Hi all, im new here, i have been looking for a ford truck forum for awhile, found this one once, and couldnt find it again till now.
I have had this truck since 1999, before i bought it my dad owned it. It is a 1989 F-150 xlt lariat with 300 6cyl and 5 speed. Ever since i have had i have had a problem even with the old alternator.
When i am idleing my truck almost shuts off and the battery indicator goes down, lights dim but when i keep the rpms above 500 its ok. If i turn the AC or Defrost it will shut off. Sometimes when i put the clutch in to make a turn it will shut off unless i give it gas to keep the rpms up. I had this problem with my old alternator, I changed it in 00 but the problem has stayed around somewhat, lately though my battery has been getting harder and harder to start in the mornings and my trucks been shutting off more. I know its because tha battery is dying and i will probably have to get a new one but i am tired of the alternator problem. Why cant it make enough power to keep my truck running? Sometimes i can let it idle and the defrost wont shut it down but the battery gauge goes way down and if i put the clutch it will shut off. same with the AC. i have to turn either one off before i stop somewhere or make a turn or it will stall out.
I contacted Advance to see if i can exchange my alternator but they havent gotten back to me yet. Is that the problem? I had the same prob with the factory one. Could the alternator have killed my batter like that? i dont want to put a new one on just to have it fry in 3 years. And i want to be able to not worry about losing my power steering in the middle of a turn off. Sorry that this is so long. Any help is appreciated.

 

Sounds to me that if you need to "keep the rpms above 500", you have an idle speed problem. A very low idle can cause the alternator to not put out enough current so the lights dim, etc... I would try to look at the idle issue first, and that will probably fix the charging issue.

 

Thanks for the reply. How can i set the idle rpm and what should i set it to? i've havent done much work on this truck other than change plugs, filters and oil. Will i have to have a shop do it? I would rather do it myself if possible.

 

I had the same problem with my 1988 4.9. After doing about everything it turned out that the culprit was that six foot ground cable that goes from the negative side of the battery to the starter hold down bolt. That cable was small in diameter like a cheap set of jumper cables. I got a 18" #2 cable from Advance auto and bolted it down on the alternator bracket using a bolt tat holds the platform for the air bypass valve. I have not had any problems now for well over a year. It not only charges better, it cranks over faster and my radio don't loose it's memory every time I start it up. I hope this helps you out.

 

it really does sound like your alternator isn't spinning enough to recharge the battery. I forget the exact RPM range it has to be above, but if the alternator isn't turing enough it won't recharge the battery and will just drain it out. Try and crank up your idle screw on your throttle body. DON'T GO OVER 1000 RPM for idle. You can mess up motor mounts and it just has extra wear on the engine. Have it idle about 800-900. If that don't fix your problem i would check the ground cable to the starter like the above said. Hope this helps.

P.S. The charging problem is common with people who run underdrive pulleys on their vehicles. The pulleys actually make everything turn slower and the alternator don't turn enough to recharge the battery.



Matt

 

I'm pretty sure the '89 is fuel injected. Adjusting the "idle adjustment" screw won't do much as this is just used as a way to reference the voltage for idle. The throttle position sensor provides this voltage to the ECM. The output should be just under 1.0 VDC at idle (somewhere between .48 VDC and .98 VDC depending on which manual you read). The idle speed is commanded by the computer but will depend on the correct operation of the associated elements of the truck. For instance if the Idle Air Controller is not working correctly or its housing is contaminated the idle is affected. If the EGR is not functioning correctly you may be getting bypass exhaust at the wrong time and this too could effect the idle. Even a clogged air filter can reduce air input and lower engine idle. Start with the basics. Get everything clean and replace filters where necessary. Go to Auto Zone and have them read any Diagnostic Trouble Codes that may be in the ECM memory. If there are some repost here and we may be able to diagnose this further. Check all your vacuum lines for tight connections and that there are no leaks. Your alternator is probably working just fine but as stated above if you don't have more than about 500 RPM the current drop off through the voltage regulator is significant. If you still have the idle problem then start looking at the fuel system and its associated pressure regulators and sensors.

 

Thanks for all the replies guys,I just went out and took a quick look at everything and found something i somehow missed before, my negative battery cable is starting to brake right at the connector and there is another place on it that is cracked and i can see some green corosion. Would this be causeing my problem? I am going to try to find somewhere so i can read my trouble codes, i will also check filters and other things.Anyone ever change a battery cabel? is it very hard?

 

Changing a battery cable is one of the easiest things to do. If you have another vehicle, take the old one off and measure it so you're sure to get the right length (or even take it to the store with you). If not, at least try to get as close a measurement as possible. It wouldn't hurt to replace the old wire with a larger gauge one. While you're at it, check to make sure the positive cables aren't getting corroded as well. If a few bucks isn't an issue, I'd replace the positive ones anyway.

 

By all means, change the battery cable if it need it. However, this is not the cause of your stalling and low idle. There is no quick fix here. If you feel you do not have the ability to fix this, get it to a qualified shop for an estimate, but expect a heafty diagnostic fee to have them tell you the same thing that we posters have so far. Or roll up your sleeves and get to work on it yourself. All the recommended things are will within the abilities of an average person with a few regular tools. Keep us informed.

 

Keep in mind that the shorter the cable is and the larger the diameter is (wire gage), the less resistance you will have. My negative cable ran all the way from the battery to the starter, almost 6 feet! When first starting the truck in the morning it was dragging the voltage down to the point that my radio would loose the pre-set stations memory. I have not had any problems since I ran a short #2 cable to the alternator bracket. The problems I mentioned became worse with the air conditioning on because of the extra power draw, and I did have a problem with stalling when going slow around turns etc. It has not stalled since then either.

 

Well i changed the battery today, seemed to help a little, then i took off the negative battery cable. At advance they told me that i would have to get one from the ford dealership because of the connector that comes out of the side of the cable. I went down there and ordered it and it was 50 dollars! geeze that seemed high to me but i ordered it anyway. I thought normal battery cables were like 10 dollars. It really needed to be changed anyway so i will try to get that done and go from there.

 

50 DOLLARS!!!!!!!!!!!! That **** they told you about having to go to ford is bull****. I would cancel that order at ford and find one online or go to a different parts store. They are usually only 10-15 bucks.

 

Well after changing the battery and cable my truck is still doing the same thing, just not as bad probably because of the new battery giving off more power than the old one did. I am ready to start looking at other things i guess first off i will check the IAC. The problem is i dont know where it is on my truck. Is it just an electrical conector or what? Can someone give me a descrpition of where it is or a picture? It is fuel injected. I looked it up in my Haynes manual buts its not very detailed and gives no pics.First i will clean it or change it if its bad. Are they expensive?

 

The IAC is on top of the throttle body (roughly). Two screws hold it on. There is a small motor atached to it with a connector. Very easy to clean once its off. Just use some carb cleaner.

 

Hey guys i just wanted to thank you for all the replies and advice. After cleaning the idle air control valve the truck runs like new again. It was really nasty probably had never been cleaned before. Problem solved after all this time