I often use engine braking to descend a long downhill, I just got my exhaust all welded up from scratch, old one was full of holes.

Now when I descend the same hill I hear pops and bangs which are pretty audible. They range in volume, but they aren't loud or violent.

 

I know it's cool to some, but I do not think this is the way it is supposed to be. 

 

I got my timing set with a timing light, but we had to offset it slightly to the left of the factory timing mark (about 3mm on the crank) since on factory setting, the engine would run too slow.

The engine is now very lively, and does not hesitate to tach up to 4500 (have never gone over that lol).

 

Could the slightly offset timing cause the pops and bangs? If so, why is it running so slowly at factory setting?

Doubt it, ignition advance will be bigger under high vacuum conditions down hill. Might be pressure difference expansion. If loud bangs  then unburnt fuel. Ask someone to drive behind and look for flames at dusk?

My cousin thinks that my idle fuel mixture is somehow too lean, that would explain why the low engine speed on factory timing.

 

I thought everything is electronically controlled?

Quite often, you get the 'popping and banging' that you describe when there ARE holes in the exhaust system, I just wonder if the exhaust was so noisy previously, that you didn't hear them?

Your cousin is probably correct, a weak mixture will cause that.

So I am going to have to find out how to tweak the idle mixture.

I do remember two allen bolts on the rear of the unit, those might do something.

 

Will update.

Usually a sign of over fueling, is there a strong smell of fuel? 

You still don't have working lambda sensor, right?

Hmm, well indeed the lambda sensor doesn't work, but I am guessing that it can't affect the fuelling that much. 

 

I mean, with factory ignition timing the engine ran at about 500 or 600 RPM, I assumed because of the lack of fuel, but now the pops and bangs came up.

 

 

Basically this just a lot more silent.

There is some sort of clear liquid coming out of the exhaust, it does not smell of petrol despite going through all the way.

Just condensation (white smoke / steam) in cold?

 

Is coolant going down?

 

Nope, it's thankfully not drinking coolant, I had replaced my coolant about 8 months ago and still not a drop missing.

 

The thing is, during winter it is like half of what a tea pot puts out on boiling, but now it just sort of dribbles down the pipe.

 

I'll try collecting some and see if it's flammable, hahaha.

 

But if it is condensation, where is it coming from? Humidity is almost always over 60%, 70% right now, could it be just the air?

If burning perfect to use all oxygen (and make lots of nitrous. oxides for the cat to absorb) 10 litres of petrol needs over 150 liters of air .. it uses the 21% that is oxygen

That's 90 liters of water at 60% humidity.

Edited 28 April, 20188 yr by dvderlm

Do de-catted cars usually make all this fuss? Because somebody before me either sold theirs or got it stolen (common occurence in my country).

 

My friend's 1.2 liter fuel injected straight piped Fiat Punto likes to make the same type of noise, albeit plenty louder than mine.

Yes. 'Afterfire' condition can occur when car is decatted.

https://en.wikipedia.org/wiki/Back-fire

 

Big exhaust too

http://www.mikuni.com/tg_backfires_in_exhaust.html

Edited 28 April, 20188 yr by dvderlm

Rather than being too rich, you will get popping if the idle mixture is too weak.

When the throttle butterfly is closed, if there are any air leaks on the inlet side, extra air will be drawn in (via the leak) weakening the mixture.

If there is a restriction in the fuel reaching the engine at idle speed, this will have the same effect.

I would recommend that you check for air leaks before doing anything more drastic.

If you can get hold of some 'Easy Start' (basically ether) with the engine idling, spray some of this around the inlet manifold joints and listen for any change in engine speed, which would indicate a leak.

CAUTION: this stuff is VERY flammable.

Regards

 

Tried the easy start, nope, no change whatsoever. Keeps a steady 750-850 rpm. Made a long trip today and actually surprised me the car did 35.6MPG. (whaaa???)

 

Nothing then, I will write off the decat as the pops and bangs culprit. I will also have to find a brand new throttle valve actuator and replace it before winter so that I have a steady warmup procedure. (Haven't had self redlining for about 3 months).