...Misfire detected on cylinder #5

That's the code my Aerostar is now throwing. A little while back it started behaving like it was misfiring at idle - shaking and running unevenly. It's harder to tell at speed, but it continues to run unevenly there as well.

It finally threw the code a little while ago, so I plugged in the reader and found it reporting P0305. I replaced the plugs and wires about 6 months ago, so my first thought was that one (on #5) had popped off either the plug or the coil pack. I dug into it last weekend with the van on the lift. I checked the wire connections on both ends - no sign of being unplugged. I pulled the coil end and verified that it ran the same with/without the wire plugged in. I also verified that there appears to be a healthy spark jumping the gap if it was held close.

I pulled the plug on #5, hoping it would prove to be fouled and fuel soaked from not sparking. That was not the case. There was no sign of fuel on the plug; it wasn't wet. In fact, the lead was almost a eggshell-white, rather than a normal condition brownish/tan color. I then pulled the neighboring #4 plug for a visual reference. That one was, in fact, a normal color.

So, I now have to believe that my misfire isn't ignition related. The signs (to me) point to a sparking plug but no or very little fuel, making in burn very lean. The only thing I can think of is a faulty injector. I tried running Seafoam in the fuel as an injector cleaner, but it has made no difference yet. I cleared the code, then drove it around hoping for the Seafoam to work or for the code to be thrown again.

Well, after abut 125 miles, the same P0305 code popped up again. It's the only code being thrown, so I have to believe that the issue is concentrated around #5 only.

So, does anyone have any insight as to what else I should try? Or am I looking at replacing a fuel injector for certain? I can't imagine that getting into access them is easy. I looked it up in a Haynes manual that I found in a junkyard - on the 4.0L, the upper intake has to be removed and the fuel rail is sandwiched in between that and the lower intake. I also found the general-purpose removal instructions that were posted last summer, but they didn't look like they referred to anything specific to working under the cowl of an Aerostar. Any advice on that? Any thoughts as to were I can get a reasonable price on injectors?

 

hope and pray it's the injector

may also be an air leak in intake manifold gasket for #5 runner
much more work

pulling the injectors and sending them in to a professional injector shop for cleaning and spray pattern testing is less costly than replacing with new or even rebuilts but takes about 1>2 weeks turnaround time. ordering rebuilds and having them on hand if far faster.

almost impossible to spray test for a leaking gasket on #5, it's buried.

several universal joints for 3/8
male torx head studs that have to be removed because of lack of room to lift plenum. believe it's an 8mm female torx socket.

check injector mount holes in aluminum fuel rail for corrosion, can cause sealing problems. use new O ring seals, the dealer ones are outrageously overpriced.

use the new upgrade 2 piece lower manifold seal if you have to go that route. holds seal far longer with all the shaking parts and small bolts on the 4L top intake end

 

Could it be a faulty spark plug?

 

I suppose, but that wouldn't account for why it had no fuel on it when I pulled it immediately after shutting the engine off. If the plug were faulty and the fuel injector behaving normally, then it should've been fouled with fuel and wet still. What I found was a dry, super-lean plug...

96_4wdr, what makes replacing the intake gasket (I assume you meant the lower manifold to block gasket) so much more work than replacing an injector, if I've already taken that much apart? I would think that if I've already burrowed in far enough to take the upper intake and fuel rail off, removing the lower intake would be incrimentally more effort. What I'd much rather avoid is digging in that far, putting in fresh injectors, put it all back together again, only to find I have to do it all over again for an intake gasket that I could've done when I was in there before. Again, that's how it appears to me, but since I've tried it yet, I may be missing something that's a glaring problem.

Can anyone direct me to a write-up that tells how to tackle this in an Aerostar (as opposed to a Ranger/Explorer)?

 

Ok, you have either a bad or plugged injector or an intake leak. Fixing the intake leak is the same amount of work as replacing the injector. The injector however is more expensive.

I would tear in an plan on replacing all the intake gaskets.

You first have to obviously remove anything that is in your way. I like to have ziplock bags and every time I remove a small part, put it and its bolts into the bag. If you have larger parts that do not fit in the bag, label the bag and just put the nuts and bolts in. For the most part the procedure is the same as a Ranger or Explorer, just that there is a little less room. But all the same stuff has to come off.

You can inspect the injectors closely to see if they have any obvious signs of problems. It is possible to bench test injectors. You connect them to a fuel source and then trigger them to fire. What you are looking for is the spray pattern, the amount of fuel that flows, and that there are no leaks. Make sure that you do not make any sparks while doing this. If in doubt, you can just replace the suspects. Injectors are not the cheapest parts to play guess with.

Additional notes in disassembly, label the injectors to the cylinder# they go to, it is always a good idea to put them back where they belong.

Also replace any old vacuum lines while you are in there. No point in not doing so, vacuum hose is cheap, and vacuum leaks are still on the suspect list even if only one cylinder has the miss.

 

Rick,

Check out this thread on replacing the intake manifold gaskets:

https://www.ford-trucks.com/forums/9...ke-gasket.html

I have some pictures here:

Picasa Web Albums - GCC - Aerostar

I did this a couple years ago, and it was actually easier than on my Mustang. On the Aerostar, you can actually get to the back of the manifold through the doghouse. On the Mustang, the back of the manifold is a few inches in front of the firewall, and you have to have small, but really strong hands to get at all the fasteners and brackets back there.

