serious engine issue, everyone please help

[dsm4444]

Ok I have a surging issue with my 95 non-turbo eagle talon. Whenever i hit about 3,000 rpm to 3,800 it freaks and surges. The weird thing is, is that it only does it when my engine is completly warmed up. Its not overheating because my temp guage still reads fine. I've recently taken it into a shop and they did a complete scan of the ecu and everything seemed fine they said. I asked if it might be my 02 sensors and they said they were "slow" but still functioning. They told me to get a new coil pack and plug cables, so i did. Didn't help anything. I've also replaced the alternator and belts and checked out my egr valve and everything seemed fine. I say the egr because last time i had this problem the shop said it was my egr and fixed it, but now its back and i'm told surges can come from anywhere. I've put a lot of money into trying to fix this and i'm running out. Please throw out any ideas at all. Ill try anything!

 

[TwoLiterLaser]

...it freaks and surges...

What exaclty do you mean, please be more specific.

 

[dsm4444]

It feels like im hitting big gusts of wind while im driving. Thats how bad the surges are. Like my ecu is trying to kill my engine but only when i am moving at 3 grand to 4 grand. It idles perfectly and revs through all the rpms fine. Its when im moving. No one can help me. I just paid 80 bucks for a guy at a shop to hook up and computer to it and tell me my sensors were fine just slow oxygen sensors and then they drove it and came back with a "wow that sucks to be you" expression on their face and said it had to be the coil pack or the wires for the spark plugs. I replaced it all and nothing benefited from this.

 

[TwoLiterLaser]

How many miles on the engine, what type of fuel have you been using, have you done any internal work on the engine. What mods do you currently have. Automatic or manual?

 

[dsm4444]

105k on the engine. no internal work done. magnaflow cat back with high flow obx cat and obx headers. Then just a cold air intake. I use just regular gas at shell or mobil 1. Its a manual.

 

[95TalonOwner]

Might need a new MAP sensor. It's on the top left side of the intake manifold.

 

[TwoLiterLaser]

A MAP sensor should through a CEL. What exact gasoline, base 87 or do you use premium 94. I need to know if you use premium a LOT.

 

[95TalonOwner]

There is no reason for him to use premium because he is non turbo.

 

[TwoLiterLaser]

I agree; but he may have been using it regardless. You cannot know what someone else does just because they should not neccessarily do something. When you begin to assume things then you make mistakes and overlook the answer to your question. If he has been running on premium for a good amount of time then he could have carbon build-up.

 

[da_reeseboy]

Have you recently done any work? It doesn't matter how small or insignificant it is, this might help in figuring it out. Also, does it surge under heavy throttle, mid throttle, light throttle, or all of the above?

- Jesse

 

[hopwoodp]

It may have something to do with your mas airflow sensor. I had something similar to that happen a few years back. I messed it up by getting it wet. Don't ask why.

What is your fuel mileage like? What are the conditions of your spark plugs? How about ignition timing? Try to let us know these conditions and we'll go from there.

 

[95TalonOwner]

We don't have Mass Air flow Sensors, only Manifold Absolute Pressure sensors on 2gnt's.

 

[dsm4444]

i have never heard of or had any issues that i know of with an MAS

 

[dsm4444]

o and my plugs are burning perfectly, gas mileage has always sucked. Probably about 18 mpg. Im not sure of the ignition timing, and it surges in heavy mid and light throttle. as long as its in the three thousand rpm range

 

[dsm4444]

And lastly i've never used premmium gas. Too expensive......

 

[95TalonOwner]

Gas mileage is most likely related to a bad o2 sensor.

 

[TwoLiterLaser]

MAS, MAP my bad. Either way a dying MAP sensor with put out a CEL. How often you do oil changes?

 

[hopwoodp]

Ok, did you do any work to your car before any of this happened?

 

[dsm4444]

not really. The only thing i've really done is install the new exhaust system and that was a month ago. And i do oil changes every 2500 miles. The only thing i can think of is that since i have this "high flow cat" (which is actually a straight through) makes my second o2 bad. The weird thing is, is it never did this when i first installed the exhaust. and why would it only do this when its hot?

 

[95TalonOwner]

The only thing the second o2 sensor does is turn the light on when your cat is bad. Mine has been on forever because I have no car and am lazy and haven't got around to getting an o2 simulator.

 

[TwoLiterLaser]

The OBD-II system changes fuel trims based on readings from both O2 sensors. It is not there only for a "bad cat sensor".

You stated that the mechanics told you your O2 sensors were "slow"? What did they mean by "slow"?

 

[dsm4444]

i have no idea. They just said the sensors were slow and not to worry about them.

 

[DJYoshaBYD]

Try actually changing your spark plugs.... Check ignition timing... What about fuel? Have you done a fuel pressure test? Maybe you have a bad fuel pressure regulator... if its not spark, then its probably fuel..... Also check for leaks in the throttle body or loose vac lines...

Since you have already changed a bunch of spark stuff, then move to fuel... check (again) or replace O2 sensors, fuel pressure, fuel pressure regulator, etc... maybe a bad fuel filter? just start tracing the problem... My first test would be to hook up a fuel pressure gauge and check that out... If its out of spec, then your fuel pump might be bad..

(Not going to say "just my .02" because its played out by everyone..

 

[Locke]

The OBD-II system changes fuel trims based on readings from both O2 sensors. It is not there only for a "bad cat sensor".

You stated that the mechanics told you your O2 sensors were "slow"? What did they mean by "slow"?

The OBD-II spec is to have the downstream o2 monitor the effectiveness of the catalytic converter. Some vehicles may go beyond this, and actually use it to adjust fuel trims. The 420a he has does not use the downstream o2 for anything but monitoring the cat.

 

[hopwoodp]

Is your fuel filter or injectors clogged?