My 85 f150 has an inline 6 motor in it and it runs well when actually driving, but the idle pulses really badly. It goes from running fine to almost dying during the idle. Other than this it runs well. Any suggestions?

 

I'm guessing you still have the feed back carburetor? I'm betting that's at least part of the problem.

I'd start with some basic diagnosis: Check compression numbers first. Low compression in one or more cylinders can cause that symptom, as can many other things.

My '85 with the same engine ran like crap when I got it. Got rid of the air pump, the computer and all the associated solenoids and wiring. Replaced the feed back carburetor with a standard Carter YFA. Replaced the distributor with a DUI Ignition. Converted the EVAP and EGR to old-school vacuum control (no computer). Runs and idles like a champ.

 

I would pull the codes first thing (assuming this is still a computer-controlled carb & ignition).

 

Okay that makes sense. I know i need a new valve cover gasket on it (Which i'm not going to get fixed before the winter) I would assume that would help some with compression issues?

 

Replacing the valve cover gasket will certainly help with oil leakage, but will have no effect on engine compression. Do what ctubutis suggested.


If for some reason you cannot find someone to do this, the computer system can be checked by way of counting flashing lights [test lamp]. The internet can explain how.


This beloved [by me] six cylinder engine absolutely hates vacuum leaks, which cause all sorts of running issues. Your truck is 30 years old, so all vacuum lines are suspect. Originally, yours had numerous plastic vacuum lines, which dry out and have hairline cracks. It is best to replace these with the appropriately sized rubber vacuum hose. Also, the carburetor is held down by two bolts and routinely vibrates loose. Remove the air filter housing and snug down [not too tight!] the nuts [1/2 inch]. There are 4 screws located on the bottom of the carburetor, holding the top and bottom together. See if the top part wiggles? If so, the carburetor will have to be removed and turned upside down to reach these screws.


With the engine running [idling], spraying carburetor cleaner along the intake manifold [next to the engine block] and any other suspected leakage prone area will cause a change in idle speed, if a vacuum leak is found.

 

timstheman5,


Here is a link which ctubutis provided for me. It explains how to check any stored codes which are stored in your truck's computer.


Ford Ranger - Testing EEC-IV Equipped Engines

 

Thank you so much, Ill do all of that. It very well could be a loose carb being part of the problem, I did recently replace all the main gaskets in it. And for sure vacuum lines are suspect. Thanks again guys!