Real easy to check the throttle position sensor and see if you can get 100%. Without a code you have to go hunting and you will not always guess correctly. I say start with the simple stuff and then work your way up to the more complicated (expensive) possibilities. I would start with fuel. Check the fuel pressure. A low fuel pressure does not throw a code. Maybe a stuck pressure regulator? Then maybe a bad injector. Maybe a dirty fuel filter.More then likely the bracket on the throttle pedal that the cable attaches to is bent and you are not getting true full throttle when you put the pedal down to the mat.
Common issue on the V8, the convoluted (in my opinion anyway) throttle linkage puts considerable strain on the connection point @ the pedal bending it over time.
Check this before getting crazy chasing ecu gremlins...
There is also a rough road sensor that is supposed to cancel knocks caused by rough roads. But if either one was going off you would see stored codes, if not a lite MIL. Bad fuel could cause the knock sensor to operate but again, you would see codes.The throttle position reads 100% and it's not a bracket issue.
Does the knock sensor often fail and if so does it ever fail by becoming too sensitive resulting in the ECU getting a lot of knock signals and having it retard timing? I guess I could simply make a test run with my laptop connected and check the knock counts.
Things that affect spark control:Hi guys,
I did a little data logging during a couple test pulls and wanted to get some insight from the team. I'll post a graph with some data after I re-take it with fewer channels captured to improve the sampling rate.
All the mundane stuff is fine (throttle position sensor reads 100%, temperatures are good, etc). Also, the mixture is fine and the O2 sensor readings indicate no hint of fuel starvation and at wide open throttle and full boost the O2 sensor is reading a little rich which I'm sure is intentional to protect the engine. The recorded boost is exactly where it should be.
However, the timing advance does indeed look pretty strange. At low load and partial throttle leading up to the pull I have about 28 degrees. When I put the hammer down the advance is retarded and drops back to 16 degrees by the time the RPM's are at 3000 and boost is building. When at 5000 RPM and full boost the timing advance is down to only 9 degrees. After a gear change and hammer down again the advance comes down to 7.5 degrees at 5500 RPM and full boost.
With such retarded timing at high RPMs it's no wonder I have no acceleration at speed.
So now for a couple questions -- what kind of timing advance should I be expecting at reasonable engine RPM's? I'd expect far more than I'm seeing, but I'm not sure what is typical since I don't have a baseline that recorded this on my car.
What are likely culprits for my ECU retarding the timing so badly? The knock sensor seems like a primary input the ECU uses to retard timing, so is it susceptible to failing in a way that makes it falsely trigger?
Knut
There is a main grounding point at one of the upper bolts on the bell housing for the engine wiring harness. Grounding isn't a big problem on the V-8's unless someone didn't put all of the wires back. The only good data logger I know of that can also do snapshots is a Tech 1. Bad power or grounds would manifest itself in other problems too and would not necessarily be so repeatable. One of the subtle clues here is that everything was running fine and all of a sudden this problem appeared and is very repeatable. Something changed and is of such nature that it can't or won't change back. At least you will know when you fixed it! When you have an intermittent you can't be sure for a while, always wondering if it will come back! Was any service work of any kind done just before the symptoms appeared?That's a great thought Atwell; even if Knut's problem is different; low, or unstable power to the ECU certainly could manifest in odd ways. Wonder what the current draw is on the ECU and how is it grounded.
:clap:
Refer to my previous post (16)What kind of map values are you seeing? I think it would be helpful if you made a list of all the pertinent sensor values during a pull and posted the values here so we could evaluate them.
Refer to my previous post (16)What kind of map values are you seeing? I think it would be helpful if you made a list of all the pertinent sensor values during a pull and posted the values here so we could evaluate them.
