[Mk2] [Turbo] Misfires/stumbles under boost with rebuilt engine

[toecutter]

I'm getting a misfire/stumble when the boost comes in/revs are up. It will boost and the revs do climb but not smoothly.

Didn't do this prior to changing the engine with rebuilt one (standard build bar steel head gasket).

Running actuator pressure (10psi) till engine is run in.

Would normally suspect ignition components but they worked fine with the old engine.Has a new dizzy cap and rotor. Running copper plugs, can't remember grade will check. Leads are aftermarket that came with it. Original coil pack.


Where should I be looking first?

[Ryan S]

original coilpack?? i;d be replacing that first

maybe check the fuel pressure too since it doesn't cost anything to do

[MartinF]

For the price of a new set of spark plugs and the ease in which it is to change them I'd try a new set first. I've chased a similar fault to this before only to be caught out by the spark plugs.

[toecutter]

Have ordered another set of BKR7E, will see if they help before I buy a new coil.

Also forgot to mention I retarded the exhaust cam 6 degrees, don't know if that could affect it.

[slipping clutch]

1992 turbo - Possibly afm related? However thinking back I had this same problem years ago and as sheppy has pointed out your issue could be fuel pressure related as mine turned out to be.

[Peter Gidden]

Usual question - error codes?

[mrfil13]

I had stuttering under boost.

Gutted the cat, replaced the plugs (only done 2k)

Stuttering gone.

[toecutter]

It's showing codes 12 and 13, these might be caused by my 2 step limiter, when I fit new plugs I'll clear the codes and not use the limiter and see if they still come up.

Has a decat so can't be that.

[Willenium]

I'd be tempted to try some new genuine Toyota leads. I was chasing a misfire for a while and after replacing plugs and dizzy cap I ended up changing the leads which has made a massive difference. The ones that were on it weren't old but they were aftermarket and I had heard they often fail.

[toecutter]

Put new plugs in gapped to 0.8mm, worse than before struggles to pull from 4k.

No error codes showing.

Will try coil pack then leads.

[Driftlimits Performance]

just keep guessing a risk terminal engine damage

[toecutter]

What would you suggest to find the problem?

[laze]

How soon after the rebuild have you been hitting boost? You need to give the rings a few hundred miles to bed in first.

[Peter Gidden]

How soon after the rebuild have you been hitting boost? You need to give the rings a few hundred miles to bed in first.

New engines SHOULD be boosted - to bed the rings in.

[toecutter]

Have been careful with it while running in, but as Peter says the rings need to bed in properly, only get so long to do it before cross hatching wears off.

[toecutter]

Had it out again to try a few things, was stuttering as normal but after a while pulled so well it hit fuel cut, around 15psi, this was just on actuator pressure.

Reset ECU and adjusted FCD and tried again today. Not quite right but still revs and boosts OK, was hitting 15/16psi, again on actuator pressure. AFR was 10.5 under full load.

I thought actuator pressure was about 7psi? TVSV is disabled and boost controller was off. Are AFRs usually that rich? Might be why its stuttering.

[Ryan S]

do you still have error codes?

[toecutter]

No they were only caused when using the 2 step limiter.

[SrSilkie]

Put new plugs in gapped to 0.8mm, worse than before struggles to pull from 4k.

No error codes showing.

Will try coil pack then leads.

Seems strange that you put in new plugs and its worse?

Maybe its actually fiddling with the leads thats made it worse? bad connection perhaps... not sure just my 2 cents

[toecutter]

Good shout on the leads but turned out to be the coil pack.

It was split in several places, got a new one (pattern part) for £40, lasted less than 10 miles before complete failure, had to get RAC to drive me back to house to pick up old one.

A phone call to Toyota and £120 later it's running great again