Jetstar 3 voltage drop at coil while cranking

jetstar3

New User
A couple of years ago, I bought an old Jetstar 3 that was customized by Parsons with a 510 backhoe. It was in rough shape when I bought it.. and still is.
The tractor had been sitting outside for a couple of years before I bought it. To make it drivable I had a lot to do.
Finally, I got to the electrical. I had to swap the coil and resistor (inside of the distributor) After messing with the firing order, it started up and I drove it 10 miles home. It ran ok for a while. Then, last year I went out to start it... It had no spark. So I tested the coil. It seemed to be just a bit out of range so I replaced both the coil and resistor again.. No luck.. Still had no spark.. I let it sit through the summer.. and fall... Now, I have to move this to my new place so I can start restoring it.. So, Last week, I tested and found fluctuating 12v while jiggling the ignition and 0v going to my coil while cranking. The engine cranks as normal. So, I replaced my Keyed ignition and push button starter with new from amazon. Everything bolted in place the same way. I cranked the engine... Still had no spark. I tested the voltage at a solid 12.5volts whith the key on engine off. I tested power to the coil wire @ 4volts while cranking.. An improvement, but not enough to power the coil. I am using my power probe 3. The voltage is very erratic between 2-4 volts while cranking.

I tested on all 3 sides of the switch and push button. All read the same drop. I can trace the drop all the way back to the + battery terminal/ post While cranking.
I tested the starter with my low dollar ampmeter and it seems to readout 145 on the A~1000 setting or 14.5 on the A~200 setting. I have heard that anyhting over 250amps would be cause for concern (by pulling too much voltage? and not leaving enough for the coil/dist.? ) anyways.. I replaced the battery terminals and soldered them in. I checked the battery with my high dollar tester and even replaced the battery with another just to rule that problem out...

The starter may still be a problem. I have not tested any further. The starter solenoid seems to be the power distribution point. There are no fuses in the system.
Checked to insure that the wire going to the coil is connected to the ignition post on the switch.
Checked all connections. There is not too much corrosion. I cleaned the Battery terminals and posts.
I'm prepared to replace all of the wiring. As well as put in an electronic ignition.
Something tells me to keep looking into the starter. Maybe it is grounding or having another resistance issue that is creating and pushing back into the battery?
Although it cranks the engine just fine, I did over crank the starter last year. That may have stressed the starter a bit. but it ran just fine after that.

I'll pull the starter and take it in to the parts house and have them test it.
Also think it could be a defective switch, although, I tested voltage drop all the way back to the +terminal/ post. If it was a defective switch, wouldn't one side be read 12v and the other drop?


Its pouring down rain right now. So, I thought that I would write this with the hope to get some other ideas, before I go back out and work on it..

Thanks for reading this.
 
I pulled the starter off. The starter looks like it was the origional. It looks over all to be in good condition. Then, I checked the 2 small posts for resistance. I found 6.9-7.0 ohms of resistance that was fluctuating between offline (no connection.

Ipulled the starter solenoid cover off and found that the bolt/post closest to the frame was completly corroded on the inside. This is the post with the piece of plated brass that contacts the copper wheel inside. The copper wheel had some tarnish on the contact spots. So, I sanded it smooth with some 400grit.
I pulled out my MAC tools digital meter and retested. Now I have 8volts going to the coil.
I have replaced a few wires, but now I must remove the gas tank to access the oil soaked rats nest between the insturment panel and tank.
 
I assume this is an MM Jet Star 3

Check the resistance across the 2 small posts on your coil. Is it 1 1/2 ohms or 3 ohms? Check the resistance of the wire between the ignition switch and the coil. Is it 0 ohms or 1 1/2 ohms?

If your coil resistance is 3 ohms, you should have near 0 resistance on the wire from switch to coil.

If your coil is 1 1/2 ohm it should also have 1 1/2 ohms between switch and coil . Some did so by adding a resistor, others used a special wire with added resistance in the wire.

The 1 1/2 ohm coil is used in 6 volt systems. The 3 ohm coil is used directly in 12 volt systems with no added resistance.

The added resistance drops the voltage and limits current so you can use the 6 volt coil in 12 volt system.

Some of the Jet Star 3 used the 6 volt coil and resistor, then added a wire from ?I? small post on the start solenoid to the coil side of the resistor. This gave momentary 12 volts to the coil while cranking to give hotter starting spark.

Check voltage on wire from other post on coil to side of distributor. It should have near 0 volts with points closed and near battery voltage with points open, switch on, and engine not running.

If positive ground system, + post on coil goes to distributor, if negative ground the ? post goes to distributor

Since it has set for some time, I would guess that your main problem is a film has developed on the points so they are not making good contact. Remove it by pulling a folded dollar bill between the closed points.
 
