Re: 1995 Chevy 350 LT1 misfiring - need Help Post by Cogburn » Sat Jan 30, 2016 5:02 pm I came across one that had the vent for the distributor hooked up to vacuum so the cap sucked down on the rotor. All models got a convex tail and square taillamps, previously installed only on the hyper-performance ZR-1 coupe. 2011 Ford F-350. And everytime we tried it it would say cylinder 6 misfire. And it wont start again. Of course, a misfire while accelerating meant the Toyota V6 got even slower. It started with the engine light being on for a while, with a slightly rough idle but otherwise ran great. P0307, witch is Cylinder 7 misfiring. The customer stated that the misfire seemed most noticeable on a cold engine before it hit operating temperature. Start by checking for intake leaks and if no leaks are found the next step is to replace the spark plugs on cylinder 2. Chevrolet Tahoe and GMC Yukon Truck Answers. 4L distributor type ignition system. I had a BB Chevy with an edelbrock manifold on it. i keep getting a code for a misfire on cylinder 7. Hi Demario. No Misfire Diagnostic Trouble Codes. Misfire issue, '96 Chevy Astro V6 4. Chevy V8 Misfire Caused by Excessive Cam Retard. If misfire happens only at idle, the EGR valve and purge valve need to be checked, as either one could be stuck open. 1998 Chevy Vortec 350 5. You access these usually by shorting 2 terminals on a diagnostic connector which is sometimes inside the car, sometimes under. In 2008, for example, the 5. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. Fairly inconsistently while accelerating it will start sputtering, hesitating, misfiring and any other way an engine could run bad. The vehicle may exhibit a SES Light due to a P0300 and misfire. Motor Trend reviews the 2010 Chevrolet Silverado where consumers can find detailed information on specs, fuel economy, transmission and safety. It has been working great, although I think itÂ’s a bit sluggish uphill. Start by checking for intake leaks and if no leaks are found the next step is to replace the spark plugs on cylinder 2. 4L Accordind to this you don't set the timing but the timing offset. ok first the vehicle 2003 silverado LS 2500HD 4x4 automatic former plow truck fleet vehicle 114,000 miles 1800 hours ok the lq4 in the truck has developed a misfire at 2500rpm or above the only cylinders that are misfiring are 1,5,6,and 8 it is only throwing a p0300 random misfire code. Once the combustion gas enters the fuel rail in the cylinder head, it then distributes to other injectors, typically on the same bank. 0 Mercruiser. 7 Vortec that I think I’ve figured out. Combustion gas may leak past the injector’s needle and seat, or the copper combustion seal. I did this on an old beater Nissan pickup I had and two cylinders that were at 120psi before ended up matching the others at 180psi after the service with a smoother idle. The telephone prefix 436 is one local city while 572 is another. They use similar internals, exhaust manifolds and oil pans. Consumer writes in regards to diesel engine failure - service bulletin refers to vehicle misfire/ runs rough due to a broken injector hold down clamp. 7L Vortec 350 V8 engine. What causes multiple misfire on 1998 chevy silverado 1500 5. 40 mile one-way trip to work so I want to be sure the problem is fixed before getting on the road again. The truck only misses when under heavy load or going up a steep hill. , 350 Vortec. In most four-cylinder engines the numbering is 1-3-4-2 while in the Chevy 350 small block engine the firing order is 1-8-4-3-6-5-7-2. If the timing chain was the issue it would be random misfire, not limited to 1 or 2 specific cylinders. 3 vortec engine its misfiring. The engine would not restart or idle. I did a full tune up including plugs, wires, cap rotor and a new distributor. Hello gents I'm helping my buddy to solve a problem his '95 Z28 Lt1 350 is showing. hey guys new to the group I have a freshly rebuilt Chevy 350, got it running yesterday but had some concerns, the timing was set dead on the distributor but it had a odd misfire. P0302 CHEVROLET Tech Notes The P0302 code means that the cylinder 2 is misfiring or is randomly misfiring. One way to detect a misfiring engine is by sensing the Corvette's engine. The code P0300 stands for random misfire. after a few miles shut down and had to be towed. If the miss doesn't move, it's time to look at fuel. It may crank for several seconds before starting because the fuel injectors are not delivering. That P0302 can also be a the coil and plug. I have changed the spark plugs and spark plug wires and the distributor cap and the fuel filter. But at least the misfiring was gone, I took it on a 800 mile round trip on my vacation and no misfires it ran good. If the engine speed fluctuates enough to cause the Crankshaft Position sensor signal to vary, the Engine Control Module can determine that a misfire is occurring. Chevy 350 misfire / start. Hard starting: Another symptom is difficulty starting the engine. I have spent almost $1000. 