'86.5 slow-cranking 928 race car.

[MarkRobinson]

Wierd, my race car (stock engine currently installed) has very slow cranking when starting.

Ruling out things, I've tried the following:
-Newer starter vs lightweight starter: no change (both work great on my nice 928)
-1050cca battery vs 850cca battery: no change
-new 2ga battery, ground straps, even directly to starter: no change.

I wouldn't suspect that the signal wire to "start" from the ignition relay could have any effect as all I feel it does is "signal" the starter to engage: the speed of the starter is related to its power, load, and voltage: all of which are covered by my "ruling out" above.

Any thoughts??

[Mrmerlin]

Is this a 5 speed or auto?
If a 5 speed is the clutch disengaged fully are the TT bearings going bad?
Have you tried to turn the driveshaft with the clutch pushed in?
do this in gear see if the clutch and drive line are free
If an auto has the flex plate check been done?

Have you check the connections at the 14 pin connector above the hot post?
Look for corroded wires, Is the ground wire clean and tight at the engine block and chassis as well as both of the battery terminals clean?
did you try adding a jumper cable to the negative terminal and then to one of the shock mount bolts ,
could be a bad ground cable from the battery.

Are the big red wires that connect to the alternator and the starter and the hot post all clean and tight

[MarkRobinson]

5-speed, Y, N, rebuilt TT & trans, spins freely with clutch disengaged.

Y, Y, No, will try another jumper ground tonight. Tried a ground directly from the battery to the starter bolt (on the 1050cca battery, no change), but not to the car yet.

Mark

[Pete R]

Are you running a thick oil like a 60 weight for racing? That will bog down a starter when cold

[MarkRobinson]

Not yet, stock "flush it out" oil: 20/50 dinsaur poop.

[Danglerb]

Freshly assembled motor?

YIPES.

[MarkRobinson]

freshly assembled? No.

Stock shortblock (not-disassembled), fresh valve job, turns over by hand as easy as any 32v I've freshened/built before. STock compression, valve springs, etc.

Mark

[Danglerb]

Does it start?

Maybe try a total bypass, jumper cables to the starter and use a remote start button.

[MarkRobinson]

oh yes, runs & drives, just cranks at about 40% what my red turbo 928 does. I tried a pair of 24" 2-gauge cables (new) from the battery under the starter, to the starter directly, no change in cranking.

I'm beginning to wonder if all the grounds on the car, including the main ground at the battery, are connected through the unibody via one cable. I plan to run a ground back to that point & see if that changes anything. I also plan to re-make the main engine ground strap, though I have the two other grounds (at the coils-to-heads) that are fresh...still scratching my head.

Mark

[riber.bentsen]

Maybe your chassis got tired of carrying the ground and gave up?
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[1982_928]

This is more than likely not it, but if it has a blown head gasket and has water in a cylinder, having to compress it and push it out would make it crank slowly. But then again, it would push it all out the first crank, or put a rod through the block... Its probably a power issue

Put the battery beside the car and go directly from the battery to the starter with some jumper cables (Jumper box would be even better), if you haven't already done so..

[Danglerb]

Originally Posted by MarkRobinson

o
I'm beginning to wonder if all the grounds on the car, including the main ground at the battery, are connected through the unibody via one cable.

Ground strap from battery to unibody, and EVERYTHING through the unibody to the various ground points and straps to local devices.

914's used to have an issue when warm that the resistance through the block to the body ground would be too high, and solution was a direct ground to the starter from the battery.

[924CarreraGTP]

My '84 does this too with Castrol 20/50. I just changed my '83 to Castrol 20/50 and it's now doing the same thing. Verify that your battery is NEW and it might make the issue a little bit better. There also may be a slight current draw from somewhere. It's probably a symptom of cold weather and thick oil. If they start once and warm up, they start at full power the rest of the day. Is this what happens with your car?

[Danglerb]

I "think" the 86 needs one revolution of the crank to "wake up and sync", but I don't recall if speed is very critical.

Small drains, even bigger ones like leaving on headlights, are tiny compared to the starter drawing maybe 200 amps or more. Say Mark, any chance you have a DC clamp meter to measure the starting current? Even starting voltage would likely point a finger at something (measure at the batter posts and at the starter terminals).

I have a set of LoadPro test leads and a cheap Craftsman DC clamp meter that would sort this out in minutes, bring it by if you are in Orange.

[tmpusfugit]

Timing way advanced?

[MarkRobinson]

hot or cold, 20/50 oil is used in all my cars, have not tried a jumper box lately, will do so again. Timing is stock as it cannot be changed without the Sharktuner (haven't done so yet).

Motor is fresh, fluids are perfect, compression/leakdown are excellent, compression, cams, bore/stroke are all stock. I do need to measure the amp draw.

Total race car: battery powers engine only: all other electronics besides new gauges have been removed.

[txhokie4life]

Mark,

Preaching to the expert here.....
If you do get it started and let it warm up to temp (oil).
If you shut it off -- is it still slow cranking? (isolate temperature as factor)

Another factor might be to watch the voltage drop in the two cases. V=IR,
so if you can't measure I, you can infer it by looking at the voltage at
the 14pin post while cranking (or any other convenient power point). This might not tell you
why -- but will tell you the starter is working harder or you have that you have a high resistance.

you could also measure the resistance of both power and ground to/from battery to starter
and compare to your "nice" 928.

I'm using 20/50 in my '82 Euro -- new Battery -- but I haven't completed
my ground cleanings and even when cold I fire up pretty good.
Usually 2 revolutions at most and she ignites.
Haven't observed actual voltage when cranking tho.

Mike

[MarkRobinson]

Yes, even when warmed up, still slow to crank. Cold or hot air, cold or hot engine, all the same.

Strong battery vs weak, thicker battery cables vs thinner: all the same.

Voltage checking: need to do for sure. Cleaned the 14 pin, all grounds have been polished (wire & plate recessed into the chassis). My battery ground is NOT to a factory-intended grounding point, but to a plate on my roll cage: wonder if that could be it?

However, I have tried the 1050cca battery linked directly to the starter, which should bypass this.

Mark

[MPDano]

Hey Mark,

You have two 928's, have you tried to hand crank your 86.5 with and without plugs? Sounds like a tight engine. I dunno, just throwing stuff out there.

[txhokie4life]

Doesn't sound like the oil.

Measure the resistance between your battery and your starter.
Compare the to your street car.

After that ??? -- measure the torque required to turn the crank, maybe something is binding up?
Hate to suggest to pull the plugs on both and compare.....

maybe disengage the tranny (just cause it's easier than pulling the clutch)
and see if that helps.

m