Thanks for the reply. The system/ maybe converted? a 12volt. Point voltage is secondary. already filed the points and adjusted them.
I also checked the voltage. wire from the ignition side of the starter switch to the coil+
Ohms at the small post to small post were at 6.9-7.0 with the wires on. I removed the wires from the posts and then the meter read ofl. I pulled the starter and then pulled the solenoid apart and found some serious corrosion on one of the posts. Cleaned and reassembled. Still reads ofl. On the meter. No other problems found. Retested voltage to coil while cranking. Doubled the voltage from 4 to now 8volts. Still not enough to energize the coil.

I'll check to see if there is an "I" or similar on either starter posts.

Would the resistance of 1 1/2- 3 @ the starter be during cranking? Other than the post, I have found 0 resistance in the wiring, thus far..

Other than the wiring that I replaced today I have not replaced any special wiring or any in line resistors
The tractor Ran one day then the next it wouldn't.

I haven't come across any special wires or resistors in-line.

will check resistance while cranking at the starter posts. Will also check the resistance while cranking between the switch and coil.

Thanks for the advice.
I'll update tomorrow.
 
Do not try to do resistance checks with switch on or while cranking. You can do voltage readings with main switch on or engine cranking or running but not resistance...you could damage your meter.

What is the resistance reading on your meter with the two probes shorted together.

What is the voltage reading from tractor frame to grounded post (not cable clamp) of the battery?

What is ofl reading?
 
. KS has it covered . Looks like no bypass if it's a six volt coil and if it has a ballast .
Could be a 12V coil with a ballast with out a bypass which will barely start or run.
 
Its a 12 volt coil with no external resistor required.
As I stated in previous posts. I did not replace any wiring and it ran fine until it would not start.

I removed the fuel tank and found a rats nest of wiring. There were 4-5 wires that came off of the starter solenoid that were open circuits (wires cut off) stuffed into mud (in the crooks of the engine and tranny castings). There were also many wires that were corroded. I replaced the whole harness with 4 wires. Not minding the gauges for now. I just need to get it onto a trailer.

Another problem that I ran into is when removing the harness, there were 2 wires coming through a hole in the frame that looks like it connects to a sensor that sits on the transmission. Is that the clutch safety switch? My manual has nothing on electrical diagrams. I used google to find one. Its a pretty simple diagram for the engine ignition only.

one of the wires went to one of the small posts on the starter. The other went to open circuit (cut off and partially exposed)

I have not found any special resistance wire or any resistor in the wiring that I have removed.





Hopefully these post. On the solenoid, The first 4 gauge wire (+black+)goes to the Ignition switch BATT pos, the second red+ goes to the alternator 3rd (kinda hard to see) goes to battery.
the small post on the left no longer has a wire on it. As that wire went from that solenoid post to the transmission wire. (that I cut) The other wire went to open circuit (cut years ago)
The small post on the right closest to the block has a wire that attaches to the push button (starter button).
[/b]
 

Ofl means that there is no connection or reading but its not 0.000

o.fl is the acutal reading. which means there is no continuity.

Using a jumper wire I connected both small posts together. Then tested ohms of resistance touching red to solenoid and black to frame. I get 0.1 ohms.
 
OK,Sounds like a digital meter. Ofl would indicate "overload" or "out of range". For instance, if your ohmmeter section has 200, 2000 ,200000 etc ohm ranges, if set on 2000 ohm range it will indicate resistances up to that level, but anything over 2000 it will read Ofl. Switch to 20000 range and it will indicate anything up to that level.

Are you shorting 2 small posts on starter solenoid or ignition coil together and checking to ground. Either test would be basically irrelevant.
 
?Its a 12 volt coil with no external resistor required. ? OK Pictures are helpful also.

3 big wires on top post of solenoid will work but are not correct. Semi-hidden wire to battery is correct.

4 ga Red wire from alternator is battery charge wire, but should go to one side of ammeter and from other side of ammeter to this top post on solenoid. 4 ga. Wires are an overkill for size, 10 ga would be more flexible.

Remove the 4 ga black wire from solenoid to switch, then add a 10 or 12 ga wire from switch to alternator side of ammeter.

With ammeter connected turn on lights and/or ignition switches. Do not engage starter. If ammeter needle swings to -- it is correct, if ammeter swings to + reverse the ammeter wires.

There should be a wire from start button to whichever small post on solenoid activates the starter. This originally went through switch on side of transmission. Purpose of that switch it to only allow the starter to crank the engine when gear shift is in neutral thus preventing movement of the tractor when it starts.

Other small post on solenoid is not used with 12 volt ?no resistor required coil?

There should be a wire from switch ignition output to + post on coil. --post on coil to side of distributor.

