All ready done valve job . They are taller and have special oil holes. At least Dodge admitted they had junk transmissions in the early 2000s and picked up sales each. The VLOM consists of 4 electronically operated solenoids and is bolted to the top of the engine block beneath the intake manifold assembly. Ive read at many websites that the GMCs envoys, Chevys and saabs did start to come with AFM in 2005 with the LH6 motor,It says here it started in 2006 on the saabs, then the pick-ups got AFM in 2007. I can tell you for the past 2 years I changed out my LC9 5.3L fully synthetic oil every 3,000, even though Mobile Oil claims 10,000 miles or more. A 17 with 5.3. Took the heads off again. I am wondering the same thing. Only running on drivers side cylinders. I told her to never pull the gadget out. But it also restricts passages that the oil runs through. module (ECM) will command the cylinder deactivation system ON to deactivate engine cylinders1, 7, 6, and 4, switching to a V4mode. 2015 SILVERADO 1500 44 crew cab with 5.3L engine: So two weeks ago with approx 70K miles, I had an odd noise when accelerating and then engine light flashing and riding rough. This lowers the cost of building it [], [] aluminum block engine. Truck has an active P0300 code and runs very rough. Hi my name is noel I am a mobile mechanic and I have a client that was having trouble with the lifters on a 2011 gmc yukon Denali 6.2 I placed the lifters after finishing I still had a problem with cylinder 8,6,3 rocker arms were not moving so I replaced the cam OEM part but still having miss fire on cylinder 6 what should I do to get rid of this problem, [] computer cannot switch over to four-cylinder mode. It was in the late 70s or early 80s and it was a POS, Your memory serves you pretty well I too have the same nightmares lol. The system uses solenoids to deliver oil pressure to control. I just got new warranty engine and dont want this issue again? My 2012 Silverado 5.3L just did the same thing as your Tahoe Brian. Another option is to plug it entirely if the AFM is already removed. I guess they also went to aluminum blocks in 2007, not sure if that has anything to do with this issues thanks for the advice! Now the problems back, I have 180k miles on it now. They lasted one year with big problems. How did your turn out? Its got a hundred forty-five thousand miles on it. If I were to put a 2006 5.3L in a 2007 Avalanche and buy the unit to plug into my OBD2 port would it work? What would you do if you were in my situation? This video covers the steps youll need to take before upgrading to a larger [], I am installing a complete delete system, just wondering what it will do if dont plug the oil pressure relief valve? If you installed a factory truck cam, there shouldnt be any particular reason for it to be down on power. Only wish Id did my homework, nothing but issues, from 14,000 miles it starts this motor noise,as if lifters at cold starts, let set up for 8 hrs same noise, this noise is on the right side of engine, it lasts 5 seconds but never heard this until we had this cold spell in the state low temperatures or it was just time for this to start? My ignition lock cylinder is completely stuck in lock position with the steering wheel locked as well. Disable the afm. The engine will operate on 8cylinders, or V8mode, during engine starting, engine idling, and medium to heavy throttle applications. do you fill to capacity anyways???? The detergent. Should I buy a Diablo AFM disabler to prevent the new block from dropping to 4 cylinder? put tran fluid in oil for a day till lifter became active, had to change the fouled plug. The engine also had 799 or 243 casting heads which are closely related to the LS6. Would it be fine to go ahead with the AFM Disabler? Ditto , never buy a throw away vehicle again is my recommendation and my fix . Thanks for the advice Brian! Should I wait until the warranty runs out, or will that be too late to stop possible damage? I have also heard that the oil pump is to be changed and I have also heard that it does not matter. They may be able to find some of those missing ponies. The only problem is the extra spray on the cylinder models if a deflector isnt used and this can show up as increased oil consumption. What was happening to the first is slowly (or quickly in your case) happening to the others. What type of ODBII gadget did you use? Jusy 3 weeks ago I quit driving it because of the lifter, but it worked fine when i started it back up. im going to plug in a dissabler when im done to keep it V8 mode all the time. Help appreciated. Hello Brian, I just purchased a 2018 Silverado with a 5.3 AFM engine, I have 200 km on it. [], [] rugged iron block 6.0L came with VVT, but without Active Fuel Management, which saves you the cost of an AFM delete [], [] The LH6 engine is a 5.3L Gen. IV aluminum engine that replaced the LM4 in 2005. Is there any potential down-side to doing this in other words, might this do more harm than good? Thank you. In 2015, I purchased a new Tahoe with the AFM and two weeks ago with 71K miles on it, the