Just another misfire/rough idle thread...

[StkmltS]

My misfire has become undeniably worse than when it first started. Not worse, as in more misses, but worse, as in a new condition causes the motor to miss. It misses at idle like usual, but now it also misses (almost) whenever the motor is steadily running in the stumble/studder range (2300-3000 rpm).

 

I bought a pressure sensor that I'm going to plumb into my fuel line so I can monitor fuel pressure through the ds TGV. My thinking is that my miss is fuel related. Maybe I should just rebuild the entire motor and fix the problem forever... $$$... ouch. The new pressure sensor is identical to the one I'm already using to monitor oil pressure, so I'll easily be able to swap back-and-forth between without messing with the parameters in BtSsm. All I need to do now is come up with a way to T the new sensor into the line. There are plenty of options online, but for who-knows-what reason a couple weeks ago I mentally committed myself to sourcing the Chinese fittings locally. I've spent a few nights tinkering and scrounging around in my garage looking for a safe way to make a T (chunk 'o metal + drill & tap + hose barbs), but it looks like a trip to Home Depot needs to happen because my lack of confidence isn't comforting #JustSaying

Edited April 26, 2017 by StkmltS

[xt2005bonbon]

Aaaaaand you still have not checked your spark plug in #2

[StkmltS]

I refuse. Do you know how hard it is to get a socket on one of those suckers?

[xt2005bonbon]

Yes I know. It will take you 15mn to do that task including taking off the battery and coil pack. Piece of cake man.

[StkmltS]

Yeah but I need to take out two plugs to look for a difference in color. So that's at least 20 minutes. Plus 1:60 min to reset my stereo presets and levels (very important to get right).

 

Maybe... maybe... I'll pull them out tonight when I mess with the fuel line.

 

Home Depot doesn't have the exact fitting I wanted. How dare they. After staring at their board-O-fittings for almost 10 minutes I decided to use a 1/4" to 1/4" 90° elbow. When I got home I drilled a new hole and tapped it to accept the 1/8" NPT pressure sensor, effectively turning the elbow into a "T". I didn't install the sensor last night because I'm not sure if I want to be risky and use the white TPFE tape that I have, or be safe and buy something else.

 

Prediction:

Birkhoff will suggest a $25 tube of specialty thread sealant that comes in a metric-only tube, and is only available from a retailer in England who only accepts Euros.

xt2005bonbon will suggest that I check my valve clearances.

StkmltS will find a DIY recipe for liquid thread sealant online from some super-sketchy website, make it, but then decide to buy a $6 tube of Permatex anyways.

[xt2005bonbon]

As MaxCapacity keeps saying 'check your oil, these cars need it', xt2005bonbon says 'check your valve clearances, these cars need it'

 

In all seriousness, I remember heiche rechecking his clearance after his heads rebuild or something and was surprised to find out some of them already changed. heiche, you can confirm this.

 

In any case, inspecting the spark plug may give a clue in what is still wrong in that cylinder.

 

 

Oh, did you think of checking that fuel pulsation damper on the driver side rail? Very rare they get faulty but it can happen.

 

Edit: can't remember if you have stock side feed fuel rails though.

Edited April 27, 2017 by xt2005bonbon

[StkmltS]

My fuel rails and injectors are stock. A problem with the fuel damper would make sense because it's on the rail between 2 and 4, and my problem is in 2 but not 4. Does the fuel flow from 4 to 2? How does one go about inspecting the damper? Will my fuel pressure gauge be able to indicate a problem with the damper? Don't fret, all of these questions will be answered soon.

 

Stay tuned!

[Smithcraft]

It's still running rough after two years?

 

This is having just started for me, and after swapping coil packs, and having the missing follow the coil pack, and replacing the coil pack only to still have that cylinder keep missing is frustrating!

 

I can't image how I'd feel if I was going through it as long as you have!

 

SC

[xt2005bonbon]

I see that you found that recent thread about a misfire probably caused by that fuel pulsation damper. Time to seriously check yours out!

[StkmltS]

It's still running rough after two years?

 

This is having just started for me, and after swapping coil packs, and having the missing follow the coil pack, and replacing the coil pack only to still have that cylinder keep missing is frustrating!

 

I can't image how I'd feel if I was going through it as long as you have!

 

SC

Yep, 2 years. It's very much a love/hate relationship.

 

I see that you found that recent thread about a misfire probably caused by that fuel pulsation damper. Time to seriously check yours out!

I popped off the cover a day or two ago to mess with it. The screw wasn't tight, but it wasn't loose either. I played around with it for a while and nothing I did changed the misfire. I haven't looked up the cost of a replacement, but if it isn't expensive it may be worth replacing just for the love of throwing as much money at the problem as I can.

Edited May 5, 2017 by StkmltS

[xt2005bonbon]

Yep, 2 years. It's very much a love/hate relationship.

 

 

I popped off the cover a day or two ago to mess with it. The screw wasn't tight, but it wasn't loose either. I played around with it for a while and nothing I did changed the misfire. I haven't looked up the cost of a replacement, but if it isn't expensive it may be worth replacing just for the love of throwing as much money at the problem as I can.

 

did you do that fpr hose thing fix too?