Along the way, you can service the injectors if necessary.

I recently had to clean out the injectors in the Mustang because it was stumbling badly after sitting for a long time; it was obviously not running on all 8. The plugs were old, so they had little white showing through, so that was not a good indication. I took off each injector and activated it with a 12v battery, and sprayed carb cleaner into the pintle long enough to flush out stuff from the inlet. In my case, it worked; after assembly, the engine ran great. But there were no obviously visible problems with any of them. Note that most of the work was to clean off all the crud on the intake so they do not fall into the engine.

 

No matter what..... the first thing to do is replace that #5 plug! It may be slightly cracked resulting in an intermittent misfire. Cheap to replace even if the problem is fuel related which yours does seem to be. Make sure the plug is seating fully onto the taper or the compression leak may cause misfire. I suggest engineers blue on the taper to make sure it seats properly, Maybe run a tap down if the taper does not contact the head.

If you had an air leak you would probably get a code , Fords throw this code p0171 174 quite easily although not so readily on our Aeros for some reason.

Swap plug wires between 4& 5 just to see if the code follows.

May well be the injector....... If you go in that deep I would put in a new one; but check the signal with a noid light first. Do you have EGR ? if so then this could also cause the lean misfire problem.

 

You can get injectors on ebay cheap..
You may have a vacuum leak as said above. I would snoop around with some propane to see if you can get it to run different..I did two of my 96's recently..So I can help with whatever you need. The stock intake system is flawed if you are going to mess with the injectors take the whole manifold off and redue with felpro gaskets and new valve cover gaskets..The intake bolts loosen up causing all kinds of problems. Both of mine were loose..The upper intake gaskets lose their seal..The injectors can be a bear to get off even with the intake on the bench never mind under the tunnel of doom. Injectors rarely go bad as a rule..Never had a bad one in 4 4.0l aero's or any car for that matter..Look for a vacuum leak..cyl no 5 is right near the IAC and the vacuum lines rear drivers side.
The intake job isn't a big deal if you are a mechanic and have the tools you need. If not it could be a challenge for sure. Its still fresh in my brain I could do a write up to save you the headaches.

Dick

 

Before you start, you should get a Haynes manual too, there are a lot of things that are supposed to be torqued to specs, nice to have the specs handy as well as have a teardown guide.

 

I'll write down all the needed torque's etc..I don't like those manuals much I have 3 of them...I use the ford cd.


Dick

 

Update: I got the gasket set in last week, so I dug into it over the weekend. It took the better part of Saturday and Sunday, but I finally pulled the lower intake out yesterday afternoon.

I didn't see any obvious signs of a gasket leak, either on the gasket, the intake or the head around the #5 port. But as it would be an air leak, I'm not sure I would see anything anyway. I decided that since I have it this far apart, I'd send the injectors out to be rebuilt, especially since I haven't ruled that out as the problem. So, those will go out this week, and if all goes well, I can reassemble it next weekend. I'm kind of hoping that they'll take longer than that to turn around - next weekend is supposed to be real nice weather-wise, and I'd hate to loose it stuck in the garage...

Another thought - since I have it this far apart and things are excessible, I thought it would be a good idea to replace the heater core lines, especially those that run under the cowl and back to the rear heater. But now I see that they are one-piece molded lines that are "T" shaped. I couldn't find replacements, even at Rock Auto. Is this a dealer-only item? Are they even still available through the dealer? I'm not crazy about dealer prices for something like this, but I'm also not crazy about having a hose go bad and not being able to fix it readily.

 

Pretty sure you would have to make your own lines..Injectors get tested and maybe cleaned don't get ripped off. Not much rebuilding in there..

 

Well, I finished putting the van back together over the weekend. New intake gaskets, cleaned out the injectors, put a fresh spark plug in #5. However, all of that was well and good, but didn't solve my problem. Not only do I still have a misfire code for #5, but also on #3 now.

I think had put too much weight on the fact that the #5 plug looked like it had been lean and missed the bigger picture. If just #5 continued to misfire, I'd be tempted to think that maybe a plug or wire was faulty. But with multiple misfires, that's less likely. So where does that leave me? Got fuel, got compression, so ignition? Maybe the coil pack? Is there any way that a vacuum leak could be mistaken by PCM as a misfire? I'm taking wild guess here now...

 

So you've tested for compression? A couple things that come to mind would include possibly a head that has cracked or a warped valve. This will cause a consistent misfire. In my brothers van, two cylinders were affected, but it caused misfire codes beyond the affected cylinders. Its possible you might have a similar issue where a misfire is creating enough shaking and uneven operation that it causes false codes on other cylinders.

Another idea does look at the ignition system again. You could have a weak coilpack or a faulty cam sensor that could cause a misfire.

 

On my 94 the heads were junk all cracked and the seats were pounded..No problems with any on my 96's though..Man I feel for you all that work and still the same crap.
Compression test... On the 94 the van turned over weird before it started due to some cyl not having propper comp..


Dick