..says you need to change the power relay for the maf.
It can be bad and bleed voltage /wrong voltages. The burn off relay only in the picture for a few seconds when you start.
It is used to burn off any residue at start on the filaments. Did you check tps voltage sweep?
Look this over
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 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 addition, they should be inspected for corrosion and/or bent pins.
And here is the part number of the revised relay, don't be confused about the part about it being intermittent I would still have the revised relay installed just in case.
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.
The following test need to be done when the problem is present.
Leave the MAF sensor connected, but rotate it around for access to the wiring for testing.
Turn the Key On Engine Off (KOEO). Check for 12 volts from the maf power relay on the Red wire.
Check for 0.05 volts or less on the Black and the Black/White wires.
Check for 2.5 volts on the Dark Green wire. If 5 volts is present, the (ECM) is doing its job, but the MAF sensor is defective.
When replacing the MAF sensor, it's a good idea to also replace the power relay and the burn off relay. These relays can cause intermittent MAF sensor problems
If the dark blue wire has 3 volts and the relays have been changed check the following .
Unplug the MAF sensor, burn off relay and power relay one at a time to see if the 3 volts on the Dk Blue wire drops.
If the voltage does not change when any of the devices are unplugged,check the connector for voltage bleeding across from the 5 volt reference signal on pin C. .
Done a lot of reading..from diff searches..either a bad relay..wire..or like said ecm?? I,am leaning toward a maladjusted tps ??
Trouble Code 33 indicates that the Mass Air Flow (MAF) sensor is reporting more air is entering the engine than makes sense based on RPM and TPS. The MAF sensor produces a frequency output; around 30 Hz at idle to 150 Hz under acceleration. The frequency varies proportionally to airflow. The ECM monitors the frequency and thus determines airflow into the engine. Typical idle MAF is 5 to 7 grams per second.
The conditions for setting this code are:
- no Code 21 or 22 (TPS Error) present, and
- the air flow reported is > 40 grams per second, and
- TPS indicates < 10% throttle position, and
- the engine speed is 1400 RPM or less, and
- the above conditions exist for over 5 seconds.
Typical causes for this code include:
1) Faulty MAF-to-ECM connection
2) Exceedingly noisy spark plug wires
3) Poor routing of MAF harness (i.e. near coil packs)
4) Maladjusted TPS sensor
5) Defective MAF sensor
6) Defective ECM
Ignore the new part numbers for relays??