I dont even no where to begin lol, I have a 98 blazer/jimmy, but the other day, I drove to emessions, got tags then at the gas station the truck died. I have replaced damn near everything except internals, therefore figured it was the pump.

I replaced the pump beause, what I thought was the fuel pump relay kicking was another. This problem was intermitten, I went to tow the truck home and it started, put the new pump in and it primed 3-4 times. Now I have no power at the gray wire on the pump pig tail. I can jump the test terminal to 12 volts and I now have power. I replaced the relay 2 times still nothing. I have pulled the the oil press switch and metered it and it is aprox .30 ohms on two pins and overload one one so possible short inside but hard to believe this will stop relay for engauging.

As far as the security light it seemed to kick on then off normally but after the switch is replaced I am going to focus on this being a possible issue.


I am at a loss and dont know where to go from here. Thanks for any help!!!ready to be back on the road haha.

 

I forgot to include, when looking at the relay socket, top right is hot, bottom right is accesory hot and left top and bottom are both common or ground and my ecmb 20 amp fuse is good but replaced to be sure

 

I would look for DkGrn/wh on blue connector loc F7

But yeah.. leaning over fender, I did that.

 

The fuel pump relay wiring is as follows and can be checked by removing the fuel pump relay and probing the terminals:

Dark green with white trace: From VCM to trigger the fuel pump relay. Must show battery voltage for 2 to 3 seconds when the ignition is initially turned to the RUN position. After the 2 to 3 second "pump prime" voltage should drop to zero.
Black wire must show less than 5 ohms resistance to ground at all times.
Orange wire from ECM B fuse must show battery voltage at all times.
Grey wire goes to the fuel pump. The grey wire at fuel pump module should only show battery voltage for 2 to 3 seconds when the ignition is initially turned to the RUN position.

The "pump prime" terminal on 1998 is in the underhood fuse panel right next to the fuel pump relay. It's a small single female terminal. The wire goes directly to the fuel pump module. If you apply battery voltage to the terminal, the pump must run. If it does, wiring from the relay to the pump is good. If not, check for open circuit, or poor ground at pump.

The oil pressure sending unit circuits can not stop the pump from operating. It merely supplies an additional path for amperage to flow to the pump while it is running. The only possible way the OPSU could cause the pump to stop running is if the grey wire shorts to ground between the OPSU and the grey wire splice inside the fuse panel. In which case, ECM B fuse would blow. If the ECM B fuse is good, your OPSU is NOT the problem, guaranteed. The wiring diagram that pettyfog posted above, shows all circuits correctly except the OPSU circuits. Some, not all, GM vehicles are equipped with the OPSU circuits. Your 1998 Blazer is equipped with the circuit.

FYI: easy way to tell if a GM vehicle is equipped with the circuit is if there is a grey wire present at the OPSU electrical connector.... no grey wire, no circuit.

After verifying that your circuits are good, check the fuel pressure.

 

Sorry for the late response, finally got it fixed and lol it was the oil pressure switch.

allthough my all data shows a diff diagram than posted previous so either way its fixed, Had a hell of a time resetting the ignition timing, I think it needs a bit of fine tunning due to the long *** cranks when cold.

but got the crank sensor reprogrammed and its finally driving

thanks for all the help

 

Ignition timing is not adjustable on 1998 CSFI systems, it is controlled by the PCM. Timing lights are obsolete tools on this system. Rotating the distributor adjusts camshaft retard, not ignition timing. Camshaft retard is checked and adjusted only by using a capable scan tool. I hate to be pesimistic but I doubt your troubles are over by just replacing the OPSU. As mentioned earlier, you might want to check fuel pressure and leakdown for the long cranking time when cold.

 

LMAO when you guys are right, you are right! back to square one but noticing that it may be the socket or something similar the fuel pump relay plugs into.

I have all along been checking the fuel pressure and im within the range i need to be. 60 psi key on, we have an excellent snap on scan tool. I was only having issues with the timing, because i saw the marks on the distributer I made when i did the intake gasket a few months ago.....totally forgot i changed the cap and rotor so I dicked myself.


I have noticed that pump is not engaging if i prime via test term it will start up great. I am a bit curious on what to think about this once it is running if you touch the pump relay it goes nuts and just opens and closes at an alarming rate. doesnt matter what relay is in there it goes hay wire.


I am a bit lost but i guess after enough time i will a fix the truck or b detonate it in a field


But thanks for all the input and help I will be checking all advice given and I hope I find the solution, Im going to check my ignition switch tonite. Doubtfull it is it but dont know where to go from here

 

Are you kidding?!!!

You put your finger exactly on the problem, so to speak. Read your own post again.

 

That's the correct schematic! You know that the grey wire from the fuse panel to the pump is good because it starts and runs fine if you apply battery voltage to the test terminal. Next step is check the circuits for a poor connection. May as well start with ground. The black wire, (relay coil ground) exits the fuse panel through a connector and goes to ground at G102. G102 is at the left rear of the engine block, (possibly cylinder head???) Remove the fuel pump relay, check resistance on the black wire terminal in the fuse panel to battery negative, must be 5 ohms or less. While the ohm meter is connected, wiggle the wire harness and black wire all the way to the ground connection on the head. There are no other connections until it reaches G102, which is an eyelet style terminal. Resistance shouldn't change during the wiggle test. If it does, find and fix the problem. There might be a ground buss bar inside the fuse panel and you might need to take the fuse panel apart and check it.

 

hehe well i feel like warry the wetard. I dont even wanna explain this, but basiclly, I sat down an went through everything I physicslly touched on this truck in my head. Long story short I managed to stretch the damn socket connectors to the fuel pump relay out....

as soon as i put a slight twist on the relay connector, reinstalled and turned key to on position HOT DAMN lol we have fuel pump and injector primage


I sincerly apologize fior the waste of time but good and viable lesson learned.

I did cycle they key upward of 10 times and it consistently turned on properly!!