5L and 2007 2008 Isuzu I-370 3. Between 1975 – 1984, an integrated cylinder head was produced, with one-barrel intakes for passenger cars, and two-barrel intakes for trucks after 1978. The customer stated that the misfire seemed most noticeable on a cold engine before it hit operating temperature. I have been working on trying to find what's causing it. Adjust the #1 exhaust valve. The blinking would stop after a few minutes and the light would go away. replaced cap, rotor, plugs and wires, spider, fuel pressure regulator, pi … read more. I have a 1992 chev k1500 pickup with a 350 engine it misfires and stumbles just off idle. Msifres bad under acceleration. I hooked up a obd II scanner to the computer and it said cylinder #8 misfire. A rough idle/misfire usually starts out as being merely a nuisance, but if the causes are not identified and corrected, it may result in your engine not starting, or stopping altogether when you least expect it. the truck only misses when you start it the first time of the day. Chevrolet Tahoe and GMC Yukon Truck Answers. 98 Chevy S10 Misfiring Problem I recently replaced my intake manifold gasket. The truck doesnt run right at all. This issue is known to be there in various Chevrolet models. Read the tech article on HEI Coils And Modules, brought to you by the experts at Chevy High Performance Magazine. Is this a completely stock '79 350?. misfire in cylinder 4. 7 Vortec P0300 Random Misfire Discussion in ' Chevy C/K Truck Forum ' started by BajaBrad , Aug 14, 2011. The others were something to do with the 02 sensors or somehing? But they said that could be popping up due to that misfire. hey guys new to the group I have a freshly rebuilt Chevy 350, got it running yesterday but had some concerns, the timing was set dead on the distributor but it had a odd misfire. The misfire would come and go and has been getting worse. But the Silverado SS was a bit of a misfire. Rough Idle causing a Misfire Condition Case Study. That P0302 can also be a the coil and plug. i have replaced cap, rotor, plugs and wiresand it has 175 pounds on all cylinders. It's free and can be the cause of your misfire, which could cause your excess fuel, which could cause. Can almost 99% guarentee you will fix this problem with new wires, plugs and opti. Generally, the firing order for a Chevy 350 (5. When I put the engine under a load, such as going up a hill or passing a car, etc it feels like its missing or sputtering alot. So i have a chevy 350 i rebuilt recently and have put about 50 miles on it and it ran great. I just thought of something else. Where is cylinder 7 on a 5. We went and got gas in a few towns over and it stopped. 8L V8 Vortec engine started flashing a check engine light. Basics Causes of a Misfire Condition. What causes Random Misfire on a 2003 chevy Siverado 4. If you have spark, and compression,,then you need fuel. 7 Vortec P0300 Random Misfire Discussion in ' Chevy C/K Truck Forum ' started by BajaBrad , Aug 14, 2011. i checked the timing and its 8* before tdc thats where i set it at. The blinking would stop after a few minutes and the light would go away. The problem usually stems originally from water, dirt or wear and their effect on engine performance. The truck doesnt run right at all. After that the misfiring was gone, the truck still felt a bit more sluggish than it should have been. I changed the spark plugs and wires, coil, and cap, but it's still missing. I put a 350 engine with a 400 turbo transmission in the vehicle. It does it sometimes at idle when cold and does it just going down the road at 40-45mph when it gets into overdrive and is running in the 1500RPM range. Also, make sure you jot down the other codes, as misfire can be caused by a malfunctioning component or system. Plugs r new. Thread starter Jack; Start date Nov 8 I had exactly same symptoms you described on 2000 savanna with the 350 engine Click to. That is what sets a no activity code as the 02 sensor will read a lean condition due to the misfire. I have a 2002 chevy Silverado 1500HD 4x4 with the 6 Lt Vortec engine and auto tranny. Parked it, a few hours later I got in it to go get new plugs and wires. Awards based on 2013-2019 model year vehicles. Week To Wicked: 1955 Chevy – Day One Build Recap. It will often manifest as random misfiring, which can also be caused by the ignition