Misfire on idle B230FK 940

[Laird Scooby]

I know this sounds like a "snake oil" fix but add some synthetic ATF to the engine oil, if you can get between 0.5 - 1.0L of it in that will be great.

Then run it for a few days, giving it the occasional Italian decoke when you can.

I'm thinking sticking valve, either way the ATF won't do any harm and will do all kinds of good. It may well cure the misfire/poor compression because you might also have a sticky piston ring that isn't expanding/contracting as they're designed to.

Silly question, have you swapped #1 plug lead with #2 plug lead and also #1 & #2 plugs just to confirm you haven't got a faulty lead or plug? If the fault moves or reduces then whichever of those causes the move to happen is the culprit.

I know they're meant to be new and therefore perfect but stranger things have happened.

[ie940]

I've refitted a second hand but working cap and leads, and swapped plugs 1 and 2 and it's not moved so we can rule out spark components I think.

I'll read up on your ATF idea, I've never heard of it! If it's broke I might as well pull the head off. I didn't hear any hissing through the inlet when I pressurised the cylinder.

[Rversteeg]

Does the misfiring move to another cylinder if you swap the injectors?

[Laird Scooby]

Originally Posted by Rversteeg

Does the misfiring move to another cylinder if you swap the injectors?

Originally Posted by ie940

Volvo 940 estate B230FK 2.3 1996

Developed a misfire on idle only. Drives and accelerates fine. Cylinder 1 has the problem.

If it's idling, very lumpily below 1000rpm, then I can pull the #1 HT lead or injector plug off and the idle doesn't change. It'll pop and fart on the exhaust, but unplugging the injector stops this.

I've changed the injector, checked it's ohms, changed the FPR, cleaned and gapped the plugs, fitted new Bosch leads, cleaned the recently replaced Beru cap and rotor arm.

Compression is slightly down on #1, but not to the point it wouldn't run? Approx 120psi opposed to 135psi on the other cylinders, which equates to low 8 bar instead of the Haynes specified 9 minimum.

Thoughts?

I was thinking along similar lines to you so double-checked his original post earlier, he's changed the injector and several other unrelated things.

It sounds as if the problem is internal, either sticking rings or valve or possibly a burned exhaust valve on #1 causing loss of compression and lower output from the power stroke and maybe popping through the exhaust.

Could be worth putting a boroscope into #1 pot to see if there's anything obvious, they're cheap enough on ebay and hook up easily to a laptop or similar. I've used that method in the past to evaluate an engine before it was ultimately stripped for bits.

[360beast]

ATF has less cleaning properties than engine oil. It will mess with the viscosity of engine oil so adding it your engine even 0.5l is more likely to cause excess wear than anything else.

[aardvarkash10]

Originally Posted by 360beast

ATF has less cleaning properties than engine oil. It will mess with the viscosity of engine oil so adding it your engine even 0.5l is more likely to cause excess wear than anything else.

If its left in there, yes. If not, no

[Laird Scooby]

Originally Posted by 360beast

ATF has less cleaning properties than engine oil. It will mess with the viscosity of engine oil so adding it your engine even 0.5l is more likely to cause excess wear than anything else.

Considering most ATFs have a viscosity of about 30, it's not going to throw the viscosity of a 10W40 out that much, especially in 10-20% dilution in engine oil.
It also contains "Seal Swell" to help revive and condition the rubber seal throughout the engine.
It still contains certain detergents not present in engine oil and has a better "creep" action than engine oil. For this reason, to plagiarise a lager advert, it reaches the parts other oils can't reach. This makes it particularly good at getting past carbon, gum and similar residues left by engine oil, dissolving the worst of them and freeing hydraulic lifters, piston rings, cleaning blcoked oil separators and so on.
It also has friction modifiers that help reduce friction.

A few cases of success, most recent first.

A friend recently bought an MX5 that had 3 noisy tappets and a leak from the front crank oil seal. Added 0.5L of synth ATF after an oil/filter change, now totally silent and leak free - also goes a hell of a lot better due to restoring lost compression due to sticky piston rings being released.

