Engine holding back at wide open throttle

[shnazzle]

Kit posted
and now we wait

[The Arch Bishop]

Kit posted
and now we wait

Indeed! I'm not here this weekend so the wait may be a little longer than expected, but I'll get on it the first opportunity I have! 

[The Arch Bishop]

Well, I've managed to fit the parts that Shnazzle has kindly sent through, but irritatingly, there is no change in the way it's driving.

So far then, I have changed;

• MAF
• Manifold O2 sensors
• TPS

Still the minor kangarooing, lack of power and struggling at half and full throttle remains.

Anyone got a match?

[lamcote]

Have the fuel trims etc changed after fitting the parts shnazzle sent?

[shnazzle]

The figures actually look more normal.
I can see some key indicators that everything is responding as it should
- warming up. Revs slowly dropping and timing slowly dropping to 13.5-14.5. So your idle air control is working
- timing bottoms to 8 and low rpm high throttle (78%). As expected.
- max throttle value I saw in your recording is 80% and min at 12.5%. Minimum is spot on. Max is a tiny bit low but you may not have had foot to floor.
- you're missing some LTFT due to the reset. Fine.

Your short terms on the other hand show both massive under- and overfueling.
All your sensors are doing their jobs.
It's mechanical

[mattbrown82]

I had a similar issue when I first bought my MR2. Slight hesitation when on full throttle, especially after changing gear. Cleaning the MAF made a small improvement but replacing the pcv cured the problem.

[The Arch Bishop]

It's mechanical

Are we talking ancillary or darkest depths of the engine? 

What's weirding me out is that it was (moderately) fine at the start of the day, then a simple plug and filter change and as if by magic, it's suddenly unhapppy. Much like its owner...

[shnazzle]

It's mechanical

Are we talking ancillary or darkest depths of the engine? 

What's weirding me out is that it was (moderately) fine at the start of the day, then a simple plug and filter change and as if by magic, it's suddenly unhapppy. Much like its owner...

Matt may be onto something with that pcv.
Cheap as chips via TCB.

[The Arch Bishop]

PCV in terms of it being stuck open and letting increased air into the intake? OK - is it worth removing and cleaning out (more for speed than being a miser) before replacement?

[shnazzle]

Block it off as a test.
Undo the clip, pull the pcv pipe off and shove a spark plug or big bolt in the pipe. The pcv will just vent to air.
Reset and drive or drive for about 10-15 mins.

[The Arch Bishop]

Right you are. Will give it a go! Thanks for sticking with it everyone!

[The Arch Bishop]

Good and bad news...

This evening, I had a visit from a local MR2 hero Andrew, who came over to try and find out what on earth is going on with the car. First thing he did was to check the timing, so the rocker cover was removed to reveal a ridiculously clean and unworn engine. It looks like it may have had a recent rebuild or swap.

the timing was spot on, so no worries there. He put it back together and started it up and instantly decided from the sound of the engine that the plastic intake had started breaking up. After removing the throttle assembly, he managed to poke a camera inside to find that there was indeed plastic shrapnel in there.

Sooooo... obviously step one is to source an intake that isn't as brittle as Easter egg chocolate. Step two is deciding whether it is possible to replace the intake with the engine in situ. Andrew is prepared to give it a go, but thinks it may be a case of dropping the engine.... Larks ahoy!

Can I just say a huge thanks to all of you on here that have been so helpful and for putting up with my stupid questions! I owe you all a beer!  :notworthy:

[shnazzle]

Wow. The failure rate is absolutely tiny and only increased in high power forced induction builds.
I don't suppose you know if the car has a history of having had a turbo?
Engine rebuild could be related

[The Arch Bishop]

Doesn't look like it - I've got a lot of history with it and there's no evidence anywhere in that or with the car itself. It is bog-standard in every regard - just a pampered (for the vast majority of its life) car. But it's certainly had a new short engine and it hasn't done many miles on it either.

Andrew tells me it was a (low failure rate) recall for all of the other early applications of the 1zz but strangely not the MR2. Possibly because it was such an utter pain to do....

He's bringing an endoscope to double check but he's pretty confident.

[The Arch Bishop]

Pics;

Fresh looking top end;



And inside the intake (lot of oil in here as well);



The rings are the suspicious bits. orangey sealant used inside of them and a bit of plastic wedged in the runners. This is related by myself so it may not be entirely accurate but that's what I remember!