system. I forgot to mark the distributor when I removed it (well I didn't know you had to, and my dad (he was helping me, he's the certified mechanic, an HVAC mechanic by profession) forgot about it) and so the timing got messed up. When the engine warms up though, the misfiring occurs. If the spark plug wire for. This test will tell you if the computer is pulsing the fuel injectors open when cranking the engine over. unwrap your whole harness that you wrapped and check your wires and see if they could pissibly be arcing over. 7 vortec gets a P0304 code and has a noticable misfire while holding rpms steady. All sensors are tested and verified, all tune up parts are new. Motor Trend reviews the 2010 Chevrolet Silverado where consumers can find detailed information on specs, fuel economy, transmission and safety. Chevy Check Engine Light Codes. Likewise, if you find a misfire code for a cylinder and also an ignition coil code for a multi-coil distributorless ignition system or coil-on-plug ignition, you can probably assume a bad coil is causing the misfire. That seems to indicate that I have no spark in that cylinder. If you have spark, and compression,,then you need fuel. 2 problems here. Hey so I need some help on diagnosing this thing. The consumer advises the failure should be a recall. The black smoke doesnt mean your running rich, it just means fuel isnt being burnt, so one of you cylinders is definatly misfiring. Based on GM’s. Wires only have about. #2 1997 Chevrolet C Pickup 5. Can we turn a pile of parts into a whole car in. If the misfire is related to the information below, it will typically happen while cruising uphill, pulling a trailer or on hard acceleration and then stop misfiring shortly after returning to an idle. 7L (350CI) Throttle Body Injected automatic with 126,000 miles. i would let it rest for a night and. 3L with 100K miles on it. First, let's pinpoint exactly what's going on. I have been working on trying to find what's causing it. The problem that I seem to be having is the truck misfires at idle only. New distributor cap and rotor. I have a 2002 chevy Silverado 1500HD 4x4 with the 6 Lt Vortec engine and auto tranny. No Misfire Diagnostic Trouble Codes. When sitting still you can rev it up with no miss. 7L/350 Engine Rebuild Kits and get Free Shipping on Orders Over $99 at Summit Racing!. The nice thing about it is that the P0302 has tracked the problem to a particular cylinder, which makes diagnosing the problems simpler than P0300, which means that the cylinders are randomly misfiring. If the timing chain was the issue it would be random misfire, not limited to 1 or 2 specific cylinders. If the misfire is related to the information below, it will typically happen while cruising uphill, pulling a trailer or on hard acceleration and then stop misfiring shortly after returning to an idle. Learn about this problem, why it occurs, and how to fix it. Initial problem was the infamous hot start issue that gradually got worse. If the miss doesn't move, it's time to look at fuel. 7L (350CI) Throttle Body Injected automatic with 126,000 miles. I did a full tune up including plugs, wires, cap rotor and a new distributor. yesterday i took it to lunch took it back to work and all was good. I have a problem with a 98 Chevy 4x4 5. There is no check-engine-light or any other lights that come on. Chevy Misfire cylinder 3 20 Answers. I have a 2002 chevy Silverado 1500HD 4x4 with the 6 Lt Vortec engine and auto tranny. hey guys new to the group I have a freshly rebuilt Chevy 350, got it running yesterday but had some concerns, the timing was set dead on the distributor but it had a odd misfire. Read the tech article on HEI Coils And Modules, brought to you by the experts at Chevy High Performance Magazine. Problems regarding Chevy 5. 7 vortec gets a P0304 code and has a noticable misfire while holding rpms steady. How to correctly and easily adjust your engine's valve lash. This issue is known to be there in various Chevrolet models. for BOSCH it is about $350 for all six and for the DENSO ones expect to pay a lil more about $430 for all 6 how ever you can buy them individually but you will. The blinking would stop after a few minutes and the light would go away. ) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly. Engine misfire is a severe condition that requires immediate attention to avoid expensive repairs. so I started with the simple and cheap tricks. We've shown you the Malibu Maxx SS, the HHR SS and the Trailblazer SS, all of which we labeled as cool. Is this a completely stock '79 350?. When the engine warms up though, the misfiring occurs. Chevrolet Tahoe and GMC Yukon Truck Answers. Is there