First time posting here so if I'm doing something wrong let me know. I have a 1999 Ford F150 4.2l with 256000 miles. I replaced the upper and lower intake manifold gaskets and all six fuel injectors this past week. I was having intermittent rough idling with slight coolant loss. Also had minor white exhaust with excess moisture at tailpipe. I was also getting a p0171 and p0302 codes. After installing the gaskets and injectors the truck now runs rough as if the timing is off. Hooked it up to my laptop and the short term fuel trims on both banks are at 32.8 with no change. Also the MAF is below 1 at idle. Checked vacuum at the manifold and is steady at 17 in/hg. Fuel preasure at the rail is a steady 33. Shouldn't the STFT's fluctuate as I drive. Any help would be appreciated.

 

It sounds like you cleared the codes and now are not getting any codes. Even though the vacuum is reasonable, going back to the last thing done, I wonder if you are getting a vac leak at an intake runner. Can you spray carb cleaner or something around the runners and see if you can get the miss to subside mementarily?

I expect you've already done it, but make sure you check all vac line connections, sensor connections and such that were effected by the manifold R&R.

BTW, your posting seems fine. Welcome and I hope we can offer some help.

 

Thanks for the reply, I really appreciate it. I'll take your advice and check for vacuum leaks at the runners. Thanks again.

 

Agreed its a vac leak. Its either you didnt clean the surface enough or scarred the soft aluminum or somethings warped and it wasnt ur fault. And they can be tricky to find cus they dont throw any clear codes. Best way is to break out a bottle of water and drip it around the intake. If you hear any change in rpm youv found it. Much safer then the starter fluid trick lol

 

Starter fluid? I suggested carb cleaner. WD40, or most anything would do it though. Anything to momentarily seal the leak long enough to hear it pick up speed for a few revolutions.

 

Your fuel trims should flucuate steadily.

 

Thanks for the input, really appreciate the help. Tracked the problem down to faulty fuel injector electrical connectors on cylinders 1 and 5. Had spark at the plug without the fuel injectors operating. I'm in the process of replacing them. A little tricky as I do not want to remove the upper manifold again. I replaced cylinder 1 but had to stop due to rain, no garage! I'll let you guys know how I made out. Thanks again.