2007 M6 Base w/ ~51k miles. 3 days ago it fired up and then promptly stalled. Cranks strong and good, but it's not getting fuel. Things I've done:
1. Depressed the schrader valve on fuel rail. It just dribbled a couple drops out.
2. Swapped the fuel pump relay with AC relay and verified the 20 amp fuse is good. Both relays ohm'ed equally ~81 ohms. No discoloration.
3. I split the fuse/relay block and I don't have the burnt relay terminal at the bottom half. All looks good.
4. Pulled the DS rear wheel and splash guard and check continuity to fuel pump harness. On the body harness side, I have tone to the from the relay pin to the thick white wire, surmise this is fuel pump power. I also have tone on large black wire to the filler neck ground lug. Surmise this is fuel pump groud.
5. Battery has good voltage, but I did not load test it yet. I don't think this is the issue.

Questions:
1. Feels like I'm gonna be dropping the DS fuel tank and buying a fuel pump assembly (huge PITA from what I'm searching). Before doing so, I'd like try to bump the fuel pump with a 12V source. On the pump side harness plug, is the thick white wire the pump power and the large thick wire ground? There are 2 smaller wires that I surmise are the sender signal and ground. Is this correct? If not, please correct my test. I don't want to apply 12V incorrectly and cause an issue instead. My through is to apply power and ground from the battery to the these 2 pump side harness connections.
2. What else should I check before throwing a new pump at it and spending the time replacing? Did I miss anything in the diagnostics?

Thanks to any who help.

 

What is this "tone" you are referring to while testing ??…a “Power Probe” ??...with the relay removed did you try jumping the load side of the relay ??...that is terminals 87 and 30 and they sit diagonally across from each other...you must check all 4 terminals of the relay to determine if it is good…yes looking at the wiring for a 2007 (below) the gray wire is 12 volt feed and the black is ground...if the pump is not operating you can't really do a "load" test...you will have to substitute the inop pump for a roughly 5-6 amp load...I use a big incandecent test light as a substitute...I’ll check for a voltage drop from B+ of the battery to the load which is the bulb…anything over .5 volt is excessive but .1-.2 volts is best…I’ll use this bulb to check the ground to be certain the ground can carry 5 amps BACK to the battery…resistance checking of a ground is wrong !!…OK, give the pump 12 volts and a good ground and see if it runs...if it does you will have to find either a bad power or ground...the smaller dark blue and the black are for the sender.

 

Thanks for your reply!

Sorry, by tone I mean I have continuity from the really pin (87 I believe) to the plug power wire pin on the body side of the fuel pump plug. Tone meaning the multimeter beeps to indicate continuity.

Yes, I forgot to write the I verified voltage across relay pins 85 and 86 with ignition in accessory mode. It matched battery voltage. I also jumpered pins 87 and 30, the pump did not come on.

I will next try your load test. Great idea! I will also see if 12V across the pump power and ground turns the pump on.

My gut feel is that I’m in pump replacement territory. 👎🏻

Lastly, where did you source that diagram in PDF?!? I worked on 300ZXs for years and a pdf version of the FSM and wiring diagrams were the most important tool. I really don’t want a hard copy, have searched for PDFs before to no avail.

 

I would jumper 12 volts and a good ground first to see if it is the pump…if pump works we will have to examine the circuit in detail…and like I mentioned when it comes to powers and grounds you have to make sure the circuit can carry that current flow and just not that you have continuity…if that power or ground wire has 100 strands of copper wire for example you will have continuity if all but one were broken but will it be able to carry the current flow…NO !!…the wiring is from Alldata…you can get a 1 month sub for $19.99 and is worth it if your car has issues once and a while.

 

So, I'm a bit at a loss here. I've jumpered the pump gray and black wires to the pump with leads from my battery. No response, not good, but also then I jumpered an incandescent 9005 headlight bulb to the body side harness of the fuel pump, also gray and black wires - it does not light up when the ignition is in accessory mode or cranking. I find it odd that neither the pump responds or bulb lights up when that plug should be getting power. I must be missing something here.

