Intermittent crank no start issue

The brown with pink wire is the actual power to the pump wire. The white with red wire is the duty-cycle wire between the powertrain control module (PCM) and the fuel pump control module. I attached a quick test that will rule out the fuel pump module by putting direct power and ground to the pump. If you want to scope the pump all you would need to do is put an clamp on amp lead onto the fused jumper between terminals nine and ten.

Update: I have not been able to conduct the test you gave as the car has been starting. While running the fuel pressure went to 0 PSI it wanted to stall I blipped the gas and it ran fine.
The next time it doesn't start I will conduct your test. Would I disconnect the fpdm for the test, hook up wires then turn on key? Also I have a Kenne Bell supercharger with a Boost a Pump installed will that interfere with the test? Thank you

Just to jump in, yes you would disconnect the module. What he has you doing is just bypassing the module by putting those wires in place.

However, if you have confirmed the pressure is going to 0 then you know the pump is not supplying pressure. Which means we can just go to the pump and monitor the voltage. If it has 12 volts then you know the module is good and the pump needs replaced. Basically you are doing the same thing by bypassing the module but I always find it easier to leave everything hooked up and just monitor the voltage.

Let us know what you find or what questions you have. Thanks

Thank you Kasekenny, was going to do the bypass test today upon disconnecting the fpdm connector, every pin had green corrosion on them, cleaned with electrical connector cleaner. Went one step further and disconnected the fuel tank connector, only to find green corrosion on every pin, cleaned and blew compressed air on every connector. Put it all back and the beast started up. Going to let it sit until tomorrow and see if she starts up.Thanks for your input, I will let you know how it goes. This has been an intermittent problem I am hoping the corrosion on the pins was causing this problem. So the wire to monitor for pump voltage is the BN/PK right on the fpdm connector? Thank you.

That is great news. The dreaded green corrosion is the worst because we don't always find it and it can cause all sorts of odd issues. I would put dielectric grease in each of those connectors as that will help keep the water out.

Yes, that is the power wire to the pump so that is what you would need to monitor but the fact that you found that, I suspect all the components are fine and that corrosion is the issue.

Thank you Kasekenny, it's a load off my mind, was hating the thought of replacing the fuel pump. I am going to put dielectric grease in those connectors as per your suggestion. I have a good mind to go over all connections and check their condition, because since that corrosion was there it might be other places. Thank you for taking time to write, I will let you know if the beast starts up tomorrow.

Kasekenny,

Good news, car started right up this morning, going to try it throughout the day to see if it's consistent. I believe it will be!!

Kasekenny, car has been starting up all day at different times. One thing I noticed after prime pressure at 30 PSI when cranking pressure drops to 20 PSI until it starts don't know if that's normal, never really noticed if it did that all along.

That is good news that it is starting however, that pressure does sound slightly low. It is normal for it to drop when you are cranking the engine as the injectors are opening and that is relieving the pressure. However, you will just need to keep an eye on it if this issue starts coming back as your minimum spec for pressure is 35 PSI. Again, not cause for alarm but I don't imagine it will get better over time.

Thank you for your input, I will keep an eye on the pressure, the car is supercharged along with a boost a pump installed, I would hate to lose pressure under boost and send my supercharger through the hood. I will not go into boost until I am satisfied things are normal.If the problem comes back would you put blame on the fuel pump or the FPDM? I plan on checking the connectors on the ccrm, crank position sensor and the fuel rail pressure sensor for corrosion. Again, thank you

The most likely cause would be the pump as the module should just be supplying a steady 12 volts. So if the pump is getting the proper voltage which you can check, then the pump is the issue.

Thank you Kasekenny, I will keep an eye on things. For the record the fuel pressure has always been 30 PSI since I got the car just the nature of the beast I guess.

Yep. That is fine. It is only slightly low. That could be a combination of things as it is only about 15% low which is nothing to worry about.

Thanks again. Talk to you next time.

Thank you Kasekenny for all your help, I really appreciate it.

Kasekenny, I am disappointed to report this morning was testing start up. The car does one of three things.

1. will prime to 30 PSI upon cranking will go to zero PSI no start.
2. will prime to 30 PSI and start up like normal.
3. will not prime at all.

I want to read the voltage to the fuel pump like you suggested, what wire on the FPDM would I monitor to check for momentary voltage?
If it gets momentary 12V for prime and doesn't prime would that mean the pump is bad? Thank you

Sorry to hear it. You are correct. If the pressure is dropping to 0 then I suspect the pump is the issue. If the module was the issue then when it primes, it would not bleed the pressure. Granted when you crank the engine the injectors are opening and the pressure will bleed off but it should fire for at least a few seconds before it sputters out if the pump was holding pressure but just not continuing to run.

However, your approach is the correct way to figure it out. You should have 12 volts on pin 10 at the module brown/pink wire. Then when you crank the engine it should bring the voltage back. The red/black wire is the return or ground for the pump so you can check that as well if you want to.

Kasekenny, once again thank you. I am beginning to suspect the pump.
Going to check the voltages just for good measure.