engine light came on. I would rather stay a V8 full time than deal with AFM issues in the future. I had the same issue and had to have the AFM information deleted from the computer and the car tuned. I only have ~ 5k miles on it, and it hasnt been driven hard, so Im assuming the lifters are fine. So I did the job one more time. Having a hard time finding one .. All eight cylinders are now powering the engine. Thanks for the detailed post! Will this AFM DISABLER damage anything???. In four-cylinder mode, they act like air springs and allow for smooth operation. Thank you for your time. The market for nonhybrid gasoline-powered vehicles is expected to fall by 20 percent during that time, but with tech like smarter cylinder deactivationin these upcoming GM V-8 trucks, for . It has the orings in place, that seals the towers. He unstuck it and I took it for a drive and same thing happened. Put everything back together proper torque, gakets, valve seals, etc. I have already dropped a lot of money on this truck (08 suburban). AFM or active fuel management is a GM/Chevy technology meant to improve gas mileage. AFMengines use special lifters for cylinders 1, 4, 6, and 7. GM uses 3 different styles all are engine specific. of cranking pressure because the duration is longer on those cylinders to being with to offset the AFM lifter design. In October of 2010, GM added a deflector (p/n NAL-12639759) to keep oil from being sprayed directly on the rear cylinders. I remember those Other GM vehicles that the consumer tested for GM and paid GM for the honor. Brian, we have a 2007 Yukon Denali in our shop with a 6.2L v-8 that has suffered a lifter failure with camshaft damage. This is in response to pretty much everyone. They took the engine down today found so much damage inside they ordered a new engine from Detroit. I couldnt agree with you less, yet I respect your opinions. Plugs spark fine engine has power at higher RPMs although it is still in Limp mode / stabilitrack message, even after driving it a few times above 60 MPH then clearing errors with handheld programmer. One month to the day driving on the highway got the Service Stabiltrak message quickly followed by the misfire code. September 2017, I got talked into trading for 2017 AFM this was a bad choice 5.3 engine. If a lifter has already started to fail, an AFM delete kit and non-AFM components are the way to go. How is that an improvement. In 2010, GM added a deflector (p/n) NAL-12639759 to redirect in into the pan. Thanks. There is no way cylinder deactivation and the resulting temperate decrease, with sudden piston heat expansion when all cylinders are engaged, can't have undo wear and tear on the rings, valves, piston and bore. The car runs great apart from the shuddering at those speeds. The LH6 in 2005-06 was a little different than the one used in 2007-09, but both had AFM. It came back on last Wednesday starting with a flash. thx Brian, Knock on wood I drive a 2011 silverado 44 Ltd with the 5.3 AFM/DOD not tuned out or delete being used and have experienced no problems or any sign of problems for that matter juat rolled over 210,000 all original factory parts would you suggest I tune it out or juat let it ride I change my oil religiously and also use lucas products for all aspects of my motor. The GM 2.7-liter L3B Turbo four-cylinder engine for Chevy Silverado and GMC Sierra pickups is meant to change minds about power and torque in a small package. Drives way better for my mostly paved road driving. An electromechanical system deactivates and reactivates all 16 of the engine's hydraulic valve lifters, controlling valve actuation. What if the pressure relief valve is stuck OPEN and the oil pressure never gets up to where it needs to be? Driving around with a bad AFM lifter is the fastest and easiest way to destroy an engine. Perhaps a flaw by design would be a more appropriate description . Nine plaintiffs filed the General . Been driving with no issues but I did notice that the AFM disabler removed a P0449 code (Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction) dont know if this is a coincidence or they are related??? Given maximum engine power is not required during the majority of everyday driving, AFM works to deactivate engine cylinders when they are not needed, such as when cruising on the highway, thus. Hello Mike, if you dont have any obvious signs like check engine lights etc., there are couple different possibilities. The secondary pressure relief in the back of the pan began to open at 55 psi and was completely open by 75 psi. There are so many more oil passages on engines these days. Plug the tuner into your GM vehicle's OBDII diagnostic port, and follow the instructions provided to update the engine control module's program The new program will make sure that AFM never engages. Remembered that after I bought my Tahoe. Just had my afm lifter fail had to drive 500 more miles home on 7 cylinders in my 6.0 lt chev. NOTE: Some parts are not legal for use in California or other states with similar laws/regulations. She drove it for another 35,000 and it