Thanks for the info. I'm pulling it out of dealership, I just can't afford that bill at the moment. I will say after reading your post I called the guy I was working with and asked about why he is saying I have a PCM. He told me " both the pre-powerstroke and powerstroke have a PCM. However the pre-powerstroke do not have an injector control module" that's exactly what he told me.
It's a matter of wording really: PCM stands for Powertrain Control Module, aka the computer that controls the engine and transmission in a vehicle where both engine and transmission have electronics in them. In case of the IDI trucks the engine itself has no electronic controls, the computer in question only runs the E4OD transmission - Ford used to call it a TECA (stands for Transmission Electronic Control Assembly if I remember correctly), now most folks call it a TCM (Transmission Control Module) so kinda like a PCM but for the transmission only. If it controlled the engine only and not the transmission, as was the case with most '80s vehicles with fuel-injected engines but non-electronic automatic transmissions (AOD, C6, TH350 and TH400, TF727, etc.) then it's called an ECM (Engine Control Module).
Personally I think it's just nitpicking, cause even on newer stick-shift vehicles where the PCM in question still only controls the engine (and thus technically is only an ECM) it's still called a PCM - I don't really give a darn what the politically correct term for the thing is, if the dealership calls it a PCM and the parts stores call it a PCM then that's what I'm calling it too. You should have seen a thread on here a few months ago, people got so picky about what to call the stupid thing they completely ignored the actual question regarding it... So yeah, like the dealership mechanic said, you do have a PCM, it just controls the transmission only, and has no injectors or high-pressure pump controls built in it.
He also he told me when they where diagnosing the problem they by-passed the "PCM" ( his words) and the tach was working fine. So the sensor works. He said that if they left the wiring that way the truck would not shift at all. So my next question is what did they bypass?
What they bypassed was the entire PCM. The way the system is wired the signal from the tach sensor on the engine goes into the PCM via one wire, then from the PCM it exits via another wire and then goes into the tachometer gauge on the dash. If the PCM is not powered, or has internal issues, it will not "copy" the tach sensor signal and send it out towards the tachometer gauge, thus you end up with the gauge reading zero all the time, the needed does not even attempt to move. So I bet what the dealership did was unplug the harness from the PCM, then jump the two wires that carry the tach signal in and out of the PCM, effectively connecting the tach sensor directly to the gauge on the dash. It's the same thing people do when they swap an E4OD out for whatever manual transmission fancies their tastes. Why Ford deemed it necessary to have the PCM act as a middleman I don't know, maybe if the PCM is wired in parallel with the gauge the signal is not strong enough to run both at the same time, and therefore the engineers decided to feed the PCM the full signal and then use the PCM itself as an amplifier so the gauge also gets nice and strong signal? No idea, and I no longer have an E4OD transmission to experiment what happens when the PCM and the gauge are wired in parallel...
All that said there is no way replacing a PCM costs $1100 unless the PCM itself costs nearly $1k - getting to the PCM is actually fairly easy and should not take more than an hour. However if the PCM is indeed dead as a door nail then your truck won't be very pleasant to drive at all - you will only have 2nd and 4th gear (well, and reverse too), and you'll have to shift them manually, and she will shift so hard she will shake quite violently. If you have no such behavior, and truck shifts just fine, then I suppose it's possible the only part of the PCM that went dead is the amplifier or whatever that is responsible for forwarding the tach sensor signal to the gauge. In which case you'd still need a new PCM if you want your tach to work, but at least it won't have to be done like right now. You can confirm this by scanning the PCM for diagnostics trouble codes (DTCs), you'll need a scan tool for that but those can be had fairly cheap these days, like under $50 cheap - actually I think if you like the truck and plan on keeping it for a while you should buy such a scan tool anyways, as they can be invaluable for pinpointing issues down the road.
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