JimMueller

iTrader: (9)

I believe it was last Wednesday or Thursday night when I accidentally drove through puddle which was deeper than I thought it was going to be. Car didn't stumble or stutter, and I have the factory air intake location (not the FRA/FTRA/etc). Over the last few days I've noticed a couple of backfires at low RPM's and one in a parking garage... I wonder how loud they'd be with the cutout open

Anyway, what do I need to check to get rid of the backfiring? Do I need to alter the frequency or type driving until it is resolved? Could it resolve itself? Could it cause damage if it is not diagnosed/repaired?

2000formulaluvr

Could have gotten water in the crank sensor connector?

LS6427

iTrader: (2)

Probably just needs to dry out wherever that water is sitting at some electrical spot...?

When people wash their engine bays and spray water, a lot of times the engine has issues for a couple days.

.

LS6427

iTrader: (2)

If your fuse box took a hit....it'll take a few days to dry out. And actually, the more you drive it the BETTER, the heat in the engine bay will help dry things out.

Just do not go WOT or drive aggressive at all while its missing or hesitating. Drive easy..............

.

JimMueller

iTrader: (9)

It is not happening very frequently, and I've intentionally been easy on the throttle to try to minimize the backfiring. It seems to only be doing it when the RPM's are in the teens under decel or light accel.

I'm going to check the filter tonight and get the oil changed mid-week. I had a suggestion from a 20+ year GM tech to monitor for cylinder misfires to see if any are unusually high, he said the heat would have dried out any wet spark plugs. He actually suggested taking it to redline a couple of times to blow out any remaining residue, since the drivability otherwise seems normal and it hasn't stuttered/stalled as a result of the water.

Darth_V8r

iTrader: (4)

An exhaust leak can backfire under decal. You might have ruined your AIR pump check valve with the water. For a quick test, you can disconnect it and plug the hose with something to see if it quits.

JimMueller

iTrader: (9)

I removed my AIR system a few years ago, pump, hosts, etc. I presume that check valve was included in that removal unless there was something I missed.

JimMueller

iTrader: (9)

New symptoms: The check gauges indicator is flickering very lightly in stoplight traffic, but the other gauges don't indicate a problem. My OEM radio outright lost power while listening to the radio, then a few seconds later it came back on by itself. Backfiring frequency is increasing in stop'n'go traffic.

Checked cylinder balance and the results were 94-99%. Misfire counts on all cylinders are not unreasonable, it wasn't quickly climbing into the hundreds like years ago when I bent a valve. Fuel trims indicate it's running a little leaner below 1600RPM, up to 17% on one bank, much higher than it was last month. Taking it to a shop tomorrow to at least change the oil, we'll see what else we can get done.

JimMueller

iTrader: (9)

Today I replaced the PCV, replaced the air filter and cleaned the MAF with MAF cleaner. I took it to my normal shop and requested they verify the water didn't cause any harm, and to isolate & resolve the backfiring. They managed to duplicate the backfiring during their test drive. They said the oil was fine, no water in it. Looking for reasons there might be extra fuel in the exhaust, they checked the fuel pressure at each injector and found that with the motor off the pressure would start at 60psi but quickly bleed down to 32psi (cylinders 1-7) and 22psi (cylinder 8), meaning they are effectively stuck open and allowing too much fuel. After cleaning they would only drop to 52psi. They thought perhaps the injectors could be dumping extra fuel, but then again the fuel trims should accommodate for that. I tune with a NGK AFX using lambda, but I see that the LTFT's are a bit lean below 2000RPM.

On the way home from the shop it backfired another half dozen times but the tech says without a hard failure the intermittent nature makes it difficult to troubleshoot... he truly doesn't feel it's mechanical, but rather electrical or engine management.

Edit: On our trip to a theme park today, noticed it was also randomly hesitating while driving.

JimMueller

iTrader: (9)

Still happening, any further ideas? I've been on vacation the last week so not driving it as frequently as normal, but it will still intermittently backfire. I'd like to make a few multi-hour trips this upcoming week and I'd like to know whether there are any concerns with driving it with the source of the backfiring still unknown. I started looking up replacement part numbers for various sensors and plugs, but I find it very irritating to randomly replace parts due to the lack of a hard failure.

Darth_V8r

iTrader: (4)

Does your fuel pump maintain pressure at higher rpm?

hrcslam

O2 sensors.

drew408

^^^^^o2 sensors.....

JimMueller

iTrader: (9)

I haven't verified fuel pressure at anything other than engine off or at idle, didn't think pressure at WOT would be involved since the backfiring only occurs near idle, although the minor hesitation is most noticeable under 2000RPM.

Regarding the O2's... I'm running a normal closed loop tune, both banks are cycling normally during data logging (well, normal for headers), there have not been any O2 DTC's (only the rear O2 DTC's are modified), and the fuel trims aren't out of whack. If the O2's were damaged, wouldn't it show up in data logging?

Darth_V8r

iTrader: (4)

Yeah, you're right. I was responding to something in the hesitation, but your getting backfiring when fuel demand is at its lowest. To me, it is starting to sound like an exhaust leak. Maybe the water created it, maybe it just exposed it.

So, let's follow that train for a second. Water gets in - maybe does some damage to the O2 sensors maybe it doesn't. If it got in, there's a hole somewhere. With a *theoretical* exhaust leak where the Y-pipe meets the collector, the O2 sensors could read lean, causing fuel dump. Then, when you let off the gas for decal, the sudden pressure change causes an in rush of fresh air, combined with high temps and unburned fuel = BANG!

True story - when I was in college, my roommate's car backfired every time you shifted gears due to a rust hole in the head pipe. He drove up next to some hot girls and called out the window to them, and right then shifted gears and backfired really bad. The one girl just looked at us out the corner of her eye and said "Yeah". The look on here face! Even though it was 95* in SC, we had to roll the windows up and cut the heat on, it got so cold...

hrcslam

If the O2s (either one of them) got compromised by the water they can be sending false signals, which will cause real AFR issues.

redbird555

iTrader: (14)

o2's my buddies does the same thing since he refuses to get rid of the extensions... water gets into the o2 connections and shorts them out. they will work perfectly fine at times and foul out the rest.

JimMueller

iTrader: (9)

FWIW I'm using the Denso 234-4617 O2's in the front, no extensions. But I plan to replace them with the same model anyway just for peace of mind. I guess I should replace my wideband sensor also.

JimMueller

iTrader: (9)

It hasn't backfired in about a week under similar driving conditions, still feel the hesitation though. The only things I've done since the backfiring began (regardless of whether it was to cure the symptoms) was clean the MAF, replace the PCV, replace fuel filter, clean injectors, began running Techron additive in tank, swap to an underdrive alternator pulley and an oil change (including replacing the oil cooler seal & oil level sensor).

If the O2 voltages/switching are the source of the hesitation symptoms, then I should be able to put the car in open-loop fueling mode so that the O2's are not affecting fueling, and then see if the hesitation continues in open loop...correct?

hrcslam

Yes, but only if your open loop tune is spot on. The issue could be water in the O2 sensor(s), as time went they dried out. It could continue to improve all on its own.