LS6 Powered Kraut-mobile - Electrical issues

[egon]

Ok, go ahead, flame away cause its not a Jeep. I figured I'd toss this one in here as we have some really sharp folks.

Here's the problem. The car will run fine, will get up to temp, fans go on. If you turn the car off it labors restarting. If it does start, any successive shut downs, the restarts are slower until the car won't crank at all.

1972 Porsche 914
LS6 - 500HP
GM ECU with custom tune
GM CS Style alternator
Recently rewired engine/ECU harness
Cabin wiring mostly Porsche
Partially rewired forward harness
Moroso HD switch and alternator relay
Twin Bosch GT3 fans up front
All grounds redone, several added
4 fuse blocks (2 rear, 1 front, 1 cabin) all can be isolated and are behind master switch
ECU memory is the only draw direct to the battery

There are no shorts, there are no drains, more then half the car has been rewired and many problems were fixed. Battery tested good. Alternator tested good. The car ran for several years without the alternator remote sense circuit connected. I recently hooked this up and the car ran perfectly, for 24 hours. Once the car is warmed up, it doesn't like to restart.

Any ideas?

--Matt

 

[vt98xj]

Sounds more like a fuel issue/heat soak rather then electrical to me.

 

[BIGSLVRXJ]

I can't help you on your problem but can you please post a picture of the Porsche? It sounds badass.

 

[Johnnie Walker]

This ^^

How hot do you exhaust mani's get? Does sound like a heat issue.

 

[egon]

I really don't think its a heat or fuel issue. Toss a charged battery in or jump start it and it fires right up.

--Matt

 

[egon]

...and some pictures as requested. The car belongs to a good friend of mine. I turn wrenches, fix, and fabricate stuff and he lets me autocross it, when it runs.

The Beast:

I don't have a recent engine bay pic:

yup, battery charger:

The NAC guys will recognize the trailer:

...and the gas can:

--Matt

 

[BIGSLVRXJ]

That is a thing of beauty! Thanks for posting the pictures, good luck with the troubleshooting.

 

[eflores]

...and the gas can:

--Matt

That is a thing of beauty! Thanks for posting the picture

i agree

 

[bluejeepkid]

How cclose is the exhaust to the starter? An overheated starter could give you that problem.

 

[egon]

From Monster Mopar via a PM:

Can't post in the section you posed your question but...

From what i took from your post it's a cranking issue and not a firing issue you are experiencing. Correct?

We thought there was an issue with heat and the starter. Installed a high torque starter, insulated, and rewired.

When you experience the problem what is your battery voltage?

12.5 - 13.5 ish

Once jump started I assume it runs normal?

Yes. Until you stall it or turn it off.

Does it start normally once cooled off? If you don't jump it that is

No

I'm leaning towards a heat soak issue into the starter causing loss of efficiency, may simply be because the starter is faulty or because the overall packaging not allowing sufficient cooling.

If your loosing battery power could be a similar issue with the alternator instead of the starter though.

The alternator bench tests good every time and for 24 hours after the remote sense circuit was hooked up, everything hooked fine.

This is nearly as much fun as troubleshooting a Renix FI issue.

--Matt

 

[egon]

How cclose is the exhaust to the starter? An overheated starter could give you that problem.

It's close, but not that close. It has a heat shield.

 

[Talyn]

Whats the voltage at the starter? Doe the engine block have a good ground?

I don't care for 914s, but that one is bad ass. Also, who coated the headers?

 

[egon]

Whats the voltage at the starter? Doe the engine block have a good ground?

I don't care for 914s, but that one is bad ass. Also, who coated the headers?

I've yet to check voltage at the starter when the issue arises, the heat shielding makes it tough. All the wiring to the starter is new and oversized. Can't remember the exact gauge though.

The block and trans have 4 grounds total, 2 @ 2 AWG and 2 @ 4 AWG.

Not sure who did those headers but I they were recoated after they cracked.

