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931 S2 cuts off @ 5800 rpm
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ideola  



Joined: 01 Oct 2004
Posts: 15501
Location: Woodstock IL

PostPosted: Thu Jul 06, 2017 1:31 am    Post subject: Reply with quote

There is no information at all that I can find on what the DITC does with rev limiting. However, it is conceivable that if the different pre-programmed maps can do things like timing retard, they may also have different rev limits that kick in when different conditions exist. If your engine is running hot, maybe it's causing a different map with a different rev limit to be selected.

I would want to figure out why the engine is running too hot first. Maybe if you get that sorted, the rev limit problem goes away. First thing I would do is double check coolant bleeding, ensure there are no air pockets in the system. Make sure to bleed system with heater controls set to full heat. Make sure the vent line isn't plugged, and make sure you have a fresh cap on the expansion tank.

Have you swapped in the colder-range thermostat and fan temperature switch? If not, you should definitely do that. I also like running a bottle of water wetter.

Try running colder plugs.

You still haven't indicated what boost pressure you're running. I would set that back stock level, and possibly consider eliminating the boost controller (are you sure it's installed the correct way? maybe you're overboosting and don't know it???). The best way to plumb the boost gauge is to tee into the line that is also feeding the DITC, this way your gauge is showing you exactly the same signal as the DITC is seeing.
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1005
Location: The Netherlands

PostPosted: Thu Jul 06, 2017 2:10 am    Post subject: Reply with quote

I got a 80c celcius themostat and low temp sender

Boost was already turned back to +/- 0,65 bar
I will T it in the DITC line (now it is just before the intercooler)

AFR is set to 14.7/15 @ idle, under boost is is around 11

Spark plugs I did change, previous engine it was NGK racing, now Bosch, I will search for the numbers
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937 trackday car
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951S turbo and intercooler
937 DITC
Fast road camshaft
Forge recirculation valve + boost controller
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ideola  



Joined: 01 Oct 2004
Posts: 15501
Location: Woodstock IL

PostPosted: Thu Jul 06, 2017 3:59 am    Post subject: Reply with quote

Dutch924-racer wrote:
Boost was already turned back to +/- 0,65 bar
I will T it in the DITC line (now it is just before the intercooler)

So, just before intercooler, you mean pre-throttle body but post turbo charger...yeah, that's an issue. You need to read boost from the inlet manifold.

But I would still be very concerned about the running hot issue. I think that is a bigger concern right now...fix that and then let's see what's going on with the RPM cut out.
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1005
Location: The Netherlands

PostPosted: Thu Jul 06, 2017 6:21 am    Post subject: Reply with quote

the running hot and ignition problem could be related.

The cooling system hasn't changed I only changed the coolant cap of the reservoir. It was 150kpa and changed it for a 100kpa. I will swap it back to rull it out.

So far thanks for all the advice, got enough to do now

14 juli is a trackday, hopefully I get it fixed before that date.


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937 trackday car
Series 2 engine
951S turbo and intercooler
937 DITC
Fast road camshaft
Forge recirculation valve + boost controller
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1005
Location: The Netherlands

PostPosted: Fri Jul 07, 2017 2:45 am    Post subject: Reply with quote

Just another test day, replaced the DITC sensor, still the same problem, cuts of @ 5800 and the tacho bounces down and then up again at that moment.

The cut off is not temperature related, the coolant gauge was just in the middle at that moment.

I haven't changed the spark plugs yet but they can't be the problem of this cut off.

I don't have a spare coil, so have to buy a new one.
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937 trackday car
Series 2 engine
951S turbo and intercooler
937 DITC
Fast road camshaft
Forge recirculation valve + boost controller


Last edited by Dutch924-racer on Fri Jul 07, 2017 5:22 am; edited 1 time in total
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Cédric  



Joined: 27 Aug 2004
Posts: 1732
Location: Sweden

PostPosted: Fri Jul 07, 2017 3:24 am    Post subject: Reply with quote

When i had ignition module problems the tach bounced alot and i got ignition issues, but it was much more random, its super cheap to replace. Do you have a spare ditc box?
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1005
Location: The Netherlands

PostPosted: Fri Jul 07, 2017 5:05 am    Post subject: Reply with quote

All the ignition parts have now been swapped for good working components, except from the coil en ignition leads. Makes no difference.



