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NA-T leaning out under WOT -- advice/help?


sunny
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Hi guys,

 

I recently had the my NA-t mapped and it was running perfectly ok for a day or two then I installed a catch can as recommended by one of the garages where I had the car checked before mapping. After this, the car has developed a problem where it is leaning out under WOT and anywhere after 1/4-1/2 throttle (12-13+ afr and climbing). I already upgraded to the 255 walbro pump, fuel filter, even put the intake side of the PCV back to stock and car is still leaning out - AFR just keep climbing. Funny thing is at 1/4-1/2 throttle in boost, it never leans out and AFRs read ok at 7psi. There are no misfires, CEL, stumbling or anything like that, car idles, drives and pulls fine which is confusing me now.

 

Anyway, I am waiting on a block off cap to arrive so that i can block off the catch can outlet to the turbo inlet pipe and ditch the catch can completely and test it but I would doubt that would be the issue?

 

Is there anything else i need to look into or maybe i just need to buy bigger injectors? (running 330s currently at 7-8psi). I was going to get bigger injectors in the future but didn't think i would need them this quick, just wanted to enjoy the car for a little bit.

 

Should I do the 12V fuel pump mod?

 

My rear main seal is getting done in 2 weeks so I have some time to figure this out and would really like some input into what to look for.

 

Thanks in advance for any help.

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Get a fuel pressure tester on the car, you will see quickly if you have a fuel supply issue under boost. Pressure should rise almost 1:1 will boost pressure if using factory FPR.

 

If you are having a fuel supply issue then check that your pump is not dropping voltage under boost. If it is, then you need to redo the wiring / bypass FPC using 12v mod etc.

 

If you don't have a fuel supply issue but are still leaning then chances are you are at your injectors limit. Factory 330's are not going to support much boost. Your tuner should be able to confirm what duty cycle your injectors are running at, assuming you are running a standalone.

 

Catch can should make 0 difference to your engine's air/fuel ratio.

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Right ok i will check the fuel pressure and see what reads.

 

Also, could a bad pcv valve be causing this aswell? Ive been doing some reading and apparently if a pcv valve has gone bad, it can allow unmetered air into the engine and cause lean issue? But then it would read lean all the time right?

 

My pcv valve does look in bad shape, i need to take it out and check it aswell but i'll see if i can get hold of a fuel pressure guage and test that out like u said.

 

Otherwise, just going to have to fork out for bigger injectors already i guess.

 

Thanks a lot for your advice. Will test it out and see what happens :D

 

 

Edited by sunny (see edit history)
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I didn't think you could run as much as 7psi on stock injectors so you might just be running out of fuel as Mike said.

 

right ok. I'll get bigger injectors aswell next month to be safe. Am i right in thinking the rx7 550cc purple top ones fit straight onto the na rail and stock clips?

On the dyno, my tuner did say the injectors got maxed out after 6000rpm and so had to rev limit the car or just watch my rpm till i get bigger injectors. but below that it was fine and i drove it home that day and the next day too and the AFRs were ok and then suddenly this happened after the catch can install :/. Now it leans out on any rpm range under WOT and under boost.

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Don't think the N/A PCV has a positive shut off under positive pressure, but in any case i would say its down to the way you have the catch can system installed and the plenum is sucking in unmeasured air, can you post a diagram or pic of how its installed.

 

 

This is the way it is done. I even put the intake side to stock (i.e.: manifold to cam cover) and just ran the exhaust side to the catch can without the T piece but still same issue. The catch can does not have one of those mini filters on it and gets the vacuum source from the turbo intake/inlet pipe.

 

attachment.php?attachmentid=228818&stc=1&d=1534863834

pcv-sunny.png

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If you are running with a MAP sensor, then there is no risk of you having unmetered air causing the ECU load signal to go lean. So catch can plumbing is irrelevant.

 

In the event that your PCV is borked, and allowing a massive boost leak then your manifold pressure will drop accordingly under boost. Perhaps into an unmapped area, thus causing the lean. But if your boost levels has not changed then I doubt this scenario is happening.

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This is the way it is done. I even put the intake side to stock (i.e.: manifold to cam cover) and just ran the exhaust side to the catch can without the T piece but still same issue. The catch can does not have one of those mini filters on it and gets the vacuum source from the turbo intake/inlet pipe.

 

http://www.mkivsupra.net/vbb/attachment.php?attachmentid=228818&stc=1&d=1534863834

 

If the intake is blanked off with no leaks then its not that that causing the problem, with the cam covers going to the catch can and then to turbo intake is also not going to cause any problems, and if all was OK before then i suspect its just coincidence and perhaps the FPR is playing up is the vacuum source OK, or the pump has decided to play up, other than exes air or not enough fuel i can think of nothing else.

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Yea boost pressure is ok at 7psi. I have a new pcv valve and grommet coming from keron this week so will change that over and check. There was some oil on the outside of the pcv valve today when i took the rubber hose off. Does that indicate/help with diagnosing anything?

 

Will also try get a hold of a fuel pressue guage and check that and see what i get.

 

I replaced the pump with a 255 last sunday so doubt it is that. Replaced the fuel filter at the same time. The old one was pretty clogged up.

 

Wont be able to get injectors till september now if it is that :( which sucks. If it is the injectors, do you guys recommend upgrading the FPR at the same time?

 

Anyway, hopefully i'll have some success this weekend. Cant get a day with the car until something else goes wrong :/.

 

 

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