went out again. These trucks cost too much to have a terrible product. I only had 81k on the motor. I did noticed the oil consumption but it was rare that I would have to add oil. I also have 08 Burb, but have different symptoms (high oil consumption, blue exhaust smoke at start, and now a really rough start after sitting overnight). AFMis good for gas mileage and can be 5-7 percent more fuel-efficient under certain conditions. He claims that GM used the same engine whether it was or was not equipped with AFM in this year and model? (Bought car 1 day before lifter died!) hi brian when you replace the lifters do you have to change the guides also? How stupid do you have to be to whine like a welfare check cashing idiot when there are literally 3 or 4 different ways to totally disable AFM. It has AMF. Hi Mike, the metal shield you noticed is probably the windage tray. Loved the looks and interior and thought a I got a great deal at $6k even. If you installed a performance cam intended for a car, it may be bleeding off some low end compression. Hi Grant is that disabler still working for you ? if GM wont make a dependable truck for 60,000 Toyota is sure to take over even with very poor gas mileage . For a primer [], [] cathedral port cylinder heads and used Active Fuel Management (AFM). stalled in a certain way a warning wouldn be a bad idea. Any truth to that? Carbon Build-Up in the Intake Ports. Just one or two. Can you tell me what needs to be done with the VVT? Hopefully more is known by then. This is my second Avalanche and I never had any issues with either of them. Service manager said nothing else needs to be replaced because the engine has a Teflon coating. My 5.3 is. Pod. I am a long time GM fan but after reading how they messed up the 5.3 ( I had a fantastic 2003 Z72 off road) Ill look else ware for my next vehicle. Also putting in a new transmission vs. rebuilding. They have plastic casing, so you can imagine what will happen with aged plastic. NOTE: A disabler device should ONLY be used if the valvetrain is in good working order. []. You will get codes thrown if the afm is physically removed without telling the ECM you did so. In the mean-time I found that you can keep the engine from going into 4 cyl mode by using the manual shift (if so equipped) and keeping it out of 6th gear. Thanks. We did take it apart to check for metal possibly being trapped inside, it looked like brand new. Getting 20 mpg in town and 24-28 mpg highway and love the truck now with these mild tweaks. Now I learn about the cylinder deactivation issue and suggestions to add the Range Technology module to deactivate it. As a side note, Range Technologies recommends removing the disabler between visits to the dealer as they will need to access the OBD-2 port. The LFA was upgraded with AFM and [], [] improvement over AFM, DFM has 17 different cylinder firing patterns and switches seamlessly between them to provide just []. The L76 is an adapted version of the LS2, featuring new rectangle port cylinder heads and Active Fuel Management (AFM). The vehicles affected were 2007 to Feb. 2011 AFM equipped engines (Aluminum or Iron block-L94, LZ1, L99, LC9, LH6, L76, LFA, LMG, and LY5). Replaced the engine with remanufactured one and had the AFM turned off with a computer hooked to the ECU. has 92,000 miles and was just told I have cam and lifter failure. I would appreciate any feedback. Accept i only have 60K on my truck and it hasnt recovered. misfire or anything. [], [] Its a Gen. 4 5.3L iron-block engine, so youre getting the better intake manifold, connecting rods, and ECM. After reading these forums Im a little concerned about my decision to stay with GM. I ordered a electronic disabler for it today. I just did the delete and replaced the cam as well. 2012 5.3 Tahoe AFM, #4 lifter collapse,replaced all lifters,started engine ran ok, then rough, got #6 misfire code. A new class-action lawsuit has been filed against General Motors over alleged issues with its Generation IV 5.3L Vortec V8 engines. Any advice that you could offer would be great. Im curious as to how much tran fluid you put in? Or is the shuddering indicative of failed/failing lifters that need to be replaced before moving forward? I had privilege to work on some of that garbage they never did work . Gary, [] 3 engines didnt have AFM (Active Fuel Management) or VVT (Variable Valve Timing), so you dont have the expense of an AFM or VVT delete []. GM offers the following diagnostic steps in determining if this is the problem. It looks as if Ill need to start saving for a complete AFM delete kit with a new cam. Dont want to make a move on a new truck or jump to a 2500 yet. I bought a new 2017 Cadillac CTS back in January 3.6L V6 with 8-speed trans. Do you think it would be wise to put a AFM disabler on a brand new truck to avoid engine damage? 