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lundy · 07-03-2013, 03:54 PM

I have a '11 Newmar BayStar motor home with V10 Engine. Since new I have had a fuel starving situation that 3 Ford Dealers cannot find and correct. It occurs under various conditions of early morning or after short lunch breaks or refueling. It always starts easily but intermittently upon acceleration, starts to die untill you pump the accelerator. Keep a steady foot (at least 3/4) and it will come to a stop but won't die. Once you reach road speed, it runs as smooth as silk and won't miss again. At first I thought it was a vapor lock-type stall but it sometimes happens when first starting up in the morning.

The Ford dealers have never been able to replicate the problem and no code has shown up. I have been told that there is sufficient fuel pressure, filters are clean but I still have the problem. I am frustrated and there have been situations where this stall could have caused an accident if it had occured at that moment, eg. moving from a stop into a busy street.

garykk · 07-03-2013, 04:17 PM

Throttle position sensor?

Walter5555 · 07-03-2013, 04:43 PM

If your fuel filter is clean and the other thing could be your fuel pump screen or the pump it self.

I had the same problem but it would not run very well going up hills.
The first time it happened it was a fuel filter.

The second time it was the fuel pump which is located in your gas tank.

It could be a loose wire to your fuel pump.

Just a thought.

TeJay · 07-04-2013, 06:33 AM

Here's a few points. Electric fuel pumps were incorporated into gas tanks to avoid the possibility of vapor lock. It can't happen because if there is an air space in a fuel line the pump will pump fuel and compress the air.

With the change to fuel injectors, or throttle bodies, pumping the gas (air) pedal will not inject fuel as the accelerator pump did on carburetors. I'm not saying that this did not help your situation but by doing that and thinking that fuel is being added may cause one to draw the incorrect conclusion.

Intermittent situations are always to most difficult to diagnose. Good call on the TPS garykk. The accelerator pumping does lead one to think TPS as was suggested. The throttle position sensor is actually a variable resistor that sends a voltage to the PCM. The voltage starts out around .5 volts up to about 4.8 volts. As you accelerate if that voltage drops off to .5 V the PCM thinks you are back at idle. The change in voltage from .5 to 4.8 is what tells the computer how fast you are wanting to go. That is not a very expensive part and it can be checked very easily with a scan tool. Get it checked and or just replace the thing and let us know.

TeJay

subford · 07-04-2013, 10:45 AM

Quote:

Originally Posted by TeJay

Here's a few points. Electric fuel pumps were incorporated into gas tanks to avoid the possibility of vapor lock. It can't happen because if there is an air space in a fuel line the pump will pump fuel and compress the air.

Ford had a problem with vapor lock on the inline six engines after they went to fuel injection. To try and over come this problem the raised the Fuel pressure to around 60psi at idle and put on an extra blower to blow air on the fuel injection rail (manifold) to fix the problem.
So yes vapor lock does happen with the fuel injection engines if the engine bay gets hot enough.
I do not know what the fuel pressure is on the 2011 V10 engine at idle but the 460 only has about 32psi fuel pressure at idle.

C-Leigh Racing · 07-04-2013, 05:45 PM

Let me ask you folks this, can enough vaccum build up in the tank, if the fuel tank caps not venting proper, to stop the flow of fuel, even though the pump is in the tank.
Neil

clyon51 · 07-04-2013, 05:56 PM

No personal experience but, I have heard this happening if the vacuum becomes too great, or the vent is totally blocked.

C-Leigh Racing · 07-04-2013, 06:52 PM

Ok, cause the reason I ask that, last year during the hot days of summer, we were having problems with the get set cutting off going down the highway. As a test after a fill up, I left the gas cap loose so the tank could vent easier & the cutting off of the get set didnt happen anymore.
It even to some amount, felt like the coach engine even performed better on hills & such, so I'm wondering if maybe his gas cap could be the problem causing the starving out ordeal.

What I was guessing was happening, all the vacumm in the main fuel tank, was over coming the fuel pump on the gen set, old 99 year gas hoses from the main tank up to gen pump was sucking flat & no fuel flowing, starving out the gen carb.
Neil

clyon51 · 07-05-2013, 07:59 AM

I'm sure you nailed it Neil. This is exactly what I have read in other threads and a new vented fuel cap was the fix.

