This Start Problem....

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
I've got an unfounded phobia of simply leaving this demon somewhere in the truck and bypassing it with a new wire......

I'm going to pick up a new relay today to see if that might not be the issue -- even though the relay does seem to be working right, maybe it activates, but is deteriorated inside enough to cause this voltage drop?

However, I'm wondering about something that has been bugging me about this the whole time, though: When the key turn does actually start the car, more than likely it turns the engine a bit slowly... However, if I take a simple wire and run it from the positive battery terminal to the solenoid connection, it fires up 100% of the time, and it turns the engine much faster, like it should. Can someone explain to me why the low voltage to the solenoid would cause the starter to turn slowly? I thought the starter motor itself turned off of the main feed from the battery.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Interesting..... I imagined that the solenoid would be engaged, or not, and that the starter motor was "separate" from that voltage.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Yeah. I'm wondering if maybe it is getting just enough voltage to fire that solenoid in a rhythm. As in, instead of being solid on, it is actually coming on-off-on-off really fast so that it turns the starter, and keeps turning it, but not as quickly as if it were actually locked on.

I'll report back once I get a new set of relays to drop in later today.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
There are two relays behind the fuse panel that both click on when the key is turned to start. I believe one is fuel solenoid, the other is the start solenoid. Both seem to work, but I replaced them anyway—no change.

EDIT: I thought up a new test for this. The relay has a constant 12.7 volts going to it, when the 12.7 volts from the key energizes it, the constant feed then goes to the start solenoid. So, when I test those spots, I am able to confirm that indeed, I get 12.7 volts of signal from the key to the relay. And if I use a hot wire, and jump the relay OUT feet to the solenoid, the starter rolls perfectly. However, if I plug the relay in (new, old, or random one from my pile of random stuff) the 12.7 volts from the key signal runs through the relay, and comes out the other side as only 9.6 volts! This is tested on the relay itself by leaving just a big enough gap to get the probe onto each blade. Again, this happens with a new relay, or old. So my question now is..... maybe the wrong relay has been in there all along? Maybe it's just that it is left over from the V8, or maybe it was simply replaced by a previous owner, but with the wrong size? Maybe I need a relay that allows for more amps/volts once the gap closes?
 
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NPT90

Well-known member
I used a LR disco relay I pull from a junkyard for my start relay, no idea of the specs but if you go to a pick and pull the whatever you can fit in your pocket rule applies
 

Napalm00

Well-known member
fyi unless you disconnect whatever is after the relay the voltage you read at the pin will be impacted by it. So if you plug in a relay and see 9.xx volts and the rest of the circuit still has a partial short or something you will get a bad reading.

So disconnect the wire that leads from the solenoid to the pin on the relay (at the relay) and retest. if you see 12v at the relay pin (you prob will ) then as thought previously you have a bad wire to the solenoid AFTER the relay. then replace the wire. then retest with the wire disconnected from the solenoid and test for the voltage at the end of the wire right were it would connect to the solenoid. now you know you have a good circuit all the way there.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
I’ll do the test again, but I think I did eliminate this error. In other words, I tested the output to the solenoid connected to the solenoid; disconnected from, but at the end of the wire; and at the relay output pin itself. But I’ll double check.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
OK.... I think I solved it. Skip to the bottom to look past my words.

I'm annoyed that it took me so long, but part of that is my schedule. But I'm glad that I was sort of right all along, that it really does seem to have been a simple issue, and that I didn't go out and buy (another) new starter or alternator. (See the thread on the alternator issue, and then come back here, because both problems are now solved.)

Basically, I'm an idiot, and I was thinking about this all backwards. In my mind, I was looking at the problem as an issue with the circuit for the starter: Ignition switch, wiring to relays, wiring to start solenoid, etc.... I was seeing this voltage drop at the starter. But all along, I had this void in my mind, a sort of "missing link" where I felt I was not seeing a fuse, relay, connection someplace that must be behind the dash or something.

The fact is that all of that FIRST goes from the battery, through the starter, then through the alternator, then to the harness, then to the starting circuit.

Well, if you looked at the alternator thread, you saw that I did check wiring. In fact, between these two problems, I pulled a good chunk of the wiring harness out and cleaned, and reconnected a lot of stuff over the last few weeks. No change. I checked the main cables from the battery to the starter to the alternator. Nothing seemed broken or loose or....? Battery was replaced. Starter was switched and switched again. A new ground was put in. New wiring, cleaned wiring, checked junctions, etc..... I was baffled.

BUT! I finally got the time to give it all one last try before taking the alternator in. I spent an hour de-wiring, the re-wiring everything from the battery to the main harness. And as I got to the alternator, it all dawned on me. I never did find anything wrong with the wiring. Just normal dirtiness from normal on/off road driving over the last few years. But nothing was loose or corroded. Some of the wiring was new. However, after cleaning and reattaching everything, it suddenly all worked. I'm now having 100% normal starts, and I'm getting a solid +/-14.7 volts while the engine is running at any RPM. I don't know exactly, but I'm guessing something at the alternator was loose, or partly disconnected, but did not feel loose. Or maybe something was dirty, but didn't look dirty from the outside. Either way, it's working as it should now, so I'm glad I don't have to keep jump starting, or roll starting the truck in public!
 
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