Well....the light is back. I tried a couple of converter break-in procedures, one was simply let the engine warm up for 5 minutes, then hold it at 2500rpm for 2 minutes. The other that jsdirt pointed me to requires driving at highway speeds for 25-30 minutes, stop and shut it off for one minute, then drive for 10-15 minutes more at highway speeds and then stop and shut it off for one minute. I performed both, the short one at startup before leaving the parking lot and the long one after .When I got off work (here in the Houston area) I had to drive for about 45 minutes of stop and go traffic to get out on a freeway where I could drive 30 minutes uninterrupted, but once I did I was able to drive about 70mph for 30 minutes, turned it off for one minute, turned around and did the same for 15 minutes, then had almost an hour of mixed driving getting home. So the cats should be burned in by now. I was pleased coming home since I had no light thinking I was done... and the darn thing came on again I the neighborhood. At this point I'm suspecting a leak before the cat. The driver side (bank 1 that seems to be OK) has a flat plate type flange gasket, but the passenger side has a donut. A new donut was used when the cats were installed, but a week later the heads were pulled. I guess it's possible the guy pulled the exhaust manifold completely out and then re-used the donut, or may have just left the manifold attached to the cat and worked the head out since the exhaust manifold fasteners are bolts not studs, and made the donut leak. You'd think the head gasket set would have come with a new donut and he installed it, but who knows. Either way, I think I'm going to replace the donut, (which I know will involve breaking the driver side loose too and replacing that gasket) and while it's pulled down I'm hoping to have enough room to snake my gooseneck camera down and take a peek at the media. I think it's pretty unlikely, but I guess its possible that driving it for a week after the new cats were installed while I still had the bad lifter it could have been throwing off some extra carbon and got the new cat dirty. But, I only live 6 miles from work, all neighborhoods, never got on the freeway for more than 5 minutes after installing the cats to see if it made a difference. And besides that, the bad lifter was on Bank 1, the opposite side of this code for an inefficient cat. I may go as far as replacing the exhaust manifold to head gasket as well. If I do that I'm sure I'll be able to just look down into the cat. Most of my life, for our 'second car', also known as the one I drive, I've bought used but nice and clean vehicles, usually with high mileage understanding that it's a roll of the dice, and understanding I'd just have to fix whatever happened. I've bought many cars that way and overall I've done OK. I'm starting to think this is the karma truck. patiently waiting until I'm 60 years old and then deciding to drag my butt through the dirt. I'm quite sure I saw a smirk on her grill last night as I closed the garage.
Jsdirt you just took a load off my mind! I was messing with the misfire for 3 months and digging out, saving and printing all kinds of info, and actually while this has been a real pain in my behind, it's also been an education. At some point I remember reading about converter break in, told myself to keep that in mind if I decide to change the cats, but didn't save a copy of it. With everything else going on and finally just taking it in, I totally forgot about it. No doubt that's what the deal is with the code. Since the cats were put on, I've only driven highway speeds for short runs to take readings and absolutely have not driven 30 minutes at any time. I'll go do that break in drive per that article after work. Thanks!
