Hello everyone perhaps you guys can help me get my weak start problem figured out. I know its either the battery or the alternator. I tested the voltage with a multimeter and its around 12.5 at idle, raises up to 14.7ish when giving it gas.
The voltage also reads low on the dash but no battery alert.

Last week i was headed up to the woods and after driving it for about a hlf hr I stopped for gas, when I tried to start her again I barely got a crank, I let her sit for about an hr and repeatedly tried to get a crank, she finally fired up after that hour. When the truck is cold I get a good strong start, I really dont want to get stranded again when its warm what do you guys think?

 

Anyone out there have this issue?

 

kinda sounds like your timing is off a hair my ramcharger does the same thing when it get warmed up or the starter might be getting hot and dragging.

 

Check the battery cables closely, positive and negative. I believe the 4.9L engine has a funky spade connector on the starter that is known to cause this type of issue as well.

I also suggest to have the battery load tested.

 

voltage shouldn't be below 13.6-13.7 at idle and should really be around 14.1-14.3, might need to check the alternator. have you ever jump started anyone from your truck. could be a prob with diodes.

 

A stock 1989 truck has a 2G alternator. At idle RPM it provides little, if any, charging current. That's why the measured voltage, which is marginal, is on the low side. Another reason why I suggested testing the battery.

 

Hello everyone, strange issues persist. I replaced the wire that connects the push start button on dash and the solenoid (truck came with a push start not sure of that wire name) due to is degraded nature. I also had a friend let me borrow a good used battery of his to see if that might also help. At first it seemed to work but I drove it about 15 min turned it off and got that weak start again until finally no crank, I was close enough to home to get my car and jump start the truck, so yeah jump starting it did the trick, with the better battery in, where is the smoking gun?

That was yesterday, decided to give it another longer run today, did about 15 miles on the hwy. I was sure it would happen again but when I got back and turned off/and turned it back on, it fired right up. Opposite from what occurred yesterday with the same battery. I just tried turning it on now again about 30 min after the drive and a nice strong start again. My original problem happened when I drove it about 45 min on the hwy, stopped for gas, then got that nasty weak crank, it left me stranded for about 1 hr until it got enough juice to barely start again.
I dont trust the truck even after this recent drive.

** I have tested the starter and original battery(not the one that my friend let me borrow that is in the truck now) at the parts store machines and was told they were good to go. What do you guys think, do these recent symptoms have an obvious source?

 

Measuring voltage at idle won't really tell the tale, need to measure with an electrical load on the alternator and at a higher RPM, a zone where the alternator spends more time anyway, and is more effective at charging. The way you do that, is turn on the headlights, heater blower fan, radio, dome light, etc while running the engine at a fast idle. Then measure the voltage right at the battery posts. Should be 13.8 to 14.3 volts DC, right in there, at "normal" temperatures. When it gets cold, real cold, it needs be higher. When it gets to be hot, real hot, it needs to be lower.

Anyway with the cables themselves and the grounds pushing 30 years it's a safe bet they are a problem by now. Any resistance, anywhere in the charging circuit, will cause a huge reduction in the ability of the alternator to supply current. The same problem will cause a noticeable slowing of the starter. In hot weather this problem is aggravated. This website sez .06 ohm - six hundredths of an ohm! (almost nothing) will reduce alternator output by almost 30%; it will walk you through some checks. Suffice it to say, replace those old, corroded original battery and starter cables and grind down to bright shiny bare metal at block, frame, firewall, etc and tighten securely. Put the battery on a charger overnight while you're doing all this.

http://www.aa1car.com/library/voltage_drop_testing.htm

http://www.aa1car.com/library/charging_checks.htm

 

My truck always had something wrong with the ground. I home runned a cable from the chassis ground point to the starter, and another cable from the ground point to the engine block. I also cleaned down to bare metal the main chassis ground point and the other two connections. I was done with poor charging and bad starting after that. I've never had a vehicle so finicky with grounding issues.

To verify a grounding problem, next time it does this run a jumper cable from the ground post on the battery directly to the starter. If it starts right up then you have the problem I had.