'96 Ford Windstar - P0304 misfire anomaly

Swap #4 coil with #5 and see if the code changes. Then swap #4 injector with #5 and see if the code changes. Check for vacuum leaks around #4 cylinder intake manifold gasket with either propane or carb cleaner and note any changes in RPM (checking fuel trims is better). Be careful checking vacuum leaks...it only takes about 2 weeks for your eyebrows to grow back. I'm sympathetic to your condition...I blew my knee out a couple of years ago...no surgery but 15 months in physiotherapy.

Can you feel the misfire? Sometimes on this engine a misfire can be felt at about 1200 to 1500 rpm and this could be one cylinder or several cylinders. The cause is the EGR passages in the intake get clogged. The way this system is designed (ford 3.8,4.2 nissan 2.4, 3.3 honda 2.2) is that there is a hole in each intake runner for the egr gas to mix into the combustion chamber and is designed to go to all cylinders equally. When several get stopped up then too much exhaust gas gets dumped into the open ports and will cause a misfire. Easy way to check would be to disconnect the vacuum supply to the egr valve and block off and drive and see if the misfire goes away. If it does then the ports are stopped up probably all but #4. You have to remove the upper intake to clean no chemical will clean. Hope this helps.

I'd agree, probably EGR passages blocked or possibly a sticky #4 injector . More likely EGR.

What year of windstars had all kinds of problems with the vaccum elaks from around the intake bolts? I think there's revised gaskets and procedures. As well the egr ports is quite a good possibility

I had a 1995 Winstar with the exact same problem. The injector was bad... I replaced all that you replaced new plugs, wires, coil pack with no luck. Hope this helps.

I do know if you have a #4 cyl misfire on those vans the exh manifold gasket leaks on them and gets the #4 plug wire boot hot and causes that code.

he already changed the plugs and wires

I too have an identical misfire code on cylinder 4 of my '97 3.8L Windstar (94k). The 'Check Engine' light started to burn steady about three months ago, but without any perceivable engine miss. Three weeks ago, the engine started intermittently 'stumbling' (misfiring), followed immediately by the light blinking. This would pass, and the engine would run smoothly again. I replaced the plugs, wires, coil pack, but the light came back on the next day and the intermittent misfire/blinking came back. I rechecked one new plug a couple days later and it showed some carbon build-up already. I did find a cracked vacuum connector on top of the upper intake, just downstream of the throttlebody. I wrapped rubber electrical tape around it, but that seems to have no affect on the misfire issue (maybe it fixed some other issue I didn't even know about! LOL). I did notice that the engine seems to stumble more frequently when it's raining or when the weather has been wet. Over a 3-day dry spell, the misfire went away. This seems to indicate an electrical issue rather than an EGR clog. Also, the EGR system operates most often during cold startup, doesn't it? This would suggest the EGR cylinder dilution issue shouldn't cause a misfire after the engine is hot. Maybe the EGR valve is malfuntioning? Anyway, I'd rather not rip off the plastic intake manifold unless I'm sure this will lead to a cure. Anyone?

No the EGR works when the engine is in closed loop so the engine would be hot not cold. A quick way to tell without pulling anything off is to disconnect the vacuum line to the EGR VALVE and see if the misfire goes away.

damp weather misfires normally point to an ignition system breaking down

Thanks for the posts..... Sorry about my EGR goof earlier, I was confusiong the EGR with GM AIR devices that kick on when the engine is starting up cold (yes, I know the Ford 3.8L doesn't have an AIR system!). The flashing light/stumble is a transient condition, so it has been impossible to actively check the OBDII codes or tinker with the #4 cylinder while it's actually missing. In fact, I don't think it's ever missed while idling. BTW: What tools and gaskets (kits?) are necessary to remove the upper intake manifold and replace it? Is cleaning the carbon from EGR ports a pretty straightforward process, or are there special techniques? When the light isn't blinking, the engine runs very smooth and strong.

