1996 k2500 question help

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Bigred1951

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Hello everybody I’m Michael. First post here. First I love these old trucks lol. I have a 96 1500 z71 but frame is broke and it’s been patiently waiting a frame swap. But anyway. I just today got a 96 k2500 regular cab 5.7 vortec. Was auto originally but somebody swapped a 5 speed nv4500 in it. First question is sometimes it wants to idle high sometimes it don’t. I don’t know anything about it as the guy I got it from didn’t know. It ran and drove ok for the hour drive home. He did do a intake gasket on it before he sold it to me. Also the speedometer doesn’t work. Other gauges seem to. I have found a couple frame spots that need attention but better then a complete frame swap like my other one. Any and all advice is greatly appreciated. If this has been discussed before which I’m sure it has I’m apologize. I’m not to tech savvy and just trying to figure out as I go. Thanks.
 

ralmo94

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I would say the random high idle could have something to do with the manual swap. There are a lot of idle routines in the computer that are different between manual and automatic. If you have both bin files for same engine same year, only difference is auto and manual you'd be surprised how many thing are different.
 

1998_K1500_Sub

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sometimes it wants to idle high sometimes it don’t

They'll often "idle high" while the vehicle is in motion, e.g., while coasting up to a stoplight with the transmission in neutral.

Then, upon reaching low speed (~5MPH, thereabouts, and lower) the engine will idle down.

@ralmo94 mentions other concerns.

It appears, from what I've seen, that can re-program the 1996 ECU to change it from "auto" to "manual", if it's important to you.
 

ralmo94

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Also, a lot of things won't work right without vehicle speed. You need to figure out if pcm. Sees vehicle speed or not.
 

Bigred1951

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Borrow/rent/buy a scan tool and see if the ECU is reporting the correct vehicle speed.

There may be other ways but this one's pretty simple.
Oh ok thanks. My buddy bringing his scanner over later. I’ve read about people having their pcm or computer flashed or something. What does that mean. And can it be done with one of them scanners.
 

Bigred1951

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ralmo94

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Flashing is re writing the chip that stores the calibration data for the pcm. Scan tool usually is not capable unless it's a dealer tool. I would also look to see if the pcm reports the same vin as your truck. It may have been swapped out to a manual one.

As far as I know there is not anything to flash 96 black box pcms. You can however swap in a ls1 p1 severice number 1220411. Called the 0411 swap. This would open the door to open source tuning and flashing tools, also how tuners and EFI live, if you are interested in going down that path check out gearheadefi forum for files.
 
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