This is all you should need to get it running.

Not unusual on old tractors to find a rat's nest of wires. I've found that a rewire job is some of the best repair and preventive maintenance that can be done.

Attached diagram is for U302 which is "big brother" to Jet Star 3. Wiring should be similar.
a208605.jpg
 
(quoted from post at 10:07:20 12/16/15) ?Its a 12 volt coil with no external resistor required. ? OK Pictures are helpful also.

3 big wires on top post of solenoid will work but are not correct. Semi-hidden wire to battery is correct.

4 ga Red wire from alternator is battery charge wire, but should go to one side of ammeter and from other side of ammeter to this top post on solenoid. 4 ga. Wires are an overkill for size, 10 ga would be more flexible.

Remove the 4 ga black wire from solenoid to switch, then add a 10 or 12 ga wire from switch to alternator side of ammeter.

With ammeter connected turn on lights and/or ignition switches. Do not engage starter. If ammeter needle swings to -- it is correct, if ammeter swings to + reverse the ammeter wires.

There should be a wire from start button to whichever small post on solenoid activates the starter. This originally went through switch on side of transmission. Purpose of that switch it to only allow the starter to crank the engine when gear shift is in neutral thus preventing movement of the tractor when it starts.

Other small post on solenoid is not used with 12 volt ?no resistor required coil?

There should be a wire from switch ignition output to + post on coil. --post on coil to side of distributor.

This is all you should need to get it running.

Not unusual on old tractors to find a rat's nest of wires. I've found that a rewire job is some of the best repair and preventive maintenance that can be done.

Attached diagram is for U302 which is "big brother" to Jet Star 3. Wiring should be similar.
a208605.jpg







Thanks KC for the diagram. Also for the breakdown. I found a jetstar diagram a couple of days back I have a drawn diagram of the electrical system wiring. There is no ammeter in the system. Wouldn't think it would be necessary. Something for the restoration for sure.
The wire is very much overkill.. but it's what I have available for getting this tractor running. It is not giving me too much hassle. I will head down to NAPA to buy the correct wire for the restoration.

I shorted 2 posts on the starter for the test. I figured that it would be irrelevant. that was mentioned, or how I understood it at the time.
I checked it out again today. Had 2 charged batteries. Cranking voltage increased from 8 to now 9.5v, after I replaced the wiring. I've kept all of the wiring in their original locations. Just replaced with new mostly overkill wiring. Still not enough to fire the coil. I connected my battery charger to the battery, put it on 40 amps. that gave me 14-15 volts and 10.5 while cranking at the coil. Still not sparking. I have a spark tester on #4 cyl. I used a ground strap from the -terminal to the frame. No change in voltage.
I found that the small post on the starter solenoid, close to the frame puts out 0.5volts with the ignition key on, and the same 9.5 volts while cranking. I ran a jumper lead from that post to the ignition post on the switch. No increase in voltage. None expected. Just ruling things out.

I have a feeling that the switch is bad. Should have a new one tomorrow from amazon. It was locking up this morning and feeling plastic crushing while turning the key to the on position. It is the cheap dorman switch and button. The plastic on the back of the starter button is also able to spin 90 degrees inside its own metal case.

Although cranking voltage is the same on both sides. I can check it all the way back to the battery. It reads the same 12.5-15 volts (depending on if charger is on) 9.5-10.5volts drop while cranking.
I also removed the alternator wiring from the system and retested. No change.

If this is not a bad switch then everything is pointing to a bad ground. The starter is showing some wear. It is spinning but sometimes not actuating/ the bolt/ cranking intermittently. I have to push the button a couple of times then she'll crank. Also sounding like the starter is pulling a lot of amps. It's humming pretty good while cranking.

I have a harbor freight ampmeter/ multi meter for testing amps. It has the halo clamp on the top. Its cheap but compares pretty well to my MAC multi-meter.. so far.

I'll do some more testing on it, replace the switch and button and remove the starter again. Probably take it down this time to a starter/ alternator shop
 
What is voltage from positive battery post to ground when cranking?
What is voltage from negative battery post to ground when cranking?
What is voltage across the large top and bottom posts on solenoid when cranking?

What alternator do you have?
 
The alternator is a Delco Remy 2 wire. I still have the alternator wiring completely removed from the system while testing. Although wired to the system, It never charged the battery . There was no resistor in the wiring either. I have a couple of the same in a box somewhere that are known good. Again, I'm saving it for the restoration.

I Just performed the voltage tests,

Started with freshly charged 12.5v battery
+post battery to - post battery while cranking 10.5v returns to 12+volts when stopped.
+post battery to frame ground- 10.5v
Top post on solenoid 9.5v while cranking
bottom post on solenoid 9.5v while cranking

Battery post - to ground 0.233 volts while cranking. 0v otherwise
 


Also did a ohms test according to this picture from a google search.
I connected the battery - terminal to -post then turned the switch.

