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Crank, no start, no tach bounce, but...
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GregSC  



Joined: 19 Jul 2008
Posts: 87
Location: Lovely, KY

PostPosted: Sat Apr 04, 2020 6:52 am    Post subject: Crank, no start, no tach bounce, but... Reply with quote

Hey all,
So I'm at my wits' end with a no start issue on my '81 931 and would love some direction. As the title states, it will crank (sometimes a little slower than others quite randomly), but not start. There is no tachometer bounce as I'm cranking and after reading multiple threads on here I figured it was the crank sensor. However, after testing its continuity and resistance it is in spec with findings posted here. Was relieved, but now a bit frustrated as I'm not sure where to turn next.

Bit of recent history, car was running, but since last spring has had intermittent starting issues, thought it was temperature related and had the WUR rebuilt, up until a few weeks ago if I cranked it enough it would eventually come to life but the last couple of weeks no amount of cranking brings it to life. I've replaced the plugs, distributor cap, rotor, coil, and checked plug wire resistance. I've also replaced the ignition control module on the left fender. Lastly, doing a few tests today, the coil checks good between 1 and 15, and 1 and 4, but I'm not getting any spark from the coil (used an ignition wire and plug connected to post 4 to try to get spark while cranking).

Admittedly I don't have much experience with a car's electrical system so any help will be much appreciated.
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1085
Location: Washington DC area

PostPosted: Sat Apr 04, 2020 11:58 am    Post subject: Reply with quote

I'd suggest that you make sure you have a goodly amount of voltage at the coil while cranking the engine.
My race car was starting fine when I parked it in the fall after the last race. In December, I took it to a shop in my trailer for some bodywork. It wouldn't start with my battery. The shop had a jumper box and it turned over a bit faster but still wouldn't start. I took it home, charged the battery and had the same problem. I put a separate battery on the coil and it started. It turns out that my starter motor was going bad and drew down the voltage below whatever the coil/computer/ignition assy needed. I replaced the starter motor and it starts fine with the battery in the car.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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palin  



Joined: 25 May 2017
Posts: 18
Location: Singapore

PostPosted: Sat Apr 04, 2020 2:31 pm    Post subject: Reply with quote

Sounds exactly like my situation. My 932 was running fine but I allowed it to sit for awhile till it canít start at all. It will crank but never starts. After a new ignition control module was plugged in with same result, my mechanic confirmed its more or less the crank sensor.

On advice of forum members, I even bought a E90 BMW crank sensor that was rumoured to fit but alas it donít. Thanks to Carrera RSR, I was introduced to Mittlemotor 123ignition distributor and just plonked it in, stripping out all related DITC parts. Now the car starts every time
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1970
Location: Somerset, UK

PostPosted: Sat Apr 04, 2020 8:41 pm    Post subject: Reply with quote

No idea if its your problem, but as above I had a starter going bad. It was probably just the solenoid but I bought a complete new unit. Couldnít believe how much faster it cranked over with the new starter. New versus 20-30+yr old starter was night and day.

When I start I turn the key enough to hear the fuel pumps prime for a few seconds. If not I keep toggling the key until it primes. Then I fully crank to start. I know then I have full fuel pressure and engine fires instantaneously.

Make sure the overboost switch is earthed properly. If not it cuts the FPR and you have no fuel pressure.

Letís hope its not the sensor
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1970
Location: Somerset, UK

PostPosted: Sat Apr 04, 2020 8:43 pm    Post subject: Reply with quote

palin wrote:
Thanks to Carrera RSR, I was introduced to Mittlemotor 123ignition distributor and just plonked it in, stripping out all related DITC parts. Now the car starts every time




Iíve just installed the new Bluetooth electronics for my dizzy. Fantastic service at Mittelmotor. Happy to help.
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252
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palin  



Joined: 25 May 2017
Posts: 18
Location: Singapore

PostPosted: Sat Apr 04, 2020 10:43 pm    Post subject: Reply with quote

Carrera RSR wrote:
palin wrote:
Thanks to Carrera RSR, I was introduced to Mittlemotor 123ignition distributor and just plonked it in, stripping out all related DITC parts. Now the car starts every time




Iíve just installed the new Bluetooth electronics for my dizzy. Fantastic service at Mittelmotor. Happy to help.


