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Posted: 2/8/2024 7:24:34 PM EDT
08 sierra. 5.3
Long story short. Started idling extremely rough. Thought one of the afm lifters was coming apart so I parked it and decided it was time to do the amf delete. Pulled the engine, replaced the cam,lifters, push rods, oil pump, water pump,timing chain and gears, buttoned it up, put it back and it would start but I had no throttle response and it would run extremely rough for a few seconds and die. this is the camshaft I used. I pulled the codes and there was 4 for the afm which I expected and one for the sending unit. It was popping thru the throttle body. I had a friend (real mechanic) come down and take a look. He was pretty sure it was a timing issue. So I pulled the front off the engine and the cam was out 1 tooth. I fixed that, put it all back together and he came down again and using a real obd scanner checked all the sensors and all are working as they should. I replaced the tps sensor and maf just to eliminate them. We had it running but still idling very rough. I messed with it the next day, got it running for a few minutes and checked the cylinder temps on the exhaust manifolds and #2 cylinder is dead..I could touch the manifold as soon as I shut it off. I had to fix a stud on one of the exhaust manifolds which I did today. I have read a bad exhaust leak can cause a rough idle.. I didn't gain any ground. I had moved the coil on #2 to the #1 cylinder to see if the no spark followed it but I couldn't even get it to start today. I'm at a loss. No codes except for the ones I mentioned. The bottom end of the engine was rebuilt as my cam bearings were worn bad and some pistons had scuff marks on the skirts. The engine has close to 200 000 miles on it so neither were a surprise. The only thing I can think of is the valve lash isn't right on some valves. I did the #1 tdc, set the intake and exhaust, set specific valves then rotated the engine 360 degree's and did the rest. I rolled it over numerous times by hand after to make sure nothing was hitting anything and nothing was. Has anyone every run in to this? |
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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.
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Quoted: 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. View Quote I grounded out the plug on the dead cylinder and there was no spark. It's most likely the coil (original) but my luck it will be the wiring harness if I order a coil. We'll do the compression check. I had a coil go bad before and it still ran although it shook bad enough to trigger the traction control disabled warning. |
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I am not an LS guy by any stretch of the imagination but everything you've said is screaming timing.
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Quoted: I am not an LS guy by any stretch of the imagination but everything you've said is screaming timing. View Quote the cam position and crank position sensors all checked ok on the scan and none have ever thrown a code which has both of us baffled. I don't want to throw anymore parts at it to see if that fixes it although I priced coils and fuel injectors this morning. |
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Move a working coil over to eliminate wiring issues if compression and leakdown looks good.
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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. |
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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. |
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Quoted: Valve lash on hydraulic roller LS engines is 22 ft lbs. View Quote View All Quotes View All Quotes set to that with a quality torque wrench. 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. wires and plugs are brand new and I double checked to make sure they are connected well. 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? I bought factory length melling pushrods Any chance the #2 rocker slipped off the pushrod? anything is possible..seems to be my luck..but again it was doing this before I did the delete. You didn't say if you did anything to the heads. Have you checked for a broken valve spring? I didn't have any machine work done but I went over them looking for that, burnt valves, bent valves.. Maybe you didn't fix the initial issue and whatever was causing the rough idle is still lurking about. most definitely. I thought it was an afm lifter coming apart but they were all together and looked to be in good shape. Before you removed the cam gear, did you put it and the crank gear dot to dot (6 cam and 12 crank)? The entire short block was gone over but when I put it back together yes I had the marks lined up but man this sure sounds like a timing issue. I am asking because I have known people to install the cam 180* off. |
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Quoted: 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. View Quote View All Quotes View All Quotes Quoted: 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. 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. 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. 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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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. View Quote 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. |
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Quoted: 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. View Quote My a/c clutch gave up the ghost on me over a year ago. When I saw what was involved in changing it I decided to wait until I did the cam delete so I could get at it easier than laying on my back under the truck. My friend that is an actually tech checked all the sensors, fuel pressure with a snap on scan tool and they are all working as they should. What is very puzzling to both of us is..it's never thrown a code for a misfire in the #2 cylinder but does for the afm. As for that. In all the reading I've done the consensus is the ecm will throw a code for it (which itr has) but the engine will run. This all started before I did the afm delete too which makes it all the more bizarre. To me that narrows it down to coils, injectors or broken valve springs which I very well could have missed, but I didn't notice any difference in felt resistance when I torques the rockers down. A compression check will let me know.. |
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here is a plot twist..
I cleared all the codes and it fired right up, idled normally then quit. Did it 3 times. I have good fuel pressure at the rail but it's throwing a code for the sending unit. I know it's bad (another story). Would that cause the ecm to shut it down? |
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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
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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 View Quote |
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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.
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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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Check the grounds on the heads and block. Leaving a ground off will cause all kinds of issues.
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Quoted: Check the grounds on the heads and block. Leaving a ground off will cause all kinds of issues. View Quote 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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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. View Quote |
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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. View Quote |
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The ECM Still thinks you have AFM installed and is killing the cylinders.
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Quoted: This makes sense. Logically it should kill fuel and spark to the deactivated cylinders but I honestly don't know the ecm logic. View Quote 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. |
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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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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. View Quote 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 $$$ for a tool that will see pretty limited use. How does it ground? Our 274 engine won't run if the harness isn't bolted down, the little screw holes in the plastic are the ground for the coils. |
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Quoted: Voltage drop test it with a load. You can measure 12V across 1 strand of wire with no load, that's not telling you the whole story. A Hioki milliohm meter would help, but that's $$$ 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. View Quote 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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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. View Quote View All Quotes View All Quotes 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. 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. |
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you say the harness grounds are connected to the block, but do you have the main ground from the block to the chassis connected?
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Quoted: you say the harness grounds are connected to the block, but do you have the main ground from the block to the chassis connected? View Quote The other ground is the neg to the battery..cleaned up and tight. |
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Quoted: 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. View Quote |
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Quoted: pin in the plug damaged? View Quote It still made absolutely no sense to me that I was losing power from one side of the plug to the other. Discovered the probe on my multi meter wasn't small enough to make contact. I used a small paper clip as a probe and all 4 coils have power in the pink wire. This very rough idle started before I did the afm delete. It's why I parked it and started the delete. So whatever happened, happened on it's own. |
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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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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.. View Quote 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.... :) |
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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. View Quote View All Quotes View All Quotes 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 |
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Quoted: 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.... :) View Quote 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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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. View Quote |
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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. View Quote |
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Quoted: 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. View Quote View All Quotes View All Quotes Quoted: 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. This is from Summit's website for one of their kits. A programmer capable of disabling the displacement on demand is needed to complete DOD removal. 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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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. View Quote 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 |
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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. View Quote @striker you did an afm delete but didn’t do the tune for the delete? |
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