Hi all, im new here and hopeing someone can help me. I just bought a 95 e-350 rv with a 7.5. Truck has 85,000 miles on it and had been parked for about 3 years that i know of. I own a diesel repair business so wasnt to concerned when purchased it. We have renewed all suspension, tires, brake system (including lines) tires, wheel bearings, seals on diff, and trans. New yolk on drive shaft, center bearings, u-joints, and im wont go into what weve done with coach side of unit! Unfortunately I went in the wrong order, truck has had a hesitation since bought but I really thought it would be no big issue so the money went everywhere else first! So the engine has a miss to it when idleing and at light throttle. I drained fuel and put in new, renewed plugs, wires, rotor and put and MSD cap on it with brass terminals, cold air intake, and a Banks muffler 3" in and out with 3' pipe to rear, new ditributor, and ignition coil. Set timing, 24 degrees at idle. No change at all!!!! So now myself and all my mechanics are stumped...no codes found truck tracks open to closed loop for a while then will stick in either closed or open loop...its random. Oh new fuel filter also. Took unit to a local Ford dealer that has a truck shop.. they been around forever....They had it a week and said "we dont know" I picked it up and brought back to my shop, we put a new MAP sensor in it yesterday (just a guess) didnt help at all!! Does anybody have an idea for me???? any help at all is greatly appreciated...I do have my old snap-on MTG2500 scanner so i can read data if needed....to me everything seemed good but i am stuck

 

It sounds like just about everything's been done that could be without actually going into the engine.
On something like this that has been sitting around for a while, the very first thing I would check is the compression. These powertrains where used hard and put away wet, so I would suspect engine damage or a problem somewhere.
You didn't mention i the plugs looked ok (I suspect they are), but one might appear wet. This style of fuel injection didn't have a misfire monitor, so you'll have to find the misfiring clyinder the old fashoined way by looking for it.
I know how much of a pain it was working on these (it makes my ribs hurt just thinking about it; It hurts between the second and third rib if you're close to the number 2 plug).
You might listen to the injectors to see if they all click and are injecting fuel.
One other thing. You didn't mention if the miss goes away at speed; I'll bet it's always there, just not as noticable at a higher speed.
Let us know what's up!

 

plugs are good i just put em in used motorcraft...the miss does go away when you get to speed...say above 35 mph.....I just put in a new fuel pump another filter and a regulator...(desperation throw parts at it)...same problem....the O2 is also new today it doesnt track from open to closed....not sure if it should on this.....the if i unplug the map sensor problem dissappears???? the map is new as of last night....due to the fact the problem does go away when map is unplugged i did not pull compression test or leak down test.....im actually sitting next to it now and seems worse since i put in new pump???? on my scanner im seeing ecp(psi) on the data screen not sure what that is but with map plugged in its at 5 psi and unplugged jumps to 125 psi? reserved a house in pheonix set to leave may 31 first ever family vacation with all 4 kids me and wife...money for house isnt refundable and cant change dates this is horrible spent all savings on buying and fixing this damn thing dont know what were gonna do if i cant get this thing to run!!!!!!!!!

 

Sometimes a suggestion from out in left field may uncover a problem.
Since you had this problem from the time you purchased the vehicle, it is possible someone may have placed the plug wires in the incorrect place.
What you need to do is check the firing order for that engine, and make sure they did not switch one of the plug wires. Something like this happens more than folks would like to think.
It requires a little bit of effort, but is worth it to know if that is the problem or not.

I believe the firing order for this engine is; 1-5-4-2-6-3-7-8. Make sure the wires for 7 & 8 do not run next to one another, separate them with the other wires.

 

Thanks I will check them for sure...any thoughts as to why this would clear up when MAP sensor is unplugged??

 

You have to be absolutely positive that the problem really, really does go away at speed. If you are, then I'll take you at your word.
The MAP sensor will default when unplugged to 125 Hz, or whatever, as it's programmed to do that. As for the O2, it uses Fords Famous "Jumpback" strategy of O2 useage, where it doesn't look at what the O2 does at idle, only when running around at speed (yes, I'm right about it; it's a long story, but they actually taught us that).
If it smooths out at speed, I'd check the wiring (Hanky is ALWAYS right), then you could have a possible valve problem (a rich mix will cover for a weak compression issue in the beginning). I doubt it's an injector issue, but did you notice ANY differences with the plugs? Were any wet or too dry compared to the others? Do you have spark (strong, repetitive) at all plug wires?
The problem may be hard to cure, but sooner rather then later, you'll get onto the cause.

 

Plugs are all consistent looking wires and spark are good i guess i am left with either valve or compression issue...cannot get fitting into cylinders 1, 2, 5, and 6 due to the chassis....were gonna check compression and leak down on th e ones we can access...what should compression be?

 

Hey Guys,
I have a question, If the engine smooths out with the map out of the system wouldn't that mean the compression and valves are OK ? You can tell I don't know the answer to this thing, but maybe if I ask the right questions It might help to come up with the answer.

 

Another question,
Have you been able to check the EGR valve for a piece of carbon stuck in it keeping the valve from closing completely? Can you tell us what emission controls you have on this engine?
The tool you have, can it get any codes from the computer? It would help if we knew which cyl was misfiring.
Also, if you have the old EECIV system , you should have a hard code for the cyl misfiring and possibly some continuous codes which might offer some direction.
There are some tests you can run where the ECM does all the work and all you need to do is turn the steering wheel a half turn in both directions and step on the brake once, and cycle the Trans OD switch. I believe this is called dynamic testing and it sure would help if you could run them.

 

the tool is my old snap on mt2500 scanner it was last updated in 1999(honestly never thought i would need it again)....i ran the dynamic test it pulls no codes each time (thats the test where u cycle over drive hit brake and turn wheel)...i have been looking into this all day on line and im seeing that from 90 to 94 a common problem was inductive crossfire on cylinders 7 and 8... i did have wires zip tied together and when it idles i can hear the snap like an arc at the back of the engine but i never see anything....it has always done this but i just never paid to much attention to it....im gonna put in another set of plugs and wires in it and keep them seperate this time...anyone agree or do u think im just spinnin my wheels???????