Misfiring.....WTF now??

[NI_Volvo_Nut]

Don't think the 740 has them, but I'll stand too be proved wrong...

I think its ignition side anyway, inlet manifold gasket & surounding pipes appear ok and no change in idle speed when WD40 applied, inc injector seals, think I'll order a cap and rotor, it deserves one if nothing else lol

[Chris740R]

Yeah, I don't think K-jet uses any of that.

[OldBlueVolvo]

I thought that the B230E/200E engines have the EZ-118K ECU, hall sensor, and power stage? At least that's what my green manual tells me, so I hope it's correct.

[NI_Volvo_Nut]

In lay-mans terms, B200E is mechanical injection, B200F is electronic.

[OldBlueVolvo]

Originally Posted by NI_Volvo_Nut

In lay-mans terms, B200E is mechanical injection, B200F is electronic.

but the ECU controls the ignition. My carb'd engines certainly have an ECU and I think the ignition side of things is very similar on the k-jet 740s. I guess you must have a crank position sensor if you're sure you don't have a hall sensor.

I would have started by inspecting the dizzy cap, rotor, sparking plugs, and HT leads. Then connect a vacuum gauge up to the manifold.

[NI_Volvo_Nut]

The B200E has the sensor in the distributor, I susspect this my be at fault, I'm only noticing its due a service too, so I'll get onto Rufe and get a cap, rotor, and oil filter, plugs and leads were fitted a year ago and have only done 6,000 miles since.

What will connecting the vacuum too the inlet manifold tell me?

[Citizen.Agfa]

Originally Posted by NI_Volvo_Nut

The B200E has the sensor in the distributor, I susspect this my be at fault,

I think, on reflection, that you could be spot on there; a duff dizzy sensor can fail sporadically, leading to the symptoms you describe.

C.A.

[OldBlueVolvo]

While you're waiting for your cap to arrive you could take the old one off and have a look - check there's no oil inside and that the copper/brass is bright (not black or green) and not heavily pitted. Check the rotor in same way. This might be a lot of messing around though if you're just replacing the parts anyway.

A vacuum gauge might not tell you anything useful, but then you might just find a vacuum leak or another problem if the reading isn't steady at idle.

Another thing to think about is whether the misfire is regular (same cylinder) or not. Does pulling the HT leads one at a time make little difference for a particular lead?

I remember a thread recently where someone sprayed carb cleaner around the injector o-rings but didn't find any problem. But spraying water did show a problem.

[NI_Volvo_Nut]

Another quick question...

Would 15/40 be too heavy an oil?

[minesa240x3]

Just because it happened to me although mine is electronic b200F,since last winter I have had very similare symptoms to you.check very carefully the concertina air pipe between the air filter and inlet manifold.I had a small split in the inner crease.I have tried all the usual fixs with some effect but until last saturday when I was cleaning the engine it was still missing and reving all over the place.it always got better when hot ~I think this was because as the pipe warmed up it closed the gap up.
regards Brian.