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Volvo 940 wont start.

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Old Apr 18th, 2018, 21:31   #21
aardvarkash10
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Originally Posted by Laird Scooby View Post
Another way of doing it is to download an oscilloscope "freeware" program and use an audio-USB interface to connect to the latop ...

Loads of options there for a "cheap" 'scope, some better than others!
Like this for example...

https://www.trademe.co.nz/electronic...8f8ee0ca31b1ce

Thats about 25 quid in the old money
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Old Apr 18th, 2018, 22:07   #22
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That's the sort of thing, yeah. Came up about £27 on ebay here when i saw one earlier.
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Old Apr 20th, 2018, 01:46   #23
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Hi all. I had another look earlier. Seems I have no spark on any leads? And also the fuel pump priming issue. Could these be ecu related?
Also do ecus differ from auto to manual.
I have two spare ecu's from same year but manual trans?

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Old Apr 20th, 2018, 04:28   #24
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The ignition system is linked to the ECU. So is the fuel system.

Do you have ANY test equipment?
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Old Apr 20th, 2018, 08:24   #25
Laird Scooby
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Hi all. I had another look earlier. Seems I have no spark on any leads? And also the fuel pump priming issue. Could these be ecu related?
Also do ecus differ from auto to manual.
I have two spare ecu's from same year but manual trans?
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I'd start checking for bad earths in that case.
Why was the car taken off the road in the first place? Was it playing up back then?
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Old Apr 20th, 2018, 10:34   #26
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Hi just to clarify, I'm trying to jump start from my land-rover defender which has a large battery and some decent jump leads. What I'm finding is that when I turn the ignition on( dash lights on) I hear the fuel pump Prime...... Go to start and just turns over. Then if I switch the ignition off and back on the fuel pump doesn't prime again...... So even if I put a new battery on it will only prime the first time I put the ignition on then never again unless I discon the battery????
What can stop the pump from priming? I've swapped relays and checked fuses.
Cheers Darren
Had this issue a few years back, an other member on the forum stated "no crank pulse no start", I fitted a new one and it fired up immediately, worth a try
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Old Apr 20th, 2018, 15:11   #27
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Had this issue a few years back, an other member on the forum stated "no crank pulse no start", I fitted a new one and it fired up immediately, worth a try
I was just wondering about that.
Crank sensor is on top of the bellhousing at back of engine. And directly below the non return valve for the screen washers. When the valve leaks, water can drip onto the crank sensor, which may not be a good thing. Also, follow the wires from the sensor to the plug connector, see if the connections are ok. The sensor is fixed to the bellhousing with a 10mm bolt, so it might be worth trying another one to see if it cures the problem.
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Old Apr 20th, 2018, 22:30   #28
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Hi all worth a try with crank sensor then?
The car was apparently running when laid up. Only have a voltmeter.
So would a crank sensor mess with fuel and spark?
How prone are ignition amplifiers to faulting? And would that cause this issue?
Cheers for the help guys
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Old Apr 20th, 2018, 23:18   #29
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Hi all worth a try with crank sensor then?
The car was apparently running when laid up. Only have a voltmeter.
So would a crank sensor mess with fuel and spark?
How prone are ignition amplifiers to faulting? And would that cause this issue?
Cheers for the help guys

It would be worth a try with a crank sensor from the point of view that they have a tendency to go sooner or later and even if it isn't the fault now, you'll have fixed it in advance of anything else.

However, it must be said (and i know if i don't say it, Ash will say it) that there isn't any substitute for proper, methodical diagnosis. You're a bit limited with only a voltmeter but there's still a fair bit you can do.

The ignition amplifier modules (hidden on the inner wing behind the L/H headlamp usually) can fail but will usually give some sort of indication of impending doom.

I think i'd start with checking all your fuses. Time to get the voltmeter out!

When you look at a fuse, you can normally see the tops of the two contact pins in the upper face.



You can see what i mean there, the silvery bits either side of the "10" on the upper face.

Connect your voltmeter black/-ve probe to a good earth point. Switch the ignition on and check both of those silver contacts on the top face of the fuse and you should have power on each. Repeat for all fuses in the fusebox.
You may find some aren't powered up such as certain lighting or other fuses but most should show a voltage with ignition on.

Renew any that are suspect.

After that, if you've found any blown fuses and replaced them, give it another try at starting.

If it still won't, re-check any fuses you've renewed.

See how you get on from there, may have to go down a couple of other fault finding routes but let's check the simple stuff first!

As for "The car was apparently running when laid up." - i believe you, i'm just not sure i belive the person who told you that!

Wouldn't be the first time someone has sold a non-runner and insisted it was running last time it was used.
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Old Apr 21st, 2018, 00:53   #30
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Its normal for 1997 to prime just once. It needs to be off for >10s before it will prime again. No idea why they did that its very annoying when diagnosing or opening the fuel system.

To check sparks, check that the rev counter is moving a little during cranking.

Priming once tends to mean fuel+relay is good.

If no rev counter flicker, then either crank sensor or ignition amp maybe.

Spark checkers (£16 in halfords) are handy to have.
If you have primed it once, turn off then on again quickly without starting, fuel pressure will still be up and ecu wont have had signal to say engine has actually ran.

My 740 did something similar, was the fuel pump relay.
Mines now bypassed with a standard 4 pin relay and car is so much better in every way, starts 1st compression cold or hot and doesnt randomnly take a break every so often!
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