190k on the motor always ran AMSOIL full synth since new. That inherently less smooth operation requires additional NVH dampening. The biggest difference between the Vortec engines that used to be found in Chevy and GMC vehicles and the EcoTec engines found in them now are the fueling methods. You will be placed in derate if the ECM does not see the correct resistance from the ATF intake. Your email address will not be published. Did Obama make them do this? I had to replace them all and the camshaft as well. [] engines is that when VVT (variable valve timing) appeared and was later followed by AFM (which is Active Fuel Management, when the engine deletes four cylinders under light load) both of these packages drastically affect []. Regardless of the AFM solenoid being commanded on or off. I could just transfer over the AFM lifter cover, but it is really nasty on the bottom side & I do not want to risk damaging this replacement engine if it is loaded with debris from the lifter & camshaft failure. I wouldnt trade my 2000 Silverado, 5.3 liter that has constantly gotten 20 mpg since I bought it 15 years ago, for a dozen of these new $50,000 POS. Friend will send to me from Arizona. I have no clue what to do now. I just bought a 2015 5 3 17000 miles I was thinking about eliminating the 4-cylinder if I delete it with just the programmer will it hurt my motor? I just bought a 2018 Silverado. It is usually first noticed during highway driving. A bad lifter can be a minor repair if you get it fixed immediately after you hear an issue. With the AFM tuned off, it shouldnt be trying to switch over to four cylinder mode. Yes thats true. My 2011 Tahoe has a LMG motor in it with a build date of May 2011. Toyotas 5.7 is one of the biggest gas guzzlers among half-ton trucks. Then I guess I have to spend a bunch of money and get the delete kit. Have misfire code and engine has what I would call a surge while driving. I have a 2008 Buick Lacrosse super that I am having a hard time finding a tuner or a tune shop that can turn off the afm. Changing the sensor didnt help. Better airflow reduces drag on the pistons and the associated pumping losses. When you don't need the full power of the engine, it provides better fuel economy." Good point which begs the questuion, why does the Service Stabilitrak error seem to coincide with lifter failure? thank You so much! Vehicle has 40k miles been maintained well and shows no signs of lifter concerns at present. My question on a 2007 Chevy Tahoe 5.3 AFM TheAFMcylinders are opposite of one another in the firing order. Very expensive repair too! Oil 0w or 5w -20 [] block engine used in GM hybrid trucks and SUVs between 2008 and 2009. When a deactivated cylinder is reactivated, the control system opens the exhaust valve first to evacuate the trapped exhaust gas, before reactivating the intake valve to allow reactivated cylinders to revert to the normal operation of the compression/combustion exhaust/intake cycle. I have an 08 Suburban that is currently getting the lifters replaced a second time within a three month span. Pushing forward. Why this happens is a more . Active Fuel Management (AFM) is a trademarked General Motors technology that improves gas mileage by shutting down half of the cylinders under light-load conditions to reduce fuel consumption. This system was originally used in early 1980s Cadillacs. Junk . Definitely dont want to do anything to fix one problem and create another. They replaced all the lifters, said no other damage, problem lifters were on cylinders 6 and 7. Getting ready to diy for $450. any help? Have a lifter problem on my 2010 5.3 Silverado. Im crossing my fingers it does the trick! I am trying to find out of this is true. Really could use some pointers. There has been a lifter noise since I bought the truck 1 year ago. No other V-8 truck of similar weight can do that (except another GM with AFM). Pulled the inntake and replaced valleypan With all the solenoids. An AFM Disabler is an electronic device that plugs into the OBD-II port, under the dashboard. There are so many moving components in an engine these days as opposed to the past. This basically deactivates the cylinder deactivation system. This system is the most effective way to disable AFM. . Not sure what else it can be. I have 217,000+ on it and it never fails meever! Ive only put a straight pipe exhaust, intake, and a boost controller on it. Hi Brian, Right now I have just over 77K miles with no lifter problems Knock on wood I am thinking of the AFM disabler. Although the last oil change I had they offered a more expensive oil that would let me go every 5,000 miles and when this happened I was almost at 4,000 so needless to say I will never do that again. 