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Posted: 2/8/2024 7:24:34 PM EDT
Link Posted: 2/8/2024 9:29:35 PM EDT
[#1]
Well you know you have a dead cylinder, and your friends pro scanner should graph misfires confirming. Do a compression test then if needed a leak down test.  I know the bottom was redone but what about the heads? Did you have them pressure tested? If compression is good, make sure you absolutely have spark by grounding out the plug as it’s cranked. Next check for injector pulse at the injector with a noid light. All those results will determine the next step.
Link Posted: 2/9/2024 8:26:39 AM EDT
[#2]
Link Posted: 2/9/2024 10:03:44 AM EDT
[#3]
I am not an LS guy by any stretch of the imagination but everything you've said is screaming timing.
Link Posted: 2/9/2024 2:19:29 PM EDT
[#4]
Link Posted: 2/9/2024 2:38:10 PM EDT
[#5]
Move a working coil over to eliminate wiring issues if compression and leakdown looks good.
Link Posted: 2/9/2024 3:48:17 PM EDT
[#6]
Link Posted: 2/9/2024 7:20:25 PM EDT
[#7]
Valve lash on hydraulic roller LS engines is 22 ft lbs.

Have you checked the spark plug wires?  If they aren't pushed all the way onto the coil and plug, it will cause a misfire.  Also check the wires.  Move those around like you did the coil to see if the issue follows if you can get it started.

Did you buy a cam kit with push rods or just buy new OEM pushrods?  If you bought new pushrods (not with a cam kit), did you measure for pushrod length?

Any chance the #2 rocker slipped off the pushrod?

You didn't say if you did anything to the heads.  Have you checked for a broken valve spring?

Maybe you didn't fix the initial issue and whatever was causing the rough idle is still lurking about.

Before you removed the cam gear, did you put it and the crank gear dot to dot (6 cam and 12 crank)?

I am asking because I have known people to install the cam 180* off.
Link Posted: 2/9/2024 7:54:11 PM EDT
[#8]
Might need dyno tuning......
Link Posted: 2/9/2024 9:43:03 PM EDT
[#9]
If this was mine, I would do a leak down test on all cyls, then pending those results move onto the electrical side of things. The electrical side of things  can be anything from the ecm to the plug itself and everything between. As for the pushrods length, the stock ones should work without issue with that cam but checking those are allways recommend.

When you tore down the engine originally, was the cam lobes on the original cam wiped or pitted at all?  How about the lifters? That will help to know if you solved an issue with the partial rebuild or not in the 1st place and give you a direction to go with your current problems.

If the leak down checks out, pull the valve cover and have someone crank the engine with the fuel pump relay or fuse pulled and watch to see if the rockers are working on them. This is assuming the timming is now correct of course. If you have one not working, this would indicate a collapsed lifter. ( I have had them work at 1st and then stop as the engine cranked longer)   I also hope you used gm lifters as aftermarket lifters suck in my experience.
Link Posted: 2/10/2024 10:39:53 AM EDT
[#10]
Link Posted: 2/10/2024 10:43:43 AM EDT
[#11]
Link Posted: 2/10/2024 6:31:11 PM EDT
[#12]
Discussion ForumsJump to Quoted PostQuote History
Quoted:



I didn't check every lobe (I will) and all the lifters looked good, even the afm ones..but the new cam and lifters would have eliminated that as a possibility.


I will do that.I got the cam and lifters from my engine builder for that very reason. He doesn't use crap parts.

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Checking the parts on tear down just confirms if you are fixing the issue at hand. That info is valuable during diag. That's all I was getting at with that.

You more than likely don't have a lifter issue but a compression and a leakdown test will confirm the rebuild is good to go. After that is confirmed, you have to find out why # 2 isn't firing. This method of diag starts at the core and works backwards to see if you can find the problem. Engines are pretty simple, it is the electrical side that can throw people through a loop and that unfortunately is hard to diag. through the internet.

