95 4.6l shudder and engine trouble

[Thunderwagon]

Sorry for the length: OK my 170K baby has been coughing, shuddering, stalling and backfiring really bad, recently. The shuddering has been growing for quite some time. As has the hesitation and stalling. My odometer has been acting up for years (just delayed fixing it) - my recent autozone readout of errors showed: P0500 - Speed sensor malfunction (no surpirse), P0443 Evap Emis. Control System Purge Valve Fault, P1400 & P1407 Auxiliary controls - for the O2 sensors... This after I have changed the spark plugs and fuel filter. The wires, plugs MAF and tranny fluid were all changed right around 120K. It has always required premium fuel to run without bucking...before going to the dealer - anyone have some recommendations?

[RickwithaTbird]

how long did you use premium fuel, and when did you stop using it. They say that if you run high octane fuel for a long time, and then go to lower octane fuel, the car will have such symptoms. Apparently youve got other issues, but maybe running premium fuel again will help a little.

[RickwithaTbird]

and oh yeah.. dont worry about the length, that was pretty short actually. I especially write long posts.

[Thunderwagon]

I have been consistently using premium for the past 100K miles, never stopped - and actually if I using anything other than Shell (expenisve) premium, it acts even worse - seperate and apart from the above problems.

[J_ROC812004]

yes he does like to write long ones lol

[overl0rd]

there is a pin/connector on the fenderwell ommonly know as the octane pin, a dagnostic helper that retards the timing when pulled. if memory serves me right its on the right side of the engine bay. try pulling it and seeing how it runs.

[RickwithaTbird]

Ive never heard of this pin, and Im also no car expert, but that just sounds really fishy to me. Plus your name kinda creeps me out too. I personally wouldnt take that advice.

[J_ROC812004]

well rick i have never heard of it either but u can never out rule anything. You should always take something into consideration and if anything (your not sure) just study up on it before u do anything

[compewterman]

This shuddering is it all the time.. or mainly during first startup and acelleration? As far as octane I have only and will only use 87 But I also use the occasional SeaFoam in the tank before fillup.....mainly when its about empty... that will clean up all the carbon deposits in the intake and such. Believe me it works. These 4.6 v8's are designed to run on reg unleaded. go to TCCoA forums and read tech tips... you will see what I mean about the 87 octane. Higher octane tends to burn more slowly and leave carbon deposits. My bird had bad acceleration and when I started it ....even in park it would cough and never reach above 2.5 - 3k rpms. The problem ended up being the MAF sensor... I had cleaned it thourghly but that didnt help... when changed out.. my bird runs as if it was new again... (87 octane) Hope this helps some

95 T-Bird LX
92,000 miles
4.6 V8
all still stock

[RickwithaTbird]

Originally Posted by J_ROC812004

and if anything (your not sure) just study up on it before u do anything

that was basically the idea I was trying to get across. Its just that anybody could come in here and say, "yea, unscrew the white coolant drain valve on top of the engine, then start your car, and see how that goes"... you know? Thats why I made sure to say im no expert. Im not accusing him of trying to mess the car up, just giving my 2 cents in case it actually was fishy. of course however, I still dont know, and to me its a 50/50 whether is valid information or not. No offense over10rd, I just dont know you yet.

[Thunderwagon]

Understood. Thanks. I've used seafoam in the past and it works well. I've had the tranny fluid changed (it was time) and tried disconnecting the MAF as a test - didn't help. Its in for diagnostics right now -though expecting a plugged EGR or bad EGR pressure valve, after conversation with mechanic. Will let you know...

[Thunderwagon]

OK, diagnostic says that a misfire in cylinder 5 has started all this. Changed the spark plug wires - viola - no more shudder, misfire, backfire. Also running seafoam through as they pointed out a high degree of carbonization. attempted to sell a whole EGR set-up. Now if I can jsut figure out how to reset the engine light - and no leaving the battery unplugged for X amount of time doesn't do it. Any suggestions?
Thanks