Hey guys I'll try to keep this brief. I had a P0305 misfire that I posted on here with several responses, long story short it's fixed, it was a bad exhaust lifter and wiped cam on #5. Got the truck back, runs great, drives great, all is well. That said, prior to the repair, one of the things I did was replace the y-pipe/cats with a new set from AB Catalytic in Canada, direct fit aftermarket cats (the truck has 129,000 miles and ordering online was less expensive). These were put on about 4 weeks ago, and the truck was driven a limited amount for about 6 days with the bad lifter before dropping it off for the lifter repair. So, I got the truck back, running great as mentioned, but about 2 days in it threw a P430. Scrolling through the scan tool I noticed the long term fuel trims were both running about -17 to -18 consistently, with little variation between idle, acceleration and cruise. I also noticed in the fuel system screens that the alcohol content was about 39%. I didn't make any changes and took the truck back to the shop. (Meanwhile researched alcohol composition levels). The truck is a flex fuel version but I've never run E85 (commonly sold around here) gas since I bought the truck in November. However, in the last 10 or so fuel fills I've been stopping at about 3/4 tank trying to get the monitors set, and I read where multiple partial fills can cause the alcohol percentage to get confused. He reset the alcohol composition, and it went back down to 3%, and he reported that the fuel trims went back to normal, but he didn't say he performed a fuel trim reset. I took the truck and after an hour or so the P430 came back, and I noticed the long term trims had gone back to the negative numbers, just not quite as low...maybe -12 or so. The alcohol percent still looked OK after filling the tank, actually came up to about 6% (all the gas sold around here says "May contain up to 10% alcohol), so I cleared the P0430 and executed a fuel trim reset (last night) So far the long term fuel trims appear to be staying normal now (maybe +2-ish) and the short terms fluctuate around -1 or 2 and +1 or 2. Fingers crossed the P430 won't come back. If I understand correctly, my 2010 Tahoe does not have a physical alcohol percent monitor device, and it does it automatically by crunching numbers after fuel level changes after adding fuel, correct? I can't imagine one of the brand new cats was damaged with less than a week of driving 6 miles to work, had a misfire and bad lifter but wasn't running terribly. Is there any thing else that could create a P430 I can check for? I'm not sure if there's anything in the engine top rebuild he could have done wrong that might cause that code, it's running beautifully. Could the cat have gotten maybe a little saturated while it was running rich before catching the high alcohol % and negative trims and maybe with some driving it'll dry out? I looked at the downstream O2 sensor data, bank 2 did some fluctuation. I swapped the bank 1 & bank 2 downstream sensors trying to eliminate a bad sensor, but no change bank 2 still showed fluctuation. I've read where exhaust leaks can contribute to P430, and considering the new cats were installed one weekend and then a week later the heads were pulled off, it's possible there could be a small exhaust leak, but if so it's not audible.
Well, I gave up and dropped the truck off at a GM certified shop near me. After a couple of days messing with it he called and said he was pretty sure it was a lifter so I told him to go ahead and dig in. He found the exhaust lifter on #5 to have a roller that was kind of chewed up and the cam was damaged as well. I attached a pic of the lifter, I hope it's visible. It's frustrating because No. 5 not even an AFM cylinder. He said the plastic lifter tray wasn't cracked and it didn't appear the lifter had rotated, not sure why it did what it did. However I'm not the original owner, it was a trade in vehicle at a Ford dealership when I purchased it back in November. It may have had repairs prior to me buying it that were done poorly just to make it run to trade it in. So of course that meant new cam and all new lifters. I made sure he got the newest updated GM lifters, replace the plastic lifter trays, and had him change the VLOM to the newer updated version. Knowing he was going to have the timing chain cover off and would be looking at the oil pump, I had him replace that too. The truck now idles quietly and smoothly, no misfires, and has the throttle response of a new truck. On a side note, a week prior to the repair I put new y-pipe/cats on the truck, bought it online from AB Catalytic, exact bolt up replacement. Since I got the truck back it threw a P430 code, poor cat performance bank 2. The cats are literally 3 week old and only ran a limited amount on the engine with the bad lifter before the repair. I know the cats are good. I don't want to continue on that topic on this thread, I'm going to start a new one on just that subject. Just wanted to say thanks to all who shared their thoughts, and post the solution to the P0305 misfire in hopes it helps someone who finds this discussion later.
mckpaul replied to mckpaul's topic in Gen III and IV Small Block & DrivetrainWell, I gave up and dropped the truck off at a GM certified shop near me. After a couple of days messing with it he called and said he was pretty sure it was a lifter so I told him to go ahead and dig in. He found the exhaust lifter on #5 to have a roller that was kind of chewed up and the cam was damaged as well. I attached a pic of the lifter, I hope it's visible. It's frustrating because No. 5 not even an AFM cylinder. He said the plastic lifter tray wasn't cracked and it didn't appear the lifter had rotated, not sure why it did what it did. However I'm not the original owner, it was a trade in vehicle at a Ford dealership when I purchased it back in November. It may have had repairs prior to me buying it that were done poorly just to make it run to trade it in. So of course that meant new cam and all new lifters. I made sure he got the newest updated GM lifters, replace the plastic lifter trays, and had him change the VLOM to the newer updated version. Knowing he was going to have the timing chain cover off and would be looking at the oil pump, I had him replace that too. The truck now idles quietly and smoothly, no misfires, and has the throttle response of a new truck. Just wanted to say thanks to all who shared their thoughts, and post the solution to the P0305 misfire in hopes it helps someone who finds this discussion later.
