Misfire problem diagnosed!

[grindMARC]

Cliffs Notes: Tank screen/strainer/sock on the fuel pump was caked with crap!

My wife's P5 has been plauged with misfire problems for months now. It would ONLY happen if there was less than 1/2 a tank of gas in it. CEL would come on and it would kick out Misfire Cylinder 1. Sometimes it would get really bad and the car would limp. But as soon as the tank was full the problem would go away.

Here's what I tried.

1. Techron fuel system cleaner -- 3 bottles.
2. $69 fuel system cleaner at jiffy lube
3. new plugs

I was about to order a new set of coils and start moving around the fuel injectors to see if the misfire would move with it... Over the weekend I pulled the fuel pump outta the tank. Careful with those soft screws fellas!! The 'sock' that covers the fuel intake on the pump was covered in grime. I cleaned it with a brush and dipped it in some gas, the gas drained out of the sock about twice as fast as when I first took it out of the tank.

[edit: the screen can be replaced: link to part]

Not only have I not had a misfire or hesitation when having less than a half a tank of gas, but the engine runs better all around!!! Power band is much broader.

Car has 70k miles on it. Y'all might want to throw this into your 60k maintenance schedules!!

30 minute job start to finish.

Now that its fixed, I get to drive the WRX again. (thumb)

 

[changedman]

70k miles....

spark plugs..... were not the reason of the misfire? 70k on spark plugs would lead me to say it was them, because the fuel pump will still suck enough gas thru....

interesting.

 

[grindMARC]

EXACTLY. Everyone was telling me it was a spark related issue.
OEM plugs were changed well before this problem started.
Changed again after the problem and no affect.

I'm guessing that the added gas in the tank actually created pressure and pushed gas through that initial filter. When the tank went down, so did the pressure. Just a guess though.

70k miles....

spark plugs..... were not the reason of the misfire? 70k on spark plugs would lead me to say it was them, because the fuel pump will still suck enough gas thru....

interesting.

 

[mogi]

you got a howto with pics?

that'd be great!

 

[grindMARC]

you got a howto with pics?

Sorry, no pics. You should probably disconnect the battery, but I didn't.
Edit: See pics below.

1. Open the gas cap and release the pressure in the fuel system. Expose the fuel pump by moving the driver side back seat forward into the foot well. Its under the flap of carpet in the 'hump' between the two back seats. Before you even start disconnecting stuff, I strongly recommend vaccuuming out the road dirt and sand that's probably all over the fuel pump housing. Why take a chance knocking sand and dirt into the tank?

2. Disconnect the two electrical plugs. On one of them, you'll have to remove both sides of the plug from the housing. After you disconnect the first half, just push it forward toward the front of the car and it should come out of the little metal tab that holds it in place.

3. Now the hardest part (if there is one). Disconnecting the fuel lines. Unless you have the Mazda tool specificially designed for this task, you'll have to use 2 little flat head screwdrivers to pry up the green locking tabs. Its not hard. Just take your time. YOU DO NOT NEED MUCH FORCE, BE CAREFUL NOT TO BREAK IT!! If you need to, you can rotate the connector to give better access to the tabs.

4. Next unscrew the 12 or so soft little screws that hold the cover on the tank. Be very careful, these strip EASILY! I was much more successful with a larger screwdriver than seems appropriate for those little screws.

5. Pull the fuel pump out of the tank and be careful not to get stuck on the fuel level float that is connected to it. It doesn't just pull straight out. Take your time!

6. Put a towel or bucket under it to catch the dripping gas and take it out of the car. Using a really soft brush (toothbrush?) and some gas, brush all the grime off the fuel filter. Dunk it in some gas to rinse off all the grime you dislodged with the brush. The filter should be white/off white when you are done. As far as I can tell, this part cannot be replaced without doing the entire pump. There is some sort of fancy rivot-type fastener that holds it on, so do your best to clean the one you have! Edit: it can be replaced. Its listed as a "Tank Screen."

7. Before you remount the fuel pump, now might be a good time to peek into your tank and see what's what. A simple siphon will probably suck up any major pieces of crap sitting on the bottom of the tank.

8. Install in reverse.

 

[Mike R]

Interesting.

