97 gmc 5.7 p300

[97moneypit]

Not sure what to check next but could use some help. Bought this truck and its living up to my user name.

Took the truck to get smog and it passed. California smog to be exact

P300 random misfire was pending during the test but dash light was not on.

New spark plugs
New wires
New rotor and cap
New ign coil
New fuel filter
New O2 sensors
New catalysis
Exhuast headers (shorties)
K&n intake

I have cleared and road tested several times and I keeps coming back, any suggestions

 

[JOHNGAAA1]

Try spraying air intake cleaner near sides of intake manifold and vacuum hoses, see if idle or code pops up. i have been there. Possible bad intake gasket.

 

[1997]

are you using a scanner or code reader?
can it display misfire codes on each cylinder, ex P0301.?
many code readers don't.

my p0300 code took way longer to repair because my code reader didn't display all the info.
turned out to be the spider poppet #1 not popping .....
is your spider original?

 

[Schurkey]

P300 random misfire was pending during the test but dash light was not on.

P0300?

As said, you need to access the cylinder-by-cylinder misfire counts.

K&n intake

Probably a mistake. I'm not fond of oiled-gauze air filters on vehicles with a MAF sensor.

Most aftermarket "air intakes" are poorly designed. There's very little wrong with the original parts.

I have cleared and road tested several times and I keeps coming back, any suggestions

As said...you likely need a better scan tool. Misfire counts, and misfires should also show up in the O2 sensor voltage especially when viewed as a graph.

What is the fuel pressure? Does the system hold pressure?

 

[97moneypit]

Try spraying air intake cleaner near sides of intake manifold and vacuum hoses, see if idle or code pops up. i have been there. Possible bad intake gasket.

Sprayed a whole can of brake cleaner around everything. No change

are you using a scanner or code reader?
can it display misfire codes on each cylinder, ex P0301.?
many code readers don't.

my p0300 code took way longer to repair because my code reader didn't display all the info.
turned out to be the spider poppet #1 not popping .....
is your spider original?

Im sorry I though I put that. Its a simple Bosch code reader. I am getting p0300 and p0303. I have tried shaping wires and plugs. P0303 is constant.

Supposed the last owner change injector at 180k, it's now 210k miles ... but as I am working on this truck I don't trust anything he said... or his work

P0300?

As said, you need to access the cylinder-by-cylinder misfire counts.

Probably a mistake. I'm not fond of oiled-gauze air filters on vehicles with a MAF sensor.

Most aftermarket "air intakes" are poorly designed. There's very little wrong with the original parts.


As said...you likely need a better scan tool. Misfire counts, and misfires should also show up in the O2 sensor voltage especially when viewed as a graph.

What is the fuel pressure? Does the system hold pressure?

I was going to check fuel pressures next... need to order a tool or borrow one

 

[97moneypit]

Little up date.

After a 20 mile drive on the highway

P0300 is intermittent
P0303 went away.
No dash light.

Im going to try different spark plugs. I put ngks in because that what I had. Going to put acdelco in them

 

[Frank Enstein]

You already have A/C Delco plugs in it. A/C Delco hasn't made a spark plug in 35 years.

I recommend a Platinum tipped plug listed for your application. They last longer and the platinum tip helps jump the gap with lower voltage and they don't foul as easily.

Double platinum plugs won't help more than the single platinum on any engine with a distributor so don't pay extra for them.

Any of these are fine.

1997 CHEVROLET C1500 5.7L/350 Chevy small block Gen I Spark Plugs Spark Plugs & Glow Plugs Ignitions & Electrical - Platinum Electrode Tip Material - 0.708 in. Spark Plug Reach (in.) - 0.709 in. Spark Plug Reach (in.) Parts & Accessories | Summit Rac

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www.summitracing.com

 

[Schurkey]

Sprayed a whole can of brake cleaner around everything. No change

SOME brake cleaners are not flammable. They don't do anything even if there is a vacuum leak.

Other brake cleaners break down into phosgene gas when burned. That will foque you up in a hurry--maybe even kill you.

I use aerosol carburetor cleaner, NOT brake cleaner. I've used propane, but I don't like that much.

Im sorry I though I put that. Its a simple Bosch code reader.

Ideally, that would change to something more sophisticated.

I am getting p0300 and p0303. I have tried shaping wires and plugs. P0303 is constant.

Compression test of #3 is warranted. Also, pull the valve cover, verify that #3 rocker arms are moving like they should--no failed cam lobe, or lifter, or bent pushrod.

If you have compression and spark, about all that's left is fuel/air mixture. That could be a vacuum leak you haven't found yet; or a failed injector system.

I was going to check fuel pressures next... need to order a tool or borrow one

Many parts store have "loaner tool" programs. Around here, O'Reilly and Auto Zone are good for that.

 

[Frank Enstein]

If you want to re-gap the plugs DO NOT pry on the platinum! It'll pop off!

 

[97moneypit]

Installed acdelcos double platinum. Gapped to .60

Right away after starting p0300 and p0303.

Spray a whole can of intake cleaner. No change.

Said **** it sprayed a whole can of starter fluid. No change.

Looks like I going to have to check fuel and compression.

I have a snap on scanner at work