ANYTHING else that could be causing this? Burb is 91 w/ TBI 350 and 4L80E. Error Code P0303 is a common error code that indicates a misfire problem in the engine's cylinder, specifically cylinder #3. Online shopping from a great selection at Automotive Store. Diagnosing Misfires Download PDF. I did a full tune up including plugs, wires, cap rotor and a new distributor. P0302 CHEVROLET Tech Notes The P0302 code means that the cylinder 2 is misfiring or is randomly misfiring. But at least the misfiring was gone, I took it on a 800 mile round trip on my vacation and no misfires it ran good. The sensible method is to gather available knowledge about the engine misfire, focus on steps necessary to eliminate suspects and let the process guide you to its cause. Deposits on the center electrode create a ground path for the spark, causing a flashover misfire if the plug is dirty. Typical signs of a misfire include the engine shaking at idle, steering wheel vibration, or if the engine is difficult to start or stalls at start up. An engine that hesitates, stumbles or misfires when accelerating or when it is under load, is an engine that is either sucking too much air, not getting enough fuel, or misfiring. By the time I backed out of the driveway the check engine light came on. Data from a professional data scanner will store the conditions when the misfire occurs. What Would Cause a Misfire Under Acceleration? An engine misfires under acceleration due to faults in the spark plugs, plug wires or coils, or a weak fuel pump. i have a 96 chevy k1500 with the 5. Msifres bad under acceleration. My 96 chevy 1500 4x4 with a 5. ) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly. 94 Chevy tbi 350 2wd automatic. The 2007 Chevrolet Avalanche has 9 problems reported for engine misfiring. Read the tech article on HEI Coils And Modules, brought to you by the experts at Chevy High Performance Magazine. Full functionality requires compatible Bluetooth and smartphone, and USB connectivity for some devices. I replaced the plugs, wires, cap, and rotor. I have piston o-rings leaking oil so I clean my spark plugs one at a time every once a month it gunks up. If the Check Engine Light comes on, you may find any of the following codes: P0171, P0174 Lean fuel condition codes; P0120 to P0124 Throttle position sensor codes. When I going to start, he just blow a black smelly smoke, and won't start. Learn about this problem, why it occurs, and how to fix it. Question: I have a 1996 Chevy C1500 pickup with a 5. P0301) indicates which cylinder is misfiring. Engine misfiring usually results from simple, easily fixed problems. Truck is a 350,auto,carb. In 20 seconds you can become part of the worlds largest and oldest community discussing General Motors, Chevrolet and GMC branded pickups, crossovers, and SUVs. 2002 Chevy 1/2 ton truck. Scanned misfire cylinder 1, then 3, then 4, then 2. This is designed to make sure there's no gap when it's plugged into your Chevy 350 engine, which prevents the risk of erosion. Dec 12 2011, 1:47am. I have replaced just about everything once. The Chevy 350 engines benchmarked for the midsize light truck segment and pickups offers an unexpected combination of features that provide increased functionality and capability. ) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly. I have a 2003 Silverado, 5. This article applies to the C5, C6 and C7 Corvette (1997-current). Full functionality requires compatible Bluetooth and smartphone, and USB connectivity for some devices. 7L/350 Engine Rebuild Kits and get Free Shipping on Orders Over $99 at Summit Racing!. The consumer stated while driving the engine suddenly lost power and stopped. With key on i have about 60psi fuel pressure but idleing i only had. I have found that an ignition misfire will usually happen more under a load than at idle. 98 Chevy S10 Misfiring Problem I recently replaced my intake manifold gasket. Ok so i have my car tuned up pretty well, ignition timing at about 12 degrees, brand new plugs and wires. drove it home about 15 miles spitting and sputtering up every hill. They are usually limited to a specific set of vehicles based on things like model year, manufacture date, and VIN range. Ok so i have my car tuned up pretty well, ignition timing at about 12 degrees, brand new plugs and wires. If the engine is or has been misfiring, do not install the new ignition module until after the source of the misfire has been corrected. The 2007 Chevrolet Avalanche has 9 problems reported for engine misfiring. Chevrolet Silverado 1500 Check Engine Light and Misfire Due to Stuck Fuel Injectors - 56 reports. runs a little rough, while driving under normal conditions it sputters, hesitates, and also will backfire, under heavy acceleration no noticeable skip, no sputters, and does not hesitate or backfire. On 1996 and newer vehicles with OBD II, spark plug misfiring will usually turn on the Check Engine light and set one or more P030X misfire codes where "X" is the number of the cylinder that is misfiring. We're talking about engines that start easily and accelerate smoothly, but then, after a few minutes at a steady speed, either surge in speed or misfire, causing the car to "buck. 7l, misfires between 45-55 mph. Its also possible you lost 1/2. 