1989 Corvette Shows A Trouble Code #33

Grumpy · Jul 17, 2019

Long story short, on an error code 33, check the Instrument panel fuse first.

typical symtoms
car starts and does not idle consistently (so you might think TPS (set at .54 volts)
or the IAC is gummed up, (clean and test if required) look for vacuum leaks.
it also helps to throw a can or two of fuel injector cleaner in the fuel tank and get out the multi meter and verify the OHMS resistance in the ignition wires,
and changing to new spark plugs won,t hurt either,
changing the fuel filter can,t hurt.

http://garage.grumpysperformance.com/index.php?threads/maf-burn-off-relay-info.661/#post-908

http://garage.grumpysperformance.com/index.php?threads/testing-1985-89-m-a-f-sensor.1475/#post-3325

http://garage.grumpysperformance.com/index.php?threads/adjusting-your-tps-and-iac.168/#post-82331

http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/#post-70653

http://garage.grumpysperformance.co...vette-fuel-pump-replacement.15269/#post-88619

http://garage.grumpysperformance.co...-won-t-start-intermittently.14212/#post-72158

http://garage.grumpysperformance.co...asic-trouble-shooting-on-the-c4.302/#post-367

http://garage.grumpysperformance.com/index.php?threads/tpi-fuel-pressure-issue.10385/#post-42943

http://garage.grumpysperformance.co...-runs-rough-idles-and-sometimes-stalls.10688/

be aware the electrical grounds 104-105,106,107 must be checked and firmly connected to the engine

here i copied this :Just some additional info for the codes for the 85-91 tpi OBDI .
http://www.corvettedoctor.com/1985_91_DTC_Codes.html

http://garage.grumpysperformance.co...rouble-shooting-flow-chart-info.596/#post-793

1990-chevy-c1500-fuse-box-diagram-truck-silverado-1500-corvette-panel-electrical-wiring-house-o-diagrams-f-1043x592.jpg

Code #12: Normal No Codes.
Code #13: Open Oxygen Sensor Circuit.
Code #14: Coolant Sensor Circuit Low.
Code #15: Coolant Sensor Circuit High.
Code #21: Throttle Position Sensor High.
Code #22: Throttle Position Sensor Low.
Code #23: Manifold Air Temperature Circuit High.
Code #24: Vehicle Speed Sensor.
Code #25: Manifold Air Temperature Circuit Low.
Code #32: EGR System Failure.
Code #33: Mass Air Flow Sensor High.
Code #34: Mass Air Flow Sensor Low.
Code #36: Mas Air Flow Sensor Burn-Off Function Fault.
Code #41: Cylinder Select Error.
Code #42: Electronic Spark Timing.
Code #43: Electronic Spark Control.
Code #44: Lean Exhaust indication.
Code #45: Rich Exhaust Indication.
Code #46: Vehicle Anti Theft Fault.
Code #51: Faulty Mem-Cal.
Code #52: Fuel Calpak Missing.
Code #52: (1990-91 Corvette Only): Engine Oil Temperature Sensor Low.
Code #53: System Over Voltage.
Code #54: Fuel Pump Circuit Low Voltage.
Code #55: Defective ECM.
Code #62: Engine Oil Temperature Sensor Circuit High.

CODE 33

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

Re: MAF & code 34

the threads linked below may help, but its more than likely a bad temp sensor or the TPS OR IAC is out of adjustment. so the first thing Id suggest is to adjust the TPS and IAC per the linked info and check for loose connections and vacuum leaks, and loose plenum and intake runner gaskets
34 Mass Air Flow Circuit (1985-1990) Clean the throttle body. Check MAF connections. Replace MAF relay. Replace MAF Sensor. Possible ECM failure.
34 Manifold Absolute Pressure Low (1984) Check Vacuum hoses associated with MAP sensor. Check wiring and connections, particularly at ECM. Replace the sensor. Possible ECM failure.

MAF SENSORS AND RELAYS ARE FREQUENT SOURCE OF INTERMEDIATE OR HARD TO ISOLATE RUN ISSUES ON EARLIER TPI CORVETTES SO CHECK THEIR FUNCTION

a factory shop manual and a v.o.m. meter come in handy for testing!
http://www.chevythunder.com/Flow chart index.htm

http://www.mamotorworks.com/corvette-c4 ... 6-893.html
https://www.zip-corvette.com/85-89-high-performance-adjustable-maf-sensor.html
85-89 High Performance Adjustable MAF Sensor

https://www.rockauto.com/en/catalog...,exhaust+&+emission,mass+air+flow+sensor,5128

--------------------------------------------------------------------------------

CODE 34

Trouble Code 34 indicates that the Mass Air Flow (MAF) sensor is reporting less 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 < 4 grams per second, and
TPS indicates 10% or more throttle position, and
the engine speed is 1800 RPM or higher, and
the above conditions exist for over 5 seconds.

Typical causes for this code include:

1) Faulty air ducting to or from MAF sensor
2) Faulty ECM-to-MAF connections
3) Poor routing of MAF harness (i.e. near coil packs)
4) Maladjusted TPS sensor
5) Defective MAF sensor
6) Defective ECM

1989 corvette shows a trouble code #33

Grumpy · Jul 18, 2019

very helpful related videos

how to Read & Remove Codes on the OBD1 & OBD 2 corvette.
I am not a writer, I am just a retired City Cop. This method does work (I did it on my vette last night)
I hope this helps someone out, or answers a few of the unknown questions in regards to the mystique of the OBD system.
Best of Luck
Woody

HOW to Read & Clear Corvette OBD-1 & OBD-2 Codes

1, Car off, Key in the ignition (OFF position)

2, Install a paper clip or jumper between contacts #4 and #12 on the
16 pin OBD-2 connector, or the Top Right and the Bottom Left
terminal for the 12 pin OBD-1 connector.

3, turn key to the ON position (ON, NOT START)

4, watch the dash display as it flashes through the code sequence, I recommend having a pen ready and writing down the codes because you will forget them.

If you see three large dashes “---“ that means there are no codes for that specific module.
As the codes flash they will run through three separate modules showing the Codes for each.
You can determine what module is being scanned by the small number displayed,
#1, #4, or #9
#1 shows codes in the CCM
#4 shows codes in the MOTOR section
#9 shows codes in the ABS/ASR EBTCM

So when you insert the jumper into the terminals, and turn the key to the On position, you will see flashing codes, either three dashes (meaning no codes) or the code numbers will be displayed, The small number (below the codes) 1, 4,or 9 (representing the module being scanned) will also be displayed below the code numbers or dashes

The system will automatically show the codes or dashes for module #1 then continue to module #4, then continue to module #9.
(YES there are only three modules 1, 4, 9)

5, If you made a mistake or missed part of the sequence, all you
have to do is turn
the key off, wait 10 seconds, and turn the key back on and the scan
sequence will
repeat itself from the beginning.

6, After the code scan of all three modules is complete, you will see “1.0” displayed,
If you just wanted the code info, then you can opt out now (or any
time) and turn the key off and remove the jumper.

Or if you want to Remove the codes, do the following

7, remember there are three modules with separate codes in each, so to remove
all of the codes, (or any individual ones), you will have to navigate between the
three modules by doing the following.

When the scan is complete and the 1.0 is showing, press the
TRIP/ODO
button repeatedly until 1.7 appears.
1.7 is the designation meaning “clear codes”.
With the 1.7 now showing, press the ENG/METRIC button until
the three dashes “---“ appears (remember the three dashes means no codes),
confirming you just cleared them for that module.

Now you must go to the second module by pressing the TRIP button, (TRIP not TRIP/ODO) you will see the new second module number appear (1, 4, or 9).

Repeat the sequence as before and press the TRIP/ODO button repeatedly until 1.7 appears. 1.7 is the designation meaning “clear codes”. With the 1.7 now showing, press the ENG/METRIC button until the three dashes “---“ appears (remember the three dashes means no codes), confirming you just cleared them for that module.