Also, I found 2006 wiring diagrams on the web. I know it's not for a 2007, but it still helps. I attached them for others' benefit. I also created an overall LS2 engine wiring diagram so I'm not paging back and forth. Also uploaded for others' benefit.

 

Thanks a ton for that video. I checked the C6 wiring and they are identical for relay terminals and test. I was having trouble ensuring I was doing this correctly so I made my own pic to carry into the garage.

Test A: Passed
Test B: I did not get the temporary prime. I did get 12V bias voltage, but you're correct, very low amps and could not light up a 9005 bulb with the residual bias voltage/amps.
Test C: Passed
Test D: Failed. Assuming fuel pump is inoperative so no continuity to ground

My only reservation is results from Test B. I don't want get a whole new pump bought and installed only to still have an issue. Any reason why the C6 would be different than the C5 in terms of fuel pump priming? Maybe PCM needs continuity to fuel pump ground to initiate the command for prime?

Last question: Do you have a recommendation for a new pump? GM OE is $584.12 and from my reading they are not super reliable - in that there's a small consensus that if folks run the tank low they can overheat and prematurely fail. My "91 300zx fuel pump was 27 years old and still kicking. Is Racetronix reputable? They hand assemble their replacements and are using Walbro (I believe).

I also tested the pump again with12V source. No response.

"Deleted pic, had incorrect relay positions, see correct bic in post #14 below"

 

Glad you enjoyed the video…looks like you did some great testing so far…ok, so no 2 second prime on the fuel pump relay control feed wire with your test light so what would be your next step in the diagnostic process ??…since your pump is at the top of the tank vs the majority of C5’s which are accessed from the bottom of the tank there is no way to be certain you don’t have a wiring issue between your harness and the pump but with the testing you’ve done you have a 50-50 shot…did you jumper 87 and 30 to see if you have power down to the harness you’re checking ??

 

Yep. Have 12v with 87 and 30 jumpered back in the DS rear wheel well. That the last accessible plug before the fuel pump.

I ordered a replacement from Racetronix. They have good reviews on multiple sites.

I’m still unsure why I wouldn’t get the 2 second prime. I remember it priming before when all was working. I’m very aware of it bc the 300zx pump was very loud and a good indicator of fuel pressure when trouble shooting.

 

Ok, so what we need to do is “go to the horses mouth” as they say and check that dark green/white wire AT the ECM…I believe you have the pinout so if you don’t have a back probe you can use a thin safety pin to back probe whatever pin and connector it is at the ECM (pin 50 on the C1 connector) using your test light…if it lights at the ECM you have an open somewhere between the ECM and fusebox relay maybe a broken wire or a bad connection at the fusebox….if no light at the fusebox maybe a bad ECM but will have to do a little research.

 

Before I ask anything. Thanks for all your help so far. It’s very helpful and exactly why I joined this forum.

Can you please elaborate on where the safety pin should be inserted? See pic of the ECM connectors. I have little knowledge about these ECMs. I guess I could just find the wire and safety pin through the sheathing, it’s small enough. I’m pretty sure I can’t access the top/backs of the physicals wire pins into the ECM like I’m used to. Maybe those plastic boots with the red tabs lift up?

 

Pleasure helping you guys out if I can !!…this ECM connector is different from my C5 which is easy to backprobe…I believe on your ECM the back shell can be removed to backprobe…you can see those tabs on either end that you will lift up…you can pierce the probe with a t pin as in this video but I use a special piercing probe which is on the right…they are made by Pomona (available on Amazon) and are the best…a red back probe on the left which you can buy on Amazon and 2 different size t pins..if you pierce you should cover that pierced wire with liquid electrical tape so you don’t let moisture in..on the top is my Phil’s Electrical Probe and is great in tight spots…it was designed by an auto tech and I hope he makes a ton of money on it !!…it’s a good idea to get 4mm banana jack leads for your DVOM since almost all of these electrical testing probes use a 4mm banana jack end.

