740 poor running and stalling

[Laird Scooby]

Originally Posted by Beadybc

Yeah you're correct about the MoT part, completely forgot about that screw you mentioned before I was struggling to think of new ways to adjust the mixture. Cold start valve came up when searching for a fix but no where did it say how to test whether that was the problem so cheers for that.

Just to be clear, the test i suggested of simply disconnecting the electrical plug from the cold start injector is only a very simple test and won't cover all eventualities possible with it, however it should yield enough clues to help with the rest.

Hopefully it's something fairly simple from here, most likely is it started misfiring before it was laid up and has got worse since. They probably tweaked the mixture screw to get it through MoTs before that so it's running as rich as anything now. On my 760, i had similar (although that's LH-Jetronic) because my injectors were dirty. When i replaced them with some Vauxhall Omega V6 injectors (cross-referenced to the Bosch replacements for the OE injectors, then found the GM V6 used the same injectors!), the performance was vastly improved, however the idle CO shot up from ~1% to about 9%!

I tweaked the mixture screw on the MAF to get it back to where it should be and still had improved performance, response and economy, hence my suspicion about what's happened with yours.

[Beadybc]

Originally Posted by Laird Scooby

I suspect someone has played with the mixture adjusting screw on the fuel distributor to keep it running due to the clogging injectors. Also check the cold start injector isn't staying on past 8 seconds as that will flood the engine.

Bear in mind it could be burning off previous excess fuel from aborted start attempts.

As a first "go/no-go" test of the cold start injector, i would suggest getting it started from cold then pulling the plug off the cold start injector - squeeze the wire clip and pull the plug away from the injector at the same time.

If you locate the mixture screw on the fuel distributor, use an Allen key to make the mixture leaner once it's warmed up a bit until it sounds "happiest" once hot and idling. Bit of a Heath-Robinson method but should get you to a paoint where you are able to adjust the mixture in the MoT bay. Once you've done that, reconnecting the cold start injector plug will show whether it has a permanent feed or not, if it does, a quick solution would be to install a pushbutton switch on the cabin that you can press for cold starts and release once running.

I am guessing the important bit here is to get it MoT'd/drivable so while these methods aren't ideal, they will get you up and running and the rest can be sorted properly after you have that vital bit of paper from the MoT station.

Sorry I didn't notice earlier but the problem with this method is that the car is putting out an excess amount of fumes which fill the entire street pretty quick. Is there no possibility of adjusting the mixture screw whilst the car isn't running or is that going to cause further damage? The car doesn't idle and will eventually die so getting it warmed up is quite hard but if that is the only way then so be it.

[Laird Scooby]

Originally Posted by Beadybc

Sorry I didn't notice earlier but the problem with this method is that the car is putting out an excess amount of fumes which fill the entire street pretty quick. Is there no possibility of adjusting the mixture screw whilst the car isn't running or is that going to cause further damage? The car doesn't idle and will eventually die so getting it warmed up is quite hard but if that is the only way then so be it.

You could try turning the mixture screw anticlockwise one flat on the Allen key and then starting it. That should make it a bit leaner and reduce the fuems somewhat. As it warms up, you can tweak it anticlockwise a bit to keep the fumes down as it warms. If memory serves it's a 3mm Allen key you need.

[Beadybc]

Originally Posted by Laird Scooby

You could try turning the mixture screw anticlockwise one flat on the Allen key and then starting it. That should make it a bit leaner and reduce the fuems somewhat. As it warms up, you can tweak it anticlockwise a bit to keep the fumes down as it warms. If memory serves it's a 3mm Allen key you need.

Had a look into the tube where the screw sits and it was filled with a few mm of fuel, is this normal? I tried turning it but it's fixed solid so the 3mm allen key is just stripping the head. WD40 time or will warming up the engine first loosen it?

[Laird Scooby]

Originally Posted by Beadybc

Had a look into the tube where the screw sits and it was filled with a few mm of fuel, is this normal? I tried turning it but it's fixed solid so the 3mm allen key is just stripping the head. WD40 time or will warming it up first loosen it?

Shouldn't be any fuel in the tube, also the Allen key should turn it fairly easily.

I'm not a fan of WD40 as a penetrating fluid, i prefer a 50/50 mix of acetone and synthetic ATF. I'm wondering if it was in fact water that was in that tube and it's partially seized teh adjuster?

[Beadybc]

Originally Posted by Laird Scooby

Shouldn't be any fuel in the tube, also the Allen key should turn it fairly easily.

I'm not a fan of WD40 as a penetrating fluid, i prefer a 50/50 mix of acetone and synthetic ATF. I'm wondering if it was in fact water that was in that tube and it's partially seized teh adjuster?

The liquid was black and the inside of the tube is coated black also, probably was just dirty water though. I've seen you mention that mixture as a penetrating fluid in other threads, would you say that it works better than WD40?

[Laird Scooby]

Originally Posted by Beadybc

The liquid was black and the inside of the tube is coated black also, probably was just dirty water though. I've seen you mention that mixture as a penetrating fluid in other threads, would you say that it works better than WD40?

Definitely! I can't remember the lsat time i bought WD40 except once in my local fasteners place and there was a minimum charge of £5 for a card transaction. The nuts/bolts i was buying came to a couple of quid and i literally had no cash on me apart from two old £1 coins so i bought the nearest thing to hand which happened to be a small can of WD40 for about £3 to bring the total just over a fiver.

I put it in my "(Get me out of the) Sh!t Kit" toolbox and there it has stayed for the past 5 years or so!

[Beadybc]

Originally Posted by Laird Scooby

Definitely! I can't remember the lsat time i bought WD40 except once in my local fasteners place and there was a minimum charge of £5 for a card transaction. The nuts/bolts i was buying came to a couple of quid and i literally had no cash on me apart from two old £1 coins so i bought the nearest thing to hand which happened to be a small can of WD40 for about £3 to bring the total just over a fiver.

I put it in my "(Get me out of the) Sh!t Kit" toolbox and there it has stayed for the past 5 years or so!

I think this is definitely a “(Get me out of the) Sh!t” moment so I will use some to attempt to get that screw to turn slightly and will report back soon.

[Beadybc]

Originally Posted by Laird Scooby

Shouldn't be any fuel in the tube, also the Allen key should turn it fairly easily.

I'm not a fan of WD40 as a penetrating fluid, i prefer a 50/50 mix of acetone and synthetic ATF. I'm wondering if it was in fact water that was in that tube and it's partially seized teh adjuster?

Sadly I think that it was fuel that was covering the mixture adjustment screw, went outside and found a big puddle of fuel underneath the car. Traced the leak back to the air inlet hole of the air-flow sensor, took off the air hose quite a bit of fuel came out and this is what was left inside (image below). Does this mean that the plunger on the fuel distributor is no longer fuel tight and is leaking into the air-flow sensor?

[lynns hubby]

I'm not a fan of WD40 as a penetrating fluid, i prefer a 50/50 mix of acetone and synthetic ATF. I'm wondering if it was in fact water that was in that tube and it's partially seized teh adjuster?

Agreed. WD 40 is a water displacement and nothing else. Despite what it claims, people think its a magical cure for most things. If you use it to lubricate when things are moving then great. Plus gas is a penetrant/release agent or as Scooby says 50/50 of his magical mix is far better than WD 40