Sputtering Stalling Rough Riding '99 Mounty

[mounty_man]

Hello all,

I have had my '99 Mountaineer 5.0L V8 AWD for 1.5 years now. Since I bought it, I have replaced: MAFS, A/C Clutch, 2 Front Wheel bearings, Front Pads & Rotors, Intake Manifold Gaskets, Fuel pump, Fuel filter, Idle Air Control, and PCV Valve and have done a rebuild on the front drive shaft CV joint. Things still broken that need attention: the radio and dash lights do not work, the cigarette lighter hole has broken free of its mounts and is rattling inside my dashboard, and the current problem.

(NOTE: This is not a thread to complain about the reliability of this wonderful vehicle but rather a cry for help.)

I was recently on a 400 mile trip from Pittsburgh, PA to my home in New Jersey. On the trip, the cruise control was set and things were going great until I began going up a rather steep hill that required the computer to press the accelerator and down-shift to maintain speed. The problem is that the pedal went down, but the engine was not responding. After the car slowed down (due to the engine not responding), the car came back to life, jolting me back in my seat, and continued as if nothing had happened. I thought that it was weird until it began doing the same thing in every similar situation. When I got closer to town, I slowed down to navigate the windy streets and to my surprise, the pedal was unresponsive at times at slow speeds as well. I got home and parked the car for the night and waited to see if it was acting the same way the next day. I haven't had a problem since then...

...Until tonight. I was almost home from work when I came to a red light. As I slowed to a stop, the car sputtered and stalled but not before the oil pressure gauge quickly jumped from normal to high to low. When the light turned green I desperately tried to get it started again but no luck. I let it rest for a few seconds and tried it again and it started (roughly)! I pulled it over to the side of the road but it sputtered terribly again so I shut it off. I immediately thought that there might be an oil pressure problem because of the erratic needle movement so I checked the oil. The oil was lower than the last time I checked it but not so low as it should cause problems. To be safe, I added some oil that I had in the truck and checked the level again and it was back up to a good level.

I let it cool a bit before starting it again and drove it down the street to the advance auto in hopes that a computer check would show some indication of what was happening. They informed me that the computer check would only show codes that would trip the check engine light on the dash. Their recommendation was to go to a local repair shop. I only live down the block from the advance auto so I was able to get it home in spite of its objections.

Again, the symptoms include sputtering, unresponsive gas pedal, rare stalling, rare oil pressure gauge fluctuation, very rough idle at times.

Leading suspicion: Bad FPR.

If anyone has any ideas, please let me know! This forum has never let me down with any of my other questions, I hope this is not the exception!

Thanks,

Mounty

 

[my pos mounty]

My leading suspicion would be a clogged fuel filter or faltering fuel pump. Do you own, or can you get a fuel pressure gauge and hook it up to the schrader valve on the fuel rail? That would give you an indication as to whether or not your on to something about a fuel starvation issue.

 

[mounty_man]

Thank you for the quick reply!

I worked on it a little bit last night and rented a fuel pressure testor. I was getting 40 psi @ idle. I think its supposed to be around 60 psi. I then took the vacuum off of the FPR to see if it would make a difference. There was no change at all.

Also, just to be clear, in the '99 5.0L AWD, The FPR is in the ENGINE BAY, not the fuel tank. When I was looking through the forum last night, I saw a claim that starting in 1999, the FPR's were moved to the fuel tank.

As an experiment, I left the testor in and drove around the block a few times just to see what would happen to the fuel pressure. I couldn't get it to sputter or cut out, but I noticed that I was slowly losing fuel pressure. When I got back, it was idling at 30 psi.

Unresponsiveness to loss of vacuum makes me think it is FPR but I have no idea what would make the pressure go down while driving it.

