Altitude, rain and performance?

[fordfan]

Can anyone explain the relationship of altitude or rain on performance?
About a year ago my B2 suddenly started bucking badly (1st gear) in hot weather/sea-level, but I have noticed it is better in the rain. I am at sea-level.
Recently, I was quite happy with it's performance and pick up at only 2000 ft above SL, which appears quite against the normal expectations I have read. It practically floated!
How does this stuff effect the engine so I can search for the problem or tune it? Currently I get about 750kms/450 miles to a tank.

Could this be the FPR? it shows no gas, but smells. With my finger on the air intake or off there is little difference, and no, I have no means to measure the pressure.
2 yr old fuel pump, filter, new injectors, coil, plugs, wires. Cleaned IAC, air filter.

I am very curious as to how this works, and haven't found anything simple to explain it, thanks!!

 

[Surrey]

There is a diaphragm in the FPR (I think thats where it is? someone else can confirm) that can leak gas into your intake.

If you smell gas in the vacuum line that is likely your problem - the vacuum line pulls gas into your intake, flooding the engine. This can also cause bad mileage.

 

[fordfan]

We were arguing about that. I let it run for 5 mins and no gas came out, but it would have to be a relatively large puncture I assume.
So even the smell of gas is a suspect FPR? I don't even know if I can get one anymore....
How would that make it run BETTER in a higher altitude???

 

[RonD]

Higher elevation has less air pressure, so computer controlled engines can't mix as much fuel, horsepower goes down, it can be as much at 15% loss in Denver, 5,000ft above sea level.
Running better at higher elevation would seem to point to a failing sensor, it is reading air flow/pressure incorrectly.

Moisture/rain, shouldn't have any effect, but rain usually means it is cooler.

Hot and cold do effect engine, hotter air is not as dense so not as much fuel can be mixed, colder air is denser so more fuel can be mixed.

I think your '89 2.9l was the last year of the speed density system.
It used a MAP(Manifold Absolute Pressure) sensor as one of the primary sensors for air/fuel mix.
In 1990 they switch to MAF sensors which adjust better to different conditions.

I don't know of an practical way to test the MAP sensor, you need a frequency reader.
It should be located on the passenger side firewall, it will have a vacuum line connected and an electrical connector.
Check the vacuum line carefully for cracks or holes, any leaks will throw the computer off.
Check connector for corrosion.

A vacuum leak anywhere in the engine can through off the MAP/computer.

 

[Shran]

MAP sensor would be my guess as well, I have always just tested them by unplugging it. It has a very dramatic, immediate effect on how the engine runs (if it is working properly.) Then check the vacuum line that runs to it.

 

[fordfan]

Thanks for the explanation. I was trying to figure why it drives better rather than worse. The shop just put a new MAP in (haha), but I have terrible luck with shops-) 0 for 3
What would I be looking for on the MAP vacuum line, specifically???

 

[Shran]

Holes/cracks/leaks etc. If it even looks crusty I'd replace it just to be on the safe side.

 

[fordfan]

K thanks, it's going to take me a short while to get to, but then I'll let you all know.

 

[adsm08]

MAP sensors were also known for diaphragm ruptures. When they go bad they spit something the old guys call "snot" into the line. It's a white/yellow kinda goo.