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Old 06-01-2011   #1
Hoonbash
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87 GTA with code 33

Hi Gents

Finally getting around to working on my car again after having it parked for years.The car was speed density based but have decided to go back with the MAF set-up & to that end have re-connected the MAF wiring,installed the sensor in-line with the air-cleaner(snorkel-hood).Should add it has a custom chip done by lsracingchips(Jamy)for MAF

Used my old gutted MAF sensor & it flashed code 33 on me so I bought a used Granatelli adj MAF sensor & it is still doing the code,the SES light takes longer to come on now though,on start up it's running extremely rich & very sluggish on throttle up,wont idle without help

I've found a code 33 diagnostic chart on 3rd gen & have been following it until now.I don't have power where I should & the wiring circuit shows the oil-pressure switch is connected to the circuit.

Could a faulty oil-pressure switch be causing no power on the circuit?

Thanks
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Old 06-01-2011   #2
Hoonbash
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Re: 87 GTA with code 33

Here's the flow chart I'm using.I have no power at terminal C on the MAF power relay
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File Type: jpg Maf tree1.jpg (423.4 KB, 14 views)
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Old 06-02-2011   #3
rhomanski
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GTA Year: 1988
GTA Engine: 350 TPI Automatic
Re: 87 GTA with code 33

These are the two you should be using I think.

Regards,

Ron.
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File Type: jpg img783.jpg (954.2 KB, 9 views)
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Old 06-02-2011   #4
merc3065
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Re: 87 GTA with code 33

The used granatelli, has the resistance setting on it been modified? I remember that those can be changed/modified to account for more air coming into a modified engine. I think there is a small adjustment screw for a variable resistor on it.

Hoping you cleared the codes too yes?
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Old 06-02-2011   #5
Hoonbash
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Re: 87 GTA with code 33

Yes there is a small screw on the MAF have played with it & makes no difference,cleared the code also.
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Old 06-02-2011   #6
merc3065
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Re: 87 GTA with code 33

Would read up on the granatelli site or manufacturer on how to set it up properly. Then try again.
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Old 06-02-2011   #7
Hoonbash
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Re: 87 GTA with code 33

Not much to it,clock-wise to richen,counter to lean,but to do it right I'll need to drive the car.
http://www.granatellimotorsports.com...Mass%20Air.pdf

What about the oil-pressure switch?
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Old 06-03-2011   #8
rhomanski
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GTA Year: 1988
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Re: 87 GTA with code 33

The oil pressure switch should be made when you have oil pressure. Your taking the voltages with the engine off. That voltage comes from the fuse through the fuel pump relay then to the switch as per the wiring diagram I gave you. Otherwise it comes straight down to the relay from the splice. I would check the fuse first. Then check the relay's and finally the wiring.

Regards,

Ron.
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Old 06-03-2011   #9
rhomanski
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GTA Year: 1988
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Re: 87 GTA with code 33

Here's an extra wiring diagram and the location of the fuse.
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Old 06-03-2011   #10
red88tagta
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Re: 87 GTA with code 33

Went through the same code 33 problem. After having replaced the maf sensor, repairing the wiring at the maf sensor an maf burn off relays, replacing the relays, turned out to be a bad component in the ecm not powering the burn off relay. Replace ecm with a rebuilt unit, no more code 33
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Old 06-03-2011   #11
rhomanski
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Re: 87 GTA with code 33

If I remember right those are called quad drivers. They actually run four things. A relay and a couple sensors or whatnot.
With mine it was a bad sensor once and then a bad relay a year later. Since then it's been okay.
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Old 06-03-2011   #12
Hoonbash
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Re: 87 GTA with code 33

I tried to save the first pic but it's too small,blurs when magnified.

I'm guessing that since the car will run I can rule out the oil switch & fuel pump relay

First thing I did was replace all the relays,am now looking at wiring,found the red-wire for the MAF sensor harness was cut & spliced into something for the speed density.Repaired that hoping that was it but it didn't help



Following the diagnostic tree it fails right off the bat,no power to terminal E on the MAF sensor harness when G of the ALCL is 12 volt jumpered,moving on to the MAF power relay,have power to terminal E but not C (circuit 120) This is where I sit

Is there a way to check the ECM? It would flash a code if buggered?


