Exhaust popping

metz · Post by **metz** » Mon Aug 22, 2005 11:31 am

had my timing done and emissions tweaked the other day, when we shoved the probe up the exhaust and checked lambda 1 (on the tester) it showed the car running lean, so i put that down to the exhaust popping a little, so we tweaked it to midway between lean and rich on idle.

Anyway its still doing it..if not more now.

While driving along..if i lift off and let the car roll along against the gear (like down hill or summat) theres pop pop popping sounds coming from the exhaust....as always i'm worried)

mods are (incase it makes a difference) decat, jetex filter with front cut off the airbox, polo ace GT chip and full standard cl exhaust.

lamda was switching ok while on the Co tester.

MadManMike · Post by **MadManMike** » Mon Aug 22, 2005 12:45 pm

I can't help, but my girlfriends 106 is doing the same, it'll be interesting to find out your problem.

amstrange1 · Post by **amstrange1** » Mon Aug 22, 2005 12:49 pm

[random babbling] What did you adjust? The CO screw on the airflow meter? If your exhaust is blowing the lambda reading from a probe shoved up the exhaust pipe might be incorrect. On idle (with the car's lambda probe plugged in) you should find it cycles from rich to lean anyway. How was the timing set, I'm guessing it was done in service mode with the blue temp sender unplugged?
Assuming the timing and CO are spot on, the popping could be from a leaky exhaust (before I got mine rewelded it would pop flames at night!) or a missfire of some description. How healthy are your ignition leads, rotor arm, dizzy cap etc.?[/random babbling]

Having said all that waffle, Yoof's car with his Barry exhaust does exactly the same - the fuel injectors temporarily shut off when you lift off, but don't react quite as quickly as you snapping the throttle shut. So a bit of unburnt fuel is going to get through (especially on a decatted car) and pops - especially if the exhaust's hot. But if it's a pain in the ass, I'd check the exhaust for leaks first.

metz · Post by **metz** » Mon Aug 22, 2005 1:07 pm

erm....yea on screw the airbox, didnt unplug the lambda to see it cycle.

not sure if he unplugged the sensor to do the timing..added 5 degrees like haynes said though.

better check the zorst for leaks today i think...maybe centre box is leaking.

hope its not running even leaner now or too rich due to summat not being right..i dont have access to the tools nrmally it was just a one off.

dizzy cap and rotor arm are new..plugs n leads arnt but they looked ok when i removed em other week, car idles ok and pulls like an ox but i did have to adjust the idle speed slightly as the revs dropped a lot if u put full beam on.

Andy should we have adjusted the Co screw with the lambda disconnected? as we unplugged blue sensor instead.

MadManMike · Post by **MadManMike** » Mon Aug 22, 2005 1:24 pm

Metz, I checked my g/f's receipts for the car (It's newish to her) and the exhaust was repaired in Feb, so I reckon our problem could be blown exhaust. I'll have to have a butchers at it tonight, since her car isn't tuned and nothing has been tampered with I reckon that's her best bet.

Let us know your problem

metz · Post by **metz** » Mon Aug 22, 2005 1:27 pm

I'll go lay under the car in a bit and let u know later mate.

amstrange1 · Post by **amstrange1** » Mon Aug 22, 2005 3:16 pm

I'm pretty sure all adjustments to the GT should be done with the blue temp sender unplugged, but with the lambda still plugged in. The ignition timing should definately be set with the blue temp sender unplugged.

Not too sure about the process of altering the CO, but it only really affects the mixture at idle - at partial and full throttle openings it doesn't have much of an effect.

I'm a bit rusty on GTs, not messed with one for a while - where's Barningfield when you need him?!

metz · Post by **metz** » Mon Aug 22, 2005 10:09 pm

been under the car today and it was leaking (exhaust) fixed it and its still the same..1500rpm and under when u lift off and it pops for england..any ideas?

potentionmeter thingy? as im sure there was a fault registered but it was cleared and didnt return that day

hardhitter · Post by **hardhitter** » Mon Aug 22, 2005 10:26 pm

I'm here

Like Andy said, the timing should be adjusted in service mode other wise it's going to be miles out. I'm sure I adjusted it before and got it running well, was something else out ?

If it's popping flames and everything else is fine, your ignition timing will be out.

metz · Post by **metz** » Tue Aug 23, 2005 12:08 am

yea u adjusted the timing bafore pretty good dan but i had the dizzy off since then fixing a water leak.

its only popping on lift off between 1500rpm and less, seems to still pull well though just noticed theres a lot of soot in the exhaust tonight..gunna take a look at the plugs tomorrow.