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13b turbo misfire at high boost

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Hi all,

I have been wrestling with misfire problem for some time now.

The engine is a 13b turbo out of a series 5 rx7 and is controlled by a Haltech Elite 1000.

Below I’ve outlined some observations. I’m hoping the brains trust can give me some ideas.

Observations whilst misfire occurs

· Misfire present at high boost (above 12psi).

· I can rev through the misfire and it clears up once boost level has dropped. So, it appears the misfire depends on boost pressure not rpm.

· Advancing/retarding the timing doesn’t have an effect.

· Changing to hotter plugs doesn’t have an effect.

· Increasing coil dwell times has no effect (currently set to 5ms)

· There is good earth to ignitor box and ECU

· AFR is 11:1

· Battery voltage is 14V

· No CAS trigger errors

· Fuel pressure is 65psi

· Both primary and secondary injectors are active at Injectors and ignition components are new (see below).

o Ignition components

§ Microtech X4 ignitor box

§ Bosch HEC715 coils

§ BR10EG spark plugs

§ Eagle 11mm leads

o 1650cc Bosch injectors used for primaries and secondaries.

Tried closing up the spark plug gap by 5 or 10 thou'?

Your setup should have plenty of reserve voltage, but some OEM spark plugs have rather large gaps, and that might narrow it down, as a denser mixture needs more voltage.

The other thing I would be checking up on - don't have direct knowledge - is that all the electrical components in the ignition side are compatable with each other.

Looks like a fairly standard micro setup, bring plugs in to about 0.5mm and try again. It may be the igniter box is on the way out too.

Check all your earths are good.

You shouldn't be having issues with that ignition system at 12 psi so I'd suspect you've got a dud coil, lead or plug. Plug gap, as mentioned by others, is another consideration however at 12 psi you really shouldn't be having issues, even if the plug gap is a touch optimistic. The only other points I'd make is that 11.0:1 (I'll assume that's what you meant) is quite rich for that boost level and will make it harder for the ignition system to light off the fuel/air charge, and 5 ms dwell is a little long (not that a longer dwell will reduce spark energy but you risk damaging the coils). I can't now find data on dwell for those coils but from memory you should be around 3.5-4 ms at 14 V.

Hi all, just a quick update...

Leaning the fuel off and decreasing the spark plug gap to 0.5mm seems to have fixed the problem.

I'll also drop the dwell time back down as advised to prevent the coils from being damaged.

Thank everyone for the help.

Did this ever get resolved. Having a similar issue on a car I am tuning. It gets a nasty misfire at ~5900 rpm under boost. Ive changed out pretty much everything but the engine at this point, including a new engine harness.

Just noticed the OP said he had tried "hotter" sparkplugs - they should have been "colder".

Matthew, your "pretty much everything" may be quite different from others' meaning.

There are some smart folks here that may be able to make suggestions - but without the engine, management, ignition, fuelling, etc. details it's not going to happen. Then there's the things you have already tried, and details of things like the affect different "boost" levels have - basically running through that mis-fire rpm range on part throttle?

[edit] NM, just opened your other post on this.

A 13b from ~1989 probably doesn't compare too well against a Nissan juke engine to be fair :|

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