the 96-97 4L uses an EDIS waste spark system with series plugs.
if the problem were the coil pack or plug wire, would cause misfire on 5 and it's paired plug #1. the spark timing is totally controlled by the crank position sensor and the PCM. cam position sensor controls FI timing.

Ford DIS/EDIS "Waste Spark" Ignition System

not going to be easy to troubleshoot this intermittent.
may be intermittent short on injector lines 5 and now 3?

the wiring and connectors are getting long in the tooth in these Aeros, mine's 15 years old, starting to have corrosion problems in connectors. caused several gremlins for me.

if you have access to a pro. shop engine analyzer with the Ford package in it, can do a number of tests.
individual injector turn off and contribution/efficiency of each cylinder.
spark voltage, dwell and timing of each cyl. fuel inj. timing of each cyl.
notes and records every dropped ign spark, cyl miss or missed fuel injection.

does your CEL flash on/off when the engine misses. can use that as a troubleshooting tool as wires/components are wiggled.

try another new plug in #5. see if it displays the same lean condition.
may be worn intake cam lobe/lifter/push rod/rocker arm on #5 hole not allowing full air/fuel charge. the rocker arms on the 4L are not reliable due to poor oiling, the end holes wear out. seen worn broken off ends on the push rods also
engine will develop normal crank speed compression pressures on a cyl compression test but not getting enough air/fuel in at higher rpms for good combustion.

the 97 Aero is the first year to have the "lean burn" heads.

 

This is a coil pack ignition on 96 or later models. If the misfire occurs at idle speeds you can use a test light to watch the signal from the coil driver in the PCM, although as pointed out above a faulty coil or driver will show up in the paired cylinders, it looks like this is not the case. Can you get another PCM to replace yours with temporarily?

If not this we are back onto the fuel system or EGR . Possible you have plugged EGR ports which will create a misfire under load & cruise speeds. From what I have read these passages will have to be cleaned to eliminate the problem. I had what I thought was a light misfire under slight acceleration, seemed like EGR, but has since dissapeared after a couple of relatively long distance trips (like 200kms). You can disable the EGR system by disconnecting the vacuum to the EGR valve & plugging the line, see if this stops the misfire ( even though you may get another code ,ignore it). Have you replaced PCV in the last year or two? Can you get ahold of a noid light set?

 

As far as I can tell, the misfire occurs at idle, it doesn't seem to misfire under load or at highway speed (but it could be that I'm just not perceiving it). If it where a random misfire caused by EGR or something upstream of the coil pack, wouldn't it occur on different cylinders at different times? I've tried clearing the codes and got the same misfire codes over and over.

Also, as far as I can tell, this isn't an intermittant misfire. It can be felt any time the engine comes down to idle, so its either happening all the time or at least whenever there's minimal load on the system. I do not have access to an engine analyzer without paying a garage to fix it.

At this point, if I can't fix it readily by replacing the coil pack or a faulty sensor, it really doesn't seem worth pursuing any further - it isn't worth spending a lot more time/money on fixing something major. I think it more likely that the van will get donated or something.

 

my experience with the 4L Aero is that a miss at freeway rpm is very noticible because of the weight of the Aero and the sensitivity of the PCM to power changes which will cause a drop out from TC lockup.
mine had intermittent plug wire miss issues that were most apparent because of the TC lockup dropout on the slightest miss and then it quickly recovers and goes back into lockup. the OBDII 96 97 are very sensitive, seen it in Rangers/Explorers also.
if you had a road miss at cruise, you would most definitely notice the buckboard effect.

must be idle miss only?
that points to the IAC or its wiring or the PCM driver of the IAC. it's a high speed digital pulse width modulated signal. sticking IAC can cause either a rich or lean condition.
my 4L has never been the smoothest idling rig. nature of the 60d V6 beast.

my freeway miss did not always set a CEL or even a code. only showed up at times on my scanner as loss of TC lockup and the rig bucked as the TC went in and out of LU. drove me crazy, was ready to drive the biitch to the car crusher and leave her. finally found the problem

 