I'd like to say thanks to all for the input so far. We're going out of town next week so I won't get back to the truck until the following week. I did buy the pdf shop manual which will help. Just want to say I didn't give up or get things resolved without posting what it was, just out of town for a week.
I wish it was that easy, I really do. I've swapped that plug with cylinder 1, and I've had all the plugs out twice for compression test and changing the #5 cylinder valve springs, making sure they were all clean and making sure I put a different plug in #5 the first time, and completely swapping sides of the engine with plugs when doing the springs. The wires and plugs are less than 6 months old and have moved them around as well, and swapped two other coils into the #5 position. Did the same with injectors and #5 now has a new injector. Misfire stayed on #5 through all of that. I've had a noid light on the injector and a spark plug light on the plug wire and neither misses a beat. Got over 170 pounds of compression on #5. While changing springs I took the air pressure off and both valves travel up and down smoothly in the guides. The rockers are rocking with oil coming out on the rocker arm from the rods. I've been beating my head up against the wall over it. But the deeper it gets, the more it seems that, similar to spark timing, the whole misfire thing may be a side effect of something else.
I just put new cats on this past weekend, didn't have codes I know...throwing parts at the problem but the O2s were indicating they were headed south. I have a Foxwell NT520 with the GM software loaded. It may monitor the VVT system but haven't found anything in the menus or data displays that says VVT, it may be calling it something else. It won't do as much as the Tech 2 tool, but it will do quite a bit.It will do graphs and record, but came with about 6 small pages of basic instructions so I'm learning on the scan tool as I go. I have used it for idle relearn with the new throttle body and crank position relearn after changing the crank and cam position sensors. Didn't really expect those to fix the misfire, more throwing parts but they were cheap. Also changed the knock sensors. Good to hear about being able to purchase the pdf shop manual, will definitely do that. All I have is the Chiltons. About the plug, I do appreciate the input and suggestion, but have changed the plug, wires, moved coils around, changed fuel injectors, intake gaskets, and other things, and still had the misfire and started another discussion about it here - Not trying to sidestep your post or help or suggestions at all, and I still do have the misfire. That other long post lists everything I've done trying to solve it, but recently realizing my mileage was so bad I thought there must be something larger going on and thought I might try to restore drivability and come back to the misfire.
When it always drives more normally is during the warmup period. Unfortunately yesterday I sat on the driveway with the scanner going through menus and looking for fuel rail pressure and by the time I drove it was already at operating temperature. Then when I saw the drop in fuel pressure I thought for sure that wasn't right and didn't go far, However I found another post on this site from a pickup with the same issue, same pressures and behavior, and it ended up being normal. I looked in the Chiltons and it says key on pressure should be 50-60, and idle should be 43-45. It doesn't say idle in park or drive. Idle in park after starting stays at 58, but once I put it in gear and start moving and it drops tp 43 it does stay about 43 idling when stopped but still in gear. Not much info on the net about fuel pressure while driving, but so far it's looking like what I'm seeing is normal. Hey Paintor, thanks for the input. This has been ongoing for a while. RIght now with this mileage I get gas often and have bought from several places. Also right now when it says low fuel it goes down pretty quick so I've put gas from almost empty a number of times. Also, there was an updated driver side valve cover released for these trucks (the ones with AFM lifter problems and consuming oil) that changed the inside of the cover to prevent it from excessive oil pickup into the intake. Mine had the updated cover. The spark plugs are the recommended AC Delco 41-110. I haven't ohmed the coils, I have moved them around trying to make the misfire follow the part. That is something I can do, might have a weak coil or two. Will have to research the values to expect. I haven't ruled out the transmission all together. I still need to document the rpms per speed per gear as Doug recommended and possibly stop by a transmission place to see they can do a test drive and see what they think.
