free hit
counters
V8 Engine Backfire / Popping - Engine/Ancilliaries - The Lotus Forums Jump to content
HowardRoark

V8 Engine Backfire / Popping

Recommended Posts

Hello all,

I recently had my 918 engine completely rebuilt, and it has driven very well for about 4,000 miles so far, but it has started to backfire a bit when decelerating.  It normally does it when I take my foot off of the throttle.  It is quite loud and sounds like the crack of a gunshot.  It never backfires when accelerating.  

When accelerating in 2nd gear, there sometimes is a very slight hesitation in acceleration, but not sure if these two issues are related.   

Also, when idling, it sounds smooth, but there is sometimes a very faint “poof” sound.  Not a distinct pop, but very faint and intermittent.

I know some owners will say that the backfire/ popping sounds are normal, but I do not think it is normal, and I think it can be fixed.   Any suggestions on what to check or change?

cheers!

 

8E20935F-1D64-4EE4-86CA-455A8CBD6DB1.jpeg

Share this post


Link to post
Share on other sites
Upgrade today to remove Google ads and support TLF.

Had the exact same symptoms and was getting a bit worried that something bad was going wrong - turned out to be a leaky exhaust joint.

Share this post


Link to post
Share on other sites
1 hour ago, march said:

Had the exact same symptoms and was getting a bit worried that something bad was going wrong - turned out to be a leaky exhaust joint.

Back in the old days whenever you heard a car popping on the over run it was always a sign it's exhaust was on the way out. :thumbup:

Share this post


Link to post
Share on other sites

A few years back on my 2.2 the exhaust valves were worn and caused the popping and banging. Similarly on an old GSXR750 a small hole in the exhaust manifold created some impressive back firing too.

Check the manifold studs the original Lotus studs have a habit of shearing off and could be causing a leak at the manifold(s). I replace mine with ARP rolled studs when I had the chance.

cheers

-Chris

Share this post


Link to post
Share on other sites

Hi all, my tech has checked the exhaust and there doesn’t appear to be any leaks.

Question  -  would a faulty Waste Gate valve cause some backfiring, by letting too much gas back in the exhaust??  I am wondering if it could help with the issue?  As I understand it, the WG prevents too much boost going back in when you let off of the throttle, and my car does backfire when I do let off of the throttle.  Are these related?

cheers

Share this post


Link to post
Share on other sites

Hi Matt,

Not sure if you have sorted this already or not but I happened to stumble over it again and spotted what looks like a slight misunderstanding of what the waste gate is doing. I think you are confusing it with a dump valve (or blow off valve).

The turbo is driven by the exhaust gasses and once the desired amount of boost is reached the waste gate valve opens to let exhaust gases bypass the turbo and exit via the exhaust, it cannot let too much gas into the exhaust, this is just exhaust gas the more the merrier.

A dump valve or blow off valve is not fitted to the Esprit as standard, if you add one it would sit between the turbo charger and the throttle body (or maybe even the intake port itself ??) and when the throttle is closed the valve opens to release the boosted inlet charge to the atmosphere or sometimes into the air intake on the other side of turbo. This prevents a pressurised air from pushing back on the turbo compressor and stalling the compressor wheel.

It is possible I suppose that the waste gate valve on the turbo might be leaking via its actuator arm but I'm not sure that's common at all.

cheers

-Chris

Share this post


Link to post
Share on other sites

 

Idk if this will help but this is what mine is/was doing on the drive home. the left exhaust is the one that's doing all the popping at idle. 

compression check showed just  a slight drop on one of the left cylinders. Dont think it has anything to do with turbo. I believe excess gas is being dumped out of an injector or there is a bad coilpack which would explain the intermittent hesitation under load on hot days. 

Share this post


Link to post
Share on other sites

Matt sorry no help with your issue but what is your garage floor made of? Can’t be tiles otherwise you must have had the worlds strongest tiler. I really like it and as building a garage I am interested 

thanks in advance 

Dan

Share this post


Link to post
Share on other sites

Looks like textured and polished Concrete Dan,  Lucky Americans have bben doing it for years  !  

V8 backfire i would say is over fueling ! 

Share this post


Link to post
Share on other sites
15 hours ago, v8GTmac1 said:

Idk if this will help but this is what mine is/was doing on the drive home. the left exhaust is the one that's doing all the popping at idle. 

compression check showed just  a slight drop on one of the left cylinders. Dont think it has anything to do with turbo. I believe excess gas is being dumped out of an injector or there is a bad coilpack which would explain the intermittent hesitation under load on hot days. 

Popping on idle can indicate a cracked piston. An inspection camera will allow you to check this. 

Lamda sensors are also known to cause popping as well

Share this post


Link to post
Share on other sites

A simpler cause could be a faulty O2 sensor(s). Do you have a OBDII? if so check the operation of the O2 sensors closed and open loop as had a similar flame event which was traced to a faulty o2 connection which was frustratingly intermittently loose causing over fuelling. The consequence was back fire on lift off also causing flames out the back, (driving during the day so not immediate apparent to me), however there was a hesitation on acceleration, dry to nurse the car back now with the EML I got the car recovered.  I replaced the connection and needed a new cat but right as rain now. 

PS I've always had popping on my car

Share this post


Link to post
Share on other sites
11 hours ago, Barrykearley said:

Popping on idle can indicate a cracked piston. An inspection camera will allow you to check this. 

Lamda sensors are also known to cause popping as well

the 02 sensor could very well be it. Maybe explains why i'm reading lean fuel trims on that bank.....I wont know again till it's a runner later this year. 

Edited by v8GTmac1

Share this post


Link to post
Share on other sites

Also consider air leaks from the inlet manifold and exhaust manifold. This can also lead to slightly rough running and an air leak will lead to a weak mixture.

Exhaust manifold studs are a known weak point so have an inspection in that area.

Share this post


Link to post
Share on other sites

f7ea5c25cfd740a1a47ec4c168803b76.jpeg

turned out to be true in my case.  2 missing nuts, 1 sheered off stud. 

Edited by v8GTmac1
  • Sad 1

Share this post


Link to post
Share on other sites

Seriously ???  the car was sold in that condition with the manifold simply not secured at one end?  With all the oil on the manifold, it looks like the nuts were soaked for removal.

Share this post


Link to post
Share on other sites

Engine out job unfortunately and makes sure you use replacement stainless steel lock tabs. Be careful when removing the broken stud ( if broken below the casting surface) as these are a blind hole and you need to watch you dont drill into the head casting otherwise you will create another problem. This if it occurs can be solved but better to be aware of the potential issues before you start.

The low torque rating for these stud nuts which I recall is something like 6 - 10 ft/lbs, is to allow for thermal expansion and prevent the manifolds cracking. The manifolds expand and contract when they get hot ......very hot when boosting .......and then cooling after engine stopped.

Quite common for exhaust manifold bolts/nuts to work loose on any engine and the Esprit tends to suffer from this quite a lot and more so than any of the numerous V8 engines I have built and worked on road or track.  In fact I probably hear of one/two type similar problems per week with rough running some of which can be attributed to sensors, but also head gasket failure and air leaks from the inlet and exhaust manifolds.

Good Luck

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


×