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Okay so this may be lengthy but I’ll try to go through each step I’ve done so far in trying to diagnose what the heck’s going on.

1. The past couple weeks I had noticed my trip computer was dim and that it would take a couple cranks to get the starter to turn over. Only in the mornings though which was weird because it wasn’t like it was cold out or anything. The rest of the day it would turn over fine.

2. I drove home after putting gas in the car and a mile away my car died. I saw my speedometer drop straight to zero and my RPMs slowly going down. My trip computer had also said “low oil pressure”. I pulled over to the side of the road and stopped. I figured maybe an overheat but not sure why. Anyway, I turn the key to crank the starter and only a single click. My odometer is all dashes and still says “low oil pressure”. I got towed home.

3. Went through the whole schpeil of checking the starter and it and it’s wiring from the relay socket appeared fine. Even used a jumper wire to try to get it going and it would (but no turn over of the engine or even a fuel smell).

4. my relays which I replaced for the PCM and starter just in case click when I turn the key to the run position so I figure the pcm must still be supplying ground right?

5. I’ve checked my grounds and the ground for the pcm. Cleaned them up but I still can’t start. My obd2 scanner gets a communication error as well. The car’s own system check was pressed next.

6. everything I know the system check does from the GEM side is done correctly. What I figure the PCM checks such as charging system and engine temp throws back stuff like “engine temp data error”,“charging system data error”, “low oil pressure”, and “fuel cap data error”.

So far this is where I’m at. I’m pretty sure I have an electrical gremlin. The engine can be turned freely with a cheater bar on the harmonic balancer so my engine’s not seized. I just put a new alternator in back in February. My battery still has plenty of juice. Coil pack was replaced back in June of last year. Where should I be looking next? I’m pretty sure the car won’t start because of the failing to check the system from the PCM’s side but I know the pcm is getting power and making the relays click right? If the relays click then the pcm can’t be bad right? The GEM must be good too if it can check everything on its side of the system check correctly. I’m scared I fried my PCM but I don’t know. I suspect a short or draw because of the dim trip computer but Now I’m at a no start condition. Where should I check next? Trying to get this fixed on my own and I want to avoid the dealership.
 

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Discussion Starter #2
Oh and I already replaced the ignition switch and of course that didn’t fix it. Any suggestions of where to go from here?
 

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Not clear which engine you have under the newer revised format. I have a Vulcan overhead valve and the starter is prone to becoming oil soaked during oil changes. I had intermittent no crank, no start and it turned out to be the oil soaked starter. The frustrating aspect is that every time this happens to me upon removal and bench testing they tell me it is fine. These cars are very sensitive to low voltage so make sure your battery is fully charged, 12.6 volts, connections and cables are clean and tight. You stated you cleaned the grounds, check the PCM ground especially. How long since the starter was replaced, how old is battery?

Scott
 

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Discussion Starter #4
Not clear which engine you have under the newer revised format. I have a Vulcan overhead valve and the starter is prone to becoming oil soaked during oil changes. I had intermittent no crank, no start and it turned out to be the oil soaked starter. The frustrating aspect is that every time this happens to me upon removal and bench testing they tell me it is fine. These cars are very sensitive to low voltage so make sure your battery is fully charged, 12.6 volts, connections and cables are clean and tight. You stated you cleaned the grounds, check the PCM ground especially. How long since the starter was replaced, how old is battery?

Scott
The new battery was put in back in February of this year. Not old at all. I have the DOHC 3.0 engine. I should note that I tested the starter while it’s attached to the car and it appeared fine. I honestly don’t think the starter is the issue, especially since my car died while driving at 50 mph on the road. A bad starter wouldn’t cause your car to stall I believe.
 

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Discussion Starter #6
^ Fwiw, if you have an '06 Taurus, you don't have a dohc Duratec eng. '06/'07 are ohv Vulcan eng. only. '06 can be gas/flex (ffv). '07 is gas only.
Ah I misunderstood the name. Regardless, my pcm isn’t communicating with my OBD2 scanner nor the GEM from what I can gather. That lack of communication with the PCM and the GEM seems to be what’s preventing me from getting my car started. I checked the PCM fuse and I am getting power through there. When I turn my key to the run position, my relays click so I would assume that the pcm is supplying ground in that regard to the relays. My anti-theft light isn’t illuminated and I can’t connect my obd2 scanner as I’ve said and the car’s system check does everything correct for what the GEM module checks for (parking brake disengaged, brake fluid level, etc) but the pcm side gives read errors. The red flag here seems to be that the system check says “low oil pressure” on the trip computer and my low oil pressure light is on during this fiasco. If my PCM checks the oil pressure sensor, and it’s giving data errors for the rest, would my PCM really be fried?
 

