I have a 99- F 150 5.4 with 61000 miles. About 3000 miles ago, I replaced the fuel filter, coil packs and plugs because of a sputtering under acceleration. It ran great, but now it's starting again. It runs fine when cold(what passes for cold in Miami), but as it warms, it sputters, especially when accelerating. If I let off, it smoothes out, but continues when accelerating. The problem is mainly intermittent, but the longer I drive, the worse it gets. I've been fooled by brand new bad parts before, but if this were a normal, sensible vehicle (carb and distributor), I'd tear apart the carb. I've had suggestions of re-replace the coil packs to replace the MAS and injectors. It's against my nature to go to a garage unless I'm dying, so I want to do it myself. Any iideas? Thanks

I am not a tech at all. Have you checked to see if there are any DTC (diagnostic trouble codes) stored in the computer?

If you do not have a scanner, most auto zone parts stores will scan for free. Just don't let them sell you a bunch of non-needed parts. Write down the codes and report back with the numbers.

Hopefully, one of the techs will be along soon to help.

Welcome aboard! There are a lot of good guys and gals around here. There are several ford techs on board too.

sounds like a mass airflow sensor issue. do you have a k&n filter by chance?

fuel or ignition

Yes, I have a K&N filter. A friend who used to work for Ford said that the MAS was suspect after 60000 miles (I have 61000). I have had my engine check light on since my son drove it to New Mexico and came back with a better exhaust system. It breathes a lot better. The truck is relatively cherry, KYB shocks, heavy sway bars, free flow exhaust with Flowmasters, 9" rims and sticky tires. I like the engines torque and I'm trying to leave it alone until I finish 2 other cars and build a house in north Florida. The truck wants to be a convertable when it grows up. The steering is slow too- I used to do club events (slaloms) with a TR-6 and I expect the truck to handle better. Prior to this, the biggest problem I had was everybody thinks it's a work truck and they want to borrow it and haul heavy stuff that'll damage their vehicle.

theviking said:

Yes, I have a K&N filter. A friend who used to work for Ford said that the MAS was suspect after 60000 miles (I have 61000). I have had my engine check light on since my son drove it to New Mexico and came back with a better exhaust system. It breathes a lot better. The truck is relatively cherry, KYB shocks, heavy sway bars, free flow exhaust with Flowmasters, 9" rims and sticky tires. I like the engines torque and I'm trying to leave it alone until I finish 2 other cars and build a house in north Florida. The truck wants to be a convertable when it grows up. The steering is slow too- I used to do club events (slaloms) with a TR-6 and I expect the truck to handle better. Prior to this, the biggest problem I had was everybody thinks it's a work truck and they want to borrow it and haul heavy stuff that'll damage their vehicle.

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Remember, the MAF measures the amount of air going into your engine. The calibrations are set for a certain amount of air flow. The oxygen sensors measure the amount of oxygen in the exhaust flow. Adjustments are made from there. Any changes in the air flow going in, and adjustments/measurements are off.

you might keep in mind the iat sensor as well.