 

[my pos mounty]

While that was informative, it doesn't really help much. Still looking at the 3 different possibilities. For the relatively low cost, I would replace the fuel filter, unless you have done that recently.
This article talks about testing the fuel system, mainly focusing on the fuel pump:
http://www.aa1car.com/library/2003/us60324.htm

This article talks about testing the FPR:
http://autorepair.about.com/od/troubleshooting/qt/fuel_fpr_inspt.htm

 

[mounty_man]

I replaced the fuel filter and pump in early September '09. I had between 15-20 psi of fuel pressure and would lose power going uphill. Once I changed both of those, it was great.

Shouldn't pulling the vacuum line off the FPR change the fuel pressure reading if the regulator was working correctly?

I will try to look at the pump when I get home from work today.

 

[my pos mounty]

That would be the logical thought wouldn't it. For about 75 bucks, it isnt all that much to give that a try, if your willing.

 

[hworksinc]

I replaced the fuel filter and pump in early September '09. I had between 15-20 psi of fuel pressure and would lose power going uphill. Once I changed both of those, it was great.

What kind of fuel pump did you get? I've seen many aftermarket fuel pumps fail for some reason. People seem to have better luck with OEM.

 

[mounty_man]

That repair was done at a garage. I assume they used an OEM pump, but I can't be sure until I drop the tank tonight.

The FPR is turning out to be a tough part to find OEM. A lot of aftermarket stuff. I found one a couple towns over for $40 bucks so I'm gonna grab it on the way home and try it out.

Thanks for all the suggestions so far! You guys have been awesome, especially my_pos_mounty! I will let you know how it goes.

 

[ranger7ltr]

If you do have a 1999 Explorer,

Thank you for the quick reply!

I worked on it a little bit last night and rented a fuel pressure testor. I was getting 40 psi @ idle. I think its supposed to be around 60 psi. I then took the vacuum off of the FPR to see if it would make a difference. There was no change at all.

Also, just to be clear, in the '99 5.0L AWD, The FPR is in the ENGINE BAY, not the fuel tank. When I was looking through the forum last night, I saw a claim that starting in 1999, the FPR's were moved to the fuel tank.

As an experiment, I left the testor in and drove around the block a few times just to see what would happen to the fuel pressure. I couldn't get it to sputter or cut out, but I noticed that I was slowly losing fuel pressure. When I got back, it was idling at 30 psi.

Unresponsiveness to loss of vacuum makes me think it is FPR but I have no idea what would make the pressure go down while driving it.

Your fuel pressure regulator is indeed in the tank... The part you removed a vacuum line from is called a fuel damper...And by removing the vacuum you did nothing that would impact the system pressure of the fuel system...

Your correct fuel pressure should be 65 psi +/- 8 psi...40 psi is barely enough to sustain the fuel needs of the engine...

NOW if your truck is a pre 99 MY the fuel system pressure will be 35-40 psi and it will have a fuel pressure regulator and a fuel return line on the fuel rail on top of the lower intake manifold...

Fuel pumps, imho, die from either heat or particles that get pumped through the pump that the strainer does not filter out...If the external filter has rusty or dirty fuel coming out of it, then the pump sucked it through the strainer and the fuel pump does not like running solids through it... I have had to replace a fuel tank thanks to the rust inside killing 2 fuel pumps...

 

[mounty_man]

I stand corrected! Thank you very very much! I will check that out ASAP!

 

[mounty_man]

It all makes sense now.

Fuel pressure regulators are hard to find...because they are part of the fuel pump assembly (at least on my truck). It also seems that it is not vacuum regulated at all seeing as the only line other than the fuel line going to the gas tank was a hose that, according to the mercury dealer parts specialist, is used for "vapor management". I ended up replacing the assembly even though I still don't believe the pump itself was defective, just the regulator. Sure enough, everything runs fine now...

...well almost. Now, it has a hard time settling into idle. It will start to idle at 500 rpm then drop down to 100-200 rpm, then gas itself to get back up to 700ish rpm then drop back down to 500 rpm. It just cycles through that several times but eventually smoothes out. I'm not too concerned at this point. Mainly because I want to take a little break from fixing this thing.

In any case, thanks so much for all of the posts, ideas, and advice!

-Mounty