When I was trying to reset the codes (with the jumper in place)
I turned on the key…
Fans were high…
I grabbed that computer connector and kinda yanked it all around…
there was no change…fans were on high and the check engine light still wouldn’t give me codes…(like it was ‘dead’)
Took my key out…
came back 10 hours later…key on…no fans…fuel pump kicked and it started…
sigh…
I guess what I’m getting at is…
For such a catastrophic failure… I guess I would have more constant trouble…Rather than the 4 hour drive…perfect…then 1 mile…then attitude for 20 hours of not starting/ running like crap/. not starting…then you do all these things to test…give up…come back…and it’s like…“I’m perfectly fine”…
Damn thing has 66K original miles on it…If it had 150K, I’d junk it…
1995 Mercury Sable 3.8L AT
Had 49K on it when I bought it 2/3 years ago…
I had a hard shifting car and a power steering problem( I thought.)…
Changed out the Power steering pump and no improvement in the steering…
Come to find out, the VSS Vehicle Speed Sensor was shot (it caused the “power steering problem” too… high pressure ? I don’t get that… but it fixed it too)
Kinda ran hot , but i just put a cool thermostat in it because I was too lazy/ cheap to change the radiator (sure it’s not too good looking at the stuff floating the coolant…)
The codes i WOULD get indicate the O2 sensors…but I’ve ignored those because I can’t believe that it would be catastrophic. I’ll change them soon anyway with my latest rockauto slap on what it could be and see…
Is there a warranty on the computer?
no warranty but are cheap on ebay… $ 40- $80 bucks
i’ve thought about it…or i guess what i thought was IF it’s the computer again…what is causing it…then it works perfect again…the power/ground ideas seem more likely…but then I think again…WHY doesn’t it just stay working or just stay broke…
??? MAYBE i should have turned the key OFF then ON again…after jerking that connector around…instead of giving up and coming back 10 hours later… ???
Power and grounds should be verified while the problem is occurring before replacing the computer.
Rock Auto lists several replacement PCMs for this car. Unusual for there to be replacement computers available for an old car, this suggest that there is still a demand for them and there is a high failure rate.
It sounds like the powertrain computer is faulty or confused. Suggest to verify one-by-one all of its critical inputs are to spec.
- V+ (battery + voltage)
- Ground (connected with low resistance to battery negative)
- OBD II port to scan tool connection (Presuming a 95 Sable is OBD II)
- VSS
- Engine coolant temp sensor
- MAF/MAP
- O2 sensors
- Crank position sensor
- Throttle position sensor
- Communications with other modules (body control, abs, tcs, whatever modules you have)
- Alternator & battery: Before first start of the day, battery should measure about 12.6 volts; then immediately after starting engine, 13.5 - 15.5 volts.
- Idle rpm (both cold and warm)
- Ignition timing
- Ignition components (distributor, dist cap, dist rotor, or coil packs if so configured)
I’m guessing your problem is either a faulty powertrain module or ignition module.
Verifying Power and Grounds would be next to impossible vs. the location of the Computer. Even if I have the correct wire to test… I do not know how the connection of the connector to the computer status is… I would have to have a “BAD” condition…then I would have to remove the connector and computer from behind the glove box,. Move computer to engine compartment… reconnect cable…I would then have to open the computer and do a measurement to be sure it IS getting to the computer board internally. Since I have such an intermittent problem, all this jostling, reconnecting, etc would be pointless. Thus the cheap, take my chances, ebay computer. I know what you are saying…but I don’t think it can be done reliably. If I had access to the inside of said computer as it sat in the bad condition, by all means, you should do this. But in reality… I don’t think this can be done accurately…
If a circuit board is difficult to place a test probe b/c of where it it located, sometimes I’ll connect jumper cables to the test points, then probe the end of the jumper cables. I’ve even soldered jumper wires to pcbs if there’s no convenient test-clip point. Suggest to not attempt this sort of testing unless you have experience and access to the necessary wiring diagrams, b/c it is easy to damage something.
V+ good
Ground to vehicle good
OBD II …no luck…its the original
VSS was changed 2 years ago. (WAS BAD)
Engine coolant temp sensor…NOT CHECKED/REPLACED
MAF replaced 4 weeks ago
O2 sensors. (look new, but will replace this next week)
Crank position sensor NOT CHECKED/REPLACED
TPS NOT CHECKED/REPLACED
comms…uhhhhhhhhhh
Alternator & battery GOOD
Idle RPM is spot on when it runs
Ignition timing GOOD when it runs
Ignition components / distributor NOT CHECKED/REPLACED - Dist cap REPLACED - Rotor REPLACED - Coil will be next week - sparkplugs and wires next week.