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Have your battery tested and alternator also. I had a 2006 that would crank but not start and it was solved with a new battery. Crank your car and measure the voltage at battery, that's the real test. Voltage should be above 9 volts. You also have the OHV engine, Vulcan.
 

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Have your battery tested and alternator also. I had a 2006 that would crank but not start and it was solved with a new battery. Crank your car and measure the voltage at battery, that's the real test. Voltage should be above 9 volts. You also have the OHV engine, Vulcan.
Did that...no avail. I know the relays click so the PCM has to be sending ground. It’s not getting the other power it needs. The fuel pump’s also not engaging either when I turn the key to run. No fuel, and no crank and ignition. The starter and ignition share the same relay too. I’m also unable to communicate via my obd2 scanner. It’s got to be either a bad pcm or the pcm not communicating with the Ford GEM. Question is, how do I check that?
 

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^nector and ^^^ Agreed.
Check for VREF (5 V sensor reference voltage). IMO, easiest place to do this is at the TPS. Unplug TPS and with key in RUN measure voltage between orange and black wires at harness connector. Should be very close to 5.0 V. If well under 5 V, you have a shorted sensor.
 
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Thanks for the great vid. Whaddaya bet that junkyard engine ended up in the junkyard because no one could figure out why it wouldn't run? Sad to think how many good cars go to junkyards because the mechanics were unable to diagnose a simple problem.
 

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^^Im to assume that if it’s low voltage there in the run position then the shorted sensor could be anywhere correct? So the TPS shares a 5v reference circuit with all of the sensors related to the PCM? Just making sure so I don’t miss anything when I’m doing this tomorrow.
 

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Yes, all sensors (TPS, ECT, IAT, DPFE, etc) share the 5 V VREF and a common internal PCM ground called SIGNAL RETURN. SIG RETURN is not the same as chassis ground.
 

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Discussion Starter #14
Out of curiosity, how would I check the signal return circuit? I’m learning a lot and excited to check on all of this tomorrow. It may give a huge clue. Also, if I find out I have a shorted circuit, how would I be able to determine which one in particular is shorted?
 

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PCM ground is in the pic, lower right, and common sensor return = ground. It is off because a bad ground where Ford bolted the eyelets over paint and in time bad ground. Bad idle traced to return being significant level different from body ground. Sand the paint off and coat all with anti corrosion compound. Any grease will do to keep the sanded metal from rusting. Wire brush the bolt threads and coat inside and out side threads. Ford is sensitive to voltage and they bolt grounds over paint. Same goes for the battery negative wire to the fender. Sharing my experience.
-chart-
 

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Okay so I sanded down that ground today and the ground wire itself where it attaches. No change. I also couldn’t get ANY voltage from that 5v reference thing. I decided by chance to bring out my test light and go through the fuses underneath. What surprises me is that when I have the key to the ON position, I took my test light over to the GEM logic fuse. Aka fuse 34. The music was playing from the radio! Somehow my test light is supplying ground to wherever that fuse goes. The GEM logic fuse....what’s it do? And me supplying ground to it with my test light and getting the radio playing through my speakers must be a big hint about something but at this point I’m still lost. Can someone tell me where to go from here?

 

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Sorry for the double post but if I have my key in the On position and I find out that fuse 34 (GEM Logic) when I put my test Light on there that it turns on the radio speakers, isn’t that an indication that the GEM isn’t being supplied ground power? Where should I look? I feel like I’m really close to figuring this out now.
 

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It sounds like you have a ground issue.https://www.youtube.com/watch?v=uyncVz_HAtA
 

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Ugh.....I found the ground issue. You guys aren’t going to like what I have to say about what I found on the ground either. It’s the part of the body that holds the air box. Well....I went to clean up around it to unbolt the ground and....it was too rusted and rotted. This damn Taurus has a unibody construction. I’m junking it. I don’t like saying that but the New England rust is just too much. Most of the body has rotted after further inspection. I’m giving up on my Taurus.
 

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You can just add a longer wire to the present ground wire to get to a better area if that helps you. I junked two decent running 2001 Taurus because the rocker panels were totally rotted. Cars looked good but really not safe and the one only had 121k miles. My 2006 has a bad rocker panel so it too will be heading to a salvage yard soon. It has 225k miles so it doesn't hurt that bad.
 
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