Hi guys, I know this has been covered but none of the usual suspects apply. I did have a sizeable leak in the exhaust but I had help from a guy on Angelsey, modifying the exhaust so that it now lines up perfectly. He does custom exhaust builds and mods to a very high standard if anyone is interested.

 

There should be no overfuelling, I'm running the same tune as I did on my previous engine without any popping. I don't see how it could be an intake leak as this would lead to unmetered air and therefore lean if anything. It's making good boost anyway so I'm confident it's all sealed up nicely.

 

It runs well, not perfectly smooth at idle, but I do have a lightened flywheel. No misfiring, popping etc when under load, only pops on the overrun at lower speeds when warmed up.

 

The engine has allegedly had some cam work done on it, could this be the culprit??

 

I actually quite like the odd pop but just concerned it may be indicating a problem somewhere...

 

Cheers

RobH

Yes, I have access to all the fuel maps and scales via Nistune, it's a more or less standard map (apart from Injector size) I'm running at the moment with the factory enrichment, fuel cut etc, shouldn't really be a problem there...I had disabled O2 sensing to set the base AFR at idle and did suspect it might be the issue, however reactivating the sensors has made very little/no difference :(

 

Oh well, I'll just have to put up with it ;)

 

Cheers

H

I used to get it on my tt and also flames on full boost so my mate told me as i neally toasted his car ..over fueling an expensive thing fun thou

On overrun with no accellerator all injectors stop so no fuel going in, I guess you mean overrun with a little throttle on, assuming no leaks either intake or exhaust you have some unburnt fuel getting into the exhaust somehow.

 

Jeff TT

Yeah Mike, often get a pop when changing gear, almost a bang sometimes..

 

Jeff, that's the thing that's confusing me, with throttle fully closed it still pops whilst engine braking is slowing it down. I've had boost leaks before (some pretty massive ones) and they've never caused this. We checked the exhaust quite thoroughly and confirmed no leaks. TPS is relatively new, setup to 0.42V and reading correctly. I wonder if the MAF sensor could be over reading somehow? Or perhaps air is still being drawn past the MAF with throttle closed??

 

Just a thought, I have Blitz dump valves, my new engine should have way more compression than the old one, perhaps the dumps could do with adjustment?

 

Cheers

again

H

I'll double check the throttle cable adjustment as well just to be sure...

I would check your compression as it normally indicates badly sealing exhaust valves which allows fuel on the compression stroke to exit into the exhaust which then fires when the plugs ignite. If allowed to continue it can eventually blow your silencers apart.

Perhaps you have a coilpack failing - that leads to some unburnt fuel in the exhaust. I think I have a similar problem at the moment. (well I did the last time it was driven !)

Leaky injector?

Thanks for the suggestions guys. I think if I can get a wideband O2 sensor on each bank it should help identify whether there is a problem on one side, unfortunately I only have one wideband and getting a bit fed up throwing money at the old heap :(

 

I am still running in so will wait til I've finished (400 miles to go) and installed correct oil, new plugs etc before splashing out any more cash...

 

Old Zed, presumably valve timing being out could have a similar result? I'm not 100% sure the belt was timed correctly (I didn't set it), I had to rotate the CAS significantly from its marked position to get base timing to 15 deg.

 

SY, you mean leaking when it should be closed or leaking around the seals? They're Nismo 555cc with only a few thousand miles and a couple of years on them, should be fine but wouldn't take it for granted...

 

Cheers

H

If the CAS is a long way off the usual position and the electronic timing is done correctly (eg no auto/man gearbox conversion probs and the correct timing loop is used) then I'd guess the timing belt is a tooth out.

Thanks Andy - though not what I wanted to hear LOL! I use a piece of HT cable and a plug cap with a traditional timing gun on Cyl #1 to time it up, I don't trust the induction loop.

The car was converted to manual a few years ago but presumably so long as the base timing is set right it should make no difference (?) I know some folks have had some issues with the neutral switch but it's not clear to me what problems this causes.

 

Is there any obvious way to tell if the cams are timed wrong without removing the rad, belt covers etc? It's not something I want to embark on unless I'm sure that's the problem.

 

Cheers

H

OK, sounds like you can't go wrong with the timing, that's the way I do it too.

If the neutral switch is not wired correctly, then you will have timing about 10 degrees off from base if I remember correctly. Can't remember what you have to do now -try a search, I've certainly written on it before.

 

I think the only certain way to know if the belt is out is by looking at the marks on it - Jeff may have another suggestion.

Hmm.. my base timing was actually at 5 deg ATDC when the engine was first run so being 10 deg advanced (due to not modifying the neutral switch wiring) it was actually 15 deg ATDC in total(?!)

 

From what I've been reading, if I wire up the neutral switch correctly I'll be back to 5 deg BTDC at idle/warm and as I have no more CAS advance available I'll be a bit knkd! Does this confirm that cam timing must be out by a tooth or more??

 

Is the neutral switch rewired just to get the base timing back to where it should be without adjusting the CAS or is there some more fundamental reason why the CAS can't simply be adjusted to compensate? The car generally runs well whilst driving, not perfect at idle but not bad. The timing maps are being accessed according to load/rpm so it's not as if the neutral switch is preventing this.

 

Cheers

H