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Starting issue LPT

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Old Apr 17th, 2018, 08:27   #1
skidje
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Default Starting issue LPT

Recently the 940 is not starting first attempt. On 2nd attempt it immediately starts and idles perfectly. Is the pump on its way out or does it loose pressure somewhere?

Input welcome. Thx Joseph
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Old Apr 17th, 2018, 08:56   #2
Laird Scooby
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It sounds as if it's the fuel pump relay. Try this little trick to see.

Switch ignition on (warning lights on but don't try starting)

Wait a couple of seconds

"Flick" the starter with the key (turn briefly to start position and release)

Wait a couple more seconds and hopefully you should hear the fuel pump run after flicking the starter for a second or two.

Without switching the ignition off, try starting again. If it immediately starts then the fuel pump relay is suspect.

However, it will only be the "priming circuit" that is suspect. You can continue to use the car for quite some time using this little trick.

In very simple terms, there are two separate relays inside the fuel pump relay that deliver power to the fuel pump. One only operates when the engine is turning over (either on the starter or when the injection ECU senses pulses from the ignition coil to tell it the engine is running) and the other operates in a priming capacity only.

The priming relay is operated by the ECU when the ignition is first switched on for between 1-2 seconds. It is meant to get the fuel pressure up in the fuel lines so when you turn the key to start, full pressure is available for the injection process.

It sounds as if the priming function is missing. My method above will confirm and get round it.
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Old Apr 17th, 2018, 09:32   #3
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Thx Dave, guess a spare relay can be sourced easily from a scrap car. But will try above procedure first to have your expectations confirmed. Thx again. Joseph
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Old Apr 17th, 2018, 10:02   #4
Laird Scooby
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You're welcome Joseph - if that procedure works there's no reasn why you couldn't just adopt that procedure and save a few Euros on a replacement relay.

It's a false economy fitting a secondhand one, you don't know for example if the car was scrapped because it had a starting or running problem because of the fuel pump relay.

New ones aren't that expensive if you go for aftermarket.

Also if you're any good with a soldering iron, there's every chance you could repair it yourself, a lot of fuel pump relay problems are caused by poor quality solder inflicted on the electronics industry in the late 80s/early 90s to prevent factory operatives inhaling fumes from traditional solder. It meant the removal of lead from a lot of solder so over time the joints became brittle and went dry.

The cure is to wet the joint with a little more solder, remove the solder from the joint with a solder sucker/desoldering pump then resolder with new solder and if you wish, a little extra flux just to clean things up.

Once all the relevant joints have been serviced in this way, clean the PCB with a brass (soft) bristled wire brush and isopropyl alcohol (IPA) to remove all traces of the flux and resultant sticky residue.
If you want to go all the way, once it is cleaned, give the printed/soldered side a coat of clear lacquer to protect it.
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Old Apr 17th, 2018, 13:05   #5
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yes the re-soldering of the relais already crossed my mind. Will let you know the outcome soon.

would these fuel-relais be the same as the 240 models?

thx again Dave. All the best... Joseph
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Old Apr 17th, 2018, 13:24   #6
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Quote:
Originally Posted by skidje View Post
would these fuel-relais be the same as the 240 models?
I'm not sure Joseph - best idea would be to get the part number from your 940 and do a search online.
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Old Apr 18th, 2018, 08:25   #7
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Seems the LH jetronic 200/700/900 al use the same relais. The universal one at Skandix costs around 20 gbp. (Volvo partnr 3523608) Ebay shows them even cheaper.

My son confirmed last night whilst following above procedure that the car started first attempt. so seems the relais is the cause.
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Old Apr 18th, 2018, 11:46   #8
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That's good news Joseph - you now have a choice. Either live with it as it is, use that procedure for a quicker start, repair your relay or buy a new one.

I've been using that procedure for about 18 months on my current 760 and about 2 years on my last 740 so it can be used long term if you like.
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Old Jun 3rd, 2018, 17:46   #9
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Default After changing fuelrelais and fuel pump starting issue rema

Still need by default 3 attempts to make it run. Perfect at idle.
But when the 940 starts at idle it runs perfect. Best to stay away from gaspedal since that makes starting more difficult.....
Is it an idea cleaning the injectors and changing the pressure regulator?
Is the ECU confused with wrong temperature sensor signals? Need for changing the one for the coolant?
Any input appreciated..

Note: the volvo runs LPI / LPG and when running it we do not have any issues. When running petrol it tends to stalk after a while but this doesn't explain the starting issue.
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Old Jun 3rd, 2018, 18:11   #10
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Maybe not but gives a good clue - have you tried adding 2L of methylated spirits to the fuel tank? Make sure there is at the most 18L of petrol in it as you need the meths to be at least 10% concentration in the petrol to do any good.

From what you're saying it sounds like condensation in the tank.

My Rover 827 Coupé, also LPG converted started giving similar symptoms then misfiring on petrol only.

Filled two 5L cans with petrol and got 2L of meths, ran it on petrol until it was out then stopped, added the first can of petrol, added the meths into the now empty can, added a couple of litres of petrol from the full can, emptied this into the tank and then added the remainder from the second can. Drove to the nearest filling station (by which time it was behaving better already) and added another 9L of petrol.

Switched the LPG switch back to auto-changeover to gas and drove it normally - starting much better and no more missing on petrol.
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