First, Hello All--I've been away for awhile, yet here I am again, hat in hand, with a question. (Some people have no shame....)

My '88 F-150 has the truly wonderful 4.9--at 170,000 miles, it barely uses oil and has excellent power. However, it's also got the Ford gas gauge sending unit blues, so...no working gauges. Consequently, even though I watch the mileage on the tripometer, once in a while I screw up and run out of gas. Switching is always a hassle if I run out first, but extended cranking will get her switched to the full tank. If I switch tanks while underway, it seems to switch fine but I suspect it the actual transfer is somewhat delayed--I know it switches sluggishly.

Now, this truck has run perfectly for the 3+ years I've owned it, having rescued it from a hard life of landscaping. Like a retired greyhound, it is gray, has had a lot of owners and was run hard and put away wet. The only thing it has needed is normal TLC and an EGR valve, which I found by pulling codes and talking to you all. I keep this truck tuned, and recently replaced cap, rotor and plugs. Wires were done a year ago, but are FoMoCo OEM wires, and I've put less than 10,000 miles on these wires. I do O/F every 3,000, but did run the previous fuel filter 3+ years, as the truck gets few miles and I'm lazy. In fact, last year, it sat for weeks at a time, for 8 months, doing a few 6 hour trips and biweekly short trips, especially in the winter (I know, bad deal, but I was stranded on an Island and only got into town by quad or sled, over the ice and just used truck to get groceries/supplies).

The Problem:
Last week, I may have run out of gas, as I was low, but it acted slightly differently than the few other times I've run out of gas. Instead of cranking strongly without firing at all (or very little) on the restart, this time the engine would fire up quickly, but run at a "sub idle." Alternatively, it would run at a normal idle, then the tach would do that sickening, delayed drop that says "I'm not really running anymore," usually right after I hit the gas. This makes me think it was running way lean, and "lean spiking" as soon as I tried to accelerate. Interspersed in all this was a disturbing amount of backfiring/popping, something it's never done.

I switched tanks, to no avail. However, unlike when I have run out of gas previously, this time, it would restart yet run terribly. With many restarts I managed to limp into a gas station.

I filled both tanks. No joy. It would still fire almost immediately (unlike the normal scenario when I've run it out of gas) and do one of two things;
1) either run below normal idle speed (which it's never done before) while running roughly, or
2) idle at a normal speed, but then, when I attempted to put a load on by engaging the clutch, it would die so quickly that if I hadn't seen the tach drop, I wouldn't have known it. Just *poof!*, before I could even start loading it with the clutch.

I Suspect a Fuel Blockage
After sitting, starting, running, etc..., I found I could keep it running, somewhat raggedly (and it's usually very smooth) for 15 min. in the gas station, but only above 2,000 rpm. Then I noticed the temp. gauge climbing to the mid range--it never does this. From this I deduced the engine was running very leanly. I believe that this is why it would run at 2,000 - 2,500, but die as soon as I tried to engage the clutch, or shortly thereafter, when I had gone a few feet. It was too lean to fire under any load.

During the above, with full tanks, it was also popping and backfiring, something else it has never done.

I Replaced Fuel Filter--Problem Continues....
Yeah, so I had one card to play--I replaced the factory, inline fuel filter, up inside the frame rail. It immediately started and, unlike before, didn't stumble when I fed it gas above an idle. I let it run 20-25 min., idling, while helping the neighbor. I even moved it around the yard--no problem. I prematurely congratulated myself on (again) getting away with murder, i.e., running an EFI-equipped vehicle out of gas, so that all the crud in the bottom of the tank can clog the filter.

Then, a day or so later, I went to start the truck. Instead of immediately firing up and staying running, as is normal, it fired and died, repeatedly, exactly as it had before, when I had run out of gas, and even afterwards, after I filled up. It took several such attempts before I got it to stay running, and even then, for a few minutes, I got the popping/backfiring I had earlier. It also seemed to be running on less than all cylinders for a minute or two, at least at certain rpms. I ran it 5 minutes and shut down. During this 5 min., it smoothed out, but I still felt it was stumbling a little as I fed it gas off of idle.

