Altitude and Fuel Controllers

[bogey]

I am well into my 3 week trip out west and have discovered some information about the PCPro and the Split Second Injector controller.

I have found that if you are traversing a lot of altitude changes - i.e. 5000 feet or more, the PCPro (and Split Second) tend to get confused about when to add fuel.

I first observed this behavior when starting about 2000' altitude and driving over the New Mexico mountains in excess of 8000'. I was seeing conditions where the engine would suddenly go lean under boost.

I talked to Tom about this when I visited him, and we made some adjustments to cure vacuum leaks and boost leaks, which seemed to solve the problem.

What I have since noticed is if you start at a low altitude and go up 5000', the controller does not "see" the boost until about 5psi. Normally it sees at about 2psi and starts adding fuel.

If you start at a high altitude, 10000' and drop to 5000', the controller will start adding fuel at vacuum. (5 inches of Hg)

I estimate each 1000' equals about 1/2 pund of boost.

I have traversed up and down repeatedly from 5000' to 14000' altitude today and have really been watching this closely to identify the pattern.

It make sense. When the car is started, the ambient air pressure is calibrated in the PCPro as "base". Then as you go up in altitude, the lower pressure offsets from the base, causing the controller to need more boost before adding fuel. It is only a problem when the offset gets too big and things start leaning out after 5-6000 change. The opposite happens when you drop altitude. The PCPro starts adding sooner.

It really is not an issue unless you are climbing mountains. Something to be aware of, and the fix is to reset the base level by shutting off the car.

[Kyp J]

I've never been able to get mine more than a few inches off the ground. Stupid speed bumps.

[MarkB]

I thought Tom said one of the main advantages of the PC-Pro is that it would adjust for altitude changes on the fly without needing to turn off the car like other inferior systems. I plan on making a trip thru the mountains without an A/F meter so this worries me... :confused:

[bogey]

I thought Tom said one of the main advantages of the PC-Pro is that it would adjust for altitude changes on the fly without needing to turn off the car like other inferior systems. I plan on making a trip thru the mountains without an A/F meter so this worries me... :confused:

My observations is that it will not adjust unless reset. I have been watching the lights on the PCPro and see them come on preboost if I have reset at high altitudes and descended.

I don't see how it can possibly auto-adjust for this.

Tom - can you check on this?

[MarkB]

Bump?

If it doesn't adjust automatically, that makes it almost a necessity to have a wideband controller it seems...

[Tom @ Fast Forward]

They are looking into the problem.

[bogey]

Tom - its been a month. Have you received any more information on this?

[Chris Papa]

Boy I'm glad I live down under.......its flat as a pancake! :)

[Tom @ Fast Forward]

Nothing back from them that is definitive. They have looked at the problem and will continue to do so, I'm sure. It appears that it calibrates during key on before starting and, if you go from key off directly to start, it may improperly calibrate as the intake manifold drops in pressure pretty quick during cranking. That could cause an error. They suggest a key on, hesitate a second or so and then start. Give the card a chance to see atmospheric pressure to calibrate. That kind of makes sense. I have an electronic vac/boost gauge in my 99. If I don't hesitate for a second, it can read really weird. That is all I know for the minute.

[bogey]

OK. Right now I won't be doing any major elevation changes until next summer when I travel out west again. Not sure if I will brave the heat and humidity of Coolidge again, but I definitely want to make the trip again with my other son.

[FormerDatsun510Man]

What if a second MAP sensor were added to the PC Pro, except that it simply remains open to ambient air pressure? This way the PC Pro could continually correct by taking (Absolute Manifold Pressure) - (Ambient Pressure) to get Boost Pressure. If this calculation slows it down too much, it could correct the Ambient Pressure every 100 loops (what about every few seconds or so? :) ).

I'm sure they have bright minds figuring this one out, but I thought I would make a suggestion :).

Bill

[Tom @ Fast Forward]

Next time we get together here it should be in cooler weather. :)

[Tom @ Fast Forward]

I would assume it is only a matter of $$$$. It is my understanding that the next generation of the cards will have more memory and a much faster processor and will do more stuff. What I don't know is when and how much $$$$? In the meantime we will simply have to suffer along with the best device for the $$ that I know of. ;)

I do believe that the simple hesitation of a second or two from key on to key start solves the problem.

What if a second MAP sensor were added to the PC Pro, except that it simply remains open to ambient air pressure? This way the PC Pro could continually correct by taking (Absolute Manifold Pressure) - (Ambient Pressure) to get Boost Pressure. If this calculation slows it down too much, it could correct the Ambient Pressure every 100 loops (what about every few seconds or so? :) ).

I'm sure they have bright minds figuring this one out, but I thought I would make a suggestion :).

Bill

[MarkB]

Solves the problem? Isn't the problem not the initial calibration, but the ongoing calibration through elevation changes? Not sure how how the initial setting would solve that. Hope they get back to you soon.

[Tom @ Fast Forward]

It appears to be the initial calibration. Not much effect if atmospheric pressure doesn't vary much but, if you change altitude of 4000-5000 feet and don't turn the engine off, it did have an effect. If it is allowed to do a better calibration, that problem appears to disappear. It is rather a rare case where you change elevation of 4000-5000 feet without shutting off the engine to at least to view the scenery. ;)

As the engine cranks, the manifold pressure drops. If it is trying to do it's calibration while the engine is cranking it can get an erroneous zero (atmospheric pressure). Normally. it calibrates so fast that the eror is insignificant. However, even a small error becomes significant if you jave large changes in atmospheric pressure. Like climbing up 5000 feet non-stop.

[bogey]

Stop for the scenery? Why? I was having too much fun driving....

[Kyp J]

.... It is rather a rare case where you change elevation of 4000-5000 feet .....
.

I thought we were talking about altitude. :oops: