'86 930- Fuel pump wire harness issues
06-06-2005, 10:27 AM
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'86 930- Fuel pump wire harness issues
I've been having some fuel pump problems since obtaining my 930, which was not caught by PPI.
At any rate, I was able to trace the source to the wire harness that enters the back side of the metal relay tray that resides on the left firewall (if you are standing behind the car & facing the engine bay). After pulling the end of the wire harness out, I opened the plastic end clip that holds the metal pins of various wires in place. I noticed that a couple of these wires right before it enters the soldered pin connector seem slightly "charred."
BTW, I'm diagnosing this harness as my problem b/c with the key in the on position (fuel pump suppose to be running), I do not hear the rear fuel pump. When I tap the harness, I hear that noticeable wine of the pump.
My question is it feasible to cut, mend, solder & replace the slightly burned portion of wires or replace the entire harness itself? How expensive is a new or used harness? How difficult to replace DIY?
I would post a pic, but some low life b@$tards decided to break in my car at the hospital emergency room parking lot & take my former beloved laptop w/ my digital camera in it.
At any rate, I was able to trace the source to the wire harness that enters the back side of the metal relay tray that resides on the left firewall (if you are standing behind the car & facing the engine bay). After pulling the end of the wire harness out, I opened the plastic end clip that holds the metal pins of various wires in place. I noticed that a couple of these wires right before it enters the soldered pin connector seem slightly "charred."
BTW, I'm diagnosing this harness as my problem b/c with the key in the on position (fuel pump suppose to be running), I do not hear the rear fuel pump. When I tap the harness, I hear that noticeable wine of the pump.
My question is it feasible to cut, mend, solder & replace the slightly burned portion of wires or replace the entire harness itself? How expensive is a new or used harness? How difficult to replace DIY?
I would post a pic, but some low life b@$tards decided to break in my car at the hospital emergency room parking lot & take my former beloved laptop w/ my digital camera in it.
06-06-2005, 05:09 PM
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Lex: Your fuel pumps are NOT supposed to run until the engine is cranked. Intake vacuum lifts the sensor plate, which allows the fuel pump relays to start the front and rear pumps. I need more info to try to figure out what you've found in your harness. By the way, what is the car doing wrong? FYI, a slight darkness at wire ends is actually OK, fried insulation that has split and is falling away is no good.
Pete
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06-06-2005, 07:43 PM
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Let's see.
I do hear a distict buzzing noise at the engine bay w/ the key in the position right before cranking. Whenever I do not hearthat "buzz," the car does not start nor run.
There are 2 specific wires inside that harness which are giving trouble. I do not have a schematic, but if I were a betting man and you know we all are with these cars, I believe 1 leads to the fuel pump & the other may be related to my tachometer.
Over the weekend, I pulled out my i/c to get better access to the metal tray where the wire harness is entering. Upon removing the slender plastic cover which looks like it is "forcing" the metal pin end connectors into the female connector to make a connection, has a burn spot (i.e. melted plastic that would otherwise be present to make that electrical connection for that specific wire).
I placed some black high temperature silicone to build up the missing edge for time being. In addition, I also cut away the frayed wires that were also corroded & spliced in some fresh wiring. I then soldered these new wires to the pins which in turn are placed inside the plastic cap.
In terms of what the car is doing, it sporatically cuts out. I'll be simply driving down the road & blip, rpm's drop off to zero, the battery & alternator lights kick in and I cruise to a stop. Several times without touching the key, I go to the engine bay to discover the previously mentioned "buzz" and I do not hear it. So I just tap the wire harness and next thing you know, the buzz comes back and the car starts allowing me to continue on.
As far as the tach goes, it just started fluctuate high & low today. I would imagine this is a result of something I touched over the weekend. If I'm cruising in 5th gear at about 2.5k rpm (car has a 5 speed conversion), the needle will just randomely fluctuate to about 5k or 6k, bounce back off the 0k & then find its place right at the appropriate engine speed. The engine itself is making no audible indication that it is in fact increasing or decreasing speed.
I hope that was detailed enough. Please let me know if there are any more you may need. I did drive the car again today & that is when I noticed the "dancing" tach. In terms of performance, the car drove virtually flawless w/o cutting out.
Oh yeah. One of the charred wire coverings had about 4 to 5 stands of wiring inside, so I determined that this couldn't possible be making a good electrical connection.
I do hear a distict buzzing noise at the engine bay w/ the key in the position right before cranking. Whenever I do not hearthat "buzz," the car does not start nor run.
There are 2 specific wires inside that harness which are giving trouble. I do not have a schematic, but if I were a betting man and you know we all are with these cars, I believe 1 leads to the fuel pump & the other may be related to my tachometer.
Over the weekend, I pulled out my i/c to get better access to the metal tray where the wire harness is entering. Upon removing the slender plastic cover which looks like it is "forcing" the metal pin end connectors into the female connector to make a connection, has a burn spot (i.e. melted plastic that would otherwise be present to make that electrical connection for that specific wire).
I placed some black high temperature silicone to build up the missing edge for time being. In addition, I also cut away the frayed wires that were also corroded & spliced in some fresh wiring. I then soldered these new wires to the pins which in turn are placed inside the plastic cap.
In terms of what the car is doing, it sporatically cuts out. I'll be simply driving down the road & blip, rpm's drop off to zero, the battery & alternator lights kick in and I cruise to a stop. Several times without touching the key, I go to the engine bay to discover the previously mentioned "buzz" and I do not hear it. So I just tap the wire harness and next thing you know, the buzz comes back and the car starts allowing me to continue on.
As far as the tach goes, it just started fluctuate high & low today. I would imagine this is a result of something I touched over the weekend. If I'm cruising in 5th gear at about 2.5k rpm (car has a 5 speed conversion), the needle will just randomely fluctuate to about 5k or 6k, bounce back off the 0k & then find its place right at the appropriate engine speed. The engine itself is making no audible indication that it is in fact increasing or decreasing speed.
I hope that was detailed enough. Please let me know if there are any more you may need. I did drive the car again today & that is when I noticed the "dancing" tach. In terms of performance, the car drove virtually flawless w/o cutting out.
Oh yeah. One of the charred wire coverings had about 4 to 5 stands of wiring inside, so I determined that this couldn't possible be making a good electrical connection.
06-07-2005, 06:04 PM
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Oh boy. The harness with damage, is it the one to the engine, or the one from the tunnel of the car? Whichever, it sounds like you're going to have to replace it, or have it replaced. What is the history of the car? Miles? Original engine? Theft recovery? The reason for asking, your problem is really unusual...
Pete
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06-07-2005, 09:15 PM
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Hmm. I am not certain, but the harness that is giving me fits connects to the metal tray that holds the various relays just to the left of the motor itself.
From what I can tell via the service documentation, I am the 4th Owner. Nothing unusual in terms of the car's history. The 2nd Owner came w/in a smidge of doing a 3.6 transplant, as I see the estimate and there are turbo 3.6 decals on the rear engine lid. The odometer currently reads 54k, but I do not believe that is accurate. I did buy it from a fellow rennlist board member here.
From what I can tell via the service documentation, I am the 4th Owner. Nothing unusual in terms of the car's history. The 2nd Owner came w/in a smidge of doing a 3.6 transplant, as I see the estimate and there are turbo 3.6 decals on the rear engine lid. The odometer currently reads 54k, but I do not believe that is accurate. I did buy it from a fellow rennlist board member here.
