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Discussion Starter #1
Help converting 1990 lx from 4cyl to 8 cyl

I have a 1990 LX convertible with some sort of fuel pump problem. Guy I bought the car form says the car needed a new pump he put it in but could never get the car to run again. I figured i would just start over with an 8 cyl to begin with. What would be better the 5.0 or 4.6. Can i still retain the automatic tranny that came with it? I know the rear is not as stong but will be ok to drive for a while correct. Also is the fuel pump assembly the same or what cause I still have to fix that problem also.any help would be greatly appreciated and I am trying to do this as cheap as possibe as in mostly used parts.
 

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Definately go with the 5.0. the computer switch that you will need to make wont work with a 4.6. You are going to need a new trans as well cause the four cyc trans wont match up to a V8.
 

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You can easily find a 5.0/AOD combo still mated together for cheap. The 4.6 CAN be done, but it's a whole new ballpark.
You'll need the 5.0, transmission, harnesses and computer. Your best bet is to find a Lincoln Mark VII that's been wrecked and take the whole drivetrain from that. It's the 5.0 HO, just like was in Mustangs, but most people don't know that, so they don't buy 'em up.
 

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Yes, Mark VII = LSC. Yes, 5.0, transmission, harnesses, and computer. Depending on whether your intake points to the driver or passenger side, you may need the throttle cable from the 5.0, too.
 

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Discussion Starter #6
Re: Help converting 1990 lx from 4cyl to 8 cyl

I feel like an idiot asking so many questions but its the only way to get answers. I am able to get a 5.0 from a 1984 GT and it has a carb. Should I get this and convert to efi or get it and use the carb or should I just find an engine from a 90? Thank-you for all your help!
 

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You'll want the engine from a 1987-1993 Mustang or Lincoln Mark VII. The '84 heads weren't that great and it's a pain in teh ass to convert to EFI, but without EFI, you'll never get more than 15mpg. Just take your time and keep your eyes peeled.

Edit- Oh, and ask all the questions you need. That's what this forum is all about!
 

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Discussion Starter #8
Alright thanks freshmeat for your help. I was offerred a 1986 GT coupe for $300 with the 5.0 and aod. I think I will go with that because I get the entire car engine,tranny,ecu,crossmembers,dual exhaust. I'm just thinking it would be more cost effective. As far as I know the efi system is different correct. But I could pick up a new intake or used to make power like a newer engine would right?
 

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I actually recently picked up a 1986 GT myself, but mine has T-tops and was free!

The EFI system is the same from 1986-1988; it's called Speed Density and uses O2, water temp, air intake temp, manifold absolute pressure, and throttle position sensors to determine how much fuel is sprayed. However, in 1989 they switched to MAF (commonly known as mass air), which added a sensor to read the amount of air going into the engine to more appropriately determine how much fuel to spray. If you're leaving it mostly stock, don't bother with the MAF conversion. In fact, I know a guy first-hand who has a 500rwhp Mustang running on SD (speed density). It's not hard to manage a SD-based system.

The primary difference with the 1986 motor is the heads, upper intake, cam, and throttlebody. They're also flat top pistons, so you can't do most aftermarket cams or heads. However, you could switch to the E7TE heads, which are on the 1987-1993 HO motors.

Some cheap upgrades you can do:

Swap for a 1987+ throttlebody. The '86 is a 55mm, while the later models utilized a 60mm. You can even go with a 5.0 Explorer throttlebody- they're 65mm, but you'll need to swap the throttle lever from your stock unit to the Explorer piece. I know several guys who give away stock TBs and the Explorer pieces can be had for $50, max, on eBay.

Swap for a 1987+ upper intake. The later designs simply flow better. Avoid the 1994/5 models, because they had a neck that angled the throttlebody toward the front of the car and they're hard to deal with on the older models. I got my upper for free. Just gotta know who to call.

Swap for a 1987+ ECU. Slightly better fuel curves. Not that big of a deal. Local junk yard sells 'em for ~$20.

However, I know of people who pull 30mpg out of their stock '86 motors. The designs are so efficient that they get decent power and great mileage. Drive it around for a while before you really think about upgrading things.

Hope this helps- good luck!
 
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