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202 popping through exhaust at idle.


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#1 D-Train

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Posted 11 June 2021 - 06:04 AM



G'day guys, I need some help.

My engine is popping through the exhaust at idle. When I give it some throttle, it stops popping until it goes back to idle.
Its a newly built black efi 202 at 30thou with a m90 supercharger. I'm using a megasquirt 3 gold box for the ecu with a 36-1 trigger wheel.
9.2:1 compression roughly.
Xu1 grind cam
Running 100% e85, usually only 80% ethanol at my stations.
Yella terra 56cc alluminiumt head with  1.6 rockers.
Compression is rouggly 165 psi on all pistons.
I've checked that its getting spark with a check light. No 6 plug is black while the other 5 are normal. I swapped coils but no change, new leads amd plugs, but nothing.

I thought the rocker arm on no 6 exhaust might be hitting the rocker cover as it'd originally cover but I can't see any marks. I was thinking of.starting it without the cover but thought it might make a huge mess.
I'm running out of ideas. Any thoughts

#2 yel327

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Posted 11 June 2021 - 08:19 AM

Cut the lid off an old rocker cover and use it if you want to run it with the rockers exposed.
How come you used a big cam designed for triples with a blower? Just curious.

#3 jd lj

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Posted 11 June 2021 - 09:12 AM

It's potentially running too lean at idle. Do you know what the AFR is at idle. Try to richen up the idle circuit and see if it helps.

#4 D-Train

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Posted 11 June 2021 - 09:36 AM

Sorry, that was the wrong one. Cam is 208 at 50 420 lift. Cm203d.

I pulled it all tge way down to 12:1 to check that but that's total afr at the collector. It's odd it is just one cylinder.

#5 warrenm

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Posted 11 June 2021 - 10:53 AM

Could be a dodgy injector in #6, move the injector to opposite end & see if the problem moves.

#6 axistr

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Posted 11 June 2021 - 02:16 PM

Pull one spark plug lead or injector electrical plug of at a time and check which cylinder isn't working. Check for a dribbling injector, vacuum leak and spark at idle on that cylinder. Have a good look at the spark plug it should tell you part of the story. If you have a vacuum gauge put it on and make sure its not flickering at idle. I found a very weak valve spring on a engine that still had good compression on that cylinder, took me a while to find it as it was probably the most unlikely fault in my mind. However The first thing I would be looking for is a vacuum leak at the inlet manifold on that cylinder.  



#7 D-Train

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Posted 13 July 2021 - 10:26 AM

The plug is coming out black on number 6.
I pulled the injector plug while it was running and it made no difference to the running of the car, although it did stop popping cos it wasn't sending fuel down the exhaust. I tested tge spark system with the ecu and all six spark plugs fire on command.
So the cylinder is completely dead but getting spark fuel and air. I noticed the rockers were rubbing against the cover on the #6 exhaust due to the baffle on the black efi cover but fitting another cover didn't change things. Could this have done damage down the line?
I cut a hole in another rocker cover so I could see them moving and it all looks fine to me.
The injector is definetely sending fuel cos it's popping when it's plugged in.
Any thoughts?

#8 S pack

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Posted 13 July 2021 - 11:05 AM

Exhaust valve not sealing properly on its seat perhaps? Have you performed a compression test?

Edited by S pack, 13 July 2021 - 11:05 AM.


#9 Rockoz

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Posted 13 July 2021 - 11:39 AM

I would actually check the injector spray pattern on No 6.

To my thoughts, thats where your problem lies.

 

Cheers

 

Rob



#10 claysummers

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Posted 13 July 2021 - 01:06 PM

I had this symptom recently. Turned out exhaust valve was not opening, so exhaust charge was exiting through carb when inlet valve opened. May be rocker or pushrod damage also causing the rubbing. Could also be exhaust cam lobe gone or lifter collapsed. Make sure that exhaust valve is opening properly.


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#11 Dr Terry

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Posted 13 July 2021 - 01:08 PM

Sounds like no. 6 injector is stuck open.

 

Try swapping it with say no. 1 injector & see if the fault is then transferred to no, 1 cylinder.

 

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#12 D-Train

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Posted 13 July 2021 - 02:01 PM

Yeah, all are running at 160-170. I have a leakdown tester.coming today.

#13 VIXL34s

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Posted 13 July 2021 - 02:07 PM

Crook spark plug I think, I have had similar problem with L34. Cheers

#14 D-Train

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Posted 13 July 2021 - 05:20 PM

So this arvo I swapped coils, plugs, leads and injectors and still no 6 popping.
It runs so much better with the injector unplugged and them shakes a bit more when it's plugged in. Not sure of its because it's only igniting every now and then or if it's the fuel going in and compressing causing it to shake. It's looking like it's part of the valve/rocker family. Ill still do a leak down first. Any other thoughts or this sound good?

#15 claysummers

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Posted 13 July 2021 - 06:33 PM

Swap the injectors like Dr Terry says


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#16 D-Train

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Posted 13 July 2021 - 09:34 PM

Swapped the injector over but no change

#17 Dr Terry

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Posted 14 July 2021 - 07:36 AM

It might be a riding valve. Try backing off the rockers, no. 6 exhaust might have too much preload.

 

Even if you backed them off to the point of a slight rattle, the motor will still run properly & you are then certain all of the valves are shutting fully.

 

Dr Terry



#18 D-Train

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Posted 14 July 2021 - 08:49 AM

It's a non adjustable rocker. Can I still do this with the locking bolt?

#19 claysummers

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Posted 14 July 2021 - 09:03 AM

Check the lash. Probably already loose if they are non adjustable.


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#20 S pack

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Posted 14 July 2021 - 09:08 AM

You can reduce the lash on non adjustable rockers by placing a suitable size packing washer between the pivot posts and the cyl head pedestals.

#21 claysummers

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Posted 14 July 2021 - 09:22 AM

Won’t that increase lash Dave? I reckon the only way you can reduce it is machine down the mating surfaces on the bridges or head, or build up the rocker surfaces.


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#22 S pack

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Posted 14 July 2021 - 10:17 AM

Won’t that increase lash Dave? I reckon the only way you can reduce it is machine down the mating surfaces on the bridges or head, or build up the rocker surfaces.
 

Perhaps I didn't word that well. Packing the pivot bridge posts can reduce the valve lash to zero if you so desire. Same as backing off the adjusting nut on adjustable rockers to obtain zero lash.



#23 D-Train

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Posted 14 July 2021 - 10:40 AM

When at tdc, the push rods will spin but don't have any up or down movement.

#24 Dr Terry

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Posted 14 July 2021 - 11:32 AM

I would fit adjustable rockers & adjust as per 179 & 186 procedures.

 

With a modified engine you need to set the lifter preload accurately.

 

Now I know you have non-adjustable valve gear, I would bet my left nut that you have a riding valve. i.e. one that is not fully closing.

 

Dr Terry



#25 Dr Terry

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Posted 14 July 2021 - 11:35 AM

You can reduce the lash on non adjustable rockers by placing a suitable size packing washer between the pivot posts and the cyl head pedestals.

I think you've got that arse about. Packing the rockers UP will INCREASE the lash. 

 

Dr Terry






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