I've been trying to locate a random missfire on my 94 5.8l for a couple months now. It started to do it after I replaced the Battery about 4 months ago. The Van ran great before that, so since then I've replaced the plugs, wires, coil, checked the vacuum, tried disconnecting the vac to the EGR, replaced the ign module, replaced the distributor rotor, and checked every connection I could think of.
It seems to do it more once the van has warmed up, and it's worse when I'm under a load and not as bad when I'm just cruising.
I'm going to try changing the distributor cap next but I'm running out of ideas to please help

 

I'm a bit surprised the distributor cap wasn't replaced along with the rotor, wires and plugs---that's typically part of that process.

Have you done a compression check----I wonder if its not a valve problem?

Sometimes even new parts can fail so its possible one (or more) of the new plugs or wires are the culprit here too.

The occasional problem can be the most difficult to diagnose not to mention downright aggravating especially after all that work and money put out so far. Hope its nothing too complicated or costly.

 

I tried replacing the rotor today and again no difference. So I tried pulling the plug to the MAP sensor and bingo it stopped missing every so often. So what does this mean why would it run better with the Map sensor out. It doesn't make much sense to me, any ideas??

 

So I checked my TPS sensor and found that at closed throttle the voltage output was 1.1volts. Would this cause the air fuel ratio to be off if it closed throttle position wasn't below 1 volt? other than that the TPS appears to work fine

 

Did the miss go away completely when you unplugged the MAP? Or just every so often?

The TPS may cause issues at idle, but under load when the miss happens is closer to WOT, maybe 3.5-5 volts on the sensor.

Is it a miss/stutter more at low RPM, high load? Once you get it to downshift does the miss go away? How does it run at high RPM, WOT when you wind it out?

 

The miss seemed to go away completely when I pulled the MAP. Now I didn't try driving it with the MAP disconnected but at Idle it cleared it up.
Right now it misses worst under light-medium load at lower RPM 1500 It seems to do better at WOT but still not perfect.

 

I have the same year e250 with the 5.8 and im having what sounds like the same problem. A miss/stutter while cruising under light throttle. I've replaced plugs, wires, dist cap, rotor button, TPS, fuel filter and ran some fuel injector cleaner through it and it still hasn't got any better. I hope i figure it out soon because it's really starting to get old.

 

Ignition modules can cause this problem (make sure you match the part number from the old one as there are two different ones), and ECMs can cause this. Also, check the distributor shaft for play. Stay away from A1-Cardone brand for engine management components. Just a few more ideas. Don't know what kind of test equipment you have...

 

hey guys thanks for the help it turns out this was all due to some leaky electrolytic capacitors in my ECU, I changed them out (only do this if you know how) and it runs like a dream. If you want more info check out my other posts on this forum.

 

So where is the ignition module located ? how expensive is it ?
Can you have it checked ?

 

So where is the ignition module located ? is there a way to check them ? how much are they ? Thanks in advance

 

Bulkiman.... the ignition module is attached to the side of the distributor..... It costs about 17-20$ at rockauto.com

I'll link to the part if you need.

 

I only have a miss after warm up, it does not miss when cold
My mechanic wants to disconnect gas lines and flush my system with a solvent under pressure , cost is around 100.00
Does this sound like a good solution ? or should I try the ignition module ?

PS. Plugs and plug wires have been changed

 

Well think about it like this.....
The two times that your engine needs the highest quantity of fuel is during startup and warmup from a cold state with the ECU in open loop, and also while under WOT and under load. Once it's warm, it needs LESS fuel at idle (proportionally).

If when you start up the vehicle if you slowly open the throttle with the engine under load, even though it's still cold..... Does it miss??

If it only misses when warm, then I would not suspect insufficient fuel delivery to be the issue. I'm also dubious as to the effectiveness of those On-the-vehicle fuel injection cleaning treatments.....

Do you have a vacuum gauge so you can test the vacuum reading on the vehicle?

Possibly try pulling the vacuum line off the MAP sensor and capping it with your thumb for a few seconds while it's warmed up and missing...... If it smooths out, then suspect a mixture issue (either vacuum leak or insufficient fuel) because the MAP once disconnected from intake vacuum senses an in effect higher atmospheric pressure which tells the ECU that more fuel is needed per volume of air to achieve the proper ratio. This causes the ECU to pulse the injectors longer and deliver more fuel.

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But more directly..... If I were you, I would explore other options and proceed with trying to diagnose the issue rather than start throwing 100$ at things that might have nothing to do with the problem. But I'm kinda broke most of the time, so I always try and do things on the cheap....

An ignition module from the pull-a-part is like 5$ and can usually be returned... they're VERY easy to remove and replace.....

Good luck!

 

Buki, you should perform the KOEO and KOER tests to see if the computer has anything to say, it often can determine if the ignition module is scrambled.

I can link to a document containing step by step instructions to perform this quick and easy test if you need help. What year/model is your vehicle?
And have you checked for DTCs????