poor running 4.0, help!

[pgoelz]

Here's a good one! 91 Exp 4.0, CEL light came on so went to work. Codes showed O2 sensor, so replaced. CEL still on so checked codes again, still O2 sensor, so tried a second one. CEL STILL comes on! Replaced plugs, wires, filter, oil change, MAF, cleaned ICV, replaced CAT due to carbon build-up. Guess what, CEL on AGAIN! Had Ford dealer check diags, still shows O2 sensor (always running lean by the way). 3rd O2 sensor installed (OEM this time), same ol' thing. What the heck is wrong!!?? Symptoms: 30-40% more fuel consump, idle RPM fluctuates, blows lots of carbon of course, power loss, CEL comes on after 15mins of driving and only when slowing down, CEL stays on until ign turned off, CEL back on again after another 15mins or so. Maybe a 12-gauge blast?

Going broke from parts & gas!!
Thanks,
Phil

 

[88vert]

Sounds like your fuel pressure regulator went south.Have you been resetting the computer with all the changes you have been making?

 

[88vert]

Sorry Phil

Welcome to the site.You can also use the search on this subject

 

[pgoelz]

Yeppers... sure have. Disconnected the battery for at least 30 mins - 4 hours each time, depending on the work being done. I'm guessing there is no code thrown for the reg, eh? I'll give that a shot. Thanks!
Phil

 

[88vert]

You can check the vacume line on the regulator for gas.If there is gas in the line its shot.How long has it been running like this?

 

[pgoelz]

By the way... this is a great site! I wish I would have come across it sooner. Lots of good info in here!

 

[pgoelz]

It's been running like this for 3 weeks now. I've been mainly driving to test the repairs. I have checked for vac leaks, but never pulled the vac line from the regulator. Sounds like a good place to start.

Phil

 

[88vert]

A bad regulator can cause lots of other problems like bad O2 sensors or cats or can can get into the oil

 

[MrShorty]

In changing all those O2 sensors, have you verified the integrity of the wiring between the O2 sensor and the PCM?

 

[pgoelz]

Guys... Thanks for your suggestions. I rechecked the wiring from the O2 sensor, all checked out good. I pulled the vac line from the regulator. No gas in the vac line. I'm guessing that this doesn't fully suggest that the regulator is good or not, so I'm probably going to replace that next. I also pulled all the air intake plastic apart to make sure something didn't get sucked in there.... shot in the dark! All good there. So does the fuel pressure regulator seem to be the best route to take right now? Thanks again! Phil

 

[pgoelz]

Oh yeah... probably should have mentioned... the CEL code is still O2 sensor and that the enginer is running lean. The shop tech told me that with the O2 sensing "lean",that it's trying to richen up the fuel. I've been reading a lot of old posts. Many suggest the FPR, a few also mention the computer box. Man, this problem is driving me NUTS! Not to mention costing me a small fortune in gas. Yikes!

 

[MrShorty]

Before just replacing the FPR, test it with a fuel pressure gauge. Low fuel pressure would cause a lean condition. Low fuel pressure can be caused by a bad FPR, or a weak fuel pump. To my way of thinking, it would be better to diagnose so you know which needs replacing before buying parts.
Of course, that all assumes that low fuel pressure is the cause of the engine running lean. As near as I can tell, even that hasn't been determined yet.

 

[pgoelz]

Thanks for the reply Mr. Shorty! I plan to test the pressure, just need to research how to do it. FPR's around here are running between $110 - $130 bucks. I found a used FPR at the salvage yard for $15 bucks, so I'll give that a try. The salvage guy said if the problem doesn't change, he would refund the $$$. Figured I couldn't go wrong with that. After reading some threads about related problems, there were some entries about the thermostat and not reaching temp. Guess this can cause the system to think the chokes needs to stay on. I've noticed my engine has been running cooler, just never thought that would cause this type of problem. Going to replace that as well since it's a cheapie. Will keep you posted.

 

[donzo]

Hey,

I've got the same year of Explorer and had been suffering from the same problem for quite some time. It turned out to be the FPR after all.

On mine the vacuum line at the FPR was dry (as yours was) for the "quick-and dirty" check. But from reading various threads on this it seems that 2 common failure modes for the FPR are:
1) FPR develops an internal leak resulting in fuel being sucked through the vacuum hose. This generally results in the engine running rich.
2) FPR sticks resulting in a lean condition. No gas will be present in the vacuum line if this is the case.

Mine suffered from 2).

BTW, I attempted a "quick-and-dirty" fix (as suggested by someone in this newsgroup) and it seems to have worked. I gave the FPR a couple of (very) gentle taps with a hammer and it seems to have become unstuck. The truck has been running great since I did this (about a month ago) but in reality, this is probably just postponing the inevitable (replacement). Given the age of the vehicle ('91) I'm trying to put as little money into it as I have to since there is always the risk that something else (more serious) could go.

 

[pgoelz]

To all... You guys are GOOD! Thanks for the "tap-tap" suggestion Donzo. I performed the "tap-tap" and sure enough, the idle has smoothed right out. I'm at the office right now, so not a whole lot of time to look at it. But, I was able run it for about 4 mins. Usually less than 10 secs of starting, the motor would shake. Then the idle would fluctuate. Now it's rock solid. I purchased a fuel intection pressure testing kit on the way to work. Unfortunately, I did not connect it before the "tap". When running at idle, the pressure was solid at 38psi. Not sure if this is the correct psi or not, but at least it wasn't at 0 or pegging the gauge. It leaked down pretty quick, but I think that was from not being tight enough... saw some gas drips from the connector.

Anyway... I'll do additional work this weekend. I will check the pressure straight away if it starts acting up again. I also want to test the FPR in a failed state before replacing it... just to see what the pressure does!

All you guys were dead on from the start! Thanks for the help. This is the most informative site I've been on, just love it! Will let you know the outcome of the weekends work.

Thanks!

 

[donzo]

Happy to hear that the suggestion helped! No guarantees about how long it will last.

You might also want to:
o Reset the computer so that it can recalibrate itself now that the FPR is functioning better.
o Run a good fuel system cleaner through it to clean any deposits that might have caused the FPR to stick.

Ditto your comments about this message board. Its been extremely helpful in tracking down gremlins like this one.

 

[nostarttireflat]

Does the engine have to be cool when you tap on it, I just did it & it changed the idol a little.

 

[pgoelz]

Final update... and thankfully it's a positive one!

The "tap" job was very short lived, but I expected that. It did help me in isolating the problem though, so it was worth the try.

A new FPR fixed the problem. The ol' rig runs better than ever! I'm sure all the other parts that I replaced helped as well.

Again, thanks to all for the ideas and suggestions. This is an excellent site with some very knowledgeable people. These computer controlled motors are sure more tricky than the naturally aspirated ones, that's for sure.

You guys are awesome! Thanks!

Phil

BTW... Mr. Flattire man, I tapped my FPR when it was cold just prior to starting. Not sure if it was the proper way, but it worked for me (for a short time of course!).

 

[88vert]

Glad to see you got her fixed