1990 5.0 rough start - Mustang Evolution

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Old 03-15-2016, 07:53 PM   #1
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1990 5.0 rough start

My 90 5.0 starts perfectly fine when cold but has a rough start issue when the engine is hot the gas needle drops from full to about half a tank but comes back up after a while and white smoke appears right after the start upbut does not show up again after untill its started again i dont see any mixture between the coolant and oil if anyone can help out would br appiciated
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Old 03-16-2016, 12:48 AM   #2
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What does the white smoke smell like?
Does it smell sweet like coolant?
Or does it smell like raw fuel?
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Old 03-16-2016, 04:29 AM   #3
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What does the white smoke smell like?
Does it smell sweet like coolant?
Or does it smell like raw fuel?
Does not smell like coolant but does smell like its running rich. I did have a code for a O2 sensor i swaped it but it still shows up says voltage is low system running lean
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Old 03-16-2016, 04:48 AM   #4
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What does the white smoke smell like?
Does it smell sweet like coolant?
Or does it smell like raw fuel?
It smells like fuel not sweet like coolant i looked up on it as i mentioned before i have the cts thats probably bad (code 21) which i heard can be problematic for hot starts causing the engine to use up to much fuel. Anyways code is popping up might as well change it to see if it helps.
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Old 03-16-2016, 11:17 AM   #5
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Does not smell like coolant but does smell like its running rich. I did have a code for a O2 sensor i swaped it but it still shows up says voltage is low system running lean
Make sure that there are no vacuum leaks, or noticeable exhaust leaks. They can both cause the condition that you just described.
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Old 03-16-2016, 12:44 PM   #6
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Thanks ill check and see and let you know what happens
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Old 03-16-2016, 10:20 PM   #7
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Originally Posted by 5Ohhguy View Post
It smells like fuel not sweet like coolant i looked up on it as i mentioned before i have the cts thats probably bad (code 21) which i heard can be problematic for hot starts causing the engine to use up to much fuel. Anyways code is popping up might as well change it to see if it helps.
Was the engine cold or was coolant temp below 50° when you ran the koeo test and/or was coolant temp below 160°,when you ran the koer test??
If the answer is yes,that's what caused code 21 to be set.
If no,test the ECT sensor while the engine is cold then retest it when the coolant temp is above 160°.If the ohms value for a given temp matches the chart below,the ECT sensor is OK & you'll need to test the two ECT sensor wires for continuity, between the sensor & the 60 pin connector.

When you say rough starts,I assume you mean its a hot no start issue??
When the hot no start occurs, hold the gas pedal to the floor while cranking the engine.Does it start now??
If yes,youve got a leaking fuel pressure regulator,leaking injector or a weak fuel pump.
If no,cycle the key on/off 5-6 times then try starting it.If it starts,the fuel pump is weak.
If these tests don't cause it to start,pull the spout plug then try starting it.If it starts,the pip sensor is going bad.A defective tfi module will also cause a hot no start.
A lean O2 sensor code can be caused by numerous things.A vacuum leak is the main cause,but you can click on the link below to see all of the possible causes.
As far as your car smelling rich goes,when the o2 sensor reads lean,that causes the ecm to (falsely) richen the AF mixture to bring Afr back to normal.
Be sure to check your grounds too.
1) (-) battery cable to block
2) ground strap between driver cylinder head & firewall
3) EEC ground next to the windshield washer reservoir.Check the wire & the round black connecter too.
Here is a link that details the different strategies that occur during all running modes.


Fuel Injection Technical Library » Strategies


O2 Sensor Codes 41/42/91/92 Troubleshooting
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