Hi.
It's a 1994 E250 4.9L 133K
I've had this problem for about a year now. I started out over in the Econoline forum but someone suggested I move it over here due to the higher level of expertise.

Here's the original post:

https://www.ford-trucks.com/forums/s...d.php?t=414711

As of right now:

Went to get it smogged a couple days ago. Didn't pass. "unstable engine speed caused by excessive misfiring" was the reason. Out of urgency, took it to the "family" mechanic. He's had it for two days now saying he thinks it's either the pick-up in the dist. or the "foward position sensor"??? (didn't realize there was one) Anyway, someone in the van forum suggested the cam gear may be worn causing the misfire, only thing is it runs FINE in the morning when its first started. No misses, hesitation or sputtering. However, it seems to me if it's something mechanical like a cam gear, it would be constantly missing. I prefer to think it's still the ignition, but at this point, after a year and not passing smog, I'm not sure what it is. Anyone have anything that might help me out this?

Also, I need to get this thing figured out ASAP for two reasons:
It's my work van
It needs to be registered by May 31 to avoid DMV penalty fees thus needs to be smogged (yeah, I waited till the last minute.. I know)

Thanks in advance

Aaron

 

The 4.9 has gears, not a chain. So it sounds unlikely to me that this could cause your trouble.

Pull the plugs and get a reading on the coloration to see if that gives you a hint.

Also you might just check to see if the plugs you are running are for sure, for sure the correct ones for your application.

Especially when it comes to auto parts like spark plugs, new means new, it doesn't mean good.

You do say that when you first start it up it runs fine. But you don't say what the conditions are when it starts to miss. (?) Think about that. If it starts to miss as soon as it reaches operating temperature, maybe you just have a lean condition after the enrichment cycle ends. It seems to me that the ignition is going to work best when the engine has reached operating temp.

 

Pull the plugs and get a reading on the coloration to see if that gives you a hint.
Did that already. Nothing unusual. As a matter of fact, I've replaced everything on the engine 'spark' related including the distributor AND coil. No change.

You do say that when you first start it up it runs fine. But you don't say what the conditions are when it starts to miss. (?) Think about that.
Yes. This is what pretty much rules out the likelyhood of a mechanical part such as the cam gear. The conditions are...van sits all night, start van in morning, engine reaches fast idle for approx. 10-20 seconds, no misses, running smooth and steady, no misses, engine speed decreases, no misses, running at idle for approx. 5 min. engine begins to miss, at first every 30 seconds or so then varys from every 5 or 10 seconds to constantly to almost stalling. Oh yes, almost forgot, knocks and pings rather loudly (and it ain't the gasoline) The knocking and pinging is especially violent during hard acceleration.

It seems to me that the ignition is going to work best when the engine has reached operating temp.

Not in this case, it's worse at norm. temp.

 

Since your ignition is ALL NEW, and you have pinging, that suggests a lean condition, not an ignition problem.

Other than that, carbon deposits could be causing the pinging. Try running the engine at about 2k and feed about a pint of water through a vacuum line. Watch the exhaust to see if you get clouds of junk coming out the exhaust.

 

Update:

Replaced computer. $45 off ebay. Problem fixed. Took about 10 mins. Unbelievable. Been dealing with this for almost a year. EVERYONE I asked insisted that it had to be something more serious than an electronic related problem.

 

Way to go e250, good thinking on your part.

 

where is that cam sensor located