Connected my probes to the top post on the solenoid (1 Battery cable terminal) and to the battery back strap (2)
Cranked engine while testing o.fl. until the end then it spiked at 28.744 ohms. 5 second break. Cranked again, cranking ohms fluctuated between 6 ohms/ 23ohms finally 32 ohms. With intermittent o.fl

I pulled the starter and am taking it down to see if I can get a new solenoid.
 
jetstar3
Checking voltage as you are doing is not going to alleviate the starting problems. As you indicate the voltage is dropping while cranking the starter over, this is to be expected. With 9.5 voltage left it is enough to make the electrical system function properly if all else is good. A simple way to check the system is. With the ignition switch in the run position put a test light on the + side of the coil, it should light and stay lit.Then move the test light to the distributor post wire from the coil, it may or may not show power, however it should flash if you crank the engine. A constantly lit light or lack of light are signs that the points are not operating correctly. If these tests prove satisfactory then remove one plug from the engine and lay it on the block, crank the engine and look for the spark to jump the gap on the plug. If you see a good spark then you need to asses the condition of the plug. From all the cranking you have done one would expect the plug to be soaked from un-burnt fuel. If it is dry you could try using a "LITTLE Starting Fluid" sprayed in to the air intake. Should the engine start or fire at this point it would further point to a fuel related problem and away from an electrical problem as you suspect. Good luck and keep posting your results..
 
Do not do an ohms (resistance)test on a powered circuit. Do volt meter tests on powered circuit. Ohm tests will damage your ohm meter.
 

I was using my multi meter on the ohms setting.

Here are some pics of the starter that i pulled apart, cleaned and inspected.
I'm glad that I pulled the starter apart, and didn't take it to a shop..





The starter looked ok. It was dirty and greasy. pulled it apart and cleaned it with some gasoline and a brass brush.

The brushes look good. They have some chips removed from grinding. The edges are no longer 90 degrees They do not look bad though. I cleaned them up as well. these look like delco brushes. D746.

I'm headed down to town tomorrow to see if I can find a new solenoid.
Part number ABC1179. I'll pick up some 8 gauge and 10 gauge wire at the same time.

Ordered a carb rebuild kit off this site. I imagine it wont be here till after x-mas...

I have a power probe 3. Its kinda like a test light (with more functions). When I get the starter back together I will test the coil, and points. but Its all new and properly gapped. Distributor looks fine, has very little play It should work. If not I have backup that I will test. I'm going to check out an electronic ignition setup tomorrow at NAPA as well.
If the price is comparable to the price on here, I will probably pick it up. I have already spent too much on points and condenser.
 
"Here are some pics of the starter that i pulled apart, cleaned and inspected.
I'm glad that I pulled the starter apart, and didn't take it to a shop.. " Personally, I think you need a second opinion on the condition of the starter. Skip the electronic ignition and buy a new starter.
 
(quoted from post at 06:13:52 12/18/15) "Here are some pics of the starter that i pulled apart, cleaned and inspected.
I'm glad that I pulled the starter apart, and didn't take it to a shop.. " Personally, I think you need a second opinion on the condition of the starter. Skip the electronic ignition and buy a new starter.

I went down to the parts store today and learned quite a bit about this starter.
It seems to be a common starter with GMC. The only MM starter I found online was around $400. It looks though, like a GMC pickup starter will work if I replace the nosecone from my existing starter. That's about $350 less.
I bought a new Echlin (NAPA) solenoid for $18. Also picked up new brushes. Set of 4 is $5. I found the same brushes on amazon for $6 each.
I also decided to pick up some proper gauge wire.
I'm going to "rebuild' it tonight. I have a full afternoon.

There is quite a difference in the wear between the old brushes and new ones.

The first 4 pics below are to show the radius of the communicator. It looks good. I do not see any melted windings. Or anything bad on the armature.



















I soaked the starter case and armature in gasoline. I found that the black paint didnt like that too much and started to wrinkle. It looks like it is some thick paint. Insulator? ill go back over it with some flat black spray.
 
Well, today around 4pm I was able to get out there and install the starter with new solenoid and brushes. I only had about an hour break in the weather and about the same amount of daylight left. I installed the starter and while checking voltage I noticed that my spark tester was pinging. Reads 9.5 volts while cranking. Then my battery pooped out.. before I put the tank back on it needs to be cleaned and flushed. I think the carburetor at minimum needs to be pulled and cleaned. Same with the air/oil filter. I think I'll keep the points inside of the distributor, for now.
Thanks for all the help KS and jo
 

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