Overheated 940 won't re-start

[Othen]

Originally Posted by mv10tc

thanks, the first thing I did check fuel pump fuse (1), it is Ok, will try for hot start, but keeping foot away from pedal does it.
Changing head gasket is expensive job, I had some preliminary over the phone quotes up to £800.

It is nice to see a 12 year old thread revived!

This doesn't particularly sound like a head gasket - the intermittent starting would seem more like a sensor somewhere. See if you can borrow a compression tester (or buy one, they are not expensive) - that will quickly show whether there is an issue with the cylinder head gasket.

If it does need a new head gasket than that is a job you could easily do yourself for a great deal less than £800. I'm guessing this is a red block engine, so the gasket will be around £40, the rest is just normal tools and stuff. If you do it then it would be sensible to change the rocker box gasket (£5), cam belt (£25) and idler (£20) at the same time.

Good fortune,

Alan

[mv10tc]

Hi all
Tony:” Red light in the fuel gauge? This is a reserve indicator for the fuel level. as far as I am aware its not any indication of pump or pressure level. “
Tony you are correct, I was wrong, as I got it from someone few years back.
Othen thanks for suggestions, yes it is red engine block, had the car for just about 25 out of its 30 years, so hate to give it away for scrap. Agree, it is worth doing things you listed.
Here is latest report:
- there was spark but intermittent and flash in the test lamp wasn’t particularly bright, tested only on 2 out of 4 cylinders.
I suspected that ‘ignition amplifier’ connectors may be problem since lot of hot water was squirted over air filter box, and this module is behind it. Took it off soaked all connections with contact cleaner, cleaned both plates, put lot of thermal compound (normally used for high quality components in computers), put everything back, good regular flash from test lamp, but still no ignition.
- did a smell test on two of the spark plugs (tips are brownish grey colour), there is smell of petrol but not particularly strong.
- Eventually managed to pull off fuel line from fuel pressure regulator on the pump side, some fuel came out but not as much as I expected.
Could not disconnect the other side that supplies injectors rail.
The above would suggest fuel supply problem, pump or injectors pulses failure.
Tried to trace harness with injector cables but it disappears somewhere under and behind back of the engine.
Don’t understand why either of two would go bad if engine overheated for short period.

[Laird Scooby]

I'd investigate your CPS (Crank Position Sensor) if i were you. Also remove, clean and re-gap the spark plugs to 0.65-0.7mm and also check the carbon brush inside the distributor cap to make sure it hasn't broken or simply fallen out.

Which hose did you pull off the fuel pressure regualtor? You can only remove two, one is the return to tank (~8mm bore) and the other is a small vacuum hose (~4mm bore) - if it was the latter and you got petrol out of it the FPR is knackered.

[940volvoman]

When I had this problem on my 940 estate i went straight for the crank position sensor following guidance from people on here. Its a bit difficult to access,but it solved the problem

Shaun

[TonyS9]

Without crank position you won't get any sparks.

Have you checked the distributor for water causing a weak spark?

When it started did you have trouble reving it up or accelerating?

[mv10tc]

Hi Tony, You may not have seen my 'report' at further above where I said
Here is latest report:
- there was spark but intermittent and flash in the test lamp wasn’t particularly bright, tested only on 2 out of 4 cylinders.
I suspected that ‘ignition amplifier’ connectors may be problem since lot of hot water was squirted over air filter box, and this module is behind it. Took it off soaked all connections with contact cleaner, cleaned both plates, put lot of thermal compound (normally used for high quality components in computers), put everything back, good regular flash from test lamp, but still no ignition.

Judging by your comment I would assume that 'crank position sensor' might be OK.
Next step, disconnected battery, then shorted + & - leads with key left in ignition for about 15 min in II then III, will check sometime tomorrow if the draining ECU makes any difference.
Have you any idea where about is ECU earthing on 940. automatic, non turbo non AC. If 'earth' is bad, starter would take voltage down to the rest, with further drop on the earth connection and ECU may not operate as expected.

Hi Scooby,
Vacuum side is fine, it is the long fuel (possibly return ?) line going to the side of the engine going back towards fuel reservoir, that had a bit of fuel in it.

[Familyman 90]

Lots of assumptions here.

Bottom line is its been overheated, and is now difficult to start. With persistence it might start, but runs only a few seconds. These are classic symptoms of a cooked engine.

Go back to the beginning.

Check the compression. Every likelihood your quest will end there.

Then check the fuelling.

Then check the sparks.

The scattergun approach won't get you anywhere, but seeing as the thread is over a decade old you probably know that by now.

[mv10tc]

Hi Familyman
It run at least on 4 occasions (got it back home ok, went for a shop next day) and 2-3 stationary runs (one for Radweld work) and on tests for about 5-10 min to see how engine temp is rising, I had very smooth idling (possibly best for long time) but at higher revs than usual. If there is a serious compression problem on one or more cylinders I would expect very rough idling.

[mv10tc]

Hi all
PROBLEM SORTED !
BAD EARTH ON ECU
Will be going slowly through as many earth connections as I can find.
Thank you all for valuable advice.