350 tbi has a bad misfire. ****read****1991 chevy 2500. Is this a completely stock '79 350?. The vehicle may exhibit a SES Light due to a P0300 and misfire. Both types of misfires will store a P0300-series diagnostic trouble code (DTC) in the diagnostic ­memory. 1999 Yukon - Finally fixed misfire under load at 70 mph Yukon Car Forums I've got the Chevy techs baffled as to why it is happening, so I may give this a shot. Chevy Forums FREE technical assistance for your restoration and repair. truck started to misfire. Error Code P0303 is a common error code that indicates a misfire problem in the engine’s cylinder, specifically cylinder #3. Diagnosing Misfires Download PDF. The Chevy 350 engines benchmarked for the midsize light truck segment and pickups offers an unexpected combination of features that provide increased functionality and capability. The loss of 25% of the engine's power output is the equivalent of a horse trying to run on three legs. How to correctly and easily adjust your engine's valve lash. I have a 2003 Silverado, 5. I am troubleshooting a 1970 Chevy truck with a 350 small block. how do i check to see if the vaccum advance is working properly? i want to check all the possiblitys it could be before i go and tear down the carb and rebuild it. Answer: I didn't. P0307, witch is Cylinder 7 misfiring. Question: I had it in a gm dealer. 7L/350 Ignition System Combo Kits and get Free Shipping on Orders Over $99 at Summit Racing!. If you have spark, and compression,,then you need fuel. On a vacuum diagram for a 1980 Chevy 3/4 ton truck with a 350,. If anything, problem is now worse. truck started to misfire. Basics Causes of a Misfire Condition. The main difference in the LT1 is the reverse cooling design, which cools the cylinder heads first, then the block. I replaced the plugs, wires, cap, and rotor. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc. This article will help you to understand some of the most common causes of misfires and misfire codes (P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308) on the GM 4. Having a a major dilema with a rough idle / Multiple Cylinder Misfire on my 2001 Chevy S10. Posted to GM Driveability on 7/27/2009 21 Replies. In the early-to-mid-2000s, Chevy was adding a SuperSport trim to everything. ****read****1991 chevy 2500. Between 1975 – 1984, an integrated cylinder head was produced, with one-barrel intakes for passenger cars, and two-barrel intakes for trucks after 1978. Skip to Main Content The classic 350. 1999 chevy 350 runs rough at idle. This case study is on a 1996 Chevrolet Blazer with a 4. 7L/350 Engine Rebuild Kits and get Free Shipping on Orders Over $99 at Summit Racing!. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. recently DENSO has made aftermarket coils to suit. More than 448,000 owners were asked to rate the quality of their vehicles. The Chevy 350 charged up engine enables the production of 350 horsepower and 350 lb. Passenger car use of the 250-cubic-inch (4. There is no spark and and fuel pump does not run. Consumer writes in regards to diesel engine failure - service bulletin refers to vehicle misfire/ runs rough due to a broken injector hold down clamp. P0306 2002 Chevrolet Trail Blazer Description When a misfire occurs, engine speed will fluctuate. 7 vortec misfire at idle. The truck had been running fine and then suddenly lost power and picked up a bad misfire as soon as you cracked the throttle but would idle fine. Q: My engine light came on and is said it was a code p0300 random misfire what could this be? My car has 201354 miles. Of course, a misfire while accelerating meant the Toyota V6 got even slower. Well I did that and this has never done this before but now I'm having a big misfire and its getting worse while it runs. My 96 chevy 1500 4x4 with a 5. com, scroll down to “Can I test my FICM to ensure that it is the culprit?”, and follow instructions on self-diagnosing the FICM. The engine computer or PCM can detect a misfiring cylinder by monitoring the engine speed. If the spark plug wire for. runs a little rough, while driving under