K.C.Kustoms

Hello everyone.

I have been trouble with my 1991 Firebird v6 and cant seem to fine the problem. For background story click - https://www.thirdgen.org/forums/elec...d-v6-vats.html


Today I drove it to my local auto parts store thinking I had fixed the engine trouble. But when I came out the thing would not start. It would start stay on for about a minute and then while driving it would just shut right off.

So I left it there and decided to check the codes on a code reader.

The code reader then displayed the following "Code Errors."

33. High voltage (low vacuum) at mass air flow sensor (or MAP sensor)
43. Low voltage at electronic spark timing circuit
54. Low voltage at fuel pump OR Low voltage at Fuel pump relay OR Output failure at quad driver module.

Now I'm not exactly sure what these codes mean or how to fix them so if anyone could help it would be greatly appreciated.

K.C.Kustoms

I do have a feeling though that it has something to do with the fuel pump because it sounds like the engine is starving for fuel.

I put my ear to the gas tank while we tried to start it and I could not hear the pump running.

So, my first thought is the fuel pump. But still am unsure.

Maverick H1L

iTrader: (8)

I can almost guarantee there isn't anything wrong with the fuel pump. If you can crank the engine for a long time and have it start, then there is either a problem with the ECM (seen this in person many times) or the fuel pump relay, and the oil pressure switch is turning on the fuel pump when the oil pressure gets high enough.

Code 33 could be a failure in the MAP sensor. Jack one from another car and plug it in to test. It's either that, or there is a problem with the vacuum source to the MAP.

And the code 43 means that the knock sensor in the coolant plug hole on the pass side of the block is either disconnected or bad. Or the wiring between it and the ECM is.

K.C.Kustoms

Today I checked my fuel pump fuse and it was fine so that was not a problem. But Then I check the relay like Maverick said and found that it was not working correctly. So, I went to the auto parts store and bought a replacement.

When I installed it and then turned the keys to the "on" position and put my ear by the gas tank I could hear the fuel pump working. Which I could not hear working previously.

So I tried starting it and it started up, but then shortly after quit on me. I did this a few times and it still had the same results.

So what could be the problem now? I don't think its the fuel pump anymore but could it be the fuel filter? Now I did have the back of the car up on jack stands in the air. So could that have stop the fuel from getting to the engine? Or is it another problem.

After all this the engine still sounds like its starving for fuel.

Edit: Also to note is that I just check the codes again after replacing the relay and they are still the same 33,43,and 54.

Thanks for the help Maverick.

Maverick H1L

iTrader: (8)

Did the engine run long enough to get the ignition parts hot?

With your 91, there isn't a way to bypass the ECM to trigger the fuel pump relay from inside the car via the ALDL as there is on the earlier cars to diagnose the ground signal coming from the ECM. Having replaced the relay, does the ECM post a code 54 again (did you clear the codes)?

Pull any spark plug and note the color. The ECM may be dumping fuel into the cylinders and killing the engine by flooding it instead of leaning it out.

Check the voltage at the MAP sensor's green wire with the engine running. Should be less than 2V at idle.

K.C.Kustoms

Could you explain what some of these terms mean and where they are located such as ECM, ALDL and MAP? (Sorry I am kind of new at this.)

But the car did not run more then a few seconds and now its doing the same thing as it was before. So, it could be what you are saying if you could explain what I need to do to check. But the car doesn't really stay running or starting for that matter.

And how do you clear the codes? I plugged it in first and it registered 12. Then turned off the car, took out the code reader, and then plugged it back in. Turned the car back on and it registered the same codes. 33,43,54.

Maverick H1L

iTrader: (8)

MAP: Manifold Pressure Sensor, mounted by the A/C or heater box on a bracket bolted to the lip where the cowl screen is, has a 3-wire green connector.
ECM: Engine Control Module (computer)
ALDL: Assembly Line Diagnostic Link connector, by the fuse panel, is a 12-pin connector (where the scanner plugs in).

Reset the ECM by disconnecting the battery for 10 seconds and then hooking it back up to clear the codes. This way you can figure out which ones are old and which ones still exist.

