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Hesitation stumble on 1995 460. Goes away when MAP unplugged. Happens at idle and when under power. I’ve replaced the map sensor and it made no difference. Have replaced fuel filter, fuel pressure regulator, map and tps with no avail. Also chased the block to battery ground to make sure voltage stuff might not be a problem. No check engine light unless I unplug a sensor. plugs look good as well. Nothing has changed on the distribuor/wires. Did some sea foam in the intake but haven’t removed it since it’s a job on a e350 ford van chassis, not Sure what to check next.

I figure since it disappears when the map is unplugged that it’s a valve or sensor related to fuel system but probably not the injectors or fuel pump etc.

I did some searching but didn’t find much. Any help is much appreciated.
 

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Did you check ignition timing with spout disconnected?

Check fuel pressure and and replace fuel filter?

SJ
used 2b RHP


.
 

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Check for vacuum leaks. Spray edges of intake manifold with carburetor cleaner or some other highly flammable aerosol while the engine is idling, and listen for changes in idle quality or speed.
 

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Discussion Starter #4
yes in the filter. I haven’t put a pressure gauge on the system yet.

I’ll check for vacuum leaks. that could give the map variable readings etc. I did pull the cap off and cleaned up the contacts to make sure that wasn’t it. No change.
 

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It might not hurt to check for vacuum leaks, but that won't be the problem. In MAF metered engines, a vacuum leak causes unmetered air, so the PCM delivers fuel to match the air it metered, and ignores the air that leaked in so it runs lean.

In a MAP metered engine like yours, a vacuum leak just raises the pressure in the manifold, and so the MAP sees it, and the mixture is unaffected.

Have you checked for codes? These PCMs can have codes without showing a malfunction light.
EGR valve might not be closing, checking fuel pressure is not hard, although you need to check it while the engine is under load.

If you disconnect the MAP, the PCM runs the engine off the TPS and engine RPM.

Have you checked the condition of the rubber pipe between manifold and MAP sensor?
 

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All the ideas that people posted are good, but u might want to check at idle vacume. Also might want to install stand alone air fuel gauge, those 460s are so lean from factory it's kinda scary. It all works good when brand new , but once things worn it's a different deal. Hook up map sensor, that has to be hooked up. Try running it with o2 sensor disconnected, this will put system into open loop. If it drives better, it's probably lean for some reason, could be fuel, fuel pump ECT.
 

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Discussion Starter #7
Well gentleman i want to thank you all for the advice. I did a good amount of debugging and all was a dead end. Somewhere during my searching some thread on some forum talked about the ECM going bad so i figured why not just dig into that as well. So before ordering a replacement i got a cheap code reader from Autozone and i couldn't get the computer to return any codes at all. Not even the 000 which is A OK from my memory of reading the book. So i dug (literally on these motorhomes) out of the firewall and took it apart. Easily discovered that a cap had leaked out and failed. (Pic Below)..
91790


cap was a 10uf 63v cap.. Ordered a capacitor bundle from amazon for $14 that had that size plus others and replaced it. (pic below)

91791


Put the computer in and ran the computer test and got back a response from the computer in the code reader. Cranked the unit up the motor and let her run a good 5 min and didn't get the hesitation in the idle. The hesitation would show up in less than a minute from what I remember. So tomorrow i will do some more testing but so far i think that the bad cap might have been my problem. Hopefully, someone will find this in the future and these pics etc might help.
 

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Like Scotty says,nice work! On a motorhome ,there are all kinds of boards or "brain boxes",all costly to replace.If you can figure out which part in the box is defective,you can get pretty good with a soldering iron...literally buy individual components for pennies on e Bay.
 
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