Repeat the sequence to advance to the third module and clear them as the first two.

If you see code C-12, it is the designation for CODES HAVE BEEN CLEARED.

Turn the key to the OFF position and remove.
Don’t forget to remove the jumper from the OBD terminal

You should familiarize yourself with the location of the three buttons on the dash you will be using.

TRIP will advance you to the next module
TRIP/ODO will advance you to the 1.7 (clearing code)
ENG/METRIC will clear the code (while in the 1.7)

Originally Posted by Casethecorvetteman

On a 94-96 you can check the codes with a paper clip as follows:

You short pin "12" to pin "4" and turn the ignition switch to "On" without starting the engine.

The speedometer will display any codes using the same protocol as the 1990-1993 model but there are some changes in the designation for the modules plus additional modules are added:

Module "1" is still the CCM module.

Module "4" is now called the PCM module (Powertrain Control Module) because automatic transmission computer control was added to Engine Control Module in 1994.

Module 7 (on the 1996 model only) is the RTD module. (This is the Real Time Dampening module which replaced the Selective Ride Control module in 1996).

Module 9 is the ABS/ASR module number from 1994 through 1996.
Finally, Module "A", the DERM (Dynamic Energy Control Module --- (the air bag control module) will be requested to show any codes.

Just like the 1990-1993 display, you read the codes on the speedometer (big) and read the module number on the trip odometer (small).

A series of dashed lines for instance “ - - -“ indicates no more stored codes for that module.

A code showing as “C12” for the CCM module (module #1) means no codes are stored. So C12 is a good thing to see.

Again, you can cause the codes to repeat by turning the ignition off for five seconds and then back on.

Turn the ignition off and remove the short to restore normal operation.

To clear the codes,

1. With ignition "off" ground terminal #12 of the DLC (use bent paper clip to connect pin 4 to pin 12)

2. Turn ignition "on".

3. Press trip/odo button on the DIC until 1.7 appears in the trip
monitor area of the instrument cluster.

4. Press eng/met button on the DIC & hold until "---" appears in the
speedometer area of the cluster, this will clear CCM DTC'S.

To clear PCM/ECM codes do the following:

1. Press the trip reset button on the DIC until the desired system is displayed. In this case it will be 4.0.

2. Press trip/odo button on the DIC until the desired diagnostic mode(4.7) is displayed on the trip monitor area of the cluster.

3. Press & hold the eng/met button on the DIC until "---" is
displayed in the speedometer area of the cluster, this will clear PCM codes.

To clear ABS/ASR codes do the following:

