LS1GTO Forums banner
21 - 40 of 54 Posts

· Yea, I belong to a club!
Joined
·
1,604 Posts
Problem is dirty fuel injectors. My 04 GTO daily driven 160,000 miles has this problem every once in a while. Some high quality fuel injection cleaner fixes the random misfire every time. I use double strength. If the can says use with 20 gallons of gas I used it with 10.
I'm confident the fuel injectors are fine. I was running a bottle of Lucas Injector cleaner in the gas tank at every oil change until I switched to Race Gas a few years ago since she doesn't get driven a whole lot. Oil changes are done between 1,000 and 2,000 miles with a new Wix filter at each change. I would also add Stabil and top off the fuel tank at the end of every fall before she'd hibernate for the winter when running gasoline.
Total miles on the car right now are 14,513. The random misfire has been an off an on issue since I bought the car new. Way more on now than off.
 

· Premium Member
Joined
·
6,048 Posts
I'd recommend pulling the cam and inspect. If it looks good. Run it. Any signs of abnormal wear....... tear it down further

metal in oil will go everywhere. Ask me how I know. Destroyed a very low mileage LS in my truck. My first symptoms were..... random misfires
 

· Yea, I belong to a club!
Joined
·
1,604 Posts
Here's a bit more info;
The SLP Bobcat 455 package was installed by the dealer prior to me taking delivery in May of '07 with 110 miles..
The High Flow SLP Cats blew out their catalyst within the first few thousand miles.
Jeremy Formato recommended I change the original spark plugs to NGK TR6 (I gapped them at .037") and replace the front O2 Sensors to stop the misfire. It worked for a while, the misfire came back. That was in 2012 at 9,200 miles when they were replaced.
With skipopeye's HP Tuners we saw the O2 sensors had failed again and they were replaced with two he had from one of his 2004. 2019 at 13,376 miles.
The day we noticed the O2 sensors had failed again we saw very odd fluctuations in oil pressure. After a bit or research it was discovered there was a DOD valve in my oil pan. That was replaced with a plug at 13,406 miles.
I've now put in NGK TR5IX Iridium plugs and have them gapped at .040"

Yes, I keep meticulous records...
 

· Super Moderator
Joined
·
32,068 Posts
I'm just throwing this out here and it's probably not the case but is there any possibility that the grounds on the back of the heads are loose or not hooked up?

Tearing up O2s and constant misfires sounds very ground like to me.

The other long shot possibility is that the PCM could be bad.
 

· Worthless reject member
Joined
·
84,741 Posts
You picked up on something I saw but couldn’t confirm: Those green striped springs don’t look stock. The Pontiac dealer he bought the car from new installed the SLP 455 Bobcat package on the car. From research it came with new rockers, springs, retainers and keepers. Can’t find any info on those springs at all, but look like LS6 springs as I believe some LS6’s came with green striped springs, but can’t confirm what these springs from SLP are.

The engine is stock other than headers and a FAST 92 intake, so should we find the trunnions to be the issue, and are able able to save this motor by replacing the rockers, do you also suggest all new valvetrain or are they OK to leave on an otherwise stock block?
i bet they're slp valve springs. fairly sure they sold the rockers in a kit with the springs/retainers/keepers.

wish i could find info on the spring rate. the pn might be the 53003 if you want to ask around. but i doubt they're real heavy, definitely not the 400+ lb'ers you see on bigger after market cams.

if they've done you fine so far, though, i don't see much reason to change them. maybe have the spring pressure checked.
 

· Worthless reject member
Joined
·
84,741 Posts
I'm just throwing this out here and it's probably not the case but is there any possibility that the grounds on the back of the heads are loose or not hooked up?

Tearing up O2s and constant misfires sounds very ground like to me.

The other long shot possibility is that the PCM could be bad.
i wonder if his rockers have been the issue with that, too. i mean, as the trunnion wears, it's going to get a little looser. the lifters should take that up, though. he'd just have less preload as time went on.

it's not an even wear. i've taken these apart and they look like scallops taken out of the bottom of the trunnion where the rollers dug in. they're probably going to feel real notchy and hard to turn when he takes them off.

just wondering if it's throwing his valve events off, maybe effecting lift, and it's misfiring a little.
 

