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940 LPT 2.3 problems starting in damp

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Old Aug 14th, 2019, 09:45   #141
Laird Scooby
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There was a typo in my email above, when I wrote 'I also tested the negative battery terminal to chassis ground' I meant to say I tested the positive battery terminal to the bolt at the end of the battery - body earth strap. Wouldn't you expect to see the same voltage here as between the battery terminals? Sorry - I'm confused to why the readings from positive to this ground would behave different to positive to other grounds in the engine. For example, with the engine off I measured 12.53V between the positive terminal and the each of the grounds at the rear of the engine bay.

I've checked the air filter I still need to replace the vacuum lines. I'm also going to reread this thread make a list of all the suggestions that have been made in this thread and work through any outstanding ones. For example, I still need to better check your method of engaging the starter once before cranking the engine fully again. I've done this once, but not directly after the hot start problem happens.
Did you recheck your voltmeter was still working after that test? Assuming it was, with bolts that have been on there for quite some time, you often have to use the point of the probe to scratch the head of the bolt to ensure good contact.

If you check batt +ve to engine block you should get the right (battery voltage) readings both running and not running.
Also if you check engine block to battery -ve with the engine running, it will show up as a small voltage if there is a bad connection.

Bit of a wild card thought crossed my mind. After switching the engine off, put your foot on the brake repeatedly and count how many pushes it takes before the pedal goes hard. Should be in the region of 4-5 pushes, any less and it might point to a problem.

Then keep your foot on the brake and maintaining an even pressure, start the engine and the pedal should sink slightly as the engine starts and builds vacuum. It should do this in a matter of a few seconds. If it takes longer or the engine is harder to start then i think we might be looking at the non-return valve in the servo hose.
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Old Aug 14th, 2019, 20:08   #142
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Yes the voltmeter was working afterwards - I've also used it again to check out your suggestions

With a lot of scraping off dirt I managed to measure the right voltage between the battery to chassis ground (cold and with engine running). It took a lot of tries and a lot of scraping though. For the first couple of tries it was a volt below the voltage between the terminals (hot and cold). When I scraped enough though I managed to get the correct readings. I'm wondering whether this ground might be worth cleaning up? The bits of the bolt that are still dirty and the ground cable itself still give much lower readings. Could it be that the dirt is acting as an insulator and making the ground ineffective? I did not have the same problem with the other engine grounds.

Reading between the engine block and -ve terminal of battery was - 0.02V with the engine running, is this the kind of low voltage that would indicate a bad ground ?

I tested the brake servo using your method and the pedal sank quickly - the engine was not harder to start.
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Old Aug 14th, 2019, 22:00   #143
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Reading between the engine block and -ve terminal of battery was - 0.02V with the engine running, is this the kind of low voltage that would indicate a bad ground ?

I tested the brake servo using your method and the pedal sank quickly - the engine was not harder to start.
Going from the engine block to the battery -ve tests everything in between, the voltage drop of 20mV (0.020V) is negligible and perfectly acceptable. In fact, i designed an electronic ammeter around this very fact, on the car i designed it for, at 70A discharge, there was a 70mV drop in the battery to fusebox lead which made my life easy for designing the circuit.

Anyway, i digress! When you tested the servo, how many pumps of the pedal did it take when you switched the engine off before the pedal went hard?
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Old Aug 15th, 2019, 09:02   #144
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Ah rats, well at least I know now that the grounds are good!

The pedal took 3-4 pushes to get hard. It didn't get completely hard. You could still push the pedal down a little way, but the pedal was noticeably a lot harder.

The car has actually been running better over the last couple of days - the gremlin is having a rest! I ran the tank quite low when running the injection the cleaner and the problems as the fuel got lower. Once I reached about half a tank full then I had to hold the accelerator whilst starting - this hadn't happened for a while although the engine had run rough sometimes.

Could there be old fuel at the bottom of the tank causing problems? Over the last couple of years I have been filling up at around half a tank because I don't trust the fuel guage.
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Old Aug 15th, 2019, 12:08   #145
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Ah rats, well at least I know now that the grounds are good!

The pedal took 3-4 pushes to get hard. It didn't get completely hard. You could still push the pedal down a little way, but the pedal was noticeably a lot harder.

The car has actually been running better over the last couple of days - the gremlin is having a rest! I ran the tank quite low when running the injection the cleaner and the problems as the fuel got lower. Once I reached about half a tank full then I had to hold the accelerator whilst starting - this hadn't happened for a while although the engine had run rough sometimes.

Could there be old fuel at the bottom of the tank causing problems? Over the last couple of years I have been filling up at around half a tank because I don't trust the fuel guage.
There's a very high chance there is water at the bottom of the tank. This will cause the problems you've got but i thought i had suggested a long time ago adding meths to the petrol tank. If it's down to 1/4 tank, add 2L of meths, if it's 1/2 a tank, add 4L of meths. Toolstation is about the best on price for meths :

https://www.toolstation.com/methylated-spirit/p99550

It will form an emulsion with the water and mix with the petrol allowing the water to be burned off. Ideally it needs to be in about 10% concentration meths:fuel so 2L of meths will treat 18L of fuel and so on. Any more is a waste, any less doesn't work properly.
However it's better to overdose than underdose.

Reminds me in fact, i need to do both of my beasts!
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Old Aug 15th, 2019, 23:36   #146
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Sadly I tried this twice earlier in the year and it didn't help. Thanks for the suggestion though - also, the car showed the same symptoms again earlier.

I also had to hold down the accelerator after starting the car when the engine was cold earlier in the weak to keep the engine running whilst the idle settled down, so it's not just a hot start problem
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Old Aug 16th, 2019, 00:07   #147
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May be worth trying again, just to eliminate it from the diagnosis.

Beginning to wonder about your fuel pumps to be honest. Not saying it is that, just wondering. Let me think a bit more on it.
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Old Aug 18th, 2019, 17:22   #148
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I cleaned the throttle body today (without the taking it off the car). I used a rag and some white spirit plus some throttle body cleaner. I plan to take the throttle body off and clean it more thoroughly when I get a new gasket.

First signs are positive, the car drove much better with the throttle body cleaned - so finger crossed.

I managed to break a small plastic part though on the throttle cable (not the linkage thankfully). I'm not sure what purposes it serves:

https://imgur.com/a/5IppPYn

Does anyone know what this piece of plastic does and whether it is worth worrying about?
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Old Aug 18th, 2019, 20:19   #149
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I cleaned the throttle body today (without the taking it off the car). I used a rag and some white spirit plus some throttle body cleaner. I plan to take the throttle body off and clean it more thoroughly when I get a new gasket.

First signs are positive, the car drove much better with the throttle body cleaned - so finger crossed.

I managed to break a small plastic part though on the throttle cable (not the linkage thankfully). I'm not sure what purposes it serves:

https://imgur.com/a/5IppPYn

Does anyone know what this piece of plastic does and whether it is worth worrying about?

If you buy "Carburettor & Air Intake Cleaner" with the nozzle/straw you won't need to remove the thorottle body or change the gasket.

Which part exactly have you broken, if it's the bit you've ringed it's difficult to break but probably won't cause any problems.
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Old Aug 19th, 2019, 09:38   #150
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That's the cleaner I used - I used white spirit at first then realised I had the right stuff in the shed

The plastic piece I broke is the black cone circles. Looks like it screws into the tube the throttle cable goes into behind it. I found a way of breaking it sadly - I can be a bit ham fisted sometimes
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