Same as above but you’re looking for “9.7” on the trip odo

And here are the codes

1994-1995: Diagnostic Trouble Codes
DTC #11: Malfunction Indicator Lamp Circuit.
DTC #13: Bank #1 Heated Oxygen Sensor #1 Circuit:
DTC #14: Engine Coolant Temperature Sensor Circuit Voltage Low.
DTC #15: Engine Coolant Temperature Sensor Circuit Voltage High.
DTC #16: Distributor Ignition System Low Pulse.
DTC #18: Injector Circuit.
DTC #21: Throttle Position Sensor Circuit Voltage High.
DTC #22: Throttle Position Sensor Circuit Voltage Low.
DTC #23: Intake Temperature Sensor Circuit Voltage High.
DTC #24: Vehicle Speed Sensor Circuit.
DTC #25: Intake Air Temperature Sensor Circuit Voltage Low.
DTC #26: Evaporative Emission Canister Purge Solenoid Valve Circuit.
DTC #27: EGR Vacuum Control Signal Solenoid Valve Circuit.
DTC #28: Transmission Range Pressure Switch Assembly Fault.
DTC #29: Secondary Air Injection Pump Circuit.
DTC #32: Exhaust Gas Recalculation.
DTC #33: Manifold Absolute Pressure Sensor Circuit High.
DTC #34: Manifold Absolute Pressure Sensor Circuit Low.
DTC #36: Distributor Ignition System High Pulse.
DTC #37: Brake Switch Stuck On.
DTC #38: Brake Switch Stuck Off.
DTC #41: Ignition Control Circuit Open.
DTC #42: Ignition Control Circuit Shorted.
DTC #43: Knock Sensor Circuit.
DTC #44: Bank 1 LF Heated Oxygen Sensor #1 Circuit Lean.
DTC #45: Bank 1 LF Heated Oxygen Sensor #1 Circuit Rich.
DTC #47: Knock Sensor Circuit Or Module Missing.
DTC #48: Mass Air Flow Sensor Circuit.
DTC #50: System Voltage Low.
DTC #51: EPROM Programming Error.
DTC #52: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #53: System Voltage Low.
DTC #55: Fuel Lean Monitor.
DTC #58: Transmission Fluid Temperature Sensor Circuit Low.
DTC #59: Transmission Fluid Temperature Sensor Circuit High.
DTC #62: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #63: Bank 2 RF Heated Oxygen Sensor #1 Circuit Open.
DTC #64: Bank 2 RF Heated Oxygen Sensor #1 Circuit Lean.
DTC #65: Bank 2 RF Heated Oxygen Sensor #1 Circuit Rich.
DTC #66: A/C Refrigerant Pressure Sensor Circuit Open.
DTC #67: A/C Pressure Sensor Circuit Sensor or A/C Clutch.
DTC #68: A/C Relay Circuit.
DTC #69: A /C Clutch Circuit.
DTC #70: A/C Clutch Relay Driver Circuit.
DTC #72: Vehicle Speed Sensor Loss.
DTC #73: Pressure Control Solenoid Circuit Current Error.
DTC #74: Traction Control System Circuit Low.
DTC #75: Transmission System Voltage Low
DTC #77: Primary Cooling Fan Relay Control Circuit.
DTC #78: Secondary Cooling Fan Relay Control Circuit.
DTC #79: Transmission Fluid Overtemp.
DTC #80: Transmission Component Slipping.
DTC #81: Transmission 2-3 Shift Solenoid Circuit.
DTC #82: Transmission 1-2 Shift Solenoid Circuit.
DTC #83: Torque Converter Solenoid Voltage High.
DTC #84: 3-2 Control Solenoid Circuit.(Auto Only).
DTC #84: 2nd And 3rd Gear Blockout Relay Control Circuit.
DTC #85: Transmission TCC Stock On.
DTC #90: Transmission TCC Solenoid Circuit.
DTC #91: One To Four Upshift Lamp(Manual Only).
DTC #97: VSS Output Circuit.
DTC #98: Tachometer Output Signal Voltage Wrong.

To run a diagnostic on the PKE system, connect pins 4 and 8 on the ALDL (see pic below to see pin label order)

This image has been resized. Click this bar to view the full image.

Report this image

And the PKE diagnostic system works as follows:
With pins 4 and 8 connected, the PKE light in the Driver Info Centre will flash the codes.

Here is the list of DTCs and what they mean:

DTC #12: Receiver Memory Bad
DTC #13: Transmitter Not in Range
DTC #14: Non-Valid Transmitter Received
DTC #15: Valid Transmitter Received
DTC #16: Passenger Door Button Depressed
DTC #17: Hatch Button Depressed

95s are NOT OBD2.

Grumpy · Jul 18, 2019

https://www.corvetteforum.com/forum...-adjust-your-early-c4-tps-and-idle-speed.html

http://web.archive.org/web/20040202184835/corvetteforum.com/techtips/viewtopic.php?TopicID=2

85 and 87a -> Ground

86 -> Power

30 -> Output

-30 = constant [positive (+)] power (usually wired directly to car battery)
-85 = coil ground (wired to the negative (-) battery terminal or any grounded metal panel in the car)
-86 = coil power (wired to the control source. could be a switch, or it could be the car's IGN or ACC circuit.)
-87 = switched [positive (+)] power output. (when the relay coil is powered, lead/pin 87 is connected to lead/pin 30)
-87a = [on 5 lead/pin relays only] this lead/pin is connected to lead/pin 30 when the coil is NOT powered.

