280Z Difficulty starting

[EuroDat]

It would be handy to add your cars build info to your signiture or at least year and model. I had to go back to the first post to find it again.

Your car is a 78 so it should have the two prong sender unit unless someonechanged the efi system to the later type.

I think they changed somewhere in August 77. I know that is different to what MSA is quoting, but and I know two around my build date have the single prong unit and we (mine and the other two) are all 2 to 4 months after the March 77 change over MSA is quoting.

I believe Datsun didnt have a fixed change over method. They seem to use bins as they come. If a bin of old parts came along a month later they would be installed. I have seen a very early N47 head with a spray bar and I have heard of someone else with one. They are not modified combi spay bar internal drilled setups. They only have they spray bar and N42 cam.

Back to your problem. You could also be having problems with the fuel pump relay. It could be failing when the voltage is low during stating. You could wire a test lamp to the fuel pump wires to see what is happening.

[Zed Head]

It would be handy to add your cars build info to your signiture or at least year and model. I had to go back to the first post to find it again.

Back to your problem. You could also be having problems with the fuel pump relay. It could be failing when the voltage is low during stating. You could wire a test lamp to the fuel pump wires to see what is happening.

These are good points. I didn't make a picture of the very well-written relay test procedure from the FSM.  It's all there though.  1978 might be the best FSM out there for descriptions and test procedures. 

[Marios280Z]

Here's the 1978 fuel pump control scheme.  BUT, back to my other point, this scheme does not provide power to the pump by turning the key On/Off as described earlier.  In a correct system you should not be able to "prime" the fuel system with the key.  

 

So you're studying something that has already been shown to be modified somehow.  OR, your oil pressure switch is bad, but this would just give power via two methods, one when the switch is open, and one when the switch is closed.  Neither scenario cuts power to the pump.  The Start circuit bypasses the control scheme anyway.

 

I see FSM avoidance.  It's not as bad as it seems, it's actually very educational and a good read.

I do read FSM, I just have not gotten to all section of it . I have hard time following that fuel pump control system diagram... Not sure what to tell you about this pump and it being energized when ignition key goes to ON. I even spoke with the PO today and he said he never touched any wiring on the car. I have performed the Functional Test for fuel pump. Back then I did not have fuel pressure gauge to perform the discharge pressure test, but now since I do have the gauge I can do that test.

 

But I want to challenge you guys on the fuel pressure thing. Wouldn't I have driveability problems as well if my fuel pressure wasn't high enough?

 

 

It would be handy to add your cars build info to your signiture or at least year and model. I had to go back to the first post to find it again.

 

Fixed.

 

 

Your car is a 78 so it should have the two prong sender unit unless someonechanged the efi system to the later type.

I think they changed somewhere in August 77. I know that is different to what MSA is quoting, but and I know two around my build date have the single prong unit and we (mine and the other two) are all 2 to 4 months after the March 77 change over MSA is quoting.

 

 

Yes, I do have the two prong oil pressure sender.

 

 

Back to your problem. You could also be having problems with the fuel pump relay. It could be failing when the voltage is low during stating. You could wire a test lamp to the fuel pump wires to see what is happening.

 

 I will look in the FSM for the section where it talks about the fuel pump relay and as Zed Head mentioned I will follow their test procedures.

 

So here is what I have to do as my next steps as I gathered from you guys in the last couple of days:

 

1) Clean and verify all the ground wires in the engine bay are good

2) Perform fuel pressure discharge test per FSM

3) Perform fuel pump relay test per FSM

 

I will also have my wife crank the car for me as I film the pressure gauge during priming and during cranking so you can have a look at it.

 

Do we still look a the oil pressure sender as a potential offender?

[siteunseen]

If you're pressure is zero in the mornings something other than what we've been discussing is suspect, in my opinion. You could have a bad fuel pressure regulator dumping the excess through the return to the tank. What about clamping off the return after running your car and see if the pressure stays up? That would make first start up way better, the pressure already being in the system.

You could have a leaky fuel injector letting the pressure leave out. Try tapping them with a screwdriver handle. It could knock the debris loose that's keeping it from sealing up. Just ideas.

[Marios280Z]

sieunseen,  I will try clamping the return line as well as tapping on the injectors. It actually takes just few (3) hours for the pressure to go to 0.

[Zed Head]

Not sure what to tell you about this pump and it being energized when ignition key goes to ON.

That's for you, not me.  Your wiring is not normal.  You should understand what's not normal.  One screwed up thing can lead to other screwed up things.

 

It could be that your fuel pump actually loses power at Start, because of some unknown wiring or relay problem, and is starting on the residual pressure from when you primed it.  