91 GMC Sierra K1500 F44 6.2 NA Plow truck with 7.5ft Leo Plow 94 K3500 CC DRW 6.5TD DE exhaust . There are two ways to disable or delete Active Fuel Management on your GM or Chevy Gen IV LS or LS-based Vortec engineone is to install an AFM Disabler, and the second is to install an AFM Delete Kit. Stopped at nearest gas station and found I was a quart low on oiladded oil and lights eventually went off and luckily we made it the 5 hour drive home. This reduces expense when you build it [], [] intake, and a cable-driven throttle body, plus Im also installing Trick Flows VVT and AFM delete kits. But if you dont like it. After a stint in the U.S. Air Force, Brian Nutter studied at the Houston, TX-based School of Automotive Machinists in 1997. Looking forward to input from the forum, Thank you. Weve written some articles on the various Vortec engine upgrade paths, such as this one on LQ4 and LQ9it discusses some of the better options for choosing a cam intended for use in a truck. We chickened out though and just bolted the AFM solenoid plate onto the used engine. I have a 12 wit 4.8 Silverado 75000 miles The Jury is still out on the Gen. 5s but the warranty could be an issue. Many people find the four-cylinder sound annoying if their vehicle is equipped with a louder aftermarket exhaust. New plugs and wires. If someone didnt want to spend gas buy a Toyota. CAM motion says no just have to disable the AFM and VVT with a stock tune as the camshaft is not an aggressive camshaft but a drop in. I did a delete on an 07 avalanche and no have no power, any thoughts on what might be going on? .IMHO . Thats a tough call, if the warranty will cover itId let it run out. Their tech guys have seen it all and may have some thoughts on this as well. My 2013 LC9 just had #6 lifter fail, got a misfire code but the ticking gave it away. I am going to do the full repair of the engine now, but not an overhaul (too hard to get at the pan). Install the disabler when you get your Yukon back and it will remain in good working order. Yes, always change all the lifters at once. I service plenty of these vehicles with AFM, and the ones I have to open up the engine for repair because of a failure doesnt surprise me anymore. Dale, I have a 08 Tahoe thats doing the same thing.Any info you have on this would be appreciated, [] Do they have a downside? I have ordered an ATM disabler and will be putting a can of Textron in the gas at the next fill up. Im always sorry to hear when people run into issues like these. Love the truck so far. Never did strand me on the side of the road way. 4,7 plugs foul runs rough at idle. A problem with cylinder deactivation can be solved by tuning the intake and exhaust valves. The owner of the vehicle has apparently owned a few of these vehicles and stated that this vehicle doesnt have AFMnever did? I have a noise in the engine but it seems to go away when revved up. While the system sounded good, the microprocessors scrambled to activate, deactivate, and then reactivate cylinders as driving conditions quickly changed, causing the car to hesitate, buck, and stall. Mine did at the exact same time. Would never take it on a long trip. is it still working good since you have done that with the trans fluid? If Problems regarding Chevy 5.3L engines, if the running compression of the misfiring cylinders stays below 25 PSI. I got as high as 23mpg on the highway in my 89 K1500 with 350ci and a five speed manual. Can they be faulty? the extra oil isnt needed. The tune is the best bang for the buck outside a cam swap anyway and what Id recommend. This really sucks. This update also saw the usage of cylinder deactivation technology or Active Fuel Management. Regards, The Cylinder Deactivation system, known as the Active Fuel Management system by GM, shuts off some of the cylinders when extra power is not needed which improves fuel economy. You mentioned that it will shoot oil into the pan and on the cylinder walls possibly causing some oil consumption So i have a running vehicle and my only concern is making it as reliable as possible, should I disable the AFM or not?? Chevrolet 5.3 Engine Issues and Recommendations Since the tranny oil worked, you should now change the oil, right? Brian, I repaired a 2012 GMC Yukon Denali as the AFM lifter on #4 I take failed. Brian, I have the same question as Scott. Fortunately, the old engine hadnt been shipped back to the remanufacturer. Engine oil pressure is fine. No problems with any to this point. I didnt have lifters fail, I had the 4 cylinders 1,4,6,7 have such blow by that my choice was a valve and piston job or a new motor. Covers me to 100K. Install the AFM disabler now or wait until my warranty just about to expire to get this AFM issue resolved? Keeping the oil changes regular is important and its possible that a previous owner may not have been as diligent as you are. also in the pan is another AFM oil filter near the external engine oil filter. If AFM has been deleted, its common just to use a Dorman drain plug (m14 x 1.5) to remove the pressure relief valve entirely. I guess what Im really trying to ask is,, are there any cons/disadvantages to installing the AFM delete Electronic module? If I had been able to push the issue and get the time, I would have done the full fix at first without the hassle. Will the plug in cause my truck to burn more oil or will it fix the oil consumption issue? As we were installing the sensors prior to installation in the vehicle, we noticed that there was no fitting on the oil pan for the oil level sensor. 