2zz strange misfiring/hesitating at high RPM

[Ozzy]

Hi,

Got a 2zz that's got odd misfiring issues but no engine management light/fault codes showing.

It misfires badly on cold start with the slighest bit of throttle but this goes away when warmed up. The idle itself is fine and engine sounds smooth as it should with no weird sounds.

Once warm, it hits lift aggressively but hesitates at high rpm near 8000. Feels like a soft limiter and makes brrrrrr noise lol like a DSG gearbox for a second.


- I've tried new sparkplugs, working coilpacks and MAF from my Celica Tsport separately.

- Tried temporarily running without my panel filter.

- Have removed the cat for a decat pipe incase its clogged.

- Tried spraying engine bay for vacuum leaks but nothing and all hoses are fine.

- No leaks from fuel injectors. Look and sound fine.

- O2 sensors are reading between 0.1v and 0.8v and fluctuating as they should however short term fuel trim is -3 and longterm is -13 and car is smoking black sometimes.


Any experiences or suggestions what to do? 🤔

Thanks

[jvanzyl]

Replace the O2 sensors. They may still "work" but they get slower to respond as they get older.

[Alex Knight]

Definitely sounds like lambda sensor(s) to me.

I'd replace the primary first, and see what that does.

[mr2garageswindon]

Crank sensor earth?

[Ozzy]

Thanks, I'll give these a check and I do have a spare o2 sensor so I'll try that out but never experienced one causing major issues like this before.

[Ozzy]

Update, new O2 sensor didn't help and crank sensor seems fine also.

[JB21]

Could be as simple as batch of dodgy fuel, as I've had this previously. You've not used E10 have you? but sounds air/fuel related.

Maybe pull the fuel rail out and run an injector spray pattern test to make sure they're consistent.

You could try an O2 fooler on the post O2 sensor, but doubt its this if you've changed the O2 sensors out.
https://www.ebay.co.uk/itm/404022650900

Could also be you cat is dying, or maybe something random like a weak battery.

Other things to check TPS output, lift and VVT OCV filers, TB for gunk and/or leaks, check the PVC is working correctly. If all ok I'd then start looking at wiring in the engine bay, make sure nothing has melted or fused together.

If all that fails Ive got a mate who is a whizz at fault finding who you could take it down to, he's Cheshire based though.

[jvanzyl]

Update, new O2 sensor didn't help and crank sensor seems fine also.

Ah nuts.

Out of curiosity, what's the status of your fuel pump and filter?

[Gaz mr-s]

Update, new O2 sensor didn't help and crank sensor seems fine also.

Just checking...it was the earthing bolt you checked. I had the fault on a 1zz.

[Carolyn]

When checking the earthing of the crank sensor, it pays to unbolt it and give the whole thing a good scrubbing.

Have you considered a cooler grade of spark plug?  The wrong heat range will show up when the engine is working its hardest.

[Dev]

Hi,

Got a 2zz that's got odd misfiring issues but no engine management light/fault codes showing.

It misfires badly on cold start with the slighest bit of throttle but this goes away when warmed up. The idle itself is fine and engine sounds smooth as it should with no weird sounds.

Once warm, it hits lift aggressively but hesitates at high rpm near 8000. Feels like a soft limiter and makes brrrrrr noise lol like a DSG gearbox for a second.


- I've tried new sparkplugs, working coilpacks and MAF from my Celica Tsport separately.

- Tried temporarily running without my panel filter.

- Have removed the cat for a decat pipe incase its clogged.

- Tried spraying engine bay for vacuum leaks but nothing and all hoses are fine.

- No leaks from fuel injectors. Look and sound fine.

- O2 sensors are reading between 0.1v and 0.8v and fluctuating as they should however short term fuel trim is -3 and longterm is -13 and car is smoking black sometimes.


Any experiences or suggestions what to do? 🤔

Thanks

What kind of air intake are you using?

[Ozzy]

Sorry for the late reply guys, not had a chance to mess with the car.


JB21 & jvanzyl - I've since filled up a few times and only use Tescos super unleaded.

I do suspect its air/fuel related but can't find anything wrong unless as you said it is injectors or pump. I've double checked for vacuum leaks. I am suspecting a failing fuel pump also now as I recall one of my cars breaking up the same way a few years back under load.

Plan is to check and clean ocv, iacv, tps and throttle body next.


Gaz mrs & Carolyn - I checked crank sensor to see if it was connected and secure but will admit, I didn't take it off 😬

Dev - I'm using a Blitz panel filter which is quite clean. Ran it temporarily  without but still breaking up the same.

[Ozzy]

Just tried PCV with no luck and plan was to check IACV, TPS and OCV next but may have spotted a potential cause of the problem.

Spotted the battery terminals shorting out on my strut brace with several burn holes in the strutbar. The hole where the battery clamp hooks into has broken and battery has been sliding about. Don't know what sort of damage this could have caused and how long it's been happening.

Don't think I've knackered ECU as everything still works. I've temporarily removed the brace until I can secure battery properly and have brought a new battery tray off ebay but gave it a quick run and it's still breaking up under load.

Battery voltages are good but don't know if a battery can still be faulty and show correct readings. Thinking to temporarily try swapping batteries as well. If nothing helps after all this, then I'm guessing fuel pump.

[jvanzyl]

Great opportunity to upgrade to a lifepo battery with cage...

[mr2garageswindon]

Have you checked and cleaned the earth wires for coils etc like on the 1zz on side of the head?
Had that issue on one last week.
Customer fitted new engine due to oil consumption and ran crap soon as fitted.
He had connected the earths just not tightened the bolt.
That was missing only when being driven.

[Dev]

Dev - I'm using a Blitz panel filter which is quite clean. Ran it temporarily  without but still breaking up the same.

 Not the filter the intake. Are you using the 2ZZ intake, 1ZZ intake or some other aftermarket intake.