Should I replace the Fuel Pump next? [Archive] - Forum


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05-23-2012, 10:33 PM
It's an 05 Grand Am SE. It has the 3.4. It had come through a dealer auction with major front end damage (that's how we got it). We know it sat for a while before it even got to the dealer auction. The body has 80k on it, but we put in a new radiator, condenser, drier, and a 3.4 motor with only 15k miles on it that included the fuel rail, fuel injectors and the such. We did put on the upgraded Fel-pro gaskets on the engine (it was pristine showing no corrosion unlike the orig motor) and properly torqued everything down. It was having starting issues with the autostart while sitting on inclines and such so we decided to run a bottle of Valvoline dry gas though it (it would have to be started 2-3 times). Let's just say it coughed, didn't want to stay running, and you had to give it alot more gas than usual until we got to the Sunoco gas station about 10min. away and filled it up to full. It's never had any starting issues anymore so there must have been a bit of moisture in it. But, it must have seriously stirred up some stuff in the gas tank that had been "settled in it".

We changed the fuel filter and it must of had a lot of stuff in that tank since when we blew through it hardly anything came through the other side of the filter(unfortunately we had to run it a week with the clogged FF due to time restraints which wasn't good on the FP I'm sure). We also checked the fuel pressure (after new FF )at the fuel rail at idle and it met the GM shop manual specs and very quickly took off the vacuum hose (to the FPR) to make sure the FPR brought the pressure up to where it should be under a high load situation then hooked the hose back up. And that stuff all checked out (pressures wise). We are thinking the FP since, after running the dry gas it started having issues where it acted like it loss guts on the low end and then you gunned it out on the freeway it hesitates a bit then would pick right up (this got a bit better with the FF change but not much). Prior to running the dry gas the motor ran great except for trying to start it on inclines. Do you guys concur with our conclusion?

Is the Ac-Delco pump module assembly MU1374 the correct entire assembly for my combo from your guys' experience? Does it include the O-ring for fitting the entire module assembly to the fuel tank? Any problems with your fuel guage not being correct after putting in this fuel pump?

05-24-2012, 04:44 PM
The pump may have got some corrosion or something, depending on how long it sat with bad gas in it collecting moisture. If it was a car I knew had been sitting a long time I would have dropped the tank and drained the gas from it and put new gas in before starting it. I would have replaced the fuel filter first too. That's one of those things that people normally don't think about and change like they should, so I always do that on a used car. Anyway... it's possible the pump is ok but the filter sock in the tank if clogged with crap as well. Really no way to know without dropping the tank and looking, and if you are going to do that you might as well change the pump at that point.

However... if all you are getting is a loss of power, but the fuel pressure at the rail is fine, your problem may not be the fuel pump. It could be something else like a clogged catalytic convertor.

05-25-2012, 10:59 PM
We did replace alot of things when we swapped in the 15,000 mile motor, but we were getting tight for time since we needed to do maintenance to our back up vehicle and we figured the fuel filter would be easy to do later.

We are going to try taking out the current fuel filter and see if it has a restriction in it again Sunday (its only been in a week), if it does we are going to try putting in a second one. If it fills up this 2nd replacement fuel filter we are going to drop the tank and try cleaning it out with clean rags and put a new filter sock on the fuel pump and replace the fuel filter again (we are using quality WIX fuel filters) and see where it goes from there.

05-29-2012, 10:56 PM
Well, the fuel filter on Sunday we took out was clean. No real restriction when you blew through it. The MAF readings didn't fluctuate a alot but were a bit high in comparison to one we had off the 04 grand am motor. We would use the one off the 04 grand am motor permanently, but the mesh is a bit screwed up, but it did give reading closer to the called for factory specs. the motor of course was running fine the day we decided to bring it over to my parents house to do all the tests. We are starting to think we have have an electrical ground issue since the problem is now being intermittent.

05-30-2012, 04:05 AM
Yeah, it's always a good idea to make sure your power and ground wire contacts are all clean, at the battery and the chassis attachment points, just to avoid those intermittent electrical problems they can cause.

05-30-2012, 08:51 PM
Have you ever heard of a a MAF that isn't consistent (ok one startup, bad the next)? We've seen a few instances of such of similar vintage Camaro's over on that forum with the 3.8's after alot of reading. The car is rust free except for one spot on the hood where the paint got chipped bad, so one wouldn't think a electrical ground would be a problem. All the easily visible grounds under the hood look good and all the battery terminals are good. The 04 MAF had a reading of 2134 Hz at idle, while the orig. 05 MAF had a reading of 2174 Hz at idle.

