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Voltage drop at starter when trying to start engine
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Van Quixote
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PostPosted: Wed Jun 13, 2018 11:09 pm    Post subject: Voltage drop at starter when trying to start engine Reply with quote

Low Voltage at Starter When Cranking / Slow Crank Starter / Voltage drop at starter when trying to start engine

Hello again guys and gals. Hereís a new puzzle to solve. And thanks in advance for yíallís help and wisdom, I do very much appreciate this community.

I have an Ď84 1.9L 4-speed Westfalia that has had a very slow crank speed for the entirety of the time Iíve owned it (about a year and a half). I rebuilt the top half of the engine (and a slew of other repairs) last year and it runs fine (some hunting idle issues and it is running a tad rich, but otherwise feels, sounds, and drives great). I have read every message board post I can find about the current (no pun intended) problem I'm having and still cannot seem to find the issue with my van.

When starting, the crank starts off slow as all get-out. It usually fire up after the second or third crank-surge sound. But, if not, the cranking decreases from very slow in speed to zilch, where it just plain quits cranking altogether. At this point, I push start the van and it runs fine. Itís never been a problem to push start the van when the starter doesnít get the job done. It just sucks. I have:
-a brand new Bosch starter (the problem existed with the old starter as well)
-a brand new battery (I have had it load tested and it has passed; the problem existed with the old battery as well)
-cleaned ground posts (engine, transmission, battery box)
-a new ground cable for the battery
-checked fuses, all good
-I have unplugged the auxiliary battery, so it wonít interfere with our troubleshooting.

When the key is turned, but not in the cranking position, the voltage at the post on the starter is in the 12-13 range (I measured it a few weeks ago, but forgot to write it down) but when I turn the key to crank it, the voltage drops quite a bit, bouncing from high 7 to low 9 volts.

I donít think the problem is the cable running from battery to starter as when I bypass the vanís starter cable using jumper cables, the voltage is the high 7 to low 9 volts range as well.

Any ideas as to what to do to get this problem fixed? Thanks again!
-bob
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DuncanS
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PostPosted: Wed Jun 13, 2018 11:35 pm    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

I don't know what you mean when you say you bypassed the starter cable using jumpers. Did you disconnect the battery to starter motor cable and the use the jumper to run directly to the starter motor solenoid?

This smells to me like you have a bad surface corrosion electrical connection which is causing high resistance and heat which then runs the resistance up creating more heat and resistance until-----zilch. The problem could be internally in the starter cable half way along. There could be a bunch of corroded and broken wires and you only have a few left. Unless you disconnect the battery cable completely when trying a bypass you don't know whether your "jumper " is actually carrying the load or if the old wire is still trying to to do it. Jumper cables end clips are notorious for not delivering what is needed. I'd take the battery out and put it under the car and with short BIG temps to the starter solonoid and body ground. Run something smaller back to the battery location to pick up the rest of the circuit and see what happens.

Have you cleaned the end of the starter cable terminal? Did you clean the connection of the tranny ground at the body? And have you used dielectric grease on all these connections?

Is the Bosch starter really totally new, or rebuilt? I went through three starters before I could get ruum, ruum ruum, instead of waaaaaah, waaaaaah, waaaaaah.
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Van Quixote
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PostPosted: Wed Jun 13, 2018 11:53 pm    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

Thanks for your reply. Here's more info:

"Did you disconnect the battery to starter motor cable and the use the jumper to run directly to the starter motor solenoid?"
I completely disconnected the cable and ran a heavy duty (new) jumper cable from the battery to the starter and it cranked just the same (and had the same voltage drop) as when the van's cables were connected.

"Have you cleaned the end of the starter cable terminal?"
Yes.

"Did you clean the connection of the tranny ground at the body?"
Yep. And at the battery box, as well as all grounds in the engine compartment.

"And have you used dielectric grease on all these connections?"
Yes.

"Is the Bosch starter really totally new, or rebuilt? I went through three starters before I could get ruum, ruum ruum, instead of waaaaaah, waaaaaah, waaaaaah."
It is rebuilt, but it is the third Bosch starter and all have had the same problem.

I was hoping the new (rebuilt) starter would fix the problem, but it did not. This is when I pulled out the multimeter and started measuring volts. It would seem to me that the problem is happening before the starter as the voltage drop happens before the volts get to the starter proper.
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Last edited by Van Quixote on Thu Jun 14, 2018 12:08 am; edited 1 time in total
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PostPosted: Thu Jun 14, 2018 12:06 am    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

Iíve forgotten if your Vanagon uses a ground strap between transmission and frame but that is another thing to test by $4 replacement from FLAPS
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Van Quixote
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PostPosted: Thu Jun 14, 2018 12:10 am    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

There is a ground cable at the front of the transmission that bolts to the frame. I have inspected and cleaned it. The cable and bolts are in fantastic condition and the connections are shiny-clean. They weren't very dirty before I took the brush to them, but they shine now. And the problem persists.
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Wildthings
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PostPosted: Thu Jun 14, 2018 3:24 am    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

After you try to start it, something should be hot, just feel around and find it.