Later that day, I restarted (engine now cold) and it started right up and didn't stumble off idle, as it had been, but I suspect this was due to the enriched start cycle, and didn't mean it would run without this (new) off idle stumble. I did not warm it up to check this out.

The muffler parted company with the truck last fall and it's so quiet with just the cat. conv. that I haven't felt like getting it repaired yet, as I am unemployed (well, working for free, to be more precise).

So, I can't figure out where to begin, as my buddy has my cheap code puller and excellent, factory shop manuals upstate, hours from me.

Can anyone suggest any things I can check? Got any theories?

I already added some STP E.F.I. cleaner to the tank I'm on, after I filled up on the day it all started. I should add that it ran okay after it finally got it's head cleared, that day I ran out of gas, and it was not until the next day when I drove it that it exhibited the same stalling as before, when I thought I had run out of gas. It was after this second day of poor running that I changed the fuel filter. I now am not sure I ran out of gas at all on Day One---it may just have been this problem, whatever it is, striking.

When I opened the lines to change the filter, the fuel seemed to flow freely out of the lines.

Is there any point to unscrewing that chamber under what I suspect is the fuel switching valve, the one that looks like it should contain a second filter, but doen't? I did it 3 years ago, when I changed the filter, and there was some grit in there, in the bottom of the plastic cup which unscrews, which I cleaned out.

The fact that full tanks and an new filter haven't eliminated the problem makes me suspect either the pump in the tank I'm on, or the high pressure pump (on the frame?) is bad/partially blocked.

 

Sorry the first post was so long--used to be a Ford Service Writer--the techs always wanted more info, not less....

Took truck out for 2 mile drive and switched tanks--no joy. It stalled once upon starting, backfired too much and definitely was down on power. It didn't stumble when I floored it, like a carbureted engine would, if it were too lean--it just didn't accelerate like it normally would have. Usually, if you stab the gas, it jumps, and it will definitely spin a tire around a corner, normally in first gear. Not today.... In the two mile drive, I probably restarted 6-8 times.

However, it didn't run on less than six cylinders, unlike before I changed the fuel filter, when it would sometimes misfire for seconds at a time, revving up slowly until they all fired properly. Today, no misfiring, just the stalling, backfiring and p-o-o-r power.

It stalls at lights, but restarts. It doesn't seem to stall under acceleration, unlike before I changed the filter. It also does, intermittently, that "sub idle" thing, where it idles below it's normal 700-800 rpm, and the tach seems to drop slightly and "go dead" but the engine is still running, but slower than an idle, and usually roughly. Rev it up over a normal idle speed and the tach works normally.

The (high pressure?) fuel pump you normally hear when turning key to on, before cranking, is cycling as it normally does--zzzhuuuummm--click! Off!. Nothing different there.

I also seem (could be imagination) to notice a smell of burned gas, but not necessarily like it's too rich...just...different. (That's helpful, isn't it?)

This truck consistently gets 15-16 mpg, sometimes a little higher. It passes it's emissions tests w/o bribery as well, although the last time was a year ago.

My fear is there is an obstruction downstream, i.e., between the fuel filter and the engine.... Or in front of, or inside, each injector.... Is there something I can open on the engine to check for crud? Please don't say take out the injectors as they appear to be fused, by rust, into the head.

I will also cut the old fuel filter up to see how much crap is in there. ? (Btw, I put the filter in just like the last one, per the arrow, i.e., rounded end toward the tailgate.)

Theory: The rear tank, which I was on when I (may have) ran out of gas, has sucked up so much crap into the in tank fuel pickup that it cannot produce enough flow to "shunt" the fuel tank switch block over to the front tank, despite the fact that I've switched it. Other than physically switching the lines at the switch block (done that previously when it wouldn't switch when I had run out of gas) how can I verify which tank is feeding engine?

What is my first move, beyond dropping that empty, plastic cannister under the fuel switching block, in the gas line, and seeing how much crud is in there?


Help!

Thanks,

Peter, a.k.a. BigSix1, formerly BigSix

 

possible that its out of time ?

 

Sounds like the Fuel pressure regulator might be bad and is leaking by thru the vacuum line. Pull the line off and check for WETNESS! If wet get a new regulator.

