'85 4-Runner: rough idle, only when electrical load is on

[DanS HJ-45]

So, my wife's '85 4-Runner has started idling really rough, and almost dying. The problem is, it mostly does it when there is an electrical load turned on. She says it does it when it's the blower that's on, or the headlights.

The truck is in CA right now, so I can't go put my hands on it to check anything. It has a new vatozone alternator with perhaps 2000 miles on it, and I don't remember offhand if the battery is newer, but I seem to remember replacing it sometime recently.

Any ideas, or should I just give up on that hunk of 22R-E and start searching for a 3L?

Dan

 

[Bogo]

Check the alternator, and the ground wire. The ground wire goes from the battery (-) post, to the frame, then on to a bolt on the engine by the motor mount. It is critical that it is good.

Also new alternators can fail. If it is a rebuilt, then the diodes likely tested OK when it was rebuilt and so they weren't replaced.

 

[DanS HJ-45]

Check the alternator, and the ground wire. The ground wire goes from the battery (-) post, to the frame, then on to a bolt on the engine by the motor mount. It is critical that it is good.

Good idea. That would explain why the engine would have a hard time running but the electrical stuff would otherwise work--other than almost causing the engine to stall.

Also new alternators can fail. If it is a rebuilt, then the diodes likely tested OK when it was rebuilt and so they weren't replaced.

Can an alternator fail and make the engine run rough? If the bearings in the alternator were shot it would sieze up, but it wouldn't matter if electrical loads were on or not.

Kate knows her way around a multimeter, and the battery and alternator are both good.

She's going to check the cables, and then maybe I'll look for a spare ignitor or something. It has over the past two days gotten bad enough that it's not just the big electrical loads that cause it, but it even idles rough (on and off) when the blinkers are on.

Dan

 

[Bogo]

Under load check the voltage difference between the engine block and battery
negative terminal. Anything over a few millivolts, and change that cable. It may take a bit of scraping to get a bare metal spot on the engine block.

Also check the alternator output to battery wire to see if it is failing.

I really think it is a failed alternator. Either the diodes or the coils.

I have no idea what a seized alternator bearing would do other than make a belt squeel or break. I highly doubt they are bad. You hear them going out long before they go

 

[Bogo]

When the truck is idling, what is the voltage across the battery terminals? With lights on and with everything off?

 

[pappy]

Dan,

My idle always drops with an electrical load. It's especially noticeable if the idle is set too low. Also, the battery grounds to the fender, not the frame. Check both ends are tight and clean. The ground for the engine is at the back of the engine to the firewall. I've had that wire fail.

 

[DanS HJ-45]

Dan,

My idle always drops with an electrical load. It's especially noticeable if the idle is set too low. Also, the battery grounds to the fender, not the frame. Check both ends are tight and clean. The ground for the engine is at the back of the engine to the firewall. I've had that wire fail.

Kate has adjusted the idle up to try and help--no difference.

I think today she was going to check out those cables.

Dan

 

[toyminator]

Can an alternator fail and make the engine run rough? If the bearings in the alternator were shot it would sieze up, but it wouldn't matter if electrical loads were on or not.

Yes because the fuel injection system requires power, as does the fuel pump. If the alternator is not charging properly when under a load it could dip below 12 volts.

 

[raevenzero]

I'd start looking at primary wires. Maybe you have a good + and - cable and that allows it to start (most draw and usually have issues there when not grounded). Instead, I think that there is a bad connection somewhere between the batter and the fuse block. You may have enough to start it, but once you start kicking on accessories, you start robbing power from the life support systems such as the ignition system, fuel pump, computer, etc.

 

[pappy]

I'd start looking at primary wires. Maybe you have a good + and - cable and that allows it to start (most draw and usually have issues there when not grounded). Instead, I think that there is a bad connection somewhere between the batter and the fuse block. You may have enough to start it, but once you start kicking on accessories, you start robbing power from the life support systems such as the ignition system, fuel pump, computer, etc.

Good point. The thick cable that feeds the starter does not feed the fuse block next to the battery. That wire can also fail. Also that wire crosses over one side to the other with a brass block that can also break.

 

[morganism]

That is definately the main fuxe box wire, go get a HEAVY gauge replacement at HD or Lowes, and some large o connectors and replace. There is a consistent weak connection on the bottom of the fuse panel in the engine compartment. Need to replace the connector, and the wire is seriously understrength too.