Hello everyone, my build is a 1992 Nissan 240sx with a 2004 Pontiac GTO ls1 and t56 transmission. It is a full track build that I personally built from the ground up in my garage. All oem wiring has been removed and I built a custom chassis harness and I am using a Wiring Specialties harness for the engine and trans. All stock internals, long tube headers, hp tuners flash to delete the security functions, rear o2s and emissions. Aeromotive fuel cell/340 pump with all -8an lines and fittings. At one point the engine was running very well, idling perfect and I was able to drive it up and down the street with no problems.


-My Problem-


After having the engine running for awhile I noticed that my battery was not receiving a charge from the alternator (reading around 11 or lower Volts at the battery and on the main terminal on the alt). So after replacing the battery with a new optima and doing some testing I replaced the Alt. After replacing the alt the engine would no longer hold an idle and seems to run very rich. Also After replacing the alt it was still reading lower than 11 volts. So I did more research and come to find out that on the two pin connector going to my alt I only had one wiring receiving voltage which was the wiring that needs 12 volts. The wiring coming from the "indicator light" was dead. So I now have about 9 volts going to the second pin on the connecter via a resistor. However the engine still does not hold an idle and runs very rich.


Fuel pressure is at about 60psi when running and drops to about 45-50 when not running.


Vacuum is over 30 which seems very high to me but im not sure what would cause the vacuum to be excessively high.


Using a snap on scanner I pulled the following codes
- p0522 Engine Oil pressure sensor circuit signal low (sensor is not hooked up at all but it never has been even when running perfect)
- p0645 A/C compressor clutch relay control circuit (no a/c at all)
- p0650 MIL control circuit problem
- p0654 Engine speed output circuit problem
- p0101 Mass air flow circuit out of range


Any and all advise would be greatly appreciated.

 

The p0101 could be the cause of your fueling issue and I would guess having the MAF sensor that close to the air filter is an issue.

 

I have been wondering if my intake setup could be a problem although I have had about two hours of total run time with that same setup in which the engine ran very well (until replacing the alternator). Would you think that the intake setup could just now be causing the engine to not hold idle and run rich? I almost feel as if when replacing my alt I may have sent improper voltage to the pcm in which doing so maybe the pcm was damaged?


Thank you for your response btw!

 

I suppose pcm damage could happen so don't rule that out completely. For now I would look at long term fuel trims and see if they are maxed out, which can take some time for the pcm to adjust. That combined with the load that is now on the engine from the alternator actually charging, plus the fuel curve change in the form of injector pulse width voltage modification from having low voltage could be the cumulative issue that is now causing your headache.

I have seen first hand what having a conical filter attached to the MAF sensor can do to the readings. Basically the incoming air travels the walls of the MAF and very little air flows across the metering wire at an idle.

 

You have a very interesting point about the fuel trims. Do you know of any way to basically reset the fuel trims or the pcm all together other than just taking voltage off of the pcm for a certain amount of time? Maybe I need to access a tuning program so that I can see more in depth information of what is going on?


I am going to try a new intake setup because you do have a good point and I have been slightly concerned about that. That could very well be the reason for my maf circuit code. Do you know if there is any certain distance that the maf needs to be away from the throttle body?


Also, could it be possible that my fuel volume may be too high with the performance fuel pump and much larger fuel lines? The fuel pressure seems to stay steady at about 60 psi while the engine is running. I am running an Aeromotive 340 fuel pump, oem Corvette fuel filter/regulator (from Oreilles) and -8an lines/fittings


Thank you!

 

You mentioned a snap on scanner, the Verus or Motus is capable of resetting fuel trim with out a battery disconnect.

The MAF can be mounted close to the throttle body, 8-12 inches is about typical or just in front of the "turn".

Injectors are interesting in that raising pressure to them also increases volume from them and vice versa. As long as the pressure is correct for the injector constant, too much volume to the injector is not a concern.

You may want to consider running a speed density set up and eliminate the MAF.

 

I was going to suggest the very same thing.

Also, you do have the red 'exciter wire' running from the ECM to the top connector of the alternator harness, correct??

Nice build, is that an NRG, or Personal steering wheel?

 

Im pretty sure it was the Verus scanner. I will look into that so as I can get ahold of the scanner again. I do believe that could be a possible problem.


I am very interested in the speed density setup I just haven't done much research on it yet. Im guessing it is all done with a program such as hp tuners?


Thank you again!

 

Thank you!


Right now on the two pin connecter going to the alt I have a constant 12v to one pin and about 9v going to the other pin threw a resistor that is pulling power from a switched 12v source. Iv been told that the GTO ECM does not have the "exciter wire" like the earlier gen ls1 ECM. But I am not exactly sure how accurate that is. I know on the earlier gen ECM its like pin 12 or 14 on the red connector but the GTO connectors are blue and green.


The steering wheel is a Nardi. I wouldn't trade it for any other steering wheel in the world.

 

You should post this in the conversions and hybrids section. That is the forum where you will most likely get an answer.

 

Yes, they are the 'parent company' of Personal.

I feel the same way about my Sparco mod 383 suede wheel.