Misfire in car wash / heavy rain

Mounce

Silver Supporter
#1
2003 Silverado 5.3 118k miles currently.

So, I mentioned a while back in the whore thread after I first got my truck that I had taken it through a car wash and it fell apart. P0300 flashing check engine light, the whole nine. Was around 108k miles then.

That's fine, I have just hand washed it since. That's better anyways. And thusly it hasn't had another episode until Friday evening. Drove through a torrential down pour that was flooding roads. Pulled up to an intersection and it was chugging. Solid misfire but no codes this time. Pulled into a gas station and got gas and let it air out a minute while the down pour became a drizzle and all was fine after that.

Has also had a slight miss at idle as long as I've had it. Misfire counters can't catch it and no codes.

After the first incident I done plugs/wires hoping that would cure it but now I've seen the issue again so it didn't help. Tried googling my issue and best I could find was mostly unrelated threads blaming intake gaskets so that's what I've figured it was. Water pours through the back of the hood/cowl area and gets on the intake. Tried spraying with carb cleaner with no results.

Had always said I'd do a water test but never got around to it until now and sure enough, splash of water around the intake mating surface and she starts bucking. P0300, flashing cel, cylinders 3, 4, and 5 all throwing high misfire counts 50-1100 counts.

Now my main reason for posting, of course water got on the injectors as well but still safe to assume intake gasket? I've looked over all the wires and see no obvious issues that could be affected by water.

I've decided it's safe to throw gaskets at it and see how it responds BUT still thought I'd get a couple opinions beforehand. Will also take care of leaking valley cover and valve covers while I'm in there that deep.
 
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Mounce

Mounce

Silver Supporter
#3
Oh yeah, of course. I'm very observant when I'm doing work. Also makes me kinda slow at the job but I'd rather take my time and make everything perfect than rush though it and have to do it again.

At work I'm decently quick with jobs but that's because there's a customers time frame on the line, with my personal stuff I ease through it and enjoy the process.


BTW intake gaskets are a common failure on the v8's
 
#4
If you're doing that you might want to check the knock sensors and harness if you'll be down low enough. I know those can get water in them when they age and start causing issues.
 

littleblazer

Gold Supporter
#5
The Escalade would do this too. Only when cleaning the engine bay and it would steam up. The majority of it was the throttle body because it would actually trip REP. The injector harness weather packing is what I would suspect. If the engine was hot, steam travels mighty quick...

You can pressurize the manifold with a shop vac and spray soapy water around the mating surface too. That will confirm before you have to tear it down.
 

MRRSM

Lifetime VIP Supporter
#6
There is yet another possible problem area that is worth checking as well that would not readily come to mind because as soon as we hear the word "Fuel...", it is easy to forget that right along with the Coil On Plug Packs... The EFIs are serviced by Electrical Connectors Locking Tabs with Metri-Packs loosening that can also fail when exposed to Steam and Heavy Ran or Wash Exposure and Dead Short as a result. Once the Fuel Sprays stop for lack of the PCM Pulse Width Modulation Signals... then here come the P0300 Codes... or in some cases ... Maybe NOT.

This video gives a great illustration of how this problem can develop if the EFI Connectors get Sketchy and perhaps get overlooked as a possible place to look for problems whenever we think of "Mis-Fire" issues when the the Engine Bay gets Wet. Take note of how 'cracked and gnarly' the edges of the Orange Metri-Pack Grommet look in this example of the Clogged and Dirty #8 EFI Connector...it cannot be a coincidence that the Misfires and the Broken Locking Tab on that connector are in the very same location:

 
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#7
Check the plugs. My son had a mysterious misfire only at certain RPMs/throttle and it turned out to be that it had the wrong plugs (platinums). Put in some NGK Iridiums (couldn't find ACDelco), runs like a top.
 

MRRSM

Lifetime VIP Supporter
#8
Using the Straight 12 Volts might actually damage the EMC (Electro-Magnetic-Coils) inside. If you want to see videos and still images of what the GM Multech II EFIs look like with the Internal Filter Baskets removed and when being cleaned in Two Stages using an Untrasonic Bath and an internal Pressure Cleaning with my "FrankInjector Machine" ... Visit my Photobucket here:

http://s557.photobucket.com/user/60dgrzbelow0/library/HOMEMADEEFICLEANER?sort=3&page=1
 
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Mounce

Mounce

Silver Supporter
#9
With all the parts in from Amazon I began the R&R this morning. Smooth sailing so far other than difficult fuel injector harnesses and the valley cover fighting me. The knock sensor tube seals were adhered to the knock sensor posts and ended up tearing both seals when it finally came loose. Luckily the new valley gasket came with the tube seals.

