Ok so i just talked with the guy who owned the car before me. He took the 42# injectors off and put the stock ones back on. Stock is 24# right? When he finds the injectors with the rest of the paperwork for the motor that he couldn't find tonight, he's going to give them to me. For now though, I at least need to change the injector constant back to 24#.

I'm trying to think if this would cause the problems i'm seeing. It seems like smaller injectors would actually cause the care to run lean but maybe thats not the case.

If there's only half as much fuel (roughly) as the computer thinks how does this effect air/fuel calculations and blms? With my limited understanding (although I'm an engineer and could handle the math if someone wanted to go deeper into it) it seems like the following would be true. Computer shoots for 14.7:1 sees how much air is going through the maf does something with the map and comes out with a number to pulse the injectors. So the air/fuel that it actually creates is 14.7:0.5 or 29.4:1 and so the O2 sensors see this and say "need more fuel." BLMS get maxed out and the pulse for the injectors is super high. Anyone agree?

 

You are correct... running smaller injectors than its programmed for will make it run lean, and drive the BLM's upward.

Minor point on the calculation process - the MAF sensor measures mass air flow. All the PCM needs to do to calculate the fuel requirement is to divide the mass air flow by the target A/F ratio, to get mass fuel flow. No need to consult the MAP sensor. The PCM uses the injector constant to calculate the pulse width required to deliver the required amount of fuel. The equation adjusts the required amount of fuel using the short terms and long terms as "multipliers" (INT/128, and BLM/128).

MAP is used in the speed-density system, where the PCM can calculate the volumetric air flow based on the RPM, displacement and the volumetric efficiency (VE) table, then convert the volumetric air flow to mass air flow by calculating the air density based on manifold absolute pressure and absolute inlet air temp. Once the PCM calculates the mass air flow, the process is identical to the way it works with the measured mass air flow from the MAF sensor.

 

Thanks, i can pretty quickly derive the equation based off the maf. thats straight forward. Do you have equations for speed density (i'm sure i could derive that too but why go through the trouble if someone else can get me there faster).

Would the lean condition based on the incorrect fuel injector size cause carbon build up by the exhaust? Or the black streaks on my garage floor behind the exhaust? I thought that indicated a rich condition. Could it cause the computer to read lean but the car to run rich or do I just not know what rich looks like?

 

There are two possible conditions - a true lean condition, where the BLM's elevate and correct the condition, and a "false" lean, where the BLM's elevate in response to a reported lean condition that is not real. Exhaust leaks before the O2 sensors, misfires, faulty O2 sensors and wiring, incorrectly adjusted valves, a cam with high overlap can all cause the exhaust to read lean due to the presence of oxygen. The mixture in the cylinders is fine, but the O2 sensor readings are midleading. The PCM raises the BLM's to add fuel, and it's fuel the engine doesn't need. As a result it runs extremely rich.

A huge mismatch in injector size vs. programmed values can also cause problems, because the BLM's can only add 25% extra fuel. So it has to rely on the short terms (INT's). But the INT's also have to move up and down over a slightly rich to lean range to allow the cats to work. So the PCM is using the INT's for two different purposes. The results may not be satisfactory.

Carbon in the exhaust and a strong fuel smell are signs of an excessively rich condition. At this point, if its running as rich as you describe, you may have a problem with the excess fuel washing the lubrication off the cylinder walls, and diluting the oil. Recipe for ring and bearing failure. Does your oil smell of fuel? Do you still have a cat?

Have you checked the fuel pressure? Have you checked the vacuum line to the fuel pressure regulator for wer fuel?

 

You can also get a really strong fuel smell from a lean misfire which you likely have.

Carbon turds in the exhaust ports can be caused by a lot of things.

 

Ok, cars running better, but that right O2 is screwed up. I'm going to replace it but, it definitely seems like the injectors were the fix.

 

Ok got the o2 replaced and it seems to be working. Its amazing how much carbon built up in like 20 minutes or so of running. Makes me concerned about the left side but it seems to be reading ok. Car is running better it seems but still not great. Anyone see any problems, things i should look at? I'm thinking maybe that pcm needs some time to relearn.

http://www.mediafire.com/?lasbe3hu4kos2cs