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97 4.0 mystery fuel/vacuum issue

BigRedDangerRanger

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Alright guys (and gals), I'm hoping y'all can get my butt out of a sling one more time.

I have a 97 XLT 4.0 with 306,000 miles. I've had this gal since 80,000... original motor. She's my daily driver.

Three months ago I put in a new fuel pump.

A few weeks ago I was on a road trip and after about 300 miles of interstate driving I got onto a state highway, going around 60mph and, out of nowhere, my rpm's dropped, the throttle went unresponsive, and she sputtered to a stop. The engine would turn over fine, but wouldn't start. I went through the basics: air filter, fuel filter, checked power to the fuel pump, etc. Everything looked fine.

I checked for fuel at the schrader valve and had fuel, but what looked like a little vapor also. After a while, I pulled the air intake hose loose and tried using a little starting fluid. I got it to start, but couldn't keep it running with the throttle. After about an hour of cussing and tinkering, i finally got it to start, but the idle was rough and the response to the throttle was still really slow. Hooking the air intake hose back up helped the idle, but the throttle response was still really slow. Things never improved enough for me to get back on the road, so I had it towed to a mechanic (that was a first... and it sucked.)

This was on a Saturday, so the mechanic couldn't get to it till Monday. When I got it back he said he didn't do a thing to it (other than top off my coolant). Said he got to it early Monday and it fired up and drove fine. Murphy's Law, right? I drove all the way back home (300 miles on the interstate) with no problems... not a single one.

Till yesterday. I was driving around the farm (literally just putting around in 2nd gear all morning) and turned the truck off for a few minutes. Hopped back in, fired it up and the same thing... sputtering, coughing and then it died. Couldn't get it to start, and after about 45 minutes of trying, I left it alone. (This time I could walk to the house). I came out this morning and it fired right up.


Any ideas? Is this a vacuum or a sensor thing? I live in the deep south now, would the heat of the day have anything to do with it?

Any ideas are welcome, I'll check back regularly. Thanks a bunch!
 


SenorNoob

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My first thought is: Do you know what the fuel pressure is when it acts up?
 

BigRedDangerRanger

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I have no idea what the fuel pressure is. Other than using one of those fuel pressure gauges on loan from the parts store, I don't know what to do to estimate it. There's a pretty substantial stream of fuel/vapor coming out of the schrader valve when it acts up though.
 

RonD

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What was the brand of the fuel pump?

Many have found some brands need to be replace, under 1 year warranty, at least one time to get one that lasts past the 1 year mark.

Fuel pressure would be good to test because of the above, tester is $20 here: http://www.harborfreight.com/fuel-injection-pump-tester-92699.html
Or DIY tester here: http://www.nicoclub.com/archives/diy-fuel-pressure-tester.html


Also try loosening the gas cap, vent the tank, and see if problem comes back, you should get CEL and EVAP code after a bit with loose cap.
EVAP system creates a negative pressure in the gas tank so fumes don't pollute the air.
It shouldn't be able to lower the pressure in the tank enough to slow down fuel flow but............loosening gas cap costs nothing to try.
If you can do it after another no start, listen for a big rush of air into the tank when cap is loosened and then see if it starts right after that.

The vapor in the fuel rail would cause symptoms you described, but not sure how that would happen, fuel line close to exhaust could be causing the vapor issue but if you haven't changed the routing of that line recently then ???
Do you have a recent exhaust leak that could be directed at a fuel line?
Has it been much hotter recently?

I know in the old days, lol, I had to put those wooden close pins on metal fuel lines in engine bay as heat sinks to prevent vapor lock, haven't ever run across that with fuel injection.

Do you have an EGR system?
Could there be an exhaust leak in that tube directed at the fuel rail?
 
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enjr44

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The vapor in the fuel rail caught my attention when I read this yesterday. I don't know much; but, I do know that if there is air in the fuel lines that is bad. They just won't run on air.

Back in the tank, is there a line between the pump and the fuel pick-up sock (or someplace else) that could be sucking air instead of fuel?? Does it do it with a completely full fuel tank??
 
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BigRedDangerRanger

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Update: I filled up yesterday, and already three separate times this morning I've had the same issue. I was driving along ~20 mph and all of a sudden it was like I was running out of fuel. Y'all know that feeling… no throttle response, a couple seconds of bad missing and hesitation, then it shut off. I sat for about 10 minutes before I touched a thing, after that it cranked back up on the first try. Three miles down the road, the same thing, only this time I left it in gear and let it coast downhill. After about 20 seconds, the throttle response came back and everything was back to normal.

RonD - the fuel pump I installed was a basic one from Advanced Auto. Very Asian. I didn't loosen the fuel cap at all, but I'll give that a shot this afternoon.

enjr44 - That's what I've been thinking too. I mostly just don't want to admit that I may have screwed something up with my fuel pump swap… and I don't want to dive into that PITA job again. I drove 400 interstate miles through a tank of fuel and never had a problem. And now it seems to be getting worse, no matter the fuel level.

Could the exhaust system or an injector be a problem here? I've never messed with either, and this gal's got some age on her.

As always, thanks for any ideas
 

enjr44

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Well, I think, for what my opinion is worth, you are in for a new, again, pump because it sounds to me like your problem is air getting pumped into to fuel rails. And that has to be between the pump and the fuel in the tank.

I did hear once about when a person changed just the pump (not the whole assembly), he replaced the in the tank fuel line with regular fuel line and later found that regular fuel line wasn't made to be submerged in fuel and it dissolved. I also heard about one that the in-tank sock got pushed up against the pump inlet tube during installation an blocked it; but, that wouldn't explain the air in the fuel rail.

Did you change just the pump or the whole assembly. And what brand did you use? They all are not equal. I got Delphi because they have a good rep and I think that is who makes them for Ford. The assembly costs more; but, I didn't want to do it twice.

When mine failed (in my 02) I put in this because for something this hard to change I believed it was worth it.

http://www.napaonline.com/Catalog/CatalogItemDetail.aspx/Fuel-Pump-Assy-Electric-In-Tank-Type-Actual-MFG-OEM/_/R-DFPFG0872_0391342450

Hope you get it figured out!!
Ed
 

RonD

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Exhaust or injector issue doesn't fit symptoms.
 

adsm08

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Vapor in the fuel rail won't be caused by the pump sucking air. That pump won't move air, it isn't thick enough. It can be caused by low fuel pressure allowing evaporation in the rail. This reads like a bad pump or a bad wire through and through.
 

BigRedDangerRanger

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Thanks guys. I replaced my pump yesterday with a new one from Advance Auto Parts. I didn't notice anything wrong with the old pump, but who knows. On the plus side, the old pump had a LLR warranty, so I didn't have to pay anything for it. I'll let y'all know if anything changes.

Thanks again, y'all
 

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