My 2005 CTS-V

[A//// Guy]

I highly doubt your fuel filter is clogged with only 40k on the clock, you also would have noticed junk on your pumps prefilter if that were the case, but Id replace it anyway just to rule it out. Im leaning toward your pump being the problem.

[asshanson]

Oh, I forgot to mention. Last week when we had the pump out of the tank to install the check valve, we noticed that the sock had fallen off the pump. This could have easily caused some junk to clog the filter or make the pump weaker.

My question is, what happens when the sock comes off, besides not pre-filtering? Does it affect the flow without the sock on?

[turbotalon1g]

I don't think so, from what you are telling me I would suspect the pump.

[asshanson]

Replaced the fuel filter, didn't fix the problem. Installing a new pump tomorrow, hopefully that's it.

[asshanson]

Replaced the pump with a brand new 255hp, still has issues around 4500rpms.

[TalonFiero]

Fuel pressure regulator?

[turbotalon1g]

Well I'm kinda glad that its not the pump, but I'm really surprised. Good luck.

[asshanson]

I doubt it's the regulator. It holds about 60psi pretty steadily just cruising around, so I don't know why it would drop pressure under high load. It's in the tank, it's a returnless fuel system.

I'm going to test the fuel pump voltage, see if my boost a pump is failing maybe.

[TheBlizzard]

Yeah I was just going to say check the voltages under load, you could have a loose connection or a failing boost a pump like you mentioned. Weird issue though.

[C3L1CA]

Do you still have it hooked up to the little dial switch?

Mine would go lean under boost and thought it was my maf at some point, turns out those dials go bad.

Try cutting the wires that go to the dial for lean/rich and solder them together. This will cause the boost a pump to run at full voltage all the time and fixes the dial switch problem.

[asshanson]

I hooked up my multimeter to the pump output on the BAP and sat the unit in the passenger seat and went driving around. 13v cruising around, go WOT in any gear and around 3000rpm it goes to 18v and holds solidly. I haven't had a chance to check actual voltage at the pump since there is nowhere to connect to the harness, I'll probably have to tap into the lines with a pin or something to get that reading. I highly doubt it'll be any different than at the BAP but who knows.

I even went WOT in 5th gear up to 4k rpms or so, man the car feels strong, it's awesome.

I bought a wideband that I'm going to install in the pop-out cigarette compartment so it'll be hidden most of the time, I just want it for future use to be on the safe side. I suppose a fuel pressure gauge would be just as useful for this issue.

I'm going to post up on the CTS-V forum to see if anyone there has any ideas.

[asshanson]

Some guy on the V forum suggested a kinked line so I checked that, but everything looks good/normal. At the same time I followed the BAP wiring back to the trunk where the fuel pump signal is actually tapped into and there are no shorts or melted spots in the wiring that I could find, it's heavy gauge stuff with a really thick coating, and it's secured really well. I still want to log voltage at the pump just to cover all the angles.

I created a very crude drawing of how I think my fuel system works, it's really weird and I'm not familiar with GM LS motor cars. Anybody on here work with them and can verify this is what's actually happening?

You can see the pump feeds the filter, and there is a return line to the tank and and an output to the rail. What I think this accomplishes is the regulator in the tank can bleed off any post-filtered fuel that the rail doesn't use above 60psi (operating pressure). So at idle the regulator is working hardest, and at full throttle it won't be bleeding off much at all since most will be used by the motor. Is this correct thinking? (Ignore the evap part)

What I thought was weird is that the fuel feed goes into the side of the first rail, and there are two lines connecting the rails, like a big closed loop, not in series as I originally thought.

I took out the rails and injectors tonight thinking maybe something was clogged and found nothing, everything was clean as new. I'm going to see if I can pull out the fuel feed line and check it more thoroughly for kinks and possible clogs.

Edit: just thought of an easier way to verify my pump is working at full capacity (at rest) and the line isn't clogged. I'll hardwire the pump to the battery and see how long it takes to fill a gallon, shouldn't take more than a minute or two if everything is working properly. I believe this would eliminate a flow restriction.

[craig]

The cross over lines at the front and rear of the rails is to help keep equal pressure in both rails it is usually an upgrade to do and is quite nice to have.

[mlomker]

Originally Posted by asshanson

Is this correct thinking?

Can't speak to how your system works but that sounds logical from your description. The Evo uses dual voltage to control the amount of return during idle (uses a relay to switch from 10volts at idle to alternator voltage).

I can understand your desire to remove the BAP for simplicity but keep in mind that it isn't *just* a step-up transformer. You can disable the step-up function and it'll still act as a voltage regulator. In theory you should get more stable power delivery to the pump(s) even if you don't up the voltage.

[asshanson]

Here is a pic of the fuel feed line that had a hole in it. Whoever installed it tightened the clamp way too much and made the line really weak there.



When I was re-installing the fuel rails and injectors I forgot to grease the orings, so three ripped on me and fuel was spraying everywhere, that was fun to take the rails back off again, not an easy thing with all the supercharger lines running everywhere and blocking access to the bolts.



