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Ford Focus Fuel System problems...HELP!

I don’t know what to do and my mechanic has thrown in the towel! Help!

My 2003 Ford Focus ZX5 which has been faithfully maintained and serviced since purchase started sputtering and stalling when the engine is warmed up. It started a month ago and has been in the shop 4 times now.

Computer diagnostics indicate “misfire” and so far we have replaced the pcv valve, fuel filter, spark plugs and wires, ignition coil as well as flushed and cleaned the gas tank and fuel injectors. The problems only happen when the engine is warm.

What else could be wrong?

My first suspect would be the CTS sensor that monitors the coolant temperature for the ECU is bad. This is not the same sensor that is used for the dash temperature gauge. If the sensor is bad it may be telling the ECU the engine never warms up even though it has. The sensor is supposed to resistance as the engine changes temperature. Other areas to check include a cold start valve, and EGR valve.

What exactly is the misfire code? It will be either P0300 (random/multiple cylinder) or P030x where x is the specific cylinder. If it is specific to one cylinder, have that cylinder’s fuel injector swapped to another cylinder and see if the misfire follows.

Have your shop check the compression and do a leakdown test to look for any sign of valve problems.

Does it do it all of the time or randomly?

I believe it was PO300. Got fed up and took it to the dealership where I know someone. It does appear to be running hot. Isn’t random because since the problem started it happens whenever the engine warms up. Usually after a few miles the engine light comes on. Gonna share both thought with the shop now. Thanks!!!

Well, with that description I’d start with Cougar’s suggestions - especially the coolant temp sensor and EGR - if it sticks open it will act like a vacuum leak.

But I’d also say check the compression any time there is an elusive misfire.

Also double check the codes to make sure, and esp. report if there is more than just the misfire code.

You need a new mechanic that can properly diagnose the situation, If you don’t mind throwing dollars at parts I would replace the fuel pump.

I discussed your suggestions with the dealership service manager (lucky he’s the guy I know!) and he agrees especially since he says he would have done just what my local mechanic did to track down the problem. I’ll share the results when I hear but thanks to you both for the help.

Waterboy - Given that the dealership would have followed the exact same process in diagnosing the problem, I don’t feel I need to get a new mechanic. In fact, I have much more respect for him for saying that he didn’t know if he could find the problem and not charging me for trying. He followed the computer diagnostics and traced it as far as he could. Honesty counts in car repair and if I could afford to just throw dollars at parts then I’d go buy a new car. Still, thanks for giving my conundrum some thought…

I have a 2001 Focus and I had a recall notice sent me some time back in regards to the fuel pump as my car was bogging down. Got it taken care of per the recall and now it runs fine. I’d check to see what if any recalls are out there in regards to your 2003 model.