nightmare of a problem, need help - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars
Ford Probe Forum | Mazda MX6 Forum Forum for discussion of the Ford Probe and Mazda MX6.

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 33 (permalink) Old 03-03-15, 05:56 PM Thread Starter
Registered User
 
Join Date: Mar 2015
Posts: 13
confused nightmare of a problem, need help

to make a long story short, i dropped the egr pipe when removing it on a 97 probe 4 cylinder automatic transmission. i did not remove the battery while doing this and the pipe hit the starter. after a lot of sparks i assumed i'd be replacing a fuse or fried wiring.

all the fuses were fine and all the wiring was fine (i later unraveled the harness to make sure). but here is the problem;

when i turn the key to the run position the following happens. the fuel pump relay and the low speed fan relay click rapidly. the cooling fan runs full speed. the fuel pump runs but does not stop. i have no spark when its turning over and i can no longer access it with a scanner. after extensive diagnostics and walk through advice from a master tech we thought it was the pcm.

i purchased a used pcm and the swapped it out with absolutely no change.
after redoing all the diagnostics again and triple checking the wiring im looking back at the pcm.
is it possible i have two bad pcms? i would think they wouldnt have the same symptoms

the tech recommended i find someone near by with a 97 probe with autotransmission and see if they were willing to let me try my pcm in their car... so anyone near medina ohio thats willing?

has anyone out there ever had a similar problem with similar symptoms?
i've been tinkering with this problem for about 5 months now and any help would be great

grantscho is offline  
Sponsored Links
Advertisement
 
post #2 of 33 (permalink) Old 03-04-15, 11:06 PM
Registered User
 
Join Date: Feb 2015
Posts: 182
Re: nightmare of a problem, need help

If the PCM was not in the direct short loop it could easily be OK. Your switchout seems to verify that. You'd have to look at the wiring that was close to the short area to see what circuits could have been affected and need a electrical schematic to deduce what is common to all those things powering up when they shouldn't. FYI, one tends to look for shorts right where the incident happened but if the EGR tube provided the short path then the entire power supplying leads' length could be suspect. I've seen a short that when done also melted wires say 3-4 foot from the incident area, the overloaded wire can go red hot anywhere and not necessarily right at where the accident was. The whole length of wire does not necessarily melt down at once, sometimes one piece of it before the rest does. So, simply opening up harness for maybe 6 inches or so can easily miss the problem.

Everybody wants to blame the PCM, they rarely go bad. And two in a row? Unthinkable. When I was in auto parts close to 90% of all the ones changed out for being bad 'for sure' had nothing wrong with them at all. People tend to blame the most mysterious part least understood when they cannot figure out a problem. If the wiring that was overloaded does not go to PCM then PCM is all right, you send 150 amps or so all day long to starter everytime you start car but it does not blow out the PCM which is electrically hooked into the same power system does it?
amc49 is offline  
post #3 of 33 (permalink) Old 03-05-15, 07:50 PM Thread Starter
Registered User
 
Join Date: Mar 2015
Posts: 13
Re: nightmare of a problem, need help

yeah, i assumed wiring also but whats frustrating is that i've unraveled ALL the wiring involved with the starter as well as the harnesses with the wiring that is in common with the symptoms and its good. the tech has been looking through the schematics and having me check voltage, resistance and proper grounding to no avail. been searching this out since november :(
grantscho is offline  
Sponsored Links
Advertisement
 
post #4 of 33 (permalink) Old 03-05-15, 08:33 PM
Moderators
 
Join Date: Feb 2001
Location: Bibra Lake Western Australia
Posts: 3,584
Re: nightmare of a problem, need help

I am not familiar with the probe and have no access to its wiring diagrams but would swap out the pump and engine start relays; you may have welded their contacts shut when you shorted out the starter. Or test the N/O (normally open contacts) on relays haven't gone closed circuit see http://www.the12volt.com/relays/relays.asp if you need to know more about relays. Also check all your fusible links for continuity; don't rely on their appearance (just because the bit in they window is intact doesn't mean the FS is necessarily OK) use a multimeter or swap them out. Normally the fusible links should have provided some protection in your situation. Ditto with fuses; use a multimeter to check for continuity.

Regards Blue
Aussiblue is offline  
post #5 of 33 (permalink) Old 03-05-15, 09:20 PM
Moderators
 
Join Date: Feb 2001
Location: Bibra Lake Western Australia
Posts: 3,584
Re: nightmare of a problem, need help

And does the battery check out OK. No chance you reversed it's polarity is there? Extremely rare but it can happen Battery Myth | Can a Battery ‘Reverse’ its Polarity? ? The welded relay contacts followed by a failed fusible link seem the most likely candidate to me.

