Help needed with understanding my Datamaster scan
Thread Starter
Launching!
Joined: Jan 2007
Posts: 233
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From: Mooresville,NC
Help needed with understanding my Datamaster scan Hey guys the car is a 1995 lt1 camaro. Comp 218/224 .565 lift cam, ported stock heads, 355ci, 32lb injectors, 52mm edelbrock tb, descreened only maf, moroso cai. I also have headers and a few other bolt-ons. I decided to do a datalog with data master to see how she's running. It felt like it was pulling out timing from 2200-3600. It just seemed to make a lot of noise but not go anywhere. I also thought it seemed to be running rich at low rpm and idle. I'm having trouble posting the datalog (can't get my laptop to connect to internet). So my question is what areas and what range of numbers do I need to be watching on my scan to confirm what I am looking for(timing being pulled out,normal knock counts, fuel/timing at low rpm, blms and o2 mv)? I also have tunercat available to make changes if needed. Please let me know how much more specific info will be needed. Thanks guys.
TECH Enthusiast
Joined: Mar 2009
Posts: 680
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From: Clearwater
the spark retard field will tell you if you are pulling timing or not which should pretty much always be 0. (assuming you are not producing any false knock)
the knock count will go up when starting the car and should also not increase while it is running. (also assuming you are not producing any false knock)
the BLM should be as close to 128 as possible. i always get these screwed up but I believe when the number gets lower and lights up red it is trying to lean out and when it goes higher and lights up green it is trying to add fuel.
the O2 mV should be constantly bouncing around between 1v and some value greater than 0. if it seems hung up on a value you could have anything from a faulty O2 sensor, exhaust/fuel leak or some other mechanical condition on that side of the motor.
the knock count will go up when starting the car and should also not increase while it is running. (also assuming you are not producing any false knock)
the BLM should be as close to 128 as possible. i always get these screwed up but I believe when the number gets lower and lights up red it is trying to lean out and when it goes higher and lights up green it is trying to add fuel.
the O2 mV should be constantly bouncing around between 1v and some value greater than 0. if it seems hung up on a value you could have anything from a faulty O2 sensor, exhaust/fuel leak or some other mechanical condition on that side of the motor.
Teching In
Joined: Jan 2013
Posts: 13
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From: Columbus, IN
Try putting the screen back in the MAF. descreening brings up the CFM but devastates the accuracy. If the stock MAF is a bottleneck, you're better off going bigger (and still accurate) than descreening and dodgy measurements.
yup, knock retard=pulling the timing back.
yup, knock retard=pulling the timing back.
Try putting the screen back in the MAF. descreening brings up the CFM but devastates the accuracy. If the stock MAF is a bottleneck, you're better off going bigger (and still accurate) than descreening and dodgy measurements.
yup, knock retard=pulling the timing back.
yup, knock retard=pulling the timing back.
Been running a descreened MAF for 13 years.
Thread Starter
Launching!
Joined: Jan 2007
Posts: 233
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From: Mooresville,NC
Well I took a look at one of my first scans from Wednesday and it is showing anywhere from - 3 to -9 degrees of timing retard when going through the rpms from about 2500 to 3400(if I'm understanding the scan correctly). Knock count starts at about 3000 counts at start up and cycles up to 65000 and starts over during a 8-10 minute drive. I have mid length headers and no cat on the car with borlamouth exhaust so it is hard to hear it knock when/if it is. I can't honestly remember what knock sensor I put in it when I rebuilt it in 2006. I think it was just a stock new GM lt1 sensor. I've been told that headers, no cat, roller rocker noise can cause enough noise for false knock. One other possibility is maybe the fuel here has too much ethanol? I run 93 but the stations here claim up to 10% of ethanol. I'm trying to work on getting a scan posted. Also what is the box for the egr dc?
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TECH Enthusiast
Joined: Mar 2009
Posts: 680
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From: Clearwater
i think that measures the duty cycle of the EGR valve (open/close?). mine has been eliminated long ago so i never look at it.
what is your spark advance set to?
3-9 degrees seems REALLY bad as i have rarely seen more than 4 degrees of retard and that was when i had a cracked piston that eventually took out a rod. i have not personally seen a LT1 car with enough false knock to cause that much timing to be pulled.
what is your spark advance set to?