· Yea, I belong to a club!
Joined
·
1,604 Posts
I'm just throwing this out here and it's probably not the case but is there any possibility that the grounds on the back of the heads are loose or not hooked up?

Tearing up O2s and constant misfires sounds very ground like to me.

The other long shot possibility is that the PCM could be bad.
The passenger's side head has a ground where the catch can bolts up to it, and the driver's side, I can see the ground bolt with it through a group of wires into the head.

I'd purchased a remanufactured ECM a year or so ago, just in case the issue is electrical. It's still in the box it came in.
 

· Registered
Joined
·
86 Posts
I'm confident the fuel injectors are fine. I was running a bottle of Lucas Injector cleaner in the gas tank at every oil change until I switched to Race Gas a few years ago since she doesn't get driven a whole lot. Oil changes are done between 1,000 and 2,000 miles with a new Wix filter at each change. I would also add Stabil and top off the fuel tank at the end of every fall before she'd hibernate for the winter when running gasoline.
Total miles on the car right now are 14,513. The random misfire has been an off an on issue since I bought the car new. Way more on now than off.
Could be one or several defective fuel injectors then. I would not dismiss the fuel injectors so easily. Also primary oxygen sensors can fail for no reason. Just sayin.
 

· Holdiac Performance
Joined
·
2,422 Posts
Long story short, it looks like a 14k mile LS2 in a friends GTO (Dave “BRZN”) is beginning to consume itself.

We’ve been chasing an intermittent random misfire for years. All the typical electrical items were checked (plugs, wires, coils) to no avail. Swapped on some new Kooks headers last month as well as some new plugs. Winter hit here and didn’t get a chance to take it out for a drive and do some data logging to see if somehow the headers and new plugs miraculously fixed the issue.

Last week Dave decided to do an oil change as it’s been awhile since he last did one (roughly 1k miles and a couple of years as it’s a summer garage queen). Found some crap on the magnetic drain plug and thought he’d open up the oil filter.

I can’t upload the video, but attached is a still picture of the video. There’s a lot of glitter in there. Took the valve covers off and saw what you see circled on the passenger-side. These are SLP 1.85 rockers if that makes any difference.

We’re already prepared to pull the engine in the spring, but anyone want to guess what’s going on? This is a bolt-on LS2 with the stock cam and heads, so nothing more than the aforementioned rockers and headers on the car.

Rockers deteriorating? Lifter failure resulting in taking out a cam lobe? Bearing failure?

We did a compression check last weekend and all cylinders were down 5-10lbs from when we last checked the compression in 2016. Began a leak down test before I had to leave and those results all seemed around the same as previous and within the normal range, so we don’t believe it’s a dead cylinder somewhere.

Planning to pull the rockers next to see if one of those SLP rockers is destroying itself.

View attachment 523536
View attachment 523537
View attachment 523539
View attachment 523540
Oil Pressure's fine. JHP gauge on dash shows around 47psi. Skipopeye and I took her for a romp last spring connected to his HP Tuners and confirmand good oil pressure. We did see the random misfire on most all cylinders but worse on cylinder 3 which is where my scan tool shows the misfire coming from.
The consensus seems to be that too much sitting is hard on hydraulic lifters. Stiffer valve springs would compound that. Maybe you got lucky and caught a lifter on #3 in the early stages of failure, just taking a few to too many revolutions to pump back up. The other random misfires could be unrelated. I would pull that head off and visually inspect the #3 lifters and cam lobes.

I often let my GTO sit for weeks without driving it, and had the pleasure of replacing the cam and lifters at just over 70k after a lifter on #2 collapsed on cold start up and started knocking like a mofo. I wasn’t smart enough to diagnose it, but the ace mechanic who fixed it chased down a misfire code on #2.
 

· Administrator
Joined
·
11,736 Posts
Discussion Starter · #31 ·
One thing at a time. The initial smoking gun right now looks to be a failure of the SLP rockers which sure could be the cause of the random misfires. #3 peaked at 8 misfires at one instance during a 30 minute data log last spring, but every other cylinder showed random misfires as well.
 

