I know that you said that you don't have the service manual before you but the connector on this '96 Mark VIII for the PTCM has 104 pins.
Also, the PTCM doesn't ground the relay directly, it communicates with the variable load control module and tells it to ground the relay.
I have already checked the wiring from the PTCM to the VLCM and all is good. If I knew what signal the processor (PTCM) is supposed to be sending to the VLCM in order for the latter to ground the fuel-pump relay, I could eliminate one of those boxes by verifying that the signal is either good or bad from the PTCM.
It is so easy to get to a certain point but after that, there is really no trail to LOGICALLY follow as the information is not there to continue. It is a brick wall and that is the challenge and why I asked if there are any real experts on here that may be familiar with this PARTICULAR problem.
So now, it is either the PCTM or the VLCM or both that is the source of the problem and there just has to be an intelligent way to resolve this.
I don't see it the way that you described. Help me out here.
The way I see it, is that the PTCM sends either a data signal or a level signal to the VLCM. Naturally, the data would be sent over the data buss. Now, pin 80 on the PTCM is connected to pin 12 on the VLCM and pin 12 is labeled as FUEL-PUMP CONTROL INPUT. In my view, pin 12 is looking for a signal from the PTCM be it either a high or a low.
However, this pin 12 could be the information from a sensor telling the pump to turn on for a tad (this after the 2 second prime) and is supposed to be a natural running condition.
Okay, so you say that the VLCM is the only LOGICAL think it can be and if the PTCM returning no codes guarantees that, then, I will agree with you about it being the VLCM. What hits me between the eyes is that I checked the mosfet that runs the pump and it is good. So, due to physical contraints in the module, I can't trace the gate to tell whether it is triggered by just an independent signal or, if it is being triggered by some LSI that is on the data buss.
I ran the diagnostic again tonight and the only code that is showing is P0113 which is the intake air sensor high message. That is valid as I have the engine cowling off and the sensor is not hooked up.
In looking through the data codes, there are primary and secondary codes in the protocol but, of course none of them are displayed or I would have said so.
I sure hate to spring for a VLCM and it be something else.
Okay, well, suppose that it did give a code about the pump failure. We already know that it failed or the car would start. What good would a code do?
Also, we don't know that the PTCM is sending the proper signal in spite of no codes being indicated that the PTCM is at fault.
So, you say to look at it logically and the only thing that it can be is the VLCM. I can't yet agree to that UNLESS I knew what signal was being sent to the VLCM and whether it is on the pin 12 on the VLCM or the 'run condition' of the pump is sent on the date buss.
Am I exlaining myself clearly? I know what I mean to say but it may be confusing in the way that I put it.
What seems to be upsetting you? Are you upset because at one time I mentioned that there are a lot of crooks in this business and some crooks got upset and began a flame war to run me off and I wouldn't run?
That is exactly the truth and you know it. I see that you are still a person who likes to cause and stir up trouble.
Backyard Mechanic seems to be a very nice and knowledgeable person. I didn't expect to meet someone on here with as much knowledge as he demonstrates.
Bob, again, why are you trying to stir up trouble?
Cass opined in news:bjm5mt$e8j$ snipped-for-privacy@pita.alt.net:
Here's the thing... the VLCM apparently gets its commands from the DLC (nothing else shown on my 94 version) which is a data buss. See if the VLCM will control the EDM fans... Guess the way to do that is to hold the FPR on, start car and turn on A/C.
If that works, the PCM is working with the buss. Since the PCM uses "Hard Coding", the probability that the "Turn on FP" subroutine is somehow bad is pretty remote. Remember that there's quite a bit of decoding logic in the VLCM before the MosFet gate gets the signal. How do conditions at gate of that FET compare to the fan drivers?
And I'm NOT "nice"... in fact the tone of your original post annoyed me and I'm only playing because this is a good mind-bender. And I've learned a lot.
Otherwise I think you're going beyond the practicality pale on this
Here's a really far-out thing... for some reason the page on my evtm showing nothing but FP circuitry includes "BOO" (Good to know that term stays the same). Brakes On/Off
Do your brakes lights work? Did you try to start it with foot on brake pedal?
Me upset? Nothing could be further from the truth. I'm actually pretty amazed at how polite you can be when you need something. I just thought backyard should know who he is really dealing with. Bob
I think we are going astray here. I guess this is normal since you have a book on the '94 and my book is about the '96.
I don't recall what you are calling the DLC unless it is the main computer (PTCM - Powertrain Control Module). Nevertheless, the VLCM gets at least one signal on its pin 12 which is labeled fuel-pump control input. That comes from pin 80 on the PTCM. However, the what I am calling the low-speed feed to the pump or regular running signal exclusive of the '2-second' prime pulse, may be coming from the data buss. This is where we run afoul of normal trouble-shooting.
I don't know what EDM fans are unless you mean the air-conditioning fans/blower/s. The VLCM does not control those/it. The VLCM only controls the engine cooling fans, i.e., on-off and variable speeds.
I can't dynamically test the gate of the pump control mosfet and compare it to the fan driver mosfets UNLESS I got to one heck of a lot of trouble by making up a patch-cord to tap into those gates while the VLCM is installed and under power.
I don't know about you being nice. You seem nice to me. However, my orignial post was intended to provoke thought. I knew that by saying 'any REAL experts', would gain attention and only the most confident of the lot would respond, if at all. It was a sort of 'throwing down of the gaunlet' alerting the incompetent that this was a problem that was going to take some real thought and in-depth analysis. Yep, that probably sounds haughty but, as you know, there are a few folks out there who will say to change the fuse and buy a new box..
Being polite is what most mature adults are in their normal state. Those adults have learned that courtesy and friendliness is a lot more fun and helpful than being nasty and mean.
I don't know where you came in on the original brouhaha but I had only made a comment about there being a lot of crooks in this industry and it upset some folks (apparently the crooks) and it all went to Hell from there.
Now, as you know, I don't run from trouble. My personal philosophy is that if you run, you only embolden the cowards and bullies to continue with the next fellow that they don't like. So, I always try to hit harder and more often. If you come in the middle of a fight, it is hard to tell who started it and who is simply refusing to take it.
Regarding Backyard Mechanic, I am not sure but I think he doesn't need you telling him who to talk with and who to ignore.
If you are saying that the VLCM controls the air-conditioning blower/s, I disagree. I could be wrong but I think it (VLCM) controls the engine cooling fan, the fuel-pump and the a/c clutch.
It really doesn't matter for my problem but it may help if we agree on this as that will mean we are on the same page.
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