Hey everyone. I have a 2004 silverado with an LQ4 and it is sputtering and not running right. Seems like there is extremely low power, and it has s lot of hesitation. I dis the plus and wires, and a full seafoam treatment as well as a compression check. It is currently throwing a P0300 code

Here are how the cylinders tested...
1 - 150
2 - 140
3 - 150
4 - 160
5 - 160
6 - 170
7 - 180
8 - 180

none of these are really that low. A little low on a few, ya but it seems the problem numbers are around 90 or 100. Could this be caused by a bad injector, fuel pressure regulator, or something else? Head gasket, dirty intake manifold? Is there any way to test for the bad injectors or pressure regulator?

 

That's a random misfire, in case you didn't know. (you don't say above)
I would check all grounds as it sounds like you have some iffy coil/injector connections.
Mainly those grounds in back of the heads.

 

https://ls1tech.com/forums/generatio...erheating.html

See this post. I think someone else maybe had a similar problem but didn't follow all the way through on troubleshooting. But maybe it'll help

 

Yep that was me. After that I re did the comp test and it came out about the same. I pulled the intake and the heads look dirty AF. Here's a pic. Also one of the injector grommets was underneath the intake.

 

EEEEEEeeeeeeeeeeewwwwwwwwwwwwww...

A serious case of long-term neglect.

Good news is, your valley cover bolts look to be the 13mm head. Which most likely means, not for certain but most likely, that your motor has the later-model floating-pin rods.

 

When I tore down my 74 camaro after it had been sitting in a field for 2 years, it wasnt even close to this bad. They are 317 heads, though too. I feel like I should pull the heads too and just take them in for a complete overhaul.

 

Not a bad idea; or trade em in at Texas Speed or some such for a pair that are potentially a bit less ... experienced.

 

I'm looking into fuel issues now. Is there any way I can test my fuel pressure regulator and clear out the injectors in case they are clogged?

 

P0300 is a random/mulitiple misfire

Which in general means you are having misfires on all cylinders

If you have misfires on all cylinders you need to look at common source issues. Such as fuel pressure, fuel condition (old or have water in it?) vacuum leaks, crank sensor..

The compression is decent but it's odd that it goes up in such a steady pattern. Makes me thing something else was causing the numbers to go up as you went on with the test, comp numbers are usually super random. Not that it means you have a problem but it sure is weird. I don't like the 150 psi, even though, that's still enough. And yes you don't normally see a misfire occur due to compression until you get down around 100-110 psi per cylinder.

To test your fuel pressure regulator, check your fuel pressure. If it's in the proper range then the regulator appears to be doing it's job. But you also need to take it out and hammer it to see if it can maintain fuel pressure under load which will tell you if the fuel pump is keeping up.

If the gas is old or questionable get it out and get a tank full of new fresh gas and go from there.

Also try a crank sensor, seen a few of these posts recently where it was mentioned the crank sensor took care of the issue. Keep your old one, also saw several threads where guys said they had to do 2-3 of them to get a good one.

Are you getting any codes other than P0300?

I had one in the other day with a p0300 code and that's all it would give me. The wiring was f'ed at the crank sensor and the connector was glued into the crank sensor. Replaced the pigtail and sensor and for the first time the car started spitting out actual individual cylinder misfires. It was running poorly and had 3 cylinders misfiring but the PCM was receiving garbage info from the crank sensor so it couldn't tell which cylinder was misfiring and set a p0300. After the crank sensor replacement and wiring I could then get info on which cylinders were misfiring and go to them and fix their individual issues.

 

Replaced the crank position sensor and throttle body sensor. Anything else I should try while the intake is off?

 

I used a 9 volt battery to unclog my quad fuel injector. Just get an old pigtail for the injectors hook up battery. i put a switch on the positive side to open and close injector while using berryman b-12. Took like 30 seconds to unclog my injector.

 

I just bought a 01 4x4 with a lq4 because the price was right. Same symptoms.
found mouse nest in air box. Cleaned maf. New plugs and wires. Put 600 miles on it last week. Runs perfect . Scanner still doesn't work on it. Not sure why yet.

 

Yes do all new pcv lines and hardware. Bypassing a lot of oil it looks like to me. Possible vacuum leaks due to oil soaked and rotted lines.