Popping Exhaust

[tte200]

Hi could anyone help…..

Have been driving round north Wales today and the car is a pleasure but when lifting off the throttle especially going down hill the car pops in the exhaust.

Also in the short term I have owned the car I have found difficult to start form cold (need to press the throttle and turn over a few times)

If anyone could point out any potential problems or suggest what cause of action I should take I would be grateful

Thanks

Terry

[MattDon]

is it a standard exhuast? i had this with my peco, i kinda liked it except for the occasional realy big pop. the only thing i know of that causes more popping is the timing being out.

[esprit888]

Does the car idle/tickover high? make sure the thrittle cable is correctly adjusted. Has the exhaust been modified at all? Typically the popping is unburnt fuel igniting after it was supposed to I.E in the exhaust or cat.

Hi could anyone help…..

Have been driving round north Wales today and the car is a pleasure but when lifting off the throttle especially going down hill the car pops in the exhaust.

Also in the short term I have owned the car I have found difficult to start form cold (need to press the throttle and turn over a few times)

If anyone could point out any potential problems or suggest what cause of action I should take I would be grateful

Thanks

Terry

[tte200]

Think the exhaust is standard, as for the timing was thinking the same thing. Have ordered CD workshop manual from eBay and when it arrives will check.

Thanks for information

[tte200]

Does the car idle/tickover high? make sure the thrittle cable is correctly adjusted. Has the exhaust been modified at all? Typically the popping is unburnt fuel igniting after it was supposed to I.E in the exhaust or cat.

Hi could anyone help…..

Have been driving round north Wales today and the car is a pleasure but when lifting off the throttle especially going down hill the car pops in the exhaust.

Also in the short term I have owned the car I have found difficult to start form cold (need to press the throttle and turn over a few times)

If anyone could point out any potential problems or suggest what cause of action I should take I would be grateful

Thanks

Terry

Tickover is around 800 RPM and the exhaust is standard (but possibly blowing upfront suspect down pipe)

[Nige]

Terry, the manuals are available for nowt from here, see the manuals link at the top of the page. Also have a look in the Wiki and the repairs section (also at the top of the page) how to check and set the base timing is all in there. I stri=ongly recommend you do this as it is not a service schedule item but does drift off and when set correctly it makes a big difference. As said previously the popping is unburnt fuel in the exhaust, more common with a big bore exhaust and higher than standard boost levels.

When starting, turn the ignition key until you hear the electric fuel pump whirr, hold the key in that position until the pump stops, this ensures the injection system is primed and pressurised (no more than a few seconds) then turn the key the rest of the way to crank the engine, don't even touch the accelerator until the car is running or you'l confuse the Idle Air Control (IAC) thingy.

[RayD]

And ... with it ticking over slowly ... see here

[esprit888]

And ... with it ticking over slowly ... see here

Does the ECU adjust to 950 when the A/C is turned on? or should it have a higher base Idle?

[GeoffSmith]

And ... with it ticking over slowly ... see here

Does the ECU adjust to 950 when the A/C is turned on? or should it have a higher base Idle?

I've got a feeling it automatically revs slightly higher Colin - stick ElanScan on and find out!

[esprit888]

Thanks Geoff,
Makes sense and once i get the fascia back together you can bet i will be running Elanscan (Hint for mystery ? number 2 ) I am waiting for the adhesive to harden so in the meantime i am looking for the Acc/ign on power wire to the radio. There are three purple wires, two of which have power continuosly, the third is the remote ant. So which one on the original harness is the acc/ign power? Or did Lotus have it pwoered 100% of the time? because i do not have any in the original radio wiring harness that is off when off and on when switched to acc. ?

And ... with it ticking over slowly ... see here

Does the ECU adjust to 950 when the A/C is turned on? or should it have a higher base Idle?

I've got a feeling it automatically revs slightly higher Colin - stick ElanScan on and find out!

[rip]

Back to the original issue of popping...

Mine currently pops quite a bit. I mentioned it to Geoff at Castle Combe & he immediately replied that "Timing is out".
When I had my Piper 'zaust first fitted, it ran lovely, but I knew the timing was out. I tried to set it but had a bad day & no adjustment appeared to have any effect???
Elanscan then showed some knock, so I knew the timing was too advanced, so knocked it back a little until no more knock was detected. I hardly ever heard a pop at this stage.
I later went back to set the timing (actually a Lotus specialist did it) & found it was running at 46 degrees BTC, which is a whopping 30 degrees too far.
Since the timing was reset correctly, I have lost power & economy, it overboosts more readily, the exhaust is very sooty & popping is very common.