Nice! So you able to do some programming of the timing with a laptop over the air instead of plugging in?
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GregSC  



Joined: 19 Jul 2008
Posts: 87
Location: Lovely, KY

PostPosted: Sun Apr 05, 2020 2:49 am    Post subject: Reply with quote

First, thanks to everyone that's taken the time to post a reply, it's greatly appreciated.

Secondly, just got back in from attempting to gauge voltage getting to the coil as the vehicle is cranking. As I'd mentioned in my previous post I don't have much experience trying to diagnose electrical issues, so let me relay what I did and the results. I put one lead on the black/blue wire going to the coil and the other on the negative post of the battery. With the car not cranking I got battery voltage (over 12 volts), with the car cranking the voltage dropped to a little over 10 volts. This occurred with the black/blue wire going to the coil both connected and disconnected from the coil.

Perhaps this would indicate a faulty starter as Fifty50Plus mentioned? Is there anything else that I should check since I've gotten these results. I've already tested the crank sensor and it passed the continuity and resistance tests given in the Workshop manual and on this forum. Thanks again for any and all help!
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DootToot  



Joined: 31 Oct 2018
Posts: 6
Location: Australia

PostPosted: Sat Apr 11, 2020 6:50 pm    Post subject: Reply with quote

Had similar symptoms on my 931 when I got it, it ended up being an electrical grounding issue, and It was solved by adding an extra ground wire at the DITC. It sounds obvious but check you are getting 12V at the DITC unit.
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924RACR  



Joined: 29 Jul 2001
Posts: 8293
Location: Royal Oak, MI, USA

PostPosted: Sat Apr 11, 2020 9:45 pm    Post subject: info/link for Mittelmotor Reply with quote

Any link or similar detail on this Bluetooth distributor, beyond the base Mittelmotor website? Or do you just have to call them?

Just had a "new" late 931 owner in my area reach out to me yesterday, he's also possibly looking at a crank sensor failure, and this might end up being a good option... plus I'd like to know more about it.

Mine thankfully still works, at the moment, but I'll be installing a Microsquirt and eventually also switching the ignition over as well, but...

EDIT: Maybe this?
https://www.123ignition.de/123-ignition-en/ignition-distributor-porsche-924-usb-1.aspx
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Vaughan Scott
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'82 931 Plat. Silver
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1970
Location: Somerset, UK

PostPosted: Sat Apr 11, 2020 9:53 pm    Post subject: Re: info/link for Mittelmotor Reply with quote

924RACR wrote:
Any link or similar detail on this Bluetooth distributor, beyond the base Mittelmotor website? Or do you just have to call them?

Just had a "new" late 931 owner in my area reach out to me yesterday, he's also possibly looking at a crank sensor failure, and this might end up being a good option... plus I'd like to know more about it.

Mine thankfully still works, at the moment, but I'll be installing a Microsquirt and eventually also switching the ignition over as well, but...

EDIT: Maybe this?
https://www.123ignition.de/123-ignition-en/ignition-distributor-porsche-924-usb-1.aspx


What do you need to know Vaughn? Both MM and 123ignition websites have limited info. MM have created a 931/937 control board using 123 software and inserted in a stock dizzy housing so it looks oem. Bluetooth connection to iOS or android phones. However, once the right ignition advance / retard curves are keyed in itís unlikely you need to change for most users unless adding performance mods Such as IC etc.
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252
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924RACR  



Joined: 29 Jul 2001
Posts: 8293
Location: Royal Oak, MI, USA

PostPosted: Sun Apr 12, 2020 2:46 am    Post subject: Reply with quote

Primarily, I was hoping at least just to confirm that was the bit everyone was talking about...
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Vaughan Scott
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GregSC  



Joined: 19 Jul 2008
Posts: 87
Location: Lovely, KY

PostPosted: Wed Apr 29, 2020 12:32 am    Post subject: Reply with quote

Just wanted to circle back to this thread and let those interested and those that may stumble on this in the future know the resolution.

