Backfire upon lifting
05-03-2009, 08:25 PM
#3
Thanks for the reply
That's the problem, it won't tune out. The fuel trims keep dumping fuel in bank 2. I am trying to find a mechanical explanation. There is lifter tick & two of the pushrods & rocker cups (where rod seats in rocker) are more shiny/worn than the others. Trouble is that I don't see how lifters would cause the 02 sensor to read lean & then dump gobs of fuel trying to richen it. Everything in the valvetrain checked out OK. All that remains are lifters. The valve covers & valley nipple do not connect to the vacuum @ the intake. So, that can't be doing it. Also, it's only bank 2.
For example: currently, bank one STFT's are -3 to 0 & bank two are 9 to 19%. I can't find any exhaust leak before the 02 sensor, intake & valvetrain are good, except for the lifter tick & the shinny pushrods & rocker cups mentioned.
Can partially collapsed lifters cause this problem? When looking & the rockers while turning the engine over w/ the starter, there was no obvious lack of rocker motion. I'm kinda lost. Plan to replace lifters tomorrow to see if that changes anything, but am not optamistic. Am also gonna put 12v on the injectors to make sure that one of them isn't sticking.
In regards to the OL, VE, MAF; The MAF seems to be correctly scaled according to bank 1. Am not sure when the car is using OL or VE. Am assuming that OL is upon start up & the table is rich per advise I got on EFI Live. Am not sure that OL needs to be rich. I have gone up & down w/ the VE table during idle & bank 2 fueling dumps fuel regardless. Currently, the off throttle BANG (sound from unburnt fuel in exhaust) is gone. Now, only the BANG @ idle remains. You can almost time the BANG by the amount of time the fuel is heated in the exhaust pipe before igniting.
Last edited by LS1-450; 05-03-2009 at 08:36 PM.
05-03-2009, 08:51 PM
#4
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Sounds like a bad o2 sensor.
or it could be a sticking injector.
Check your plugs, maybe one is fouled.
Do you have a wideband o2?
If not, you should buy one, you will get alot better tune with it.
or it could be a sticking injector.
Check your plugs, maybe one is fouled.
Do you have a wideband o2?
If not, you should buy one, you will get alot better tune with it.
05-03-2009, 10:09 PM
#5
Thanks for the reply
Could be the 02 sensor, in regards to the fuel trims adding fuel, but the 02 doesn't explain how the fuel is getting into the exhaust header. Have tried two sets of plugs, none are fouled. I have & use a wideband. Can't get the tune correct because of the fuel into the header problem.
05-03-2009, 10:55 PM
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I didn't see anywhere above where you have tested your injectors.
The quickest way would be to grab an infrared thermometer, and shoot each primary tube. They should all be about the same temp, but if one is way off from the others that injector is sticking most likely. If you find a stuck injector, I'd pull them all out and get them cleaned and tested. Then go from there.
The quickest way would be to grab an infrared thermometer, and shoot each primary tube. They should all be about the same temp, but if one is way off from the others that injector is sticking most likely. If you find a stuck injector, I'd pull them all out and get them cleaned and tested. Then go from there.
05-04-2009, 01:54 PM
#7
Yah, it's noted on post #3. Thanks for the tip though; didn't know the infrared thermo on the header test.
Did find the issue today...................Finally! After I hit the injectors w/12v, in order to check them, found that an injector wire had been dissconnected inside the connector. The injector connectors have that rubber seal that the wires run through, so it is impossible to see. Luckily, it had come out where it could be seen this time. Checked the plug & the previous set of plugs & sure enough, the insulation was brown from heat on the current plug & one of the plugs from the new previous set was brown. Figured that the brown one had been installed in the same cylinder. So, I put her back together w/ the corrected wiring & she purrs like a kitten again. It's intesersting to watch how quickly the PCM reacts to corrections. The STFT's began pulling the previous added +23% (from PCM memory) & reduced down to -3 to 0% within several seconds.
Thanks guys, as always, I appreciate the help.