Taking a break, gotta finish cleaning the mating surfaces then start reassembly.

Deep in the depths of an LM7 lies a tear of hope and a sore back. :thumbsup:

20180819_140309_HDR.jpg 20180819_155645_HDR.jpg

Oh joy, good ol sideways pics.
 

MRRSM

Lifetime VIP Supporter
#10
FWIW... If you have not as yet picked out any Camshaft Kit(s) to install during your repair... Melling Makes Two Rare Kits that include the Higher Performance Camshafts, Heavy Duty Valve Springs and Keepers. Both can be installed without having to remove the Engine Heads and should not require having to get any Tune installed into the PCM... although the -8 Version of these two should probably have the Tune done. Besides a decided bump in HP and Torque... Both Camshafts have an improved "Lope" that is very attractive... but not TOO Radical:

https://www.melling.com/parts-lookup/

MELLINGCAMSHAFTKITS.jpg
 
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Mounce

Mounce

Silver Supporter
#11
Another rotated pic.. BUT got her pieced back together. Intake gaskets (updated aftermarket design with steel core instead of plastic), valley cover and knock tube gaskets, knock sensors, throttle body gasket, and steam tube gaskets. Even done the ol' rtv horseshoe TSB. Yeah, pretty shaky horseshoes but the old sensors had surprisingly never seen water to begin with so I'm not too concerned about it.

Figure I'll give the new gaskets a couple days to make themselves at home then do another water test to confirm the fix. All wiring was perfect, injector harness seals looked mint, and the old gaskets were completely flat, degraded, and oil soaked.

And yes, I see the valve covers, that's somewhere close to next on the list.

20180819_201623_HDR.jpg
 
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C-ya

Well-Known Member
#12
Interesting. My 5.3 TB does that if I go through the underbody spray at the car wash too slow. Now when I go through, I zip past that and get to the park position.

I'll keep an eye on this. I doubt I will do anything more than drive fast through the spray. Haven't hit any rain yet that bothered it.
 

littleblazer

Gold Supporter
#13
@Mounce you happen to have the exact list with the part numbers for everything? Dad wants to do this on the escalade but he only wants to go in once, I don't blame him...
 
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Mounce

Mounce

Silver Supporter
#14
@Mounce you happen to have the exact list with the part numbers for everything? Dad wants to do this on the escalade but he only wants to go in once, I don't blame him...

Valley cover and knock tube seals: felpro MS92465

Knock sensors: acdelco 213-3521

Intake gaskets: felpro MS98016T

Throttle body gasket: felpro 61070

Coolant bypass seals (steam tube seals): Dorman 56390

Don't have a knock harness number as I didn't replace mine. Also check your steam tube style, some go across the valley cover lengthwise to the back of the heads, others (like mine) only cross from one head to the other in the front and does not require removal or seal replacement. I still replaced all 4 seals even tho I didn't need to. Have seen one leaking on one at work ONCE so it was enough to justify going ahead and replacing them while I was there, plus I already had them on hand so why not. Will dump 3 times more coolant than expected when you pull the first one off...

Might wanna do the oil pressure sensor if it's never been done, way easier to get to with no intake in the way.

Acdelco D1846A

(disclaimer: verify parts are the same for yours as mine. 03 5.3 Vin T non-flex)
 

littleblazer

Gold Supporter
#15
Valley cover and knock tube seals: felpro MS92465

Knock sensors: acdelco 213-3521

Intake gaskets: felpro MS98016T

Throttle body gasket: felpro 61070

Coolant bypass seals (steam tube seals): Dorman 56390

Don't have a knock harness number as I didn't replace mine. Also check your steam tube style, some go across the valley cover lengthwise to the back of the heads, others (like mine) only cross from one head to the other in the front and does not require removal or seal replacement. I still replaced all 4 seals even tho I didn't need to. Have seen one leaking on one at work ONCE so it was enough to justify going ahead and replacing them while I was there, plus I already had them on hand so why not. Will dump 3 times more coolant than expected when you pull the first one off...

Might wanna do the oil pressure sensor if it's never been done, way easier to get to with no intake in the way.

Acdelco D1846A

(disclaimer: verify parts are the same for yours as mine. 03 5.3 Vin T non-flex)
Thanks. Oil pressure sender was already done so... and of course I'll double check part numbers. Thank you so much.
 

littleblazer

Gold Supporter
#17
Just so you know, all part numbers are exactly the same. :yes: +1 for the ls family of engines.
 

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