these charts are for the 1985-89 vette cooling fans

# Check fan fuses in the underhood fuse/relay panel
# Check fan relays (same location). Aside from getting out any electrical equipment to test the relay, you can swap it with another one (such as the fog lamp relay) and test for function. See if the relay works for the fog lamps and/or the swapped-in relay makes your fans work. Nearly all the relays in the panel are the same, except for maybe the ABS relay.
# You can jumper two pins on the DLC that should cause the fans to come on. 1993-1994 cars with the 12 pin DLC can jumper pins A and B. On a 1993, that is the same way that you would retrieve trouble codes from the ecm. The 1994 won't give you any codes, but the fans will engage. 1995-1997 uses pins 5 and 6 on the 16 pin DLC to initiate what is called "field service enable mode". That will cause the fans to come on and operate most sensors for sanity checking. After placing the jumper on the correct pins, turn the key to ON (don't start). If the fans work after jumpering the DLC, your PCM is capable of operating the fans and all fan wiring/relays should be ok.
# Deeper problems can be solved through testing and using the wiring schematic.

~Fans don't come on except when the a/c or SES is on~

~Temp gauge continues to rise with no automatic fan operation~

# With a scan tool, check to see what temp the PCM is seeing from the sensor in the water pump. Make sure you are aware of the temps the fans come on (stated in the beginning of this article). If the temp it sees is incorrectly low, it won't know to turn the fans on. Another possibility is that the temp is really ok, but the gauge is reading wrong. That is why you need to use the scan tool to see and compare the readings. Info on testing wiring and sensor can be found here.
# If that looks ok, then your PCM may have issues. You could always try resetting the PCM by pulling the PCM BAT fuse for about 30 seconds.

viewtopic.php?f=70&t=3504&p=9220#p9220
Testing the ECT (Engine Temperature) Sensors and Connections

THE DIAGRAM ABOVE HAS THE CORRECT WIRE COLORS

Pro tip before starting - Label your relays Relay 1, Relay 2, and Relay 3 according to the wiring diagram (your first post) and what your physical relays represent. Even if its just a sticky note. Get it all straight and stick to the same annotation while you troubleshoot.

You'll need a multimeter than can measure DC voltage and continuity:

Remove all three relays so you're only dealing with the sockets

DC Voltage tests:
1. Confirm 12V between the socket for pin 85 and the negative battery terminal on all 3 relay sockets
2. Confirm 12v between the socket for pin 30 and the negative battery terminal on relay sockets 1 and 2

Continuity tests:
1. Confirm continuity with the end of the dark green wire and the socket for pin 86 for relay 1
2. Confirm continuity with the end of the dark blue wire and the socket for pin 86 for relay 2 AND relay 3.
3. Confirm continuity between the socket for pin 87 for relay 1 and side B of the left cooling fan connector
4. Confirm continuity between side A of the left cooling fan connector and side B of the right cooling fanconnector AND the socket for pin 87 for relay #2.
5. Confirm continuity between the socket for pin 87 for relay #3 and Negative Battery Terminal
6. Confirm continuity between side A of the right cooling connector and Negative Battery Terminal.

Do the steps in order and use the negative battery terminal for your connection when I specify to. Verifying at the negative battery terminal will ensure you're circuit is making a good connection to the chassis ground. If it doesn't make it all the way back to the battery, it's a crap ground and testing it my way will reveal the problem

ECT Temperature vs. Resistance Values

ÂºC ÂºF Ohms
100 212 177
90 194 241
80 176 332
70 158 467
60 140 667
50 122 973
45 113 1188
40 104 1459
35 95 1802
30 86 2238
25 77 2796
20 68 3520
15 59 4450
10 50 5670
5 41 7280
0 32 9420
-5 23 12300
-10 14 16180
-15 5 21450
-20 -4 28680
-30 -22 52700
-40 -40 100700

Use a Digital Volt Meter (DVM) set to ohms to measure resistance. Note: Use a high impedance meter (at least 10 megohm) when dealing with the PCM. Most modern DVMs will do, but your old analog meter can damage the PCM. It is also a good idea to get a " reference" from the meter you are working with. With the DVM on the ohms scale, touch the two meter leads together and note the ohm reading. It may not always be perfectly zero, but may be within a tenth or two. Now when you take an ohm reading, you will know what the meter will show when there is really no resistance.

