My '89 F15 has the 300 6. When you crank it up,sometimes it wants to die from lack of power,If you floor it,it might continue running. And each time it does this,the volt gauge jumps back. Or if you turn something on,it'll go back. Heres a pic with EVERYTHING on at idle.

And here it is with only the engine running at idle. Sometimes its a little higher,depends on the RPMs.

I had autozone,Oriellys and a starter/Alternator/Battery place test it and they tested it from the battery. They all say its fine. If it was fine,it would'nt do this. Could the voltage regulator be giving out or something else? Any help is appreciated. Thanks guys. It died in the driveway and almost did'nt crank back up.

 

You can't put alot of trust into the gauge. If several places are telling you that your Alt, starter and battery are ok then I would tend to beleive them, they are in the business of selling you parts and by telling you that you don't need anything isn't making them any money. On the plus side you know you have honest places there!

If you are concerned about your gauge reading then clean your grounds, there are several. The battery cables ground at the block & frame, theres a body ground right by the battery. Theres a few other grounds that need cleaning too, such as the pcm, ecm. I think the TFI grounds thru your distributor on that year. I'm not sure if there is a cluster ground under the dash. If you really want to get into it then take off the starter clean the starter & block surfaces. Repeat for the Alt. (Both these high current items ground thru their mounts to the block) Also, clean and check your battery cables, replace them if you see any corrosion.

Your rough starting sounds like a different problem. An engine running, or trying to, isn't drawing alot of juice from the battery or alternator. Because you have to "floor it" sometimes makes it sound like a fuel problem. Whens the last time you replaced the fuel filter?

Check your fuel pressure at the schraeder valve. It should be about 55psi running. Pull the vacum line off of the fuel pressure regulator, the pressure should go up a few points and you should not see any gasoline in the vac line or the port on the regulator, replace the regulator if you do. It should hold within 5psi for 30 seconds after you shut off the engine/fuel pump. If you don't get 55psi then we need to troubleshoot the delvery system. I think your year has a low pressure in-tank pump and a high pressure pump mopunted on the fuel rail.

Visit fordfuelinjection.com and learn how to pull your codes and post your results. OR go back to Autozone and see if they can pull 'em. Some stores can and some can't, depends if they have the right code reader. Post any codes you get back here and We'll be happy to help. Theres quite a few awesome people here :-)

Take care,
Popa Tim

 

It only had a hard time cranking once because there was almost "no power." The guage was in the red when trying to crank. At first,I thought the gauge was messed up,but when the lights,engine,etc... run down with the guage,i started to belive it. I replaced the fuel filter last month. I don't have a pressure guage for the fuel reading.
Heres the codes IF I did this right. Fords code reading is harder than GM.
Bey here they are:
KOEO:
11
12
22

KOER:
3

I cranked her up with the ground wire still on the computer so it would show me running codes,she ran perfect! I took the wire out and went back to her old running ways.
you're right Popa Tim,she does have 2 fuel pumps,The in-tank was replaced about 5 years ago I think.

 

Bump ..................

 

The voltmeter behaviour is fairly normal for this truck. Not enough output at idle to keep up with a heavy electrical load. Read some of my posts about the Ford second gen alternator.

 

Huh. Yeah,I guess mines is a 2nd gen because it almost did catch fire one night. But I was also told It could be the IAC not letting air into the engine which makes the RPMs lower so the alt. doesnt spin as much and lowers the output. I unhooked the IAC (Power) and the engine barely turned. Voltgauge dropped. anyway to bypas the IAC and let the TB its self control the air intake?

 

Like Popa Tim said, check your fuel pressure. The guage costs around $40.00. It is a good investment basic to diagnosing any fuel injected vehicle. It is as important as a timing light in ensuring the engine runs properly.

The computer uses the IAC to control rate of decelleration, for engine start and warm-up, and to attempt to "save" the engine from stalling. All these in addition to basic idle speed control. If you disconnected the IAC and engine speed dropped to around 400 to 500 RPM, it is a sign that the IAC is most likely working correctly.

A fixed setting of the throttle blade is not nearly as versatile or effective. Give the fuel injection system what it needs to run right, rather than trying to hack it.

The low voltage output is a SYMPTOM of your idle quality problems, possibly exacerbated by corroded connections. Alternator output is a function of engine RPM; when she gets too slow, the voltage is going to drop. If the drop is too severe (due to high resistance connections), the voltage may drop enough to adversely affect the computer, which in turn might make it run even worse, which in turn etc. etc.

 

Hrrrmmm,I don't think its a fuel problem,because when I grounded the computer to pull the codes,she ran fine. Like its a problem with the computer or something.

 

I would start with cleaning the battery connections. If your battery cables look shabby, replace them. One thing to absolutely make sure of is that the ground wire running from the battery to the body has a good connection, and is in good shape. If the wire is greenish in color, it's time to replace. "Green disease" as I like to call it, creates major electrical resistance.

Since grounding the computer allowed the vehical to run fine, starting there would be an obvious(and very cheap)place to start.

I do recommend running one piece sealed battery cables, as well, once installed, brush on a coating of die-electric grease, or spray with silicone spray to help seal them from corrosion.

Another one to check. The little white plug that plugs into the alternator. I've seen this connection get dirty, and actually take out an ignition module or two on several vehicals(not mine). Electrical ghosts are fun and time consuming to track down, but starting with the most obvious, and working back from there will often eliminate them with little fuss or trouble.