AFR pegs lean when trying to get going..

[aaronjb]

So, the car left me rather stranded at my parents house at the weekend, and now I'm stuck at home until I manage to find the fault and fix it, so.. here's a story for you:

On Sunday I had all the intake pipework from turbo to throttlebody off and disassembled.  Then, reassembled it all and put it back how it was before I started.

After that it was idling a little leaner (roughly 12.5:1 instead of it's usual cold idle of 11.5:1), and when I tried to trundle up their road (on a hill) the AFR would hit 16-17:1 and the car would stumble and fail horribly.

Sounds like a vacuum leak post MAF, right?

So my dad and I dismantled everything and put it all back together five or six times, tried replacing bits of silicone in case that was it, tried doing the clamps up super-tight and not-so-tight.. no dice.  After one iteration of this process it did seem 'better' - not 'right', but 'better', and on-boost it was fine and rich (which again supports the idea of it being a vacuum leak).


Checked the PCV line is still attached to the intake manifold - check.
Checked the brake-booster line is still attached to the intake manifold - check.
Checked that the rubber bung for the pre-TB PCV line is still in place - check.
Checked the O-ring on the MAF - perished, replaced with silicone sealant (had no O-ring) - check.

There are only four points it can leak on the intake pipework after the MAF, and I've been over them a dozen times  s:( s:(


So.. any suggestions?


My plan for lunchtime today (since I'm stuck at home) is to:

Wave a butane torch (not lit!) around the intake while the car idles, and listen for a change in engine note.  Will a butane torch work for this?  s:? :? s:?
Plug the line to the brake booster with a bolt (leaving me with no servo assistance) and see if that changes things - in case it's a blown master cylinder.
If I can get hold of a spare MAF to try, try swapping the MAF out.


Other than that, what alternatives are there?  Low fuel pressure?  Dodgy injector?


(Couldn't have picked a better time to fail eh than on my 30th birthday!)

[markiii]

dead IACV? if it's stuck open could cause that

or a blown intake manifold

how was she driving before teh problem?

[aaronjb]

She drove fine all the way down there - in traffic, on boost.. perfect.

On Sunday we had all the pipework off to mock up the chargecooler (which all fits now btw) and then put it all back together and I went to take a test run and BAM. .That problem was back again  s:? :? s:?

[markiii]

so again only when you've had it apart, that would imply dodgy silicon or dodgy clamps

[aaronjb]

Yep - we had the original (blue) silicone on.. so we tried some of the yellow stuff - same deal.

Tried the clamps screwdriver tight, then we tried them socket & wrench tight (very tight!) - same deal.

Which confuses the crap outta me  s:? :? s:?

If there was a hole in the IM or something that large I'd expect a runaway idle, but it idles steady and smooth, just a touch leaner than it should.


I'll try the "gas around the intake" trick and see if the idle goes up..

[markiii]

crack in the hardpipes or MAF mount?

something that opens when you tighten a clamp a certain way?

[aaronjb]

There were no cracks that I could see - in the metal pipework, at least, but the o-ring on the MAF was perished and split so we re-sealed that with silicone (turns out the tube is a little too small for the maf too, so the O-ring wasn't really 'in' the tube).

Could be something disloged on the IM though I suppose - the brake booster hose or something that opens up as the engine torques around.. or I'm just not getting a good seating on the clamps for some reason (read: I am a muppet) maybe.

[markiii]

moneys on teh o ring

Hesth ran like a dog after we siliconed it following a fubared o ring

replace teh o ring first

[aaronjb]

I shall try  s:) s:)  The O-ring 'seat' has got a bit.. mullered, I believe is the technical term, because the tube is slightly too small.. Quality TopSecret design  s;) s;)

Fingers crossed it's that and not a dead MAF.. although, a dead MAF would be an easy fix (albeit expensive) at least!

[markiii]

tbh with yourmileage and turbo I'd be tempoted to replace teh MAF and be done with, rule it or rule it out, either way it's probably about due

[aaronjb]

I'm thinking that too - so I'll try Stu's (I really hope it's not pi**ing it down with rain later!) and if that makes it better or changes the behaviour in any way, I'll buy a new MAF from Chris @ CTP.

Heck I may get one, long run, as a spare just in case.


I really need to get the Nissan fixed/taxed/insured, don't I.

