Thanks for your insight. I'll look into the MAF tomorrow. In looking around the net, I found this bit of info. Maybe it will apply to some w/ this problem.

This piece is from:

ALLDATA -- Jim Grant's Tech Tips --94 Ford Ranger, No Power and Surging

Your vehicle has a device called a Mass Air Flow (MAF) sensor. The MAF sensor measures the amount of air entering your engine in grams per-second. The computer uses this information to calculate the fuel needed. The problem we’ve been seeing with these sensors is due to air filter fibers or other debris contaminating the wire used to sense air flow. The biggest offender is the discount air filters. The paper fibers used in these filters breaks free from the filter and just loves to wrap themselves around the MAF sensing wire. The result is clouded information that the computer just doesn’t know about. Nothing is broken so there are no computer codes, you just have a vehicle that doesn’t run right when everything else checks good. A keen eye and some electrical contact cleaner is what’s needed to remove the offending fibers or debris from the MAF‘s sensing wire.

 

I would disagree. I would think the biggest culprit is oiled air filters. I have never seen or heard of fibers on the sensor element. I would agree, using higher quality filters can prevent a lot of problems.

 

Blow-through turbo or superchargers are a real problem as well. They create strange air flow paths that really confuse Ford's bypass-type MAF sensors.

 

Ok, so I took it to the dealer to have the pump replaced under warranty, and after they looked it over and diagnosed it, they determined the flow and pressure were within specs, and that the first shop had come up with an incorrect diagnosis. The dealer went through it and found the MAF do be defective, the brand new one that was just installed. So the first shop is gonna need to replace it under warranty. It just bugs me having to take it to the dealer to get a correct diagnosis, only to confirm that it was what I thought it was in the first place.

 

Really? Anyone here ever supercharge their Aero? Like to read about that experience.

 

Gentlemen,

I do not understand this "backpressure thing". How can a cylinder fill better working against a higher pressure on the exhaust side.

All racing engines and aircraft engines seek to lower backpressure. P 51 Merlin engines have 4" exhaust stacks period. No pipes, mufflers or anything. They are even canted back to generate a suction at speed. I understand exhaust tuning for pulses of negative pressure to enhance filling during valve overlap but I think this thing about "necessary" back pressure is an urban legend.

Ken

 

I'm not sure about an Aero, but many people have put forced induction on Mustangs. They always put the blower AFTER, not before, the MAF sensor because it can not properly measure the pressurized air stream.

I've looked at various options for putting a blower in an Aero, but time and again, I just can not find the room. BBK used to make a roots type blower for the 4 liter engine in an Explorer or Ranger, but it sits too tall to fit in the Aero's engine compartment. There is no room to install a Paxton or Vortec blower in front of the engine, nor is there room for even a small turbocharger.

 

Most car/truck engines are designed to run with some type of restriction for low end torque...Low rpm. I agree race high rpm the bigger the better in most cases. In the real world of fuel mileage and driveability it seems that flow isn't always better..


Dick

 

On the MAF with forced induction, you are kinda right. But if they use a stock MAF they will have problems one way of the other. For forced induction, they almost always need a larger MAF, then they need to tune the PCM to read the new MAF correctly.

So after getting the MAF replaced the second time, that seems to have fixed the problem.

On the backpressure thing, backpressure is always bad. What is important is the speed or velocity of the exhaust. Smaller pipe results in higher exhaust velocities, and if the exhaust is moving fast through the pipe, it won't stop easily. This means that when there is no more exhaust flowing out of the cylinder, the exhaust will continue moving away from the engine, and will actually start to pull a vacuum in its wake (vacuum is the opposite of backpressure). This vacuum helps draw the fuel air mixture into the cylinders and helps fill them more fully (increased volumetric efficiency), which means more power per stroke, or torque. The equation changes depending on the RPM and the volume of air flowing to the motor, and at some point the velocity maxes out, and does create backpressure, which becomes increasingly intense as RPM increases. So larger pipe is good for top end power because the larger pipe can support the volume of gases flowing through it. But at low RPM, the volume is insufficient, the pressure waves collapse, and that reduces the amount of vacuum being created.

Its all very complex. But people often attribute backpressure, largely because they do not fully understand the Bernoulli effect and how it applies to an exhaust system. In an exhaust system the effect is largely called the scavenging effect where essentially the waste energy in the exhaust is drawing the remaining exhaust from the cylinder and increasing torque as a result, and that is a function of pipe size relative to the motor.

 

Now there, the velocity thing makes sense to me. I can work with that.

Ken

 

Most aftermarket MAF sensors are just bigger versions of the same design; a small bypass passage with a sensor element in it next tot he main larger passage. These are calibrated for atmospheric pressure and assumes a uniform flow pattern across the opening. When you use forced induction to blow more air into it, these assumptions no longer hold true; the pressure obviously increases, and the viscosity effect creates a very uneven flow pattern across the opening. If the boost is so high as to introduce turbulence, it complicates it even more.

On exhaust back pressure, some hot rodders install exhaust dumps ahead of the muffler to reduce pressure at high rpms. Check out the new 2012 Boss 302 Mustang, where Ford actually installed one of them from the factory. but with a diffuser to control noise. They are using a standard sized fitting so you can easily install your own aftermarket dump pipe.

 

If your forced induction system blows into the MAF, yes, that will cause problems. I said larger MAF, not just any aftermarket. Ford actually makes several sizes depending on the application. When the opening is larger, the air moves more slowly and stable. They the computer gets recalibrated so it understands the change.