C-Leigh Racing · 07-05-2013, 09:20 AM

Another thing though, I'm hearing from some people, that the gas tank cap must be tight to maintain a vacumm in the tank, or either the computer will throw the CE light on the dash.
I know during fill ups on ours, when the cap is removed, if it should happen to be anything close by, it would get sucked into the gas tank theres so much vacumm when the cap removed quickly.
Once the cap is removed, in a second or two, the engine will change sounds like it has freed up & idles a little higher, like it was under a strain just to run.

Maybe it is just an issue with ours & nobody else getting a heavy vacumm build up in their gas tanks.
Neil

Hikerdogs · 07-05-2013, 09:39 AM

Quote:

Originally Posted by C-Leigh Racing

Another thing though, I'm hearing from some people, that the gas tank cap must be tight to maintain a vacumm in the tank, or either the computer will throw the CE light on the dash.
I know during fill ups on ours, when the cap is removed, if it should happen to be anything close by, it would get sucked into the gas tank theres so much vacumm when the cap removed quickly.
Once the cap is removed, in a second or two, the engine will change sounds like it has freed up & idles a little higher, like it was under a strain just to run.

Maybe it is just an issue with ours & nobody else getting a heavy vacumm build up in their gas tanks.
Neil

I believe the fuel tank is supposed to carry a slight positive pressure. When the pressure exceeds a certain threshold the sensor sends a signal to the PCM and the excess vapor is routed to the purge canister.

The gas cap is supposed to have a 1 way valve that allows air to come into the tank to replace the gasoline that's being used. If the cap is defective it may not allow air to enter thus creating a vacuum.

C-Leigh Racing · 07-05-2013, 10:10 AM

All right, copy that, so there should be a pressure when the gas tank cap is removed, not a vacuum.
Now that make sense to me & what I was thinking it should be like to start with.
If the system was gravity feed, the fuel tank pull a vacuum & that engines not going to be running long.
How do I know, working on mowers & saws over the years & customers coming in with a Clorox jug cap on the fuel tank, cause they lost the normal gas tank cap & couldnt figure out how come the engine would only run after they loose the gas cap.

Well, look like its off to the auto parts store for a new gas tank cap.
Neil

redfire312 · 07-05-2013, 11:17 AM

the tank does foul up on my 97 with the 7.5 v8, one time last year it wouldn't start, had some pressure at the fuel rail so I suspected the fuel pump. tried swapping relays, checking grounds etc, no dice. This went on for about 3 days. Started taking fuel lines loose and got to the one that goes to the generator which shouldn't be pressurized but fuel was streaming from that line. I took the fuel cap loose and the stream stopped, so on the off chance that the fuel pump was reading pressure and not kicking on I snapped the lines back together and voila it started right up! I was so happy about not having to drop the tank, buy an expensive pump and whatever. worked perfect on our 2000 mile trip to colorado and a trip to georgia and several quick trips to the lake, then just last week I was having problems with the starter relay, got that fixed and I was testing out the starter, started a few times, then I'll be darned if it would crank and not start just like last time. I went in to eat supper and came back to try again, same thing, so I opened the fuel cap, put it back on and low and behold it cranked right up. So I don't know if my cap is not working right, the fuel tank vent, or something else, but now I know to take of the cap off first before I start buying parts.

cb1000rider · 07-05-2013, 12:04 PM

Quote:

Originally Posted by TeJay

With the change to fuel injectors, or throttle bodies, pumping the gas (air) pedal will not inject fuel as the accelerator pump did on carburetors. I'm not saying that this did not help your situation but by doing that and thinking that fuel is being added may cause one to draw the incorrect conclusion.

Actually, modern EFI has the equivalent of an accelerator pump programmed in. On the systems I deal with, it's called "acceleration enrichment" and is quantified by extra injector pulse width depending on how fast you push that peddle down.

I assume that the ford dealers have replaced your fuel filter and didn't find evidence of clogging? These machines go through gas fast and it's not unusual to need a new filter in 30k miles.

Beyond that, does it indicate a check engine light? It should. It should trigger an error related to the 02 sensors being too lean. That code "captures" the computer sensor data at that moment.

I don't have an '11, but on a '99 and an '05, OBD-II scanners do not pick up data on fuel pressure. If you really suspect a fuel pressure problem, the Ford dealer won't know unless they can replicate on the bench. You can add aftermarket fuel pressure gauges, but they probably shouldn't be installed by you average backyard mechanic...

If this problem happens frequently, I'd probably rig up a temporary or permanent fuel pressure gauge to confirm your theory. From there, I'm most likely looking at the fuel pump if the filter is new-ish.