My own 760 had suffered from neglected oil/filter changes so the oil separator was badly clogged. Also quite noisy in general and when i first got it, lucky to achieve 19mpg on a long run. Granted i've done other remedial work but the oil separator is now a lot cleaner, the emissions are better and economy is up to about 26mpg doing mainly short runs, i have seen 37mpg on a longer run.

Jeep Cherokee 4.0L HO Limited, predecessor to the 760 - when i first got it, it had at least 3 noisy lifters that sounded like 3 pile drivers in the engine when cold. Oil leaks from various places round the engine including the rocker cover (rubber gasket) and was prone to a cloud of blue smoke when either applying power or after coming off the power and slowing on engine braking.
Oil/filter change (the old oil was very clean), replaced 1.25L of engine oil with synth ATF (Carlube ATF-U) and within a few hundred miles the tappets were quiet, the blue smoke had disappeared and i was getting 24mpg on LPG, also went like stink!

My Rover 827 Coupé - again had suffered neglected oil/filter changes and when i first got it, only ran on 4 cylinders, would chuck out a big puff of blue smoke when blipping the throttle or giving it some beans.
Engine flush, oil/filter change and added ATF-U, within minutes it was running on all 6 pots, emissions have got cleaner year on year with continued use and blue smoke reduced.

My last 740GLE - wasn't too bad in general but again, the engine was dirty inside, barely scraped a pass on emissions the day i got it. A year later the MoT guy put it back on the ramp after the emissions test as he wanted to find the cat! It didn't of course have a cat and was running K-Jetronic injection.
Also the power and economy were well up on when i first got it.

My 827 Sterling - on the whole very good but suffered noisy tappets as the C27 Honda engine is prone to having. Now silent after treatment with ATF-U and errr, oh yeah, i've had 43mpg out of it on a run and wasn't hanging about either! Also i have quite a few emissions print outs from MoTs that show an improvement over the years i've owned it.

There are others i could cite but they are all pretty much the same story. The tip was given to me about 30 years ago by a mechanic who had in excess of 30 years experience at the time, i've also known many other mechanics recommend it, many have never heard of it admittedly but i can assure you it works.

In short,

don't knock it until you've tried it!

[Laird Scooby]

Originally Posted by aardvarkash10

If its left in there, yes. If not, no

It would take a very long time though Ash and the one i use (Carlube ATF-U) has a viscosity of about 30 so isn't going to effect the 10W40 in the engine that much. Also it's possible to use that one as hydraulic jack oil (manufacturer cites this as a selling point) and has better friction modifiers than many others.

Simple fact is reduced friction means reduced wear as a generalisation so as it doesn't thin the engine oil but enhances its friction reducing properties it really can't do that much harm.

[aardvarkash10]

Agreed Dave. In an engine like Moomin's with knocking on 230,000km on the dial, I'm likely to need gap filler, not slippery juice!

At 0.5l that's just 10% of the oil capacity of the engine. Its not going to cause catastrophic failure and is unlikely to cause demonstrable wear under normal conditions.

I've used this trick to "cure" ticking hydraulic followers previously in early Mazda 12 valve engines (notorious for it). Again, high km's but no harm and did the trick.

[Laird Scooby]

Originally Posted by aardvarkash10

Agreed Dave. In an engine like Moomin's with knocking on 230,000km on the dial, I'm likely to need gap filler, not slippery juice!

That mileage isn't that high really Ash - my last 740 had about 235000 miles (380000km ish), my Jeep had 245000 (395000km ish) and both responded well - no need for gap filler to "beef" it out!

Originally Posted by aardvarkash10

At 0.5l that's just 10% of the oil capacity of the engine. Its not going to cause catastrophic failure and is unlikely to cause demonstrable wear under normal conditions.

I've used this trick to "cure" ticking hydraulic followers previously in early Mazda 12 valve engines (notorious for it). Again, high km's but no harm and did the trick.

When you also consider that some manufacturers including Rover and Volvo changed the service specs of certain manual gearboxes so ATF is used instead of engine oil then ATF can't be that bad as a lubricant anyway. I believe (though may be wrong) this was to improve cold shifting characteristics because of the better friction reducers in the ATF - i've heard/seen differing reports on how effective it is at that but the majority of reports have been favourable.