I've read a lot of the posts, but still am not sure which way to go.

I have a 1997 Aerostar AWD with 132k miles. I've been struggling to fix a problem with the engine for about six months now. The problem is a miss at idle and light throttle. Full throttle seems to be ok. The engine service light comes on and my code reader says "cyl 5 misfire".

I replaced the plugs a while back and that fixed a bucking problem I had whenever I lugged the engine going up a hill on the highway. The idle miss started sometime after that. I've tried different kinds of plugs, but the idle miss is still there. The plugs I tried are BOSCH SUPER R6 482 and AUTOLITE DOUBLE PLATINUM APP 103.

I replaced the plug wires and the idle miss seemed to go away for a couple days, and then came back again. I used the cheapo brand DURALAST wires from Autozone. I guess this is a no-no, but they were too tempting. I just replaced the coil ($87!!). No luck. I didn't really think it would help, but I'm running out of options. I have purchase an EGR valve, but I can't get the old one off. The threaded tube on the underside will not come loose. I don't think this is the problem anyway, because the problem seems to be specifically with cylinder 5. If using the cheap plug wires is the problem, wouldn't it tend to miss at full throttle too?

I've read some posts that say this could be a cracked head. I think it does use a little anti-freeze, but I can't see any steam comming from the exaust.

Anybody got any ideas? I'm stumped.

 

Well, since the duralast wires fixed it or a whiles, I would suggest switching to motorcraft or autolite wires and hope that the plugs have not fouled in the meantime. Decarbon the engine with your favorite treatment, I use Seafoam, everyone has there preference, and they all seem to work.

It probably is missing at higher RPM, but it is hard to detect a miss as RPMs increase. I'm thinking fouled plugs and/or faulty wires. Another good plug to use is Denso Iridium, can't remember the part number I had pulled up. However, go with Autolite double platinums again, they are cheaper. When you check the plugs, check compression on cyl#5 and see if compression is low. If you have a slow loss of antifreeze, I don't think it is the head unless it has been allowed to overheat.

 

generic code P0305 can be caused by more than just ignition problems...

check injector...dirty, sticking, weak coil, poor spray pattern
switch 2 injectors....if trouble follows injector, pull all and have professionally cleaned and volume spray pattern tested...volumes must be within 10%, <5% tolerance is best
can try in fuel tank cleaner first as quick and dirty fix...use only Gumout Regane or Chevron Techron Concentrate 20oz...full can in 10 gal. or less fuel....may take 2 treatments....will not work in all circumstances such as damaged injector

check for vacuum leak around cyl 5 intake manifold and plenum...any unmetered air intake will cause 1 cyl. to be lean=misfire...pinpoint spray throttle body cleaner with spray tube at intake manifold and plenum seams....increase in rpm=leak found.....tighten all manifold and plenum bolts even if no leak found....they loosen over time on Ford V6s

sticking intake or exhaust valve from dirty or bent stem, carbon chunk stuck under valve face, fuel deposit buildup on valve tulip backside affecting cyl. fill, cracked valve seat, broken compression ring....some of these may not apply to your symtoms....do compression and leak down tests

stick with the Autolite double plats. for long plug life...autolite may be discontinuing them...so next best is the Extreme Performance Iridium center elect. platinum side electrode.

 

Actually, the Denso Iridiums work very well, Toyota refers the them as a 'Lifetime Plug' though I would not leave them in there for more than 100,000 miles. They can still foul or get deposits. I can't remember the correct part#, but it is in one of my other posts here, could do a search for it.

 

Thanks for the info. I'm going to try some of the things you suggested. I'm preparing myself for the possibility of having to remove the heads, but I hope one of these other solutions will fix the problem before I go that far. Thanks.

 

I've have already installed the two different sets of new plugs and the problem didn't seem to change. None of the plugs I took out looked wet, carboned or abnormal in any way. I think I will try the Denso plugs for what sounds like better performance. I think the plug wires could be a possibility and I'll try to decarbon the engine and check compression.