I've been asked a number of times about my fuel pressure, and I did check it a while back with a fuel rail test gauge. I have always commented back that my pressure is 58 lbs key on, and maintains about 58 with engine started and also revving up. Today I located the fuel rail pressure on the scan tool and went for a drive while watching. It was 58 on the driveway, but while driving, it dropped to around 43 pounds and stayed within a pound or two of that while driving. I stopped and put it in park and it stayed at 43-ish for a while and then suddenly jumped back up to 58. When I drove again it dropped back to around 43. It's a 5.3 Flex fuel engine, but I have never put E85 in it, only regular gas. Are those pressures correct while driving?
Hey Doug, thanks I'll do that. Yep, I come from pre-computer times as well, was doing the points and condenser thing back in the 70's. But what I do for a living is low voltage systems in commercial buildings (fire, sound, etc) that is all computer controlled now days with a lot of it living on the customer's network. So I've kept up with technology as it applies to all that, but just recently got a scan tool that I can actually see the input and output values on the truck ECM. However I am definitely still learning what a lot of them mean, what readings are normal and which inputs cause what outputs to change if they are out of range. It'll show me data on the transmission module as well, but haven't spent much time there.
No other codes other than P0305. And that's what started all this a couple of months ago. It is a miss you can see counting on the scanner on cylinder 5, but can really only feel it when creeping at a red light, when you ease off the brake to slightly move up. You can barely notice it while stopped. I started monitoring the gas mileage on the dash and what started at 13.8 has evolved down to 11.8, but I don't think it's accurately tracking. I put 18 gallons in when it was empty and warning me to get gas and went 135 mile before getting to that point again. (18 gallons as opposed to a fill up due to still trying to get all the monitors set, and EVAP needs not more than 3/4 of a tank)
You know I never thought of it from that angle. I guess I kind of took a bit of a leap there looking at 'spark timing' on the scanner and associating it with 'variable valve timing' on the engine and just put it all in the 'igintion timing' slot in my head. I get it, two different animals. So I'm guessing the ECM either runs on a set ignition timing, or can adjust it as needed based on info from preloaded tables maybe? And has the ability, via the VVT system, to adjust valve timing as well to further fine tune as needed? Buying a vehicle with over 100,000 miles, I kind of had the mentality at first of not minding throwing parts at the problem when it developed the misfire, some of it was basic tune up stuff that I wanted to do anyway, not knowing the maintenance history, just wanting to have a baseline of what had been done and when. And some of it was just to make sure I was getting the best fuel economy out of it that I could, updating the things that take away from mileage as they age. Like changing all four O2 sensors when I saw one of the downstream sensors was sitting at just over 800mV constantly never changing. With new O2's and seeing that the downstream sensors were pretty much following the graph of the upstream sensors (just slower), changing the y-pipe (cats) could be considered a little overboard without further confirmation it really needed to be done. But it wasn't terribly expensive, I bought them online from Calnorth in Canada and installed them myself. And considering the fuel consumption and lack of response, I figured it couldn't hurt. I could see the media in the third cat (after the 'y' joint) and it wasn't crumbled, so shouldn't be any trash downstream in the muffler. So with new cats, now the graphs look much better, the upstream sensors are switching high and low and downstream are way more steady. However, the downstream sensors may still be a little high. Most info I've seen says they should average about .45 volts and mine both hover around .700 volts. I'm not 100% sure the transmission is shifting correctly all the time, but in the morning from a cold start when I'm not experiencing the bogged down feeling, I can count all 6 gears listening for them and watching the tach. A while back I put a fuel pressure test gauge on the schrader valve on the rail and it showed 58 pounds at idle and really didn't fluctuate when raising the rpm. I have noticed I can see the fuel rail pressure on a couple of the scanner screens, but haven't watched it while driving. I can take a look at that after work, specifically when it feels bogged down. I guess since I saw fuel pressure on the rail I've just been taking for granted it's there. I know I should just take it to the dealership or a shop and say 'just fix it', but that doesn't allow me to learn and keep up with this stuff. I know I have a lot of questions, but the answers are filling in the missing puzzle pieces. It doesn't seem there are too many things that can cause this kind of gas mileage and response behavior. But I also know it's not really possible to diagnose an exact cause with only words. It's kind of like calling the doctor and saying 'Hey doc I have a bump on my arm, what is it?' I do appreciate input from you guys, and when I get the bottom of this problem, as well as the misfire on the other post, I'll post what it ended up being. I've spent a lot of time reading discussions and I know how frustrating it is to read three pages of posts on something similar to my problem and the solution never gets stated.