 

Pull relay and jump pins. On the driver side fuel rail, have a schrader valve you can put a gauge on to see the fuel pressure at the rails.

If no pressure, then would probe the down side line of the fuel pump wiring to see if you have power on the postive line just down line of the fuse box.
If not power, then may be time to open up the fuse box to clean the U connectors for the fuel pump relay,since they may be burnt, or spread too far open.


https://www.corvetteforum.com/forums...connector.html

If you have power on the wires, and have doubled checked the wires again at the connector just before the fuel pump in back, then fuel pump is cocked, and it time to drop the tanks to replace it. When buying the fuel pump and having the tanks out to get to the passenger tank as well to change out that fuel level sensor, make sure its the right pump and fuel sensor for your year car. Early in the C6 cars, they change the way the Fuel levers read in continuity on the sensors.

To add, if you are running a BAP, and someone tried to use the oem wires from the fuse box to the tank to send the BAP power to the pump, the wire gauge is way too small for the increased voltage, and will bank that the wires burnt up on the way back to the rear pump connector. Also, since the BAP is sending higher voltage to the fuel pump, it burns it up faster as well.

 

So, I had the original pic above incorrectly labeled. While the relay will work in either direciton, there is an intended orientation so the diagrm on the side actually lines up with the 12V constant, 12V switched, signal ground and device. The corrrect orientation for this relay is shown below with the tests suggested by @C5 Diag.

Test A: Passed
Test B: Still no temp prime, but get 12V with ignition at acc.
Test C: Passed
Test D: Failed. Assuming fuel pump is inoperative so no continuity to ground

I accessed ECM pin 50 and got the same results as the test at relay position 86 below. Also have continuity (I do understand the drawback of continuity testing, but at least I know they're connected.)

I tested the pump again at the rear harness connector with a separate 12V source. No response. I have a pump on order and will test it primes when it comes in by jumpering from the rear wheel well flat plug to the square fuel pump plug, before dropping the thank.

@ C5Diag - I've heard the fuel pump prime before but cannot duplicate the temporary prime that you show your C5 test video. It is possible the C6 is different in some way? i.e. will the prime only initiate with feedback from the pump? Possibly the sender and having pump continuity to ground (though the winding)? I ask because my gut feel is the the ECM is fine and the only reasonable explanation for a no prime is that the ECM is bad or it has something to do with the inop pump. My gut feel is the latter. What do you think?




@Dano523 - that thread is very helpful in understanding the fuse box. I did split the halves and checked the contacts. I only wish I had the more common loose contact issue. It'd be a much easier fix, but it appears I need a fuel pump. I don't have a Boost A Pump (had to look that one up, I'm still a novice!). And I did source a replacement pump from Racetronix and called to make sure I ordered the 07-13 level sensor (later model).


Does anyone disagree with my gut that I likely just need a new pump?

 

Well if you jumpered the pump with 12 volts and a good ground and it still didn't run we are only assuming the connector at the pump has no issues...what you can try as far as pin 86 is crank the car over and see if the 12 volt test light illuminates while cranking...I'm pretty sure if it doesn't illuminate during the 2 second prime it may not illuminate while cranking either...the ECM looks for an ignition reference pulse (coming from the crank sensor) while the car is being started...what you will see if you had a fuel pressure gauge installed is a normal prime pressure for that 2 seconds but as the car is started fuel pressure will drop like a rock with a bad crank sensor...I think we are possibly looking at 2 separate issues here...were you able to back probe or did you pierce ??...now if you had a bad connection at the ECM on that pin that can possibly be the issue...the only time I'll pierce is in a case like this...if you back probe you may unintentionally fix the problem without knowing it...I would remove the C1 connector and check.

