Hard warm starts 1999 4.0 SOHC

[CDW6212R]

That's an interesting concept, and if true it's another tiny reason to like the return system(should always purge any vapor).

I think the pump should be the main check valve, but the regulator could also be since the fuel is not supposed to return. How warm is the coolant running, anything odd there?

 

[99SportX]

Don,
The dash gauge shows in the normal range and when I was hooked to my xcal device I was reading about 183.

"Residual Fuel Pressure Test
When the pump is turned off or stops running, the system should hold residual pressure for several minutes (look up the specs to see how much pressure drop is allowed over a given period of time). If pressure drops quickly, the vehicle may have a leaky fuel line, a leaky fuel pump check valve, a leaky fuel pressure regulator or one or more leaky fuel injectors. Low residual fuel pressure can cause hard starting and vapor lock during hot weather."

http://www.aa1car.com/library/fuel_pump_diagnose.htm

 

[cnsheets]

I successfully replaced both temp sensors and thermostat. Problem still exists, so it looks more like the fuel pump......

Good luck with yours.

 

[2000StreetRod]

rapid bleed off

I doudbt that the problem is due to "vapor lock".

The PCM disables the fuel pump after a few seconds if the crankshaft position sensor doesn't report the crankshaft is rotating. The rapid bleed off of fuel pressure after key turn on makes for hard starting. When the starter cranks the engine the PCM energizes the fuel pump building the fuel pressure back up and the engine starts.

I think if you solve the rapid pressure bleed off you will eliminate the hard starting.

Before dropping the fuel tank it would be good to determine if your fuel pump is weak. If you find a way to keep the fuel pump energized with the engine not running, you should hear it stop when the pressure reaches 65 psi and then restart as the pressure bleeds off. If you have a good intank fuel pressure regulator (FPR) the pressure should not fluctuate much. Let it run that way for 30 minutes (connect a battery charger to prevent draining the battery). If the pressure drops significantly within 30 minutes then your fuel pump is probably weak and should be replaced.

One possibility is the hose between the pump and the FPR is split or the clamps are loose. When the fuel is warm it leaks more than when it is cool.

 

[99SportX]

I think if you solve the rapid pressure bleed off you will eliminate the hard starting.

I feel the same way.

Before dropping the fuel tank it would be good to determine if your fuel pump is weak. If you find a way to keep the fuel pump energized with the engine not running, you should hear it stop when the pressure reaches 65 psi and then restart as the pressure bleeds off. If you have a good intank fuel pressure regulator (FPR) the pressure should not fluctuate much. Let it run that way for 30 minutes (connect a battery charger to prevent draining the battery). If the pressure drops significantly within 30 minutes then your fuel pump is probably weak and should be replaced.

I am not sure if I completely understand this. I may be wrong, but my understanding is that the fuel pressure regulator is a purely mechanical device, not electrical. It functions as a relief valve. If the pressure begins to exceed 65psi, the valve opens and dumps fuel inside the tank. If I jump the fuel pump relay, it will run constantly whether the FPR is dumping fuel or not. This would be a way to see what happens when the pump gets hot though. If pressure began to drop off I would see it. I don't think my issue is so much related to the fuel pump getting hot though. It would still do this in the middle of winter when the fuel in the tank was quite cold; 20degF or even less. I have to assume that maybe since the fuel line is near the exhaust or EGR, there is some issue arising from that when there is low pressure in the line.

One possibility is the hose between the pump and the FPR is split or the clamps are loose. When the fuel is warm it leaks more than when it is cool.

I am hoping this is the case, although it seems to leak down just as fast with a completely cold engine sitting all night. Either way, it shouldn't be leaking down. Do you know what type of hose is required? I found some gates submersible rated fuel hose but oriellys wants $25 for a foot. The OEM stuff in the tank can't be that specialized. http://www.gates.com/brochure.cfm?brochure=5091&location_id=541

 

[2000StreetRod]

Fuel Pump Driver Module

. . .
I am not sure if I completely understand this. I may be wrong, but my understanding is that the fuel pressure regulator is a purely mechanical device, not electrical. It functions as a relief valve. If the pressure begins to exceed 65psi, the valve opens and dumps fuel inside the tank. If I jump the fuel pump relay, it will run constantly whether the FPR is dumping fuel or not. This would be a way to see what happens when the pump gets hot though. If pressure began to drop off I would see it. I don't think my issue is so much related to the fuel pump getting hot though. It would still do this in the middle of winter when the fuel in the tank was quite cold; 20degF or even less. I have to assume that maybe since the fuel line is near the exhaust or EGR, there is some issue arising from that when there is low pressure in the line.]

You're correct. It's the third generation modles that have the Fuel Pump Driver Module (FPDM). According to the Ford 2004 OBD System Operation Summary:

There is a fuel rail pressure sensor that is tested by the PCM. P0191 is set when demand minus actual is greater than 40 psi.

"Electronic Returnless Fuel Systems (ERFS) utilize a Fuel Pump Driver Module (FPDM) to control fuel pressure. The PCM uses a Fuel Rail Pressure Sensor (FRP) for feedback. The PCM outputs a duty cycle to the FPDM to
maintain the desired fuel rail pressure. During normal operation, the PCM will output a FP duty cycle from 5% to 51%. The FPDM will run the fuel pump at twice this duty cycle, e.g. if the PCM outputs a 42% duty cycle, the
FPDM will run the fuel pump at 84%. If the PCM outputs a 75% duty cycle, the FPDM will turn off the fuel pump. The FPDM returns a duty cycled diagnostic signal back to the PCM on the Fuel Pump Monitor (FPM) circuit to
indicate if there are any faults in the FPDM. If the FPDM does not out any diagnostic signal, (0 or 100% duty cycle), the PCM sets a P1233 DTC. This DTC is set if the FPDM loses power. This can also occur if the Inertia Fuel Switch is tripped."

