650

[5.0zone]

Dave,
I think I figured out what the problem is!
Your engine is running too lean. Like 28 to 1 instead of the normal 14 to 1.
Here's why I think this: lets say at any particular engine speed the MAF reads that there is 40 cfm of air flowing through it.
That would be 10 cfm per cylinder, so the computer fires the injector to match the 10 cfm/cylinder flow rate.
In actuality the flow rate into the two cylinders would be 20 cfm.
Make since? Correct me if I'm wrong.

The next question is how to correct this condition.
1) One way would be to put a spring in the MAF with exactly half the tension of the original. This would fool the computer into thinking there was 80 cfm flow through (20 cfm/cylinder)
2) Another would be to replace the injectors with ones that have twice the flow rate.
3) another would be to tap the intake manifold for two more injectors and put the ones in that you removed from the other two cylinders, so there would be two injectors per cylinder.

That's all I can think of at the moment.

[packrat427]

Remember how all the old , I mean OLD cars and trucks, and tractors had the spark and advance on the steering column .

Well put a cable operated mechanism to the VAF to open it on the highway , and to help it idle :lol: :lol:

[Kraig]

I think 5.0Zone is on the right track. The computer doesn't know two cylinders aren't there, that the air flow is being split in half not in quarters.

It might be more complicated than that though. The input from the throttle position sensor and reading from the vane air meter are out of skew (wide open throttle and no corresponding airflow) with the data that is looked up in the tables in the processor so it's defaulting to some other data (limp home mode?). Even with a lighter spring the position of the vane will still correspond with the old airflow values...(right?)

[Nerd Racing]

And all the things stated in the previous paragraph are why I Love my 81 dodge... computers can be great... but they sure kill major modifications...

[5.0zone]

Kraig makes a good point. I don't the the spring change in the vane air meter will work. At least not like it should.

[poeee]

What is the signal from the VAF? Is it a pulse or does it work through resistance like a fuel guage sender? If it's the later, could you just put a resistor or something in to either double or half the current (depending on which way you need to go)?

[Kraig]

The farther it opens the more voltage it sends.... a resistor might work in combination with a weaker spring. I think you still need a weaker spring so that with half the air flow the vane will still swing wide open at full throttle.

[poeee]

The vane only needs to open as much as it is now, as the engine only needs 1/2 the air. I'm sure someone with more knowledge with electronics could design a simple system to double the voltage that it sends? I just think that an electronic mod rather than a mechanical mod is a better (easier??) way to go about it.

[Dave G]

What is the signal from the VAF? Is it a pulse or does it work through resistance like a fuel guage sender? If it's the later, could you just put a resistor or something in to either double or half the current (depending on which way you need to go)?

It varies the voltage through resistance. Wish I knew more about electronics, but my very limited knowlege makes me think some sort of electronic modification would work as you describe. I'll have to ask my brother; he actually understands how stuff like that works

[Nerd Racing]

any updates? I have no fingernails left!!!

[Dave G]

any updates? I have no fingernails left!!!

No, nothing much Just piddling around (as time permits) getting the original engine ready to go back into the yellow car. It was a lot more fun working on the 650; now I know I'm just going to get the yellow Festiva back, just like it was :roll: (Well, with quiet valves and no oil leaks, I hope!)

I *am* thinking about how to test and modify a VAF unit for the lower airflow. Leaning towards using weights on a string somehow or another to first establish "before" benchmarks, then measure the results of new springs.

Speaking of the VAF thing, has anyone got a good spare one they want to part with?

[25Horseplay]

How about a stop so it doesn't have as much travel?

[Dave G]

How about a stop so it doesn't have as much travel?

It's not traveling far enough! The problem is that it is only drawing half as much air, which makes the computer think that the injectors only need half as much fuel. The further the vane travels, the more fuel is delivered (I think, pretty sure :? ). My theory is that if the spring is half as strong, then the vane will operate the same as it does normally, thus the injectors will get the same amount of fuel as normal, thus the engine will run "normally" (but with approx half the power).

Know what I mean?

[muscle_Car1]

Maybe add a resistor or 2? to fool the ecu to thinking its getting different amounts of air.

[Dave G]

Well I asked my brother about it (he's the only person I know who really and truly *understands* how things like transistors work ) and he liked the mechanical solution (weaker spring) better than an electronic solution. Since we're seeking to *increase* the voltage at lesser vane openings rather than decrease it, tossing in a resistor won't work. There would need to be some sort of amplifier created, which would get complicated. So I'm going with spring fabrication. One of these days :roll:

Hey, I'm reluctant to even ask this (reason follows), but as I am getting ready to pull the 650 I've discovered that I'd failed to connect part of the wiring harness during the test runs. It's the blue plug that goes into the cylindrical gizmo bolted onto the left side of the intake manifold (transmission side). This thing has two small diameter water hoses connected to it on top, and two larger diameter air hoses at the bottom. I'm guessing it is the EFI equivalent of a choke (or something like that). Here:



What effect would having that disconnected have had on the engine's performance?