[shnazzle]

That oil don't look like oil From that pic it looks like your IACV coolant passage gasket went.

Hopefully it's all sorted soon. Getting the manifold out without removing engine might be interesting. Lots of universal joint connectors on tools

Fingers crossed mate that it's the manifold

[The Arch Bishop]

Oh I certainly hope so! Got to love the Roadsters and their foibles! 

[The Arch Bishop]

An update on this finally!

The manifold was swapped (it was not easy - I never want to do one again) and the whole thing's been put back together. The issue has not been resolved, but at least the car is working to some extent again!

Giving the car a fairly light throttle opening will make it cough before picking up.

So, today I've been faffing around with the MAF. I swapped my replacement out for my original one and it ran worse - occasional misfire at idle and coughed at any throttle opening. I took off the plug to the MAF and as if by magic, no stutter - throttle is sharp and responsive.

Put the replacement MAF back in and the cough was back but better than the old one. Again, unplugging the MAF solves the cough.

So is there any chance that I've been extremely unlucky and have two bad MAFs or does unplugging it and forcing it into a base map just get around an issue elsewhere?

Once again and again - any help/opinion/ideas are welcome!

I will flipping fix this car!!!

[jonbill]

My recollection of unplugging the MAF is that the engine dies, but obvs not. I think the chance of two duff cheap MAFs is quite high. What value do they read at idle? Somewhere near 2?

[shnazzle]

There's always the possibility of a bad ecu

[The Arch Bishop]

My recollection of unplugging the MAF is that the engine dies, but obvs not. I think the chance of two duff cheap MAFs is quite high. What value do they read at idle? Somewhere near 2?

It does if you pull it while running, but if you restart and give it some throttle, it'll then idle and run. Not sure on the values - can certainly give it a look.

There's always the possibility of a bad ecu

I guess there is! The reason I'm obsessing about the MAF is because I was changing the air-filter just before the problem cropped up. Could just be coincidence though!

Anyone had the wiring or plug go bad?

[The Arch Bishop]

Well I've gone through all of the things I can do without throwing new parts at it.

Checked for vacuum leaks at the MAF (found a new O-ring which seals it perfectly), checked the various other pipes that come off the throttle body/intake manifold - all fine. Sprayed some stuffy around to see if I could detect a stumble. Nothing.

Truly stumped!

I had another look at the trims - weird that the long term trims adjust seemingly on the fly from -8 on one bank -12 on the other at idle and then instantly changes to 0 and -4.6 at around 1500rpm. I'm not sure I'll ever really understand this thing! 

[lamcote]

Air leaks should give positive fuel trims not negative.

I would replace the PCV valve first. If that doesn't sort it, try checking for leaking or sticky injector/s.

[shnazzle]

Agreed. Or, pull the pcv valve pipe off and block it with an old spark plug. Then you'll know as well.
Very easy test. It's just one little clip on the pcv valve holding the pipe on.

On the LTFT. You're not seeing rapid changes in fuel trims, you're seeing the different values in the table across rpm and load. On the Toyota these are very granular.

[The Arch Bishop]

Agreed. Or, pull the pcv valve pipe off and block it with an old spark plug. Then you'll know as well.
Very easy test. It's just one little clip on the pcv valve holding the pipe on.

On the LTFT. You're not seeing rapid changes in fuel trims, you're seeing the different values in the table across rpm and load. On the Toyota these are very granular.

Air leaks should give positive fuel trims not negative.

I would replace the PCV valve first. If that doesn't sort it, try checking for leaking or sticky injector/s.

I have previously checked the PCV valve and all seems well there. I also did do the test by blocking off the vacuum pipe but no improvement sadly.

I have ordered a new Denso MAF just so I can be sure that this is not the issue. Opie oils had a good price on therm and even if that doesn't sort it, I can be confident of that not cropping up in the near-future.

A sticky injector is a good idea for where to go next. It has history if this previously according to the history and looking at how Toyota replaced the dicky one (at the time - i removed the rail when removing the inlet), it's not the neatest solution. Basically, all bar the replaced one had a small black cap that fitted over the business end other than cylinder three which was replaced. Due to the missing cap on the replacement injector, they used a seal with a smaller internal diameter to fix the difference.

Thanks for the suggestions by the way. Internet diagnosis is about as far away from ideal as you can get, but it does at least give me a direction to go in so I am extremely appreciative of any help!