Regards Blue
Aussiblue is offline  
post #6 of 33 (permalink) Old 03-05-15, 11:15 PM
Registered User
 
Join Date: Feb 2015
Posts: 182
Re: nightmare of a problem, need help

That makes sense, a possible toasted relay issue. Don't know myself on that earlier model but often a main 'EEC power relay' is used to power up lots of those things you are complaining about, could be an issue with that too.

You're missing something, no magic there, you're getting power when not wanted or grounded shorts to activate those devices, the wiring (at least some of it) CANNOT be good with that present.

You can always start yanking fuses to power down the shorted devices and see what leg of harness that sends you to. The shorted fuse may kill devices without even being the fuse for them, that would point toward where it could be.

I'd be looking close at any diodes in there anywhere as well, although they didn't use as many back then as now.

Biggest issue will be sitting down and carefully thinking about every step you take, it is very easy to get lost in that stuff not doing that. One person doing it rather than two or more is better, too easy to get out of communication there, but it means the one person must be sharp at it.

One of the first things I'd be sorting out is whether the errant devices are grounding when they shouldn't be or powered up with a permanent ground and powering up is the problem there. The schematic may easily sort that out.

Another horror story possibility.............there can be short(s) in there in such a way so that every GOOD PCM that plugs in is instantly blown out. Not a happy thought but pretty unlikely.
amc49 is offline  
post #7 of 33 (permalink) Old 03-06-15, 03:18 PM Thread Starter
Registered User
 
Join Date: Mar 2015
Posts: 13
Re: nightmare of a problem, need help

ive done a lot diagnosing since november, so much that i didnt want to try re-type it all here. i have a spare parts car ive been yanking parts to swap out but to narrow down some of the suggestions made,

i swapped out the battery, the alternator, all the relays in the fuse box under the hood as well as the fuses, iac valve, ckp sensor and the distributor.
ive also pulled the fuses 1 by 1 to to find which one stops all the relay chattering and found it to be the f/p inj 60amp fuse.
ive checked the wiring in that fuse circuit and gone as far as pulling the fuse box up and checking the wiring going into the sockets as well as unraveling the harness that goes under the wheel well before entering the cab near the inside fuse box.

i took voltage readings from each pin on the pcm with key off/key on pcm unplugged and key off/key on pcm plugged in and charted them. i noticed an unusual amount of voltage (14volts)coming from 3 pins (pin #'s 71, 86, 97, which are w/r power wires and the pk/y wire for the a/c input) i say unusual because the car was not running and the voltage at the battery at the time was 11.6 (it was 12 something with the key off) there may be more testing that i did that i forgot to mention.

i appreciate all the suggestions. this helps a lot to just bounce the collected data off of other minds.

i also realized i never checked all of the harnesses that included that pink/yellow wire to a/c fan input so now i have something i can work on. i'll let you know what i find.

as for the insight "....there can be short(s) in there in such a way so that every GOOD PCM that plugs in is instantly blown out."....... stop it! you're giving me nightmares! lol
i so hope thats not the case.
grantscho is offline  
post #8 of 33 (permalink) Old 03-06-15, 04:30 PM
Moderators
 
Join Date: Feb 2001
Location: Bibra Lake Western Australia
Posts: 3,584
Re: nightmare of a problem, need help

OK given all that, next I'd check the ECU ground for continuity between where it is earthed and the ECU and also check the engine ground for continuity. Also check for battery voltage at the diagnostic port +B terminal and continuity between the GND (Ground) terminal of the diagnostic port and the engine and body.

Regards Blue
Aussiblue is offline  
post #9 of 33 (permalink) Old 03-10-15, 04:23 PM Thread Starter
Registered User
 
Join Date: Mar 2015
Posts: 13
Re: nightmare of a problem, need help

Quote:
Originally Posted by Aussiblue View Post
OK given all that, next I'd check the ECU ground for continuity between where it is earthed and the ECU and also check the engine ground for continuity. Also check for battery voltage at the diagnostic port +B terminal and continuity between the GND (Ground) terminal of the diagnostic port and the engine and body.

the ecu ground and engine ground are good and the ground on the dagnostic port is good, however im not getting any voltage from +bus terminal
grantscho is offline  
post #10 of 33 (permalink) Old 03-10-15, 06:47 PM
Moderators
 
Join Date: Feb 2001
Location: Bibra Lake Western Australia
Posts: 3,584
Re: nightmare of a problem, need help

Quote:
however im not getting any voltage from +bus terminal
Double check that engine start fusible link. Do you get 12 volts at one terminal of the link when it is unplugged?

You may also have melted the inside of the main cable from the battery to the starter; do you get 12 volts where it connects to the starter? If you disconnect both ends of this cable what is the resistance (should be close to zero).

Regards Blue
Aussiblue is offline  
Sponsored Links
Advertisement
 
Reply

  Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars > Ford Cars and PAG Vehicles > Ford Probe Forum | Mazda MX6 Forum


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome