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post #1 of 9 (permalink) Old 01-31-2007, 04:05 PM Thread Starter
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3.8 problems

I picked up a 90 Tbird w/3.8. It wants to start hard after sitting awhile. The motor is actuallty out of 88. The person I bought it from changed the motor but not the computer, I was wondering if mayber there might be enough difference in the computer from 88 to 90, that could be doing it or if there are any other opinions I am open to all. The car had sat for a while, and the fuel pump seems to be working good. Nate

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post #2 of 9 (permalink) Old 01-31-2007, 04:11 PM
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Well, I think they changed from a MAP sensor to a MAF sensor from 88 to 90, but mechanically I think the engine is the same. As long as he reused all the sensors on that were already on the car and hooked everything back up correctly, I don't see why there would be a problem.

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post #3 of 9 (permalink) Old 01-31-2007, 04:15 PM
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The 89 is still MAP sensored.


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post #4 of 9 (permalink) Old 01-31-2007, 04:24 PM Thread Starter
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If we get a break in the cold I will have to check into a little further and get back here and see what else I know.

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post #5 of 9 (permalink) Old 02-02-2007, 12:41 PM Thread Starter
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I completely agree but its all I have right now. When I find another cheap 5.0 then I can switch it.

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post #6 of 9 (permalink) Old 02-02-2007, 01:17 PM
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88 had the balance shaft, but I don't see that as being an issue with the way it runs (other than smoother).

I thought the 3.8 went MAF in 91, I know my 89 is MAP (MAS?, I know i don't have a MAF sensor in the zip tube), but either way, as long as they retained all the sensors and accessories from the 90 it should be fine, and just just used the long block.

My 89 with the 3.8 and 160k miles is sitting right now since I don't have time to fix it, but I have to move it around and start it up to keep it from getting a dead battery and such, and it fires right up, even the day it was 18 degrees (which is like the coldest temp EVER where I live).

Does it crank slow? Does it crank at the right speed but take awhile to fire? Does it start then die? Can you keep it running with slight input on the gas pedal?

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post #7 of 9 (permalink) Old 02-02-2007, 01:40 PM
 
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I'm pretty sure the 3.8 went Mass Air in 91 also. Your 90 ECM should be setup for Speed Density (the system using a MAP sensor). If it wasn't, the car wouldn't even run right. Or it was changed.
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post #8 of 9 (permalink) Old 02-02-2007, 03:41 PM Thread Starter
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It cranks good but will not fire, but once it does start after a while of trying, it runs fine and will restart right away after turning it off. Just not after it sits for a day.

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post #9 of 9 (permalink) Old 02-02-2007, 06:37 PM
 
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90 was still set up for Speed density. The only difference is the balance shaft which wont affect anything. Have you checked the fuel pressure itself at the rail? A fuel pump on its way out will cause hard starts like that. When mine was dying it would take a couple tries first thing in the morning, and struggle for the first couple seconds if I put it in gear right away.
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