I've got a 97 cobra that i'm having an issue with... The problem is it's pulling about 10 degrees of timing out at WOT, i've data logged it and the iat's are normal, 80-85 degrees on a 70 degree day, and the ECT temps are running around 190-195. I've talked to the tuner and those were the two he named as usual culprits. The imrc's are deleted, so the spark adder table shouldn't be an issue, should it? I'm supposed to be going to a big car show this weekend and was planning on dynoing it, but i need to get the timing back first. Any and all suggestions will be explored, i need this fixed! The tuner said the timing is much more aggressive than what is being data logged, and that something in the car is pulling timing, knock sensors are turned off...
What pulls timing?
- Thread starter eric88gt
- Start date
Just a thought, but did you degree the cams. If the tune is trying to adjust then you may very have the cams out of time between the two banks. I am not an expert by any means.
I was experiencing exactly the same problem with my '96 Cobra. On the dyno or on the street, the timing would jump around between 28 and 18 degrees back and forth at WOT. Here is a plot... (as you can see, it was costing about 10rwhp on the dips).
Here you can see that there is absolutely no feedback from the knock sensors during the 10* swings in spark advance:
I logged the knock sensors, and those were not the culprit. Plus knock sensors can retard as much as 5*, certainly not 10*!
Next, I thought maybe it was the IMRCs... I deleted them, and the timing was still retarding down to 18*.
I discussed it with my tuner, and he threw out the idea that it might be the cam sensor. He sent me a base tune which I will be logging this weekend and reporting my findings in this thread.
If you are interested, feel free to go through the thread as it goes into quite a bit of detail about what you are asking.
http://www.svtperformance.com/forums/sn95-cobras-24/689723-project-1996-cobra.html
Best of luck!
Luke
Here you can see that there is absolutely no feedback from the knock sensors during the 10* swings in spark advance:
I logged the knock sensors, and those were not the culprit. Plus knock sensors can retard as much as 5*, certainly not 10*!
Next, I thought maybe it was the IMRCs... I deleted them, and the timing was still retarding down to 18*.
I discussed it with my tuner, and he threw out the idea that it might be the cam sensor. He sent me a base tune which I will be logging this weekend and reporting my findings in this thread.
If you are interested, feel free to go through the thread as it goes into quite a bit of detail about what you are asking.
http://www.svtperformance.com/forums/sn95-cobras-24/689723-project-1996-cobra.html
Best of luck!
Luke
I've read, reread, and then reread that thread again and again haha, I'm just at a loss as to what's causing the timing to be pulled as the tuner is saying it is. I've logged the knock retard and it's at a continuous 0, as it should be with the knock sensors turned off. I've now received 2 new tunes today, and the timing is getting closer and closer to what i would think it should/would be.
If i add the timing in on top of the last tune i was sent, i can get it to about 26 degrees total at WOT, it pulls way harder the more timing that is getting put into it, increasing timing down low has an unbelievable effect on torque, it's like a completely different car/motor. The car actually feels stronger below 3250 now with the timing added, the imrc delete, and the short runner intake than it did before i touched it. I never data logged the stock tune, so i have no idea what the factory tune was doing with the timing... The tuner is still saying the timing should be higher than what i'm seeing, which is what's really confusing to me as all sensors seem to indicate that everything is working just fine.
If i add the timing in on top of the last tune i was sent, i can get it to about 26 degrees total at WOT, it pulls way harder the more timing that is getting put into it, increasing timing down low has an unbelievable effect on torque, it's like a completely different car/motor. The car actually feels stronger below 3250 now with the timing added, the imrc delete, and the short runner intake than it did before i touched it. I never data logged the stock tune, so i have no idea what the factory tune was doing with the timing... The tuner is still saying the timing should be higher than what i'm seeing, which is what's really confusing to me as all sensors seem to indicate that everything is working just fine.
Eric, hopefully we can work together on this and figure it out. The plots that you see above were with my car bone stock with the stock tune.
Just tonight I loaded the base tune from my tuner to the PCM for the first time. The car is certainly more responsive and has more low end torque than it did. I agree with your statement below:
With the stock tune, I could actually feel those 10* dips in timing while at WOT (when I was getting my stock dyno pulls before I started modding, the dyno operator said the same thing, that he could feel those timing dips while on the dyno). I definitely can't feel those same dips now with this new tune, at least not noticeably.
I will be data-logging this weekend to see how the timing and A/F looks so I can send the data-log in for tune refinement. Will let you know what I find...
Also, when you say that your data-logs are showing 26*, what does the tuner say it is supposed to be? That's certainly odd that the two do not match.
Just tonight I loaded the base tune from my tuner to the PCM for the first time. The car is certainly more responsive and has more low end torque than it did. I agree with your statement below:
With the stock tune, I could actually feel those 10* dips in timing while at WOT (when I was getting my stock dyno pulls before I started modding, the dyno operator said the same thing, that he could feel those timing dips while on the dyno). I definitely can't feel those same dips now with this new tune, at least not noticeably.
I will be data-logging this weekend to see how the timing and A/F looks so I can send the data-log in for tune refinement. Will let you know what I find...
Also, when you say that your data-logs are showing 26*, what does the tuner say it is supposed to be? That's certainly odd that the two do not match.
