Not getting enough fuel after sitting

[cmstache]

Having a bit of an issue, my explorer has been having issues starting recently. Changed the battery (it was time anyways) last weekend. The starter, while old, seems to be working fine.

Cold mornings, the starter just spins, sometimes I need to jump it with my fiance's car, sometimes it only takes a small booster (I live in an apartment complex, so we aren't always next to each other.) Often when it does crank up, it bogs down immediately, like it doesn't have gas. Sometimes giving it throttle helps, sometimes it doesn't. After a few tried (23-5 it starts fine and begins to idle. If the vehicle has been running I can restart it immediately fine. After about 3-4 minutes it takes a few tries. The vehicle itself runs fine, idles fine, and drives fine.

I think I've diagnosed the issue to the fuel pressure sensor, with the help of my more car-savy friends. The part itself is 100 bucks (I can probably get it for about $50 with connections) and as a poor 27-yr old, I don't like throwing parts at a vehicle. That being said, is there an easy way to test it? I was told to look inside for fuel, but the vaccum line facing the dash, so I can't see inside; doubt i could by the design even if it wasn't. If I unhooked it entirely, would I be able to see something somehow?

I'm not the most skilled guy with cars. I can do the basics (I've changed my EGR and IAC Valve, needed help for intake manifold gasket.), but I don't have the knowledge or ability (or space, even if i could) to tear apart an engine looking for issues.

It's a '97 Explorer Sport, 4.0 OHV V-6, manual trans., 275k miles. Pretty much stock engine. Any help would be great.

 

[C420sailor]

Don't throw parts at it. Replacing fuel system components without first checking the fuel pressure is a good way to waste $$$.

 

[cmstache]

Testing Fuel Pressure

Is there a way for me to test fuel pressure while cranking the vehicle on my own, or do I need a second person? Also, will a fuel pressure gauge work while starting the vehicle too? I was under the impression they only tested constant pressure, like what would be at an idle. Then again, maybe I'm clueless. I don't mind spending 30 bucks for a gauge if it's pretty easy to do at home.

 

[C420sailor]

I've heard of guys using normal tire pressure gauges. I'd check the pressure before start (ignition on), at idle, and while cranking if you can. Those values can help shed some light on what's going on. I assume you have no CEL/codes?

The only reason I don't say jump right to the FPR is because I had a similar issue for the last few months. Fuel pump was due for replacement (original, 212k on it), and if the truck sat for a day or so, it would need a good 2-3 seconds of cranking before it would fire. I replaced the fuel pump and the problem went away completely---it can sit for two days and fire up immediately. Sometimes when the pump assemblies get old, they allow fuel pressure to bleed off when they're not running.

 

[Robman]

There are rubber hoses that connect the fuel pump and regulator in the tank, they have been known to dry out and get little slits in them which bleed out pressure.

 

[cmstache]

Nope, I'm not throwing any codes. I wish, then I'd have a place to start...

I'll probably get around to it tomorrow afternoon. I'll post the results here. It is the original fuel pump as well. For what it's worth, the last 4 times I cranked the vehicle I let the key sit in the "on" position for about 3-4 seconds while the fuel pump does it's job, then starting the engine. It started right up. It's started right up previously though, so I don't know if it's a fluke, because I've also waited previously and had it not start.

 

[Macgiobuin]

When you first turn the key on, the PCM commands the fuel pump relay to 'prime' the system for two seconds. It last only a bit because the PCM assumes that there is fuel in the rail, and that is all it needs is to pressure up to spec, which for a '97 is 35 psi. If the fuel line is empty, as happens if there is are loose fuel injector nozzles or o rings (that happens after a long period of being parked), the time that the relay is activated on startup is not enough to pressurize the fuel rail. You can see this if you have a dial fuel pressure gauge attached. Don't use a tire gauge. The o rings or worn nozzles allow air to enter the rail slowly, and the fuel draws back into the tank. Once the engine finally catches on, the PCM turns the fuel pump on continuously, and after a few minutes, all the air is shot out of the system and the engine runs perfectly. Turn the key to 'on' til the fuel pump stops the priming, then off, then 'on' til it stops priming, 3 or 4 times, then engage the starter. If this works for you, you're on to the problem. Now if you turn off the engine and let it sit for a minute, it may start right up, because there is not enough time for the fuel to draw back to the tank, replaced by air. But if you wait over night, the car will not start unless you do the priming dance again. That's what makes it so difficult to diagnose. It appears that its occurrence is random, when in fact it is not, it fails after sitting long enough to let the fuel draw back, which can take hours, or even days. I resolved a similar problem by installing a check valve in the tank to prevent back flow. There are a couple other tricks you can use to fool the relay to stay on until the key is off--in other words don't let the PCM turn off the pump at start-up, but that would be defeating a safety feature designed into the system that I would be reluctant to do on even my personally owned vehicles.

 

[cmstache]

It can sit overnight and start fine, but not right up after just a few minutes, that's why I think it's "random." Honestly, I know there's truly no thing as random, but "inconsistent" might be a better word?

Turn the key to 'on' til the fuel pump stops the priming, then off, then 'on' til it stops priming, 3 or 4 times, then engage the starter. If this works for you, you're on to the problem.

This was one of the first things we tried, it didn't work, at least not at the time.

 

[cmstache]

Haven't gotten around to testing, but now that it's colder it happens far more consistently. It will start 100% of the time if I prime it more than once before cranking. Sometimes it takes 2-3 times. When temperatures are lower sometimes it takes 4-6 and a couple of tries.

Occasionally, it stays below 500 RPM, like it's not getting enough fuel. Eventually cuts off. Priming it a few more times and starting the vehicle fixes it.