Peachtree

Hi, I can drive this truck with the 5.4 l all day with no issues. If I have the truck in park, running with the ac on for around 20 minutes on a hot day, when I put it in drive and accelerate I'll have diminished power. If I ease up on the accelerator it'll pick up speed a little, but depress accelerator a little more, it bogs down again. It will continue to perform that way until I park it for maybe an hour it cools down then runs fine unless I get into stop and go traffic, it'll do the same thing all over again. Thought it was torque converter shudder, flushed transmission, thought it was plugs, ignition coils, so I swapped out with quality parts. No check engine light, but my mechanic checked catalytic converter temperatures on all four in and out. Looked good. I am consuming oil, maybe quart every 1000 miles. 150 k miles on a 1998 ford f150 2wd 5.4l auto. Need help. Thanks

mapleleaf1773

Maybe do a coolant flush, that will help with fluctuating temps. iinside the engine If it's been awhile since changed last.

Does your temp. Guage go up at all? If so, maybe replace thermostat as well.

Peachtree

No, the engine temp does not seem to fluctuate at all.

mapleleaf1773

Check your alternator maybe

white89gt

Have you checked the fuel pressure? Do you have a CEL illuminated?

Do you happen to have a K&N filter, or an oiled filter?

EDIT: Also, please tell us what the "quality parts" were that you purchased (brand).

Peachtree

I'll do that, thanks. But because it occurs in the heat, ac on,in park, or bumper to bumper traffic hot day, I think it could be related to a catalytic converter becoming blocked, or a sensor , fuel air, or oxygen going out without the CELL on

Peachtree

I'll check on the brand names and get back to you. No check engine light and no haven't checked fuel pressure. I know I'd have to check when the condition is occurring. Hard to duplicate the condition and then check pressure conviently. Thanks

white89gt

I said nothing about a sensor or catalytic converter. Or are you responding to someone else?

You most likely have a fuel related issue. Fuel pressure WILL NOT illuminate the CEL on these trucks. It is not monitored by the PCM. You technically could get a lean code, but not usually. You need to be around 39 psi at idle, with the vacuum removed/capped from the FPR.

My bet is a weak fuel pump.

Peachtree

Thanks. Fuel pump is something I haven't thought about. Based on your supporting info, it could be it. The sensors and catalytic was in response to a different reply

Hammer Mechanic

I was towing a small UHAUL once from Tampa. It was 400 miles to where I was going. About 50 miles into it my truck started bucking like you described. It would come and go. No CEL. I kept driving and the problem kept coming and going, Finally, about 200 miles into the drive I got the check engine light. I kept driving and made it to my destination but I went through some serious gas to get there. I put a code reader on it and said my downstream O2 sensor was bad. Changed it and never had the issue again. You could possibly have that issue. JBREW warned me that these O2 sensors sometimes go bad and it takes awhile for a CEL to show up.