Intermittent Misfire

[Steve Cronk]

Hey all. I am new here and I have been having an intermittent misfire problem with my 95 GT. So far I have had quite a bit of work done to my car this year, about $5000 worth. This problem started about 2 weeks after I replaced the fuel pump in July. When it happened my code reader gave me the code for the Air Temp Sensor so I replaced it and the car ran fine for a week then it started happening again. I am now getting a code 311 and 314 which is the Thermactic Air System. The smog pump was removed by the last owner and I have been over all the vacuum lines and ensured all have been plugged, no leaks. I drive about 20 miles to work and in the morning with no problems. I make it home from work with no problems but if I go anywhere else it starts acting up. The car chokes down and is flooding out. If I can get the rpm's up it runs smooth for a few seconds then you can hear the misfire for a second or two then smooths out, then misfires, smooths out and so on. At low rpm's it chokes down and dies. It is acting like something electrical is heating up and causing this. I have replaced the coil with a StreetFire, the Ignition Control module and the Relay Control module. I replaced the fuel strainer and fuel filter when I replaced the pump and also again in October. I have also replaced the plugs and wires since this started. The distributor was replaced in April with a stock replacement but I want to go with a MSD StreetFire soon. The cap and button were also replaced with a MSD. Any ideas? This is driving me crazy! Any and all help is greatly appreciated.

 

[toyman]

Ever cleaned the MAF sensor? Probably the first thing to do and check back.

 

[Steve Cronk]

I was finally able to take the time and clean the MAF. After running the KOER test again I am still getting the 314 and 311 and yesterday afternoon when I took my daughter to work it acted up again. It seems like something is heating up and faulting out. Any more ideas?

 

[94mustangcobra]

My aeromotive FPR gave out on me one time completely. I couldn't even start it without the pedal to the floor. The way i finally discovered it after chasing all ignition problems was i noticed my under hood fuel pressure gauge would automatically drop to zero psi after the fuel pumps kicked off instead of holding around 40 psi. I know your saying something seems to be heat soaking and causing a malfunction but when you bring the RPMs up, the car cleans up, like it's loading up on fuel maybe? what's your spark plugs look like after you've changed them? black and sooty or white?

 

[toyman]

I couldn't even start it without the pedal to the floor.[/quote

I couldn't even start it without the pedal to the floor.

The engine can never be started with the pedal to the floor. That is a "clear flood" operation that shuts off the injectors when the engine is being cranked. These aren't like carbed systems.

 

[toyman]

If the distributor was replaced with a reman unit your problem could be the PIP (hall effect sensor). This is becoming a common failure item and often the reman units pass only to fail on the PIP shortly thereafter. The best distributor is a stock one or a new Richporter.

 

[94mustangcobra]

i wish i had a video to prove you wrong but yes i matted the pedal and cranked it and it would start but the minute i let off the gas it would die.

 

[Hef5.0weisen]

No expert here....but are all of the emissions gadgets removed? I thought if it all was removed, particularly the EGR, you needed a chip or some method if turning it off in the computer....or it would load up.

I think I saw that in these forums a few times......

Good Luck

 

[toyman]

i wish i had a video to prove you wrong but yes i matted the pedal and cranked it and it would start but the minute i let off the gas it would die.

Here's what I'm thinking happens. As flooring the pedal shuts off the injectors and unburned fuel will initially ignite (start momentarily). When you release the pedal the injectors start to fire. However, if the fuel pressure drops off immediately the engine will die as you described.

 

[94mustangcobra]

ok i rechecked myself and to change my story........

it must've started and then i had to floor it to keep it alive....

my car wouldn't start with the pedal floored on initial start-up.

you were right, now i'm backpedalling but i learned something...