Let us know how it turns out....no pun intended.

 

The old mans truck had been starting great until I showed up today and then it acted up. I heard it hit and engage and then slip out as it started to spin the starter. Started fine after that but I went ahead and put a relay on it like planned. I used a John Deere 30-50 series starter relay (Ford starter relay minus the "I" terminal). I had to enlarge the holes slightly but the relay slipped right onto the studs at the firewall where the rear of the battery box bolts to the firewall. Its a nice location, out of the way, not too obvious and centrally located for this retrofit. Then I ran 10 gauge and soldered connections from the battery to the relay, 10 gauge from the relay to the solenoid, and 10 gauge from the relay to the original purple wire that went to the starter solenoid (energizes relay) because the original purple wire was not long enough to reach as is. I simply used an eyelet on the 10 gauge wire and a screw and nut to bolt it to the eyelet of the purple wire since I didn't want to cut anything in case this didn't work and needed to revert back. I started it several times in a row (which is when it would act up before) and it started perfect everytime. Only time will tell but according to tech assist ridding the voltage drop will fix it.

 

Nice Job! Does anyone know what the current draw is when the solenoid engages? Maybe GM simply underestimated the voltage drop running that much current and did not properly size the wire?

 

not sure I understand why you did it that way, and Im also not sure what you did will fix anything...

The relay in the UBEC is from the ECM (yes, ECM, no such thing as an ignition switch actuating the starter on these truck) to the starter solenoid. All the relay does is energize the solenoid. It doesnt take much to energize a solenoid, so even if you are getting a loss of voltage to the starter solenoid, as long as it energizes, you are still getting the full battery power from the battery to the starter...its not like the solenoid (not the relay) can only "half engage" (because it got only 9 volts from the starter RELAY, for example) and give less than 12 volts to the starter......

I guess what Im just saying is Im completely lost as to your diagnosis and fix for this problem.

ben

 

not sure I understand why you did it that way, and Im also not sure what you did will fix anything...

The relay in the UBEC is from the ECM (yes, ECM, no such thing as an ignition switch actuating the starter on these truck) to the starter solenoid. All the relay does is energize the solenoid. It doesnt take much to energize a solenoid, so even if you are getting a loss of voltage to the starter solenoid, as long as it energizes, you are still getting the full battery power from the battery to the starter...its not like the solenoid (not the relay) can only "half engage" (because it got only 9 volts from the starter RELAY, for example) and give less than 12 volts to the starter......

I guess what Im just saying is Im completely lost as to your diagnosis and fix for this problem.

ben

Its not my diagnosis, its GM engineerings diagnosis. I know how the starter solenoid works and I don't really know how many amps it pulls but I would say in the 10-15 max range. The only thing I can figure is at random it doesn't have quite enough voltage/current to keep the solenoid held in and as the starter disengages it grinds the flywheel as it spins down. All I did was use the stock purple wire to the solenoid to turn on a seperate big heavy duty starter relay thats mounted to the firewall that puts a consistant solid battery voltage to the solenoid when the key is in the crank position. This is the more realistic fix to what GM said to do which is replace the UBEC. Evidently through the countless connections and 10 or so feet of wire it occasionaly drops enough voltage it doesn't start all the time. So far its working perfectly.

 

most electronics have protection circuit that shuts down when voltage goes below 10volts to prevent killing ecm/pcm's.

 

Bad news. 2nd day with the relay added on it made the grinding noise again. It was worth a try but it still has got to be the starter itself causing the problem. I don't know why technical assistance said this was the fix since like you guys said the solenoid either won't work if the voltage isn't right but for whatever reason it seemed to fix the truck we had come in at work with the same sort of issue.

 

I had a similiar problem when the batteries were almost done ( for lack of better words) about a month later I changed the batteries.

 

yep...I was almost positive techline's fix wasnt going to do anything.


when you replaced the starter, did it come with a new solenoid? Or just the starter itself and you reuse the original solenoid? Are the dmax starters solenoid-shift?

ben

 

We are using Oreilly starters. I know some say they are junk but my family has used them for years and haven't had a bit of trouble with them and for the price and warranty it was the only logical thing to try. Anyway yes they do come with a new/reman solenoid. Its all complete ready to bolt on. By solenoid shift do you mean the solenoid is mechanically linked to the starter drive by the shift arm? If so then yes. The other deal is I tore the original starter down that came on the truck. It was a GM Hitachi starter. I looked things over and how it operates and from what I could tell by the very design of the solenoid there is no way the starter motor will get power to spin until the soleniod is fully seated and pushes the contact disc onto the contacts. For the solenoid plunger to become fully seated the starter drive has to fully engage since the shift lever is solid and there is no way for it to give. The the starter drive didn't engage it would result in a click as it hits the teeth and thats in. The starter would never spin because the contact disc wasn't contacting the contacts. That made me think it has got to be the starter drive itself (the roller clutch) thats causing the problems, especially since the issue gets better/worse from starter to starter. I was sceptical of techlines solution as well but the guy at our shop said on that particular truck it did cure it. Why I don't know. The only other thing I can think of is maybe there is a slight voltage drop on the battery cable itself to the starter and the starter doesn't spin up fast enough to fully engage the roller clutch each time or something weird like that. I have a hard time believing that though since it starts effortlessly. I would love to try an Isuzu or Hitachi heavy duty starter drive (bendix). I know the other small block starters had a variety of drives, 3 pinion through 5 pinion. If you had a big inch high compression engine a little 3 pinion drive wouldn't last. This seems to be the case on the duramax starters.

 

have you tried an OEM starter?

 

X2

If your fix did not work, then look at the starter!

 

These intermittant problems can sometimes fool you into thinking you fixed something. In the case of your customers truck, if the problem was with the ECM relay circuit, you replaced that circuit to eliminate the problem. In the case of your fix, you kept the original ECM relay circuit as a part of you new circuit.
You started a different post on this a few weeks ago, so I know that you are familiar with how the starter/solenoid works. If the power to the solenoid was "weak" and it could not hold the pinion gear fully extended, then the power to the starter motor would be cut when the solenoid allowed the pinion gear to retract (spring not compressed). The only scenario I know of that allows these starters to grind is when the engine over runs the starter and the pinion gear is forced back, compressing the spring.

The most likely cause for both of these trucks is a slow spinning starter motor. Question is why is it spinning slow? Marginal Battery/s? Marginal Starter? Marginal Cables? You have already replaced a starter, so my tendancy would be to focus on the other remaining possibilities.