Hi all, I have a 99 Blazer giving me a P0302 fault code. Here is what has been replaced to date:
-plugs
-wires
-coil
-distributor (to fix 0300)
Compression on that cylinder was 160, spark plug was wet. I exchanged plugs with cylinder 4 but there was no change. Verified that there is spark on the wire of plug 2. Fuel pressure leak down test passed.
I had thought that possibly the injector was no working but the plug was wet and I pulled off the throttle body and it is wet going to that cylinder.
Open to any and all suggestions. Thanks in advance!

 

sounds like the spider is leaking. common problem I've read about.

 

A leaking spider was eliminated when the fuel pressure leak down test was good. Held 60# pressure for a long time.

 

Can you actually feel the miss, or is it just setting a misfire code? Where did wetness under throttle body come from? (Injectors dump into intake ports far downstream from the throttle body). What do you have for a scan tool? Just asking.

 

That only tells you if the check valve at the regulator is working. Fuel pressure tests cannot tell you if the spider itself is bad. It is the spider that is the problem, replace it with the upgrade MPI. unit and only use AC Delco or Delphi parts in all the fuel and secondary ignition systems.

 

Lesmyer, oh you can feel it! The think shakes the crap out of you! It is wet in the ports. You can see the ports for 1&2 when the TB is romoved. I have a Mac Task Connect ET1505AN scanner.
Gregg64. I may have misunderstood the fuel pressure test. I understood that if it holds pressure then the regulator and poppets were all good. Is the spider separate from this? I am new to this truck....and Chev for that matter.

 

You are correct. The leakdown test at the service port checks for fuel leaks from the check valve in the fuel pump, all the way up to the valve plate in the regulator, the regulator diaphragm, fuel metering block, injectors, spider lines, poppets, and the entire pressure line from the pump to the fuel metering block. It does NOT check the fuel return line.

A compression test is mainly used for diagnosing leaky piston rings. A cylinder leakage test would tell you if the valves are sealing. Might be worth a try.

 

A quick note about spark, spark acts totally different under pressure in the cylinder, just because you can jump a spark at atmospheric pressure outside the cylinder doesnt mean it will fire a plug in the cylinder under 160 psi of pressure.
Also, If you used cheap over the counter store brand plug wires then thats the first place you should look, ive even seen an MSD "Street Fire" plug wire (Which is MSDs Cheapo Line) on a stock 3.1 V6 that burned up internally in less than a couple months of daily driving.
The ignition systems on these Vortec engines are very sensitive and were engineered to perform well with factory grade high quality components without much room left for error.
You need to test your plug wires with an ohm meter to start out with.
Was the distributor cap and rotor replaced with the distributor as a whole unit? If so, they were probably cheapo parts slapped on the new distributor body to keep unit cost down so the parts giants can make money and keep it cheap enough that you can afford it, they should be replaced with acdelco parts.
The distributor cap on these engines is one of the biggest problems ever created, there are metal traces molded inside the plastic that carry the spark from the point where the rotor drops it off, to where it exits the cap at the wire terminal into the plug wire. If you look at one of these caps closely you can see how the traces overlap each other, what happens is the cheap distributor caps are made of cheap plastic that dont have a high enough dielectric resistance to current flow, this allows the spark to jump internally between traces through the plastic in the cap, as soon as this happens the first time it creates a carbon track, making it easier to jump another spark the next time. Why would it do this? Maybe it has something to with what i mentioned about spark and pressure? Maybe the cylinder that the spark crossfires to in the cap is at low pressure at that moment, it would be a path of less resistance and we all know that thats the way electricity will take. Factory caps are made of a more pure and higher quality plastic resin that wont break down and allow this crossfiring to happen for a long time. Thats why your stock cap lasted 100,000 miles and the 18 dollar store brand cap from "Cheapo Auto Parts" only lasted 3000 miles Some of this is fact, some is my own theory so take it for its worth. The good news is, pretty much nothing being manufactured today by any car company has a distributor anymore, these are the last of this old technology that we will have to deal with.....
Aaanyway....
I cant stress enough the importance of oem name brand acdelco parts being used in these ignition systems, if you ignore this you may end up chasing your tail for months and throwing hundreds of dollars away tossing other parts at it. These ignition systems DEMAND the highest quality parts in order to perform like factory.


Sorry for the long post, i hope its informative, seems like ive told this same story many times, but i figure, the more i do, it just leaves more chances that someone else will stumble on it and it will help more people.

Post back what you find.

One more thing i forgot to ask, are you sure the wet plug was wet with fuel and not oil? Ive pulled a plug before and noticed it was oily but had good spark and compression, turned out one of the injector pins in the spider unit under big plug on top of the intake was bent over so that cylinder wasnt getting fuel, you could have a bent pin, or a broken wire in the harness or it could even be as crazy as a bad injector driver circuit in the PCM?

Ok now ive gone on too long..
Good Luck!

 

Dime,
Spot on! Great post with great information and advice!

The absolute best way to test the seconday ignition system is with an oscilloscope. A trained eye can spot a failing, or failed, plug wire instantly. Unfortunately, most DIYer's, and many professional shops, don't have one at their disposal, or know how to interpret the pattern on the screen.

Too many times people fall prey to advertising hype from big name manufacturers and they unknowingly install cheap quality aftermarket parts, (buyer beware). They're the ones that end up chasing their tail looking for another problem. For years we've been stressing the importance of using AC Delco/Delphi parts. Some people take the advice, and others try to cut corners on cost, or think they know better. When an OEM part lasts 15 years, and goes 100K miles, it speaks volumes about the design and quality. AC Delco/Delphi ignition and fuel system parts were designed specifically for this engine. As a result, they work better, and they last longer than anything other brand. And no, I do not work for AC Delco or Delphi

 

Had it running this morning to move it out of the garage to swap out a blower motor for a friend and ran the codes again. The 0302 is gone and the 0300 is back. Did leak down- all under 10%, compression averaged 150 all within 15%.

DimeBlazr, thanks for the information. The distributor was replaced as a complete unit. I will pick up an AC Delco cap/rotor next week when I am back in town. What should the resistance reading be on the wires? I will check them out.

I did a vacuum check, 17 in Hg at idle. Somewhere I thought saw a minimum of 20, can someone verify this for me?

Once I get the plugs back in I will record the values on the scanner and post.