Just another misfire/rough idle thread...

[StkmltS]

so, you're way lower than what the fsm says?

At idle I'm a little lower than what the FSM specifies, sometimes way lower. The inconsistency may be enough to indicate a failing FPR. I just don't know very much about this stuff yet.

If your calculations are correct, yeah that's quite a bit lower than what you are specifying.

 

On a separate-but-related note, I can't remember when the fuel pump duty cycle goes up(?) At idle, I believe it's 33% (you should still have fuel pressure at spec though)... But I wonder if your misfires stop when it goes up to 66% or higher? Just a longshot that this is what masks your low fuel pressure issue and causes the misfires to stop? You can monitor/log that value.

I have the FP set to run at 66.7/66.7/100 so that's not it. I changed it a while ago hoping it would help... nope.

 

On a semi-related note, BtSsm crashed on me yesterday/today when I was trying to view a log, so those crash reports are from me. I don't know how long the underlying issue has been present because I don't usually view logs on my phone.

Here's what happened: logging > stopped logging > unplugged phone (tactrix) > selected car profile > navigated to logs > selected the log > tapped "graph" > crash

 

You could always upgrade your fuel rails, injectors and fuel pump.

HAHAHAHAHHAHAHAHAHAHAHHA no.

 

A couple weeks ago we found out baby #5 will be here in December, so saving up to replace our minivan is a slightly higher priority than spending extra money on the LGT. I think we'll end up with a 12-passenger Ford or GMC van. I learned how to drive on a 15-pass Ford so the idea of having a big van doesn't intimidate or turn me off like I think it would most people. Anyway, there aren't many affordable options for carting around 7 people plus a yardsale-worth of junk (strollers, wagon, bikes) that my wife usually likes to keep in the van. How she still functions with a minivan and our four kids right now is amazing.

 

Big van bonus: they're as strong as full-size trucks, and you can fit multiple sheets of 4'x8' plywood and 2x4's inside WITH the benches still in.

Our van won't look cool at all... but (cheezy grin) it could.

Edited May 11, 2017 by StkmltS

[heiche]

Congrats! (again!)

[StkmltS]

Congrats! (again!)

Thanks, we're definitely blessed.

[heiche]

So are you seeing even with your FP duty cycle bumped up, your fuel pressure is still too low? Hmmm.

[StkmltS]

Here's what's happening during acceleration.

Sorry for the busy chart.

 

It's curious that my AFR is a little lean (14.9 per wbo2) in the same range as my stumble zone, and that's right around where [boost(abs)+FuelPres] = 0 psi ± 1 psi.

 

**edit**

In my original chart I calculated the combined fuel+boost as Boost(abs)+FuelPres, which is incorrect. I corrected it to be (Boost*-1)+FuelPres.

Explained: Negative manifold pressure (vacuum) increases effective fuel pressure, and positive manifold pressure (boost) decreases effective fuel pressure.

Edited May 17, 2017 by StkmltS

[SBT]

So stumble, and with/at boost onset, coupled with lower than expected FP, I'd start at the pump and work forward. It sounds like your pump is either not getting full volt/amps in that range, it's leaking slightly - check your O-rings, or it's failing.

[StkmltS]

It's difficult researching stuff online without finding evidence that supports what I'm already wanting to hear.

Example

[StkmltS]

My formula for effective fuel pressure was wrong in my last chart (duh).

It's corrected now, and the chart is a little more useful because the correct formula shows that my injectors (in that particular log) saw an average effective fuel pressure of 38.623 psi.

[heiche]

Well that's good because fuel pressure is no longer an issue.

 

But it's bad because the misfire continues to be a ghost

[StkmltS]

I don't think I'm out of the woods yet with the fuel pressure.

 

Here's my logic:

(1) Removing the pressure reference line from the FPR causes the FPR to operate solely under spring pressure.

(2) The pressure reference line on the FPR helps the internal spring to push less/more, which lowers/raises the observable fuel pressure. The purpose of this is to account for vacuum/boost inside the cylinders that's working with/against the injectors. That calculated difference (cylinder pressure vs fuel pressure) is effective fuel pressure.

(3) Effective fuel pressure changes with vacuum/boost at a ratio of 1:1 (on our cars).

(4) Because of that simple 1:1 ratio, my effective fuel pressure at any RPM (calculated) should be identical to what the FSM specifies the fuel pressure should be at idle (observed) without the the pressure reference line.

 

FSM spec @ idle w/o ref line: 41-46 psi

My calculated effective fuel pressure @ any RPM: 33.2-42.2 psi

At the worst times I'm 7.8 psi below spec (41-33.2), and on average I'm 2.38 below spec (41-38.62).

 

Looking at it as reasonably positively as I can, my FPR is at least 2.38 psi out of spec.

 

Is that enough to cause constant problems?

Is that enough to cause problems under certain conditions, like when target AFR is close to 14.7?

Is that enough to worsen the stumble/stutter issue associated with the FPR?

Edited May 17, 2017 by StkmltS

[xt2005bonbon]

But it's bad because the misfire continues to be a ghost

 

It may no longer be a mystery if he would spend the 20mn to check his spark plugs

[StkmltS]

Food for thought.

Would it make any sense if my fuel pressure were somehow related to coolant temperature?

On my drive home today I'll try to spend more time at high RPM+low speeds (the middle section in this chart), and I'll also log coolant temp.

 

*Always obey the posted speed limits.

Edited May 19, 2017 by StkmltS

[hadvw]

Food for thought.

Would it make any sense if my fuel pressure were somehow related to coolant temperature?