3-9 degrees seems REALLY bad as i have rarely seen more than 4 degrees of retard and that was when i had a cracked piston that eventually took out a rod. i have not personally seen a LT1 car with enough false knock to cause that much timing to be pulled.
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How a descreened MAF affects things also depends on the intake tract, if it is straight before and after the sensor and flow has time to even out across the cross section descreened wont cause the problems it can with say a sharp bend right in front of it causing the flow to mostly be on the inside of the bend, or short cone filters with the inverted cone in the end tend to screwup readings if mounted right to the MAF as well.
Far as how the car runs, I didn't see you mention tuning? How about compression ratio?
Did you fix the TB so the car can idle right? ALL aftermarket LT1 TBs I have seen will not let the IAC distribution circuit work right. For a 52mm you would have been a lot better off with a ported stocker.
Do you have a proper stall converter and gears?
Far as how the car runs, I didn't see you mention tuning? How about compression ratio?
Did you fix the TB so the car can idle right? ALL aftermarket LT1 TBs I have seen will not let the IAC distribution circuit work right. For a 52mm you would have been a lot better off with a ported stocker.
Do you have a proper stall converter and gears?
Thread Starter
Launching!
Joined: Jan 2007
Posts: 233
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From: Mooresville,NC
I have the stock torque converter, 373 gears, and the iac counts are around 80-135? I need to look again to make sure of that. I'll try to get a scan posted. Do you guys know how to do that?
Thread Starter
Launching!
Joined: Jan 2007
Posts: 233
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From: Mooresville,NC
I have the stock torque converter, 373 gears, compression is 10.2 to 1, the tune is from pcm4less from 2006 when I rebuilt the engine with these same mods. The iac counts are around 80-135? I need to look again to make sure of that. I'll try to get a scan posted. Do you guys know how to do that?
Thread Starter
Launching!
Joined: Jan 2007
Posts: 233
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From: Mooresville,NC
Here is a screen shot of my drive on Wednesday showing one of the points in the drive where it retarded it 9 degrees. 2600 ish rpm, 74 kpa map, 30% tps. Does this make sense to anyone?
You have to determine whether the knock is real or not.
Mix in some race gas and see if it pulls less timing at the same RPM/load. If it is less retard, then the knock is real and you need to pull timing. If it stays the same, then you should desensitize the knock sensor.
If it is already tuned by PCMforLess with the same mods, it is most likely false knock.
Mix in some race gas and see if it pulls less timing at the same RPM/load. If it is less retard, then the knock is real and you need to pull timing. If it stays the same, then you should desensitize the knock sensor.
If it is already tuned by PCMforLess with the same mods, it is most likely false knock.
There's no such thing as an LT4 knock sensor. You're thinking about the LT4 knock "module." Just don't want to see any confusion.
The LT4 module would help, but you could also desensitize the KM via tuning.
The LT4 module would help, but you could also desensitize the KM via tuning.
The knock count itself is meaningless, the number continuing to rise is meaningful.
If this ran what you thought was good for 6-7 years and then this issue popped up then you are looking for something mechanical.
If this ran what you thought was good for 6-7 years and then this issue popped up then you are looking for something mechanical.
Thread Starter
Launching!
Joined: Jan 2007
Posts: 233
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From: Mooresville,NC
Well it did drive great for about the first 1-2 years but has gradually become more noticeable lately. I mean maybe I'm just used to what my car is like but if someone else came along and drove it they might pick it out right away. Yes I meant knock module, so for now could I try de-sensitizing the sensor? Is this just as simple as decreasing the timing in the problem rpm range?
TECH Enthusiast
Joined: Mar 2009
Posts: 680
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From: Clearwater
no, you should try what everyone else has told you and that is look for a mechanical reason that would be causing it. it could be exhaust banging on the body, loose poly lock on the rocker arm studs or rock knock. my money is on rod knock. why you ask? because you notice it around 2500 RPM.
Thread Starter
Launching!
Joined: Jan 2007
Posts: 233
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From: Mooresville,NC
The rockers/lifters are fairly noisy so I will check the rocker adjustment there. Anyone think an exhaust leak might contribute to this problem too? I've had issues in the past with the y-pipe gaskets sealing. As far as rod knock, why is 2500 rpm so significant? When I rebuilt the engine it got new rod bearings and ARP studs/bolts in the stock rods. Doesn't rod knock develop because of oiling problems?