As far as replacing the Duralast wires, I just want to believe that they are ok wires. They appear to be of good quality and designed specifically for the 4 liter. I know you usually get what you pay for, but what usually goes wrong with these off brand wires? Thanks.

 

Bad wires will have weak insulation that allow the spark to jump to the nearest metal part, instead of the spark plug gap as it should.

 

Yeah, in this case it is more important to have good wires, and to make sure they are properly secured so that they don't touch each other or any metal parts in the engine compartment. If your plastic seperators are broken, I suggest you buy new ones. I would get new Autolite or Motorcraft wires and see what happens. Unless you go to the Ford dealer, these may have to be ordered in.

 

I was thinking about this Ford Aerostar ignition system and remembered that two plugs fire in series (and at the same time) off of one coil. This makes high quality wires very important.

Each plug has an average gap of .054 inch. Because there are two plugs in series per coil, the spark must jump both gaps at once. Multiply the gap by two, and the spark must jump a total gap of .108 inch to complete the series circuit. The VOLTAGE for a spark to jump both gaps, in series and at the same time, must be VERY high. To prevent shorting, the wires must be thicker and made of better insulating materials than a wire used for a single plug per coil system.

Also, if the spark shorts through one wire's insulation to the engine, the circuit is still completed through the other spark plug and that cylinder will still fire. That would explain how one cylinder can lose spark, while the other still functions.

I think Cylinder #5 has the longest wire going to it. If the wires are of poor quality, it would make sense that a problem would show up on that cylinder first.

 

Aerostar1, you fool!!! Anyone with half a brain knows there are coil paks laying all over the junkyards!
How do I know this?? I did what you did. I was convinced my coilpak was bad and that I was a troubleshooting genius, I ran over to Autozone and plunked down my 86. for a shiny new made in Italy coil pak. Naturally, this was not my misfire problem.
I decided that maybe the EDIS module was bad, but this time my half a brain kicked in and I went to the all ford junkyard.
They said help yourself, ten bucks. That's when I discovered there were coil paks all over the plce. There were no late model aeros, but several rangers and explorers that use the same part numbers. The engine tops were stripped out, but there they were, coil paks everywhere.
Just thought I would share the pain. 86 bucks, ouch!
The EDIS didnt help either.
You should follow the advice to do the compression test.
coldgeorge

 

I had forgotten about my $87 down-the-rat-hole, that is until now! I guess at least we didn't pay a mechanic to install it too - probably would have been $150+. The mechanic might have been able to check the original one for about $30 though. I think in this case the Do-it-yourself route is not saving me any money. Just think how many Peanut Buster Parfaits $86 could have bought....28.

I'll check the compression next. Thanks.

 

aero1,
may not have been such a deep rat hole....sometimes using old junke yard electrical parts that have set out in weather and have an unknown life history prior is just asking for more headaches when one is troubleshooting an intermittent difficult to locate problem....

these EDIS coil packs cook like stuck in toaster black toast under the hood of an Aero....all the testing in the world is not guarenteed to catch an intermittent coil pack.....

 

I think I remember reading the Ford manual for the aerostar and it said to use different plugs on each side of the engine. By different, I mean platinum on one side versus double platinum on the other. Has anybody experimented with that? I will look it up in the manual tomorrow and will quote exactly what the manual says.

 

only in factory installed plugs...required by EDIS coil pack system for long plug life

bean counter NOT Better Idea

crazy mess to make sure plugs after inspection went back in correct bank

not available aftermarket even from Ford dealers FoMoCo or Motorcraft....only double plats from them

 

> I used the cheapo brand DURALAST wires from Autozone.

I returned a set for when I tested them with an OHM meter, they were worse then the 4 year old Ford OEM wires I was replacing.

Considering how hot any van, especially an Aerostar, gets under the hood I would not skimp on wires or plugs. In this case you can not lose using OEM parts, even though they are more expensive.

You need the highest quality PP plugs available.