HELP: Sudden Cylinder 1 & 4 Misfire

[Ne0z]

So this may have been happening for a while and I wouldn't know because my fiance has been driving my 04 Scion xA and being female has the music cranked all the way up oblivious to car issues and sounds. Anyhow, the car has had a check engine light on forever P0420 Catalyst System Efficiency Below Threshold (Bank 1) which is a common problem with these cars and is pretty much impossible to fix once it starts happening (people have replaced the cat, both O2 Sensors, etc with no effect).

Well today on my way home from the bar I was taking a turn around 20mph or so and had down-shifted obviously and the car started sounding like a Subaru. So I get it home and it pulls P0301 and P0304 (cyl 1 and 4 misfire codes).. This only seems to happen when the car is turning and accelerating at the same time and then smooths back out once straight again. The car has never done this before that I have noticed. There is no oil anywhere that it shouldn't be. Also going from Bloomington to Burnsville Twice today (about a 20 minute drive) went through almost a half tank of gas.

I can give any more information anyone may need.

Also, I did try swapping around Spark plugs and Coil packs and I get the same results.

Curious if this could be a maf issues as I may have picked up some water in a rather large puddle I went through and could have gotten in my CAI (although it does have one of those filters to prevent it from getting that far)

[danielsatur]

After swapping spark plugs + coil packs on cylinders 1 & 4, did you reset the OBD II system?

[Ne0z]

Originally Posted by danielsatur

After swapping spark plugs + coil packs on cylinders 1 & 4, did you reset the OBD II system?

Yes I did

Things that have been suggested to me:
Fuel Filter
Fuel Pump
MAP/MAF Sensor

It wouldn't be injectors cause generally injectors go one at a time so I pretty much axed that idea.

[danielsatur]

Are you still getting a consistant misfire on cylinders 1 & 4?

1) If yes, check the compression on both cylinders.
2) swap injectors with cylinders 2 & 5.

If you were getting random misfires on random cylinders, we would look @
1) Air filter/ fuel filter
2) fuel pressure
3) MAP/MAF sensor
4) Smoke Test
5) Catalytic converter test.

[jdmccright]

This should have been posted in the Scion/Toyota forum...more people familiar with your car there.

To me, losing spark while turning and you mentioning going through deep water could be the water sloshing to one side and shorting an ignition component.

Another possibility is a poor ground or connection affected by the rolling of the body.

[shorod]

I agree with the above post, seems like a wiring issue to me based on it happening when turning. I ran in to this once on a '95 Ford Contour. It would misfire something horribly. Swapped plugs and wires around, but the misfire always remained. It was OBD-I so I didn't get good visibility in to which cylinder was misfiring and pulling one wire at a time seemed inconclusive. One day if finally left her stranded in the work parking lot. I showed up with a handheld scope and backprobed the wiring to the fuel injectors. As soon as I did, the misfire went away. Wiggle the connector and it would come back. The problem ended up being a bad connection in the harness.

I'll go ahead and move this thread to the Scion forum, maybe they can answer what's common between cylinders 1 and 4.

-Rod

[Ne0z]

Originally Posted by shorod

I agree with the above post, seems like a wiring issue to me based on it happening when turning. I ran in to this once on a '95 Ford Contour. It would misfire something horribly. Swapped plugs and wires around, but the misfire always remained. It was OBD-I so I didn't get good visibility in to which cylinder was misfiring and pulling one wire at a time seemed inconclusive. One day if finally left her stranded in the work parking lot. I showed up with a handheld scope and backprobed the wiring to the fuel injectors. As soon as I did, the misfire went away. Wiggle the connector and it would come back. The problem ended up being a bad connection in the harness.

I'll go ahead and move this thread to the Scion forum, maybe they can answer what's common between cylinders 1 and 4.

-Rod

I've been checking everything over and haven't had any luck yet, I replaced the MAF as it was suggested on another forum which did nothing.

Also, the reason I didn't put this in the Scion area is because unless you want to know how to install subs, decals, or Konigs, the Scion community is pretty pointless so I figured I'd put it somewhere people with real knowledge might look. I've posted this same question on all the scion forums out there and have yet to even get a response... But if I were to ask how to install Neons on every surface of my car I'd have 40 responses in 10 minutes lol.

[jdmccright]

Point taken, but having a good descriptive title like yours help stave off the neon-huggers, thumpers, and the like.

Problems with specific cylinders tend to be electrical in nature, and having two begin to malfunction at the same time narrows it to any electrical interaction or commonality between the two.

I would find an electrical wiring diagram and trace where the two share common wires, junctions, connectors, etc. For instance, sometimes the coil packs are fired in pairs instead of individually to help with post-combustion gases in the non-fueled cylinder and to reduce the wiring needed. If there are fuses or fusible links associated with those wires, they may be bad.

Hope this gives you a start on where to look next.