1. A tuner can often fix that as well by giving it some more ignition advance in these regions. Why would GM ever produce such problems with such little to gain. I tried the trans fluid in the oil. I asume low oil pressure cant make some of the DOD lifters to malfunction? I also notice that it doesnt go into V4 when it is cold. The result is improved combustion chamber pressure as the piston approaches top . On the caddis it helped to relocate the computer inboard the passenger compartment to keep them cool helped . So I researched and got an AFM disabler. Yesterday my motor (116,000 miles) felt like it went into limp mode when decelerating from 8 cyl to 4 cyl but it recovered.This is the second time that this has happened in 6 months so I think that I am on the slope. A problem with the software caused the engine to idle with most of their cylinders, thus overheating the exhaust . Your email address will not be published. One the other hand, it came without AFM, VVT, or flex fuel capability. HP tuners is not for someone like me that doesnt know how to use it and from what I read neither the range nor diablo plug and play device will work since the buicks pcm files are different than all other GM vehicles that came with afm because it was tuned in house at gms performance division. Took it in this morning and mechanic said cylinder 6 misfire, he said the lifter hasnt failed. Double digit MPGs in my 98 K1500 would be a dream lmao. It was good for about 10 miles and started with same loud knock noise. If you are using VVT, you could use the NAL-12612273 (L92) cam. Cylinder deactivation is very effective in reducing fuel and reducing the emissions of harmful gases. Have not had a problem yet. The most common are fuel pump failure, transfer case sensor failure, fuel injector failure, and carbon build-up. They are being forced by the feds to use stuff like AFM to meet the CAFE requirements. Question I have a 2015 Silverado and had a transmission go bad when I had it rebuilt I had the AFM/DOD turned off. I have a 08 6.0L out of a Silverado with an aftermarket oil pan that has no provision for a pressure relief valve. I will keep reading and take notes. The valve itself is part number W0133-2574213. Engines with AFM use a high-volume oil pump. Number 7 cylinder lifters stops moving when truck starts. Thanks to a properly maintained 5.3 with AFM, I can routinely get over 20 MPG on the highway. Didnt change exhaust nor tune so likely no change in power/torque. Then it takes out the lifter again and again until you bite the bullet and replace the cam. I hate it. The engine will operate on 8 cylinders in V8 mode during starting, idling, and medium or heavy throttle conditions. Once the lifter has been damaged, the cam is probably also damaged. I am not in a position to have a new cam and lifters installed but Im also not in a position to not having a running truck! Had similar problems under warranty, no telling what they rigged me up with at the dealer. They shift cam lobes by sliding the cam, never actually shutting down the value but riding a different lube! But then she passed away from cancer. I wii be using this truck to haul a camper for full time RV living and am thinking of a tuner to shut off AFM and maximize performance and economy. This allows the engine to run in V8 mode. Will the plug in deactivater fix the oil consumption or will it cause more consumption? We were getting a code that the cam position sensor was not functioning properly. . When cylinders are deactivated, the number of crankshaft rotation increases between firing pulses. Easier said than done. If doing that, the full blown AFM delete is about $1000 depending on how far you go (full overhaul or cam with lifters only). Love the truck. Because its not just GM that have engine problems. So bad theyve been rated least reliable midsized truck by consumer reports for 3 years in a row. Its ribbed with solenoids on the underside. Seafoam with syn oil change only fixed for a week. Everything was fine for two weeks, ow customer complains s it same noise it made as before. Your 1981 caddy was your fmu I got glue inside of it and it stuck the potentiometer for stochiometric if you get a new fmu or you pick the glue out of the potentiometer you can set it to stoichiometric and get a lot better fuel mileage as far as your truck why dont you look at the intake manifold I got a crack or a vacuum leak somewhere for gas mileage thank you truck service, Near 1981 its your fmu it has glue inside the potentiometer you have to either RNR it for a new one or pick the glue out of the potentiometer for stochial magic is the only variable resistor inside that you can turn with a screwdriver once you get the glue out of it itll read still kill metric just be careful and then you can set it properly with your own meter on your monitoring your O2 sensor and then on your Silverado thingy your 5.3 just check the intake manifold for lakes Ill get you a better gas mileage if you dont have any intake cuz theyre plastic and they crack and stuff like that other than that yeah thats it, Larry Jenkins, I have a 17 GMC Sierra 6.2 SLT, I got 25 to 27mpg regularly with 93 gas and cylinder deactivation.
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