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Old 04-28-2013, 10:20 PM   #1
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Location: springfield, IL
What I Drive: 2002 yolk;) zx3

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cylinder 4 misfire, tried everything (almost)

This is - technically - a duplicate post, but I wanted to get some additional exposure so I posted this in new tread.

My 2002 zx3 is having issues and "experts" have replaced bunch of parts (problems started almost 2 years ago and got progressively worse, now it really stutters almost every ride). Problem code is always P0304 (not always showing despite of noticeable miss). 1st "fix" was when I turned it in to do timing belt (~120K miles), asked them to check for the problem - really acceptable at the time but I did now want to do timing and water pump only to junk the car little while later. Could not find nothing, actually suggested replacing the MAF at ridiculous price (so I did it myself - had connector kinda cracked so OK to swap it). Car ran fine for a month or two and then issue again. Did fuel filter (this replacement might had preceded the whole problem actually), plugs, wires and even coil (ouch, gets pricey). Did also egr/dpfe sensor (had that at almost new car, similar effects while driving but not across the whole range of speed/rpm, cleaned up egr valve). Problem continued. And Cel is always P0304 - cylinder 4 misfire. Pulled injectors, tested all - seemed ok, switched 1 and 4 around. No change. Damn. Took it back to the same shop and asked for diagnostics - compression, scanner etc (whatever they had, small/medium shop, not a Ford dealer service center). They diag - injectors (right) and intake manifold gasket. Really did not like injectors idea (I had told them about all test/replacements/swaps) but I caved in. After return the car ran fine for like 2 weeks and then again the problem. Took it back to ask for warranty job. Dude took it for a test drive with me in passenger seat. Man, this fool tried to race it on city streets though the way he operated clutch made me regret letting him behind the wheel. Not only this but moron did not disengage the park brake, rear drums were smoking when he dropped me off. Told the fool to fix brakes he did. During the ride I did not feel much misfire but it's likely that if you push it like that it's really hard to notice it. After return the car was no better and all that after spending quite a bit of money (what I really hate is how difficult is to know/account for what was really done, forgot to ask for compression test readout so this is partially my own mistake). Time passed and the problem got even worse. It never stalled on me, idle is OK (not great) but driving feels like going against hurricane force gusts, acceleration suffers, fuel economy is no different from what it was. I replaced the battery (original, it was time anyway, winter forced me to), problems did not go away, my radio still goes nuts at times - I don't think this is related though. Opened ECU compartment, unplugged wires and plugged it back in, replaced fuel filter (again), fuel pump - hard to get to (will do only if have to). After driving home from work got check engine blinking, crap. Trying to gun it while it sputters does not do much. Replaced ignition coil pigtail (mid winter job, small radioshack iron - solder barely wanted to flow, did not expect that). Same issue on the test drive. Took it to another shop, asked for another diagnostics, same results - dude "drove the snot out of it", 40 miles but could not find a problem, watered my engine bad enough that spark plugs rusted. My car was having all the problems but now it stank with cigarettes. I lost all faith in mechanics (and their ability to conduct proper diagnostics). Bought an android tablet and Torque Pro app, cool - now I could run diagnostics the shop did not do/know how to interpret. Neither did I - information overload, none of data/observed issues seems unique to attribute to one thing. All I knew was that fuel pressure seems ok (it varies - never a straight line but it's not low), intake manifold pressure seems fine, fuel trim does not seem OK (long term seems to vary more than short, both run high - lean condition). O2 signal seems odd - pre cat one not always have a jumpy line (should it?) and the post cat is not always high (and will dive when missing, fuel trims will do strange things as well). Old man at the last shop did not like spark cables (Bosh) - got another replacements and motorcraft coil (autozone one had some strange resistance reading on the flat side of contacts - I could not keep it stable). Wanted to inspect the intake manifold myself so got gaskets as well. Took the thing off, checked fuel rail for crap (that would end up in the whole for injector 4 and starve the cylinder) - all clear. PCV hose kept me from taking the whole thing out of engine bay (could not disconnect it, did not wont to cut - had no spare). Cleaned up intake manifold inside, cleaned up idle air valve. Tested injector 4 wire harness - 0 resistance regardless of bending the rest of harness, did not take it completely apart - too much pain. Got a cheap endoscopic usb camera, looked int cylinders (hard to get to for real check) and intake valves. Put thing together (damn knock sensor cable/plug, what a pain). Car did the usual on the way from work. Now I'm looking for a car but really stuff is expensive, even more complicated (future repairs will be killer), too much crap but lacking substance. And colors suck (gray or silver, maybe red). And gas mileage - no progress. Stick hard to get (sure they want these future repairs). I like to keep it but it getting tough.
Now, there are some other common things with your post. Noticed recently that I could induce sputtering when playing with fuel pressure sensor (and found that I broke the clip so it won't latch securely, put zip tie to lock it in place). Then I noticed that it's actually not the FPS pigtail but the way it rocks the rest of the engine harness that causes the problems. I could push the injector wire cage/rail right above the 1st cylinder to trigger the issue. Then I pressed the plastic rail against fuel rain (so it stayed in place) and worked on the harness from other side. I don't think the issue is before the main connector next to firewall (going from ECU, right below evap(?)). What it appears is that the problem spot is at junction of main harness and FPS lead/pigtail. This will be my last thing to check replace before giving in. I hope that they have some crashed Focus at nearby junkyard (spent enough money not to go all out for replacement). If I can't source it cheaply I'll just open up the original harness and see what's in there.
Anyone has a suggestion, something that I (and bunch of mechanics missed)?
BTW, does anyone know where the knock sensor plug attaches to (it has a plastic fastener that I could not find spot for - it's hard to get to as well)?

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