Hi Kasekenny, since the car has be starting and running consistently, I would like to know if I can hook up a bench oscilloscope (not an automotive tool) just an oscilloscope I use for TV repair? I'd like to see the pump waveform if so, which wire would I hook it up to? I'd like to send you a photo of the waveform. Thanks.

You can hook it up but this is DC current so it will most likely be a flat line. I see any circuits that would be AC to give you an alternating wave form. So basically the scope will tell you the same thing a meter does which is what the constant voltage supplied is.

Kasekenny, thank you for answering. I was hoping my scope would show the waveform. Guess that's where the automotive scope comes in.

Just to be clear, an oscilloscope is an oscilloscope (for the most part) and it will show you a pattern but this circuit to the pump is a DC voltage circuit and they show up on scopes as a straight line at the voltage level they are supplied. So since this is a 12 volt DC circuit, the scope should show it as a flat line at the 12 volt level on the grid.

Give it a shot and see if that is what you get. Feel free to post a picture of it. Thanks

Thank you Kasekenny, this weekend I am going to scope the light blue/orange wire (pin 7) for feedback should be square wave. I would like to scope the control signal also what wire is that? Hopefully one of those will show duty cycle of pump and if the signal is a clean square wave. Again thank you and have a good weekend..

I am sorry. You are talking about from the ECM to the driver module and not the pump.

You are correct that the light blue/orange should be a square wave. The white/red will be your control wire which would be they duty cycle.

Thank you Kasekenny, will give that a shot on the scope and post it. Sorry for any confusion.

Hi Kasekenny, Had a friends scan my car with a Autel bt mk808 tool, it tested a lot including the fuel pump and reported the fuel pump as okay. I am going to send a waveform the tool gave me. I hope it is useful. Would like your opinion. Thanks.

I can't see the voltage scale but that looks great. Good square wave and it is stepped up which shows duty cycle is increasing.

Thanks Kasekenny, the scanner is new to us and don't know how to set the voltage scale on the photo I have of the waveform on the vertical axis scale goes from 88 to almost 120 (I know that can't be volts) I did rev it up during the scan I assume that's where you see it stepping up. Can I assume if there was bad contacts on the pump the waveform would have shown it?
From what I am reading, the fuel pump should be on during prime and crank, if that is correct what would cause the pressure to sometimes drop to zero while cranking then upon turning key off and on it primes to 30 and stays there while cranking then starts? Ghost in the machine!!
Car holds pressure for over 3 hours then starts to drop off. Thank you for your input.

Yes. The graph would should a connection issue.

Just to be clear, when the pressure drops to 0, does the engine start? It shouldn't so it is dropping to 0 because there is a leak in the pressure at the pump or the injectors. So if the pump holds pressure for hours then we know the system is sealed at both ends and you don't have a leaking injector or pump. So let's get more detail on when it drops to 0. Can you get it to do this at will? What do you have to do to get it to drop to 0?

I cannot get it to happen, it happens randomly, sometimes the pressure won't drop at all while cranking and it will start like normal. When it drops to 0 PSI it will not start. If i cycle the key, pressure comes up to 30 PSI and it will then start. Also it holds pressure for hours. This weekend I will try to get a video of the fuel pressure gauge (if it acts up).
Thank you for your input.

Hello, I'm Danny.

I have to add my 10 cents here. Number one you are not getting the even close fuel pressure your car is requiring. You mention you've only achieved 30 PSI when working-running. The specification for your GT is 35 PSI (minimum) - 65 (maximum) PSI which you need. When you add a forced induction unit to your car do you realize or were you told a few things you might have to change? Was an upgraded higher pressure fuel pump installed or is this the original? Your fuel pressure is coming in way low. Did you change the fuel injectors to add more pressure or are they stock as well? Stock injectors can be 19 or 24's. Just trying to help and keep your supercharger from launching through the hood. Get back to us and we'll continue to help. Just an FYI- I worked at Saleen for 2 years. Thanks again for using 2CarPros.

Hi Danny,

I had a Kenne Bell 1.7L intercooled supercharger with a boost a pump and 36 Lb. injectors installed around 9 years ago. It is running 9 pounds of boost. At 9 pounds of boost my fuel pressure reads 50 pounds. For whatever reason the car has always read 30 PSI at idle, on a hot day it will go up to 40 PSI regular driving out of boost. No problems until recently, here's the whole story. Tried to start car zero fuel pressure cycled key a few times pressure came up to 30 PSI car started and ran normally. Started checking grounds and connections found the connector on the fuel pump driver module had green corrosion on the pins, cleaned it really well, going further found the connector (under the rear bumper) to the fuel pump had green corrosion cleaned it. Also found a bad ground around the radiator shroud. Everything ran well for a while, thought I had it fixed. Then it happened again tried to start zero pressure no start. Got it running now I notice sometimes the pressure will drop from 30 PSI to zero while cranking, if I cycle the key it will prime to 30PSI and start. Other times it will crank and the pressure will not drop at all. (It holds pressure for hours before dropping off.) From what I read the fuel pump should be on during prime and crank, if that is correct then whatever is responsible for keeping the fuel pump running during crank is not doing it's job. Would very much appreciate your input. I am keeping this car out of boost until I get this fixed. Thank you for your input.