I have a 96 aerostar which has had an irritating intermittent misfire for the last 18 months. I have had it into a number of shops and have replaced the fuel pump twice, spark plugs three times and wires once. Each time the problem goes away for a while even months. When I get a code it is always #4 cylendar. The problem is almost non existant unless you are going up hill and go into overdrive. It will do this on level ground also but going into overdrive seems to be the driving force which causes this. I have all Ford plugs and wires and any other parts we have replaced to try to correct this have been Ford parts.

 

What about the cap and rotor? Your problems sounds almost as difficult to find as my 92 that keeps cutting out for no known reason.

 

I failed to mention this is a 4 litre engine and in light of that it does not have a distributor it has a crank trigger. But thanks all thoughts are welcome before my wife drives it off a cliff.

 

Try covering the spark plug boots with heat resistant covers made for this application. With you mentioning it does this with going up a hill, possibly the added exhaust heat is causing the misfire. Also, make sure wires are snug at both connections, but the heat insulation plug wire boot covers are worth a try. (This solved completely a misfire / pinging problem on a friend's class c motorhome, when climbing hills). Ed

 

what code are you getting? P0304 or P0354?

may be fuel injector with particle in it. run a 20oz bottle of chevron Techron Concentrate or Gumout Regane FI cleaner thru 1/2 tank of gas, both contain high concentrations of amine chemical solvents that are one of the few cleaners that are efficient FI cleaners
may be defective injector or injector wire/plug/socket or PCM output for that injector. this requires a systems analyzer at shop unless one wants to throw parts until problem goes away. shop can put on wheel dyno and load engine until problem appears, expensive.

may have vacuum leak in intake manifold or plenum at cyl 4, test with FI or TB spray cleaner when missing. try tightening bolts on I. manifold and plenum.

run a compression and leakdown test on cyl #4, compare to #5, may be sticking valve or ring problem.

does plug #4 after 10k km look the same color as others?

B.C., any chance this is related to heavy rain/snow? #4 is wide open and exposed to large hole in inner fender driver's side

 

Today I went to a muffler shop to have the cataletic converter checked and found it is two thirds blocked. They will put in a pipe tomorrow and if it clears the problem I will order the jumper to bypass the rear sensor. They seem to think this may be the problem. Keeping my fingers crossed!

 

I am doing a process of elimination and hopefully something will work and do appreciate all suggestions and will try all possibilities one at a time. Of course at this rate may be broke soon.

 

People people people, the catayltic convert did not fail by itself. Ask yourself this question, why is it blocked? I will not tell you the answer. I will tell you, that simple installing a new converter, or bypassing it is not the solution. Also, removeing catalytic converters on vehicles inteneded for street use is illegal, and the shop can get fined $2500 per incident, regardless of where in the country they are located. If you have a rear O2 sensor, things get very complicated. If you have a rear O2, it in short, means the converter cannot operate without it. It is OBD-II. The computer is doing complex tests to determine catalyst efficiency. If the rear sensor does not cycle during operation, you are going to get a CEL. My suggestion, is find out what the problem is that caused your converter to fail, assuming that it really has. I have vehicles with over 400,000 miles with the original converters still operateing at over 90% of their original efficiency. They are designed to literally last forever.

 

cat plugging is caused by over rich fuel/air mix, causes ceramic substrate to melt and fuse or expand crack and buckle.
fix rich running problem first before putting in new cat or wasted money.
most shops will put in cat. jumper pipe to complete engine diagnosis and repair then new cat. goes in when engine exhaust will not destroy it.

 

We took out the cat and replaced it with strait pipe and put in jumper from the sensor. The cat was not plugged but split. I now have more power but still have misfire, van not running rich this was taken care of last winter during one of its episodes.

 

jumper must be a resistor to feed back false correct voltage to PCM to fool it into thinking air/fuel ratio is 14.7/1
wire jumper will cause PCM to stay in open loop rich condition

 

The jumper does fool the PCM into thinking the ratio is correct. It comes dierctly from Ford with the correct info.

 

Extensive idling to warm-up the engine will greatly shorten the life and performance of the cat. I laugh at neighbors who idle their cars 15-20 minutes in the morning, before they drive off are doing more harm than good. I can accept 5 minutes in cold, single digit, or zero degree winter conditions, then drive. But a modern FI engine will warm up with an ititial 5-10 second idle at start-up, then drive at slow speeds. An engine under load, in gear, will get the oils and coolant heated much better. Cats will last for a long time with this method too. I am NOT implying this to Coolrods, only a general observation on the topic of Aerostar catalytic converters... Ed

 

Well isn't that a surprise, bypassing the cat didn't fix anything. You have a bigger problem here. The cat may have even craked from thermal stress, which caused the padding to break down. Unless the cat got physically hit at some time. The missire is in either the ignition system, fuel delivery, or you have compression problems. Do some systematic troubleshooting to determine which. Run a cylinder balance test to isolate a cylinder. If you do not fix the problem, then damage to the engine will eventually occur.
The converter eliminater the guy installed is a diagnostic tool only. Leaveing them installed is illegal. I suggest you get a new mechanic, because the one you've got is as shady as they come. He has removed the converter for purposes other than replacement or troubleshooting, and he has installed a converter eliminater for purposes other than troubleshooting, but incur fines of up to $2500 per violation. He probably charged you close to what it would have cost to get the problem fixed. I said it once, and I will say it again. Catalytic converters are designed to last forever. If they fail, the car has a serious problem.