Rb25det cranks but no start

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Joey J
Posts: 7
Joined: Sun Nov 13, 2016 9:04 am
Car: 1977 Datsun 280Z - RB25DET

Rb25det cranks but no start

Postby Joey J » Tue Nov 03, 2020 6:47 pm

Hello,

I have an rb25det that I had swapped into my 280z by a reputable shop. Ever since I got it back it wouldn’t run right. Once it got hot it would shut off. It got sent back. They fixed it supposedly and same issue when I got it back. Ran a bit longer this time but once it got hot it would stall out.

I lost the motivation in the project. I didn’t have the experience and bit off more than I could chew. Plus money was tight after the swap. This was like 3 years ago.

Now I’m trying to get the car running finally. I’ve checked a few things and can’t figure out why it won’t turn on.

Spark is good. I pulled out the plugs and replaced them just incase. I made sure they’re sparking when I turn the ignition. When I pull them out they’re wet so they’re getting fuel.

I will say the fuel pressure regulator is showing odd readings. When I turn the key the pump primes and pressure jumps to 22 psi and holds. When I crank it the engine tries to turn and fuel pressure jumps to 40 and the needled jumps between 40-50 while its trying to start.

Tested compression on all the cylinders and they all hold compression. I’m not sure if the tester I have is good because it’s old. I did cyl 1-3 and they were all 145-150. Then cyl 4,5 and 6 showed 180. I went back and did cyl 1-3 and it also showed 180-185. I assume it’s a problem with the tester. Not sure.

I tried using starter fluid into the intake manifold and nothing. It’s almost as if it has no spark but the spark plugs are definitely firing when I pulled them all out and tested them.


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PapaSmurf2k3
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Re: Rb25det cranks but no start

Postby PapaSmurf2k3 » Tue Nov 03, 2020 11:07 pm

That sounds frustrating.
So, we should tackle the no start issue first (obviously) and then worry about the shutting off while hot later.
If possible, could you key on to prime the pump, and then remove the fuel pump fuse and then crank for a bit? If you're getting too much fuel and flooding the engine, this should show you that (it will fire up briefly with the fuel pump fuse removed). If it still doesn't start, it sounds like an ignition timing or valve timing issue.

Is the fuel pressure regulator adjustable?

Joey J
Posts: 7
Joined: Sun Nov 13, 2016 9:04 am
Car: 1977 Datsun 280Z - RB25DET

Re: Rb25det cranks but no start

Postby Joey J » Wed Nov 04, 2020 10:44 am

PapaSmurf2k3 wrote:
Tue Nov 03, 2020 11:07 pm
That sounds frustrating.
So, we should tackle the no start issue first (obviously) and then worry about the shutting off while hot later.
If possible, could you key on to prime the pump, and then remove the fuel pump fuse and then crank for a bit? If you're getting too much fuel and flooding the engine, this should show you that (it will fire up briefly with the fuel pump fuse removed). If it still doesn't start, it sounds like an ignition timing or valve timing issue.

Is the fuel pressure regulator adjustable?
Wow that’s a good idea I’ll definitely give that a shot this weekend. More and more I’ve been thinking the injectors are soaking the plugs not letting it start.

If that does t work I’ll pull the injectors and inspect them.
Maybe get them tested as well.

FPR is adjustable. I realized that while doing research this week. I will see if I can adjust it to 43 psi.

Hopefully it’s not a timing thing because that I’m kind of worried about messing with.

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Re: Rb25det cranks but no start

Postby PapaSmurf2k3 » Thu Nov 05, 2020 6:10 am

Might want to drop it down if its been flooding.
...or replace it if its jumping all over the place. That's definitely odd. 5 or so psi I would think would be normal, but not 20-30 haha

Joey J
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Joined: Sun Nov 13, 2016 9:04 am
Car: 1977 Datsun 280Z - RB25DET

Re: Rb25det cranks but no start

Postby Joey J » Fri Nov 06, 2020 7:15 pm

PapaSmurf2k3 wrote:
Thu Nov 05, 2020 6:10 am
Might want to drop it down if its been flooding.
...or replace it if its jumping all over the place. That's definitely odd. 5 or so psi I would think would be normal, but not 20-30 haha
True, i'll run some tests tomorrow and shoot an update in here. Hopefully I can get it start up and idle at least for a bit.

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Re: Rb25det cranks but no start

Postby PapaSmurf2k3 » Sat Nov 07, 2020 8:13 am

Good luck!

Joey J
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Car: 1977 Datsun 280Z - RB25DET

Re: Rb25det cranks but no start

Postby Joey J » Sat Nov 07, 2020 12:20 pm

So I unplugged all the injectors to test for voltage and it started up for 2 seconds. 


Plugged them back in, car didn’t start. Unplugged again and it started for 2 seconds. 


Also on the Fuel pressure the gauge stays at 43 if I use a jumper on the pump relay. As soon as I unplug the jumper, fuel pressure falls by 20 psi. 


any ideas?

EDIT: I’m thinking it’s either the fpr is bad or the rom tune is bad telling the injectors to dump too much fuel. 

Joey J
Posts: 7
Joined: Sun Nov 13, 2016 9:04 am
Car: 1977 Datsun 280Z - RB25DET

Re: Rb25det cranks but no start

Postby Joey J » Sat Nov 07, 2020 7:29 pm

The voltage at the fuel pump was at 9.5v when it turns on. I tested all the wiring replaced the terminals and it’s still at 9.5v. 

I unplugged it and tested the voltage to the wiring only and it was over 12v. Not sure why it drops once it connected to the pump. 

i ended up lowering the fuel pressure to under 30 and it sounded like it wanted to turn on but still no dice. 


I didn’t know what else to do so I tried adjusting the CAS while it was cranking and BINGO! Turns out it was ignition timing. I adjusted the CAS a bit to the right and it started to idle. Turned it off once it stayed idling for a bit.

I got everything hooked up to set timing correctly with a timing light. The marks are no where to be found on the balancer while the light is flashing. It’s definitely there because I checked to make sure they were visible before trying to set it but I see the marks at all once trying to set the timing. 


Is it possible the timing was way off to the point the marks don’t even show? I ran out of time so that’s as far as I got. 

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Re: Rb25det cranks but no start

Postby PapaSmurf2k3 » Mon Nov 09, 2020 2:51 am

Yup, very possible. You might be a tooth off on the distributor or something.
I've re-marked my crank pulleys to make sure the markings are visible for when I'm trying to set timing, but if you're confident you can see them, you should be good.

Joey J
Posts: 7
Joined: Sun Nov 13, 2016 9:04 am
Car: 1977 Datsun 280Z - RB25DET

Re: Rb25det cranks but no start

Postby Joey J » Mon Nov 09, 2020 2:44 pm

PapaSmurf2k3 wrote:
Mon Nov 09, 2020 2:51 am
Yup, very possible. You might be a tooth off on the distributor or something.
I've re-marked my crank pulleys to make sure the markings are visible for when I'm trying to set timing, but if you're confident you can see them, you should be good.
Hmmm, I’ll give it a shot and put a mark on the pulley to see if I can see it. Someone else in another forum mentioned the harmonic balancer/pulley may be damaged so I may need to set a new tdc mark on it to be able to set timing. If that’s the case I will need a new balancer. I ordered one and I’ll change the water pump and timing belt all at once. Might as well. Mine all looks oem and untouched.

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Re: Rb25det cranks but no start

Postby PapaSmurf2k3 » Mon Nov 09, 2020 5:48 pm

It should be keyed to the crank (via woodruff key) so I can't imagine it would be off that much, but you never know.


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