 

Thanks again for your help.

While I don't want to bias my diagnosis and I am keeping an open mind that it could something like a bad crank sensor rather than the pump, the pump doesn't prime either. And I noticed that right after the failure occured. Im pretty attune the fuel pump prime sound b/c it's very loud in 300zxs which are what I cut my teeth on. If it was a bad crank sensor, I think it would still prime, build some small pressure and drop when cranking.

I pierced the wire because the C1 connector is really deep and I only had a safety pin on me and it was bottoming out at the safety pin coil elbow. I couldn't 100% tell if I was landing the pin on the top of wire anchor in the connector. The C1 connector looked good. No corrosion or anything. Looked new honestly.

 

Pin 86 should still be powered ignition on….I don’t think in ACC it will prime…did you press the bottom of the start button for 5 seconds while checking ??….a quick way to tell a bad crank sensor is if you crank the engine over you don’t have any movement of the TACH…you also have no spark or injector pulse….I myself wouldn’t confirm a bad connection without back probing…but that’s me…I like to be 100% sure !!…and like I said you can try cranking and check terminal 86 with the test light connected to ground.

 

Maybe I didn't undertstand your suggestion correctly. I always heard the pump prime in ACC, because sometimes I move the car out of the garage to keep the kids asleep and start it in the driveway. There's no priming happening, even if I hold the ingnitiion button in - but I'm not depressing the clutch when I do this and trying to physically crank the engine. It sounds like you're suggestion I actually crank the engine to see if I get voltage at relay pin 86. It can't hurt so sure I'll try that too.

If I can find a T-pin I'll def back probe it, but I did pierce the wire as close the PCM as possible.

 

#1 go buy yourself an INCANDECENT test light to do these checks...you will confuse yourself with a volt meter and they are cheap......pump does NOT need a feedback for ECM to energize terminal 86....yes, I’m not sure if the button has to be in ACC or RUN (maybe someone can chime in) but yes try cranking with the test light at pin 86…what you can try is a continuity test between terminal 86 of the relay and pin 50 at the ECM with the connector removed…you can even load that circuit with your test light…I don’t think the current to terminal 86 is more than 1 amp (to energize the relay coil) so you can try something with your test light..now you can get these t pins at Staples so I would insert a t pin into terminal 86 and connect a jumper wire from the t pin to a good ground or battery negative…connect the test light to battery positive and touch the test light to pin 50 at the ECM…the test light will be bright if it can light the test light…most incandescent test lights are around 300-400 milliamps…I don’t know of any inputs to the ECM for that 2 second prime but for cranking it’s the crank sensor input.

 

Allllllright. I was able to complete Test B successfully at PCM pin 50 (backprobed this time), at relay pin 86 and back at the fuel pump connector @ the rear DS wheel well. Test light lit up everytime. All other tests passed too but Test D for obvious reasons.

I'm pretty convinced I have a cooked fuel pump. In all fairness it is 16 years old. I recently ran the tank pretty low, much lower than normal becuase of a road trip and a flight to catch. New pump is the mail, I'm gonna test it before dropping the tanks to ensure I'm not chasing the wrong thing.

Any other things to check first. Can't do anything until the pump gets here.

 

Ok, so you back probed pin 50 and you had 12 volts or the test light illuminated for 2 seconds ??…when you pierced the wire you said you had no voltage or test light lit so either you have an open between pin 50 and where you pierced the wire OR you may have corrected a bad connection…you will have to determine this to be sure maybe with a “wiggle” test…you can try the test I mentioned grounding pin 86 at the relay and using a test light connected to B+ and probe pin 50 as you shake the ECM connector to wherever you pierced the wire or try a continuity test….if this is intermittent it still can be a bad ECM…I’d also do a “drag test”…get yourself a t pin and see how much drag there is when inserting the T pin into the terminal and compare to other ECM terminals…50 may be a little looser.