I like powertrain module idea… are there relays in there and such ?
Remember…the big clue is when the key goes ON…i have front fans on high it appears maybe the computer isn’t getting power…I also wonder if the temp sensor thinks it’s running 290 degrees? could it default to NOT START and cool the radiator ?
sigh…it used to be easy…
There are usually 2 or 3 ground wires, and 2 or 3 power wires going to the PCM. Back-probing the connector can be a tedious process that many mechanics skip and take their chances with a new module.
The picture below is not of a PCM connector, but it shows how connectors are back-probed for testing. The object is to test the wire for reliable power and ground.
Wire CAN be checked. Be nice to have a schematic… but that doesn’t guarantee that power/ground makes a good connection THRU the connector. I understand it is a 50% chance and that very well COULD be the problem (getting TO the connector). I guess what I should do is … when it appears to be running/correct… to document ALL the voltages on the harness…
Again…without a schematic…I may not know if they are INPUT voltages or OUTPUT voltages…
I’m curious now… would the 2/3 power connectors and 2/3 grounds all meet up internally for redundancy ? all tied together… so just one wire failure wouldn’t bring the entire computer down ?
This seems like a pretty important clue. Almost certainly a problem among the rotor / distributor cap / used computer / ignition module / MAF or the electrical connections to them. I think what I’d do with this problem, I start by removing, have a good look-see at each, good lighting on the work bench, then if they look ok, re-installing. Do this one by one, testing to see if the problem goes away after each. If I were venturing on a replacement scheme to debug the problem, being a firm believer in the principle of “if it isn’t broken, don’t fix it”, I wouldn’t replace anything other than those parts.
I presume you mean your car is OBD I. In some ways this is better than OBD II b/c OBD I is a less complex design. But you still have to have a working computer, working well enough it will at least spit out the diagnostic codes.
Didn’t you say you have a Haynes manual? Those usually have wiring diagrams, although possibly not the exact wiring diagram for your year and options. If necessary you can obtain the exact wiring diagram online for a small fee from a service-data business, like All Data or Mitchells. Sometimes public libraries have methods to get auto wiring diagrams too.
(sorry for the late reply…the site said I’m too new to post that much LOL)
Yet maybe another important clue…this last time it was ‘bad’ with the fan running high… I attempted to read/reset the codes. The reporting light (check engine light)…didn’t seem to care I had put the jumper in to read/reset the codes… like the computer was dead… (like no power or no ground). That’s why i was so curious about this power (powertrain) control module. I’ve seen relays ‘click’ and not connect due to corrosion or such… Do you think this module would have relays that push power to the computer ?
The Haynes says…(not for exact car, but for GENERAL reference)…in other words…useless…
A faulty relay seems very unlikely to cause these symptoms, suggest to not hang your diagnostic-hat on that theory. The symptoms are consistent w/the powertrain computer (PTC) sitting idle, not responding to requests. The engine won’t run and the OBD I diagnostic system won’t work without a fully functional PTC. The PTC is what fires the fuel injectors for example.
I outlined above most of the required inputs to the PTC. That’s where to start imo. Nevada – who’s more of an expert on this sort of thing than I am – suggests to focus first on the power and ground inputs. Makes sense. Many years ago I used to instruct non-tech folks how to use complicated scientific electronics equipment, pointing out to them the the main reason it doesn’t do as expected, either it isn’t plugged in or isn’t turned on.
So all the inputs, starting with power & ground, will have to be verified one by one; or you might get lucky by either removing and replacing the PTC, solving a connection fault, or installing a known-good replacement PTC. The problem with the replacements are that they are probably used, failed, repaired, and sold as refurbished. That sort of 30 year old electronic equipment tends to be unreliable. You might check if there’s any new-old stock somewhere (ask at a dealership), or if a general-purpose aftermarket OBDI PTC sold new is available for you car. Check over at Summit Racing’s website to se what they might offer. Note: If your car must pass an emissions test, an aftermarket PTC may not be allowed.
Pretty good chance the only problem you have is a faulty electrical connection, likely a corroded or bent pin in a connector. Has your car every been caught in a flood? Has it been kept near the sea? Both are common causes for corroded electrical connectors.
- Does this car use a CCRM (Constant Control Relay Module) or IRCM (Integrated Relay Control Module) that was popular in Ford cars of this era? CCRM/IRCM is a single unit that contained the ECM power relay, fuel pump relay, cooling fan relays, and one or two others, all sharing a gang ground.
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