Topic

Can anyone suggest how common it is to detect a “backfire” on the “over-run” please?
This relates to a TF135 and is experienced when the system is up to working temperature and when lifting off the throttle.
I have very limited history for the car and no indication as to whether the map has been “tuned” for some other purpose.
For various reasons (weather being a major factor) the car has had little or no use over winter and the backfire experiences occurred last year.
In my care we have done about 1500 miles. Fuel filter, air filter, plugs, oil filter, cam belt and water pump were all changed before the start of that 1500 miles. If pressed id have to say that this experience was more apparent as the year went on but that could be that I became more “comfortable” with the car.
The only other factor that might be relevant is the alternator. Earlier in the year it wasn’t generating properly and a replacement was fitted towards the end of that 1500 mile period. From that point on it would be reasonable to think that the voltage was right and giving better ignition conditions.
Is this backfire normal?

How severe is the backfire ? Are we talking a mild decorative popping when you lift your foot off the throttle or a loud shotgun noise that scares birds and animals

Exactly what Notanumber says. My '04 TF 135 occasionally pops quietly on the overrun, mostly when in traffic in first gear where I'm moving forward and slowing down with the car in gear. It will also occasionally pop with more energy on the overrun when I really give it some beans!

It is much more noticeable since I fitted my TT7 exhaust; it could be an effect of the exhaust or simply that I hear it because it is louder.

My car has not been remapped, AFAIK.

If you are experiencing a loud backfire, there may be a problem.

Do you know if the car has had the ECU remapped as this will cause this to happen.

As stated I do not know (and don’t really want to know) if it has had the ECU re-mapped, and I appreciate that could have a significant effect on the potential backfire.

No, we are not talking bird scarring noise, although I am going more deaf than I would like I would say it is a mild pop when lifting off to change gear ( in reality I don’t make the engine work hard probably rarely exceed 4000 rpm and probably less).
Around here most roads are 40 mph limited. It’s hard to “exercise” the engine .
More recently my concentration has been on fitting new suspension ball joints and rear brake calipers.. So now I’m ready to run it for the summer but not if the pop is unusual.
Exhaust is a Piper aftermarket item

If it has a KMaps upgrade it could have the pops and bangs addition, I didn’t want it on ours.
Over fifty years ago I used to drive a petrol LandRover to go to social events. Coming home late at night we would turn off the ignition while driving through the small villages for a couple of seconds then back on again which resulted in an almighty bang. I have now grown up a little.

MGB281 wrote:

If it has a KMaps upgrade it could have the pops and bangs addition, I didn’t want it on ours.
Over fifty years ago I used to drive a petrol LandRover to go to social events. Coming home late at night we would turn off the ignition while driving through the small villages for a couple of seconds then back on again which resulted in an almighty bang. I have now grown up a little.

I used to do that in my old Landie too….one day I drove past a copper booking some poor bastard, he was concentrating on writing the ticket on the bonnet of the cop car, I couldn’t help myself, I backfired him as I went past, he leaped out of his skin, looking about to see where it came from, I continued past as if nothing had happened.
The other trick was when driving alongside the lake there would be anglers fishing by the lake shore, the road was close to the shore, I’d backfire the anglers. Some would end up in the lake, others would drop their rods in surprise!
Always entertaining!

The Ute has a cattle call as a horn, these make a realistic cow moo, and are used to call up the cattle.
I love to moo idiot pedestrians who are too busy fiddle arsing about with their damned phones to look where they are going…….surprises the shit outta them!
I haven’t grown up yet!

All my Landies have had Diesel engines so that corrupt pleasure has sadly escaped my infant mind. They did however have Klaxon horns, original types made by Klaxon & those would induce panic if used with stealth.
The horn on my new car is travesty, it wouldn’t alert a dozing mouse a yard away. Car horns are described as “audible warnings of approach” & where I live a horn is used nearly as much as the wipers & as an instrument of self preservation. I have a Chinese Klaxon derivative in stores, it’s surprisingly good, it will be fitted shortly.
Back to the over run pops; my car is running without mapping updates & it burbled & pops nicely to the point where all the down hill villagers know when I’m off in the car.
M

Let’s assume the ECU is standard.
So should this backfire be something I ought to seek to fix, and if so how?
When I changed the plugs when I changed air/fuel/oil filters I set the plug gaps as identified in the work shop manual.
Should I seek to close the gaps to affect the timing?

MGB281 wrote:

If it has a KMaps upgrade it could have the pops and bangs addition, I didn’t want it on ours.
Over fifty years ago I used to drive a petrol LandRover to go to social events. Coming home late at night we would turn off the ignition while driving through the small villages for a couple of seconds then back on again which resulted in an almighty bang. I have now grown up a little.

That made me smile!
When I had my kit car "Gordon" (2.3litre slant 4 Vauxhall engine with twin Stomberg carbs)

I fitted an ignition cut-out with a hidden switch as a security measure.
I have to confess to the good citizens of Wells that on approaching their fair City, I once turned off this switch (by mistake of course!) then switched back on at the bottom of the hill. The Back-Fire which resulted certainly frightened ME, so a suspect that a few birds thought that a shot-gun had been fired close to their perches!
I have also grown up a little, though my wife will disagree.

Closing the plug gaps will make bugger all difference to the timing.

The bigger the spark plug gap the more energy is required to jump that gap.
If it takes time to build up that energy it stands to reason that spark plug gap can affect timing although it is appreciated that we are talking about small numbers here.
Much more likely is valve overlap, and operational conditions such as temperature.

Perhaps the question is how well defined is the process of renewing a cam belt? Or perhaps is this “pop” of a backfire normal for these cars (TF135)?