 

I mentioned also, the possibility of a voltage drop when starting causing a weak spark.  This is a real thing, and is why car makers have a specific wire bypassing the ballast resistor and turning off everything unnecessary to starting when the key is turned to Start.  Measure voltage at the coil when starting, and with the key on.  That's a simple test and is a common test for all cars with starting problems.  A bad battery, for example, can drop voltage during starting but run the car just fine once the engine starts.

 

A multimeter will be very useful.  Do those relay tests.  Something will show up.  Take good notes, with real numbers.

[siteunseen]

Ha, just saw your "vent mounted air freshener".  That's funny. 

[Captain Obvious]

I have a theory about the short "priming" pulse to the fuel pump in the 78 Z... When you start turning the key to start the car and you get to ACC position, the wires to the fuel pump control relay have the following voltages on them:

 

Black/Yel - No connection to anything. (Will go hot in START, but we haven't gotten to START yet.)

Yellow/Blk - Connected to ground through the oil pressure sender. Should have been that way since before you put the key in the ignition.

Blue - Connected to +12 through the CHG lamp and the coil of the brake warning relay.

White/Blk (input side) - No connection to anything.

White/Blk (output side) - Connected to the White/Blk input side wire, but since that's not connected to anything, the output side doesn't get any power.

 

The instant you turn the key to ON, the wires to the fuel pump control relay have the following voltages on them:

 

Black/Yel - Still no connection to anything. (Will go hot in START, but we haven't gotten to START yet.)

Yellow/Blk - Connected to ground through the oil pressure sender. Should have been that way since before you put the key in the ignition.

Blue - Pulled low through the alternator to essentially ground.

White/Blk (input side) - Connected to +12 through the ignition relay.

 

White/black (output side) - Now here's where it get's tricky... The two relays built into the fuel pump control relay will change positions, but that doesn't happen instantaneously. Before the key is turned to ON, the relay is in such a position that the input WHT/BLK is connected to the output WHT/BLK. And when the key hits the ON position and the ignition relay pulls in, and for a brief time the output WHT/BLK will still be connected to the input WHT/BLK and it could temporarily energize the fuel pump relay sending power to the fuel pump.

 

So when the key hits the ON position, the alternator controlled side of the fuel pump control relay will pull in. When this side pulls in, it makes the connection that pulls in the OTHER side of the fuel pump control relay. The pulling in of those two relays takes a little time and maybe that's the brief instant the fuel pump gets a short shot of power.

 

It's not supposed to happen, but I can definitely see it happening in reality. Especially if the contacts in the oil pressure switch are starting to get a little dirty and don't provide as strong of a connection to ground as it should. That could delay the pull in of the second side of the fuel pump control relay causing a longer pulse to the fuel pump.

[Marios280Z]

Captain Obvious, wow, that's impressive. Not sure where you got all the info about wire color coding, but I'm assuming it was somewhere in FSM or you actually had the relays appart once before. In either case, big thanks for the analysis.I'm very much visual guy when it comes to things like this so  Iwould ahve to see it myslef to fully understand and folow your line of thoughts, but your theory seems to make sense. As I mentioned above, my oil sender unit connectors are oily, so perhaps that is part of it. I will be doing ground connections clena up this weekend and I will make sure to clean the oil sender as well (will have to probalb yreplace it soon). Thantks again for putting that much thouhg into this analysis.

[Marios280Z]

Ha, just saw your "vent mounted air freshener".  That's funny. 

 Gift from my wife, she does not like the smell of the 38 your old car carpet...   Soon to-be-replaced...(the carpet, not the wife of course)

[Marios280Z]

Here some more video form Czarnomski's garage. This was a fris start up after I did the ground wire clean up per the atlanticzcar DIY o nthat topic. The only connectors I have not touch were the injector connectors :/ As you know the acces is rather tough and the palstic on those is very brittle now. I attempted to take one of them and as I expected cople pieces just broke off. The contacts looked very clean on that one.

In the video I primed the pomp before starting. It was interesting to see that in the proccess os starting, when it chocked, the pressure dropped down to around 15 psi. Not sure if it is an indication of something or just a result of the engine choking. Then I removed the vac hose to the FPR just to demostrate what I have talked about earlier in my posts about pressure going up when vac is off. Next I reved the engine few times to perhaps revial something..

 

 

After running the engine I clamped the fuel return line from FPR to see if that will prevent the fuel pressure from dropping. I will report on the result of that.

STill to do:

2) Perform fuel pressure discharge test per FSM

3) Perform fuel pump relay test per FSM

[Marios280Z]

Quick update. Looks like the clamp on hte FPR return line did not stop the pressure from falling down :/ Isn't there a check valve in the fuel pump itself that suppose to prevent from fuel flowing back? Is there a chance that the valve (if exists) failed?

 

Also, about an hour and a half after I recorded the video, I went to dirve the car (engine was cold since I only run it for about 2 minutes while recoridng the video) and after priming fuel pressure couple of times the car started right up with a touch of a key. I don't get it...