Stalling on acceleration after stopping.

[stamp11127]

I wish you luck in fixing it. You might try some of your local autoparts stores to see if they read codes. Autozone up here does, and some stores have a tool loan program. Keep us posted.

I checked the manual, just for the TPS there were pages of tests depending on which code was generated. So that little black box can mess up in about 15 different ways. Some of them being the harness. If you want I'll send the diagnosis procedure to you in a pm. A very long one....

 

[mpsjr]

Thanks. The new parts came in yesterday, so I installed the new TPS and it's doing the exact same thing. I've noticed that it only seems to happen when I slow down below 10 mph, and after moderate to heavy braking. It makes me think they put in the wrong pump. I know Ford has 2 pumps for that year, one for the adjustable shocks and one without. Another thing I would like to try is cleaning the throttle body and IAC, but I don't know what to use. I have Berryman Carb cleaner, but don't know if it's safe for the IAC. I REALLY need to know what my fuel pressure is doing during all of this, but would prefer not to spend the $$ on a tester at this point if I can avoid it.

 

[IL67BP]

Have you thought about going to a local mechanic and just asking them to check your fuel pressure and that's it? Could be real cheap and wouldn't hurt to ask

 

[mpsjr]

Have you thought about going to a local mechanic and just asking them to check your fuel pressure and that's it? Could be real cheap and wouldn't hurt to ask

Yeah, I thought of that. The three shops that I called said that I would have to leave it with them and it would be an hour minimum labor to do. Their rates ranged from $55-90 per hour. I'm cheap, what can I say?

 

[stamp11127]

Found this over on ford-trucks.com,
Original post:
I have a 98 F150 and am having a problem with the engine stalling when braking.

From Bluegrass 7:

The IAC would be the first suspect for being gummed up.
Remove it and clean with intake cleaner made for the purpose.
Also clean the inside of the throttle body around the throttle plate area.
A little background on why the motor may stall upon braking is as follows;
The speed sensor tells the PCM what is happening to the road speed by driver action (braking).
This does several things. It unlocks the convertor, shuts down the fuel and keeps the IAC open just enough so the motor won't stall.
As you see, the IAC cannot respond so the motor stalls.
The gum around the throttle plate has limited air flow vs opening angle as well.
Also the PCM has tried to account for the problem by shifting it's tables to some degree. After some drive time, the PCM will return to it's more normal operating table values as you drive.
The IAC is not looked at for much more than an open electrical circuit or malfunction bad enough to cause a code for some other reason like to low an idle speed etc.
The TPS is part of the throttle body operation so is not able to tell much about anyting but it's own travel or electrical circuit.

 

[mpsjr]

Found this over on ford-trucks.com,
Original post:
I have a 98 F150 and am having a problem with the engine stalling when braking.

From Bluegrass 7:

The IAC would be the first suspect for being gummed up.
Remove it and clean with intake cleaner made for the purpose.
Also clean the inside of the throttle body around the throttle plate area.
A little background on why the motor may stall upon braking is as follows;
The speed sensor tells the PCM what is happening to the road speed by driver action (braking).
This does several things. It unlocks the convertor, shuts down the fuel and keeps the IAC open just enough so the motor won't stall.
As you see, the IAC cannot respond so the motor stalls.
The gum around the throttle plate has limited air flow vs opening angle as well.
Also the PCM has tried to account for the problem by shifting it's tables to some degree. After some drive time, the PCM will return to it's more normal operating table values as you drive.
The IAC is not looked at for much more than an open electrical circuit or malfunction bad enough to cause a code for some other reason like to low an idle speed etc.
The TPS is part of the throttle body operation so is not able to tell much about anyting but it's own travel or electrical circuit.

I ran across that thread a while back when this first started. I have cleaned the IAC and throttle body and it's still stalling. It doesn't actually stall while braking. It stalls after I start to accelerate and will actually accelerate for approximately 1/2-1 second before stalling. In my mind, what is happening is the gas is moving forward in the tank enough to get away from the pump, which is sucking up air. In one of my previous posts, I mentioned that it did not matter how much/little gas was in the tank, but I realized last week that it will stall anywhere near 1/2 a tank or lower, while I have a hard time getting it to repeat this when the tank is full. But, I know in the past it has stalled with a full tank of gas...it just seems like a less common occurrence.

EDIT: So today on my way home, I made it a point to try to get my truck to stall with a full tank of gas. Exactly as expected, it stalled "on demand" just like usual. Again, it's not as common with a full tank, but still happens.

 

[Expy_97]

My two cents...

I like the idea of the IAC valve and the TPS personally, both of those are systems that are definitely involved during idle to drive transitions.

I cleaned my IAC valve out as well, but later reinspected and noticed that the valve was still grainy when I reached in and moved it with a screw driver. Decided to get a new one and compare how easy the new valve moved to the old valve. The old valve was still way more difficult to move so I replaced it anyway. Just a thought.

How are your brakes working? Does the brake pedal have some play in it before the brakes grab? Does it work better on the interstate than running around town? I'm wondering about your check valve in the vacuum line to the brake booster. If that isn't working properly, you could be loosing vacuum when you release the brake and hit the gas. that loss of vacuum could result in a fuel rich condition from the fuel pressure regulator causing your truck to flood out.

 

[mpsjr]

I thought about a vacuum line as well. I haven't had time to fool with anything in a while now, but my brakes are great. I've never had a problem with anything in that regard. I noticed that one of my lines from the PCV is collapsed (where it comes into the manifold) and I will be replacing that as soon as I have the time. I will also pull the IAC and check it again to see how freely it moves. Thanks.

 

[Dynamatech]

Try the fuel pressure regulator located on the driver's side of the fuel injector rails. I have the same problem and I'm going to replace mine tomorrow. I have already exhausted all possibilities and they are all leading to the fuel pressure regulator. . . Good luck everybody!

 

[Dynamatech]

I ran across that thread a while back when this first started. I have cleaned the IAC and throttle body and it's still stalling. It doesn't actually stall while braking. It stalls after I start to accelerate and will actually accelerate for approximately 1/2-1 second before stalling. In my mind, what is happening is the gas is moving forward in the tank enough to get away from the pump, which is sucking up air. In one of my previous posts, I mentioned that it did not matter how much/little gas was in the tank, but I realized last week that it will stall anywhere near 1/2 a tank or lower, while I have a hard time getting it to repeat this when the tank is full. But, I know in the past it has stalled with a full tank of gas...it just seems like a less common occurrence.

EDIT: So today on my way home, I made it a point to try to get my truck to stall with a full tank of gas. Exactly as expected, it stalled "on demand" just like usual. Again, it's not as common with a full tank, but still happens.

I would try the fuel pressure regulator located on the left side of the fuel injector rail.