FAQ: Fuel Pump - General Questions, Compatibility & Troubleshooting

Not only would I try the test light I would also lok for crank sensor signal. Unfortunately this means trying to data-log it while running. I can do with Car-Code but not sure what you might do. Point is to put a scanner on the OBD port that will log if the crank sensor is sending a signal or not, then duplicate the stall decel.

Albertj

AA wrote:

Good points. I like the test light idea, and I would have taped the gauge up earlier, but the stalling hasn't been happening frequently enough, and I really don't like driving around with the gauge there for weeks at a time. I drove the car home tonight - 30 miles - drove like a dream, no issues. I even stomped it from 65-90mph and no complaints.

The test light - I may try that. Then at least I would know if it's getting power or not. The idea that the fuel pump might be 'sticking', that makes some pretty good sense. I'd think the pump would most likely want to stick during idle (decel), or during starting, when less pressure is demanded. It never stalls during acceleration, and WOT it performs great. In hindsight, I may have ignored the pump as a possibility because it performs so well under these conditions. Question: when a pump sticks, does the sound change? Wouldn't it burn up in short time?

Thanks for the info, BMD. It's reassuring to hear a story that so closely parallels mine. I'm thinking I should just replace the pump. With so many miles, it's lived one hell of a life. If I do, I know exactly what kind I'll be replacing it with.

Oh, about the dealership - I really don't mind that they didn't solve the issue. They scanned for codes, test drove the car, and revealed a clue about the fuel pressure - at no cost to me.

A fuel pump doesn't make any noise when it's frozen. I suppose it could hum as opposed to whine if anything......I don't exactly know why, but you'd think that the FP fuse would pop as soon as it "locks" up, but it rarely does. You can usually bang on the gas tank while cranking and temporarily free up a frozen pump.....

Make sure you wire up the test light in series with the relay, even if you just stick wires into the relay slots (relay pushed over top of them) and hook the test light to those. This will test the entire circuit. If/when the light ever goes out, you can rewire it to test each "leg" of the circuit (before and after the relay).

As for the dealer.....at least it was free

AC Delco fuel pump #MU1726 for SC Riviera sells for $536 + tax at GM dealership, $322 + shipping at Rockauto, but Amazon is selling new units for $279 (no tax, no shipping):

http://www.amazon.com/gp/product/B001NZZA7O/?ie=UTF8&me=ATVPDKIKX0DERMU1726

I ordered one today. If you need one hurry up - only 2 units left!

The Carter P74910M is only $198....

I think the Carter P74910M is for base (non-supercharged) '96-97 Rivieras. For supercharged, use the CARTER P74995M ($312 + ship).

I dunno why someone would replace the entire sending unit if just the pump is bad, or why you would replace the pump too if the fuel gauge sending unit is screwing up. You can buy stock pumps pretty cheap, or even race pumps for 100$ . Changing just the fuel pump is really easy, the canister comes apart. And for any fuel gauge sending unit problems, just bending the slider some usually fixes any problems. If that fails you can get just the fuel level sender cheap at a junk-yard. Why anyone would spend 300 bucks for an entire replacement canister is beyond me. Its like replacing an entire supercharger for a bad bypass valve.


Edit: Turtle did a fuel pump writeup here:
https://rivperformance.editboard.com/t2918p15-write-up-walbro-255-lph-fuel-pump-series-i

Edit #2: and if anyone is interested in more pics, I have a bunch pertaining to the series one when I did my Walbro FP.

AA wrote:

I think the Carter P74910M is for base (non-supercharged) '96-97 Rivieras. For supercharged, use the CARTER P74995M ($312 + ship).

Nope, the P74910M is for SC.

Karma wrote:

I dunno why someone would replace the entire sending unit if just the pump is bad, or why you would replace the pump too if the fuel gauge sending unit is screwing up. You can buy stock pumps pretty cheap, or even race pumps for 100$ . Changing just the fuel pump is really easy, the canister comes apart. And for any fuel gauge sending unit problems, just bending the slider some usually fixes any problems. If that fails you can get just the fuel level sender cheap at a junk-yard. Why anyone would spend 300 bucks for an entire replacement canister is beyond me. Its like replacing an entire supercharger for a bad bypass valve.

Edit: Turtle did a fuel pump writeup here:
https://rivperformance.editboard.com/t2918p15-write-up-walbro-255-lph-fuel-pump-series-i

Edit #2: and if anyone is interested in more pics, I have a bunch pertaining to the series one when I did my Walbro FP.

I agree with this. I didnt spend over 200, but after I got the replacement unit I realized how easy it would have been to just replace the pump itself (using the existing plastic holder)

Karma wrote:

I dunno why someone would replace the entire sending unit if just the pump is bad, or why you would replace the pump too if the fuel gauge sending unit is screwing up. You can buy stock pumps pretty cheap, or even race pumps for 100$ . Changing just the fuel pump is really easy, the canister comes apart. And for any fuel gauge sending unit problems, just bending the slider some usually fixes any problems. If that fails you can get just the fuel level sender cheap at a junk-yard. Why anyone would spend 300 bucks for an entire replacement canister is beyond me. Its like replacing an entire supercharger for a bad bypass valve.

