odd missfire problem with sr20det

[Speed Industries]

Hi guys

I am encountering a very odd problem with my sr20det redtop.

It all started at a drift event when the car suddenly started to missfire around 3500rpm and up. Felt like no power at all.

I switched the Z32 maf, nothing changed.

The plugs showed cylinder 4 running a bit rich.
I changed all 4 plugs and coilpack on cylinder 4.

Then it was good for 2 laps and then the same thing again.
Now it looks like cylinder 3 is running rich but not sure.

The car also has missfires when in idle, it pops a little all 2 seconds or so.

When I disconnect the tps it runs fine in idle.
Not sure though if the tps can have such a dramatic effect on the engine while running under load.

Does anybody have any idea on this problem?

[Kingtal0n]

Do a compression test. Where is the wideband A/F before it breaks up?

[DashS13]

CAS bad? or maybe sliped a little

[Speed Industries]

Will do a compression test asap.

Not sure what the A/F was reading. Can't test it under load since the car is not registered.

But here is a video and you can hear when it switches in to the missfires:
missfire - YouTube


How can I check if the CAS is still ok or just slipped?

[Kingtal0n]

I need more info on the engine.
What injectors
what turbo
how much boost
spark plug gap size
OEM coilpacks grounded to the back of the head on OEM harness?
What ECU
Original wiring harness for that vehicle? (not a motor swap right?)

ANY modifications you have. has the engine been rebuilt. Does it have any work done (cams, rocker stoppers, anything)
It sounds like you are losing spark or fuel or compression on a cylinder.
Compression test and get back to me with those details

Right off the top of my head it sounds like ignition related. Change the coil packs again (sometimes you get TWO or THREE bad in a row- Its happened before) and drop the plug gap if it's not already down.

[Speed Industries]

Here is the info:

Car is a JDM S13 Silvia
harness is all stock
pink injectors, 550cc I reckon
Garrett GT2871R with around 1.3bar of Boost
Garage Saurus ECU based on the stock one
Plugs are GReddy iridiums heat range 8 with oem gapping (brand new)

Engine has rocker arm stoppers but is stock besides this on the inside.
No recent rebuild.

Will get compression checked asap and let you know.

I also remember that this problem was occuring at a testday for like 1 second. Was fine afterward and 3/4 of a day full drifting 3rd gear.

[Speed Industries]

compression test showed good compression on all 4 cylinders with 8.5bars

[Kingtal0n]

Gap the plugs down. Try .030. My car with the same setup same boost blows out the spark easily around 12psi. I am surprised you can get past that even.

Oh, its because your OEM camshafts. Those are serious limiters to engine VE. Nevertheless, I recommend you simply gap down the plugs. If it still misfires change coilpacks again.

550's would not work if you had camshaft upgrades. Keep that in mind.

.030 is in inches. I notice you might use millimeters over there, so around .75 mm

[Speed Industries]

Alright, will try to gap them down.

But why is it missfiring at idle then?
And why does it not when going into the safety mode of the ecu (unplug maf, unplug tps..)?

[Speed Industries]

Thanks for the help though KingtalOn. Only guy who takes his time to look into this on various forums.

[Kingtal0n]

Missing at idle can be a lean air fuel ratio at idle. what is your A/F at idle?
It can also be the plugs of course. The coil packs could be very old and cause it. The wiring or grounding can do it (unlikely). And bad compression can cause it (which is why I wanted you to check).

More than likely you have a large maf (you never said what MAF you had) and it is fluctuating madly at idle, either because you have no air filter, or the air filter is too close to the maf, or the maf is too close to the turbo. I bet your maf is too close to the turbo, that is a common mistake. You need a bit of length, and a nice bend, THEN the maf, then another bit of length, and a nice bend, THEN the air filter. I always try to get the maf as far away from the turbo as possible. If it smooths out in limp home mode, then that points directly at the maf & air fuel ratio.

Pictures always help and they are fun too. Get us some pictures of the engine bay

[Speed Industries]

I got a Z32 MAF which I also already have replaced.
Piping should be good as is. It is a Trust intake kit and worked flawless the past 3 years.

AF at idle is around 11, so should be ok I think.

Will get you some pics though, just to keep the spirits high.

[Speed Industries]

More pics to follow

https://www.facebook.com/photo.php?f...type=1&theater

[Speed Industries]

So I regapped the plugs and changed all coils.
Sounds better now at idle but have to check under load (which is not so easy around here with a race car)

[Speed Industries]

Here is some pictures of the setup.







Plugs look all the same right now.

[tom_sr20]

did the new coils fix the problem?

[Kingtal0n]

11:1 at idle is too rich. It needs to be 14:1 or 15:1. idle that rich will foul the plugs, and carbon up the engine.

[Speed Industries]

Did not have any chance to test it out so far.
Public roads could get very messy with the cops out here.
Might trailer it to our driftschool on Sunday to check there.

Might be a bit on the rich side but the plugs usually are not that black after proper driving. So I don't bother too much about idle.

[Speed Industries]

Ok so I went for a short test run and it is ok right now.
But I still don't trust it.
At the last race it was ok for 1.5 laps after switching one coil.

What can have an effect on the coilpacks?
Is there anything that can kill a coil or make it malfunction?

[Speed Industries]

Ok so the problem looks to be solved.
Not sure where exactly it was but after changing
- all 4 coilpacks
- ignitor chip
- regapping the fresh plugs
- redoing the slightly toasted wiring to the ignitor chip

it now works again.

Thanks for the help guys.