98 Century fuel pump issues

Hi folks, I'm new to the forum, and must say this looks like a great place. Anyway, now to the point of my problem. The Century now has 133k miles on it, and it's having troubles. Sometimes when I turn the key to the "on" position, the fuel pump comes on and the car starts normally and runs great for the duration of the drive. But, sometimes the fuel pump doesn't turn on. The fuel pump and fuel filter have been replaced in the past six months. In the past few days I have replaced the FP relay as well. The connections at the fuel pump are good. Today I had to use a wire to jump from a known power source to the '87' pin on the FP relay just to get it to start (I was crapped out in a bad place). :swear: This made the pump (and car) run until I could get home, but it also smoked the FP relay again. So, with a new relay in place, it is back to the same 'ol runs sometimes and sometimes not. Anyone have any suggestions? Please help! :cool:

Welcome to AF.

The fuel pump relay is controlled by the PCM module. There is some short in that circuit most likely associated with the coil part of the fuel pump relay. 12 volts is on one side when ignition is on and the PCM provides a ground (low).

OK, that makes sense. I wondered if I should check the connections at the PCM. Where is it located?

The PCM module should be located in the air box assembly, the lower half. You should see the wiring harness at the bottom of the air box. There are two 80 pin connectors at the PCM.

When you mentioned the relay was bad do you know if that was at the coil contacts pins 86 and 85 or the nc/no contacts pins 87 and 30 which passes the 12 volts to the fuel pump?

Thanks for the help so far bnaylor. The first time I replaced the relay was actually part of quick troubleshooting, since it was potentially suspect and cheap. I really don't think it was bad then. The second time was (believe it or not) when I jumpered it to get home, it welded the N.O. contacts together. The FP still ran after the key was shut off and the jumper removed.

Thanks for the feedback. That doesn't sound good. So hard to say whether the relay failing at the NO contacts or the coil. In addition to the circuits to get the relay energized I'd check for a short in the circuit before the 12 volt feed at the NO contacts back to the ignition circuits (fuse block/ignition switch) or after towards the fuel pump. Maybe there is a wiring or electrical connector problem.

Thanks for the help so far bnaylor. The first time I replaced the relay was actually part of quick troubleshooting, since it was potentially suspect and cheap. I really don't think it was bad then. The second time was (believe it or not) when I jumpered it to get home, it welded the N.O. contacts together. The FP still ran after the key was shut off and the jumper removed.

I thought your post was interesting, I'm not sure how you hurt the relay by using a jumper? You don't jumper the relay, you the jumper the terminals, where the relay plugs in.

If the relay plugs into a power distribution center, then you unplug the relay and jumper the proper terminals in the socket. If the relay has a multi-wire connector going to it, you take the connector loose, jumper the proper terminals in the connector. The relay itself, shouldn't be involved. with a standard ISO relay, the 30 terminal is voltage input for the load circuit, that terminal should be hot all the time.

Yeah, that doesn't make much sense to me either. Perhaps to help you understand a little more about what I did......it was a real rig job. But when you're standing out in sleet and freezing rain, you can do some imaginative things. I had a piece of wire that I put under the terminal of the relay, which I then reinserted back into the socket. The wire didn't go down into the socket, it was just sandwiched against the relay lead. I was careful to only expose a very short section of the wire so it couldn't short out to other leads. I know that sounds a bit hillbilly, but it got me home. Anyway, I got home, turned off the engine, and the pump was still running. This wasn't surprising since it was jumpered. But it still ran when I removed the jumper!! Pulled out the relay, FP shuts off. I dunno.

Yeah, that doesn't make much sense to me either. Perhaps to help you understand a little more about what I did......it was a real rig job. But when you're standing out in sleet and freezing rain, you can do some imaginative things. I had a piece of wire that I put under the terminal of the relay, which I then reinserted back into the socket. The wire didn't go down into the socket, it was just sandwiched against the relay lead. I was careful to only expose a very short section of the wire so it couldn't short out to other leads. I know that sounds a bit hillbilly, but it got me home. Anyway, I got home, turned off the engine, and the pump was still running. This wasn't surprising since it was jumpered. But it still ran when I removed the jumper!! Pulled out the relay, FP shuts off. I dunno.

I see your point about the weather stuff, you do whatever you have to do, to get home. I'd do the same thing.

OK, thought I would post an update with a little info in the event it could be useful to someone else. Today I installed pump #6 :screwy: for this car, along with relay #3. The first two came from GM, the others were from CarQuest (including the one installed today). This one was quite different however. It came with a new style pigtail and plug to replace the factory plug. The pump itself had a slightly different appearance, and a very different sound when it was all ready to go. I also used contact cleaner to clean the terminals at the PCM. The car is running fine again. My hopes are the new style pump from CarQuest has enough improvement to last a while this time. BTW, for those wondering, I flushed the tank each time to remove debris. Thanks for the help guys. :smokin:

As a suggestion to anyone else having fuel pump problems,when you suspect a bad fuel pump,just thump the bottom of the tank sharply.In most cases the pump will turn on at least long enough to get you home.I'm not suggesting that anyone use this for a diagnostic test.Another recommendation is to use Top Tier rated gas(not to be confused fith high octane).GM included this in a TSB in 2003,I believe the fuel has more detergent and may help get a few more miles out of your fuel pump,injectors and fuel sending unit.Good luck everyone.