Engine miss and hesitation under load?

[driftweez]

Hey

I was getting very poor fuel economy out of my BG5 Legacy GT so have replaced the spark plugs with 1.1mm gapped plugs. I have always had a miss under load but it seems to be worse now.. Checked the CEL codes and its so not sure what I should be looking for? Knock sensor, AFM, O2sensor? Re gap plugs would this help? What are people thoughts?

Cheers

[Kiwi_Fozze]

Plugs should be .7-.8 iirc, your o2 sensor could Also be shot, explaining the crap fuel economy

[scoobygt]

yeah 1.1mm are a no go 0.8 is where it\'s at if you don\'t mind changing them every 10,000 ks go for cooper ones, bkr6e or bkr7e will do the trick

[DRFVDR]

Coils would be worth a look as well,

[Marky]

It\'s a subaru, check the AFM, borrow a known good one if you can, I swear 75% of the time that\'s what it boils down to

[titian]

 Marky said:

It\'s a subaru, check the AFM, borrow a known good one if you can, I swear 75% of the time that\'s what it boils down to

Yep either that or the Knock sensor Both can partially fail and not throw a code. ???

[BLSTIC]

I had a BF GT Wagon with a good O2 sensor and it ALWAYS got bad fuel economy (I got 10km/l ONCE on the highway) but mine did have 270,000km on it. However more related to this post I also had a missfire under boost. I replaced the plugs with copper core ones (no idea on the gap, was too long ago) and the miss almost disappeared (only happened at max load) for a while then got worse.

Pull the coils and check under the rubber boots for fine cracks as the spark will go through that if it\'s easier than going through the plug (a wide gapped plug under boost is actually pretty hard to fire). They *can* be temporarily/partially sealed with a non-metallic nail polish if they aren\'t too bad (just use clear). Old school guys did this on distributor caps. But mine were actually cracked to the point of falling apart. So...

I replaced mine with 4 VL commodore coils (some wiring required) and the leads from a DOHC engine with the wasted spark setup and never had a problem with spark ever again. Cost me $80 for the coils, leads were free from a mate and I cut up my collection of dead Subaru coils for the plugs.

Incidentally the resistance of the VL coil primary circuit (across the + and - of the coil) was the same as the Subaru coils so the ignitor should be fine long term, but see my signature for my official stance on internet advice.

[driftweez]

Ok so haven\'t had a chance to check the coils or regap the plugs but it seems to be idling low as well and stalls at lights when cold. Seems real strange as it never did this before I changed the plugs and would a 1.1, gap cause this issue?

[czar loc]

Yes. I Put plugs with 1.1mm gap and it ran like shit. The gap is suppost to be .8 like the earlyer post said

[driftweez]

Ok re gapped to 0.75 seems to idle much much better doesn\'t and off boost its great it\'s just under boost its missing quite badly. It feels ignition related so possibly coils?

[Minaj]

Is the car chucking a ecl when it miss fires? what rpm does it missfire ??

[driftweez]

Hey no cel codes when it misses. It hasn\'t had a cel code logged for a few years know but this miss had got worse? Boosts are at normal standard levels at misses eight through the turbo range from 3000 onwards much less noticeable on the flat.

[Minaj]

could be cam sensors, had that issue with mine

[Durty-Sanchez]

Things that have caused my miss-firing:

- Plugs gapped incorrectly. 0.8mm ftw

- Coils got old. New coils are pricey but make a huge difference (expect a few years out of a set tho)

- Fuel pump. The factory one will be giving you grief if you haven\'t replaced it already

- Fuel pump wiring. The factory wiring seems to build up heaps of resistance, limiting the current draw by the pump. New power supply/relay did the trick

- AFM (this was more a cut-out rather than a missfire). Resoldered cracked connections. There\'ll probably be CEL\'s if it\'s this.

Misc other ignition issues & fixes:

- Knock-sensor didn\'t cause missfires but did put it in to limp mode. You\'ll get a CEL for this.

- Oxygen sensor. Probably getting old but shouldn\'t cause missfire under load (ECU ignores it). It might explain your high gas consumption though

- Cam sensor gave me starting/idling grief, no missfires (ECU doesn\'t use it for firing, only syncing at startup and idle)

My order of debugging would be:

1. Regap those plugs!

2. Check ECU for codes - fix as required

3. Reset ECU (battery off over night)

4. Check resistance on fuel pump circuit - fix as required

5. Replace stuff! Your choice if you go in order of cheapness or likelihood of being at fault (i\'d go fuel pump, coils, knock sensor, oxygen, afm)

G\'luck

(edit to categorise stuff)

[BLSTIC]

Did you pull the rubber caps off the end of the coils and check for cracks/holes? Because as I said before I had the same car with the same problem. It was the coils, fresh plugs helped a little though. If you were in cairns I would wager money on it being the coils...