Have you cleaned your MAF meter? very important instrument , unplug it & see what happens. Faulty airflow reading will definately affect idle. Could create a misfire as incorrect airflow will mean incorrect fuel injection & at idle tiny readings will make a difference. Same with the IAC, engine RPM should drop with no IAC ,to around 650RPM.. These functions which provide actual values or servo type effect in the case of the IAC. The engine can run without them. Infact an engine in good condition can run very well without several sensors connected..
As stated above if you had a misfire at load or cruise it would be immediately obvious , you would not mistake it!
The last misfire I dealt with was a loose plug or a bad wire. I think it was simply a loose plug. Although this misfire occured only under light load & idle speed. It would dissapear under heavy load due to plug heat expansion which sealed the leak at the taper seat. The last misfire on the 3.8 ford engine I dealt with was caused by leaking plug wires due to insulation breakdown. This could be seen in a dark garage as white/blue flouescence occuring on the insulation. The code was also on #5 cylinder by co-incidence. My son was happy when we "tracked" it!

 

At this stage I would go back to basics. Do an engine compresssion test with the engine cold . Disable and relieve fuel pressure in the fuel rail to keep results consistent. Get the engine hot and repeat. You may find lower compression in cyl 5.This could be a sticky valve bad lifter worn cam lobe. At least you are eliminating mechanical related issues.

 

The mystery deepens. I've been out of town, so I hadn't been able to get back to this until today. This has seemed to be at idle only, I haven't noted a loss of power or vibration at higher speeds, but I also am not going to entirely eliminate that its happening. I have checked the MAF, but found it clean. There wasn't anything in it to wipe out. I also cleaned the throttle body while I had it apart, but to no avail. I have also swapped the coil pack even though it doesn't sound like that the symptoms point to that. But I had a spare, so I tried it. No change. Then I tried another PCM, because, well, I'm at a loss here. But the code was different (LEZ2 vs HCB2).

The bigger concern I have right now is that it now won't start at all. I went to start it this morning to put it up on ramps, and it started immediately, but then stumbled. It stalled as soon as I put it in gear, then has not been willing to restart since. After cranking over a while, I can smell fuel, but the smell dissipates quickly. Since changing the PCM didn't help, I swapped the original back in, but it still doesn't run. To be clear, I had the original in when it stopped running, and tried the other to see if it would restart with another. My thoughts are now running toward this being a degrading condition caused by whatever drives the ignition operation. It's not the coil itself, and it doesn't appear to be the PCM. So, else ties into the ignition operation that might cause it to fail to fire correctly (or at all)?

About compression, I checked several cylinders (but not all) when intake was off and the spark plugs easy to reach. So it was cold at the time. Compression on all was fairly low, or at least lower than I would've expected. But all were in the same ballpark, including the #5, so I think that I can rule out compression loss on an individual cylinder. For reference, the van had been running strong up to this problem and I've never had any indication of burning oil. So I'm also not sure why the compression is lowish across the board, unless the valves aren't sealing completely anymore. But again, it never felt down on power.

So, I'm still at a loss. I had been thinking that if I can't fix it readily, that I would just donate it and take a tax write-off. But if it doesn't run, I can't even do that. So, any new thoughts?

 

Wow torture..I would like to see a fuel pressure gauge reading. Check the connectors you pulled off to change some of the things you changed..Spark

 

Have you tried a new (or different) EDIS module? With the increasing numbers of misfiring cylinders, I would think that something affecting all of them is going (gone) bad.

At this point, you can pull out one or more spark plugs and just crank the engine to see if the have any spark. As someone suggested, it would be great if you can put a scope on the EDIS outputs to check the waveforms of the signals going to the coils.

I once helped a friend whose car stopped starting. We were seeing sparks from the plugs laying on top of the engine, and we were getting gas into the cylinders, but the engine still refused to start. The problem was eventually traced to a bad ignition module.

 

You'll have to help me out with that one - EDIS is an acronym I haven't come across yet. What is this module, and where is it located?

 

Thats the gizmo in the back of the engine where the dist used to be. Give a cam signal..I think.

 

Sorry Rick.

Electronic Distributorless Ignition System. All the 4 liter engines in Aeros (and maybe Explorers) got them; my 1990 has it. It's the device that triggers the coil pack in the right sequence. So it's kind of like a multi-channel version of the Thick Film Integrated ignition module that Ford used on their engines with distributors.

