Misfiring in very hot weather.

[Offgrid]

Cinders ( 740 saloon with 2.3 n/a engine) is misfiring slightly after being parked in strong sunlight. I'm guessing that the fault may be with the ignition. Does heat weaken the insulation on the plug leads? I haven't had a chance to check for a corona on the leads when it gets dark, there are too many street lamps where I park it. Could there be a similar weakeness with some other ignition component, or am I completely on the wrong tack thinking it is an ignition fault.

[john.wigley]

Is your 744 carburetor fed or fuel injection, 'Offgrid'? I have had both in the past and have experienced this phenomena with some carburetor equipped versions. Also on earlier cars - 140s and 240s - if carburetor fed (and the majority were).

It may also be accompanied by a reluctance to restart after having been switched off for a brief period - say when popping into a shop or stopping for a quick comfort break. It will start - just requires rather more cranking than usual. It is due to fuel vapourisation and the symptoms normally abate as the engine cools down.

Regards, John.

[Offgrid]

Sorry I forgot to say. Its injected.
No problems restarting, or if it is parked in the shade

[john.wigley]

Originally Posted by Offgrid

Sorry I forgot to say. Its injected.
No problems restarting, or if it is parked in the shade

In that case, you're probably right; it is most likely to be electrical.

Having said that, as they are designed to be in close proximity to engine heat, I would expect the HT leads to be unaffected by ambient temperatures, no matter how high. Could be they are breaking down internally due to age and the recent higher than normal ambient temperatures are exacerbating the problem.

I would think that more likely than an issue with insulation.

Regards, John.

[Laird Scooby]

Originally Posted by Offgrid

Sorry I forgot to say. Its injected.
No problems restarting, or if it is parked in the shade

Electronic or mechanical injection?

[Offgrid]

The engine is a B230E which came from a 1986 240. I'll need to check to see if it is electronic, sorry I should know that. The coolant guage is at the mid point, and I seem to remember it was normally a bit lower than that. I did a Google search foir general causes of this problem, and it suggested that one reason is a failing coolant temperature sensor. The coolant level is at max, and there are no signs of any leaks or fluid loss, although I did top it up a fedw days ago. I only added a minimal amount of water. It's got a viscous ffan driven by the engine, and I'm wondering if I should replace that with an electric one. Does that improve fuel consumption by much?

[Laird Scooby]

Originally Posted by Offgrid

The engine is a B230E which came from a 1986 240. I'll need to check to see if it is electronic, sorry I should know that. The coolant guage is at the mid point, and I seem to remember it was normally a bit lower than that. I did a Google search foir general causes of this problem, and it suggested that one reason is a failing coolant temperature sensor. The coolant level is at max, and there are no signs of any leaks or fluid loss, although I did top it up a fedw days ago. I only added a minimal amount of water. It's got a viscous ffan driven by the engine, and I'm wondering if I should replace that with an electric one. Does that improve fuel consumption by much?

Google strikes a duck yet again! The B230E is K-Jetronic (mechanical) and doesn't even have a CTS for the engine as there is no ECU to use it!

What is the cold idle speed like? Another member had a similar problem and it looks, from the symptoms he describes, like the AAV is stuck/gummed up and isn't opening correctly. This would make a difference on a hot start as it is electrically heated so would cool down quicker than the rest of the engine.
Likewise thw Warm Up Regulator (WUR) is also electrically heated and again, would cool down quicker than the rest of the engine, resulting in a slightly richer mixture than needed for a hot start and consequent slight misifiring.

The temperature gauge should be at the mid-point after 5-10 minutes of running, regardless of season although in cold weather will take nearer 10 minutes to get there. Entirely up to you about replacing the viscous coupled fan with an electric one, it can give 10-15% improvement on economy if you do mainly short runs and the viscous coupling is a bit stiff or siezed.

When they're new, viscous couplings work well, however on a 37 year old one, chances are it is stiff or even siezed so won't be doing what it's designed to do.

I removed the viscous fan from my last 740GLE (and my 760GLE but that already had an electric fan) and it never overheated, even on hot summers days.

[Offgrid]

To be fair to Google, my search wasa a generic one, and not specific to any Volvos.

The cold start is fine. The problem is intermittent when the engine is up to running temperature, and mostly when the engine is under load - ie. going up hill. I'm tempted to buy a set of plug leads, and see if that sorts out the problem. As I have 2 740s, the extra leads won't be a wasted investment. I'll check the colour of the plugs over the weekend, and see if there is any indication of an incorrect mixture.
Another easy job would be to check the air filter. I'm not sure if that would be the cause. One guy posted in another forum that dirty oil could cause a carbon build up on the valve stems, and that can result in misfiring. It's probably worth changing the oil anyway, although that was supposed to have been done shortly before I bought the vehicle.

[Laird Scooby]

Originally Posted by Offgrid

To be fair to Google, my search wasa a generic one, and not specific to any Volvos.

The cold start is fine. The problem is intermittent when the engine is up to running temperature, and mostly when the engine is under load - ie. going up hill. I'm tempted to buy a set of plug leads, and see if that sorts out the problem. As I have 2 740s, the extra leads won't be a wasted investment. I'll check the colour of the plugs over the weekend, and see if there is any indication of an incorrect mixture.
Another easy job would be to check the air filter. I'm not sure if that would be the cause. One guy posted in another forum that dirty oil could cause a carbon build up on the valve stems, and that can result in misfiring. It's probably worth changing the oil anyway, although that was supposed to have been done shortly before I bought the vehicle.

That wasn't what i was asking about the cold idle - what speed is it?

However, you've just described failing plugs (possibly rotor arm and leads but more likely to be plugs) so if you're going to the trouble of pulling the spark plugs, fit a set of new NGK BPR6ES instead, gapped to 0.65-0.70mm.

Before some wisecracker jumps up and says the gap should be 0.7mm, most people don't use feeler gauges correctly so setting to a slightly smaller gap than "quoted" works better. Note that the plugs will come with a 0.9mm gap from the factory, this is TOO LARGE for the redblock, yes it'll run but you won't get the full benefit of the new plugs.

As for carbon/gum build up on inlet valve stems, this is more commonly associated with VAG engines that use FSI/TFSI or petrol direct injection - some V40s use a Mitsubishi engine with GDi (Gasoline Direct injection) and that could no doubt suffer similar.

With port injection as you have , the fuel being sprayed over the valve stem washes most of the carbon/gum build-up off so shouldn't really become a problem with yours.

Have you cleaned the PCV flame trap in yours? It's a pig to get to but worth doing - a can of carb/air intake cleaner will be needed and also follow the small bore hoses to the manifold and make sure the stub on the manifold is clean.

[john.wigley]

Originally Posted by Laird Scooby

However, you've just described failing plugs (possibly rotor arm and leads but more likely to be plugs) so if you're going to the trouble of pulling the spark plugs, fit a set of new NGK BPR6ES instead, gapped to 0.65-0.70mm.
.

With apologies to 'L.S.', whom I know from previous posts does not rate the brand as highly as he does NGK, I have a brand new set of (very) old stock Bosch Super WR 6 DC plugs which you can have for the price of the postage if they should be of any use to you, 'Offgrid'.

These were bought as spares for my old 745, which I sold in 2016. I always found Bosch products highly satisfactory on all of my 1, 2 and 7 series Volvos. As I now have a V70 they are obviously surplus to my requiements. They weigh 60 GMs a piece, so 240 GMs plus packaging. Drop me a PM if interested.

Regards, John.