I took the following readings:

pin 30 to grnd w/ key on - 12v
pin 87 to pump connector (grey wire at connector pin 3) - <1 ohm
pin 87 to ground (key off) - infinite
pin 86 to grnd - <1 ohm

note: pin #s refer to fuse box connections where relay connects to.

I also took readings from pin 1 at the connector that goes to the fuel pump (corresponding to the black wire) - to grnd - 2.6 ohms

note: the pin #s at the plug refer to the new connector that comes with the fuel pump. From left to right i refered to them as 1 thru 4, with pins 1 and 3 are the wires to the fuel pump. 1 is the grey, 3 is the black. The colors on the new plug match the colors on the old one and the larger guage wires are to the pump and the smaller ones for the sending unit. I would expect the ground to be <1 ohm....but 2.6 shouldn't be high enough to make a difference....especialy it should have no effect on voltage at pin 3......I did check the resistance between the 2 leads for the pump.....and they're not shorted together. It sounds like the relay is bad...but i've swapped it with good relays...and it has no effect .....

What is the other connector on the pump for?? On the schematic it shows a "fuel pump prime connector". Is that it? And if so what is its purpose? I checked the ground readings for that plug as well and got the following (pins from left to right)
1 - <1 ohm
2 - 51 kohm
3 - 1.22 kohm

What next? I guess I'll get a new relay.......but the other ones (for horn and others with the same part no. as the fuel pump) should have worked if that was the problem...not sure where to go next..

 

There is no fuel pump prime connector. That reference is due to the same diagram being used for the S10 pickups as well. The prime connector is only found on the 2.2L I4 equiped pickups.

What happens when you jumper pin 30 to pin 87 at the relay location? Do you get battery voltage at the pump? Will the pump run?

The problem that can sometimes occur with a bad ground is that it can show a reasonable resistance when unloaded, but can actually get worse once loaded. Is there any way that you can monitor the voltage across the pump wires with it hooked up to the pump? Maybe monitor the fuel pump ground while having the other lead on a positive wire to see if it drops out when the pump is on?

 

Alright.......indications are changing.......i am no longer getting voltage at pin 30 to ground......i was before, but not now. I checked the fuse (ecm B) and the fuse was good. I am getting voltage on the incoming side of the fuse connection. I took a resistance measurement from the output side of the fuse connection to pin 30 and its inconsistant, but stays close to 1.5 Mohm...... I had unwired the plug for the fuel pump to reperform the above readings without going through the new connector in case that was bad. the plug was good.......i even jumpered the hot side of the fuse to the grey lead coming from the fuel pump plug that i had disconnected. The fuel pump runs. Any tips on removing/troubleshooting the fuse block. If your first thought is to get someone with electrical experience.......i am an electrician in the Navy. I'm thinking there was a bad connection in the fuse block assembly from the begining....that was enough to show voltage, but once current is passed through it opens. Kinda iffy but its what i got so far. I don't know if the internals of the fuse block are accesable or if you have to change the whole thing. Thanks again for all your help.

 

don't know where you got to with yours but my 2001 uk rhd blazer lt had a similar problem. bought it for a giveaway price as previous owner had given up trying to fix it... i have been at it two weeks now. it was starting sometimes, totally at random. he thought it was the immobilser, but i checked it out and all looks good. finally after disabling vats system and overriding key passlock, i got to realising there was no fuel pressure, as no power to pump.... weird thing was there was no cranking either as if it was immobilised. finally i have wired the starter switch directly to the fuel pump relay and from relay output to fuel pump. i also put in a remote start wiring directly to starter relay. amazingly its starts and runs fine. so either it was immobilised but it only disables cranking and fuel pump ( i find this hard to believe), or the fuse box assy is faulty rendering the starter and fuel pump feeds to be bad. I am not saying its fixed 100% till i tried it for a month or so, but scanning thru the posts it seems this is a common thread and changing keys, key units, fuel pumps etc etc, only sometimes fixes it. i think there is perhaps a major issue with the fuse blocks. have ordered a replacement but coming from the us takes ages! any comments/feedback. brian