Help wanted with fuel pressure gauge

[live2_4x4]

I have been chasing an intermittant cold start problem (94 x 4.0l) for a while now and think it may be the fuel pressure regulator. My question is this, In my hanes manual it says to bleed off fuel pressure by hooking the gauge up to the test port and bleed it off using the relief valve on the gauge, in the instructions for the gauge it says to bleed off pressure before hooking up the gauge. Which one is correct, because my problem is so so so intermittant(can go weeks without a prob), I'm hoping for number 1. I'm sure someone out there has done this and has the answer.

Thanks
Glen

 

[MrShorty]

It kind of depend on how your pressure gauge hooks up. Mine screws on, and if I try to screw the gauge on with pressure in the rail, it all bleeds out (and onto the intake) while I'm screwing the gauge on. If your gage will connect and seal quickly enough, you can probably get away with not releiving the pressure before you hook it up.

 

[live2_4x4]

Mine screws on looks kind of like a tire valve?
Does yours leak out or spray all over the place?
How else can I diagnose such an intermittent prob?

 

[monkeydude3]

One way to just have at it either way... pull out your fuel pump relay. Fire it up( if it will) and let it run until it dies. Then try to start it again and crank for about 5 seconds. bam you have no fuel pressure.

If it wont start with the relay out, just crank for 5 or so seconds. you will have no fuel pressure. Then hook up the gauge, reinstall the relay and fire it up and go from there.

That's what I would do in that scenario.

Take care

George

1994 XL 4.0L OHV

 

[monkeydude3]

By the way... what exactly is the cold start problem? Does it just take a w hile to fire up or what?

 

[live2_4x4]

The problem I am having is: After sitting for a while ( min 2 hrs) the truck will not start it turns over fine but just wont run, once I got it to start by holding my accelerator to the floor while cranking, once i got it to start by repeatedly priming the fuel pump (turning the key on-off 7-8 times) and the last time it started just by letting it turn over for a long time(close to 20 sec). The other thing I have noticed is that on occasion there seems to be a lot of pressure built up in the fuel tank as if the fuel pump is pressurizing the whole system including the tank. Back when I first bought the explorer a year and a half ago I noticed a strange noise if you primed the fuel pump more than once, I described it as a bubbling noise from the area of the fuel tank as if fuel was being dumped back into the tank. A couple of tanks with fuel injector cleaner and it hadn't reoccured. Finally once while out on a hot day I opened the gas cap while the engine was running and it died as if it ran out of gas. Totally freaked me out, thought the fuel pump was dead but put the cap back on cranked for 10-15sec and it fired up ran rough for half a min then fine ever since( never took the cap off while it's running though)Someone once suggested the problem might be the check valve ( i assume the same as the FPR) letting the gas flow back into the tank.
Sorry to be so long winded but you asked, and that's the whole story.

Thanks
Glen

 

[MrShorty]

"Does yours leak out or spray all over the place?" -- Kind of leaks kind of sprays if I don't depressurize the system. As was mentioned, it isn't difficult to depressurize the fuel system first.

"Back when I first bought the explorer a year and a half ago I noticed a strange noise if you primed the fuel pump more than once, I described it as a bubbling noise from the area of the fuel tank as if fuel was being dumped back into the tank." -- This should be a normal, regular occurence. The design of the fuel system is such that pump pumps much more fuel to the engine than it needs. The FPR allows the excess to return to the tank. At this point, I would pull codes from the computer and check the fuel pressure and go from there.

 

[live2_4x4]

O.K. new update

I just ran a fuel pressure test. Hooked up the tester without bleeding the fuel rail to see what would happen. No leak, No spray, No pressure whatsoever. Turned the key on to prime the fuel pump, pressure jumps up to 30ish and starts dropping right away. Repeat,same results. Turned the key to start and it fired right up( go figure, it wouldn't start last night) Here are my results please tell me what you think.

Pressure @ idle with vaccum 32psi
Pressure @ idle w/out vaccum 40psi
Shut off truck after reattaching
vac hose pressure @ 32psi

Pressure after 30sec 20psi
Pressure after 60sec 18psi
Pressure after 3min 14psi
Pressure after 4min 12psi
Pressure after 5min 11psi

The manual says hold pressure after 5 min s/b 35-60 psi
The speed at which it loses pressure seems way to fast to be injectors leaking so I am thinking it has to be the FPR. (or I could be wrong)

All input from those wiser than I (most of you) would be appreciated.

Thanks
Glen

 

[MrShorty]

You are correct in that it is losing pressure faster than it should be. If there were an external leak, you would probably notice it, so I wouldn't expect it to be an external leak.

FPR could be leaking. Normally, unless it's leaking externally, it develops an internal leak where gas gets sucked into the vacuum hose connected to the FPR. Do/Did you notice any gasoline in that vacuum line? If not, I suspect the FPR is good, because it otherwise controls the pressure as it should. Note that the FPR and the check valve someone mentioned are not the same thing.

I wouldn't be so quick to dismiss the injectors. If one or more injectors were stuck open, it would cause you to lose pressure. How quickly is a little tricky to say, but if you ever set it up so you can disable the fuel pump after starting the engine and watch how quickly the opening and closing of the injectors can bleed the pressure off, I would believe a leaking injector could cause that kind of pressure loss. That much excess gasoline in a cylinder should show up in other ways (gasoline on the spark plug on warm start for example).

