I have a 1998 4T65E-HD in my car and when I wanted to change the tire size, I noticed that the calculated gear ratio was set at 3.29 instead of 2.92. Now my speedo is incorect (shows higher speed). As far as I know only the new 2004 CompG's have the option with the 3.29 gear ratio. My PCM is a junkyard item, but still- does anyone have an idea?
Please the explain the problem in more detail.
What car? Year/Model?
Operating System ID?
Was your speedo ever correct?
Are the Tires stock?
I count sheep in hex...
Okay, the car is a 1996 Oldsmobile Cutlass Supreme with a 1999 Buick Regal engine(3800 SC) and the wiring harness is a 1998 Buick Park Ave-to original firewall-to 1998 Pontiac Grand Prix GTP PCM. My System ID is 0000A2190. When I first installed the engine the speedo was correct. Later I added a set of tires that were 25.7" instead of the original 26.2". When I first read my PCM with the VCM Suite, for tire size I had 25.82" and the calculated gear ratio was 3.29. This is what confused me- I know that my car has a gear ratio of 2.921 and I entered the new tire height of 25.7" and the correct gear ratio of 2.921 and now my speedo shows speeds about 1.15 times faster. Could I have a 3.29 gear ratio in my car or is this just the PCM that I purchassed from www.Car-part.com for $25?
i think you are confusing the final drive ratio with the actual diff gear ratio.
on GTP's the actual diff ratio is 3.29 and the chain/sprocket drive ratio is 1.121, which combined gives a final drive ratio of 2.93 (ie. 3.29/1.121)
if things were accurate to begin with and all you changed is the tire then in the speedo section just replace the tire with the new one and enter the gear ratio as the same as it is (ie. 3.29)
I will be adding the sprocket ratio to the editor very soon for those who are transplanting GT/GTP PCMs that have varying sprocket ratios.
Chris...
I count sheep in hex...
Yep, that's my misundersanding. I didn't know about the sprocket's ratio. Thanks!
I also have another question- I have raplaced my MAF sensor with a LS1 unit. From a website called www.LS1HOWTO.com I have downloaded the maf tables for both screened and descreened 2001+ MAF sensors. When I went to replace them on the "airflow" menu, the table only goes up to 115000Hz, wheter the table for the LS1 goes up to 12000Hz, which is 4 more cells. Is the current table fine for me? I haven't dyno tested my engine yet, but it should put out about 400+HP to the wheels. Thanks!
i dunno on the MAF thing. A good indication is your LTFT's. Usually if the MAF is reading low your LTFT's will be positive (assuming your injector flow rates are scaled properly).
I count sheep in hex...
I just installed an LS6 MAF myself, Unlike the stock MAF sensor that reads to 11,500, some LS6 MAF's read to 12,000.
I'm making about 450HP and read ~11600 (average) above 6000RPM
If your making similar power, you should be ok, if your making more, you may want to checkout the GTO MAF as it has much higher g/sec flow figures at any given frequency meaning if your current MAF hit 11500 then the GTO one would read maybe 10800 at the same flow giving you the extra overhead...
Solution 2 is to get a MiniAFC and scale the table down a few pct, but I'd prefer not to have to *trick* the PCM.
-A
(99 GTP)
Originally Posted by coolflames
Does the GTO MAF flow higher than the LT1 MAF?
It doesn't flow any more or less air so much as it reports a different frequency for the amount of air that it DOES flow.
For example:
if you are flowing ~350 g/sec of Air
a 99 GTP MAF would report aprox: 11505Hz
and overflow it's max metering capacity of 349.74g / sec
100.07%
a GTO MAF would report aprox: 10620Hz
leaving 96.66g / sec of overhead below 11500
78.44%
and a Corvette MAF would report aprox: 11255Hz
leaving 24.64g / sec of overhead below 11500
93.42%
both the Corvette MAF and the GTO MAF flow to 12000Hz however this does not matter in most V6 applications as the PCM is limited to 11500
Please don't confuse these values with how restrictive the MAF is.
If that statement is confusing, imagine stretching a pair of tights over your MAF sensor. If you were to do this, the sensor would "see" less air, and thus for the table to be accurate, the g/sec of airflow at a given frequency would need to be much higher to be accurate.
And here are the tables for those interested:
1999 Grand Prix GTP MAF Table:
1.62 2 2.4 2.83 3.27 3.74 4.38 4.9 5.66 6.34 6.9 7.65 8.58 9.61 10.55 11.53 12.81 13.82 14.75 16.17 18.07 19.35 20.58 22.16 23.88 25.12 27.13 29.15 31.41 33.66 36.18 38.7 41.2 44.22 47.23 50.25 53.38 56.5 60 63 66 69.5 73 76.78 81.11 85.62 90.35 95.2 100.2 105.37 110.8 116.24 121.78 127.43 133.07 138.99 145.08 151.37 157.8 164.39 171.11 178.03 185.13 192.36 199.88 207.63 215.74 223.69 231.35 239.59 248.23 257.27 266.61 276.3 286.23 296.4 307.01 317.69 328.38 339.06 349.74
2002-2004 Corvette MAF Table:
1.48 1.8 2.13 2.49 2.89 3.33 3.8 4.34 4.91 5.54 6.22 6.95 7.73 8.56 9.45 10.38 11.38 12.45 13.6 14.85 16.21 17.7 19.32 21.02 22.77 24.54 26.43 28.41 30.49 32.66 34.95 37.36 39.9 42.62 45.48 48.5 51.66 54.98 58.44 62.05 65.82 69.73 73.8 78.03 82.41 86.94 91.63 96.49 101.51 106.71 112.09 117.63 123.35 129.24 135.3 141.53 147.87 154.41 161.15 168.08 175.22 182.58 190.23 198.21 206.34 214.8 223.52 232.52 241.83 251.34 261.13 271.19 281.53 292.15 303.05 314.25 325.73 337.51 349.59 361.96 374.64 387.63 400.92 414.53 428.46
2004 GTO MAF Table:
2.41 2.8 3.22 3.69 4.22 4.8 5.45 6.16 6.94 7.77 8.67 9.63 10.64 11.72 12.88 14.13 15.48 16.91 18.46 20.1 21.85 23.7 25.67 27.74 29.94 32.26 34.7 37.27 39.98 42.82 45.78 48.89 52.13 55.51 59 62.63 66.41 70.36 74.48 78.84 83.41 88.18 93.15 98.32 103.7 109.34 115.16 121.18 127.4 133.81 140.37 146.98 153.79 160.77 167.93 175.27 182.8 190.62 198.7 207.02 215.59 224.44 233.54 242.91 252.55 262.48 272.7 283.19 293.98 305.05 316.42 328.09 340.04 352.3 364.84 377.69 390.82 404.24 417.95 431.95 446.22 460.77 475.6 490.7 506.05
All tables begin at 1500Hz and increase by 125Hz per step.
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