89 mustang 5.0


Asked by Aug 08, 2015 at 08:33 PM about the 1989 Ford Mustang LX 5.0L

Question type: Maintenance & Repair

My boyfriend has an 89 mustang with a
super charger in it. It runs fine with the hood
up but about 5 to 10 minutes with the hood
down it completely turns off like you shut
the key off.

14 Answers


Has he tried adjusting IAC idle air control or cleaning the MAF mass airflow sensor. Both are easy to check and or clean / replace.


Sounds like the ignition control module is getting hot and shutting down. When it quits, spray some starting fluid down the throttle body. It should run a few seconds on the starting fluid. If not, you have no spark and the module is the prime suspect. HTH. -Jim




It's killing the fuel pump. It turns the fuel pump off


Thats an easy fix and it would be a good time to upgrade to a more powerful fuel pump. Dont forget to change fuel filter and maybe the injectors depending on what the set up is.


Check relay and the inertia switch, both are known failures, the inertia switch tends to melt the contacts inside the plug.


The fuel pump is still working to start the car and everything. If he takes the hood off the car it will stay running no problem it is only turning off like this when the hood is closed


So it is either vapor locking, or the relay is thermally failing. It might be a good idea to replace all of the relays just to eliminate any secondary problems.


He thought it was vapor locking so he rewired the fuel line that was sitting right next to the turbo.. That didn't help. Where is the relay located? I looked at a couple other sites and it says under the drivers seat but there is nothing there


How heavily was this modified? Mustang 5.0 was never turboed from the factory.


Here's a thought, is it possible that a wire is getting pinched when the hood is closed, creating a short, and killing the ignition or fuel pump? HTH. -Jim


That's what he originally thought was going on so then he rewired the fuel line and it didn't help. It's decently modified. Pretty much everything under the hood is after market. It's supposed to get almost 400 hp. We can't get it to that point because it doesn't stay running long enough to have fun with it. He is also a mechanic but this one seems to be stumping him

1 out of 1 people think this is helpful.

Since it takes a few minutes for it to quit (I just reread your post) I'm still thinking something is getting hot and shutting down. Have you tried spraying starting fluid down the throttle body when it quits? That'll narrow it down to a fuel or ignition problem. If it'll run on the starting fluid it's a fuel problem. If not, it's an ignition problem. HTH. -Jim


He knows it's a fuel problem

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