It's behaving like it always did.

 

OK, here are the results I got:
Pulled the Fuel Pump relay and the disconnected the Inertia Fuel Shutoff Switch (IFSS).
- Measured voltage across 30-87 (where the Fuel Pump Relay was originally) in the relay box. got 12V. Little strange to me, with the IFSS disconnected, the only other thing on the circuit is the PCM. Not sure if it is supposed to show as a ground. So, with the IFSS still disconnected, I checked resistance to ground of that line and it was 2.7K ohms which makes pretty good sense for a logic circut, although I am used to seeing 4.7K on strip resistors used in 5V TTL applications. Moving on...

- Measured voltage at the IFSS plug and got nothing (expected, relay socket empty)

- Jumpered 30-87 and measured at the IFSS. Got 12V.

- Removed Jumper and installed assumed (new) good relay.

- Measured at the IFSS plug. Zero volts.

- Turned the key on to energize the relay. Checked at the IFSS plug and it was 6V. <- strange?

I don't have anything better than the Hayes manual (page 12-24) to tell me why that would happen except that it seems that the PCM is dragging the battery voltage down to 6v before it ever gets to the pump. It still cranks well, although I can tell that it is slowing down a little. Been giving the battery a workout with no re-charge.

Anyone have any observations based on this data? Thanks.

 

If you pulled the relay and bypassed it and the fuel pump did not cycle that would point to the back of the truck in my opinion.

My thought on the topic ( and it is worth what you are paying for it )

1. Unplug the fuel pump, the connector ( C415 ) appears to be a 4 pin connector.
2. Put your meter ( set to VDC ) on the black ( ground ) and Pink w/ Black stripe wire ( +VDC from the IFSS )



3. Jumper the fuel pump relay as you did before from 87 to 30



4. Check the meter for +VDC reading. It should be ~ same as the battery.

If you get 6VDC, try a different, known good ground for the test ( trailer tow adapter if that is good ).

If you get 6VDC from 2 different grounds ( and at least one is tested good ) I would check the resistance from the Fuel pump connector to the IFSS ( after pulling the jumper out ). It should be < 250 ohms. If not, I would think there is a problem in that side of the circuit.

The jumpering of the fuel pump relay normally open contacts and it not running make me think fuel pump or wiring to the fuel pump issue. That is what my brain is pointing to this AM..

 

Thanks for your time this morning! As long as it is not raining too bad this afternoon, I'll give it a shot. Little bit more helpful information on that drawing.


Also started taking the side brackets off to get the factor bedliner off if needed to remove the bed. I'd rather grab a few guys and carry it off instead of dropping the tank. 5 of the 6 bed bolts looked like they will probably come loose, the left-rear one has me a little concerned.

 

Well. No change in situation with it. Either way, with the relay installed (and the key on), or a jumper installed, the voltage that ultimately gets to the pump is no more than 7V. That's what doesn't make much sense. The pump is out of the circuit, the IFSS is out of the circuit.

OK got the last couple checks I could do before it started raining and played Columbo with the truck, trying to get it to unintentionally trip up and get caught in a lie. Didn't quite get there but I established 2 facts.

1) No matter how much jumpering, the fuel pump wouldnt run.
2) That, with the IFSS disconnected and a meter hooked to the "hot" lead, a jumper installed in the fuel pump relay socket would give me full battery voltage at meter (and thus to the pump if the IFSS was in the circuit), but when a relay (any of the 3 I have) was put in there, the voltage would read about 6V (with the key in the run position).

Therefore, I have to think that all the relays are bad, or the current to shut the relay is inadequate. Seeing as how switching them around randomly didn't matter, pending bench testing of the relays, I have to assume that the circuit that actually latches the relay is defective.

Hopefully that makes sense. Fairly certain that the pump needs to be replaced (167K, not unheard of), but I think there is something more going on.

 

Did you try a different ground while testing at the fuel pump connector ?
- EG: Trailer Tow adapter ground.

You can try:

1. unplugging the IFSS and jumpering the Dark Green w/ yellow strip wire to the Pink w/ black stripe wire in the pass side kick panel.
2. Unplug the fuel pump ( option* )
3. Install meter at the fuel pump connector.
4. Install jumper in the fuel pump relay socket.

* I say option, you can just jumper around the IFSS and install the jumper in the relay socket and see if the fuel pump runs at this step.

If you have +VDC ( close to battery ) in the kick panel on the Dark Green w/ Yellow stripe wire, that is a short run ( fuse panel to pass side kick panel ). You still have to ID if the IFSS or the wiring or the fuel pump are the issue. This is where testing without the IFSS is a step to take.
- You could also use a new section of wire from the IFSS to the fuel pump ( both +VDC and ground ); but this is more work than 2 scotch locks and a short piece of wire.

The jumper removes the relay from the testing you are doing, and having the same issue with that many relays, while possible, it is not probable.

 

Yes, tried different grounds. The IFSS is not the issue because I have jumpered past it. (I wasn't clear about that in the previous post, but have done that). The only difference in how much voltage is getting to the hot wire for the pump is whether I have a jumper, or the relay, in the Fuel Pump Relay socket. Also checked the continuity of the IFSS and it was sat. (With the pump COMPLETELY out of the circuit).


I still think the pump is bad. Also when I was checking out the lines to the tank, a few of them are decomposing so some work needs to be done anyways.


Thanks!

 

Did you ever to the test I recommended in post #58, EXACTLY as I presented it? I see a lot of other stuff, but I haven't taken (and won't) the time to sift through all the possibly extraneous items

 

no, did not do it exactly as you said because putting the lead on the pink/black lead gives zero volts regardless - it goes straight to ground through the motor. checked it against the drawing.

however, i also put it on the yellow/green wire and watched it. it went to 12v but in less than 1.5 seconds it dropped off to 6v. so, somehow the relay is staying shut but the pcm is dropping the available voltage to the pump by shunting it away. or..... the relay is opening and the pcm is backfeeding 6v. maybe the normal running voltage for the pump is 6v. don't know. not enough experience with car computers. is there a detailed operation guide to the guts of the pcm? i fix arcade circuit boards and monitors occasionally, so electronics aren't foreign to me, it's just i don't know what 'normal' system operation looks like in this truck. for all i know, it's doing exactly as it should.

sorry for the lack of capitalization, this laptop has a broken shift key.

thanks.

 

That is normal.

That is exactly what is happening when you see about 6-7 volts (when the full battery power is not being applied). That's not power to feed the pump, it's simply voltage present at PCM pin 40 due to an internal voltage divider or pull-up.

Better than the opposite!

 

Thanks for the info! Had to grind out 2 of the bed bolts, but once the neighbor guys saw me throwing sparks by the road, I had all kinds of help lifting the bed off. It was like moths to a flame ...


Should be done with the job by the end of this weekend.


Thanks folks!

 

working again. thanks for the help. biggest hurdle was psychological. weather was 20 degrees when trying to get the bed off and that doesn't help anyone's motivation.

once my neighbor handed me his grinder and said 'cut the damn bolts off. the truck is 14 years old...', the path became clear