Thanks for the input so far!!
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Old 06-03-2011   #13
rhomanski
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GTA Year: 1988
GTA Engine: 350 TPI Automatic
Re: 87 GTA with code 33

All right, With the jumper in, the fuel pump relay should be energized .This will put 12 volts on Pin D of the MAF power relay.It should energize because of the ground on Pin F. 12 volts should be sitting on Pin A of the Maf power relay through the inline fuse and splice 166. The relay should then short Pin A to Pin E sending 12 volts to Pin E of the sensor. Pin C of the MAF power relay will only have 12 volts on it after the car is switched off and the computer runs a burn off cycle for two seconds. The only thing the computer does for the MAF power relay is energize the fuel pump relay. If you have 12 volts at Pin D, the computer is energizing the fuel pump relay.

Are you sure you still have the correct computer. Have you got the right chip in the computer. Have you verified the wiring is correct. Check resistance of the wire from end to end. Made sure it only goes where it is supposed to. The car needs to be close to stock for the chart to work.

If you are right and have 12 volts to Pin E of the MAF power relay you should have 12 volts at the sensor Pin E. It's supposed to be a straight wire. Calling Pin C of the MAF power relay, circuit 120, has me concerned that you may not understand the wiring diagram. Circuit 120 is Pin D of the relay. Pin C is circuit 994.

The computer may or may not fault itself. Some circuits are monitored inside the computer and some are not. That's why I wonder if you may have the wrong computer and chip. Speed density was for later cars than yours and mine. I use an '87' computer because I don't have vats. The parts places would try to sell me the wrong computer because of it. Never trust them guys. You know your car better than them. I went for a thermostat for my '85' once and he argued with me that I needed a 195 degree when I was sure it was 160. I ended up overheating because I gave in. Last time I drove that one. It warped the head and blew the gasket. Had antifreeze going into cylinder four.

Look these things over and come back with questions if you need to.

Regards,

Ron.
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Old 06-03-2011   #14
Hoonbash
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Re: 87 GTA with code 33

Wow Ron, that's impressive, where did you learn all this?

With the jumper wire connected there is only power to terminal E of the MAF relay. You lost me on the ground of pin F, in line fuse and splice 166.

Took off the jumper wire, connected the MAF relay, turned the key on and checked terminal E(red wire) no power. Traced the red wire back to the relay. Can't find any loose ends.

The computer I have is 16198259 which from reading is an upgrade from 1227165, the chip is correct.

Don't understand why there's no power to the MAF sensor
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Old 06-03-2011   #15
rhomanski
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GTA Year: 1988
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Re: 87 GTA with code 33

I've owned them for over ten years. I've read the service manual and a couple other books. One really good one came out in the mid nineties and covers the corvette fuel injection very well. Of course it is also good for these as well since they operate the same.

To your problem, may I ask when you are checking at the sensor for the 12 volts. It should only be there for two seconds after the jumper is put in. Since the voltage comes through the power relay and the power relay is run by the fuel pump relay the voltage will only be there when the fuel pump is running. The computer shuts it off when it doesn't get reference pulses from the distributor. With no oil pressure the switch is open so no power that way.

I was afraid I might lose you by going too deep. I'll try to do better. Make sure the fuel pump is running when you check the voltage and come back.

Regards,

Ron.
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Old 06-04-2011   #16
Hoonbash
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Re: 87 GTA with code 33

Yeah it's a little involved allright but I'll ask questions.Hard to diagnose things over the iner-net so good job. I had a more detailed previous answer but I must have been timed out & when I went to post it was all gone,asking me to log-in.


OK when I tested the MAF sensor plug-in E I did get 12 volts for 2 seconds.Before I was leaving the key on & missed the cycle
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Old 06-04-2011   #17
rhomanski
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Re: 87 GTA with code 33

I should have caught that earlier. Guess I'm rusty. After I finished mine a few years ago, it's been very reliable. Now you need to start the troubleshooting tree over and follow it through. Good Luck.

Regards,

Ron.
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Old 06-05-2011   #18
Hoonbash
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Re: 87 GTA with code 33

Followed the tree all the way down to faulty ECM connection or ECM
so looking for another computer.
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Old 07-09-2011   #19
Smokeys Dyno
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Re: 87 GTA with code 33

Is the chip in the car for the SD tune? If so, you need a new tune for the MAF setup.
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Old 07-09-2011   #20
Hoonbash
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Re: 87 GTA with code 33

I had a chip from when it was MAF,even recently tried a new MAF chip.

So it's got a new computer,new chip,3 different MAF sensors & it still lights the code 33,I've stopped tinkering on it until I can save some cash & get it thrown on a scope.

Will post the results when-ever that happens.

Fuel Injection SUCKS!!
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