2001 5.3 P0304 flashing check engine light - rain storm related?

glueguy · August 7, 2015

2001 Suburban with 5.3, 166k miles, new AC Delco plugs and wires at 152k. We had a lot of rain over the past week, including flooding. The truck idled (virtually no wake) through water that at times could have reached the running boards.

Very slight rough idle, no other driveability issues. Got a code P0304 including a periodic flashing check engine light. Changed the coil and the light went away for about three days. Now it's back again. I'll change the plug next. I'm curious if the water could have caused this condition, and how? Never had a P0300, always P0304

white1500 · August 7, 2015

Check the maf and intake for water. I got a cel when I went through the Costco car wash that has super high water pressure. I suspected that as the reason and when I took out the filter there was water sitting at the bottom of the intake, so it went all the way to the maf.

Although after a day or so it did go away.

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glueguy · August 8, 2015

Took the air filter apart and it was dry inside.

It drives fine but idles like it has a big cam. SES on and sometimes flashes. I put in a new plug, swapped coil from 4 to 6, and spark plug wire from 4 to 2, cleaned the MAF and cleared the codes.

No change. After a while at idle (like at the end of a traffic light cycle) the SES light flashes until I start to accelerate and then goes out. Scan shows a pending code P0304.

I listened to the fuel injector and it sounds like the other ones on the bank, but I know that won't tell me if it's dirty.

Any thoughts? I've changed everything spark related and it still shows the same cylinder.

glueguy · August 9, 2015

today I also swapped fuel injectors. I still had a P0304 and after clearing it hasn't come back. Still surgy-rough coming to a stop at a light and rough idle, but no driveability issues. Compression test tomorrow I guess?

Feeling like I am heading toward larger problems.....

wilsonz71 · August 9, 2015

Intake gasket leak? Normally would be a lean code and on multiple cylinders but it might be worth checking. Could cause a misfire.

glueguy · August 10, 2015

well, I think this is taking a turn for the ugly. Did a compression test - 145-150 in 7 cylinders, and 110 in #4. Any reason to not think this is head gasket? The only curious part is no coolant loss and the oil looks like oil.

wilsonz71 · August 13, 2015

well, I think this is taking a turn for the ugly. Did a compression test - 145-150 in 7 cylinders, and 110 in #4. Any reason to not think this is head gasket? The only curious part is no coolant loss and the oil looks like oil.

Low compression doesn't always mean head gasket. Could be a bad valve, valve seat, piston rings..