 

[eljefe305]

did you see a lot of deposits in the tank itself?

 

[grindMARC]

did you see a lot of deposits in the tank itself?

It looked like about a half-teaspoon of sand was spread around the bottom of the tank. I was alot more concerned about what the quality of the fuel looked like given our misfire problems. But it looked fine. I figured if heavy enough to sit on the bottom, its prolly not going to get sucked up into the pump.

BTW, a full tank of gas would probably make this job a little more difficult and messy.

Yesterday, my wife drove the car for the first time since i cleaned the filter and she said she noticed a difference in 'pickup' before she got to the end of our block!

 

[andyfatsax]

Women! No appreciation for men's duty as a husband.

 

[grindMARC]

Well, the car is now at 105,000 miles and the hesitation/misfire problem started again when the tank got near empty. I cleaned the primary filter again tonight and took it for a spin -- problem solved. This time I took some pics of the process.

Pic 1: Access to the fuel pump.
Pic 2: Vaccing out the sand and grim around the fuel pump.
Pic 3: The art of prying back those darn green tabs to release the fittings.
Pic 4: The grimey filter sock before it was cleaned. Can you believe that thing is supposed to be white?
Pic 5: The grime sitting in the bottom of that tray came off the sock!

 

[kurt]

Thanks for the heads-up and the how-to.

Sounds like you guys need to start using some different gas stations.

 

[Mike R]

What's under that snap on bottom piece? That looks like the sock is replaceable. (Not seeing the part on mazda diagrams...dumbasses)

And I have a feeling my car is doing that. Very randon misfire. I'm at 120K..Might have to pop mine out this weekend.

Edit again...found a fuel filter listed for 01-03 protege. 35 bucks.

 

[Kansei]

yeah that's crazy grime after.. 35k more miles??

you know the cars aren't meant to be filled with mud, right?

I haven't heard of anyone else needing to do this before.

 

[Mike R]

eh, he's in Jersey...Whaddya expect...LOL

 

[Skoozul]

Subb'n!!!

 

[grindMARC]

What's under that snap on bottom piece? That looks like the sock is replaceable. (Not seeing the part on mazda diagrams...dumbasses)

And I have a feeling my car is doing that. Very randon misfire. I'm at 120K..Might have to pop mine out this weekend.

Edit again...found a fuel filter listed for 01-03 protege. 35 bucks.

You'll know for sure if this is your problem if the misfires occur when the fuel level is below 1/3 of a tank. Misfires and hesitations become more frequent as you get to the bottom of the tank.

It looks like its attached with a rivot. Pay no mind to the mercedes reference in the link.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.mercedesshop.com/&cookieid=1WE15Z7R61WH17DBUR&year=2002&make=MA&model=PRO-5-002&category=E&part=Fuel+Screen

 

[grindMARC]

eh, he's in Jersey...Whaddya expect...LOL

Actually, chances are the gas was purchased in Maryland or Delaware. I'd be lying if I said my wife and I didn't have a discussion about what shady highway stations she's frequenting.

 

[Mike R]

Looks like that bottom cap holds the strainer in place. Mine has a really really rare misfire, and it's when the car is low on gas, usually when I'm heading to the gas station.

 

[TheMAN]

Well, the car is now at 105,000 miles and the hesitation/misfire problem started again when the tank got near empty. I cleaned the primary filter again tonight and took it for a spin -- problem solved. This time I took some pics of the process.

Pic 1: Access to the fuel pump.
Pic 2: Vaccing out the sand and grim around the fuel pump.
Pic 3: The art of prying back those darn green tabs to release the fittings.
Pic 4: The grimey filter sock before it was cleaned. Can you believe that thing is supposed to be white?
Pic 5: The grime sitting in the bottom of that tray came off the sock!

clean? :wtf: why don't you replace BOTH the filters? you're quite due for a fuel filter change.... it's supposed to be done at 100k

cleaning the s*** and having it happening again, taking s*** apart to clean again, etc is just NOT worth the time... time = money

 

[Bijou-MP5]

when I had rare random misfire..I couldn't figure it out..
so, I replaced most of things...such as fuel pump, EGR valve, coil pack, ignition wires... now problem is gone.
but I usually have misfire problem from ignition wires.