| Electronics > Beginners |
| Is this a bad sensor or are my O-scope settings off? |
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| McKay420:
I'm trying to diagnose an issue with my Suburban and I thought I would test the camshaft sensor. I used one of those cheap $30 o-scopes from Amazon. I just need to know whether or not this looks like a faulty (hall-effect) sensor or if my settings are just off. It is a "pull down" circuit. If I play with the vertical sensitivity settings, I can make the "noise" go away, but is my PCM going to interpret this noise as a valid signal or not? I'm not getting any check engine codes, so I'm leaning toward the sensitivity being too high or something. Sorry for the low quality pic...1 mb limit per pic is kinda inconvenient. |
| tautech:
Yep user error. Full amplitude must be on the display |
| StillTrying:
--- Quote from: McKay420 on April 17, 2018, 11:51:44 pm ---Sorry for the low quality pic...1 mb limit per pic is kinda inconvenient. --- End quote --- I'd be happy for the 1 milli bit limit to be reduced to 100kB, it's only a limit when you don't know what you're doing. :popcorn: |
| Macbeth:
...and the fault is? The reason you suspect CKP is...? even the slightest bit of info? :palm: I've had a CKP fault once - 90's Ford Fiesta, car would not turn over, CKP fault disables the car. Cleaned it and it was fixed forever until some scallies stole it and wrapped it around a lamp-post. |
| McKay420:
--- Quote from: StillTrying on April 18, 2018, 12:41:59 am --- --- Quote from: McKay420 on April 17, 2018, 11:51:44 pm ---Sorry for the low quality pic...1 mb limit per pic is kinda inconvenient. --- End quote --- I'd be happy for the 1 milli bit limit to be reduced to 100kB, it's only a limit when you don't know what you're doing. :popcorn: --- End quote --- Lol sorry I'm not a real fan of windows when it comes to photo editing and I had already had enough of google for one day trying to figure out my car problems --- Quote from: Macbeth on April 18, 2018, 01:04:20 am ---...and the fault is? The reason you suspect CKP is...? even the slightest bit of info? :palm: I've had a CKP fault once - 90's Ford Fiesta, car would not turn over, CKP fault disables the car. Cleaned it and it was fixed forever until some scallies stole it and wrapped it around a lamp-post. --- End quote --- Figured since this wasn't a car problem forum that nobody would care for the details or even know what I was talking about. It's a 2004 Suburban 1500 5.3l Z71 flex fuel with 290,000 (yes I'm aware that the problem may just be the mileage). Low, rough idle with no misfire codes and moderate hesitation on acceleration, but when I floor it and it goes in to open loop, the full 295 hp takes hold. Long term fuel trims are 22% on both banks and short term are at zero. They were at 50% until I changed my intake gasket and took care of all vacuum leaks. I've also replaced both upstream O2 sensors, fuel pump and filter, checked fuel pressure, tested injectors and coils, changed plugs and wires and changed my throttle body assembly and mass air flow sensor. The vehicle sometimes stalls but only at idle and will restart 95% of the time on the next crank and for sure one more crank after that. Problem seems to start as soon as the engine warms up for a minute and goes in to closed loop. Acceleration drops fuel trims down to around 10% (I know it sounds like a vacuum leak but it's not), and unplugging my mass airflow sensor drops fuel trims to 0%. I have tested the MAF sensor and it is functioning correctly so it has to be because open loop automatically runs rich. According to factory settings. Since it is capable of functioning at factory settings at 0% fuel trims, I'm thinking that there might be more to this than just high mileage (worn piston rings or cylinder walls, or a burnt valve, etc.) Some parts of the vehicle seem extremely well maintained, but others looked absolutely horrible, such as the area under the intake. I guess I should mention that I had an unresolved crank, no-start a few months back that just went away. Whatever was happening was disabling the fuel pump relay, because I could get the car to start and drive by jumping the relay with a paperclip. I'm also experiencing decreased oil pressure (20psi) compared to the 40 psi from earlier this year, but that could have been from the cold weather. During heavy acceleration and while monitoring the PIDs with my scan tool, I am only able to achieve about 60% engine load even though I'm moving at a decent pace, 0-60 in 12 seconds (factory is 9 seconds). That 60% load is also correlated to volumetric efficiency which should be around 85%. Engine bay sounds like a diesel, but I've checked the rockers and lifters and they seem ok, but I'm hesitant to remove the heads since I don't have the money for a head gasket right now and I've never done it before so I'm a bit hesitant. Lastly, I haven't checked the exhaust back pressure, but I can't hear air hissing through the cats or anything and the exhaust flows strong and smooth. When a piece of paper is held by the exhaust, it does not suck it in like there is a bad valve, but there is an abnormal amount of moisture coming from the exhaust. I know water is a by-product of combustion, but it will make a piece of paper soggy in 10 seconds. I am not burning or leaking coolant or oil, so I have no idea what this is all about. So I came to the crank/cam sensor conclusion (tested both now the proper way and they're fine) because I'm just running out of ideas. Next step might be tearing down the engine for a total inspection/overhaul. |
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