Need some help. I replaced the intake gasket on my 1998 f150 5.4l yesterday. I took my time, made sure everything was cleaned and hoses and wires got placed back were they originally went. I also replaced the throttle position sensor. However, the truck seems to run rough intermittenly. It seems to run rough or vibrate a little more when I am between 1000-2000 rpm's. It has not thrown any DTC's. Do any of you have any suggestions? Thanks for the help in advance. The gasket was leaking badly but now it seems as though I did more harm than good.

 

Try disconnecting the battery for a few minutes if you havent already...may help.

 

Disconnecting the battery will not help. All that does is reset the computer (again!) which would put you back to square one for troubleshooting.

Most likely, you have one of the following problems: Intermittent vacuum leak or intermittent misfire.

You really need a scanner capable of looking at Mode 6 real time data to effectively diagnose the issue. In the absence of the necessary scanner, you will need to run through several normal drive cycles to see if you can get the PCM to set a diagnostic code. If a code is posted, then it will point you in the correct direction.

If your symptom is most pronounced at the point just after the transmission shifts in OD, light-moderate throttle, light-moderate load, then it's most likely a low-grade misfire. These are usually caused by a weak coil, bad spring/insulator, moisture in a plug well, or by a failing park plug. Mode 6 data is indispensable for diagnosing this type of fault as the PCM often doesn't set a fault code because the symptom isn't severe enough.

 

Thanks for the reply, I have a small altel scanner which i can read real time data but I am not quite sure what to look for. I have access to a pegisys scanner, will that help me read mode six? I sprayed around a few vacuum lines but could not find any changes in rpms. I also disconnected the coil packs to try and check for no changes to rpm's, but all modified the engine once disconnected. I do think, that it is an inermitten issue, because at some rpm's it seems to run fine. Thanks again. You guys are a big help.

 

So today at work I was able to unplug each coil and see if a difference in rpm's was found. The number seven coil pack made no engine change so I swapped it with the number one to check and see if I would have the same issues. Why I do not know, but the rough running(presumed misfire) stopped. I drove it home from work with no issues. Any ideas from the experts? I guess that I should look into replaced the oem coil packs sometime in the near future. Just hate the cost.

 

Intermittent misfire cause by broken clips on injectors and COPs are fairly common.

 

If you want to replace all the coils, these are OEM quality:

http://www.ebay.com/itm/FORD-E150-F150-VISTEON-IGNITION-COILS-DG508-ALL-8-BRAND-NEW-/181091202637?pt=Motors_Car_Truck_Parts_Accessories&hash=item2a29e0764d&vxp=mtr