 

Wouldn't it be more a case of: most things are less efficient when hot? So, coolant heats up, and so does the entire engine bay ==> less fuel pump efficiency..

[StkmltS]

Heat in general is a bad thing because it's energy spent on something other than moving the vehicle. However, the system as a whole is most efficient when the motor is warm, which is why that's the normal operating temperature. If it were more efficient for the motor to run at 120° then I assume Subaru would have designed it that way.

 

On the other hand, the fuel pump is an electric motor and it doesn't like heat. It's even mounted way back inside of the gas tank just to help keep it cool. I'm in an assuming mood today, so I'll assume that a correctly functioning OEM fuel pressure regulator is designed to be able to handle engine bay temperatures because that's where the engineers put it.

 

If coolant temp looks correlated to my effective fuel pressure then you might be on to something. What heats up with coolant that can somehow affect fuel pressure?

 

I'll also try to log engine bay temp. My EGT probe isn't inside of the exhaust anymore for just this reason. I can't remember if I ever tried it out to see if the probe is accurate at that low of temps (compared to inside the exhaust).

[StkmltS]

After my motor warms up my fuel pressure at idle typically hovers around 30psi. So that's roughly about 5psi less than what it should be.

 

Is 5psi enough to cause my problems?

[jam007]

At idle I'm a little lower than what the FSM specifies, sometimes way lower. The inconsistency may be enough to indicate a failing FPR. I just don't know very much about this stuff yet.

 

I have the FP set to run at 66.7/66.7/100 so that's not it. I changed it a while ago hoping it would help... nope.

 

On a semi-related note, BtSsm crashed on me yesterday/today when I was trying to view a log, so those crash reports are from me. I don't know how long the underlying issue has been present because I don't usually view logs on my phone.

Here's what happened: logging > stopped logging > unplugged phone (tactrix) > selected car profile > navigated to logs > selected the log > tapped "graph" > crash

 

 

HAHAHAHAHHAHAHAHAHAHAHHA no.

 

A couple weeks ago we found out baby #5 will be here in December, so saving up to replace our minivan is a slightly higher priority than spending extra money on the LGT. I think we'll end up with a 12-passenger Ford or GMC van. I learned how to drive on a 15-pass Ford so the idea of having a big van doesn't intimidate or turn me off like I think it would most people. Anyway, there aren't many affordable options for carting around 7 people plus a yardsale-worth of junk (strollers, wagon, bikes) that my wife usually likes to keep in the van. How she still functions with a minivan and our four kids right now is amazing.

 

Big van bonus: they're as strong as full-size trucks, and you can fit multiple sheets of 4'x8' plywood and 2x4's inside WITH the benches still in.

Our van won't look cool at all... but (cheezy grin) it could.

 

Congrats! Thats awesome, I want one of these too, but with the 7.3...

[StkmltS]

After my drive home today fuel pressure @ idle was a steady 26/27 psi. I dunno if it's causing my problem or not, but it seems out of spec enough to justify spending a little money on a new/used pump.

 

Sent from inner space.

[xt2005bonbon]

Time to upgrade!

[StkmltS]

Does pressure inside the tank (or the lack of) somehow effect fuel pressure at the injectors?

[StkmltS]

1 - 2 - 3 - 4

(left to right)

 

New positions: 1 (was 1)- 2 (was 4) - 3 (was 3) - 4 (was 2)

 

I also put in four new non-OEM coil packs.

 

 

 

Edited June 11, 2017 by StkmltS

[StkmltS]

Cylinder 2 has a little bit of fluid pooled at the bottom.

Cylinders 1, 3, & 4 are dry, and look as dirty as expected after 8k+ miles.

 

I fished a paper towel around inside cyl #2, and the liquid has the distinct smell of fuel, but the color of oil. Plug #2 came out wet (not enough to drip) and smelled like fuel. So I'm saying the fluid in #2 is gasoline.

 

 

 

Edited June 11, 2017 by StkmltS

[StkmltS]

No apparent change to the frequecy of misses at idle.

 

Sent from inner space.

[birkhoff]

Can you remind us: Cylinder 2 is your misfire cylinder?

 

Something definitely is up with Cyl 2.

 

If it is fuel, you don't want to leave it like that very long. The lube oil will be washed off the cylinder walls and you'll have sealing problems over the medium run.

 

If it is oil, then lube oil is getting past the rings, diluting the fuel charge and possibly causing misfires in the first place.

 

If it is fuel AND oil (as you suspect) then kind of like the first scenario except this has been going on for a while.

 

I would run it for a couple of days. Bring it into the garage hot with minimal idling, pull the #2 plug and confirm that things really do look like that. If they do, well, . . . cross that bridge when you get to it.

[xt2005bonbon]

1 - 2 - 3 - 4

(left to right)

 

New positions: 1 (was 1)- 2 (was 4) - 3 (was 3) - 4 (was 2)

 

I also put in four new non-OEM coil packs.

 

 

 

 

 

Wow, you finally checked the plugs!!!

 

Looks like cylinder 1 is running a bit richer than others?

 

What is that darker spot on the white tip of plug 2? Missing piece?

[StkmltS]

Cyl 2 is where I see the most misses (highest roughness count), but cyl 3 also regularly misses.

 

The dark brown spot on plug 2 is a stain from something. Maybe I got a drop of oil on it when I installed it during the rebuild. There's no missing material.

 

Up close and in-person, plugs 1, 3, and 4 look almost identical to each other. The only obvious difference between any of the plugs is the color of the ceramic on plug 2. It was very slightly off-white (and has a big dark brown spot), while the ceramic on the rest of the plugs was a nice crisp-white.