Differential swap causing p1870??
Thread Starter
Drifting
Joined: Jun 2004
Posts: 1,483
Likes: 0
From: St. louis, Missouri
Differential swap causing p1870??
I went from factory 3.15 to 3.42(some of you know this). Anyway Driving a few days ago on the interstate, cruising at 70mph, MIL light comes on, scan it, P1870 Transmission Component Slipping. Again some of you know I went though and beefed up the internals and swapped to a 3.42 rear.
So I read on Mike Mercury's site that since RPMs have increased so has slippage.
Now, GM states that factory spec Torque Converter slippage is -25 to +50 rpms, w/ factory converter and either 2.73 or 3.15. Since the 3.42 are not optioned w/ A4.
Running 3.42, is there anyway to bring down the TCC slip w/ a reprogram? I'm seeing 110-130rpm slippage at 70mph As of now, I have not had the car programmed since the upgrades.
So I read on Mike Mercury's site that since RPMs have increased so has slippage.
Now, GM states that factory spec Torque Converter slippage is -25 to +50 rpms, w/ factory converter and either 2.73 or 3.15. Since the 3.42 are not optioned w/ A4.
Running 3.42, is there anyway to bring down the TCC slip w/ a reprogram? I'm seeing 110-130rpm slippage at 70mph As of now, I have not had the car programmed since the upgrades.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
So I read on Mike Mercury's site that since RPMs have increased so has slippage
actually the amount of "slip" with the converter locked has not changed; but there is a perceived slippage increase.
The PCM looks at engine RPM and MPH with the converter locked; then compares this to "slip table" values.
Even if there were zero rpm of slip; the BCM sees an increased RPM (when compared to the cars MPH) due to your rear axle ratio upgrade. The P1870 is set; but it's from a false-report of slippage. The reprogram that you need will readjust this "slip table" to include the up-to-date (higher) RPM values for the MPH traveled with your new ratio (and there's other reprog tricks that can give the same result).
Either way; you'll need a reprog. For the time being, you can clear the code and drive with the shifter in "3" . This should stop the P1870 code from being set.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
there's a few forum vendors advertising $99 mail-in tunes; but you hafta be without your PCM module for whatever time it takes.
Last edited by Mike Mercury; Jan 12, 2008 at 12:58 PM.
Thread Starter
Drifting
Joined: Jun 2004
Posts: 1,483
Likes: 0
From: St. louis, Missouri
So on a reprogram, what tables do they have to change? I'm going to my tuner on Sat. to get it adjusted, but was curious on what needs changed.
He uses HPtuners. Any problem w/ that?
He uses HPtuners. Any problem w/ that?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Safety Car
Joined: Jul 2006
Posts: 4,325
Likes: 0
From: You can't get there from here NJ
St. Jude Donor '08-'09
ECS just did a 3.42 swap for me and a tune. However, I get that code every once in a while, but I clear the codes, and it eliminates the hard shift I get from 1st to 2nd. They are going to go over it again to correct it for me. I only had the gears done last week, so I will bring it back, and according to them, the re-tune will correct this.
