QuestionDennis, thanks for your quick reply. I have replaced the distributor cap, rotor, spark plugs and plug wires since posting my question. The ignition module was replaced a few years ago with an aftermarket module when the car suddenly quit running and would not start. I have always assumed that an ignition module is either good or bad and would not cause intermittent problems. Is this an incorrect assumption? I have not checked fuel pressure since I do not have the test equipment. Is the test equipment readily avaiable and not too expensive? Is it possible to distinguish between fuel pressure and ignition module as potential causes of this problem. Thanks again for your helpful assistance.
-------------------------
Followup To
Question -
My 1985 Ford LTD Brougham (3.8L V6 with automatic transmission) has begun to misfire or stumble occasionally when cruising along the highway (it starts and idles great). The problem is very inconsistent as it may go several miles without an episode and then have several episodes within a short distance (some episodes are much more noticable than others and it feels as if the car is going to stop). I replaced the fuel filter, O2 sensor, and repaired a broken vacuum line to the EGR valve, but with no improvement. Spark plugs and wires are fairly new. The problem seems to be getting progressively worse. AutoZone was unable to recover any engine codes. Could the air pump (smog pump) contribute to these symptoms? It has begun to make considerable noise recently, but I did not want to replace until the misfiring problem was resolved. Can the air pump be eliminated? Thanks for any suggestions you can offer.
Answer -
Occasional or intermittent problems are the hardest to diagnose in most cases. The smog pumps in those days were noisey to begin with, and that won't cause the symptoms you are describing.
I would like to know if the ignition module is original, aftermarket, or has been on there awhile. And the distributor stator, although a problem in either one of those will set a code. If you pull the cap off the distributor and the stator inside is black, that needs to be replaced.
How about fuel pressure?. Is the distributor cap and rotor ok, no signs of arcing?
AnswerDo you know if autozone got a code 11, or none at all? 11 indicates a PASS.
The aftermarket modules have been a problem for some time. Your assumption about them is most likely the right one, but I have seen the modules cause other problems in timing and shutting off intermittently. Especially aftermarket parts. Did you inspect the part inside the ditributor as I suggested? Those can also cause problems.
Here is a website related to the TFI modules. It may not help you if you are over 100,000 miles on the vehicle, but you may find it interesting reading.
http://www.tfisettlement.com/faq.html
My recommendation at this point is to replace the module with a Motorcraft part, and the stator if it is black. You can search for Motorcraft parts online, or get them at a dealer or local parts supplier. I have heard from others that NAPA modules are Motorcraft repackaged, but haven't verified this myself.
Some auto parts or rental centers offer tools for rent. Whether they have a fuel pressure guage is something you will have to check out in your area.