mckpaul posted a question in Ask the GM TechnicianI've been having issues with my Tahoe (2010, 5.3, bone stock, 129,000 miles) for a couple of months now. Above and beyond a minor cylinder misfire at idle, I've mentioned a couple of times about feeling like I'm towing a pontoon boat on take off or acceleration below 40 mph or so. BUT, not all the time. Sometimes, I take off from a stop light and the truck accelerates as I'd expect, other times it feels bogged down. Same thing driving around town in 30-40mph traffic, sometimes I go to accelerate and it does, but more than half of the time I have to give it more pedal than needed and it feels held back. Same unpredictable response on the freeway if I need to accelerate, sometimes I have to really put my foot in it. Meanwhile, I'm averaging 7-8 miles per gallon. Yes I still have the minor misfire at idle, but I don't think whatever is causing that is causing this. I have a Foxwell scan tool that can do graphs, so yesterday I hooked it up and went for a drive and watched the timing. Spark timing degrees: At Idle - 21 degrees Acceleration to about 30mph - flatlined at Negative 10 (graph on scan tool appears to only go to negative 10) Deceleration - 24 degrees Cruise set at 60mph - about 12 degrees...the first time, so I pulled over and stopped, and then took off again Cruise set at 60mph - bottomed out at negative 10, constant flat line For the record, these are based on one or two instances on a short drive and I plan to do this again on a longer drive and compare readings on about 10 idles, 10 accelerations, 10 steady speeds etc. But I've been driving for two months now with this problem (only work 6 miles from home, so mostly around town) and have a pretty good idea of what I'll see when it's lacking power. I noticed on accelerations that feel like I actually have some power the timing dances around -3 or so and then climbs up, and on accelerations that feel bogged down the timing is flatlined at -10 until the speed levels off, then sometimes comes up, but sometimes, as shown above just stays at -10, and of course with the cruise set at 60 with -10 degrees, the engine just doesn't sound or feel right, like it's tired and putting extra effort into keep the car going 60 mph. If the timing is really doing what the scan tool shows, that would explain my lack of power and terrible gas mileage. So I did some digging on the VVT system and have some questions. I see there appears to be three equipment elements, the magnetic actuator on the timing cover, the cam bolt (with the built in plunger valve), and the cam phaser on the cam sprocket. Obviously the electro-magnetic actuator could fail electrically or mechanically, the bolt/valve could stick or the O-rings in it could leak, and from what I understand the cam phaser rotates and has a return spring in it. Q1 - Are there any 'regular' or 'common' failures on these items, and/or how likely is one to fail compared to another? Q2 - How likely is the cam phaser on the sprocket to fail? Obviously it has to route the oil pressure from the valve and rotate that plate somehow, but is the cam phaser prone to fail or pretty durable? (i.e. least likely of the three parts to fail?) I know the ECM monitors all this and will throw codes for failure (and I don't have codes for this, only have the usual P0305 misfire code), but, how smart is the ECM? Q3 - I see how the ECM can monitor the magnetic actuator for shorts, opens, grounds, maybe even current flow when activated, but if the ECM requests advance and signals the activator, for example, and the valve or cam phaser doesn't actually respond and advance doesn't happen, is the ECM smart enough to say 'Hey I didn't get the spark advance I asked for' and then light the light? I ask this because from what I've read, the VVT system can be failing but not throwing a code until failure reaches a certain level. Q4 - When is VVT allowed to function? All the time? After the engine reaches normal operating temperature? Only during closed loop? I ask this because in the morning before the truck warms up completely I don't experience the bogged down feeling (on my next drive with the scan tool connected, I'll start with a cold engine and watch the timing) But instead of just temperature, the unpredictable throttle response may depend on whether the system is in open or closed loop Q5 - IF the VVT is malfunctioning but not throwing a code yet, could that be contributing to my P0305 code? (I don't really think it would cause a cylinder specific code, but thought I'd ask). If you happen to know about the VVT system, or have any input on what I should expect to see on the scan tool for spark advance under different conditions, please feel free to share. I know the VVT is supposed to accomplish what used to be done with the centrifugal weights in the distributor and vacuum advance, but back then we never got to actually see what the timing really was while driving. Paul Here's some pics of the graph Pic 1 - This is at idle Pic 2 - Accelerating to 30 mph feeling bogged down Pic 3 - Decelerating (coasting) from 30 mph Pic 4 - 60 mph, cruise set, first time, engine feeling/sounding OK-ish Pic 5 - 60mph cruise set, second time, engine sounding/feeling tired and not happy.
