Boosted lsx backfiring under boost
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From: Norn Iron
Could the pipe or something be blocked or damaged ? Either that or it is a faulty sensor.
That is clearly the problem and the engine will have been going very lean on load.
And for clarity as some systems seem to use units incorrectly.
key on, engine off what does it read ? It should be around 100kpa, ie atmosperic pressure.
And what does it read at idle ?
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On The Tree
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From: Colorado
Well like my chip says it's always reading boost. And it stops at 15.2 or so psi and hptuners log reads max of 105kpa. And the logs from the dyno show 200+ kpa but I'll check what it says with engine off and at idle
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From: Norn Iron
A log of it running good and before/during the problem would be helpful. Logs will always give useful information and are good to keep records of to refer back to
But if you suspect the map sensor, the two things I asked would be helpful too.
Or via a Mityvac or similar apply pressure to it and test to see if it reads correctly
But if you suspect the map sensor, the two things I asked would be helpful too.
Or via a Mityvac or similar apply pressure to it and test to see if it reads correctly
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From: Norn Iron
The sensor has 3 wires. Ground, signal and 5v supply
When the sensor is connected you will see a voltage at the 5v pin obviously, also at the signal wire and obviously not at the ground,
If you can identify 5v and signal and short these out, that will at least confirm your ecu is able to see the voltage and you should then see a high pressure value at the ecu
Unplugging the sensor should also cause a change in reading at the ecu.
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From: Norn Iron
Testing how ? It should be impossible
Sensor ground is wired only to the ecu/sensors. It should never connect to chassis ground.
If you get the meter and stick the black onto battery ground then probe red to each pin in turn ( DC voltage ) you should only see a voltage on 2 of the pins
The pin with no voltage will be the sensor ground
Or you can identify with meter red wire onto battery 12v and probe each pin with the black probe.
Few videos on youtube explain it well too. Not sure why he's identifying the 12v supply as VSS, just use the live battery terminal.
Sensor ground is wired only to the ecu/sensors. It should never connect to chassis ground.
If you get the meter and stick the black onto battery ground then probe red to each pin in turn ( DC voltage ) you should only see a voltage on 2 of the pins
The pin with no voltage will be the sensor ground
Or you can identify with meter red wire onto battery 12v and probe each pin with the black probe.
Few videos on youtube explain it well too. Not sure why he's identifying the 12v supply as VSS, just use the live battery terminal.
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From: Norn Iron
If you unplug the sensor and test at the wiring connector from the ecu, how does it fair ?
ie you are now testing the wiring for the most part, ignoring the sensor
From battery ground to each pin in turn, DC volts
Ground should read zero
Signal pin will probably read a voltage, can vary though but it wont be a full 5v and it wont be 0v
5v pin should read 5v exactly ( or maybe like 4.999 )
If there is a wiring issue or other fault interfering with sensor ground it will be screwing up more than just the map sensor readings at the ecu, it could skew lots of readings from various sensors.
Although at minute prob easiest just to stick another sensor in lol
ie you are now testing the wiring for the most part, ignoring the sensor
From battery ground to each pin in turn, DC volts
Ground should read zero
Signal pin will probably read a voltage, can vary though but it wont be a full 5v and it wont be 0v
5v pin should read 5v exactly ( or maybe like 4.999 )
If there is a wiring issue or other fault interfering with sensor ground it will be screwing up more than just the map sensor readings at the ecu, it could skew lots of readings from various sensors.
Although at minute prob easiest just to stick another sensor in lol
Last edited by stevieturbo; Jan 9, 2016 at 06:49 PM.
I had a MAP sensor wiring pin to the PCM go bad some how. I could wiggle the wire harness and the ground wire would start seeing voltage. Was causing the map sensor to see 150+ KPA at idle, which in turn caused a seriously rich condition. Different scenario but sounds like your voltage problem on the map sensor could very well be your issue. Now for your sake I just really hope that the engine wasn't hurt. If the engine was seeing 10+psi but the map sensor was only reporting/commanding fuel for a 0 boost/vacuum air flow that would explain your lean AFR readings.
If you are having grounding issues then this could have affected some of the other 5v sensors as well. Like crank and cam sensor which could be causing the misfire problems.
Good luck with it and on a side note what do you think of the B15 engine so far? I have really been considering one for my car. You can PM me so not to clutter up this thread.
If you are having grounding issues then this could have affected some of the other 5v sensors as well. Like crank and cam sensor which could be causing the misfire problems.
Good luck with it and on a side note what do you think of the B15 engine so far? I have really been considering one for my car. You can PM me so not to clutter up this thread.
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On The Tree
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From: Colorado
Well I have had a crank shaft sensor code come up so I'll be going through grounds tomorrow it looks like and testing the harness haha and well I think it's a minor issue cause the engine runs fine until 10psi and my a/f hasn't been in dangerous spots so that's good. And the b15 so far is really better then any machine shop or anything. It's making 739hp through a 4wd truck chassis and I have 35 inch tires and I'm on 91 pump gas and water/meth. And it has a 2 year 50,000 mile warranty. And I've abused it a lot already haha it's been a solid engine. It's nice for drive ability and gets good mileage. I was getting 18mpg in a 2500hd truck so I mean in a car it'll be a lot better obviously
Last edited by Twinchargedlsx; Jan 9, 2016 at 07:29 PM.
Originally Posted by Twinchargedlsx
Well I have had a crank shaft sensor code come up so I'll be going through grounds tomorrow it looks like and testing the harness haha and well I think it's a minor issue cause the engine runs fine until 10psi and my a/f hasn't been in dangerous spots so that's good. And the b15 so far is really better then any machine shop or anything. It's making 739hp through a 4wd truck chassis and I have 35 inch tires and I'm on 91 pump gas and water/meth. And it has a 2 year 50,000 mile warranty. And I've abused it a lot already haha it's been a solid engine. It's nice for drive ability and gets good mileage. I was getting 18mpg in a 2500hd truck so I mean in a car it'll be a lot better obviously
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From: Norn Iron
Well I have had a crank shaft sensor code come up so I'll be going through grounds tomorrow it looks like and testing the harness haha and well I think it's a minor issue cause the engine runs fine until 10psi and my a/f hasn't been in dangerous spots so that's good. And the b15 so far is really better then any machine shop or anything. It's making 739hp through a 4wd truck chassis and I have 35 inch tires and I'm on 91 pump gas and water/meth. And it has a 2 year 50,000 mile warranty. And I've abused it a lot already haha it's been a solid engine. It's nice for drive ability and gets good mileage. I was getting 18mpg in a 2500hd truck so I mean in a car it'll be a lot better obviously
Ultimately yes they do all go back to battery/chassis ground.
But sensor grounds run only from the ecu to any of the sensors. At no point ever beyond the ecu will they or should they pair with chassis ground
So if you unplug the ecu and test for continuity between the sensor ground wiring and chassis ground, it should be open circuit.
But it could be a wiring issue, but as described the map sensor is very easy to test as is wiring to the ecu via methods I stated.