* The sensor in the head has only one terminal. This sensor is for the temperature indicator on the dashboard. Place one test lead on the sensor terminal and the other on a known good ground. Compare the reading to the table. If your car is cold from sitting overnight, the reading should be close to ambient temperature.
* The sensor in the water pump has two terminals. This sensor is for the temperature input to the PCM. Place a test lead on each of the sensor terminals to take the reading. (When reading resistance, it does not matter which lead goes to which terminal)

If the sensor seems to be ok, you may also need to test at the harness connector for proper lead conditions. Use your test meter set on the dc voltage scale to do this. You will need the key in the RUN position, but don't have to start the car.

* For the one lead connector at the head, place the red test lead on the connector terminal and the black test lead to a known good ground. With the key ON, you should read battery voltage (+12vdc or close to it). You can also ground the lead and see if the gauge in the car deflects to full hot.
o If you get no voltage, switch the meter to ohms to see if the lead is grounded.
o No voltage or no ground mean that the lead is open.
o If the gauge is at full hot all the tme, the lead is grounded back toward the gauge. It could be possible for the lead to be pinched and grounded toward the gauge and broken and open back toward the sensor (like in the case of the wire getting caught somewhere during some major engine work). Physically tracing the wire from the sensor into the harness should locate the problem.
* The two lead connector at the water pump has a black (ground) lead and a PCM +5vdc power lead (probably yellow). Place the black meter test lead to black connector lead and the red meter test lead to the other connector lead (yellow on my 1995). You should read +5vdc because this is monitoring voltage being supplied from the PCM.
* If you get no reading:
o Test the yellow lead by placing the DVM red lead on it and the DVM black lead to ground. A +5vdc reading will indicate the lead is ok.
+ If you get no voltage, switch the meter to ohms to see if the lead is grounded.
+ No voltage or no ground mean that the lead is open.
o You can test the black connector lead by using the ohms scale on the DVM. Place the DVM black lead to ground. Place the DVM red lead to the black lead of the connector. If the lead is ok, you will get an ohm reading close to zero. If you get no reading or a very high one, the lead is open or partially open.
* OBD-I DTCs 14 and 15 or OBD-II DTCs P0117 and P0118 are typically associated with problems the PCM sees with the sensors or circuits.

Footnote: If you ever have to test the IAT, it operates the same as the two lead coolant sensor. The same temp vs. resistance table above is applicable to the IAT, as well as the +5vdc lead and ground wire at the harness connector.
basic fuel injector test
(pull your trouble codes and check battery voltage ,alternator output and ignition spark first)

(BTW it rarely hurts to drain old fuel thats over 4 months old and replace the cars fuel filter, then add two different brands of fuel injection cleaner and 6 oz of marvel mystery oil to as full tank of fresh high test gas to the car if its been sitting un-used for very long before you start testing for fuel injection related issues

now Ill assume your battery reads over 12 volts and the starter works, and easily spins the engine
the first step
find the fuel rail shrader valve and remove the cap and connect the fuel pressure gauge
if you turn on the ignition key to get the dash and accessories to light up but don,t start the engine,the fuel pump,
should briefly run to pressurize the fuel rail to about 38psi-42 psi,
this should stay at this pressure level for at least 5 minutes minimum, if it drops slowly your fuel rail is leaking fuel.
now the fuel pressure regulator may be defective or leaking, or in very rare cases the fuel pump may be defective ,
but the most likely cause is a fuel injector(s) stuck in the open position.
next pull the injector harness,

off a single injector at a time, press the wire bar to release the clip, retention, then pull it up and off, the noid light plugs into the harness,
use the spare injector pig tail