While the car was up on jackstands I decided to install my transmission mount, since I just got my full torx ratchet set I now had the tools to get it done. I got this mount 8 months ago and never got around to installing it. Then I got ambitious and decided I might as well install the poly motor mounts I also ordered 8 months ago. That took a bit longer than I was expecting. Here is a pic of the old and new mounts, and the stock tranny mount. You can see where the stock motor mount had started to fail and leak fluid out the side where it's shiny.



And the new transmission mount installed:



The passenger mount took about 2 hours to take out the old one and put the new one in, there was plenty of room on that side to move things around, I didn't even have to remove the starter or headers like most people do.



The driver side mount was a bitch, that's about all I can say. The steering stuff is over on that side, so there is basically zero room to do anything.



That side alone probably took me 6-7 hours. I had to unbolt the header so I could move parts around, and I had to disconnect the steering linkage to have enough room to get the old mount out. On the plus side, when I took out the steering stuff I found a missing bolt, which is why I think my steering wheel had play in it. Fortunately I had a million bolts from my mitsu so I was able to find one to fix that issue.

The stock mounts were pretty messed up. no fluid left in them and you could feel the motor take forever to stop shaking on shutdown. This is what the assembly looks like, the left side mounts to the subframe, and the right side mounts to the side of the block.



I took the car out for a quick test drive and wow, the car feels totally different. The only complaint I have is increased cabin noise under 20mph. Above that I can't really tell, but down low a lot of noise is transmitted through the shifter now that I couldn't hear before. Shifting is so easy now, it's amazing because before it felt mushy, now it's like having all metal bushings in the DSM.

At idle the car does have a little more vibration, but not bad at all, and definitely not enough to rattle anything. I can feel little hiccups sometimes (probably the computer trying to relearn fuel trims, disconnected battery for a couple days), makes me feel more connected to the car while driving.

Overall I'm super happy with the new mounts, now I just have to figure out this damn fuel issue.

[Murlo26]

Have you logged the car after replacing the o rings and leaky line? Those weren't the culprits?

[asshanson]

No, I can't do any logging except at DB. I don't have the HPTuners software on my laptop and it was hundreds cheaper to get a single license through them than buying the whole thing for myself. Didn't plan on moving to Iowa at the time though, oops. The leaky feed line was a total coincidence I think, and the leaky orings were from me taking out the rails a few days ago.

I drove the car around doing errands tonight, and the steering wheel play has been fixed!! This is just as exciting as the motor mount fix. Also I forgot my back seat was out, which explained some of the louder noises haha. It should be quieter once that is back in (out for testing fuel pump voltage stuff).

I did encounter one somewhat alarming issue. It hesitates almost every time starting from a stop, around 5mph, almost like the tires slip for a split second. One time it also sounded like something clunked. I'm going to check all my connections tomorrow and make sure I didn't forget anything. Hopefully resetting the battery/ECU didn't ruin anything in my tune.

[asshanson]

I think something is wrong with the tune with the ECU losing power for a couple days. I found out that the hesitation is the car missing or something along those lines, also explains the rougher idle. Above 2k the car pulls decent for partial throttle, but say in 4th below 2k up a hill it's hesitating non-stop, and I let off the gas a bit and it pops really loud, like a backfire. Does this indicate it's running really rich?

[mlomker]

Originally Posted by asshanson

Does this indicate it's running really rich?

Sounds like it. You might want to get a few gauges into the car. I've spent the last few weeks doing exactly that on my car...helps a lot with diagnostics.

[asshanson]

I finally figured out the fuel issue. I disconnected the fuel feed line and turned the pump on for 60 seconds, and I got 1/3 gallon of gas. I tried directly out of the tank and I got the same result, so nothing in the lines/filter is restricting flow. Then I took out the pump and tested the stocker, 255, and 310 pumps I had sitting around, direct hookup to the battery. The stock pump and 310 were each able to do about a gallon in 60 seconds, and the 255 was able to do more than a gallon in 50 seconds, so clearly the 255 pump is more than capable of providing the fuel required.

I put the pump back in the assembly and dropped it into my bucket of fuel to test that out, and I found where all the fuel is going: out some stupid valve I don't think should even exist.

You can see the red line connects to the pump and the mystery white plastic item. That valve thing also connects to the hose that goes outside the tank, the connection from the other pump on the opposite side of the tank (yes, there is an active pump that feeds fuel from the drivers side to the passenger side of the hump), and a plastic tube that plugs into a dead end. I really dont know what it's for. Anyway, about 2/3 of the fuel is spraying out that stupid plastic piece and not going out of the tank.

Anybody familiar enough with returnless or GM fuel systems to know what that thing is? I'm considering bypassing it and hooking the pump directly out of the tank, and having the other pump just feed the bucket the primary pump sits in. I think it's supposed to be some merger valve that combines fuel from the other pump along with the main pump, but I think it may have broken and it's just bleeding off most of the fuel.

EDIT: I added arrows to the flow. I think red arrows should be the expected flow of fuel, but the black arrows are the actual flow. I'm thinking a seal or something inside the siphon has broken.