Severe miss-firing under load

We just inherited (family deal) a 2001 Windstar V6 handicap van (or should I say handicapped). It has 179K miles and supposedly about 5k on a new engine, what ever that may be. It looks very nice but runs pretty rough. If you keep the rev’s high or drive it on a nice flat surface surface it runs fine. However as soon as you start an up hill grade or try to accelerate from a stop or significantly increase speed the engine misses pretty severely. I just drove it a pretty good distance to get it home and here’s how I dealt with it.
-If I tooled along about 65mph at about 2k RPM, in 3td (automatic) it was fine
-When approaching a hill I’d disengage Over Drive, kicking the RPM up to about 3k. Doing so is smoother than punching the gas to down shift and nicely does the trick to keep the engine running smoothly while climbing the hill. Either will keep the engine from missing. Keeping the cruise control on seemed to make it all work better too, probably by keeping the rev’s more consistent.
-Taking off from a dead stop can really be a problem too unless you slowly raise the pressure on the accelerator, not enough to tick off those behind, just enough to have a nice smooth acceleration.

I’m not planning on fixing this myself but would like to be well armed before I take it to a shop. Supposedly it’s been looked at before but could not be diagnosed.

Anyone have any good ideas on what the problem might/could be?


Sounds like weak spark or really, really old spark plugs.

You must have a check engine light. Many auto parts stores will pull the codes for free. They look like “P1234.” Get the exact codes and post them.

If you don’t have codes then I’d be surprised if the issue is actually a misfire.

That said, what you describe sounds most like a very basic issue - something like old plugs & wires as Manolito mentioned, or poor fuel pressure, or perhaps a clogged exhaust.

I believe your motor has COP’s (coil on plug). This means there is an ignition coil sitting just above every spark plug. The plugs might be old and worn out, and you might have one, two, or more bad coils. Missing under load is a symptom of bad plugs and bad coils.

There’s a 100 things it could be but without knowing if codes are present it’s impossible to narrow it down.
If no codes are present then I’d suspect a clogged fuel filter, low fuel pressure due to a bad pump, or clogged catalytic converter, etc.

The first thing you should determine is the defintion of “new engine”. Many people assume a worn out salvage yard motor is a new engine.
In a case like this the engine is new to the vehicle it’s residing in but worn out just the same. (I’m not being facetious at all; just pointing out an often seen and well-used cliche.)

Besides ignition parts I would suspect low compression.
Get a compression test.

Thanks! Plugs and wires are a low cost task I could handle if I can figure out how to access the other 3 on the back side. I don’t see a removeable cover inside the van. Does this have to be done from below or is there access?

P.S. There is a sound like an exhaust leak around the front of the van. Bad news related to compression suggestion?

An exhaust leak won’t affect compression.

The issues with accessing those back 3 plugs on cars like this are legendary. One common way is - yes to get at them from down below. I don’t know about the Windstar but sometimes some acrobatics & clever use of various extensions & joints can allow one to get them from the top.

Not sure if this will be seen after the time lag since the last post but… Finally got the codes read. Mis-fire on cyl 1 was the report. Got an estimate of >$200 to change plugs and wires. Not COP from what I’ve been told. Does that seem a bit steep? I may have to see if I can access those back plugs and do it myself.

Other issues to be checked…An EGR valve not closing on acceleration demand. A partially plugged fuel filter…

Is the CEL (check engine) light on?? Does it come on when you first turn the key on??

You would think that if the engine was new with only 5k, the plugs would be good, but maybe the “new” engine came from a salvage yard.

My first inclination was toward a fuel pump or filter, but with a consistent misfire on #1, it could be the plug, wire, injector or low compression. I don’t think the mechanic did enough troubleshooting.

It was just a simple, free, code read. This was a family donation to my son and he’s trying to figure out where and how much money to invest in determining if he wants to keep the van or not. Paper work that came with it indicated someone diagnosed a bad PCV connection that I doubt has been fixed. To the question about the CEL, it was off when I picked it up and came on during the 300 mile trip home during one of the instances climbing a hill. I noticed it would flash sometimes during the mis-firing while pulling a hill (never saw one do that before), but not every time. Since the tech reset the light is hasn’t come back on… yet.

Seeing as how someone has mentioned a bad PCV connection maybe what’s happening is that it’s sucking air and this is affecting the MAF sensor.
There can be no air leaks at all between the MAF sensor and the throttle plate inside the throttle body so I would definitely investigate that. It should not be a serious matter to fix.

I actually went through this a year or so back with one of my cars. It had developed a miss at times (sometimes a bad one) but everything checked out fine and no fault codes.
The bucking would only occur about half the time and only around 50 MPH when accelerating out of a curve. On a rare occasion it would do it on the straights.
The PCV hose had a razor type cut in it that would open up just enough, depending on manifold vacuum, to suck a little air and this would lead to the MAF sensor not being able to keep up with it. Replaced the 3" hose and problem solved. Maybe you should be so lucky. :slight_smile:

If it’s not a PCV/vacuum fault then I’d start with a compression test and spark plugs. The compression test can tell you whether to go much further with it or not based on the definition of “new engine” which as Keith mentions is a term often applied to a boneyard motor and which may or may not be any good.

Restricted fuel flow will cause those symptoms.

Thanks all!

You mentioned a sound like an exhaust leak. Actual exhaust leaks will suck fresh air at certain loads and RPMs and confuse the oxygen sensors. Your symptoms don’t sound like they could be caused by an exhaust leak, but you definitely want to keep that on your list of things that need to be fixed if you keep the car. CO leaking into the cabin is very dangerous.

Someone said this was a coil-over-plug engine. I would check to see if that sound you hear is coming from a loose plug that is being held in its hole only by its coil.

I would disagree with the restricted fuel flow suggestion. The original post indicated that the car can pull hard at high rpm, so long as you don’t open the throttle wide to get there, and mentioned problem accelerating away from a light. Both of those clues point toward a spark problem and away from a fuel supply problem. The higher the pressure, the harder it is to fire a spark plug. It sounds like your plugs are not firing under maximum compression (wide open throttle) conditions.

Restricted fuel flow/pressure in a fuel injected car an produce these exact symptoms too…

Ok… here’s a strange twist… but first let me explain that this van was an inherited gift to my son and it’s not currently needed for primary transportation, so I’m more interested in gathering information while he puts money aside and decides what he want’s to do with it…
That said, the other day I took it for a drive to a shop to check out the handicap features that need work. It was mid 20’s when I left. The damn van ran like nothing was wrong at all, for about 15 minutes, then once it warmed up the missing started again on hills. So is that a significant piece of information to tell a mechanic about? What could that point to? I mean it ran like a top.

It may be routine maintenance, air filter, gas filter plugs etc. Do you have maintenance records? And as 1 other item comes up regularly, the pcv valve. A mechanic that can see it and narrow it down is going to be better than all the online guesses in the world!