I don´t speak EFI very well, maybe you guys can help me here again ( if this is too OT , please delete) My wife´s 84 k miles 02 GMC Savana had an intermittend engine misfire. Codes were P0171 ( lean condition left bank), P0307 ( misfire cyl 7) and P0305 ( misfire cyl 5). Everything ignition related has been replaced by the pre owners ( they said).First I put a few bottles of injector cleaner in the tank which helped a bit and after that I sprayed down the Mass Air Sensor with brake cleaner, which helped big time for a while. So I got a new MAS from rockauto and put it in. Ran flawlessly after that , check engine light stayed off and it ran without a hickup for about 150-200 miles. Now the occasional misfire is back. It does not pick up rpms when I spray the intake with brake cleaner, so I suppose the intake manifold gaskets are hanging in. Are there any typical issues that causes this with Vortecs?
Common problem ,Vortec a list to check ,,, Fuel presser I belive 46ish psi idle When rev up around 60 psi . Fuel spider , there is one on each cylinder, popett in port & injector @ top of intake Big plug where fuel lines are Feed & Return . Poppet intermittently leaking. Same with injectors intermittent ,there's is eight , Top of intake . Bad lifter @ idle bleeding off until rpms increase. Cap & rotor , , Pickup in distributor , gases from oil pan travel up distributor shaft & contaminate the electrodes on the cap and rotor button. In some cases drilling holes in cap two 1/4 inch helps to vent gases . There also fuel driver timing A plus / minus 4 degs ,, should be 0 .. need a good scan tool to access to see & adjust, You can cheat on distributor hold down By slotting so you can get back in spec Instead of new chain set. Timing chain , Crank sensor ,
@19Eddy30 has you covered. I was out of the shop and into editing when those hit the road, but remember issues with that injection. 84k on a 23 year old car is pretty low miles, so I'd look there before blowby and sensors. It's kind of the parts cannon approach, but it's such a lot of time to pull things apart and try to find a test place for the injectors. Those spiders tended to fail, too so I'd consider it a wear item. https://www.gmt400.com/threads/mpfi-spider-injector-swap-upgrade-info-and-questions-thread.38867/
@Baumi @RodStRace I have 3 with Random misfire only at idle, I've have spent too much time trying to narrow it down, I just drive them . One @ 130 thoe Then a 240 thoe Ladt one 300 thoe , this one when you go to start , engine spins so fast it sound like No plugs are in , when cold have to cycle the key like three times until it starts then it runs OK . One Vortec that I have had Misfire When Efi , 200 thoe , pulled Efi intake off Stuck in Hot rod , No Mis fire
Thanks you all for your input. Now that I put a new MAS in , the misfire situation is better and the Check Engine Light stays off. I forgot to mention the truck runs on both LPG and gasoline, and my wife feels like the misfire is only while it´s running on gas. With all the data you gave me I have a good starting point for troubleshooting. I´m gonna come back with updates . Thanks again!
@Baumi just so you know, most modern sensors are abbreviated without the Sensor and are standardized. It would be called a Mass Air Flow (MAF) sensor. One that does use Sensor is Throttle Position Sensor (TPS). Not trying to be a downer, just calling it the name that gets you the right part at the store. https://autoveteran.tech/blog/details/117/the-top-10-engine-sensors-every-car-owner-should-know/
Haha, I knew I´d get it wrong. In German it´s called a Luft -Massen-Messer so I just translated it to Air Mass Sensor but I remembered that I ordered a part called something with MA F or S , so I changed M and A around ,which is obviously not right. English always used to be my favorite lesson in school, but they never teach you the important stuff, hahahaha Thank you for correcting me, that´s the only way to learn!
Glad to help. I took a semester of French but didn't retain any of it. Typical of many Americans I'm afraid.
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