I am not sure how handy you are but look up voltage drop tests and check that all out. Also check to see if your ac compressor diode is still good as that can also take out an ecm. When the ac compressor starts and stops, the internal diode acts as a shock absorber on the electrical side to prevent spikes. Electrical spikes can play havoc on ecm and components.

You can also test out the ign harness with a meter on and off the truck. This should be enough info to keep you busy for a while. Lol I am sorry for your predicament but I hope you get it figured out. If I were close by, I would offer to stop by and  help with testing/diag.


One last question..... have you tuned out the afm in the ecm? That could be your whole issue. I have done alot of deletes, I have never fired one up before the afm was tunes out so I am not sure if it will even run without the afm manifold hooked up. I would truly start there if you haven't put the tune in yet.
Link Posted: 2/11/2024 10:03:36 AM EDT
[#13]
Link Posted: 2/11/2024 11:41:49 AM EDT
[#14]
Link Posted: 2/14/2024 9:48:43 AM EDT
[#15]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
being an old school sbc guy
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Quoted:
Quoted:
I am not an LS guy by any stretch of the imagination but everything you've said is screaming timing.
being an old school sbc guy


So am I.

Rip that thing out and put in a SBC
Link Posted: 2/14/2024 6:16:03 PM EDT
[#16]
Link Posted: 2/16/2024 9:23:23 AM EDT
[#17]
Did you reprogram the ECM after the delete. I converted my wifes old Impala a few years ago and had to send the ECM, and TCM out to get  the AFM deleted from the computer or the car would only running on 3 cyl
Link Posted: 2/16/2024 11:30:45 AM EDT
[#18]
Discussion ForumsJump to Quoted PostQuote History
Quoted:


I am asking because I have known people to install the cam 180* off.
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The cam is 180  off every other stroke.  This is a non issue.  The ecm will know what stroke it's on with the cam and crank sensors.
Link Posted: 2/16/2024 4:11:23 PM EDT
[#19]
Link Posted: 2/16/2024 11:10:44 PM EDT
[#20]
I think I would get the program done before you continue to pull your hair out. It sound like it is doing exactly what my wifes car did before the program. Once I got that done it hasnt missed a beat in 5 years.
Link Posted: 2/19/2024 11:17:17 AM EDT
[#21]
Link Posted: 2/19/2024 11:23:50 AM EDT
[#22]
Check the grounds on the heads and block. Leaving a ground off will cause all kinds of issues.
Link Posted: 2/19/2024 11:43:18 AM EDT
[#23]
Link Posted: 2/20/2024 6:46:28 AM EDT
[#24]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
I did some more digging and discovered the coils on the passenger side aren't getting any power. There is power at the main plug for the harness.
I can get that harness on rock auto which makes me wonder if this is a know issue.
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Plug in the harness and unplug each coil and see if you're getting power to each one.
Link Posted: 2/20/2024 6:49:51 AM EDT
[#25]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
I've been looking online for a schematic that shows the ground locations for an 08 sierra.
There are 2 ground wires on the stud on the front of the passenger side head, 2 ground wires on a stud in the bottom of the block on the drivers side and a single ground wire from the back of the drivers side head to the firewall.
I've looked quite a few times to see if I miss one and haven't found any.
The coils look like they ground thru the bracket that is bolted to the valve cover. when I removed them I just unplugged the main plug and unbolted them from the valve cover.
I'll take them off and see if there is crud or something between the bracket and valve cover.
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I'm pretty sure the ecm triggers the ground to fire them and that they always have positive.  ECMs tend to always give ground triggers, they don't handle higher voltage too well.  That's not saying they don't have a secondary ground, but the trigger is ground from the ecm.
Link Posted: 2/20/2024 9:45:40 PM EDT
[#26]
The ECM Still thinks you have AFM installed  and is killing the cylinders.
Link Posted: 2/21/2024 6:09:40 AM EDT
[#27]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
The ECM Still thinks you have AFM installed  and is killing the cylinders.
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This makes sense.  Logically it should kill fuel and spark to the deactivated cylinders but I honestly don't know the ecm logic.
Link Posted: 2/22/2024 9:27:08 AM EDT
[#28]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
This makes sense.  Logically it should kill fuel and spark to the deactivated cylinders but I honestly don't know the ecm logic.
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I went through this exact thing with an impala. It is doing exactly what my impala did, and as soon as I programmed the ECM it ran perfectly. I'm not saying this vehicle is exactly the same system, but the ECM is going to have to be programmed no matter what, so why not get it done to eliminate that from the equation. If I am right the problem is solved and he can quit pulling his hair out over nothing. If I am wrong something that needs to be done anyway is done and he can move on to other diagnostics to find the problem.  I have been a mechanic for almost 17 years. I have seen a thing or two.
Link Posted: 2/24/2024 4:56:42 PM EDT
[#29]
Link Posted: 2/25/2024 7:45:53 PM EDT
[#30]
Link Posted: 2/25/2024 8:01:03 PM EDT
[#31]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
well..I'm stumped..which isn't to hard to do.
Put the new wiring harness on and nothing. Still no power to the coils. It ends at the white main harness plug. It's at the pin on the engine side, plug it in and nothing.
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Voltage drop test it with a load. You can measure 12V across 1 strand of wire with no load, that's not telling you the whole story. A Hioki milliohm meter would help, but that's $$$ for a tool that will see pretty limited use.

