2009 Silverado AFM/DOD Delete
A customer brought his 2009 Silverado, 5.3L, RPO LMG into the shop that a few years back he had an “AFM Delete” done on the engine. The engine ran normally until he had a lifter stick. He brings it to a friend of his that builds “race engines.” He used to work at GM dealers doing heavy line, for whatever that is worth. This guy puts in a non AFM camshaft, lifters… Another friend uses HP Tuners to delete the AFM system.
When I first see it, the engine runs fine at a cruise and under acceleration, but misfires at an idle. A few strange things was the BARO read 82 kPa, and in this area I usually see 96 kPa - we're at 1,500 feet. The other oddities were why the fuel trims were negative, and why there is no P0300 stored. The MIL was on and flashing. All the cylinders that ‘had’ the AFM system on it originally, were misfiring - 1, 4, 6, and 7. Most of the misfire counts were on cylinder 6. At first I thought there was a valve sealing issue, but a relative compression sounded even and I checked compression on cylinder 6, 165 PSI. I did a leak down test and I didn't see anything. I checked cylinders 2 and 4 after that and came up with 160 and 170 PSI.
I hooked a PICO up and had set it up as A - Ignition 6, B - Vacuum Waveform, C - Compression Waveform Cylinder 6
I didn't really see anything and I'd like for someone that is familiar with compression waveforms to look this over. I've got a feeling there's something there…
I have HP Tuners and I saved the original file. I then uploaded the correct calibration files from TIS2Web and then went in and did the changes to remove the AFM and turned off the P3401 - P3449 solenoid DTC's. (I'm not sure if this is correct)
It now has the correct BARO readings and it also now is setting a P0300.
Here's some scan data from the engine and also the Misfire Data screen -
I was finally able to contact the guy who had done the AFM delete to try and see what he had put in this engine. He doesn't use a computer, and he was going off of memory from two years ago, that he used GM OEM camshaft, lifters…I don't have any other information than that. I'm of the opinion that the wrong camshaft was installed, but I don't know.
Any ideas?? Thank you!
As far as I know when I have done the deletes is that the camshafts are different. I believe that the afm shut down camshaft lobes have a different lobe profile.
Take running compression waveforms from the non misfiring cylinders, then measure the valve opening and closing events with the misfiring cylinders.
Hi Ray, I'll try and get that up. I figured someone had a compression waveform for a 5.3L to compare this to.
Did you take a relative compression capture? Afm cylinders do have a different camshaft lobe If an afm camshaft is installed with non afm lifters it will result in idle misfiring on afm cylinders I have had several come through but never went past a relative compression and a good customer interrogation to find the cause so i dont have any in cylinder captures
Hi Scott, I did not capture a relative compression test as my ‘ears’ did not hear a compression issue.
I recommend you check the companion cylinder on that crankshaft throw. The vacuum diagram is puzzling me. Segment/ overlay your capture to show the firing order. Your computer is recording cylinder #6 as a misfire, but that is not always reliable. Make sure you check the crankshaft sensor and trigger carefully.
Hi Glenn, The ECM is identifying the correct cylinders for misfires.
Hi Scott, Just as another member mentioned, check the valve springs beehive springs will break at the base and some are hard to tell without a good light and a mirror. They will actually pass a compression test
Hi Glenn, That's a good thought and something I've seen on these engines, but… This engine runs well off idle, (amazingly enough) and the vacuum gauge is steady, but low at an idle when the misfires are occurring. I personally have not attempted a AFM delete on one of these engines, but I'm of the opinion this has the wrong camshaft in it. I'll do as Ray suggested and try and get in a little…
Scott, My apologies, I misunderstood. It was my understanding that the truck had been fine for two years since the engine “enhancements”. That being said, low vacuum could be valve lift )as you stated), valve timing, or restricted exhaust. I don't see exhaust pressure in the wave form. I think you are on to something when you said you would compare a good cylinder wave form to number six.
Scott, I'm no expert on compression wave forms. What I do know is that broken valve springs are fairly common. When I have a misfire that is moving around, several times it has been an intake valve spring. Doesn't take 10 minutes to look. HTH
He most likely did NOT change the cam. The base circle is different on the lobes of the DOD cylinders. That’s the symptom of dropping in stock lifters in place of AFM lifters. I’m a Tuner also.
Hi Donny, That was my thought, but the guy who did the engine was adamant that the cam was replaced. I wanted the number as he said he put an OEM cam in for a non AFM engine. I'm thinking he didn't put the right cam in it if it was replaced.