Also check all of your vacuum lines and the "COFFEE CAN".

Larry

 

Larry:

Oh man, a ray of hope. I'm practicing my "U the Man!"s, in case this is it, but tell me, where is the fuel pressure regulator? I don't have my shop manuals here.

I will also check all the vacuum lines and coffee can. I presume I should see full vaccuum (approx. 15-17 lb? It's been a while...) in the line heading into the can? I also have a hand-operated vacuum pump if you've got any nifty little diagnostics I can perform.

Thanks for caring.

Peter

 

Peter: The Regulator is inside the "CAGE", that the Intake manifold makes(at least i call it the CAge!) It's a cylinder about 1" tall with a vacuum hose coming out one end and the fuel rail on the other.

It's outboard of the fuel injectors under the #2 intake runner.

As for the coffee can you can use the hand pump (oh that brings up a myriad of images!) to make vacuum. There is a check valve on the intake side. Plug off the accessory side (follow both lines from the can and mark) and use the pump to pull a vacuum. If it holds for a couple minutes yer ok.

As far as engine vacuum I'd look for 15 and hope for 17. with the amount of emissions stuff anymore it's a wonder most engines make 15. (Oh for the days of '54 studebaker Inline 6's making 23" on all six at 1000 rpm and sounding like a concrete mixer truck full of rocks.)

Larry

 

Larry:

U the man! Okay, this might be somewhat premature, in that I didn't actually figure out what it was, but it is now running normally!

Found Fuel Pressure Regulator
When I started it, it simply fired quickly and died a couple of times, then misfired for about 10 seconds at a couple grand, on like 4 cyl., then cleared out but ran crappily, in driveway. I shut down and followed your excellent instructions. I found the fuel pressure regulator under the #2 intake runner, right where you said it was--thanks! (Isn't it nice that the runners are actually numbered?). It is held in by small allen head bolts, right? I unhooked it's vacuum connector, and no wetness. Felt like decent vacuum on the connector. I rehooked it.

Got Great Vacuum!
Then I checked my vacuum, by pulling a red vacuum hose off of the multiport fitting on top of the manifold. 19.5-19.75 in., at approx. 950/1,000 rpm! I'm thinkin' that's very good. The idle jumped up a couple hundred with vacuum line off, pf course, and was somewhat high and erratic with vacuum diverted to gauge.

Then, I started it and ran it a couple of minutes with that red vacuum line off, shut down and reconnected this line as well.

Upon restart, I noticed it was running better. I went for a drive and the power felt normal. Just to prove it to myself, I lit 'em up around a few corners...and then a few more. I feel bad, in that I never beat this truck, I just run it fast and often heavily loaded. But today I got a little crazy, yet it ran great.

The backfiring that had been occurruing is gone. There's the same slightly erratic rumbling on decel that I've noticed ever since I left the muffler and tailpipe in another city, months ago, but none of that loud popping it only did during this episode. A lean mix can make it backfire, right?

My Theory Seems More Likely Now (to me)
When I ran it out of gas, I bet my luck also ran out, and the pump in the tank I was on got it's pickup patially blocked. As the truck has always switched tanks sluggishly, given the week fuel pressure out of the tank whose pickup inhaled the (presumed) crud, it was unable to switch tanks. Then either coincidentally or because of running it with the vacuum line open, briefly, the tank switch finally switched, and now it runs good on the second tank, only. (These trucks do switch tanks using fuel pressure only, rather than a electromechincal solenoid, correct? Does this mean the pumps are switched on and off via the dash switch, and they have to "shunt the fuel switch valve" via pressure along?)

If you think the above is the most likely explanation, how can I attempt to verify it, so I don't get stranded should it happen again? I don't have a fuel pressure gauge, but I saw the Shrader valve on the fuel rail, I believe--is it worth checking pressure, then switching tanks, and if it runs crappy again, rechecking the rail pressure?

Any Other Ideas?
But if I'm all wet in my theory, what other ideas do you have to check? I have not yet checked the "can" and done a general inspection for cracked lines, but I had one once, on the EGR, and know they're hard to find.