How does it ground? Our 274 engine won't run if the harness isn't bolted down, the little screw holes in the plastic are the ground for the coils.
Link Posted: 2/25/2024 8:21:21 PM EDT
[#32]
Link Posted: 2/25/2024 9:07:36 PM EDT
[#33]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
on a gmc forum I belong to I was told they are grounded thru the wiring harnesses and looking at a wiring diagram for it that appears to be correct. they are grounded to the engine block via 2 ground wires. both are clean and tight.
that was something I was going to try tomorrow. run a ground wire from the mounting bracket to the negative post on the battery..
the ground wire in the harness may have a break in it.
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Discussion ForumsJump to Quoted PostQuote History
Quoted:
Quoted:


Voltage drop test it with a load. You can measure 12V across 1 strand of wire with no load, that's not telling you the whole story. A Hioki milliohm meter would help, but that's $$$ for a tool that will see pretty limited use.

How does it ground? Our 274 engine won't run if the harness isn't bolted down, the little screw holes in the plastic are the ground for the coils.
on a gmc forum I belong to I was told they are grounded thru the wiring harnesses and looking at a wiring diagram for it that appears to be correct. they are grounded to the engine block via 2 ground wires. both are clean and tight.
that was something I was going to try tomorrow. run a ground wire from the mounting bracket to the negative post on the battery..
the ground wire in the harness may have a break in it.



Absolutely correct about having voltage but not the amps behind it. LED test lights and such only make identification harder. When troubleshooting I use a lightbulb to absolutely verify. Make sure there is power! Run a jumper ground to verify with the lightbulb. My last ls issue was the ground. It looked perfect and was clean but 1\2 inch up from where it was bolted to the block it was corroded. After verifying you have power, back probe the harness at the coil main plug with your jumper ground.
Link Posted: 2/27/2024 7:52:53 AM EDT
[#34]
you say the harness grounds are connected to the block, but do you have the main ground from the block to the chassis connected?
Link Posted: 2/27/2024 10:04:29 AM EDT
[#35]
Link Posted: 2/27/2024 10:05:56 AM EDT
[#36]
Link Posted: 2/27/2024 10:11:16 AM EDT
[#37]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
I was using a multi meter to check for power. It was showing 12v at the engine harness side of the plug with the ignition on.
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pin in the plug damaged?
Link Posted: 2/27/2024 2:40:14 PM EDT
[#38]
Link Posted: 3/11/2024 12:43:30 PM EDT
[#39]
Link Posted: 3/11/2024 10:21:17 PM EDT
[#40]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
More updates and possibly a PSA..
Had a friend that is a red seal tech trouble shoot for me...
He discovered that the afm cylinders had spark and fuel but weren't firing..
The vlom is gone..but apparently the ECU is searching for them and when it can't find them it's shutting the afm cylinders down..
We confirmed this by unplugging the coils a cylinder at a time and none of the afm cylinders made a difference when we unplugged them.

