TJ's Motors built/in (working on KR issues now, update 9-12) - Page 18 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

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Old 08-21-2007, 01:46 PM   #171
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While there could be issues with fuel pressure (or vac leaks or any number of things), I do agree with willwren that the fuel maps are probably off in the high rpm region.

As I added mods incrementally, I pushed higher and higher each time into the MAF table. As I did so, I found that the MAF table needed to be bumped upward in the amount of air being read (by as much as 8%-10%). In other words, after adding a mod, the PCM would be under-reading the airflow by as much as 8% to 10% at very high rpm'* (and as much as 3% to 5% at low rpm'*)...this leads to underfueling and a lean condition.

(Your '95 and my '98 will likely not have identical MAF table curves, but the same trend probably holds)

Terry, do I recall you saying you were going to have a chip burned for this build? After ruling out all mechanical issues and then allowing the PCM to learn as much as possible, you may have to get a mini-AFC or MAF translator to figure out a MAF table differential to have burned into your chip.
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Old 08-21-2007, 02:12 PM   #172
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No Case learns on the 95

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Old 08-21-2007, 06:35 PM   #173
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Yea, i am going to let it learn, but i do believe i am going to have the fuel pressure checked again. Zoom and Bill both mentioned having it tested under load because just at idle and reving is not an accurate enough reading. So that may be next.

But yea, i want to rule out all mechanical things and what not, then it may come to getting a custom chip done. Ryan has his eyes on this post and we have been in contact alot so i am going to give it time and keep plucking away but may have a chip done very soon.
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Old 08-21-2007, 07:36 PM   #174
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Quote:
Originally Posted by TJ'sblackbonne
Yea, i am going to let it learn, but i do believe i am going to have the fuel pressure checked again. Zoom and Bill both mentioned having it tested under load because just at idle and reving is not an accurate enough reading. So that may be next.

But yea, i want to rule out all mechanical things and what not, then it may come to getting a custom chip done. Ryan has his eyes on this post and we have been in contact alot so i am going to give it time and keep plucking away but may have a chip done very soon.
Yeah you do want to test it under load... A couple of years back I was getting all kinds of Knock counts and some KR in Light to moderate driving as the Pump was putting the nails in its coffin

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Old 08-21-2007, 07:52 PM   #175
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yea, i am going to do a pump and filter no matter what, the car deserves it
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Old 08-21-2007, 08:35 PM   #176
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Quote:
yea, i am going to do a pump and filter no matter what, the car deserves it

yeah i think so too 13 years and youre asking for more fuel can't go wrong whit that
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Old 08-25-2007, 12:12 PM   #177
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No real update. I have been driving the car and letting it learn. I have about another 150 miles on it. Still seeing the same thing. If i mash it in first it is good to about 4900 and then i see the KR. (still 15 degrees). If i am in second gear and i mash it, sometimes i dont see any KR, sometimes i see the 15 degrees. If the car is cold and not up to temp i dont see any KR (well maybe 1-2 at the most) and the car feels amazing. It seems the only time is when the car is up to temp. I am considering doing a couple videos for everyone today. I can show the lack of KR when not warmed up, the KR when it is warm, and how i can like rool into the throttle in second gear and not get KR but if i mash it i do. Might also do a video of the scan tool and how the KR comes on. At this point i am still thinking it may be a fueling issue but i dunno. I am going to try the home made race gas next week and see if that does anything. If not i may have ryan send me a chip with very low timing and see if i still get the KR if so then he says it is something false (like a bad motor mount, or something banging).
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Old 08-25-2007, 12:32 PM   #178
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A hot spot in a cylinder(carbon)?
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Old 08-25-2007, 01:11 PM   #179
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are you suggesting i seafoam it to remove the carbon? Someone else suggested that also
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Old 08-25-2007, 01:33 PM   #180
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I wonder who that could have been.......

BTW, I'm behind a couple days in my PM'*. The answer to your LIM question is 'overporting is bad for performance'.

Another variable you need to rule out.
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