I have a 1995 aerostar 4.0l w/ 147K.

Have installed rebuilt alternator 3 times in last 2 months. First sign of trouble was alt/battery light on dash. Battery is clean and contacts good. All wire connections appear good. battery is showing full charge. Replaced alt and it was bad within 15 min of driving van. Got an exchange and it lasted about 1.5 months. Got an exchange and now I have new problems same day as alt was replaced.

While doing the last install I decided to replace the plugs and wires since it involved pulling everything that was already off. It was Sunday so I want to the local parts store and bought plugs and wires. When checking my handbook to verify spark gap it stated .52-.56 and also said use only awsf 42 pp plugs. It says that the 1-3 cyl get awsf 42 pg and the 4-6 cyl get awsf 42 p and not to interchange. Nobody I talk to has a clue about this and 4 different parts stores said just install the ones I bought (bousch platinum regapped to .52).

With that done I was driving the van and noticed that when the a/c (front and rear) is on and I make a stop the rpm drops slightly and the voltage appears to drop to around 10v (gauge goes from 8-18 with no scale in between). If the a\c is turned off then the voltage rises to about 13+/-. Also, if I take the car out of gear or idle it up while in gear the voltage returns to an acceptable range. The interior light also dims slightly when a/c is switched on. To double check I took the car to a parts store and they tested it with one of the portable testers. They said battery is good and alt is good.

I pulled the blowers and cleaned them which gave a little improvement.

I checked the voltage at the battery which is reading as follows:

Eng off 12.65v
Eng running out of gear no a/c 14.28v
Eng running out of gear a/c and fan on high 14.28v
Eng running in gear a/c and fan on high 12.60v (slowly
descending about .01 every 30 sec or so)
Eng running in gear a/c on high, front fan low, rear fan off 14.08v


A few things I noticed while working on the car while in gear and a/c running is that after 10 seconds of idle the rpm drops slightly. Still running smooth(doesnt sound like it will stall). At this point if I rap the throttle mechanism I get a small knock(1 time). Rpm goes up, a little slack in the response. If I rap the throttle while the rpm is up no knock or slack in response.

At idle there is a slight shake in the engine. Enough to see and feel but cant really hear a miss. There is a slight rythmic surge but not as frequent as the rmp.

In addition to plugs and wires I replaced air filter, pcv valve, and after noticing idle problem cleaned MAF, and air bypass valve.

I am also wondering if this engine may be different than what the parts stores have in their computers. I noticed that the firing order of my 4.0l is different than 4.0l listed in my hayes repair manual.

I appreciate any help you can offer!

Thanks,

Jeff

 

It sounds as if the regulator is starting to fail. I do not really trust the machines at the parts store because thay take the reading at what seams to me to be a higher rpm than idle. Before geting a new alternator make sure all of the grounds are good. I had similar problams so I took some 6 gage battery cable and connected it to the frame then to the fire wall. I took an othe piece from the battery ground cable to the same spot on the fire wall the I ran a third one from the fire wall to one of the studs to the altinator bracket. This seemed to help a good bit in keeping the voltages more stable.

 

thanks for the response Bear. i may have to do as you suggested to solve my problem. I decided to let it ride for a short time to see if this alt is going to fail as the others did.

 

I had a 78 Gran Prix with a problem were the alt light would glow lightly and somtimes if you nailed it when it glowed bright the light would go out for a good while. Then one day in a snow storm out side of Buffalo it started glowing and not go out. It stalled just as getting off the interstate. I got a jump and hobbed to a gas station. The guy there was going to test the alt out put as it was running when he wiggled the connector and it started charging. This car had this problem dating back about 5 years when it was my fater in laws and had it changed about 3 times all because of a loose connector. So you may want to hook up a volt meter and wiggle some wires too.

 

I let you know if I find the problem. Thank you for the helpful info!
Jeff

 

The OEM plugs are platinum (single). With the opposite spark polarity of EDIS, the GND electrode is platinum on the plugs in one bank, and the center electrode is platinum on the plugs in the other bank. This is why they have different P/Ns (P vs PG). Replacement plugs will be double platinum, (PP), so it doesn't matter which bank they go in.
If you do a search, you will find Bosch plugs do not run well with Ford's EDIS.

 

Jeff, I'm having a similar problem. Sometimes the batt light is on (which I assume means the battery is not charging). Othertimes, the batt light is off, yet voltage will drop when there's a load (lights, a/c, etc).

Checking for a good ground seems a reasonable first step, so I'll try that tomorrow.

Is there a separate regulator (not part of the alternator)? If so, where is it?

Thanks,

Gary