I suspect that changes I have made (ie exhaust) have changed the characteristics of the engine which require adjustment of base timing for optimal performance.
I will get out Elanscan & fiddle with the timing, log some data & then check to see where the timing has ended up.

I will log any findings in this thread

[John_W]

I will get out Elanscan & fiddle with the timing, log some data & then check to see where the timing has ended up.

Rip,
Be aware that ElanScan won't tell you what the static timing is; it reports dynamic timing which is additive to the static setup.
John

[rip]

I will get out Elanscan & fiddle with the timing, log some data & then check to see where the timing has ended up.

Rip,
Be aware that ElanScan won't tell you what the static timing is; it reports dynamic timing which is additive to the static setup.
John

I know.
I'm going to mark the CAS's current position & experiment without a timing light. Using Elanscan & the feedback I get from behind the wheel, I am going to determine what I feel is the optimum timing.
Then I'll get the strobe out & have a look where its finished.
If it all goes belly up, then I can reset the CAS to the mark I made before I started.

[AutoXM100]

I have also noticed a popping in the exhaust. This was a very helpful post. After I get the rest of my issues sorted I am going to check the timing. Thank you!

[Enright]

Does the ECU adjust to 950 when the A/C is turned on? or should it have a higher base Idle?

I've got a feeling it automatically revs slightly higher Colin

It definitely does (rev it higher) to offset the extra load. It also cycles the fans, which can be very useful on a hot day in a traffic jam as your temperature needle rockets up towards the danger zone!
I would recommend turning off the A/C switch before making any adjustments to idle speed or base timing. Any interference from any un-isolated system just increases the risk of your having to do the whole job again because the result came out pants.

[esprit888]

Thanks Neil/Geoff,
Makes sense as at the moment i idle at 1100 but when the A/C is switched on it drops to 950. However i believe it should idle at 950(ish) and when the A/C is switched on the ECU should compensate by increasing the Idle ? I will do a 'no load' base setting of 950 and see what happens.
Cheers

Does the ECU adjust to 950 when the A/C is turned on? or should it have a higher base Idle?

I've got a feeling it automatically revs slightly higher Colin

It definitely does (rev it higher) to offset the extra load. It also cycles the fans, which can be very useful on a hot day in a traffic jam as your temperature needle rockets up towards the danger zone!
I would recommend turning off the A/C switch before making any adjustments to idle speed or base timing. Any interference from any un-isolated system just increases the risk of your having to do the whole job again because the result came out pants.

[GeoffSmith]

Does the ECU adjust to 950 when the A/C is turned on? or should it have a higher base Idle?

I've got a feeling it automatically revs slightly higher Colin - stick ElanScan on and find out!

EMJ.2-G says "… Before energising the a/c compressor, the ECM first amends the idle speed setting via the idle air control valve…"

[tte200]

Terry, the manuals are available for nowt from here, see the manuals link at the top of the page. Also have a look in the Wiki and the repairs section (also at the top of the page) how to check and set the base timing is all in there. I stri=ongly recommend you do this as it is not a service schedule item but does drift off and when set correctly it makes a big difference. As said previously the popping is unburnt fuel in the exhaust, more common with a big bore exhaust and higher than standard boost levels.

When starting, turn the ignition key until you hear the electric fuel pump whirr, hold the key in that position until the pump stops, this ensures the injection system is primed and pressurised (no more than a few seconds) then turn the key the rest of the way to crank the engine, don't even touch the accelerator until the car is running or you'l confuse the Idle Air Control (IAC) thingy.

Have clicked on the manuals link at the top of the page some weeks ago and filled in the requested information (forename, surname, Email, address, membership name )

I put my user id in the membership name box, do not know if that is correct?

But I have not received a password? Any ideas‘?

[rip]

I tinkered with my timing last night & the regular popping from my Piper has now gone.
Performance has increased enormously too. 30-70 in 4th gear has dropped from 13 seconds down to just 7!

[tte200]

I tinkered with my timing last night & the regular popping from my Piper has now gone.
Performance has increased enormously too. 30-70 in 4th gear has dropped from 13 seconds down to just 7!

Going to do the base timing on my car this friday hopefully will have the same results..