Author Topic: Engine cut out at 2500 rpm  (Read 1126 times)

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Offline FNQ TRX

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Engine cut out at 2500 rpm
« on: Jul 29, 2014, 10:35PM »

Hi all

Have recently had the gearbox out to replace the clutch.

Went for a quick drive up and down the road and the speedo isnt working and when driving the engine begins to cut out (like hitting a rev limiter or something) at around 2500 rpm.  I thought the cutting out issues might be because the car was running out of fuel (guage was below empty) so I put 4 litres in - enough to turn off the fuel warning light however the engine cut out issue is still there.

I had a look at the speed sensor unit on the gearbox and the red and brown wires are broken - that explains why the speedo isnt working.... Must have pulled on them or been a bit rough on them getting the gearbox in and out.  I will get the wires soldered and try the sensor again, but is the speedo not working the reaosn why the engine would cut out?  Are the two issues likely related?

In reading a worksphop manual it suggests that if the ECU senses an air-flow meter malfunction the engine will not go past 2400 rpm - which seems to be what is happening - so is it likely that the speedo not working just happens to coincide with the failure in the air-flow meter?  And how easy (or expensive!) is it to fix / replace the air flow meter?

Any advice appreciated!
« Last Edit: Jul 29, 2014, 10:39PM by FNQ TRX »
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Offline squizz taylor

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Re: Engine cut out at 2500 rpm
« Reply #1 on: Jul 30, 2014, 06:30AM »
Whoa there turbo.

One thing at a time.

The broken speedo wire is all that it is. The U12 ECU requires a speed signal for certain functions to operate properly. If there is no speed signal, it goes into a limp home mode and will cut the engine at 2500 RPM.

Fix the wires for the speedo, and all the problems will be fixed.

Offline FNQ TRX

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Re: Engine cut out at 2500 rpm
« Reply #2 on: Jul 30, 2014, 08:17AM »
Thanks!

I will let you know how I get on.
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Offline noss

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Re: Engine cut out at 2500 rpm
« Reply #3 on: Jul 30, 2014, 09:45AM »
where are the wires broken? at the speedo sender (i.e. before the plug) or from the plug to the loom?

if on the sender side, i recommend you just replace the sender, you'll have to get one from a wrecker, i don't think you're limited to just u12s, don't forget there are ford corsairs as well but i believe a few other nissans of the same vintage have similar senders.

the problem with these is that you'll get oil and other crap on from the engine on the sender, right where the wires go into the unit gets quite weak and you can break them with the lightest touch. i imagine that because you've just done the clutch you've probably unwittingly broken the wires when you took the box off - i've been there done that.

sender shouldn't be more than $10 from a wrecker.

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Offline FNQ TRX

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Re: Engine cut out at 2500 rpm
« Reply #4 on: Jul 30, 2014, 07:53PM »
Hi all

I was cleaning the floor after moving the car out and came across an o-ring on the ground that looked suspiciously like the diameter of the air flow sensor shaft; so I pulled the air flow sensor off and had a look.  There isn't an o-ring groove at all, but I put the o-ring on the shaft (was a good fit...) screwed the air flow sensor in and then went for a quick drive - the engine cut-out issue seems to be gone! 

I have taken the speed sensor to an auto electrician mate to solder the wires.  I didn't think about getting a second hand part from a wrecker (good idea but!) as there are not many wreckers here in Cairns; and less that are likely to have Pintara or Corsair bits! 

So it looks like the engine cut out issue is related to the air flow sensor and not the speed sensor.  Thought I would share that bit of knowledge with you all.  Thanks for the input and suggestions.  Once I get the speed sensor in and installed I will post the results.  (The wires are broken right on the top of the speed sensor and not in the loom or at the speedo (as far as I know.....?!)
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Offline noss

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Re: Engine cut out at 2500 rpm
« Reply #5 on: Jul 30, 2014, 09:04PM »
interesting that it's working without the speedo!

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Offline FNQ TRX

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Re: Engine cut out at 2500 rpm
« Reply #6 on: Aug 1, 2014, 02:20PM »
Speedo fixed - solder on the two wires has done the job.  Clutch is done and the engine cut-out issues resolved.

This weekends job is to start on sorting out the holes in the exhaust pipe.  Muffler looks good, cant say the same for the pipe!  (Sounds good though...)
Old guy who should know better than to mess around with old cars.