[markiii]

you do

[Anonymous]

There's also a gasket between the throttle body and intake manifold.
I've read about people with turbo 1ZZs getting cracks in the plastic intake manifold.

Good luck finding it!

[aaronjb]

There's also a gasket between the throttle body and intake manifold.
I've read about people with turbo 1ZZs getting cracks in the plastic intake manifold.

Good luck finding it!

Eek, don't be saying things like that, Kevin.. (All the blood just drained from my face at the thought of having to replace the plastic intake manifold with the engine in the car)

[markiii]

it's an arse your lucky I have a spare

shout if you need it

[aaronjb]

Will do - cheers Mark  s:) s:)

Heh, perhaps I should have had the AA recover me to your house  s:lol: :lol: s:lol:

"Which garage?"
"Jones Inc., Welwyn"  s;) s;)

[Tem]

I always got some funny AFR issues when I removed the MAF from the tube and put it back. Seems like it's way too sensitive about the position and you can never get it just right when you put it back. I just do a quick autotune after that and it'll be fine again. If the AFR seems stable, wherever it is, I'd just tune it again.


Oh and if the MAF is toast, might be a good time getting a Subary MAF.  s;) s;)  I'd think the AFR was WAY off with a dead MAF though, so I doubt it's that.


Whatever it is, hope you find it.

[ChrisGB]

Hmm, rich under boost, lean under vacuum? First thing to do is plug all the vacuum and breather / PCV takeoffs to see if you get any improvement. Smoke taper around the pipework may spot leaks if it is in a place you can see.

The MAF is pretty critical in it's positioning, so may be a wise move to try remounting it with the proper O ring just to be sure.

Does AFR stay lean at fast idle? If so it is possibly more likely a leak than MAF position.

Good luck!

Chris

[aaronjb]

Well, SteveJ came around and we tried swapping out the MAF with a spare from someone (thanks Stu!)..

Fitted with proper O-ring etc, no dice - exactly the same problem.

Removed all the vacuum piping that we could and replaced it all with brand new silicone.  Eliminated the charcoal canister and solenoid. Tried again - still the same:

At idle, it's ~12.5-13.5:1 (usually 11.5-12.5:1)
At part throttle it's 16-19:1 and dies on it's arse
Under boost it's 11.5:1 - about a point leaner than normal.


So we reset the PFC and reloaded the maps.  Still the same.

Now bear in mind I have 525cc injectors:

Told the PFC it had the original 260cc injectors in... idle went to 10.5:1.
Told the PFC it had 350cc injectors in... idle went to 11.5:1.

Idle is fine - if you introduce and air leak (pull the wastegate hose off) the idle speed jumps up and it goes to ~14.5:1.  Idle is steady, not missing, no misfires, smooth as silk at 11.5:1.

Under vacuum when moving - 15.5-16.5:1 and dies on it's arse still!


I'm stumped.  It would seem like fuel pressure.. but it's fine under boost!




I really am stumped.. could maybe try changing the fuel pump out if we can find a spare, or put the stock injectors back in to see if the injectors have died.  Anyone think that's worthwhile?

Failing that, I'll be doing the same as rob and renting a car - can't afford to do that for long, though, before I'll be selling the MR-2 in bits to fund the car rentals  s:( s:(




Excuse my french, but, fucking great 30th birthday present, this.

[markiii]

pressure test the intake manifold

get yourself  a compressor attached to a hose on the intake manifold, keep teh throttle shut and everything else blanked

will it hold pressure? or do you hear a leak?

[aaronjb]

Getting a compressor is not easy without a car to get anywhere  s;) s;)

Now I'm really wishing I'd fixed the Nissan! I was even looking at cheap runarounds on Autotrader earlier  s:? :? s:?

[markiii]

tyre compressor from teh cig lighter will do it will put out more pressure than the turbo canyway

[aaronjb]

Good point *slaps forehead*

[Anonymous]

If you have your LC-1 hooked up like I do, so it simulates a narrowband sensor, try disabling O2 feedback.  If you've auto tuned already, it should run fine off the base and inj maps w/out feedback.  Wouldn't hurt to do the First Time Calibration procedure.

I think it might be that hard to remove intake manifold, though.  Time to make an access panel, maybe?   s:) s:)    It isn't that hard to do.

[aaronjb]

I never have O2 feedback turned on Kevin - I only have it emulating a narrowband on O2S1, not S2, which causes the PFC to go crazy lean if I turn it on..