on the now disconnected injector ,connect the multi meter on ohms setting and it should read 11-13 ohms injector on each injector tested.
if it reads under 9 ohms or over 20 ohms its a defective injector
now use a couple 3 ft long test leads connect one too one of the pig tail test leads
https://www.walmart.com/ip/Uxcell-2...-Clips-Test-Jumper-Wire-1-5m-2-Color/45588242

and to 12 volts, connect the other pig tail lead too a different test lead and watch the fuel pressure gauge,with the key out of the ignition , you should have 38-42 psi of fuel rail pressure, watch carefully while you tap the second test lead to ground (the plenum or alternator case works) the fuel pressure should drop as you tap the ground pig tail lead, this verifies the injector function at least partially, if you don,t see the pressure drop the injectors not allowing fuel flow through it and should be replaced.
after you complete each injector test , turn the ignition key on, to re-pressurize the fuel trail and reconnect the harness to the previously tested injector,
repeat the noid light and pig-tail function fuel pressure test on each of the other injectors individually.

youll need a fuel pressure gauge and multi meter

it helps if you have a spare fuel injector pig-tail for testing

having a NOID light injector harness tester wont hurt either
https://www.harborfreight.com/11-piece-noid-light-and-iac-tester-set-97959.html

on the TPI and LT1 efi and many other EFI intakes,
theres a shrader valve,
that can be easily accessed to check fuel rail pressure,
dealing in facts you verify is always preferable.

GM part number for the complete fuel rail o-ring kit is 17111696

if your TPI FUEL PRESSURE REGULATOR DIAPHRAGM LEAKS youll find it difficult or impossible to be starting your car

heres a link to the correct o-rings they are light blue
NAPA sells them at times
all the o-rings on the fuel rails and injectors need to be dipped in thin oil so they insert and slide into place with less friction, this tends to greatly reduce the chance of the o-rings ripping, and yes you need the correct o-rings that fit correctly to begin with if you expect the rings to seal correctly
http://tpiparts.net/inc/sdetail/10950/300

17113544 - Injector Seals
17111696 - O-Ring Kit
22514722 - Fuel Inlet O-Ring
22516256 - Fuel Inlet O-Ring

if you have a cylinder or two not functioning correctly or a injector thats barely functional, an infrared temp gun checking the exhaust port temps will generally allow you to find and isolate its location as it will be usually be running at a lower average temperature,
infrared thermometers are a very useful tool to track down issues with tuning, or mal functioning sensors , without verified facts your guessing.
this is the most consistently accurate I.R temp gun I've used for testing[/img]

http://www.testequipmentdepot.com/e...1100200223789&utm_content=All Extech Products
INFRARED TEMP GUN
Wide temperature range from -58 to 1832Â°F (-50 to 1000Â°C)
any time that your dealing with a potential temperature issue or a trouble issue where , knowing the exact temperature vs what a gauge might say, it helps to have a handy and accurate infrared temp gun handy to locate and confirm heat, levels.

http://garage.grumpysperformance.co...dding-a-fuel-pressure-gauge.15264/#post-88472

http://garage.grumpysperformance.co...njection-at-start-up-problem.7309/#post-24862

http://garage.grumpysperformance.co...oven-facts-if-your-in-doubt.13051/#post-84695

http://garage.grumpysperformance.com/index.php?threads/tpi-fuel-pressure-issue.10385/#post-42943

http://garage.grumpysperformance.co...-system-trouble-shooting-flow-chart-info.596/

http://garage.grumpysperformance.com/index.php?threads/diagnoseing-tpi-lt1-problems.1241/

http://garage.grumpysperformance.com/index.php?threads/gm-tpi-stalling-diagnosis.15194/#post-86991
http://users.erols.com/srweiss/tableifc.htm

1989 Corvette Shows A Trouble Code #33

Grumpy

The Grumpy Grease Monkey mechanical engineer.

Grumpy

The Grumpy Grease Monkey mechanical engineer.

Grumpy

The Grumpy Grease Monkey mechanical engineer.