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.

 

if you haven't had luck figuring this out yet, here's a shot. Your first 2 codes shouldn't affect the operation of the engine. The latter 2, however, might.

- p0654 Engine speed output circuit problem
- p0101 Mass air flow circuit out of range

Engine speed output circuit: this connects to your idle air control valve. Check your connections there.

Mass air control : assume this would be the +5V powering the MAF. Check the signal on your MAF pins and see how close the input power is to 5V.

Sounds like you're chasing some kind of systemic power problem. It could easily be a positive or negative problem, so don't forget to check your grounds. By reviewing the diagram for the alternator, it appears that pin "B" on the alternator plug gets +12V when the PCM requests the alternator begin charging the system. Try applying 12V manually to that plug when the engine is running and see if that causes the system to charge.

Report back, and we'll go from there!

 

That MAF uses +12V, not +5V for power. P0101 is a predicted airflow MAF diagnostic. If it wasn't getting +12V it would likely be setting a P0102 code. Could just be a matter of trying to use stock predicted airflow tables with a modified engine.

Can't help with the alt. charging problem.

 

Thank you for your input, I am just now getting back around to working on the car. I have found that when I disconnect the "MAP" sensor on the rear of the intake manifold, the engine will run just fine but with the "MAP" plugged in, the engine will want to die and runs very rich. I have changed to map, maf, iac valve, both 02s, and my vacuum is reading about 20hg on my manual gauge and about 10hg on my map sensor reading threw my bosch live data scanner. I have also checked my signal and power going to my maf and map sensor and it seems to be correct... I am pretty lost as to what could be the problem. Any ideas?

 

Key on, engine off... MAP reads?

 

I do believe so. I will double check that when I get home this afternoon. I have been doing some research on map sensors and it looks like some people have trouble using aftermarket map sensors (mine is from oreillys) so I might try to swap it out with a gm map sensor.