I believe you have no p0300 because the tuner probably deleted that?….I would put a vacuum gauge on it and if you have needle bounce…
Hi Ken, That was my thought as well as why the P0300 was not there and why the fuel trims were rich and why the BARO was at 82 kPa. The vacuum gauge is low at 14" Hg, but is steady.
Looks like exhaust valve may be leaking bit on your cylinder displayed. Vacuum -The push at beginning of exhaust stroke looks higher, then the pull directly above the center of the exhaust stroke is what caught my eye and the next pull is a pinch deeper. Did customer never this issue since onset of cam lifter replacement or is this a new development?
Hi Paul, The customer stated the engine was running normally until a lifter stuck. This was a little over two years ago. I tend to believe this as the smog test history shows this vehicle passing the California smog tests the previous times it was required. His tags expired in January and he hasn’t brought it in for a test as the MIL is on and that’s an automatic failure. He said this vehicle…
I have an 06 siera with the 5.3l non afm but has stage 1 comp camshaft in it. suppose to be ecm friendly but it runs exactly like this. Only at idle for a while it will set misfire codes. i have 14" of vaccuum at idle and on my map reading. Map reading like that will cause engine to run rich at idle and misfire. i would get a known good LS tunner shop to tune this thing
It might be worth popping the valve covers off and measuring valve lift. This issue would probably also show up on a running compression test when comparing the old AFM cylinders to the non-AFM. I agree with others possible wrong cam/lifter combo. Maybe bent pushrods. I think more mechanical tests are needed to verify unless customer can produce old invoice with part#s used.
In the first capture, the vacuum waveform shows a repeating bad vacuum pulse every 720* The second capture shows a "bump' when the exhaust valve is opening, caused by a bad roller on the bottom of the lifter. The third capture is from an 07 Silverado 5.3, known good running compression
Hi Ray and All, Here's a compression waveform for Cylinder 2 and 6. They're completely different. The capture shows cylinder 6 on the left and 2 on the right. I'm not sure what to make of this and hopefully someone can help. diag.net/file/f5bx767nk… Here's the compression waveforms for cylinders 1 and 3. diag.net/file/f7cb3tvhz…
The first GIF is cylinder 1, the EVO near 42* BBDC and it needs a roller lifter. The second GIF is cylinder 3, the EVO near 37* BBDC and it needs a roller lifter. The third GIF is cylinder 6, the EVO near 43* BBDC and needs a roller lifter.
Hi Ray, So your conclusion is that the lifters are pitted on those cylinders, and that's what is wrong on the engine I'm working on? You could be correct, but how often does this happen? The way I measured the running compression was, 1 - 76 PSI, 2 - 161 PSI, 3 - 97 PSI, 6 - 75 PSI. These looked fairly even and I'm not sure what happened on cylinder 2?? Here's a pattern from a pitted lifter on…
All of my known good 4.8, 5.3, 6.0 running compression waveforms have no “bumps” in the expansion stroke vacuum pockets, when the exhaust valve is opening. You mentioned that most of your misfires are in cylinder 6. You could re-measure the running compression in cylinder 2, when the engine is warmed up and idling near 700 rpm. You're example of the 4.8 engine is correct. This capture…
That’s bizarre! None of the cylinders show leakage. All of them show the same valve timing. Valve timing can’t increase compression pressure. Cyl 2 shows more vacuum than the others, which would cause lower compression, all else being equal. The compression variation between cyl’s 1,3,&6 is too much. Were all of the tests made with the same sensor, connected with the same connections?…
Cylinders 1 and 6 are idling near 700 rpm and cylinder 2 is running at 1,100 rpm.
I read 160ms for 720 on the posted capture, so 80ms per rev is 12.5 rev per second. 60 seconds is 750 revolutions. No? I don’t think that revving to 1100 could cause almost triple compression. youtu.be/01MlHRdz0m0 This video was helpful to my understanding of in cylinder compression.
I've never seen anyone use time to diagnose cranking or running compression waveforms, only crankshaft degrees. I know that during a 1500 rpm brake torque, the cylinders create near maximum compression.
Hi Scott, Excess valve lash will create compression differences. The valves are not being lifted consistently for all cylinders. This point directly at failing lifters and/or scrubbed cam lobes. Excess rocker wear is a slight possibility. On many roller lifters, I have seen pin and needle failures. No parts are guaranteed to last forever. If a cheap knock off kit was installed, that just…
That was my thought to at least explain cyl 2 being so high on running compression-like he hit his scaling button on his transducer and didn't realize it.