· Premium Member
Joined
·
279 Posts
Oil Pressure's fine. JHP gauge on dash shows around 47psi. Skipopeye and I took her for a romp last spring connected to his HP Tuners and confirmand good oil pressure. We did see the random misfire on most all cylinders but worse on cylinder 3 which is where my scan tool shows the misfire coming from.
Check the pushrods, and a borescope to look at the pistons and valves. see if there are any marks from piston tapping the valves. With the 1.85 rockers, you have increased the valve lift. Could be the valves and piston kissed in at least cylinder 3... or, since the bottom of the trunnions appear where the most wear is, maybe the springs are binding...
 

· Yea, I belong to a club!
Joined
·
1,604 Posts
Charlie and I were back at it last Saturday. Compression test was good with cylinder 8 at 195 psi and cylinder 4 at 210, all the others were between those two. Leak down test was good with all cylinders right about 10%+/- a little (8 to 12.5).

All the rockers are off, cleaned in my parts washer and the push rods have been blown out with brake clean followed up with compressed air. I blew the brake clean onto a white towel with no visible metal flakes on the towel coming from the insides of the push rods. It looks like I've gotten all the metal flakes from the top of the head; around the head bolts and the valve springs.

Every rocker except the one for the exhaust valve over cylinder 6 feels rough and notchy. Several are bad enough to have an audible click.

My guess as to what happened is from low oil pressure at WOT starving the rockers of oil.

My '06 had a valve in it for an engine set up for Active Fuel Management, Displacement on Demand. Charlie and I figured that out doing a data log with his HP Tuners awhile ago and I replaced the valve with a plug at 13,400 miles. At WOT the valve would open dropping oil pressure, then when I'd get off the throttle the valve would slam quickly shut sending the oil pressure high. It would all happen fast enough the JHP Gauge on the dash pod wouldn't pick it up. If I remember correctly the oil pressure would drop into the 30psi range and go up to almost 70psi where it would normally run around 47psi.

Next I'll pull the trunnions out of the rockers to look over the damage and decide if I'll just replace the trunnions in the 1.85 ratio rockers or go to a new set of complete 1.7's.
 

· The Entenmann's Shim-Sham
Joined
·
26,134 Posts
Your misfires could certainly be caused by the failing trunions.
If you go back to stock rockers, then I would replace the valve springs with some LS3 springs. The 1.85s came with new springs to accommodate the extra lift, so there isn't a reason to keep using them with factory rockers.
 

· Yea, I belong to a club!
Joined
·
1,604 Posts
Anyone know, are the stock GM 1.7 ratio trunnions the same size as would be in the 1.85 ratio rockers? Depending on what these look like once I tear them apart I may just go with an upgraded trunnion kit.

The stamping on the trunnion bearings side on the SLP 1.85 ratio rockers shows INA SCE105. A quick Google search shows them to be a Drawn Cup Needle Bearing with a 5/8" Bore, a 13/16" Outside Diameter and a 5/16" Width.
 

· Worthless reject member
Joined
·
84,741 Posts
Anyone know, are the stock GM 1.7 ratio trunnions the same size as would be in the 1.85 ratio rockers? Depending on what these look like once I tear them apart I may just go with an upgraded trunnion kit.

The stamping on the trunnion bearings side on the SLP 1.85 ratio rockers shows INA SCE105. A quick Google search shows them to be a Drawn Cup Needle Bearing with a 5/8" Bore, a 13/16" Outside Diameter and a 5/16" Width.
it's pretty much the exact same rocker as the OE rocker, the cup where the pushrod sits is just moved so that the ratio is 1.85 instead of 1.7. other than this, the rocker body is identical.
 
  • Like
Reactions: BRZN

· Super Moderator
Joined
·
32,068 Posts
If it were mine which it is not, I would still just put stock rockers/trunnions back in it an call it a day.

There is so little IMO to be gained from the ratio change that it's not worth any extra wear and tear.
 

· Worthless reject member
Joined
·
84,741 Posts
If it were mine which it is not, I would still just put stock rockers/trunnions back in it an call it a day.

There is so little IMO to be gained from the ratio change that it's not worth any extra wear and tear.
what wear and tear?

i think his only problem was really the poor trunnion design. use a different trunnion setup and and he'd be fine.
 
21 - 40 of 54 Posts
Top