Diagnosing intermittent no crank problem - please help

[CharlesJones]

Hi All,

I have an intermittent start problem where my car will not crank. I get a click from the solenoid, but the starter motor won't turn the motor over, which means I have to get a push to start the car. This used to happen occasionally so I had the starter motor rebuilt, which appeared to fix the issue for about two weeks until I got exactly the same problem again.

The car is up on axil stands at the moment, and this time I want to diagnose everything properly before I go through the pain of taking the starter motor off again. I am thinking that the culprit might be a band connection somewhere. Anyway, here's what I have tested so far:

For my first test I wanted to test for a bad ground, so I ran a jump lead from the trannie to the bolt where the ground strap connects to the chassis. Still no crank. So I hooked two jump leads together and ran them from the lower bolt securing the starter to the trannie all the way to the negative post on the battery. Still no crank. This suggests to me that I don't have an earth problem. Any thoughts on this? Do you think my jump leads themselves could have sufficient resistence to makes this an unreliable test?

For my second test I got under the car with a voltmeter, whilst my wife tried the ignition key in the car. I have listed my voltage readings below - I have used the terms "not cranking" to mean the ignition was off, and "cranking" meaning attempting cranking - i.e. ignition key on and in crank position. Of course in fact the starter wasn't actually cranking at all (which is my problem of course!).

Between live feed to solenoid (the constant live from battery), and earth (bottom of trannie):
not cranking: 12.11 volts
cranking: 0.42 volts

Between live feed to solenoid, and solenoid out to starter:
not cranking: 12.11 volts
cranking: 0 volts

Between solenoid out to starter, and earth (bottom of trannie):
cranking: 0.42 volts

Voltage across positive and negative battery posts:
not cranking: 12.11 volts
cranking: 11 volts

Do any of you have any suggestions what the above might suggest? The fact I am getting a drop in voltage at the solenoid from 12.11 volts to 0.42 volts when cranking, but the drop in volatage across the battery is only down to 11 volts, suggests to me that I have a bad connection between positive battery terminal and the solenoid somewhere, but could there be any of other problem which could cause such a voltage drop?

Also, does anyone have any suggestions on how to do proper voltage drop testing when the battery is in the trunk at the front of the car and the starter motor is under the car at the rear? I have an auto-electrics book which makes a big issue about voltage drop testing, which is all well and good in a front engined car when everything is in reach of eachother in the engine bay, but with a rear engined configuration most of that testing seems physically impossible!

Every time we attempt cranking by the way I can hear the solenoid give a loud click. Also, this is an intermittent problem - occasionally (although infrequently) the car cranks and starts fine (which scares the life out me if I am under the car with a voltmeter at the time!). When it does crank the starter motor spins the motor vigerously and the car starts instantly, just like it always used to (no labouring starter).

If any of you have any suggestions or advice about what might be problem, or what other tests I should try, I really would greatly appreciate it. I am new to such electrical diagnostics, but I am trying to learn and am keen to find out the correct way to identify this problem (as well as to actually fix the problem of course!).

Many thanks for your help.

[Joe Bob]

Whack the solenoid with a wrench.....it may not work but will make you feel better. Works with mine and my old 914/6s....

[CharlesJones]

Thanks for the suggestion, but I tried that, and whacking the starter. Alas, it didn't work!

[schumicat]

measure the voltage at the battery terminals. it should be 12.5 volts. It could just be your battery is weak. Next time it happens use a portable jump starter or jump start it to rule out the battery. What you describe is also a common failure mode for a starter (intermittent click but no crank that gets more and more frequent until it never works). I have had 2 starters fail that way in other cars. You just had it rebuilt but apparently it is not unheard of to have rebuilds that don't last.

[CharlesJones]

Yeah, I thought it might be the battery so tried a jump start with a battery giving out 12.6 volts, and I still get the same problem. However, if I jump start from a car running (reading about 14 volts across its battery terminals) my car starts fine. It's like the increase voltage from the assisting cars alternator is over-coming resistance somewhere. Perhaps if I do have a bad starter like you suggest as a possibility, then maybe the increased voltage is overcoming resistence in the starter motor itself.

[pete3799]

I still think this could a bad ground.
Clean the trans. to chassis ground.
My car did the intermittent start thing when i got it......cleaning the ground cured it.

[NOLAsc]

I think it was Warren Hall (Early S Man) who once suggested running a second ground from the body to one of the starter mount bolts. That's helped me.

Good luck.

Shawn

p.s. Joe Bob... my wife used to always kid me about the lug wrench on the solenoid trick in my 914 back when we were dating back in the 80s. She used to hold the key on start while I reached under the car to whack the thing. (Wait. That doesn't really sound quite right.)

[CharlesJones]

Thanks for the suggestions. Good point Pete - yes, I think I'm going to need to renew that ground strap no matter what - that seems so often to be the cause of problems that its sounds like its worth renewing as a matter of course when troubleshooting electrical issues.

