Extensive Tune Up Misfires

[JeremyNH]

At 200k you may want to look at your timing chain. I converted to 24x this Spring so never had to fight through the P0300 (and never will). I have a 98 K1500 5.7L with 123k. I bought a Cloyes True Roller replacement chain since I had to open the timing cover anyway so seemed appropriate to spend an extra $80 since it would only add 10 minutes of work. On my motor the existing chain was loose like a chain saw chain is. It worked but a lot of play. The Cloyes chain is like a guitar string. I have seen on the forum where some see cam gear wear on older trucks. I swapped to the 395 cam at the same time but the stock cam gear showed no wear whatsoever so that wasn't my experience.

 

[Erik the Awful]

Rotor and Cap ( timing light was erratic when placed on any wire)

The erratic timing is likely your problem.

Is your distributor hold-down tight? You say the CPM is near 0, so it sounds like you have it tight.
Check your crank sensor and make sure it's not falling out or covered in crud.
The timing chain could be a suspect, but as it's a PITA to get to, I'd check everything else first.

 

[jamesdking]

The erratic timing is likely your problem.

Is your distributor hold-down tight? You say the CPM is near 0, so it sounds like you have it tight.
Check your crank sensor and make sure it's not falling out or covered in crud.
The timing chain could be a suspect, but as it's a PITA to get to, I'd check everything else first.

Distributor is snug and I used the older screws for the cap. Seems solid to me. I’ll peak at the crank sensor. It’s under the alternator and water pump correct?

 

[jamesdking]

Distributor is snug and I used the older screws for the cap. Seems solid to me. I’ll peak at the crank sensor. It’s under the alternator and water pump correct?

It looks like it’s tight in there. The bracket that holds it is tightened down anyway.

 

[Schurkey]

98 Yukon 5.7 vortec 200,000 miles

p0300 and rough misfire under load or on hills at highway speed. Won’t accelerate past 2000rpm when it starts happening.

Is your scan tool capable of showing individual cylinder misfire history?
What is the misfire history of each cylinder?

parts replaced in order:
Plugs
Wires
Fuel filter (had black gas in it)

That can't be good. How old was it?

ICM
Rotor and Cap ( timing light was erratic when placed on any wire)
Distributor
Rotor and cap again
Replaced cat
Spider MPFI (modern)
Intake gasket (upper)
Wires and plugs checked again
Sprayed down with brake clean looking for vac leak

DO NOT use "brake clean" to check for vacuum leaks.
1. Not all aerosol brake cleaners will burn. If it doesn't burn, you don't get an indication of RPM rise from the addition of fuel. Some folks use propane, I use aerosol CARB cleaner.

2. The chemical formulation of some brake cleaners leads to the production of Phosgene gas when burned. That crap can **** YOU UP, sometimes for years or even permanently. High enough concentration of Phosgene will outright kill you.

Cap and Rotor again!
Fuel Pump (cut a hole in floor) tank looked plastic and clean through the opening anyway.

Cutting an opening in the floor is NUTS. Say you're in a rollover collision, and the gas tank ruptures. The spilled gasoline drains into the passenger compartment, you and your loved ones burn alive. That's one reason GM didn't provide an opening to begin with.

Weld that hole shut, or at least use solvent-resistant sealer and enough reinforcement that the hole won't distort open in a collision that bends the body.

runs better than it ever has. Until you get to a hill. Still throws a code p0300 or sometimes a specific cylinder 0305 and 0304 but always accompanied by 0300.

What is the cranking compression of #4 and #5? (At that mileage, I'd test all eight.) If you find compression problems, use a cylinder leakdown tester to find where the compression is going.

fuel pressure at idle 51
Fuel pressure at koeo 55
Seems low and didn’t change with new pump even a little bit.

Verify that the gauge on your fuel pressure tester is accurate.

Almost no-one verifies their test equipment.

Thoughts:
Fuel filter plugged again from **** in the lines

Maybe.

Multiple bad replacement parts

Very possible. Not my first guess.

Timing is set to damn near 0 CPM

That's NOT ignition timing. That's just the synchronization of the cam sensor waveform to the crank sensor waveform.

Haven’t touched cam or crank sensor
Haven’t cleaned MAP

MAP sensors don't get cleaned. MAF sensors sometimes get cleaned.

Is it time to compression test for stuck valves or floating?

Yes, perform a cranking compression test.

At 2000 RPM, if the valves are floating, it's because the valve springs are broken.

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All 8 plugs looked like this after 6 months of this problem.

Looks good.

I have not. But the shop I took it to told me the cats were plugged and replaced them with new ones I purchased. They likely reused the o2 sensors tho.

There's other reasons an exhaust system could be restricted beyond "plugged catalyst(s)".

Test the back-pressure.

Use the scan tool to look at the O2 sensor activity. If you can PROVE that they're working properly, you can leave 'em alone. If the sensors have more than ~50K miles on them, or there's any question about their age, or the speed that they flip from high voltage to low voltage you might as well just replace 'em all. The sensors ahead of the catalyst(s) are more important for engine performance than the ones behind the catalyst(s).

