won't start when hot

SloMvr · 07-20-2007, 10:23 PM

I have an 89 injected 5.0 that I put into my 71 bronco. When it gets warmed up and I shut it off it will not restart. Turns over, has spark, 40 psi for the fuel pressure.The only way to get it restarted is to unplug the TFI module and plug it in while cranking the motor over. Changed the module and the coil and has not fixed it. need help

thunderchikn · 07-26-2007, 03:07 PM

you need to see if your losing injector pulse at the injectors. red being power,tan being negative pulse from the computer.doesnt necessarily mean the comp is bad,sounds like a connection at the module connection and your interupting it to get a signal back. to make short work of it use a test light to check for power on red with key on cranking,then check tan for negative pulse by reversing test lead on light(clip on positive batt terminal) and probe tan wire while cranking. then get back to me if you like and i'll try and walk you through with it if you want.

SloMvr · 07-31-2007, 11:52 AM

After hours of diagnosing, we ended up reworking all of the grounds and found the problem. The electric fan was on a keyed on and a thermostatic switch. So when the truck was cranking over at operating temperature the fan was running. When the fan was disconnected the truck started. We found out that the fan has a 19.2 amp draw when running and was robbing the ecm of the constant power it needed to fire the truck in the cranking position. We rewired the fan to the ignition switch on the terminal that was keyed on but off when cranking. It now starts every time. Once again I appreciate the help.

07-20-2007, 10:23 PM	#1 (permalink)
SloMvr Junior Member Join Date: Jul 2007 Location: phoenix az Posts: 2	won't start when hot I have an 89 injected 5.0 that I put into my 71 bronco. When it gets warmed up and I shut it off it will not restart. Turns over, has spark, 40 psi for the fuel pressure.The only way to get it restarted is to unplug the TFI module and plug it in while cranking the motor over. Changed the module and the coil and has not fixed it. need help

07-31-2007, 11:52 AM	#3 (permalink)
SloMvr Junior Member Join Date: Jul 2007 Location: phoenix az Posts: 2	Thank you for the help After hours of diagnosing, we ended up reworking all of the grounds and found the problem. The electric fan was on a keyed on and a thermostatic switch. So when the truck was cranking over at operating temperature the fan was running. When the fan was disconnected the truck started. We found out that the fan has a 19.2 amp draw when running and was robbing the ecm of the constant power it needed to fire the truck in the cranking position. We rewired the fan to the ignition switch on the terminal that was keyed on but off when cranking. It now starts every time. Once again I appreciate the help.

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07-26-2007, 03:07 PM	#2 (permalink)
thunderchikn Junior Member Join Date: Jul 2007 Posts: 10	you need to see if your losing injector pulse at the injectors. red being power,tan being negative pulse from the computer.doesnt necessarily mean the comp is bad,sounds like a connection at the module connection and your interupting it to get a signal back. to make short work of it use a test light to check for power on red with key on cranking,then check tan for negative pulse by reversing test lead on light(clip on positive batt terminal) and probe tan wire while cranking. then get back to me if you like and i'll try and walk you through with it if you want.