Don't forget that new sending unit replacements can be purchased as well. They're virtually universal across the company, 48-248 ohms IIRC. I used one out of a Chevy S-10.

I bought the entire assembly because it's an exact OEM replacement, at near half the MFR price. Since I'm installing it myself, I save some there. I also don't know for sure how good the condition of the rest of my sending unit and float is. I Read somewhere else where someone found lots of rust in there, and pump removal isn't always easy. Lastly, I couldn't find the OEM pump only for sale, but I'm sure it's out there.

I saw the Walbro pump for $100 at INTENSE, and considered it, but they recommend a hotwire kit, venturi, and corrugated hose, which adds considerably to the cost. But the biggest reason I didn't get the Walbro is the very limited 30 day warranty. INTENSE says this is because "Walbro offers no warranty as they state they have no defects", which I think is complete BS.

I'm getting ready for a long trip in the Riv in a few weeks. I need a repair that will last another 100-200k miles, I have to fix it pretty soon, and the install needs to happen in one evening after work. I can't take chances with something not lining up or fitting right, so I'm gonna pay more and just drop it in. Call it a "convenience charge". I admit I like to replace stuff in a common area when I have the opportunity. When I replace the timing chain, I'm also going to do the tensioner and cam position sensor while I'm in there, even if they appear fine.

Get a new lock ring from the dealer before you do it.

Yeah, +1 what Turtleman said. Theres really no recovering a stock lock ring.

Will do, thanks for the tip!

Sorry I'm late, see that this is old. You can try jumping out the FP relay under the back seat just to make sure it isn't the relay. I used that method when I had some very bad gas - had the fuel rail draining into a bucket, and jumped the FP relay to let the pump do all the work. (and after I was done with it all I changed the filter).

Can you hear the FP at all when you turn the key?

Yes, the fuel pump is running fine 99.9% of the time. It's only when it stalls that I assume the pump sticks or stops. At that point, you can't hear because the car is rolling. Would a bad relay just quite temporarily while the car is running?

Since Monday, I've been driving the car without much issue. It stalled 2 times this week (which has been much colder, btw),and both times I was able to restart at speed. I cannot recreate the no-start issue. If it happens again, I will surely investigate for FP sound and the relay if possible. I feel like a new pump isn't a bad investment at my mileage, so I'm going to install it and see if the problem goes away.

Aaron, you mentioned that a possible write-up might be in order if you do the FP replacement. I just wanted to second that as a great idea if you are so inclined and have the patience for that.

There are already a couple good write-ups on this, but I will take some pics if the need should arise for write-up. (see Walbro race pump install and SC series II fuel pumps thread).

I've seen those and they are very helpful and informative, but your write-ups are always so detailed!

Thank you. I'll take pics and some notes. If needed, I'll add them into manofmany's write-up, as we did with Deekster's spindle/bearing write-up.

Wish me luck - I'm driving to KY to watch the Buckeyes do work!

UPDATE: since last post 2 weeks ago, the problem seemed to go away on its own. No stalls, and no starting failures for almost a week. The following week I had 3 instances of stalling while on the freeway, and each time it started right up coasting in neutral. I ordered and received a new pump assembly, but wanted to be sure before I installed it, so waited for another no start situation, which finally happened last night in our driveway. I turned the key and listened to complete silence - no pump sound! Tried it 3-4 times, same thing. Popped the trunk, grabbed the fire extinguisher and banged it a couple times on the trunk floor above the tank. Turned the key, heard the pump kick on, car started right up.

Thanks to everyone's help in confirming this problem. I wanted to be certain before replacing the pump, and now I'm near 100%. It's failed to start 2 more times since yesterday. It all makes sense now, really. A sticking fuel pump is going to do when there's less demand on the fuel system. That's why would never cut out under WOT.

UPDATE 2: put the new unit in last night. Took 5 hours! I'll add comments and pics to the Fuel pump write-up thread soon. I am glad I bought the entire unit, and hope I never have to replace it again!

Fun taking that locking ring out eh?

Wait till you see mine. It was beyond rusted, and it was no longer a ring once removed.

When the dealer changed mine he said I was lucky, the ring had rusted so bad that they almost couldn't save the tank. That is one job I do not look forward to ever doing!

I feared that possibility. If your lock ring looked like this, what would you think?



I think the dealer would have told me I was up a creek and needed a new tank.

I'd just vacuum it out and be careful to not get any in the tank...

my ring ended up being quite structurally sound, just "rust-welded" to the tabs, so it took some brute force to get off...

Mine looked pretty much like that too. You can add to the write-up something about having a shop vac around. I did a lot of stop&vac myself.

I was really worried about my tank but after installing the new ring the first time with some petrol jelly on everything, it came off fine about a year later when I took it out the second time to swap in the PRJ fuel pump. I wouldn't be too worried about taking it out again, god forbid.