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1999 Chevy Suburban K1500 LT
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Discussion Starter #1
So a few days ago I went to start up my car and it was running about as good as a beached whale running a triathlon. So i used my code reader and got 2 P0300 codes which is random multiple misfire. I looked up the causes and parts that could fail (most of the parts on my engine are original) and came up with a few that were known to cause this issue. So I changed my spark plugs (on passenger side two had small carbon build up and were thrashed), replaced the fuel filter, ignition coil, ignition control module, ignition cables, made sure I was getting power from my distributor, and have checked every electrical connector and hose on my engine. Only things I haven't checked that are possible causes are the fuel injector unit (my engine uses the wonderful spider unit that is beloved by everyone) and the fuel pressure regulator. I have a feeling I'm not getting proper fuel pressure but I haven't been able to secure and pressure tester yet so that's next on the list. Also some side notes, the engine is supposed to idle around 810 rpms and currently idles around 700 and drops to 500 when put into gear. There is also a suspicious amount of liquid coming out of my exhaust but it doesn't have a smell to it. There's also the possibility of a vacuum leak so I'll be grabbing carb medic and testing around my engine for that. Any advice or previous experience with this I'd like to hear about.
 

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2000 Silverado Z71 4x4 5.3L 460k+ miles w/ GM rebuilt motor and trans
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Check your fuel pressure first. You may have a bad fuel pump. This will also tell you if you have a leak somewhere, like an injector, adding to your problem.

The fluid coming from the tailpipe could be moisture you're just not used to seeing or excess condensation from sitting longer than usual. Symptoms always seem to crop up when I'm really paying close attention to my truck.
 

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A few thoughts.

See from your ID you are in Oregon, not sure where, but I'm a little North of you on Vancouver Island.

Are you getting hard starts too? Your symptoms are similar to what I've had a couple of times this time of year as the damp weather moves in. First thought is a bad rotor and cap, or possibly wires, esp as you are getting no direction on the misfire. 2nd is moisture in the fuel, esp if the tank is low, although changing the fuel filter should have helped that. Fuel pressure regulator issues often show up as longer cranking before start as pressure needs to build, and also might show as wet plugs. Bad poppets in the spider injectors should also point to certain cylinders misfiring. Fuel pressure issues can also show up as bogging under load, and "normally" the truck will idle OK and misfires will often throw to the most distant plugs, not so much as random.

Re the tailpipe moisture. Mine drips a huge amount all year, but right now I get a puddle every time the truck is parked. Our driveway has a slight slope and both AC drains and the exhaust all leave a trail that runs to the drain in front of the garage doors that doesn't dry overnight.
 

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Did you replace the spark plug wires? I had a similar issue years ago and replaced everything I could think of except the spark plug wires because they looked new. But when all else failed I replaced them and in doing so one crumbled into pieces once I tugged it. Problem solved.
 

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1999 Chevy Suburban K1500 LT
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7 Posts
Discussion Starter #5
I didn't replace the wires as I was thinking the same thing you were, I guess those are going to be swapped out as well now.
 

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1999 Chevy Suburban K1500 LT
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7 Posts
Discussion Starter #6
A few thoughts.

See from your ID you are in Oregon, not sure where, but I'm a little North of you on Vancouver Island.

Are you getting hard starts too? Your symptoms are similar to what I've had a couple of times this time of year as the damp weather moves in. First thought is a bad rotor and cap, or possibly wires, esp as you are getting no direction on the misfire. 2nd is moisture in the fuel, esp if the tank is low, although changing the fuel filter should have helped that. Fuel pressure regulator issues often show up as longer cranking before start as pressure needs to build, and also might show as wet plugs. Bad poppets in the spider injectors should also point to certain cylinders misfiring. Fuel pressure issues can also show up as bogging under load, and "normally" the truck will idle OK and misfires will often throw to the most distant plugs, not so much as random.

Re the tailpipe moisture. Mine drips a huge amount all year, but right now I get a puddle every time the truck is parked. Our driveway has a slight slope and both AC drains and the exhaust all leave a trail that runs to the drain in front of the garage doors that doesn't dry overnight.
No hard starts, cranks like normal, idles ok for a few seconds then starts to run into problems. Tank is just over half full and usually the only time I've had hard starts is during winter when it drops to 30~40 degrees.
 

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Do the easy ones first.
1. Spark plug wires test. One good test is to spray some water mist while engine is running outside at night when it's dark, you will see arcing or sparks jumping from a wire to a metal ground nearby. A light show will confirm bad spark plug wires.
2. As @OpalLacod suggested, fuel pressure test. Record fuel pressure when ignition switch turned not (engine not running). Watch how much fuel pressure drops over time. Report back.
3. Record fuel pressure when engine running. Report back.
4. I think if an injector is not spraying or bad, it will throw a cylinder specific misfire. e.g. P0301 - P0308. Unless one is stuck open and just dumping fuel inside the intake. Then you will smell unburned gas in the exhaust.
 
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