I have just recently converted from an SD computer to a MASS Air computer on my 92 F150, 351W, supercharged. The Air sensor is not getting enough air going in to give the proper reading, so the engine runs like crap.

So far I have disconnected the belt to the supercharger and since I also installed a new throttle body, I have been adjusting the idle screw.

Makes me wonder if I have a leak below my intake manifold (I had to remove it to get at the fuel injectors). Could a small leak be drawing in enough air at the intake so that the air sensor near the air filter doesn't get enough air?

Thanks

 

Is it calibrated? If not then that is your problem. Wait did you get the conversion from another truck?

 

It is calibrated, it came as part of a conversion kit.

 

An aftermarket kit? Maybe the computer needs to be tuned to accept the new changes. I know that when you get your conversion kit from another truck there isn't a problem because it is calibrated and made to work with the computer. Was it working fine before you removed the intake manifold?

 

I had read something to that effect today (about the computer calibration). I have talked to the companies of where the parts came from, they all know I have a truck and nobody has mentioned a computer calibration. I will ask when I call tomorrow.

Not really sure what else it could be at this point.

 

I bet that is your problem because you can't just say "oh I wan't a 90mm air meter" and plug it in. Has to be calibrated with the computer also. How big is yours anyways? And what kit is it?

 

I bought a kit from Interactive Systems & Technologies Mass Air Home Page. I like their products and the guy there seems knowledgeable. I have a 76mm housing with a calibration tube, the kit I got came with that plus the computer, oxygen sensors and bungs to weld, and a wiring harness as well as detailed instructions. It was pretty easy to install, just takes time. Oh, if you have an E4OD transmission, you also get a controller which seems pretty cool...if I can only get my damn truck to run I could check it out.

 

hmm it came with a computer. seems a bit weird that it wouldn't come calibrated. are you sure truck is not getting enough air? or is it getting too much fuel? lean or rich condition?

 

rich, definitely rich. I think the computer is calibrated but I will try to verify that tomorrow.

 

did you replace your injectors with stock ones? I think you said that you removed your intake manifold to work with the injectors. I saw their web page. They have some pretty good stuff actually. Conversion is expensive but worth it.

 

I still have the stock injectors now, plan to upgrade later. I removed the intake to get at the connectors, had to remove the old connectors and replace with the harness that came in the kit. It's hard to get those out of order, the are numbered and only have enough wire to fit on the intended injector.

 

The meter calabration is set to the injector size, so if you have stock 19# injectors the meter needs to be set to them , if you go to bigger 24# then the meter needs to be recalibrated to 24# , if you want to get the most out of it its better to do it with a tunner or burn a custom computer chip , the idle screw is set from the factoy , don,t mess with it , the computer controls the idle....Lew

 

So maybe decribe in a little more detail what you mean by "the engine runs like crap". Is it just the idle that is rough or does it run not run well at any rpm. Have you disconnected the vacuum line between the MAP sensor and the intake plenum? Have you pulled the codes?

 

I called IST where I got the kit from and they said that while the computer might need to learn my truck, that isn't the issue here. Bottom line is that with not enough proper air flow, the MASS air sensor will not send back the proper voltage to the computer. Now, when the computer gets the signal, it can decide how to run the truck but with a voltage from the sensor to the computer being so low, there will be problems.

lew52 - thanks for the comment, it is something I have considered. Just want to get the truck running HSN first. There is a company in town that might be able to tune the truck for me, the might even be able to fix my situation, just haven't decided to give up just yet.

truck runs like crap - when I turn the truck over, it usually starts and runs for less than 1 second and then dies. If I try to start it again, it will run but VERY rich...so rich that the truck will only run for about 45 seconds then will stall. Then I repeat the process. The last test I did (at the suggestion of C&L) was to bypass the supercharger Imageshack - dsc2836.jpg, so I did that and that made VERY LITTLE difference in the voltage out of the MASS air sensor and the truck still runs the same. Does not run well at any RPM. I have made the modification to the MAP sensor sit is now a BAP sensor (and I even got a new one - no difference). When I pull the codes I get 10 (number 1 piston balance test failed), 11 (all is OK - this is puzzling when there are other codes), 66 (low MASS air voltage to the computer), and 87 (I think this is because of the other issue with the air sensor).

IST is going to have me do another test, they want to see if, by chance, the computer is drawing down the signal from the MASS air meter. So I am going to disconnect the MAF SIG and MAF RTN wires from the computer, start the truck and measure the voltage. I would expect it to be the same as what I have measured in the past but we will see.

 

Just looked at your pic, this may not be your whole problem but you should have a section of pipe on the intake side of the MAF sensor to level out the air column, placing it on the end like that typically produces unstable MAF voltages, that's also one of the reasons why attaching an open air filter right on the end of the meter is also a bad idea.