*** UPDATE *** UPDATE *** UPDATE *** I finally broke down and went to a local dealership and had them do a diagnostic. Mostly because I can't afford to have this deteriorating condition destroy anything else or the VERY expensive catalytic convertor, AND they will apply the diagnostic fee towards labor charges should I decide to have them do the work. The following text is exactly what was printed on the invoice after the tech performed the diagnostic : "139716 PLUGGED EGR PORTS 1.50 EEC TEST, P1000, (P0304 ACCORDING TO CUST), PERFORM POWER BALANCE TEST, VERIFY MISSFIRE AT CYLINDER #4, FUEL/IGN SYS DIAG, ALL CHECKS OK, FIND EGR PORTS PLUGGED CAUSING MISSFIRE WHEN EGR FLOW IS COMMANDED (ALL PORTS PLUGGED EXCEPT #4, THIS CAUSES FULL EGR FLOW TO BE DIVERTED TO #4 CYLINDER INSTEAD OF BEING SPLIT AMONG ALL CYLINDERS EVENLY, THIS CAUSES MISSFIRE AT #4 CYLINDER). RECOMMEND REMOVAL OF UPPER INTAKE MANIFOLD AND CLEANING OF EGR PORTS, CUST DECLINED REPAIRS... ALSO RECOMMEND PERFORMING DE-CARB *(I.E. DE-CARBONIZING) ON ENGINE, RECOMMEND REPLACEMENT OF SPARK PLUG WIRES AND MOTORCRAFT PLUGS... CUST DECLINED ALL REPAIRS AT THIS TIME." One thing I have found out over time and through trusted sources is that some vehicles perform best witrh certain parts in some areas. For one the Ford does best on it's own ignition and electrical parts and shouldn't have cheaped out using Autolite products. As much as I most likely wont be going to the dealer for them I will be replacing the plugs and wires with MOTORCRAFT parts. Of course they tried to sell me an air filter, fuel filter in addition to the plugs and wires but I just replaced the fuel filter with a Fram, which hasn't ever given me any problems when it comes to filtration, and I can easily replace my own air filter and save a bunch of $$$ instead of paying $28.02 for it + labor! The fuel filter was double what I would pay at the local parts store too! I am going to consider replacing the EGR unit, but that will also depend on the price seeing as how the dealer wants about $150 for it. My reasoning behind replacing the EGR now is that all too often I had the opportunity to replace a water pump, timing belt/chain, or the like when it was easily accessible and lamed out only to have to do all that fun labor all over again when that simple part failed not that much later. As they say ... "An ounce of prevention is worth a pound of cure!". The neat thing is that the Intake Gaskets are only $4.13 each! Needless to say I am going to most likely be doing the work myself providing a buddy of mine who has worked for Ford dealerships can assist OR I will be locating a mechanic locally through a Non-Profit organization that my sister has connections with. These mechanics provide quality work and give the NPO a discounted rate to assist them in bringing their program cars up to a dependable level of service so the new owners getting a car through the program get one that will serve them well. After I get the work completed I will give you all an update on the outcome. If I can give a positive recommendation in regards to the mechanic I will post it here as well. I firmly believe in promoting positive feedback and directing business to those who are honorable, trustworthy, and fair in price accordingly! I hope this update will give somebody a hand up and save you a good chunk of change!! And don't forget to post up any results you may have. Try to be as detailed as possible, especially if you have any variations of the problems I am having now as to better help the others that come after us. I more than welcome any questions you may have and will answer anything I can and dont hesitate to say I dont know whats what when I dont really know for sure. I also dont mind doing some research to lend a hand when I can. Thanks to each one of you for all of your input and comments.

Isn't this what I said at the beginning of this post...Autolite I think makes plugs for motorcraft and you don't need to change the egr valve. The valve itself very rarely fails the choice of course is yours.

Yes, the choice is mine and mine alone. I saw nothing in your original post that gave me any more assurance that your particular advice is/was any better than the next guy's. Posting up what was written on the dealer's repair invoice should only serve as a reinforcement of your advice and lend more credability to it. In regards to the EGR I have yet to pull it off and once I do I will have better information in which to decide to reinstall it, clean it, or replace it. AFAIK Motorcraft and Autolite are two separate companies and it again being my choice I have chosen Motorcraft products based on very trusted personal sources with real world experience that I can verify first hand. Even if these two separate brand names are under the same parent company they may very well have different processes/methods of manufacture and use different grades of materials/components. If they used the same stuff and made it the same exact way then why the need for two different names and one charge more/less than the other?! I thanked every one who posted for their input and once more I will thank you again.

I just read my post again and it tells you that the egr ports are clogged and all are clogged but #4...The SAME THING that ford told you.. I even explained how to check to see and I am 100% sure this is how the dealership came to this conclusion. I have the same factory scan tool that ford has so I know all about the power balance feature on this tool. Glad someone else figured it out for you. AS far as the plugs(Ford doesn't actually make the Motorcraft spark plugs, Autolite(owned by Honeywell) makes them. So buying OEM style Autolites is the same as buying Motorcraft spark plugs. NKG of Japan made the OEM sparkplugs for the 2003 MY 3.9 Liter LS and Thunderbird. Replacement sparkplugs are indeed Autolite) Look it up

I guess I should have been a bit more bold when I said "thank you" again and just asked you to please let it lie. Its great that the info you gave me is the same as what the dealer told me, but I chose to go to the dealer for my own personal reasons which I really do not care to discuss in this forum. THANK YOU again and have a really great day.