Since it is a pain to drop the tank and remove the fuel pump assembly it would be good to know if it is weak and replace it if appropriate at the same time as a leaking hose, clamps or FPR.

. Do you know what type of hose is required? I found some gates submersible rated fuel hose but oriellys wants $25 for a foot. The OEM stuff in the tank can't be that specialized.

I've seen a post recently about the submersible fuel hose. I'll search for it. I know it is expensive but worth the cost. If you don't use it your hose will gradually dissolve.

The above is what I found when removing the fuel pump assembly in my Volvo 850 turbowagon.

 

[Mbrooks420]

I have a very similar issue with my 1998 5.0. If it sits all night, or all day at work it starts right up. If it's been sitting a short time, sometimes it'll start, some times I have to turn it over 2-3 separate times to get it to start. Although it does start every single time, it's getting old. If it had to do with the fuel pressure leaking down, wouldn't it also happen after it sat overnight?

 

[CDW6212R]

I have a very similar issue with my 1998 5.0. If it sits all night, or all day at work it starts right up. If it's been sitting a short time, sometimes it'll start, some times I have to turn it over 2-3 separate times to get it to start. Although it does start every single time, it's getting old. If it had to do with the fuel pressure leaking down, wouldn't it also happen after it sat overnight?

If that wasn't temperature related, it would happen all the time, and priming the system with the key a couple of times would check that.

 

[2000StreetRod]

key on to crank time

I have a very similar issue with my 1998 5.0. If it sits all night, or all day at work it starts right up. If it's been sitting a short time, sometimes it'll start, some times I have to turn it over 2-3 separate times to get it to start. Although it does start every single time, it's getting old. If it had to do with the fuel pressure leaking down, wouldn't it also happen after it sat overnight?

The time of concern regarding rapid leak down is between key on and key start (crank). If the starter is engaged too rapidly after switching the key to on the pressure will not have time to increase. If the starter is engaged several seconds after the fuel pump shuts off the fuel pressure has dropped. What's puzzling though is how warm vs cold affects the ability to start.

 

[2000StreetRod]

fuel pump jumper

If you pull the fuel pump relay in the battery junction box and then insert a jumper between the receptacles for pin 3 and pin 5 the fuel pump should run continuously with the ignition off. Be careful when inserting the jumper because the power to pin 3 is hot at all times unless the battery is disconnected.

 

[Mbrooks420]

Cycling the key makes no difference in my case. I assume it is something electrical in nature that is different between hot and cold starts. The only code I ever throw is "Generic Evaporative Emissions Leak, Large". When I clear it the CEL usually stays off for a few weeks.

 

[2000StreetRod]

check valve

Today I removed and inspected my Volvo 850 turbo wagon fuel pump assembly. I learned that there is a check valve in the top of the assembly that prevents fuel from backflowing thru the pump when it stops running. There is likely one in your Explorer pump assembly that is defective allowing pressure to drop rapidly. Replacing the fuel pump will not correct the rapid pressure bleed off. In my Volvo the check valve cannot be replaced and the assembly is very expensive. Many Volvo owners avoid the cost by installing an aftermarket check valve somewhere in the fuel line - often near the external fuel filter.

 

[99SportX]

I haven't done any more diagnosis on my vehicle since my last post in this thread. I have a spare drop in fuel pump assembly that I plan to examine for a check valve. I will have to dig it out of the attic. It is possible that the check valve component is part of the FPR or pump since there definitely isn't one anywhere else in that assembly (as I remember it). I am considering trying to rig up a bench test of the fuel pump assembly to isolate the issue and be able to see any potential hose leaks without the pump being installed in the tank. I of course don't want to blow anything up. I just need to head off the assembly so it can build pressure and then watch it leak down. The fuel will either spray out of a rubber hose or connection, slowly purge from the relief or it will backflow down through the strainer filter.

 

[CDW6212R]

I'd bet it's part of the FPR in the tank.

 

[Lemondriver]

NO start 20 min after stopping, starts immediately after stopping

was this problem ever solved? Have the same problem.

 

[99SportX]

I have not done anything about it yet. lol It still starts so I haven't been too motivated.

I had a former mechanic ride in it to lunch one day at work and he thinks it is the IAC sticking once and a while.

I do also need to resolve the fuel psi leakdown issue as well.

 

[Lemondriver]

starts immediately hot but not after 20 min

Has this question been resolved....have the same problem.

 

[wagonmaster69]

Will a dirty fuel filter have the same affect?

 

[99SportX]

Has this question been resolved....have the same problem.

Read above dude.


A dirty fuel filter will likely first show up during conditions of high fuel flow (high engine load) on a returnless system. At idle,the engine isn't consuming as much fuel as when climbing a steep hill on the freeway and pulling a trailer. I don't think you could get away with an equally as dirty filter on a return style system as the flow through the filter should be higher in most cases as the regulator is at the engine vs. in the tank. If the filter was dirty enough to cause starting issues I would expect major drive-ability issues.

 

[wagonmaster69]

Ware is the FPR I have an 1999 v6 sohc.