Just curious, in the 87 Caprice, I have an LG4.

But I also have a couple thirdgen LG4 ECM's laying around.

I wouldn't think there'd be any difference, but would a thirdgen PROM be any type of upgrade? Or just the same thing in a different car?

 

Well I'm a bada$$...but only a GM Parts Halfa$$. Could be either I suppose tho I bet the F body has a more aggressive spark map or something.

btt

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

 

Mac /Jester,

I'm more of a LameAss, but I wouldn't be too quick to jump on the 'F' car PROM over a 'B' car PROM. The Caprice is a lot heavier car, was expected to get poorer fuel mileage, and probably had to make a bit more torque at the low end to get the big lug moving on its way. If you get a PROM from a Caprice or Impala SEO vehicle, I'd say you might have a better fuel map and spark curve for the car. The 'F" cars made RPMs faster, had a higher stall converter to help out, and probably had a tighter fuel trim. The only advantage to the 'F' car PROM is that is might have been designed for a moderately better cam profile, but I'd expect some lean operation at the mid-throttle positions. The down-side of the 'B' car PROM would be the earlier lockup of the TCC.

You're "lucky" you have the LG4 - I had an '85 Caprice wagon with the carbed 305. That was my last intimate experience with a troublesome E4ME Rochester. And it couldn't get out of its own way. A real chick magnet...

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Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

Depends on the ECM that the Caprice uses. The TBI thirdgens used the 8746 and 8063 ECM's.

Look to see what model ECM you have in the Caprice, and see if one of your Thirdgen ECM's match.

You might not get much of a performance change out of a PROM swap though. So many different parameters between the two LO3's that might not jibe with eachother (ie: injector constant, spark tables, fuel tables, type of transmission, VSS, etc). I'm sure your spark and fueling will be way off considering the thirdgen PROM is most likely programmed more toward performance. Heads and cam profiles pay a LARGE role in fueling and spark, so I'm thinking you will at best run way rich....And you're most likely going to get a SES light.

Give it a shot though, you never know. It might run pretty good if you're lucky.

Post this on the DIY PROM board, and you will probably get a more accurate reply of how/if things will work.



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86 Trans Am WS6 Black with tinted windows, ZZ4, Mini-ram, true duals, LT4 HotCam, AFR 195 heads.
***Too many other mods to mention***

"In the future, cities will become deserts,
roads will become battlefields, and the hope of mankind
will appear as a stranger" The Road Warrior

 

Its a carb, there isnt much the computer is controlling in a carb car.

And Vader, the LG4 is a 305 carb engine. Thats the same as your wagon.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

Where the hell did I pull "LO3" from??? I need to take more breaks here at work I guess. Hehehhh

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86 Trans Am WS6 Black with tinted windows, ZZ4, Mini-ram, true duals, LT4 HotCam, AFR 195 heads.
***Too many other mods to mention***

"In the future, cities will become deserts,
roads will become battlefields, and the hope of mankind
will appear as a stranger" The Road Warrior

 

Honestly i doubt there'd be any gain. Also, the 86-up computers are different than the early ones. The only advantage to see is if you have an early LG5 ecm, use it instead as they are a lot dumber and thus will never give you a problem w/ false codes. The later ECM cars have 'better' diagnostic routines that tend to throw more annoying codes.
...ed