Intake backfire

[gareth29]

Hi, complete z and forum newbie here! Recently bought a 55 plate GT car with 59k and a backfire thru the intake manifold from cylinder no. 6. The engine runs without the misfire if the lead to no.6 is pulled. The coil pack appears to be ok, I have changed all the spark plugs and the fuel injector, checked the compression (which appeared higher than no. 4) and am now puzzled.

 

Has anyone experienced anything like this on a zed or offer any thoughts? Apart from "why did you buy it?"

 

Any help appreciated.

[WhackyWill]

Welcome to the Forum....

[lmc]

[Dblock]

Wrong section btw.

 

How do you know the coil pack is ok have you swapped it with one from another cylinder. Check the wiring going to the coil packs for breaks or the multi meter.

[Sam Mcgoo]

Put a intro post up (in the correct section and tell us a bit about yourself. (this post should be in technical but I'm sure the mods will move it)

 

Right, about your problem, more info needed.

 

You say backfire through intake? but then say misfire later. are you actually getting an explosion traveling into your intake? Or is it just misfiring until you remove no.6 from the equation?

[gareth29]

I've swapped it and its now on no.4, am going to try and check the wiring to the plug today.

[gareth29]

Sorry about the mistakes - it took me ages to work out how to post something.

 

Yes there is a pop back thru the intake, esp when the throttle is blipped. I've taken the top off the intake manifold and the tube down to no.6 is black.

[Sam Mcgoo]

OK. You said you have moved the coil pack from 6 to 4 and now it does it on 4?

[glrnet]

Topic now moved and welcome As others have said, stick a post up in intros and welcomes

[gareth29]

No the problem is still with 6 - thats why i thought the coils must be ok. Also I have done the pedal dance and it didnt show any codes.

[Sam Mcgoo]

Think I would be tempted to do the compression test again. Maybe with a leak down test.

From the limited info you've given it does sound like it could be something fairly serious. I believe it is number 6 that is more prone to running lean and excessive heat due to the plenum design and location near the bulkhead.

 

[gareth29]

Thanks for your thoughts on it. I'll post more info as and when.

[Ebized]

As you mention its plugs 4 & 6 - check out this thread and in particular the last 3 posts on the first page

 

http://www.350z-uk.com/topic/66607-changed-spark-plugs-but-something-not-right/page__hl__+coil%20+packs#entry989242

 

It is an easy mistake to make, if the leads have been taken off, and I'm just wondering if you might have got caught out

[samsniss350z]

to the forum.

[gareth29]

Thanks Colin, I've checked that

[Dblock]

With 6 being black it could be oil. The rocker seals fail and let in a little oil. It could be something else though.

[gareth29]

Thanks Dblock, but when i changed the plugs the one from no. 6 wasnt oily, just a bit sooty. Am now thinking sticking inlet valve(s) on no. 6. Wondering about taking the rocker cover off and trying to get some carb cleaner or similar down the valve stems, then draining/refilling with some flushing oil to try and clean it all out. Any thoughts anyone?

[Sam Mcgoo]

If your getting ignited fuel coming up into the intake it does sound like a sticky or damaged valve.

If you take the rocker cover off and turn the engine over by hand you may see if its sticking.

Bare in mind you may not be able to get an oil tight seal on the cam cover after you've removed it and i don't believe you can get the seal as its attached to the cover, so it means a new cam cover. But that's the last of your worries ATM.

 

 

[ZMANALEX]

In stock and good to go same/next day if required:

 

http://www.350z-uk.com/topic/54916-cam-rocker-covers-for-350z/

 

http://www.350z-uk.com/topic/46544-genuine-nissan-cam-box-gaskets/

 

Alex

[gareth29]

gareth it does seem to be an engine lowering job to enable head removal. I spoke to NISSAN today. let's hope it will not be necessary.B.O.L Dad.

[gareth29]

Thinking it may have been a sticky inlet valve, I've tried a couple of engine oil flush products on it yesterday, with no result. Now thinking it must be a broken inlet valve spring - does anyone know if its possible to change the valve spring without taking the timing case, chain, etc,etc from the front of the engine?

[ZMANALEX]

Unfortunately the cam shaft has to be removed to get access to the bucket and valve spring.

 

I would recommend that you run another compression check and also a cyl.leakage test.

 

Alex.

[gareth29]

Thanks alex, but can I remove the camshaft without removing the timing chain and case etc?

[ZMANALEX]

Afraid not mate.

[gareth29]

Thanks, I was afraid that would be the answer!