1989 ranger runs terrible with headlights off.

[JoshErnst1074]

I have a 1989 2.3L 4WD ford ranger. I just put a 95 engine in because the old one had a hole in the piston. The problem I'm having is it runs terrible until I turn the lights on. When I turn the lights on it wants to idle fine. Already replaced the alternator and battery among many other components. Anyone have any idea what could cause this? I thought it was a voltage regulator but I just put a brand new one in.

 

[Mikel89us]

Sounds like a wiring problem to me. I've never heard of it before, but I would almost bet my truck on it not being a part.

 

[JoshErnst1074]

See that's what I think. I wouldn't even know where to start. I've replaced so many thing. I can't figure it out. What's the best way to find a bad ground or short somewhere? Electricity is my weak subject. Can't stand it. By the way it also doesn't die completely with the headlights off, just sputters and almost dies.

 

[JoshErnst1074]

Also forgot to mention, I have no coolant temp sensor on the dash, so I'm assuming the coolant temp sensor is bad. Sure enough, the computer is telling me ect -40F. Could this cause all the problems I'm having? Also where in the world is the coolant temp sensor on these motors? For a pre obd1 this truck sure does have a lot of sensors!

 

[mattging94]

On my 94 the coolant temp sensor was on the driver's side of the block, just below the head. Should be just a single wire going to it.

Sounds like somewhere your lighting circuits are crossing over or interfering with something that runs into your engine computer. What makes the difference in how the engine runs: the headlights being on, or just the marker lights? If it's just marker lights try playing with the dimmer switch for the dash lights and see if that makes any difference on it - if it does you've probably got a wiring issue to your dash that's crossing the gauge illumination circuit with a sensor circuit or something. That's the most likely place I can think of where lighting and engine control wiring could cross, but I could be completely wrong... Good luck!

 

[JoshErnst1074]

Only does it with the headlights. Which is why I think I may have a ground somewhere. Feel like it's getting over voltage and the headlights being on is bringing it down.

 

[SenorNoob]

I might be way off but, My first thought on reading this is that you have a weak/missing ground on the ECU. It's grounding through the headlight circuit somehow.

 

[JoshErnst1074]

See I was thinking that too. But I think the headlights being on is lowering the voltage making it run fine. I'm thinking there's a short in the voltage regulator circuit somewhere. Where does the ecu ground to?

 

[JoshErnst1074]

Took all my grounds out and resanded them. Suspected it may be a bad alternator ground so I made a new one and the truck runs flawlessly. So far.

 

[Mark_88]

I did that when I first put my truck together many years ago and have had only a few minor problems...but wires can fray, rust, and spontaneously disconnect themselves leaving us with a seemingly endless task of tracing them down...

One of my aims has been to learn to trace and detect problems in wiring...still working on that...

But good to hear it was something simple...

 

[ab_slack]

The problem with wiring is that changing parts likely won't resolve things.

Sometimes odd is happening I look for other things that aren't working right or change and check ground connections. Get a long wire hook it to battery negative and then measure other supposedly ground items and see what the voltage difference is. Especially when something changes like with likes you see if ground level changes before or after. An ohm check is of limited use because things may measure okay in a check but not operating.

One thing that can happen with electrical connections is that they can become poor and intermittent due to corrosion.

You might expect when connection is going bad that it might work at light load but heavy load not work. Sort of like with a bad battery connection, the interior lights come on, instrument cluster on, but when you try to crank the engine it all goes off.

Sometimes however the reverse can happen. At light loads the current is too small and the corrosion makes for a resistance, but when you put heavy load (like headlights) instead of the voltage drop getting worse, the higher current can bridge the poor contact better. For this reason some mechanical switches that hook to near zero power inputs (like a signal that tells the computer to do something) where only a few microamps could work are intentionally biased with a higher current (maybe 5 or 10 milliamps) as it increases contact reliability.

So since cleaning the connections resolved the issue I suspect something like this was going on.

 

[JoshErnst1074]

Same here. Electricity has always been my week point. In trying to get better at it. I know they make some pretty awesome diagnostic tools. They have a meter that you move around and it beeps when it's around a short circuit or bad ground. How awesome would that be?