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700/900 Series General Forum for the Volvo 740, 760, 780, 940, 960 & S/V90 cars |
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Missfire 960Views : 984 Replies : 24Users Viewing This Thread : |
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Jun 12th, 2019, 14:05 | #1 |
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Missfire 960
Hi all. My 1993 960 380k miles has started to misfire. The engine will fire up and clearly very lumpy. I have checked the ignition side; both the two ignition amplifiers on the sides of the inlet unit are OK, checked by swapping them over; all 6 coil units are fine and produce lots of spark when removed; the wires going to the coils running along the top of the head, whilst not perfect but do not short anywhere; all 6 plugs are nearly new and checked by substitution and are OK. I can't see or detect any inlet or vacuum hose leaks...the latter hoses are recently new. Just done a cylinder pressure test and I get 150 psi on no. 1,3,4,6 cylinders, 0 psi on no.2 and about 30psi and no.5.
Unless any of you can suggest anything else to check, I think I have to take the head off and see whats up....I suspect either valves or something with the hydraulic tappets. I use only fully synthetic oil (for at least 10 years) Any views please? Thanks. |
Jun 12th, 2019, 14:21 | #2 | |
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Jun 12th, 2019, 14:58 | #3 |
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Thanks for that Clan, the car is in regular use every day and have just driven back from Malta on what I thought was 5 cylinders but after the compression test, may be only 4!
With the poor or zero cylinder pressures I suspect the head has to come off. Fortunately I have a spare reconditioned head! But I appreciate your comments. |
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Jun 12th, 2019, 20:05 | #4 |
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I suspect you're right about the hydraulic tappets Garth but before decapitating the engine, try adding 0.5L of Carlube ATF-U to the engine oil and drive as normal, at least until the next oil/filter change. At that point, substitute 1L of ATF-U for engine oil then top up with your normal engine oil.
You should start to notice some sort of difference after a few hundred miles though, improved economy, smoother running, lack of clatter on start up etc. You may still have a failed hydraulic tappet or a burned valve but IMHO worth trying the simple fix first.
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Jun 13th, 2019, 17:31 | #5 |
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Fuel injectors may be loose or seals gone on the effected cylinders, check these first as you will lose compression if they are.
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Jun 13th, 2019, 18:01 | #6 | |
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On a diesel defective injector seals will cause loss of compression but on a petrol (except GDi) a defective injector seal will either cause a nice big fuel leak from the fuel rail or allow air into the inlet manifold, causing lean running on the cylinder it serves.
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Cheers Dave Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........ |
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