--Matt

 

[egon]

Another one from Monster Mopar via PM.

Saw your reply in your thread.

I would check your voltage at the starter as another member mentioned.

Also if you have a way of checking the starter amp draw while cranking (or trying to crank) i would highly recommend checking that. Do you have a multimeter with an amp clamp?

Next time I get up to the car I will certainly check voltage at the starter.

As for an amp meter, I don't have one, but should really find one at least to borrow for this issue.

--Matt

 

[egon]

Re: LS6 Powered Kraut-mobile - Electrical issues (updated 4-Oct)

Ok, I borrowed a 400 Amp ammeter and took some numbers on the starter feed.

Cold car, Optima Red Top, 2 years old, full charge: 200A-325A, no start

Cold car, Odyssey 680, brand new, full charge: 308A, sluggish start

Hot car, Odyssey: 225A-390A (pegged meter several times), no start

Warm car, Odyssey: 167A-401A (pegged meter several times), very sluggish start

Also, the electric fans kick in at 180*. 73A at start up, 25A running. They are Bosch units from a GT3. The fans run for 1 min after the ignition is turned off.

The starter is an IMI-101. I need to confirm the sub model number. 1.4kW/2.0HP, 4.44:1, Nippon Denso motor. http://www.hitorque.com/ProductDetails.asp?ProductCode=IMI-101N

Any thoughts? Thanks again guys.

--Matt

 

[foxwar71]

...and the gas can:

:worship: All hail the gas can!!

 

[egon]

:worship: All hail the gas can!!

It cures all ailments. Except this car.

Dammit Ross, have you nothing constructive to add?

--Matt

 

[egon]

From another PM:

I can't post in the advanced fab forums for some reason... But it occured to me, maybe its a battery issue. I am a shade tree mech but I have run into my fair share of battery issues and I am wondering if its a dead cell issue. Alternatively, what about the diode trio in your alternator? If you have intermittent failures with either the diodes or the battery they can manifest in weird eletrical gremilins. Just a couple thoughts...

-Keith

Well, Paul picked up another Redtop to have a go with that. The brand new Odyssey was having fits starting the car as I think the starer is drawing too much when hot, over 400 amps.

The alternator has tested good at least twice. If you have any other ways of testing it, I'm all ears.

Yup, the head scratching continues.

--Matt

 

[markw]

Ok, I assume slow crank. Can you get it on a rack or something and put a volt meter on the starter terminal when it's cranking? You may have 12.5-13.5 at the battery, but a badly crimped connection will present high resistance at high current draw while cranking.

I've had this with my big block Olds, the cable while it looked good, was corroded inside the connector.

If it's the cable which I suspect by the description of your problem, you can measure the voltage drop between the + terminal on the battery and the terminal on the starter. Hook a wire to the starter terminal, bring it up through the engine compartment to where you can get a meter on it and the battery and crank the car. There shouldn't be any voltage drop, if you are seeing a drop then it's the cable,cable ends, battery terminal...

 

[Andy in Pa.]

Ok, I assume slow crank. Can you get it on a rack or something and put a volt meter on the starter terminal when it's cranking? You may have 12.5-13.5 at the battery, but a badly crimped connection will present high resistance at high current draw while cranking.

I've had this with my big block Olds, the cable while it looked good, was corroded inside the connector.

If it's the cable which I suspect by the description of your problem, you can measure the voltage drop between the + terminal on the battery and the terminal on the starter. Hook a wire to the starter terminal, bring it up through the engine compartment to where you can get a meter on it and the battery and crank the car. There shouldn't be any voltage drop, if you are seeing a drop then it's the cable,cable ends, battery terminal...

To expand on this further, you'll only see that voltage drop when the car is cranking, or trying to crank. Its best to do this test with things cold, then do a comparative test when its hot. I had this problem with my 69 Camaro too. It was very hard to diagnose (cable was hooked up and tight, cable looked fine).