normal conditions it sputters, hesitates, and also will backfire, under heavy acceleration no noticeable skip, no sputters, and does not hesitate or backfire. Chevy small block cylinder misfire/rough acceleration. Warning lights: engine under powered (in odometer window). Have you ever solved a misfire problem? Tell us your solution and advice in the comments below! Shop for Tune-Up Parts. Ok so i have my car tuned up pretty well, ignition timing at about 12 degrees, brand new plugs and wires. Whipple Superchargers is owned and operated by its founder Art Whipple and is located in Fresno, CA. I just thought of something else. Rough Idle causing a Misfire Condition Case Study. Warning lights: Service engine soon Codes P0300 misfire. Scanned misfire cylinder 1, then 3, then 4, then 2. Any ideas?? Thanks. this ended up being a combination of a rebuild spring that was too strong causing an overly rich condition, and later it killed the 02 sensor and the temps sensor. Therefore with AFM (Active Fuel Management, formerly known as displacement on demand (DoD)). but ive always had the problem with bogging but the backfire is new also when the car is just sitting in my drive way idleing i can press the gas and a little puff. The engine control unit can detect a misfire in some different ways, depending on what car model and engine you have. The Chevy 350 engines benchmarked for the midsize light truck segment and pickups offers an unexpected combination of features that provide increased functionality and capability. so I started with the simple and cheap tricks. The blinking would stop after a few minutes and the light would go away. I have piston o-rings leaking oil so I clean my spark plugs one at a time every once a month it gunks up. If the miss follows you will know what to replace by what cylinder is now misfiring. Typically, cylinders 3,4,5 or 6 will be the ones to experience this. this ended up being a combination of a rebuild spring that was too strong causing an overly rich condition, and later it killed the 02 sensor and the temps sensor. 0 engine misfires. The customer stated that the misfire seemed most noticeable on a cold engine before it hit operating temperature. If the 200-4R has the bolt patterns, then by all means, bolt it up. Problem is that I also have a milit cylinder misfire. 8 - 1 CR? Should I try mixing the gasoline with turbo blue? Could that possibly be the problem? Any way a bad torque converter would cause the vehicle to act like it was "missing" or "sputtering" right around 3000. 7 Vortec P0300 Random Misfire Discussion in ' Chevy C/K Truck Forum ' started by BajaBrad , Aug 14, 2011. When cold, started up perfectly. 2 chevy cavalier p0300 random misfire fuel injector in the alt. I cleaned the wires and found a couple that have heat marks and some cuts through the insulation, I will try to get some new ones tomarrow. Is this a completely stock '79 350?. It occurs around 2000-2500 rpm. I started it back up and it runs very rough code reader says misfire in #4 but when I used a heat gun to read the exhaust manifolds cylinders #1,3,5,7 and 2 run around 250 degrees and cylinders 4,6,8 are around 90 degrees. In the cold start motor works on 4 cylinder, but after 20-25 seconds cylinders just "die", one by one. replaced cap, rotor, plugs and wires, spider, fuel pressure regulator, pi … read more. 89 Chevy 350 to backfire constantly. So i have a chevy 350 i rebuilt recently and have put about 50 miles on it and it ran great. i would let it rest for a night and. 7L equipped pick ups and SUVs. After that the misfiring was gone, the truck still felt a bit more sluggish than it should have been. or when trying to rev the engine while standing still for that matter. I have a 1992 chev k1500 pickup with a 350 engine it misfires and stumbles just off idle. 179,xxx miles original motor. I have piston o-rings leaking oil so I clean my spark plugs one at a time every once a month it gunks up. sp350/385 turn-key. Its also possible you lost 1/2. Model specific subject matter experts, classified ads and more. I have found that an ignition misfire will usually happen more under a load than at idle. Why will a motor sometimes misfire under load and not in park? I was told I can run 93 octane in this motor even though it has a 10. We're not talking about a knocking engine or one that idles rough or stalls. Scanned misfire cylinder 1, then 3, then 4, then 2. I hooked up a obd II scanner to the computer and it said cylinder #8 misfire. 1965-75 Pontiac & Tempest engine tune-upspecifications including timing, dwell angle, and spark plug gap, and firing order. drove it home about 15 miles spitting and sputtering up every hill.