ICM was meant as the coil. I didn’t replace the little computer but just swapped in the part the coil wire hooks to and goes to the dizzy.

I have no idea what you're talking about.

Also that wouldn’t relate to my low Fuel Pressure after the pump replacement. Though my gauges could be cheep and from harbor fright…

As said, verify your pressure gauge, and re-check the fuel filter.

 

[El Tigre]

I dislike making a bunch of changes at one time....
Very difficult then trying to find what's wrong...

 

[jamesdking]

Is your scan tool capable of showing individual cylinder misfire history?
What is the misfire history of each cylinder?


That can't be good. How old was it?

Who knows. It’s a 98 I bought used for 2000 bucks

DO NOT use "brake clean" to check for vacuum leaks.
1. Not all aerosol brake cleaners will burn. If it doesn't burn, you don't get an indication of RPM rise from the addition of fuel. Some folks use propane, I use aerosol CARB cleaner.

2. The chemical formulation of some brake cleaners leads to the production of Phosgene gas when burned. That crap can **** YOU UP, sometimes for years or even permanently. High enough concentration of Phosgene will outright kill you.

I know about the gasses. I was in fact wreckless herr and was trying out of desperation and stupidity. I didn’t realize it couldn’t burn tho?

Cutting an opening in the floor is NUTS. Say you're in a rollover collision, and the gas tank ruptures. The spilled gasoline drains into the passenger compartment, you and your loved ones burn alive. That's one reason GM didn't provide an opening to begin with.

Weld that hole shut, or at least use solvent-resistant sealer and enough reinforcement that the hole won't distort open in a collision that bends the body.

Again it’s a 98 Yukon with a ton of miles and holes in the body. The tank is just as likely to become dislodged and yeeted from the vehicle into a bus of nuns in a rollover. It’s a rusty old truck. The seams are sealed up with flex tape actually and it’s not terrible.

What is the cranking compression of #4 and #5? (At that mileage, I'd test all eight.) If you find compression problems, use a cylinder leakdown tester to find where the compression is going.

It’s on my checklist for sure.

Verify that the gauge on your fuel pressure tester is accurate.

Is there a process for this? Connect it to my air compressor and hope it’s gauge is spot on?

Almost no-one verifies their test equipment.

I barely have money for tools let alone tools that test tools.

Maybe.

Very possible. Not my first guess.

That's NOT ignition timing. That's just the synchronization of the cam sensor waveform to the crank sensor waveform.

I understand that. I just wanted to let the community know I wasn’t using a timing light to look for Mark’s on the balancer that aren’t there.

MAP sensors don't get cleaned. MAF sensors sometimes get cleaned.

You are correct here. My terminology is killing my post. I’ll edit that.

Yes, perform a cranking compression test.

At 2000 RPM, if the valves are floating, it's because the valve springs are broken.



Looks good.


There's other reasons an exhaust system could be restricted beyond "plugged catalyst(s)".

Test the back-pressure.

I’ll look into that. I hoped the muffler shop I went to would have not just made up a problem and diagnosed it and sold the solution to my. I grew up with the kid. Not saying it isn’t possible tho.

Use the scan tool to look at the O2 sensor activity. If you can PROVE that they're working properly, you can leave 'em alone. If the sensors have more than ~50K miles on them, or there's any question about their age, or the speed that they flip from high voltage to low voltage you might as well just replace 'em all. The sensors ahead of the catalyst(s) are more important for engine performance than the ones behind the catalyst(s).

I was under the impression that this is how he verified that the cat was plugged by comparing the two. I wish I knew now if he retested after install.

I have no idea what you're talking about.

The ignition controll module is a small electronic device that is held to a mounting plate with a special glue. The coil is also connected to this bracket. I replaced the coil only.

As said, verify your pressure gauge, and re-check the fuel filter.

Thanks. I appreciate your input.

 

[jamesdking]

I dislike making a bunch of changes at one time....
Very difficult then trying to find what's wrong...

This whole list of repairs was done slowly over a couple months. The car was driven during it as well. Often I’d think I had it fixed and it would sneak back up the 4th time she went up that hill. It’s my girlfriends ride until yesterday. We bought a Subaru for highway travel.

 

[Schurkey]

I know about the gasses. I was in fact wreckless herr and was trying out of desperation and stupidity. I didn’t realize it couldn’t burn tho?

Some brake cleaners burn, some don't.

Is there a process for this? Connect it to my air compressor and hope it’s gauge is spot on?

That's a decent start. Depending on the range of your fuel pressure gauge, and the pressure generated by your compressor, you may need to regulate the air pressure downward some. Compare the gauges, see if they match (within reason.)

The ignition controll module is a small electronic device that is held to a mounting plate with a special glue. The coil is also connected to this bracket. I replaced the coil only.

Your term "little computer" in the previous post didn't make sense.

 

[jamesdking]

Some brake cleaners burn, some don't.


That's a decent start. Depending on the range of your fuel pressure gauge, and the pressure generated by your compressor, you may need to regulate the air pressure downward some. Compare the gauges, see if they match (within reason.)


Your term "little computer" in the previous post didn't make sense.

Tbh I had dumbed it down too much.