1 — Timing control unit

4 — Temperature sensor

5 — Throttle switch (tested not swapped)

6 — Flywheel sensor

9 — Ignition control unit
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937 trackday car
Series 2 engine
951S turbo and intercooler
937 DITC
Fast road camshaft
Forge recirculation valve + boost controller
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morghen  



Joined: 21 Jan 2005
Posts: 7858
Location: Romania

PostPosted: Fri Jul 07, 2017 11:14 pm    Post subject: Reply with quote

How does the limiting sound? do you have a video?
Is your tacho working right...?
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1565
Location: Somerset, UK

PostPosted: Sat Jul 08, 2017 2:23 am    Post subject: Reply with quote

When the FPR cuts fuel its quite a violent end to the revs. Almost a large backfire and complete engine shut down. I've experienced this with the overboost switch before earthing it out/disconnecting the switch

Never hit an electronic rev limit/fault to know what this is like whether its softer or not to the FPR cut out

If the tacho fails, its usually a connection from coil to FPR. They share the feed to tacho with a green(?) wire
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1005
Location: The Netherlands

PostPosted: Sat Jul 08, 2017 7:02 am    Post subject: Reply with quote

morghen wrote:
How does the limiting sound? do you have a video?
Is your tacho working right...?


Tacho works right I already swapt it with another one.

It feels/sounds like a rev limiter.

Tomorrow I am going to look in the wiring of the DICT/ fuel system.

Does the DITC box itself needs to be grounded ?

Spark plugs in the old engine where NGK B8EGV Gold Palladium. Now I run Bosch 0 241 256 517 double platina
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937 trackday car
Series 2 engine
951S turbo and intercooler
937 DITC
Fast road camshaft
Forge recirculation valve + boost controller
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ideola  



Joined: 01 Oct 2004
Posts: 15501
Location: Woodstock IL

PostPosted: Sat Jul 08, 2017 7:37 am    Post subject: Reply with quote

Plugs should have nothing to do with it. I think there is a rev limiter in the DITC, and you have somehow gotten stuck on a rev-limited map. Maybe it's in some default / limp mode, or one of your sensors is telling it something that makes it revert to a rev-limited map. If it were an intermittent wiring fault within the FPR circuit, it would be highly unlikely for it to consistently cut out right at 5800 RPM.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1565
Location: Somerset, UK

PostPosted: Sat Jul 08, 2017 10:32 am    Post subject: Reply with quote

Just a note, I've been running NGK iridium BR10EIX plugs for the last year after ditching the the 8's. colder plugs have been running fine on higher boost for me. But as Dan mentioned, don't believe your problem here is plug related. But colder plugs wil help cool the combustion a touch.
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1005
Location: The Netherlands

PostPosted: Sat Jul 08, 2017 4:50 pm    Post subject: Reply with quote

ideola wrote:
Plugs should have nothing to do with it. I think there is a rev limiter in the DITC, and you have somehow gotten stuck on a rev-limited map. Maybe it's in some default / limp mode, or one of your sensors is telling it something that makes it revert to a rev-limited map. If it were an intermittent wiring fault within the FPR circuit, it would be highly unlikely for it to consistently cut out right at 5800 RPM.


I also swapped the the DITC so the problem is not in the DITC. Could be the wiring or the cut off sensor or the temperature sensor.
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937 trackday car
Series 2 engine
951S turbo and intercooler
937 DITC
Fast road camshaft
Forge recirculation valve + boost controller
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ideola  



Joined: 01 Oct 2004
Posts: 15501
Location: Woodstock IL

PostPosted: Sat Jul 08, 2017 6:12 pm    Post subject: Reply with quote

I think maybe you're missing my point.

What if the DITC has a map specifically for limp home condition; and what if there is something about your configuration that is triggering that map?

This assumes, of course, that there is a rev limit in the DITC, which as discussed earlier has been hypothesized in several of the historic threads I've perused, but not conclusively confirmed. The FSM and all of the supplements I have say nothing about rev limiting in the DITC or elsewhere.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1565
Location: Somerset, UK

PostPosted: Sat Jul 08, 2017 7:26 pm    Post subject: Reply with quote

Is the rev limit a hard cut off or just that the motor feels strangled at the top end? I hardly ever get to 5800 as my motor starts to feel less effective. All the boost/torque is at 3000-5000 rpm. All starts to tail off over 5000.
You havent mentioned what boost you are running?
Forge bov are known to leak boost if the spring is too soft
Is the rev limit electrical or fuel related?
I had a bad fuel filter once which wouldn't allow my motor to rev over 5000rpm. Flow was too restrictive
An advanced cam has great low end pick up but the motor struggles at the top end. A retarded cam has slow pick up but great top end ability. One tooth out does make a difference

Is your fast idle and rev limitation connected?
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
Now www.924board.org/viewtopic.php?t=34690
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