86 bronco 2 wants to stall on take off

[cathryes]

I cant seem to find out why. After talking to 2 mechanics and replacing: fuel filter, throttle position sensor and cleaned the other value( forgot whats its call). The main problem with the mechanics is that its random and I cant duplicate it.

Except for the take off it runs perfect...no other stalling.


What else should I look at?

86 bronco 2

 

[jhammel85]

Is this when it's cold or warm? Has the fuel pressure been checked? When was the last time a tuneup was done?

 

[cathryes]

well

I always warm the car up before I leave so I would say when warmed, the engine was completely rebuilt about 8 months ago. I bought it with 300 miles on the new motor.

Have not had the pressure check will do that next

 

[Earl43P]

Make sure your fuel pressure test includes the fuel pressure regulator.

Fuel pressure should change when you goose the gas hard.
You could also remove the vacuum line from the FPR when testing pressure and note the pressure changes ~5 psi when connected vs. disconnected (plug the open line with your finger).

 

[RonD]

So this is a new issue, or has it been noticeable since you got it?

What is the RPM at idle when warm?
Slightly higher than normal idle means a vacuum leak

When you put your foot on the gas pedal the throttle plate opens, this creates a lean fuel/air mix unless the computer opens the injectors longer at the same time, the computer sees the throttle plate opening via the TPS(throttle position sensor), which has been checked(changed).
On carbureted engines there was an accelerator pump that gave the engine a squirt of extra fuel when throttle plate was opened, this prevented the lag/stall out when gas pedal was pushed down, and gave the jets time to catchup to air flow.

The computer also expects 30-35psi of fuel pressure at the injectors, it has no way to monitor fuel pressure, so if pressure was lower then there would be a lean mix to start then O2 sensors would report that it's lean and computer would add more fuel, but you would still have the initial lag.

On your year there is also a MAP(manifold absolute pressure) sensor, this sensor measures vacuum pressure in the intake manifold.
It is used to tell the computer when you are raising the RPM, intake vacuum pressure drops when throttle plate opens, this helps computer to adjust fuel/air mix.
MAP sensor is small and is located on the fire wall, it will have a vacuum line from the intake and an electrical connector.
If the vacuum line gets old and cracks, it will throw off the fuel/air mix.



Spark timing is also advanced when RPM increases, if it lags behind you would notice that, that can be checked with a timing light used while raising and lowering RPM, but I think your best bet is a fuel mix problem.

 

[cathryes]

Been a busy week but I've been able to make it stall. So maybe this might help.

At 1000to 1100 rmps is when it dies. If I just keep the gas bearly pressed it will die unless I floor the gas. I just came back from my parents in Columbia sc, I live in Greenville sc and it ran perfect at high rpms. I was going between 75 and 80 for over a hour and most of that was up hill.

 

[cathryes]

also

Right next to the map sensor there is another sensor that has a red and green "hose" coming out of it. It seems the green goes to something under the throttle( 11pm and no real light will check tomorrow.) But any how it seems to have been spilt and someone stuck a 1/8 hose with electrical tape to combine them. It really not sealed any more.

 

[wildbill23c]

Have you tried to clean the throttle body? Sounds like it may need cleaned out. I'm not an expert by any means, but it seems like I've been seeing this issue in small engines as well, where just as you feather the throttle it will die, after cleaning the air intake, and throttle body it helps quite a bit.