at wits end, wondering if this truck is even fixable
 

Ok, so if everyone needs a good outhouse reading, then here it is.

First the history. 1988 F150, 2 wheel drive, 4.9L EFI. Heres what was replaced. New starter, new battery, new distributor, new valve cover gasket, new intake and plentum gaskets, new plugs and wires, and oil change. The truck was running strong and smooth, then it was parked for a little over four years. I obtained the truck from a family member and towed it back to my house where i replaced the battery, drained the old gas out of the working front tank, replaced the fuel filter and tried to start the truck. Amazingly it started and ran as smooth as it did four years ago. Filled it up with trash for a dump run and went out the next day to find that my new old truck didn't start. Finally get it started but it idled rough and would run for longer than 20 seconds.

The low pressure fuel pump in the front tank was the culprit. Replaced it and the engine starts and runs, but rough idle and white smoke coming out of the tailpipe. Now heres what i've replaced recently to diagnose the problem.

New injector O rings to cure a small fuel leak.
New plentum gasket due to O ring fix
New MAP sensor
Checked vacuum lines, all seem to be clear and correctly ran although there is a question as to where the proper place to run the trans off of.
New temp switch
New T-stat
New ECT
Checked oil and it's clean
Checked antifreeze and it's clean
Checked fuel pressure and it's good
Checked compression and it's good

Now i'm at the end of my general knowledge and still do not have a running truck. Any ideas or insight would be greatly appreciated. other than the rough idle, and the white smoke, it sometimes will randomly surge up and down at idle, cut off due to the surge, and when you raise and maintain higher rpms, it seems to spit and sputter from time to time.

Also i cleaned out the gas tank and ran five gallons of fresh gas with half a bottle of seafoam in it, the exhaust doesn't smell sweet, it smells a bit rich, but it's not black or blue.

I've had numerous f150's all with the 5.0l. This is my first 4.9l and i'm starting to hate it already. Any help with this would be greatly appreciated.

Take heart, the 300 is a lot better working truck engine than the 302. I have had several of each.

White smoke sounds to me like water is getting into the combustion chamber, but it may be condensation in the exhaust from siiting for years.

The running rough at idle may be the EGR valve sticking or the control circuit opening it to early.

Have you pulled codes from the computer? I had an 88 that drove me crazy trying to fix it, I finally decided that the whole wiring harness was shot because one time it would run fine, the next time it would run like crap, with constatnly changing codes.

Good Luck,

Robert

pulling codes today, i'll post them as soon as i get them.

ok pulled the codes this morning and i got 51 and 33
51-ECT sensor signal is greater than self test maximum of 4.6v
33-EGR valve opening no detected

so does this mean the new ECT is bad and that i need to replace the egr valve as well, or could the EGR be a vacuum related problem?

side note, is there a way to test either of these?

ok replaced the ETC again with a new one. Engine light went off, and it seems to run a bit better. Now the idle surge is intermittent but still there. Have to order an EGR valve. Wh is it still giving me the same codes though? 51 and 33.

You could look around this site
Fuel Injection Technical Library » EGR Vacuum Regulator (EVR)
Fuel Injection Technical Library » Engine Coolant Temperature Sensor (ECT)
Fuel Injection Technical Library » EGR Valve Position sensor (EVP)
A Haynes manual has a few tests described...also look at the menu on the right side of the page at this link site...you should also clear the computer of the settings for the old sensors...remove battery neg for 20 mins or so

ok some fresh new insights. Checked timeing and it was at 18 tdc, set it back to the factory 10. Seems to run better still, but continues to have the idle surge. When raising rpms it runs smooth until you step on the throttle. It revs up just fine but seems to stumble if you step on the gas when rpms are dropping. Also the white smoke has slowly become more blue ish so im assuming fuel? Could it be the regulator? the high pressure pump is working fine, low pressure intank pump is brand new, and so is the filter. Relays seem to be working properly. Could this still be an EGR issue?

did the check for the EGR vacuum regulator, when unplugged there is no vacuum present at the EGR valve, when plugged in and running, then grounding it out to open it there is still no vacuum at the egr. Does this mean it's not working properly?

vacuum reg is probably bad,

will pick one up tomorrow, i'll post any changes once it's on.

Blue smoke is OIL
Black smoke is FUEL

so updating the situation. Still have not picked up a regulator/solenoid for the egr valve, Definitely smoke with a blueish tint to it, i'm assuming at this point since the truck sat for four years that it's probably something like the valve seals. Other than that i traced and replaced all vaccuum line, finding that they were backwards at the vac res. Trucks seems to start fine, and idle fine now, but at idle the engine shakes bad, shakes the whole dang truck as a matter of fact. I'm wondering if this could be motor mount, timing, or still a possible egr problem. Thanks in advanced for all the help guys, you have saved me time and money thus far, just hate to think i'm so close to fixing this thing to just give up on it now.

I recommend you get some insulated spark plug wire plyers (they are cheap) and pull one wire at a time from your distributor cap and see whice one or ones to not make a change in your idle. That would be the cylinder(s) that are missing at idle.

The 300 is normally a very smooth idling engine.

It seems to be idling smooth, just the engine shakes back and forth, when it revs up there's no hesitation and it has plenty of power so I doubt if its a miss. Ill try anyways though, thanks for the suggestion.