Im convinced that unless i can fix the odd un fixable issue in the next month im converting my 93 5.0 5spd f150 to a carburated truck. So Thought i had it fixed but today out scouting in the woods ( right before hunting season..only vacation a year!!) My truck starts stumbling and loses 2-3 cylinders which i thought i fixed with new spark plug wires last month. I currently have MSD 8.5's on it, The current issue is when i fire up it idles irradically from 500-2500 RPM Exaust smells like straight gas, shakes the whole truck violently, and after it warms up that all goes away and it drives normal unless you go up hill or under load then you lose 2-3 cylinders and its hobbles along and jerks you around like a rodeo show, KOEO codes are 29,33 in CM, KOER codes are 21,22,25,34,44,52,54,72,73,77. So out of this ive come up with my MAP sensor is ButtF'd any other suggestions? Im really ready to tear it all out and go carberated.

 

That's a boat load of codes, you obviously have more than one issue...did you check fuel pressure as well?

 

Fuel pressure is fine, literally only thing i havent replaced under the hood is valve covers and Air intake..Ive been chasing one ghost after another with this truck for 2 years now 90% replacement with new Ford parts too.

 

So how long have you had all those codes? What is the fuel pressure at idle and under load?

 

Fuel pressure is all in spec all new components and well not sure it was clear last week

 

I see you also have a coolant sensor code. That can cause severe issues if it thinks it's still cold. I had one go bad on another vehicle and it was so bad you had to keep the engine at 2000 revs at a stop light to keep it from stalling.
could also be a harness issue. With it running try wiggling the different wires under the hood and see if you can cause a stumble.

 

With that many codes related to sensor output values out of specification I would suspect the VREF signal from the computer is bad or something is dragging it down.

Before replacing any parts verify what the VREF value is. It goes to the MAP, TPS, and EVP. Pick one and measure. It's the Brown/White wire that comes from Pin 26 on the PCM/EEC connector.

 

Ok what should it measure ? I replaced the computer with a cardone reman a few months back after mine went on the fritz, and coolant sensor is new too, what issues would the map sensor cause and I'm starting to think my harness is bad and that would cause so many "failures"

 

VREF is specified at +5 VDC +/-3%. So you are looking at roughly +4.85 to 5.15 VDC.

 

I cant find a brown/white wire anywhere on that computer plug, My truck is sort of acting like the IAC is bad again..I turned on the heater and it idled up to 3000 droped to 500 then died..voltage on that was -11.7 DC...Which is baffling to me.

 

I changed the IAC and the sporatic idle is gone, but the truck still loses power and is jumping around jerking back and forth on the road when driving.

 

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Pin 26 on the PCM Connector


The IAC is fed battery voltage (+12VDC).

 

yeah i dont have a brown/white wire, i have Beige/red, Black/green, and black,white. And i cant get any readings off of the connector. My multimeter reads zero when the key is turned to on.

 

Don't know what to tell you. Those diagrams I posted come from a 1993 Ford EVTM manual.

But I do know one of those wires should have VREF (+5VDC) when the key is in the Run/Start position. If that is missing, that's why your other sensors are triggering errors.

 

black wire is 5.14 vdc on egr and map so that shows there ok.