Engine Help This Is Driving Me Nuts!!!!!!!!


Mar 5, 2011
Hello fellas,

I'm going nuts, this car is making me crazy. It does not want to run properly... to be more specific, when it's cold it doesnt GO when you press the gas, acts like it wants to die, hesitates horribly. ARRG!!! I need assistance! I'm to the point where I don't want to dump anymore money into it unless it fixes it! To give some background I have had this since it had 33,000 miles on it, it now has 140,000. I need a someone to point me in the right direction. I have replaced a bunch of stuff trying to narrow the search but so far unsuccessful.

This is what I have done:
Cleaned MAF
Cleaned IAC
Cleaned EGR
The three above all work properly. I believe, let me know if you think otherwise.

I have replaced:
All 8 Spark Plugs with Autolite Double Platinum Plugs (with the correct torque I have had issues with this)
Replaced all 8 coil Packs
Seafoamed it
Throttle Position sensor
Replaced All 4 Oxygen Sensors with new NGK's

All of the things I have replaced have improved performance but the issue is still there. I have had no LIGHT EVER it just runs like crap when its cold.

Could it be a DPFE Sensor??

Please Help!!!!!!!!!!!
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+1 on pulling and posting all DTC codes. Confirm that the check engine light comes on during key on lamp test.

Not a bad idea to post the model year of your Mustang.

How does it run when at normal operating temperature? How's the gas mileage (now compared to the past)? Does the motor burn oil or coolant?

How long has the problem been going on? What did the old spark plugs look like?

If an injector problem is suspected, consider an injector cleaning and flow test service such as injectorrx.com.

If you pull and plug the vacuum line to the EGR value does this improve performance?

Do you have an ODB2 scanner that can read operational data?
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The motor uses some oil (about 1 quart between changes)

It has never given a code ( check engine light works at key on)

I do not know what the old Spark plugs looked like (when one blew out the shop replaced all 8. They replaced them with Autolite Double Platinums they have 20,000 miles on them or so)

"If you pull and plug the vacuum line to the EGR value does this improve performance?"

I have not tried this. what would this be testing the EGR valve or the DPFE sensor or both??

I do not believe it's the injectors, it runs good once it gets going. To be honest I'm not sure. I do not know what a car runs like with dirty injectors.

It feels like the choke is stuck open on a carbed car. I don't know how else to describe it.
Double check that the fuel pressure vacuum intake reference line is connected and leak free. Double check there isn't any raw gas in the line.

Would be handy to know the long term fuel trim (LTFT) values at idle and under load when cold and warm. Also would help to know the PCM reported fuel pressure, IAT, and ECT values.
Burns has you on the right track! When there is an issue that doesn't throw a code it is always more frustrating to solve. It seems like if there was a egr flow issue or a vac leak it would throw a rich or lean code, nor would it run ok at operating temps. Sounds like the one thing you have not touched on fully is fuel pressure. FPDM may not be doing its job when cold, or the pump is going bad but, in my experience at least, they usually exhibit issues at any temp if not worse hot or just don't work. I like using a mechanical guage over PCM reporting. You can buy a guage cheap and there is a Schroeder valve on the fuel rail you can connect it to to check it at cold. If you have good pressure when the car is cold, running then the rail sensor like wmburns explained needs to be test next. As far as reading the cars fuel trims you will need a code scanner that is capable of reading live data, I know my SCT handheld does so your diablo sport may or may not as I have always used SCT programmers. If so you will need to hook up the programmer and select live data (it may be under, or named something different. Might have to consult the user guide as you will likely have to select the PIDs for them) once you start the data you can write down the average LTFT for the conditions wmburns asked for. There are also PIDs for the IAT and the ECT.