Also, only in the months since I lost the muffler did I notice that there's a slight stumble off idle (like a minor case of a carburetor with a failing accel pump) but it might have been there and I never heard it when muffled. Anyway, it's right back to being the same slight stumble I've come to consider normal. Does this tell you anything additional? As I said, ingnition parts recently replaced.

Are you aware whether a cheap, generic, older code puller (like mine) will pull a code re: my theory, i.e., that a blocked fuel tank pickup caused reduced fuel pressure. How many drive cycles does it take to wipe that history once it's running normally?

Proposed Test--Manual Tank Switchover?
As a test, I could also switch all four fuel lines at the switchblock and see how it runs. If I do that, do I have to throw the electric tank selector to the opposite tank to power the (suspected) clogged tank pump, or are both tanks pumps running all the time, and simply cycling the overpressure back into each tank individually, all the time even the one you're not sucking on?

OH! I have never known where the PVC was, due to that "CAGE" as you so aptly put it. I had half talked myself into believing that the foam breather sponge in the airbox was all it had for PCV. Now I know it's right where it belongs, at the top rear of the valve cover (on the 4.9). I will replace this, b/c I've never done it in 3 yrs. (Ouch! I know) but does this do anything for you? It looked clean as the engine is clean generally, but obviously it could be totally gummed up inside.

Anyway, thank you so much, again. You're really takin' me to school and it's great!

Peter

 

All:

I am lucky enough to know a Ford tech, actually the Foreman at his dealership, now, who has generously agreed to take on my drivability problem.

He has confirmed my suspicions that the tank switching valve is bad, in that it is dribbling (intermittently, no less!) the return or bypass fuel into the opposite tank from which it was drawn from. While this in and of itself is not proof that the bad tank valve is the cause of my problems, he notes that "bad tank valves did cause driveability problems back in the day."

Essentially, we feel that the bad tank valve is basically a diagnostic roadblock, at this point, and must be replaced. He freely admits "it may not solve a thing," but it's a likely enough candidate to be at least part of the problem, that it's got to go.

I'm reprinting today's update to this ongoing thread you are reading now (i.e., "Help! Fuel Flow Problem?") in a new thread entitled "Need Recall Info on Older Trucks" in case anyone is interested in following this saga. I felt the need for a new post as I need high visibility, sooner rather than later, to see if possibly there could be a Recall to pay for a new tank valve, prior to me laying out the money for same.

My friend/tech states that there are two possibilities here, for Recall funding for my parts, so

My Recall Questions Are:

1) Trucks in my genre ('88 F-150, 4.9) were subject to a recall on the tank vavles, for bypassing fuel into the wrong tanks. Does anyone have a link or other way to access this recall info?

2) These same trucks also had a "recall kit for restrictors in the fuel return lines" which helped maintain adequate fuel pressure. He also stated (I believe) that a new Fuel Pressure Regulator was included in this kit. Again, need info on both these recalls.

3) Is there not a Recall Section on this site, where I could simply plug in my VIN and see everything?

4) Is there an offsite location where I can search all my Recalls? I bought the Popular Mechanics/AllData software, SOLD TO ME BY MY LOCAL DOWNSTATE AUTOZONE, AFTER ALLDATA, Inc. QUIT SUPPORTING IT, (!) and they listed a recall database.

5) Would anyone would has current All Data software be willing to look up my recalls, based on my VIN? If so, could I PM you my VIN, so it doesn't turn up as being used in a crime somewhere? (My odds of giving my VIN to a psycho are at least greatly reduced this way, as opposed to posting it on the Web).

Btw, my fuel pressure tested good, like 47 lbs., I believe, in the rail. Not sure exactly what the numbers were, but they satisfied him. I know his work, personally, to be excellent. When I was an advisor there, and the previous Foreman had heavy diagnostic problems (you know, Continentals w/ phantom electronic/dashboard glitches, etc...) my friend got the car, the computer education bay, and no body talked to him for a half day at a time. He got it done, too. He is also a prince, ethically-speaking. (Just counting my blessings out loud, here).

As I say, I'll continue this post under a new one entitled "Need Recall Info on Older Trucks"

Thanks for all y'all's continued help.

Peter