On the Aerostar, it's a rectangular aluminum module about 1/2" thick bolted to the inside wall on the passenger side of the engine bay, near where the heater hoses go into the heater core. It should have words on it to the effect of EDIS-6, for a 6 cylinder engine.

 

Ford DIS/EDIS "Waste Spark" Ignition System

the 96 97 Aero 4L uses EDIS, earlier use DIS

in the EDIS 4L, the PCM has outputs directly to the coilpack that drive it's three coils for the 6 wires/plugs
the only things in the ignition loop are crank position sensor signal to >PCM which times it's driver signals (3) to coil pack > ign. wires> series plugs
the PCM uses the crank position sensor signal to measure and check for misfires based upon tightly timed expectations of pulses from the sensor. takes a number of misfires in a row to set CEL
doe you get flashing of the CEL but no permanent light at times when the engine misses? indicates misses but insufficient number to lock on CEL

the only purpose of the cam position sensor is to control FI timing via the PCM which times and fires off the FI's directly thru FET output circuits to each FI

rick,
you've got gas, the fumes and smell, so suspect spark/ignition

i think the old miss problem and new no start are 2 separate issues. the new no start is probably something i have done a number of times working on the tight cramped Aero engine bay, self induced problems.
loose control cable into coil pack
loose PCM cable
blown fuse from PCM change
hose knocked off FPR
hose knocked of IAC
ad naseum

i've quit working on mine for days because i got fed up with it.

since you have never had a miss code for any other cylinder, stick with that one cylinder. strange that it only produces physical felt symtoms while idling. indicates to me a valve problem

the secret about compression is that they all be within min. of 20% of each other, 10% is ideal. your measurements indicated good compression. test ran while cold and oil drained out of rings will be far lower than hot engine and oil spraying into cyls before test.
a cylinder leak down test on #5 would wrap up the question of a leaking valve. leaking valves will cause idle miss problems and hardly be noticible at higher rpm. the 4L is known for valve seat breakage and valve seat regression/wear. both will cause seal problems. could also be bent or cracked valve tulip, not so common these days.
most valve leak problems will not show up on a run of mill quicky compression test

 

Check your Crank position sensor (CKP) for the No-start condition. You should get a reading on a DMM of around 6000 ohms if memory serves me correctly! this is an magnetic device which generates it's own output in Millivolts. ( No CKP signal will prevent spark & injectors from firing).

The idle misfire could well be a compression problem caused by a leaky valve, Leaky valve will eventually burn & condition will worsen. If compression reading is low on #5 cylinder, put in a tablespoon of oil into the plug hole & re test. If reading then comes up to almost the same PSI as adjacent cylinders, then valve is not likely to be the cause.

 

Thanks for the inputs guys. I haven't had time to work on this just lately. Compression check showed consistancy across the cylinders. It was checked cold, and if your explanation is correct, 96_4wdr, then that explains why it was overall lower than expected. Actually, I am getting codes for more than one cylinder misfire now. After I put it back together from the intake gasket job, it started showing misfires on #3 as well as #5. I think I mentioned that before. I'm also getting a code for the evap system, because I accidentally broke the little valve that is connected by hose to the charcoal canister, so I temporarily bypassed it. I found another in a junkyard on Saturday, so I'll be switching it shortly.

The no-start strikes me as odd. It didn't just simply refuse to start at some point, as if a connection became unhooked. It ran, then sputtered out and died, then refused to restart. That was why I was thinking that the misfire was actually a deteriorating condition. First #5, than 3 & 5, then nothing. Seems like a sequence of events to me, and I tend not to believe in coincidences (although they do sometimes happen). Is it possible that cam angle sensor failed, and so even though the injectors are clean they aren't being signaled to open? Or could a deterioration in the crank angle sensor cause various cylinders to fire at the wrong times and then stop altogether? Now that I'm thinking about, I did notice that the crank angle sensor seemed to be rubbing the tone ring on the crank that it reads - I noticed a pair of witness marks on the ring that the sensor had left. Maybe there's something to that?

At this point, I'm willing to try swapping either or both out for new ones if need be. I am not, however, real willing to dive back into the engine, especially if it involves head/valve work. I just don't have that much time to put into it at the moment.