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Old 09-24-2020, 08:22 AM   #26
rtv900
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2016 STI

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Just one thing to mention that may be applicable, somebody with more experience working on these particular engines could chime in if needed:

The fact that you unplugged your MAF to do this creates a new variable that you might want to consider.
When you try and restart normally with everything as it is, the MAF of course is plugged in so the car knows it is hot and the MAF is working, so it will be fueling according to the needs of a hot engine (might be where your problem is)

When you unplug a MAF the car knows it has no reading, so it reverts to a 'safety' mode and fuels as if the engine is cold regardless, which means much more fuel. (that's why it was running so rough as you noticed)

This may be helping it start in that problematic 'hot' state.
You could actually just try it sometime hot and unplug the MAF and do nothing else just to see what happens.

Either way it still sounds like you only have a minor issue while cranking hot and your approach of checking fuel pressures and injectors is a good starting point.
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Old 09-24-2020, 09:09 AM   #27
Samurai Jack
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Quote:
Originally Posted by luv2boost View Post
Also, would absolutely appreciate any help and advice on performing a fuel pressure test on this car, as tomorrow I’ll stop and pick up a gauge kit from HF, so I can dig a little deeper.
So, this may be of some help and looks like this addresses some of your symptoms to it being an FPR.
https://www.700r4transmissionhq.com/...ure-regulator/

This will describe what you need to do to perform a fuel pressure test
https://www.wrxtuners.com/threads/fu...to-test.23080/

Very simple.
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Old 09-24-2020, 10:40 AM   #28
T-37
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Vehicle:
0304 WRX WRX
SY WRB

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yeah, IAT is in the MAF. Unplugging the MAF reverts to a speed density mode

FWIW, fuel filters are scheduled to be replaced every 60k on these.

Some of these cars have inline dampers in the fuel lines as well, so don't mix those up for the regulator (sits on the passenger side of the intake manifold/fuel rails with a small vacuum line running up to the manifold)
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Old 10-03-2020, 05:31 PM   #29
luv2boost
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2016 Wrx Limited
Crystal White Pearl

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Hey guys, it’s been a little while but I’m back with some more information and attempted repairs, but still having the same issue...

So here’s a short list of the things I’ve tried, all to no avail:

PO had installed a eBay style SRI with a cheap dirty filter, which I didn’t like and thought maybe this has ruined the MAF, so I found a complete used stock air box w/oem MAF sensor and ram air, and reinstalled everything with this new MAF- runs good, but still hard to start when warm.

PO also had installed some aftermarket BOV, which I don’t trust, so from the same seller, I picked up his used stock BPV and reinstalled that. Runs good, but still hard to start when warm.

Battery was an old Walmart group 35 from 5/2012, so upgraded that to a fresh Napa Legend 640CCA group 35 and added an extra earth to ground to the negative terminal and chassis. Starts great cold, and cranks well, but still hard to start when warm.

Picked up a Harbor Freight fuel pressure gauge and tapped it into the fuel supply line just after the little black regulator thing on the line. Here’s what I found: when priming the pump, pressure reads 70psi, when cranking, pressure reads 50psi, when first started, pressure reads 45psi and needle flutters rapidly from 42-48, then after a short while, the pressure drops down to about 36psi, with the needle rapidly fluttering from about 32-38, and stays at this point the entire time. When you shut the car down, the needle immediately drops to 30psi, then bounces back up to 36psi, and slowly rises to 42psi, where it pretty much stayed until I disconnected everything. Not sure if this info tells anything, but from what I could find online sounded somewhat normal.

I replaced the fuel pressure regulator since it was cheap and easily accessible for good measure. Since then, it seems now that when the engine is warm, the first time I try to restart will just crank and sputter, but the second time, if I prime the fuel pump and then crank, it tends to start on this second attempt often now, where before I couldn’t seem to get it to restart until it cooled off and enough time elapsed. Now, with enough manipulation, I can usually get it to restart when warm if I mess with priming the fuel pump and cranking a few times.

I also hooked up my scan tool to check the coolant temp VS gauge temp; when allowed to idle up to proper temp, the scan tool reads coolant temp at 195, and at 196 the fans turn on. At the same time, on the gauge, the needle sits just barely above the very first line on the gauge from bottom, and really never rises much more than that, and it never sits perfectly horizontally, or at the halfway mark, even when driving around town, it’s always just above that first line but below the halfway point.

Still at a loss here guys, and just frustrated as it seems like it’s probably something simple. I don’t feel that it’s leaking injectors right now, as I don’t get any kind of rapid fuel pressure loss when shut off, certainly not before I try to restart it. Would love to hear some feedback on the results I’ve listed here. Thanks in advance!
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Old 10-04-2020, 09:36 AM   #30
Shik
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GDA- D, GDA-A, VAG-A
GDA-A - ShinjiTuned

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Just for fun, remove both the cam and crank angle sensors, check wiring and connectors, clean the junk off the magnetic portion and reinstall to see if there is any change. Totally free.

The crank angle sensor can be rotten to get out due to corrosion. Just take your time and keep working at it slowly if it's being a jerk.
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