misfire at 3500 on full boost

[OleVix]

SOLVED

My turbochim has a problem. It misfires when fully hot at 3-3500 rpm on boost, only on full chat, not half. Changed plugs. pluggaps, coils etc... suspecting bad earth. The wiring loom with coils and MS3 ecu is grounded on the intake and not behind the head as it used to. Thinking of drawing up a lead from the - battery to the earth point..

Edited by OleVix on Sunday 19th June 00:49

[Boosted LS1]

It may be pinking under load which could lead to detonation. I'd lower the boost a tad to see if the misfire's still present. Then I'd rethink things. Also, what are the spark plugs telling you?

[BoostedChim]

How mcuh ignition timing are you running at that point?

[Boosted LS1]

BoostedChim said:

How mcuh ignition timing are you running at that point?

He's at peak torque/load isn't he. The danger zone.

[OleVix]

The thing is, I'm at 0,35 bar on full boost with the firmest spring. With the other spring Im at 0,25 bar
Idnition is at about 21 when it occurs. Dont think its detonation. Theres no pinking, I know what that sounds like

[Pupp]

Got any AFR data from when it occurs, either logs or real time if you have a gauge?

Ignition at 21 deg BTDC sounds quite retarded for something like 5psi; your load reference is MAP presumably?

[OleVix]

Pupp said:

Got any AFR data from when it occurs, either logs or real time if you have a gauge?

Ignition at 21 deg BTDC sounds quite retarded for something like 5psi; your load reference is MAP presumably?

yes map, in real time afr is around 12,5...

[OleVix]

it feels like the ecu is cutting out on full load... can a bad battery or ecu relay or worn ign switch do this?

[BoostedChim]

Have you made a log file of it? It might help rule out ecu resets. I wouldn't of thought bad battery or ecu relay or worn ign switch would cause it if it didn't happen on half throttle or less boost. If you havent already you could try measuring the ht lead resistance, make sure you haven't got one thats much higher than the rest and its delivering a weak spark that only gets exposed with high boost.

[Boosted LS1]

OleVix said:

it feels like the ecu is cutting out on full load... can a bad battery or ecu relay or worn ign switch do this?

I once had an ecu misfire when my electric fans kicked in and it played havoc. I fitted a much larger battery and did a few other things to sort it.

Also, have you got a really good spark ie they're not being wetted out under load?

[L88KED]

Try closing up the gaps on your spark plugs.
Sometimes the boost can blow out the spark, had the same problem on my Hayabusa Turbo.

[OleVix]

L88KED said:

Try closing up the gaps on your spark plugs.
Sometimes the boost can blow out the spark, had the same problem on my Hayabusa Turbo.

tried everything from 0,6mm to 1.0

[anonymous-user]

Stick it on a dyno.

I suspect you'll find that it's a lean misfire, insufficient fuel pressure.

Pump, regulator, leak.

[OleVix]

TVRMs said:

Stick it on a dyno.

I suspect you'll find that it's a lean misfire, insufficient fuel pressure.

Pump, regulator, leak.

leaning out would show up on the AFR meter

[Boosted LS1]

OleVix said:

tried everything from 0,6mm to 1.0

Have you tried projected nose plugs NGKBP7 or something like that? I can't remember the number exactly.

[OleVix]

Boosted LS1 said:

Have you tried projected nose plugs NGKBP7 or something like that? I can't remember the number exactly.

I really doubt its plugs related... were talking 3 psi here

[Boosted LS1]

OleVix said:

I really doubt its plugs related... were talking 3 psi here

Ah, then I'd knock out 10 degrees of timing at peak torque and see what happens. If the misfire is cured then add a few degrees back.

[OleVix]

Boosted LS1 said:

Ah, then I'd knock out 10 degrees of timing at peak torque and see what happens. If the misfire is cured then add a few degrees back.

Solved the issue. Turns out something was amiss with the TPS or the wiring to it. Set it up tu run on MAP instead of TPS and all is fine...

[Boosted LS1]

Great news. back to driving fun.

[BoostedChim]

Glad you got it fixed. It's a really bad idea to run a turbo on a TPS setup anyway as the boost is dependant on the loading eg it'll make more boost going up a hill for the same throttle opening as it would for a flat road. The TPS setup will use the same ignition timing for both situations where as MAP won't.