General: 70: - backfire

jack taylor · Oct 9th, 2019, 18:39

Hi, I have a 1998 v70 petrol, 2.5, 20v. A couple of days ago I was happily driving along the coast road beside the med about 15 mins from home. I was keeping within the 80kph speed limit when there was an almighty backfire. My first thought was the head gasket had blown but the car was driving fine and no warning lights came on. Just the one backfire and nothing more since. What could have caused this and does it indicate a serious problem. Like me the girl is getting old although only 150,000 on the clock. I backfire sometimes but that's normally down to brussels sprouts. Thanks jack.

volvo again · Oct 10th, 2019, 09:24

Can be causes by a vacuum leak, bad timing, problems in the ignition system, a faulty sensor, an exhaust leak, or some other system fault. ...

As you know the backfire is when unburned fuel ignites inside the intake or exhaust manifold instead of a cylinder.

If all is well now I would tend to leave alone...unless you fancy checking ignition /valve timing etc...

turboboy · Oct 10th, 2019, 10:23

Are you sure it was a backfire? It seems strange that there would be a single one while you were cruising along. I could understand if you had suddenly tried to accelerate hard and there had been a hesitation before.

Could it have been a stone thrown up underneath by another vehicle or even your own?

john.wigley · Oct 10th, 2019, 11:08

I was thinking along the same lines as 'turboboy'. A single backfire would indeed be unusual today without an underlying fault and in the absence of any other symptoms. Much more common 50 years ago, especially on SV Fords and BMC 'A' series engines, when a car would backfire given the least provocation!

Regards, John.

jack taylor · Oct 11th, 2019, 02:18

Hi guys, Many thanks as always for your advice. I have driven a further 150 miles since the "bang". It was a very loud backfire from the rear of the car so much so that it made me jump. I don't think a stone or small object could have been so loud. It has not happened again since and the car isn't showing signs of there being a problem. For a few months now the revs rise to about 3,000 on start-up whether hot or cold. Within a couple of seconds the revs drop to about 800. Tick-over is a bit lumpy and the exhaust seems a little louder than normal. Given your comments there may well be a small exhaust blow or a hole in one of the hoses. once on the move its responsive. It just feels as though it needs a good tune-up. Plugs have been in for about 10,000 miles and the throttle body was cleaned about 4,000 miles ago. Oil and filters are changed every 5,000 miles. Given your comments and advice I shall ask my mechanic to check for air leaks. Many thanks for your help. jack.

Martin Cox · Oct 11th, 2019, 10:50

Just a thought...

Could it have been a coil spring breaking? Many years ago I had one go at the back of my V40. It made a hell of a bang but there was no visible difference in the ride height or ride quality. The spring had broken near one end.

Martin

john.wigley · Oct 11th, 2019, 11:20

Quote:

Originally Posted by Martin Cox

Just a thought...

Could it have been a coil spring breaking? Many years ago I had one go at the back of my V40. It made a hell of a bang but there was no visible difference in the ride height or ride quality. The spring had broken near one end.

Martin

Good point, Martin. I had one (NSF) let go on my S@@b 9-3 'vert earlier in the year - it made one hell of a bang!

J.

jack taylor · Oct 11th, 2019, 21:26

Hi Guys, Most interesting I shall ask mechanic to look at the springs. I would never have given that a thought. Thanks again. jack.

Oct 9th, 2019, 18:39	#1
jack taylor Master Member Last Online: May 15th, 2022 15:53 Join Date: Jan 2008 Location: Torrenueva, Costa del Sol	backfire Hi, I have a 1998 v70 petrol, 2.5, 20v. A couple of days ago I was happily driving along the coast road beside the med about 15 mins from home. I was keeping within the 80kph speed limit when there was an almighty backfire. My first thought was the head gasket had blown but the car was driving fine and no warning lights came on. Just the one backfire and nothing more since. What could have caused this and does it indicate a serious problem. Like me the girl is getting old although only 150,000 on the clock. I backfire sometimes but that's normally down to brussels sprouts. Thanks jack.

Oct 10th, 2019, 10:23	#3
turboboy Master Member Last Online: Dec 15th, 2023 08:44 Join Date: Dec 2003 Location: Twickenham	Are you sure it was a backfire? It seems strange that there would be a single one while you were cruising along. I could understand if you had suddenly tried to accelerate hard and there had been a hesitation before. Could it have been a stone thrown up underneath by another vehicle or even your own? __________________ Turboboy Current: 1998 Volvo V70 2.3 T5 Auto. Previous: 2000 Volvo V40 T4; 1981/2 265 (x2); 1988 740 Turbo Estate.

Oct 10th, 2019, 11:08	#4
john.wigley VOC Member since 1986 Last Online: Yesterday 23:53 Join Date: Jan 2007 Location: Leicestershire	I was thinking along the same lines as 'turboboy'. A single backfire would indeed be unusual today without an underlying fault and in the absence of any other symptoms. Much more common 50 years ago, especially on SV Fords and BMC 'A' series engines, when a car would backfire given the least provocation! Regards, John. __________________ Time flies like an arrow, fruit flies like a banana .....

Oct 10th, 2019, 09:24	#2
volvo again Master Member Last Online: Apr 17th, 2024 12:04 Join Date: Jun 2018 Location: Presteigne, mid Wales	Can be causes by a vacuum leak, bad timing, problems in the ignition system, a faulty sensor, an exhaust leak, or some other system fault. ... As you know the backfire is when unburned fuel ignites inside the intake or exhaust manifold instead of a cylinder. If all is well now I would tend to leave alone...unless you fancy checking ignition /valve timing etc...

Oct 11th, 2019, 02:18	#5
jack taylor Master Member Last Online: May 15th, 2022 15:53 Join Date: Jan 2008 Location: Torrenueva, Costa del Sol	Hi guys, Many thanks as always for your advice. I have driven a further 150 miles since the "bang". It was a very loud backfire from the rear of the car so much so that it made me jump. I don't think a stone or small object could have been so loud. It has not happened again since and the car isn't showing signs of there being a problem. For a few months now the revs rise to about 3,000 on start-up whether hot or cold. Within a couple of seconds the revs drop to about 800. Tick-over is a bit lumpy and the exhaust seems a little louder than normal. Given your comments there may well be a small exhaust blow or a hole in one of the hoses. once on the move its responsive. It just feels as though it needs a good tune-up. Plugs have been in for about 10,000 miles and the throttle body was cleaned about 4,000 miles ago. Oil and filters are changed every 5,000 miles. Given your comments and advice I shall ask my mechanic to check for air leaks. Many thanks for your help. jack.

Oct 11th, 2019, 10:50	#6
Martin Cox VOC Member Last Online: Yesterday 07:15 Join Date: Dec 2001 Location: Hull	Just a thought... Could it have been a coil spring breaking? Many years ago I had one go at the back of my V40. It made a hell of a bang but there was no visible difference in the ride height or ride quality. The spring had broken near one end. Martin

Oct 11th, 2019, 21:26	#8
jack taylor Master Member Last Online: May 15th, 2022 15:53 Join Date: Jan 2008 Location: Torrenueva, Costa del Sol	Hi Guys, Most interesting I shall ask mechanic to look at the springs. I would never have given that a thought. Thanks again. jack.

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