And you could try getting another fuel damper from a forum member who has upgraded their fuel rails. Don't have to buy new.

[StkmltS]

I moved the FPR ref line from the IM to the BPV, but I didn't see any change in the misses or stumble. I used about 3 feet of silicone hose because that's what I had laying around. It's all coiled up around the fuel lines for now.

 

I "acquired" a couple brass fittings from work this morning so I'll have the fuel pressure sensor hooked up this weekend. I made a fitting last weekend but I couldn't get it to not leak. The threads I put in using my 1/8npt harbor freight tap totally suck. The same tap worked well enough when I used it in the oil pressure sensor in the block, but I used liquid gasket to seal that puppy up good.

 

I'm really hoping to learn something by seeing what the fuel pressure is doing while it misfires.

[StkmltS]

Uh oh... the guy with the fuel damper thread saw negative things (more misses) when he combined the tightened damper with several feet of hose on the FPR ref line. Coincidentally that's exactly what my current setup looks like, so maybe switching back to a shorter hose will help me.

[xt2005bonbon]

when you played with the screws, did you have the engine running while monitoring the ecu at the same time?

[rhino6303]

I moved the FPR ref line from the IM to the BPV, but I didn't see any change in the misses or stumble. I used about 3 feet of silicone hose because that's what I had laying around. It's all coiled up around the fuel lines for now.

 

I "acquired" a couple brass fittings from work this morning so I'll have the fuel pressure sensor hooked up this weekend. I made a fitting last weekend but I couldn't get it to not leak. The threads I put in using my 1/8npt harbor freight tap totally suck. The same tap worked well enough when I used it in the oil pressure sensor in the block, but I used liquid gasket to seal that puppy up good.

 

I'm really hoping to learn something by seeing what the fuel pressure is doing while it misfires.

Did you use the 3 ft for the vacuum line or the fuel line? The fix for the stumble is lengthening the fuel line.

 

You want your fpr reference line to be as short as possible.

[awfulwaffle]

Just wanted to clarify, I lengthened the fuel lines in that latest update.

[StkmltS]

when you played with the screws, did you have the engine running while monitoring the ecu at the same time?

The engine was running and I had BtSsm open. I really need (want) to get the bluetooth BtSsm adaper. Running back and forth from the engine bay to inside the car is annoying. Ugh, life in a first-world country is such a drag sometimes.

 

Did you use the 3 ft for the vacuum line or the fuel line? The fix for the stumble is lengthening the fuel line.

 

You want your fpr reference line to be as short as possible.

For the vacuum ref line. I understand that the purpose is to change the source of the reference, but for whatever reason I also though a longer line was beneficial.

For a few minutes I had a 3-ft section of fuel hose instead of the stock ≈10-in, but it didn't change anything so I cut it up into a few pieces to use for my fuel pressure sensor install (1 pc for each side of the T, and 1 pc about stock length to use if I take out the T).

 

Just wanted to clarify, I lengthened the fuel lines in that latest update.

How long of a hose are you using?

I finally got my fuel pressure gauge plumbed in yesterday and now I have about 8" more line than before.

Edited May 8, 2017 by StkmltS

[xt2005bonbon]

The engine was running and I had BtSsm open. I really need (want) to get the bluetooth BtSsm adaper. Running back and forth from the engine bay to inside the car is annoying. Ugh, life in a first-world country is such a drag sometimes.

 

Yeah. That is very nice indeed to have the bluetooth adapter (hit up bmb. He will probably sell his anytime soon).

 

That is how I was able to troubleshoot issues with my maf wiring harness; put the phone in the engine bay with the engine running, moved the wires and BAM, saw the fuel correct move around.

[swatson]

Hello,

 

i have had a similar issue with my 2002 Impreza OBS - misfire at idle, only in cylinder #1. None of the obvious culprits were responsible. After way too much time and money, I think it has been narrowed down to a "dropped" exhaust valve guide. I learned a lot from this thread but haven't seen it mentioned in here. Have you checked that out on yours?

 

thanks for all the collective wisdom in here.

[StkmltS]

Hello,

 

i have had a similar issue with my 2002 Impreza OBS - misfire at idle, only in cylinder #1. None of the obvious culprits were responsible. After way too much time and money, I think it has been narrowed down to a "dropped" exhaust valve guide. I learned a lot from this thread but haven't seen it mentioned in here. Have you checked that out on yours?

 

thanks for all the collective wisdom in here.

 

Wow, that's definitely outside of the normal realm of likely causes.

Last summer I rebuilt my heads, so I happen to know for a fact that the guides are where they should be. All of those messy details are in a different thread so don't feel bad about missing it.

 

ALL SUGGESTIONS / TIPS / TRICKS are welcome in this thread.

[StkmltS]

My fuel pressure sensor is hooked up and working as well as I'd hoped.

So far I've only closely looked at the pressure at idle.

 

With the motor warm, here's what I see.

What are your guys' first thoughts?

[StkmltS]

Maybe I spoke too soon. On my drive home I mostly saw 25-26 psi at idle.

 

Sent from inner space.

[xt2005bonbon]

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

[heiche]

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.

[xt2005bonbon]

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