Hi Paul, I have been working with engine running dynamics years before scopes and transducers came to be a ‘go too’ method for testing. An old tech explained it to me many years ago. “think of an engine as an air pump” It goes like this: If enough air cannot get in, compression and combustion will be low. If enough air cannot get out, compression will be high and the engine will pre ignite…
Glenn, I took the scope file and put an overlay on it. since I am new to wave form analisis, can you show me my mistakes. To me it is evident that #6 intake is the odd intake pulse.
Slide your overlay graph to the right so that the beginning and the end of the colors are at the in cylinder top center, then it should show cylinder 2 with a weaker vacuum pull
Gil, Thanks for looking at it for me. I have seen so many people align the overlays different ways. The colors for the overlay really threw me. The red wasn't exactly red. Again thanks for your time. Also, this overlay is a FREE program!!! Available from the Microsoft store, just log in and search pressure waveform overlay. Has lots of features, I used very few.
Your welcome 👍 I also use that same software, it has a few steps to follow but when I got it, I got it 😎
Scott, is it possible to attach the Cyl. 3 (21_0005.psdata)? It looks that 0004 file is attached twice instead, but I would like to play with Cyl. 3. Thank you!
The vacuum “pull” that is odd man out appears to be cylinder 2, a non AFM cyl. What sensor was used for the intake capture? Do you know if it shows more vacuum(less pressure) with increasing or decreasing voltage? These situations can be difficult. Trying to prove what is obviously faulty may hide what is really wrong. I would expect an incorrect cam to cause misfires on all 4 AFM cylinders if…
Hi Stephen, I have a Nicholsons Pulse Sensor. I'm not sure how he designed this, but I could find out. I put a compression waveform for cylinder 2 and 6 up. I'm going to check on cylinders 1 and 3 and put that up as well. I think that will give me the answer on the camshaft if 1 looks like 6 and 3 looks like 2.
If you blow into the Nicholson Pulse sensor, does the voltage go up or down.
Connect your transducer in the intake again with all of the spark plugs in all cylinders. Hold the throttle wide open, crank the engine and I think you'll get a cleaner capture from the transducer.
I appreciate all the responses. The customer now wants a price on replacing the camshaft. He sent me a link to a ls1tech forum site that they're talking about the AFM delete. My head is starting to hurt, but as near as I can tell the camshaft to use would be a 4.8L, part number … He also mentioned that he saw videos on doing a camshaft replacement without removing the cylinder heads. I…
I really think a remanned is the way to go at this point. It sounds like your letting the customer dictate how to repair his vehicle which usually doesn't end well. Probably what happened two years ago. Make sure you get it writing on how it's on him if his expectations are not met if you choose to follow his suggestions.
Sounds like time to cut this one loose, if the customer is internet/ arm chair directing the job. They are cheap and avoiding reality. It will cost you in the end.
Hi Glenn, I came to my senses and cut this one loose. I didn't say I wouldn't do it, but I gave a high enough price that he made the decision not to have me fix it. Thank you!
Hi Scott, It is very uncommon for me to advise ‘firing’ a customer. But there are some I can live without and move on to the ones that respect my work and appreciate it. I had a similar customer not that long ago. After a couple of “I saw it done on the Internet” conversations, I realized the customer would not listen to reason/reality. It is down the road at another shop and still sitting…
I appreciated all the replies. This one did not get resolved, as I stopped after doing the programming. The customer did not want to invest the money to do the AFM delete the way it should have been done from the start. As near as I can tell the camshaft did not get changed when the shop that did the engine work deleted the AFM system. As mentioned by a few here to slap some sense into me, I cut…
Hi Scott, It took me a couple of bad experiences on these, that I do not even entertain the thought of try to short cut one of these. I have had actual luck with another couple who realized the money pit situation and they elected to go to a complete new long block with AFM/DOD delete. This is not one of GM's better designs by far. I think it was a lot of promises of high MPG, but came up…
An update on this one - the customer reached out to me and let me know that he replaced the camshaft on this vehicle, which solved the misfire at an idle complaint. He said he installed the camshaft from a 4.8L and used dowel pins to keep the lifters in place. I asked him to come by with the original camshaft and the vehicle so I can take some measurements and collect some data. Thanks again