15 replies to this topic

[LukeFranky]

This weekend I went to Coffs to see my tuner. On the trip down Friday night the B4 ran beautifully.

Saturday morning Matt took a look and checked he could access my ECU. Saturday afternoon the car started to misfire under load. I checked Matt hadn't altered the tune. The most he did was reset the ECU.

It got worse driving around the coast Sunday morning. This afternoon I drove back to Armidale and the car chewed through a lot of fuel.

It is most noticable under heavy load, e.g. 9+ psi 2500 RPM. Higher revs have much less of an issue. Car is pretty smooth below 8psi.

Hopefully the diagnosis skills I learned in my last saga will allow me to solve this quickly. I've given the vac lines a quick once over already.

Where should I start first? I think MAF, I have a spare. Next coil packs (have spares too). Failing that I might data log it.

[duncanm]

plug gaps?

[LukeFranky]

Spark plugs have been in for a while now. Was working fine until this weekend.

[RX25SE]

Typically break down under load is an ignition fault. Faulty coil, high resistance in the leads, poor current (high resistance) flow to coil primary side etc.
If plugs are OK, I would start with checking resistance of each lead, then check coil primary and secondary side resistance.
You will need the workshop manual to compare your readings to spec.

[duncanm]

*cough* coil-on-plug.

[RX25SE]

Right. Forget what I said.

 

I assumed they were the same as n/a.

[RX25SE]

Out of curiosity, are they 3 or 4 wire?

[CRUISN]

Off topic, I had a faulty plug brand new out of the box once, would break down under load. Replaced plugs, sorted.

I'd still check your plugs.

[LukeFranky]

I'll pull the plugs to have a look. I have a spare set of used ones in alright condition I could try but I'll swap the coilpacks over first.

[duncanm]

You might find one of the plugs looks different - then you at least have some clues about which plug or coilpack may be playing up.

I'd just replace the plugs - $20

[Robbks]

You might find one of the plugs looks different - then you at least have some clues about which plug or coilpack may be playing up.

I'd just replace the plugs - $20

NGK BKR6E

[LukeFranky]

I'd just replace the plugs - $20

- Of course, I meant I'd only try the old sparkies for testing. Though, I highly doubt the current spark plugs are already kaput. This is my second set of iridium plugs and I haven't had trouble until now.

[Reevesy]

Iridium do have a problem with tips being blown away. Would be better just to go back to coppers for testing

[LukeFranky]

Pulled the plugs. All looked good except one showed signs off running somewhat richer than the rest. Replaced the coilpack on that plug and presto!

Thanks guys.

[duncanm]

Excellent