I actually didn't specifically ask him what this latest tune would end up at ultimately. I only asked about the first "baseline" tune, which he said should have showed 24 degrees total, I was seeing 14. He has since emailed me a more aggressive timing map, and with adding 4 degrees on top myself (he left some options there for timing) i can get to 26 now. I'll see if anybody has a camshaft position sensor tomorrow and give that a shot and report back what i find as well.
He's saying that the tune is far more aggressive with timing than what the logs are showing, so something in the car must be pulling timing. But if i log the timing map, it's a gradual rise with no dips or anything, it's as if something is just globally taking out 10 degrees of timing, but none of the sensors seem to indicate anything that would actually do that?
My car also had a surge at WOT with the stock tune, that is now gone with the new tunes. I'll report anything and everything i find out as i'm going through this too, and hopefully one of us can come to some conclusion as to what's causing this. Something has to fix it! I'll be curious to see if your logs also end up showing less timing than what the actual timing is set at in the tune. Our cars seem to exhibit the same exact symptoms with the stock tune, and although i never actually logged mine, i would bet money that mine was pulling timing in a similar manner to what yours was, you could feel it happen.
He's saying that the tune is far more aggressive with timing than what the logs are showing, so something in the car must be pulling timing. But if i log the timing map, it's a gradual rise with no dips or anything, it's as if something is just globally taking out 10 degrees of timing, but none of the sensors seem to indicate anything that would actually do that?
My car also had a surge at WOT with the stock tune, that is now gone with the new tunes. I'll report anything and everything i find out as i'm going through this too, and hopefully one of us can come to some conclusion as to what's causing this. Something has to fix it! I'll be curious to see if your logs also end up showing less timing than what the actual timing is set at in the tune. Our cars seem to exhibit the same exact symptoms with the stock tune, and although i never actually logged mine, i would bet money that mine was pulling timing in a similar manner to what yours was, you could feel it happen.
Per my SCT dealer training, predicting what spark advance you will actually see at any given point in time is very difficult. The equation in my training material is:
"BORDERLINE_KNOCK_TABLE + SPARK_ADDER_TO_BORDERLINE_FOR_IMRCs + SPARK_ADDER_FOR_A/F_WHEN_OPEN_LOOP + (SPARK_RETARD_ECT_MULTIPLIER times SPARK_RETARD_FOR_ECT) + (SPARK_RETARD_ACT_MULTIPLIER times SPARK RETARD FOR ACT) + (some VCT stuff) + OCTANE_PLUG_SPARK_MODIFIER = spark (almost)"
This can be a very tough issue to figure out...
"BORDERLINE_KNOCK_TABLE + SPARK_ADDER_TO_BORDERLINE_FOR_IMRCs + SPARK_ADDER_FOR_A/F_WHEN_OPEN_LOOP + (SPARK_RETARD_ECT_MULTIPLIER times SPARK_RETARD_FOR_ECT) + (SPARK_RETARD_ACT_MULTIPLIER times SPARK RETARD FOR ACT) + (some VCT stuff) + OCTANE_PLUG_SPARK_MODIFIER = spark (almost)"
This can be a very tough issue to figure out...
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I appreciate you putting that in here, it makes me wonder if the timing he's saying is there, really isn't to begin with... It doesn't explain the surging at WOT with the factory tune, but I was assuming that it was an imrc issue causing that. With the surging now gone I'm fairly certain my assumption was correct, though I wish I would have logged it once just to see...
By doing an imrc delete, and removing the spark adder table, could that be causing the low timing number? I would think the tuner would know one way or the other, but I guess anything is possible. It seems as though it's down exactly 10 degrees, which I believe is what the spark adder table typically adds when the imrc's open from everything I've read, is this just coincidence?
O2 sensors are not monitored when the PCM is in open loop, and the PCM is in open loop when you go WOT, so O2 sensor issues would not cause this.
SCT supplies base tunes with the borderline knock spark table rebuilt for IMRC deletes. Assuming your tuner used the correct base tune, then the loss of the IMRC adder table is already compensated for.
SCT supplies base tunes with the borderline knock spark table rebuilt for IMRC deletes. Assuming your tuner used the correct base tune, then the loss of the IMRC adder table is already compensated for.
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That's all i needed to know, hopefully he used the correct base tune then. Does anybody know for sure if a camshaft position sensor problem could result in the timing loss? I have no codes but i'm not ruling anything out.
I've personally never seen one fail.
Goodness...
Mark, if the O2 sensors do not give the PCM feedback at WOT, then what is the "SPARK_ADDER_FOR_A/F_WHEN_OPEN_LOOP" ?
How is the car measuring A/F without the O2 sensors?
When in open loop, the PCM looks up the Commanded AFR (in lambda form) from a table based on RPM and Load (with Load being calculated based on MAF AD counts.)
Since the PCM is commanding the AFR, assuming the tune is good, then the PCM knows the actual AFR (or at least close enough). In fact, narrowband O2 sensors can only tell you when you are either side of stoich (AFR =14.64 for gasoline). So when you go WOT, a narrowband O2 sensor can't measure if the actual AFR is what was commanded (normally much richer than stoich). You need a wideband O2 sensor for that. So it just assumes the tune is correct, and it adds spark based on how much AFR it commands, not what it reads, because all it sees is that it has gone rich.
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Can you post the full size pic of your sig pic.
Thank you.
Everyone else, carry on.
OP, have the tuner turn off the KS'ers. They ****ing suck. (I've had issues with mine for years).
Any updates?
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