Thanks for the replies. Going from a 2003 Tahoe with a 4.8 to the 2010 Tahoe with the AFM 5.3, I'm seeing a lot of differences. The oil pressure on the '03 always hovered around 40 psi. On this newer one It concerned me at first seeing it drop to near 20, even in rare instances it will drop just below 20 briefly. I don't have a 'shop manual', but I did find in the Chiltons where it referenced 3 minimum pressures at 3 RPMs and I'm well above them, and from the posts I've read the lower pressures I'm seeing on the 2010 are normal. Doug your comments are right along the lines I was thinking. There is a ton of info out there on these engines and thousands of products, but about 80% of what's out there is based on mods and upgrades and speed and horsepower etc., and after reading a bunch of that you can forget you're looking for info on your bone stock daily driver. Jsdirt, I've actually considered a long block, for a couple of reasons, one being cost, the other being time. To go back stock updated AFM, by the time I buy a set of more expensive lifters (half being AMF lifters) and new VLOM, and probably a cam (not so comfortable tearing in assuming the cam is OK and then find out it's not and delaying the job) and all the gaskets etc., I will have probably spent near the same amount of money as I would have spent on a long block. And if I choose to do it myself, swapping out the motor would probably be faster than doing surgery on mine. While I've done that kind of work in the past, I don't do it often, so I'd be a lot slower at a tear down and build back (especially when pulling the cam) than a swap out. It just rubs me the wrong way to think a minor misfire at idle (on a non-AFM cylinder) that consistently throws a code can initiate such a major repair. And before you go there, already changed/moved/swapped/replaced plugs, wires, coil, injector, intake gasket, crank and cam position sensors, knock sensors, checked for manifold gasket exhaust leaks on cly 5, checked compression, vacuum, injector pulse with a noid light, coil output with a spark check light, swapped complete 4-coil pack from bank 1 to bank 2 to eliminate the possibility of that little coil wiring harness on the 4-pack assembly (it has factory splices in it), watched the cyl 5 rockers rock and pump oil with valve over off and engine running, changed the valve springs on cly 5 checking freedom of valve movement while the springs were off, anything I could think of that would cause a cylinder specific misfire at idle with a constant count you can see on a scan tool. My next move is to install a used ECM that has been programmed with my vin and flashed with the latest software hoping that maybe my ECM isn't controlling the pulse width of the injector or something. On top of the misfire, I'm down to about 8 or 9 miles per gallon with sluggish response about 70% of the time on the low end around 10-30mph range. I changed the O2 sensors, and both secondary sensors are pretty much following the primary sensors on the scan tool, and I have new y-pipe/cats I'm going to put on tomorrow. I'm looking at the VVT valve and activator with a raised eyebrow wondering if they're screwing with my timing, but not getting any codes other than P0305. So Dirt I'm with you, I love the Tahoe but the longer I own this engine, the more I hate it.
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