Thankfully, I did get the car started again! In fact, it's started for me the last few days without hesitation. I'd love to be able to tell you I did "such and such" and that was the definitive cure, but because I had a "should of had a V8" (drink, not the engine) moment right in the middle of my frustrated efforts to diagnose the issue, I can't.

What happen was this: During the middle of the testing of the ignition system I got to looking at how the plug wires were routed from the distributor to the plugs and in my mind it didn't look correct. I remember from work on my NA that the distributor housing timing mark pointed toward the steering wheel. Which, if that were the case with this car, would have meant that the plug wires were hooked up incorrectly. So, I rerouted the wires 1,3,4,2, and went on my way checking things with a multimeter and swapping components in and out, all with no success.

Now, during that time I did replace a few electrical connections (terminals, or whatever the proper name is for them). Specifically the two terminals that go to the negative side of the coil (belonging to green wires), and the terminal for the overboost switch. Upon inspection, the wires were exposed and a couple looked as though they were hanging on by a thread. I also replaced the main ground to the battery, and the terminal that hooks to the positive side of the battery. I did notice that after doing those few things I started to get tack bounce again. Of course, still no start at that time. During the course of all this I also took the starter off to get it tested (good) and cleaned the terminals down there. Finally, I took the 12 pin connector apart, checked those connections, and cleaned some minor corrosion off the small posts that the wires connect to.

After all this still no start, and most of you can figure why. It came to me that I might as well line all the timing marks up and see if there's anything wrong with the static timing. It was at that point I saw that my distributor timing mark was not where I assumed it was! So, rerouted the plug wires and...car fired up!

Sorry for the long post, hopefully it will be helpful to someone in the future. Thanks to everyone that offered advice, it was much appreciated!

Lastly, when I was checking the static timing I noticed that the camshaft mark was about a tooth and a half off when the crankshaft and distributor were lined up properly. How much of an issue is this? Should I take the timing belt off and line everything up perfectly?
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924RACR  



Joined: 29 Jul 2001
Posts: 8293
Location: Royal Oak, MI, USA

PostPosted: Wed Apr 29, 2020 1:23 am    Post subject: Reply with quote

That does seem suspect - but you are looking at the cam timing mark on the backside of the cam sprocket right? Cars will often run (though not well) if off one tooth on cam timing.

Stock factory setup has the rotor pointing at the rear-most intake manifold bolt at TDC - not so much at the steering wheel. Per the manual.

I did round up a spare damaged (wire snipped) S2 crank sensor at that last junkyard haul. No idea if it's still functional, but I aim to do some investigation into it, still want to see if it's possible to find a substitute...
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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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GregSC  



Joined: 19 Jul 2008
Posts: 87
Location: Lovely, KY

PostPosted: Wed Apr 29, 2020 10:22 am    Post subject: Reply with quote

Yeah, definitely the dot/indentation on the back of the cam sprocket, and that's about where the distributor timing mark is pointing on this 931. I thought that on my NA that it pointed toward the steering wheel, and thought I'd read that somewhere as well but could be wrong. Either way it was definitely incorrect for this car!

So, can/should I take the belt off and adjust the cam sprocket? How much wiggle room do I have before I risk damage to valves? The car does run, seemingly well, but I don't have experience with another turbo to compare it to.
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Wed Apr 29, 2020 9:17 pm    Post subject: Reply with quote

And, just to be clear, you're aligning the crank by the flywheel mark at the back?
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Vaughan Scott
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