K.C.Kustoms

Today I took out one of the drivers side "spark plugs" and took a look at the end of it. The plugs end was really black and had almost charcoal look to it. This was a shock to me, since I just put in brand new E3 diamond fire spark plugs this weekend.

So could this be the problem that the "ECM is dumping fuel into the engine" and flooding it?

Also, we tried testing the "MAP" sensor. We had our voltmeter on the black and green wire of the "MAP" and it read no volts. Probably because we could not get the car to start or idle at all.

So, not really sure what the problem is still.

Maverick H1L

iTrader: (8)

Remove the MAP connector and check for power (5VDC) on the gray wire. Also, probe the connectors in the MAP that the green and black wires attach to with the meter set to check resistance. If there is no resistance between the 2 connectors, the MAP is shorted and needs to be replaced ($30 new or you could nab a couple of them from a junkyard for $10 or so if you find the right yard).

Yes, if the plugs are black, the ECM is dumping fuel into the engine, if the plugs are dry like charcoal. If they are wet, they are oil fouled. If the plugs ever turn bone white like new, then there isn't enough fuel in the mixture and you could be headed for worse problems (knocking, detonation, etc). The plugs should be a light gray to tan in appearance if the fuel mixture is correct and the coil is firing properly.

One more thing to check other than the MAP is that the ignition coil produces a good spark. Put a spark plug or spark tester on the coil to distributor plug wire, ground the plug, and crank the engine. The spark should be bright white. If any other color, the coil is weak and needs to be replaced, and will also cause the plugs to foul out as though the engine is running rich.

K.C.Kustoms

So, what should I do now? Is the MAP sensor the problem or is something else?

And what should I do about the engine getting flooded? It all all sounds confusing on what is the problem and what I should do next.

I just checked the MAP sensor and it had about (8DC) power on the grey wire and the green and black connector plug-in did have resistance. So I don't think the MAP is the problem since it is not shorted.

K.C.Kustoms

Just letting you know also I found that the "Mass Airflow" Sensor is disconnected. And I have no idea where to hook it up or how to. Could this be causing the problem?

Here is a picture of it.


Another view.

Maverick H1L

iTrader: (8)

The reason the airflow sensor is disconnected is because it's NOT supposed to be there. 1990-92 model cars didn't have one from the factory. Something must have happened to the factory air box and whomever replaced it may not have been able to find the late-model air box, so they used one from an 85-89 instead. BTW, would you be willing to sell the wire hanging out of it?

Like I said before, disconnect the MAP and make sure there is 5V on the gray wire and that the sensor isn't shorted between the green and black wires (don't backprobe the connector when connected to the sensor, check the sensor only). And check the color of the spark coming out of the coil and plugs.

:edit: And that vacuum coolant diverter next to the alternator is also disconnected... May cause a vacuum leak if and when you turn the heat on when it's cooler out.

The ECM controls the fuel flow based on the MAP, coolant and air temperature sensors, vehicle speed, throttle position, and the oxygen sensor in the exhaust pipe. If any of these is off or bad, the fuel curve will end up being off. Since the MAP is shorted, the ECM will increase fuel flow.

K.C.Kustoms

We did check the MAP sensor and if we did it correctly, which I am pretty we did. We found that it is not shorted. But I will check again just to make sure.

The color of spark coming out of the coil was a white spark.

And as for the coolant divider how should I go about fixing that?

Also what do you think the best course of action will be to fixing this problem of the engine flooding and not starting? Because I am really clueless on what I should do next. Probably because most of the stuff we have been checking is actually working. Or maybe we are just checking them wrong.

Maverick H1L

iTrader: (8)

The MAP is tested between terminals A and B. And if you have a vacuum gauge, you should pull a vacuum on it to see if the resistance changes. If the resistance is low, the sensor is good and there is a problem somewhere in the ECM circuitry.

There really isn't much you can do with this code without a scanner, as the scanner is required so that you can see what the ECM is receiving from the MAP.

Also check your fuel pressure. Should be between 37 and 47 PSI. May need to beg, borrow, or steal a gauge.