Holley 58mm throttle body hardware helpp
02-03-2018, 09:47 PM
#2
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Re: Holley 58mm throttle body hardware helpp
Bottom plate with IAC/passages and coolant connections is a direct swap using GM gasket. TPS is a direct swap. EVAP and PVC vent line to valve cover are direct connections. I believe the top cover plate is different, but I never tried to swap that since no reason to.
I can’t remember if the bolt (to manifold) length is different.... swap was done 18 years ago. The Holley bolts are stainless steel hex head caps. I will take a look at some of my photos of both units so I can compare the flange thickness as far as the bolt length is concerned.
Polishes up real nice:
https://www.camaroz28.com/g/picture/8151925
I can’t remember if the bolt (to manifold) length is different.... swap was done 18 years ago. The Holley bolts are stainless steel hex head caps. I will take a look at some of my photos of both units so I can compare the flange thickness as far as the bolt length is concerned.
Polishes up real nice:
https://www.camaroz28.com/g/picture/8151925
02-05-2018, 04:41 PM
#3
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Re: Holley 58mm throttle body hardware helpp
Also be prepared to modify your TPS sensor. I cannot remember the voltages, do you know off the top of your head Fred? You will just need to elongate the mounting holes, then measure the voltage with a multi meter when installing it. Mine threw a code until I changed it.
02-05-2018, 07:38 PM
#4
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Re: Holley 58mm throttle body hardware helpp
The PCM will accept any closed throttle TPS voltage between ~0.30 - 0.80 volts as the baseline for 0% throttle position percent. Typical value for an unmolested stock TPS is 0.65 - 0.67 volts. The exact value isn't critical.
The idle stop screw adjustment is important. The stock program idle speed for the T56 is 800 RPM, fully warmed up. Keep in mind the stock tach typically reads 100 - 200 RPM higher than actual at idle. Best thing to do is use a scanner. A scanner is accurate. If engine is idling high, back off on the idle stop screw until the idle is at 800 RPM on the scanner. Then check the IAC counts on the scanner. Adjust the stop screw until the IAC counts are between 20 - 40 counts. Then check the TPS volts to make sure the reading is within the PCM acceptable range noted in the first paragraph. No need to slot the TPS unless the voltage is outside the acceptable range,
The idle stop screw adjustment is important. The stock program idle speed for the T56 is 800 RPM, fully warmed up. Keep in mind the stock tach typically reads 100 - 200 RPM higher than actual at idle. Best thing to do is use a scanner. A scanner is accurate. If engine is idling high, back off on the idle stop screw until the idle is at 800 RPM on the scanner. Then check the IAC counts on the scanner. Adjust the stop screw until the IAC counts are between 20 - 40 counts. Then check the TPS volts to make sure the reading is within the PCM acceptable range noted in the first paragraph. No need to slot the TPS unless the voltage is outside the acceptable range,
02-06-2018, 10:24 AM
#5
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Re: Holley 58mm throttle body hardware helpp
Now that you say .65-.67 that rings a bell. Before modifying my TPS, I think it was down in the .1's. I thought the instruction manual mentioned the TPS, so I looked it up. It wants you to measure and record the TPS so you can reset it to the same value after installation: Jegs page with manual.
Thanks as always for the deeper explanation.
Thanks as always for the deeper explanation.
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