I did a lot of reading on the afm delete before doing it and everything I read said the engine would run on all 8 but throw a code for the solenoids and idle a bit rough..
Well  from what we've discovered that  isn't true and those cylinders are still getting fuel and spark..how they aren't firing is beyond me but with fuel and no combustion I'm washing the oil off those cylinder walls..

I bit the bullet and ordered a diablo sport tuner so I can disable the afm in the ecm..
I keep telling myself all this money I've spent is still cheaper than a new truck..
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If only there was someone out there that went through this already to tell you that you needed to reprogram in order for it to run right. a few times.... :)
Link Posted: 3/11/2024 11:34:01 PM EDT
[#41]
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Quoted:
haven't got that far yet but I have the range disabler running so that shouldn't be an issue. the shop I talked to about getting it disabled said it would throw codes for it but still run.
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Quoted:
Quoted:
Did you reprogram the ECM after the delete. I converted my wifes old Impala a few years ago and had to send the ECM, and TCM out to get  the AFM deleted from the computer or the car would only running on 3 cyl
haven't got that far yet but I have the range disabler running so that shouldn't be an issue. the shop I talked to about getting it disabled said it would throw codes for it but still run.
Pretty sure that's a critical part of the whole AFM delete. You can program it out with just the computer and leave the mechanical components, but not the other way around. IDK, it's been a minute since I messed with LS engines.

Link Posted: 3/12/2024 8:24:45 AM EDT
[#42]
Link Posted: 3/12/2024 8:40:23 AM EDT
[#43]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
I knew I had to get it disabled and already spoke to a shop..
But all the info "out there" states the engine will run fine it will just throw the codes for the afm cylinders..or it will have a bit of a rough idle and throw codes..
Nowhere have I read that those cylinders will be disabled after you remove the afm crap..except here after I started the thread and was neck deep in it.
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Hopefully this slays the dragon.  Thanks for updating this.  It can be hard when you are considering a plate of crow.  I respect that immensely.
Link Posted: 3/12/2024 8:52:34 AM EDT
[#44]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
I knew I had to get it disabled and already spoke to a shop..
But all the info "out there" states the engine will run fine it will just throw the codes for the afm cylinders..or it will have a bit of a rough idle and throw codes..
Nowhere have I read that those cylinders will be disabled after you remove the afm crap..except here after I started the thread and was neck deep in it.
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Interesting that all your research indicated it wasn't necessary. I've never heard of doing the mechanical delete without fully re-programming the ECU.
Link Posted: 3/12/2024 9:39:11 AM EDT
[#45]
Link Posted: 3/12/2024 9:44:09 AM EDT
[#46]
Link Posted: 3/13/2024 12:03:26 PM EDT
[#47]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
Some actually most of the articles I read mention getting the  afm disabled in the ECU but to stop it from throwing codes...there was no mention of those cylinders being disabled because you removed the afm stuff.
This is from Summit's website for one of their kits.
They should be more specific for those of us that have never done this and probably won't do it again. lol
Also..any idea why my range disabler didn't disable it?
Even with it plugged in the afm cylinders still left the chat.
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pretty sure for the range to work, it has to see the system in place and functioning.  If there's an error in the system it doesn't function
Link Posted: 3/18/2024 11:33:39 AM EDT
[#48]
Any updates?
Link Posted: 3/18/2024 10:45:11 PM EDT
[#49]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
Some actually most of the articles I read mention getting the  afm disabled in the ECU but to stop it from throwing codes...there was no mention of those cylinders being disabled because you removed the afm stuff.
This is from Summit's website for one of their kits.
They should be more specific for those of us that have never done this and probably won't do it again. lol
Also..any idea why my range disabler didn't disable it?
Even with it plugged in the afm cylinders still left the chat.
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@striker you did an afm delete but didn’t do the tune for the delete?
Link Posted: 3/19/2024 8:36:46 AM EDT
[#50]
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