After that I will attempt to do a proper voltage drop test on the ground side - between the starter ground and negative terminal of the battery. I think tomorrow I will fabricate some decent extensions for the voltmeter to make this possible, ending with crocodile clips. That way I should be able to make the voltmeter reach the battery for the voltage drop test.

If I find a bad ground despite renewing the ground strap I will try sticking in a second ground like you suggest Shawn - maybe the starter hasn't got a good ground anymore since I replaced it.

The fact the voltage is dropping to just half a volt at the solenoid when attempting to crank suggests there is high resistance somewhere in the circuit. Maybe this in the starter itself, in which I will need to pull the blasted thing off again. I think a voltage drop test will be the only way for the ascertain this for certain.

[CharlesJones]

Well, I found the cause of the problem, so I thought I'd update this thread in case anyone has similar issues.

To diagnose the problem I made up a couple of low-ampage extension leads for my volt meter, so that I would get the length I needed to do proper voltage drop testing despite the battery being in the front of the car and the starter underneath towards the back. I did this by simply attaching crocodile clip connectors to a couple of lengths of light 8amp wire, each of which were a few feet long. This gave me sufficient length to allow me to connect one wire to a battery terminal, the other to the point I am testing under the car, and then to have my voltmeter on the passenger seat next to me whilst I tried the ignition to takes the voltage drop reading.

What I found was that to my surprise I had little voltage drop on the earth side, just 0.7 volt, but I had a massive voltage drop on the positive side, which was nearly the full 12 volts. So I tried a voltage drop test near the battery positive terminal and found the same drop between the terminal connector and the very start of the cable which goes to the starter, just before the start of the insulation covering the wire. So I snipped the old connector off and fitted a new one, and hey presto, the starter would crank like crazy! Problem solved!

I think this highlights the importance of proper voltage drop testing, as opposed to just fitting new parts until a problem is fixed. I had already had my starter rebuilt because of mis-diagnosing the problem, and was ready to try a new battery before reading this forum made me think I ought to properly diagnose the problem. Heaven's knows how much trouble, time and expense if would have taken me to find the real issue if I hadn't read up about voltage drop testing.

I also gave each battery terminal and connector a liberal squirt of lithium grease, which should help prevent corrosion causing a similar problem in the future. I'm now just so much looking forward to being able to drive my car again with out needing a passenger all the time to help me with bump starts!

[xReddogx]

Charles,

I just wanted to take a moment to thank you for this post. I have been having the same problem with my SC and it has really been pissing me off. Took to a very trusted mechanic (former PCA tech chair) and had a new starter put in but have had the same problem. Then I removed the aftermarket alarm the PO had installed...thought it was fixed. Today at the supermarket had the same problem though. After sitting for 20 minutes fiddling with wires and connectors it fired up. I now know the issue and "just" have to track the bad connection down. Not a bad project for a weekend the wife is going to a baby shower out of town and leaving me with the "girlfriend" and a six pack.

By the way...I dont know what else can be more embarrassing than having one of these great cars and having to get a push start. In "these parts" I get sick of hearing "that's watcha get fur byin wun of dem fancy furin cars". (no insult to the south where I was born and raised...just to the "automotivelly discriminating ignorant")

Cheers and goodnight!

[grendiers]

It's amazing how a no-crank situation can have a myriad number of causes. Finding the source without throwing money at starters, DME relays, etc., causes one to lose ones mind, and wallet! Mine turned out to be an always 'on' power window relay. Didn't figure that out till I replaced starter, DME relay, which means I now have a spare, and countless hours of my time. Even the clock sucked the battery down if I didn't drive it much. I solved the problem by running a new wire to the number 86 relay terminal and to a key-on power source at fuse box. Also, in between time, I removed heater fan and jumpered the factory alarm. Arghghghghg!

[CharlesJones]

Yeah I agree, throwing money at a problem by replacing parts is the wrong approach. It seems to usually be something simple like a bad connection or dodgy relay, so careful diagnostics to find the real cause of the problem is the only way to go. Sometimes that's much easier said than done, but even then its still the only real way to fix the problem!

xReddogx, I am glad you found my post helpful. Your problem sounds exactly like my situation, so if you do the proper voltage drop diagnosis I am sure you will the fault. I expect it is just a simple bad connection like in my situation. I think the hardest part of the diagnosis is the fact that it is an intermittent problem. A couple of times when my car wouldn't crank whilst at home I'd jack it up and put it on axil stands, and get the voltmeter all attached ready to test, only to find when I do the test the car cranked and started straight away! Very annoying!

I understand completely what you mean about the embarrassing situation of not being able to start the car when in public. It wouldn't be anything like as embarrassing if it was an old VW or something, but a classic porsche gets much more attention and comment! I always dreaded buying petrol just incase the car would refuse to crank again, with someone behind me waiting to use the pumps! Not a nice situation to be in!