This is on my personal van. It is a '94 4.0L AWD. Ok, lets begin with the symptoms I am having.

On cold mornings, anything under 40 degrees, the van will misfire at startup. If I drive off, the misfire clears up fairly quickly, often before I reach the main road. The van runs great. The colder it is outside, the worse this problem is. The colder it is, the longer it takes to clear up. On warmer days, which I haven't had in a while, it will start up just fine.

For what has already been replaced, so you know what we have to work with, here it goes.
Autolite Iridium XP plugs (like double platinum, but better)
Magnacore wires (added recently, a little more power, but had no effect on the startup issue)
Accel Supercoil pack (no change)
MAF was replaced recently. (Problem went away briefly after replacement, but If I recall it also wasn't that cold when it was replaced. Not an OEM sensor.)
Intake gaskets were replaced about a year and a half ago.
PCV valve was replaced recently. No change
Fuel pump was replaced this summer
Coolant level stays good, I have not had to add any for several months.

Has anyone had a similar issue? Any ideas as to what might be going on? Any good ways to test what might be going on? The problem is so brief that it can be difficult to test for. But surely there must be some way to find out what is happening.

 

this may help

Ford Fuel Injection Strategies

Cold Start & Warm Up
The engine has just started and we have to get adjusted. Well EEC does anyway, this strategy is kind of like you waking up with a hangover next to a stranger. Where�d I set my pants, should I run fast, should I sneak quietly! EEC�s first reaction is to keep the throttle air bypass open 100% or else we�ll be back to engine crank mode. RPM will drop however, usually to around 1000RPM after a few seconds, then drop down to base idle as she gets warmer (about 160�F). EEC looks almost completely at ECT and TPS; both indicate what will occur next. The colder the more fuel gets dumped in and the more timing added. When she gets warmer (about 170�F) she will lean out the mixture. This logic will speed up the time it takes to heat up the engine and converter. Now lets talk about what happens when last nights date wakes up (driver input). If you drive away with ECT under 185�F she jumps to cold drive-away strategy. If you stay asleep and leave everything alone ECT will cross 185�F in about 4 minutes and we are now in a warm idle. See how confusing it all gets at this point.
BUT don�t be hesitant about driving your car at any time; they wouldn�t make all the strategies if you couldn�t use them. The Government wants you to drive your car as soon as you start it for economy purposes; cold cars burn more fuel so let�s get them warmer quicker! Now hold on, I recommend a few seconds to ensure oil pressure, and let�s hold up on the wide-open throttle assault until we have some nice warm oil for all the internals. Lets all practice common sense and a little love for our vehicles.

Cold Drive-Away
So the TPS and PIP are going up, the MAF/MAP is showing greater load, and the ECT is under 185�F. The TPS and MAF/MAP tell EEC that we are now �driving away.� The goal at this point is to move the vehicle without stalling and warm up the engine as fast as possible. The IAB opens 100% for insurance from stalling if the TB slams shut suddenly. We have a rich fuel mixture that leans out as temp rises. Once ECT is greater than 170F the mixture is actually less than 15:1, this rushes us into normal operating temperatures quicker. Timing is advanced and retards slowly as temps rise. Once the ECT temp cross�s 185�F the mixture should return to normal and relate to HEGO signal as long as you aren�t accelerating enough to be in another strategy. After 4 minutes if the engine is warm enough to begin EGR function it�s about time to pass command to the �Big-3.� Warm cruise, Part-Throttle, and Full-throttle acceleration can take us down the road from here.

 

Assuming all notes above are present & correct.....
It sounds like your cold start enrichment is not quite right. Does the engine have EGR? & are the ECT / ACT sensors functioning properly? I would start by checking ECT resistance at 40*F & make sure it is giving correct readings. Anything which can "lean out " cold start injector pulse on time, will affect how the engine runs when cold. Also at this time there is no O2 sensor fuel control.
This could also happen if the EGR valve is stuck slightly open....... although I would guess you should get a code when the engine warms up if this was the case & also a lumpy warm idle.

 

Mine does not have EGR, so that is ruled out. I supposed i could check the ECT, or just replace it as a matter of course. The thing is, everything starts acting right way quicker than the ECT can warm up. I'm talking like maybe 30-45 seconds after I leave my driveway the miss clears up. Thats enough time for some heat I guess, but the engine is still technically cold. I'll see what I can find.

 

Almost sounds like a miss from overnight fuel injector leak down into one or more cylinders. Time and temperature intervals you describe would seem to correlate to what it would take to clear a slightly flooded cylinder. Just a thought.

 

Hmm I hope not. I guess a leakdown check would detect that. That should be one of the next tests I guess.

 

try a couple jugs for strong FI cleaner with polyetheramine such as Chevron Techron Concentrate 20oz or the large Regane Large Vehicle FI cleaner in a quarter tank of gas.

that's one of the complaints about Arco gas here a few years ago and another reason I quite using it. Excessive amounts of products that break down and form gum and varnish exist in gasolines especially those from the heavy North Slope oil. Some refineries don't process the wholesale gasoline they pipeline out as well as others.

gums and varnish start forming in gasoline as little as 2 months old.

may have got some tanks fulls that set too long in the refinery tanks, tank farm distributions tanks locally or the station tanks.
common these days with drastically slowed gasoline sales.

I have to dope my Aero with FI cleaner and gas stabilizer every tankful now since it mainly just sets and seldom gets driven

Arco and some of the other cheap gasolines will gum and varnish plug a marine outboard to the point it will not run. I use special cleaners to keep mine running.
Shell premium beats all the others for marine use, won't put in anything else.

 

If you use the Chevron Techron additive, you should change your oil after you consume the tank of gas, as they instruct in their fine print. Apparently, whatever "Techron" is can get into the oil and break it down when used in concentrated form.

 

All our gas comes from the Sinclair wells and pipeline in Wyoming. Limited quantities of the stuff and has a high sulphur content, but otherwise great fuel stock. I have run cleaners through already, no change. A quick inspection of the tailpipe indicates I have very clean combustion, no carbon soot. Shell is one of the lower quality fuels around here. Very few stations anyway, none along my routes. Sinclair is everywhere.

 

Would a leaky injector cause a misfire at startup? You still need fire for combustion. I could understand stumbling or rough idle.
Misfires are usually timing problems aren't they?

 

It could if the cylinder is flooded. I am going to get a gauge and do a leakdown test. While running once this issue clears itself, the van runs great.

 

only takes the smallest micron sized particle of gum/varnish/dirt to hold open the FI pintle enough to leak down overnight and flood a hole.

might show on the plug

 

Gauge pressure on the fuel rail right ? 35-40 PSI should hold for several minutes. Does it smoke (black smoke) at start up? Only question I have is what about a warm start, a leaky injector would likely give more trouble on a warm start since rich mixture is not required. Remember on the older engines (lawnmower types & motorcycle) you could tickle the float valve until almost flooded, the engine started better with the float level way high.Of course they had no injectors . You could try this : Crank the engine for 3-5 secs with your foot flat on the floor, this will clear any excess gas fumes from puddling if there is one. Then start up as normal & see what happens?

 

Warm startup has no issues. Had a warmer day a bit before this last snowstorm hit, was about 40 degrees that morning. Startup issue vanished that morning. It is cold again, the issue has returned.

 

on these cold morning starts with temps in the problem range, is there any smell of unburned raw gas in the exhaust? should be. rich cold start and CAT not fired off yet

if not then ACT or ECT