Inertia Swith or Fuel Pump - Defender Source
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  #1  
Old May 31st, 2011, 11:50 AM
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Don Bunnell
'86 110 3dr ST
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Inertia Swith or Fuel Pump

I have had a weird issue going on with my 90. While at Rausch, it stalled a few times going thru the wet stuff. Thankfully Dana helped out and got me running again but I think the issues are showing up a little more now. (One I think is full pump related and the other is related to the ignition which I will address as well later)



Here are a few notes to hopefully help:
  • Coming thru the first water section at RC, truck stalled. Dana popped the dizzy cap and said things looked dry but sprayed with WD-40. Jeremy asked if the fuel pump was making a sound in key position 2, it wasn't and then we pushed the inertia switch. Truck started up. FWIW, I bumped a tree pretty good 10 minutes prior in the run.
  • Driving at low rpms around the block on Thursday night with my daughters and her friends, went into the driveway, stopped and the truck wouldn't start. I didn't notice if the fuel pump was "whirling" or not. Left it for 10 minutes, went out and it started right up. (I have a feeling this is ignition related but...)
  • Was in the driveway on Saturday teaching my son how to drive standard. He was bucking the truck naturally but it was running fine and then I parked it for a while when we were done. Went to move it to the garage that night and no start - noticed the fuel pump was not "whirling"
  • Changed the black relays to silver ones I had on Sunday - both are pretty recent. I know the black ones were from AB and from Dec 2010 (I mark them now) - still no start. The silver ones were from the begining of '09. They are in the truck now.
  • Went to start the truck Sunday night - heard the "whirl" and it started right up.
  • Left it parked on Monday and would check at various times during the day - it started each time except for last night - no whirl from the fuel pump. I pushed the inertia switch - nothing. Then did a few other things like unplug the inertia switch, and went underneath and moved the coil of wires going to the fuel pump, hit the intertia switch again. Went back in - fuel pump whirl and it started right up.
  • Fuel pump is recent - I put a new one in from Atlantic British on October 2009 when I redid the rear bumper and gas skid plate.
I am thinking either inertia switch or wiring to the fuel pump. Question is, before I pull the whole tank, how do I check if the inertia switch is good or bad? And if it is bad, who sells - I wasn't able to find on the main vendors web sites. Thanks in advance.
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  #2  
Old May 31st, 2011, 08:26 PM
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Ethan
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Testing an inertia switch is easy. If you suspect it, wait until you are experiencing symptoms, then pull the plug off the inertia switch then jump the two terminals with a paper clip (or little jumper harness if you are so inclined). If the problem immediately stops, you're in like Flynn.
Betcha RN sells them.
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Old June 1st, 2011, 11:05 AM
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Don Bunnell
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Thanks Ethan - I was thinking that was the case. Seems easy enough. The only other question is what 2 terminals do I jump on the inertia switch terminal? There looks to be 3. Not a big deal, I could test a combo but wondering if you knew off the top of your head.
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Old June 5th, 2011, 09:09 PM
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Don Bunnell
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So, I thought I had this solved. Tested the inertia switch with a jumper wire. And things kept pointing to the inertia switch. Called RN, AB, RDS and finally Will aka Roverguy said he had one that would fit (apparently '95s are NLA but mine is located on the bulkhead which might be the newer style?). Will got me one to my house in a couple of days and I swapped it with the one in the truck. The 90 started right up and I drove it around a bit that night and on Sat morning.

So Saturday afternoon, I had the hose out washing something else and figured I'd give the engine a cleaning as it was a mess from the trip to RC. Cleaned it up let it dry for a bit while I powerwashed in the fenderwells. Went to start, it fired right up. Let it run for a while to dry things off. Was doing things around the garage and after it had run for 10-15 minutes, it died. Tried starting a few times nothing.

Played around with it today and popped in a jumper. Still nothing. Got out the test bulb and turned the key - power was occuring both side of the jumper wire but no whirl from the fuel pump. Dropped the skid guard then lowered the tank to get to the wires. The connection seemed tight but I undid it anyway and replugged it back in. Tried the ignition, heard the whirl and it fired right up (still had the jumper in). Plugged the inertia switch in and no-go.

Does anyone know what could be killing inertia switches? I have dried mud in the seatbox but not sure if the ECU got wet - could a bad ECU burn out an interita switch? Relays and fuses have been fine. Could some water/dirt gotten into the fuelpump electric connection and burn out the inertia switch? Any help would be very appreciated - TIA!
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Old June 5th, 2011, 09:55 PM
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Daniel Marcello
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Could be a ECU issue. I have a spare 4.2 I could send down to you if you want to test it out. It has to be some connection between inertia and fuel pump. Did you check the ground or for a short in the inertia?

I can shoot you out that 4.2 asap.
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Old June 5th, 2011, 10:56 PM
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Don Bunnell
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Quote:
Originally Posted by ini88 View Post
Could be a ECU issue. I have a spare 4.2 I could send down to you if you want to test it out. It has to be some connection between inertia and fuel pump. Did you check the ground or for a short in the inertia?

I can shoot you out that 4.2 asap.
Thanks Daniel. I forgot to mention, I have the stock 3.9 ECU that I could swap in (I have been running a 4.2 chip that I got on the board). I could try that and see what happens.

Not sure if this link will show but got it off Dweb: http://discoweb.org/forums/attachmen...6&d=1289497036

It looks like the power pattern is ECU -> Fuel Pump Relay -> Inertia Switch -> Fuel Pump

So like you said, a short in between the Inertia and the Fuel Pump seems logical. I would not have thought the Inertia Switches were that breakable. BTW, how would I check the ground or for a short in the inertia switch? Thanks
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Old June 11th, 2011, 04:03 PM
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Don Bunnell
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Just an update after farting around with this for the past week. Hopefully what I have found out/experienced might help someone in the future.

- Checked the wiring from the rear frame to fuel pump. I noticed that the plastic outside was crimped in one area and after taking off all the eletrical tape and plastic coil covering saw a small nick in the purple/white main wire. Electrical tape over the nick as it was very small, then cleaned up all the wiring, rewrapped with electrical tape and all new plastic coil covering.

- I also check the connection to the fuel pump and noticed some burnt area where the purple wire come thru. Cleaned that up and scrapped it best I could.

- I thought I had it sorted out and ordered another inertia switch from AB. Plugged it in, and it worked fine. Then drove the truck around and at the next stop it wouldn't start up. It seems a big issue was the connection at the inertia switch. The plastic female connection wouldn't clip to the inertia switch all the way. So with the truck running and driving and with the inertia switch in a vertical position, it would vibrate down just enough to not let it start up. So, I took the inertia switch off the firewall made sure the clip latch was holding and wrapped a small zip tie around it to keep it in place then screwed it back to the firewall. I don't want to jinx it but it has been starting and running fine since.

Overall a PITA to sort out but if it finally is, I will be happy. Now on to the 50 other little projects I have for the turck....
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