The last place that would cause that much leakage is the check valve in the fuel pump. This is the check valve that was mentioned to you before, and I think this is the most likely cause. The fuel pump has a check valve in it to prevent fuel from returning to the tank through the pump. When the check valve goes bad, it allows gasoline to return to the tank when the pump isn't running, causing hard starts. Mine does this to some extent. I've gotten use to listening to the pump when I first turn the key on to hear when the pump whine changes pitch, indicating that the fuel system is pressurized. You can also hear the fuel being returned to the tank when the fuel system reaches it's designed pressure. For now, I have preferred to listen for these cues that the system is ready rather than replace the pump, because my pump otherwise works fine.

 

[live2_4x4]

If one or more injectors were stuck open would it show up if I pulled the plugs now. I am curious because you mentioned it showing up on a warm start and I have also had an intermittant problem with a rough idle for the first few seconds on a warm start. If it would show up what exactly would I be looking for.

Thanks
Glen

 

[MrShorty]

You would be looking for "wet" (with gas) spark plugs. If you wait too long after shutting the engine off, then the gas will evaporate and be gone.
A leaking FPR can show the same kind of thing, but it will also show up by gasoline in the vacuum line to the FPR.

 

[live2_4x4]

O.K. It finally cooperated, I turned the key 4-5 time to see if I could hear the change in pitch as it pressurized the system and I can't (could just be me) BUT when I then tried to start it it would not start , the fuel pressure gauge was still hooked up and while it was cranking it bounced around a bit (32-36psi range) and when it finally did fire it ran like crap for about 30 secs then revved pretty high before settling down like normal, I also noticed the exhaust had a stronger smell of gas than I think is normal. Do you think this points towards your theory of leaking injectors? I pulled the vac line off the FPR and could see no sign of gas there but the line is so small I can't be sure. Also would pulling the codes help at all? I have no CEL on now or in the past.

Thanks for your patience and help
Glen

 

[MrShorty]

Pulling codes is easy, doesn't take long, and may give some information. But the computer doesn't monitor the fuel system (other than whether or not the pump circuit responds to its command to turn on). If you get all pass codes, that will tell us that the EEC-IV system is working as it should and not contributing or detecting the problem. If you do get any fault codes, they may give us information, they may not. Again, it doesn't take long to do.

The fuel pressure while cranking was a little low, and it should have been at the 40 psi that the regulator controls w/o vacuum. This suggests to me that there is something wrong in fuel delivery, be it a leaky injector or FPR, an FPR that intermittently loses it's ability to regulate the pressure correctly, or something restricting fuel flow to the engine.
The gas smell in the exhaust indicates it is misfiring. Whether it is misfiring because it's too rich (leaking injector or regulator), too lean (not enough fuel getting to the rail), or no spark is difficult to say at this point. Diagnosis is complicated by the intermittent nature of the problem. I want to blame an intermittent fault like this on an electrical problem rather than a mechanical fault, but anything's possible.
Go over the wires between the injectors and the computer. Make sure there isn't a bare spot that could be making an intermittent connection to ground.
Beyond that, you've got to do your best to note what it does differently when it won't start from "normal." For example, you said you didn't hear the fuel pump change pitch after pressurizing the system. Perhaps it never did get the system up to pressure. Intermittent faults like this can be pretty tough to diagnose. Try to gather information about the problem over time. Figure out what it does differently when it has trouble starting. A good starting place is to listen to the whine of the fuel pump on starting to see if you can tell when it is pressured up. It might be useful to use the fuel pump test lead in the self-test connector (short end, I believe) to control the fuel pump so you can control how long the pump runs on start up and get a feel for how it sounds while pressurizing and after it reaches the desired pressure.

 

[live2_4x4]

O.K. I pulled the codes as per the haynes manual and all I got was a pass. I suppose this is in some way good news but not all together all that helpful. Also while trying to catch the codes on the CEL (took a couple tries) obviously it primed the fuel pump several times but when it was all done I had no problems starting????????????(unlike last night). I will check the wires leading to the injectors as well as all vac hoses and connections as well as keep a log of what, where, when, how it happens. Any other thoughts about where to look to find my prob?Also in your last post you mentioned using the fuel pump test lead , which lead is this, and how would I use it???

 

[MrShorty]

Fuel pump test lead is one of the leads in the self-test connector (same connector you used to pull codes). It's the short end of the trapezoid. A Haynes manual should have a diagram in the fuel pump test section. If not, Chiltons does (see the vehicle repair guides at www.autozone.com for an electronic version of Chiltons).
How to use it? 1st, you can use it to get a feel for how the fuel pump sounds as it's bringing the fuel system up to pressure. You can also use it to listen for fuel being returned to the tank when the pressure is low. Ultimately, after getting a feel for how the fuel pump should operate, it will allow you, the next time it's hard to start, to see if running the fuel pump steady before starting helps it start.

 

[live2_4x4]

O.K. thanks, I see that autozone site even has step by step diagnosis there. Maybe that will help me out some. But don't worry I'll be back soon with more questions for you or better yet some results. Thanks for all your help so far.
Glen