Sketchy RPMs at WOT
#1
Sketchy RPMs at WOT
So I was going over my log of my last run at the track. I come to find out that the reason i did so crappy was due to a fuel pressure issue. That may not be the only issue though. I'm going over the log in datamaster and I'm looking at the graph (normally i export to excel) and i see the RPMs look like an etch a sketch line. it increases but real sketchy. for example it will climb the rpm range then drop like 25rpm hold then increase then maybe hold increase then drop and so on on. it looks like a bunch of little mountain peaks. what could that be?
Last edited by C_Rules; 10-16-2009 at 08:32 PM.
#2
The RPM reads in 25 rpm increments, so a drop of only a few RPM can cause it to change by one data bit, which is 25rpm. That makes the changes look more dramatic than they might really be. Even in an engine running perfectly, using an ECU with finer RPM resolution, the rpm at WOT does not always increase uniformly or smoothly.
If the increments do become excessive, it may be a sign of a problem with the pulse pattern from the Opti, which is what provides the RPM signal to the PCM. Or it may relate to misfires, but you would feel those. Is there any knock retard when the RPM seems irregular?
If the increments do become excessive, it may be a sign of a problem with the pulse pattern from the Opti, which is what provides the RPM signal to the PCM. Or it may relate to misfires, but you would feel those. Is there any knock retard when the RPM seems irregular?
#3
I was going over my log of my last run at the track. I come to find out that the reason i did so crappy was due to a fuel pressure issue. That may not be the only issue though. I'm going over the log in datamaster and I'm looking at the graph (normally i export to excel) and i see the RPMs look like an etch a sketch line. it increases but real sketchy. for example it will climb the rpm range then drop like 25rpm hold then increase then maybe hold increase then drop and so on on. it looks like a bunch of little mountain peaks. what could that be?
Other things that cause that are things like the motor trying to REV like hell and traction holding it back, and without you knowing it things like bumps, rocks, ect all contribute to momentary loss of traction which all show up on the RPM graph, just in weird ways.
I think 25rpm error is fine, I've had some like 200 or more, dont remember exactly. It would be interesting for the ultra high HP cars show the RPM charts compared to lower HP cars (High HP cars at higher MPH's of course), or maybe even people with different Opti's, and people with aftermarket PCM's.
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