You can use your meter to read from connection to connection through the system looking for voltage drop. Battery post to cable end, cable end to cable end, etc. from one end of the system to the other. You need someone to crank the engine for you while doing this.

A 2.1liter starter will put out more HP than a 1.9L starter and is typically cheaper.

Make sure your timing is correct, if it is too far advanced it can keep the engine from cranking.
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DanHoug
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PostPosted: Thu Jun 14, 2018 4:30 am    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

my 87 Vanagon starter cable was crispy inside the rubber jacket for about a foot back on the starter end and somewhat less so on the battery end. i could hear strands cracking when i'd bend it. it looked fine, except there was visible fraying at the starter end.

in short, just replace your 30 year old battery cable. Van Cafe/RMW sells a very nice, OEM one that is the thicker spec for the 2.1. you'll likely have to drop the tank to change it as mine was fastened in at spots underneath the tank. but then you do refresh your grommets!

here's a cross section of the bad and good parts of my cable
Image may have been reduced in size. Click image to view fullscreen.

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danfromsyr
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PostPosted: Thu Jun 14, 2018 5:55 am    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

Did you clean the mating surfaces of the trans and starter?
oxidation off the trans and paint off the starter?

I'll often add an additional ground cable from the lower starter bolt to the frame as well. you can mimick this with a heavy duty jumper cable clamped to the starter ear.
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PostPosted: Thu Jun 14, 2018 6:41 am    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

Just do a voltage drop across the cables that you think are an issue. Simple easy. I would be easier if you can get a helper to engage the starter while you are testing cables/connections.

At 30 years old, I would just replace all the ground cables from the starter to the battery and you might as well replace the positive cable too [like someone else mentioned]. It would not hurt to get a larger size cable. While you're at it, replace the alternator power wire too. Again, it would not hurt to put a larger cable too.
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PostPosted: Thu Jun 14, 2018 8:53 am    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

I have seen where the trans to body ground strap looks good to the eye but has seriously degraded in the interior strands.
and I've smoked the front battery ground strap on a couple vans with higher compressions. so I upgrade those 2 as part of engine swap/conversions/wiring upgrades.
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MarkWard
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PostPosted: Thu Jun 14, 2018 9:55 am    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

Just out of curiosity, could you explain your method for measuring the voltage drop?
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Van Quixote
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PostPosted: Thu Jun 14, 2018 12:26 pm    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

With the multimeter, I measured the voltage at the positive post on the starter when the key was turned to on and then read it again when the key was cranked. Did the same on the solenoid post.

I do understand the value of new and bigger cables, but when I took the entire starter cable out of the starting equation (by bypassing it with a heavy duty jumper cables from battery to starter), the voltage drop when trying to crank problem was exactly the same. Unless I am not understanding the workings of the starting system, this would indicate to me that I can eliminate the starter cable as the problem.

Perhaps when I turn the key, something else is sucking volts away from the starter?

Also, the van starts up just fine. And very quickly. The starter is just turning scarily slow. And when I do a short stop (on a long trip), sometimes it doesnít start as easily and then the slow crank dies down to nothing and I have to push start. But it fires right up on a push start. Side note: I just put in a new Temp II sensor and the prob remains the same.

Is this something that a starter relay might fix?

Also, the ground strap from the transmission to the frame is an uninsulated wire (likely original) and is easy to inspect visually as the wires are not hidden by a sleeve. And it looks to be in excellent condition. And I did clean all cable ends, posts, and mating surfaces.
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PostPosted: Thu Jun 14, 2018 12:42 pm    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

It is normal for the measured voltage to be lower at the starter solenoid when cranking. To check for an actual voltage drop across a leg of a circuit, you would put the VOM between the positive terminal of the starter solenoid and the positive battery post. Then as described crank the engine. Ideally you'd read zero volts on the meter. Anything more is your "voltage drop". You would do the same test on the between the battery negative post and the starter housing. You may want to search you tube for a few videos on how to measure a voltage drop.

I have a set of test leads that I bought some time ago with alligator clips for testing these long runs. I think I bought it from the Matco dealer. Very handy to have. They coil up into the fixture they are stored in.
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PostPosted: Thu Jun 14, 2018 12:54 pm    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

Just watched some vids on "voltage drop" and will give that a shot. I was measuring the voltage that made it through to the starter while key was turned on (around 12 or so, if I recall correctly) and again while cranking (bouncing from high 7 to low 9). So, obviously, less volts are getting through when cranking. Exact same problem when I bypassed the van's starter cable by using jumpers instead.
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PostPosted: Thu Jun 14, 2018 1:03 pm    Post subject: Re: Voltage drop at starter when trying to start engine Reply with quote

MarkWard wrote:
I have a set of test leads that I bought some time ago with alligator clips for testing these long runs. I think I bought it from the Matco dealer. Very handy to have. They coil up into the fixture they are stored in.


that's a really handy thing to have. i made up a long jumper with alligator clips on each end to truth out wires between the engine compartment and the dash. but it has all sorts of uses including measuring the voltage drop between the remote battery and the starter. it's sorta an essential bit of kit to have as you work on your own stuff and you really only need one long lead to do everything.
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