05-31-2012, 06:19 PM
That's not a big difference. You could have that much variance just with atmospheric conditions from day to day.

06-02-2012, 01:51 AM
We checked both the MAF's on the same day within a couple hours of each other. We have found all the ground point locations given in the shop manual and are going to look over everyone of them on Sunday (the ones under the hood that is). If we find they are all good there then we'll try checking all the ones in the interior compartment another day.

06-02-2012, 07:02 AM
Yeah, many of the ground points can look ok, but still not be making the best contact. Most of them don't have much bare metal to metal interface. Most of them are actually painted underneath the ground terminal, and the only contact you are actually getting is through the bolt threads to the threads of the nut welded to the chassis, and those bolts quite often get very rusty. It never hurts to wire brush the ground terminals and bolts. You can also do any combination of running a thread tap through the nut to clean up the metal, sanding a little paint off around the hole, and/or using dielectric grease to keep it from corroding and make sure it's making good contact. :) Might be overkill, but I like the eliminate possibilities when looking for a problem.

06-03-2012, 09:11 PM
We went through and checked the grounds. Ground G101 (it attaches near the strut tower on the driver's side), had some rust, we cleaned it up and reattached it. Everything else was good. We decided to put on a new MAP sensor by Wells, there appeared to be no change when we drove it home.

06-18-2012, 06:10 AM
A new update. After some time the start ups got a bit better and motor slightly picked up some guts. So then we got a new Delphi MAF and put it in. For the first two days we saw some more slight improvements in its guts. But, then out of the blue on the first auto start crank it didn't fire like in the old days before we had run the dry gas today. Funny huh? Then on the way back across the river it didn't want to shift once (it wasn't even much of a hill) and we had to let of the gas to get it to shift. When it did shift the shift was nice and firm as it should be. It didn't act up up at all the next 30 min. home. And there were plenty of nice and long steep grades in those remaining 30min. and the transmission done just fine. The transmission filter and fluid have been changed since we got it. We are looking at getting a computer next. All the stuff under the hood looked pretty good when we swapped the motor. We are hopping we don't have some supper elusive electrical wiring issue. We are looking at getting another computer (one that interchanges according to the Hollander exchange book) and swapping that in and seeing what it does. A FP issue shouldn't be affecting when the computer tells the transmission to shift. We are hoping this car isn't going to nickel and dime us to death.

The ECM (computer) is located under the driver's side dash next to the steering column correct?

06-18-2012, 04:01 PM
Yes, they call it a PCM (power train control module) because it controls the engine and transmission both. It's under the drivers side dash left of the steering column, and is situated vertically with the connectors on bottom. There are a couple small bolts holding the connectors to the pcm. Loosen those and pull the connectors, then there is a simple clip you push back and the PCM drops out.

Keep in mind, just because you get a PCM that is interchangeable with yours doesn't mean it will necessarily work right off the bat. It may or may not have the correct program loaded in it for your car, or may have no program at all. Also the security code stored in it won't match the one in the BCM, so it may or may not start on the first try, or you might have to do the emergency start procedure. The VIN number will also need to be changed, and it will also need a crank position CASE learn procedure done. Basically you will need to take it to a dealer to get that stuff done no matter what, unless you know someone with a tuner.

As for the shifting problem, a bad PCM could possibly cause that, but it's uncommon. There are a lot of other sensors that also affect that. The MAF and MAP sensors, as well as TPS sensor help determine engine load, and those signals are used by the PCM to calculate when to shift and how hard to shift. There can also be problems with shift solenoids and other hard parts like clutches, torque convertor, etc. About all you can really do at this point is drive it and keep an eye on it, and see if the problem reoccurs or gets worse, or if you get any trouble codes for it.

06-21-2012, 04:19 PM
Aaron, we are getting a new Wells TPS this week and going to use your relearn procedure. That covers all three of major things that you have mentioned (that we have replaced) for determining those shifts. We have an OTC genisys with software 5.0. We have already done a crank position CASE relearn procedure with this motor now so that wouldn't be a problem with another computer. We know we want a PCM out of a car w/3.4 only in hopes the stuff will work. If we can't get it to work, we are willing to take the PCM to the dealership and get it reflashed for our vehicle. All the intermittent guts issues along with the intermittent trans shift issues & with replacing all the components we have is what is making us think the PCM could be a little "flaky". You can retake the hill at the same speed & relatively same throttle it just acted up on 5 min. later and it won't necessarily do the same thing . Have you seen shift solenoids be intermittent? We wish we could get a code for something, but so far we haven't. Which is what makes this all the weirder.