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RB25DET cranks but wont start. Need help.


Joey J
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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 bite 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 their 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.

 

Any help is much apprecaited!

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11 hours ago, Dose Pipe Sutututu said:

Sounds like that "shop" you took it to needs to go back to school.

What ECU are you running? do you have a wideband O2 on installed? What are the AFRs like on idle

Thanks for your response. Idk what to say about that shop... they had done the swap multiple times. I just don’t know why they would let a car leave their shop that isn’t running right twice. 
 

It has a Z32 ecu rom tuned by them. I don’t have a wideband on it. Is that something I should get now to help diagnose the issue? The car won’t run at all it just cranks. Would a wideband help at all?

ive been doing a lot of research on what my next steps should be as my mechanical knowledge if very limited. I’ll start looking into a wideband now. 

Edited by Joey J
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4 hours ago, Dose Pipe Sutututu said:

Get a wideband first, install it then log down what your AFRs are when it starts fine. When idles cold, when it idles warm and when it's about to die.

Yeah, but Johnny, it don't start at all.

I'd be looking closely at whether the fuel fail is plumbed up correctly. In vs out, damper & pressure reg.

Check the ignition timing while cranking. It needs to be in the right ballpark.

Does it need the chip tuned VG ECU because of mods? Why is it there? It's just one more way that it could have problems. Is it possible to throw an RB25 ECU at it? (Probably not, would be my guess, because of loom plug differences).

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1 hour ago, GTSBoy said:

Yeah, but Johnny, it don't start at all.

I'd be looking closely at whether the fuel fail is plumbed up correctly. In vs out, damper & pressure reg.

Check the ignition timing while cranking. It needs to be in the right ballpark.

Does it need the chip tuned VG ECU because of mods? Why is it there? It's just one more way that it could have problems. Is it possible to throw an RB25 ECU at it? (Probably not, would be my guess, because of loom plug differences).

I'll check the fuel lines going back to the pump then tank. I only checked what was in the bay. Inlet, fuel rail, FPR then outlet. Hopefully its something that simple. I'll make sure to check that out. Thanks for that. 

I'll have to look into how to check ignition timing. The one thing I really was hoping I didn't have to mess with was timing. I'll start my research on that. 

Not sure the reasoning behind rom tunned z32 ecu. The only mod on the motor is aftermarket front facing intake manifold and intercooler. Everything else is stock. Unfortunately I don't have the stock RB25 ECU. 

Thanks again for the help. 

 

 

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I was having similar things happen when my Crank Angle sensor was going out. 

It started as it was having issues running when the engine was warm and over time got worse and worse until it would barely start. I have a NEO so it might be different but might be worth checking out. 

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12 hours ago, Binarydata said:

I was having similar things happen when my Crank Angle sensor was going out. 

It started as it was having issues running when the engine was warm and over time got worse and worse until it would barely start. I have a NEO so it might be different but might be worth checking out. 

I’ve heard the CAS is a big problem with these cars. I was hoping the CAS would not go bad until I can swap over to a trigger kit and have a standalone ecu. 
 

im gonna test a few things and I may have to look into replacing the CAS if I can’t figure it out. I pulled mine out and it looked okay. The fact that plugs sparked gave me a sense that it was okay. 

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Are you sure the CAS went back in the right orientation. If the half-moon locator key in the ex cam breaks off, its possible to align the CAS incorrectly. If the CAS is even one tooth out, the engine won't start.

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5 hours ago, blind_elk said:

Are you sure the CAS went back in the right orientation. If the half-moon locator key in the ex cam breaks off, its possible to align the CAS incorrectly. If the CAS is even one tooth out, the engine won't start.

I will inspect it more thoroughly tomorrow. I' will be trouble shooting all day. When i pulled it out last weekend I was careful to not move the halfmoon key from the cam. I put it right back in how it was. I did realized during the week that the CAS affects timing which i didn't know when I was looking at it. 2 of the 3 bolts holding it in place were tight, but the bottom 3rd one was not even fastened all the way. Maybe the 4 hour shipping back from the shop caused the CAS to rotate a bit. I plan to check timing and adjust if needed tomorrow. 

Below is my to do list for tomorrow. If anyone has any other suggestions please let me know. I will update if i can get it running.

To do list

Look for all grounds and check them. Maybe replace battery terminals.

Check ECU to see if we can run diagnostics on it.

                How to check the codes of the ECU in a '90-'95 Nissan 300ZX

Check all fuses. Driver and passenger side.

Is the alarm immobilizer making the car unable to start?

Verify if fuel lines are correctly plumbed. Check whole loop (Tank, pump, rail, FPR and back)

Fuel pressure should go to 43 PSI once ignition is turned on. Why does it bounce when starting? Adjust FPR? Is it damaged? Use a jumper wire on the fuel relay to test fuel pressure.

Check voltage getting to injectors.

Check injectors, maybe it’s flooding the engine? Try and air out cylinders, dry and clean plugs then use starter fluid with injectors unplugged.

Prime pump then remove fuel pump fuse then crank for a bit. See what happens.

Clean out idle air control valve. IAC is attached to backside of the stock manifold. Is mine deleted? Remove and clean if possible.

To adjust: Unplug TPS. Adjust screw so it idles at about 750-900 RPM. Clockwise lowers revs. Counter increases revs. Plug TPS back in to set it.

Check ignition timing with timing light.

Inspect CAS again. Check voltage. Remove and spin with ignition on.

Check TPS Voltage

 

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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 lowered the fuel pressure pretty significantly down to low 30s through the fpr and it would want to start when cranking but wouldn’t fully start. 
 

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. 

Edited by Joey J
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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. 

Edited by Joey J
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8 hours ago, Joey J said:

Is it possible the timing was way off to the point the marks don’t even show?

Yes, because the outer part of the pulley can slip on the rubber so that it no longer bears any relationship to the inner part (and therefore the rest of the engine).

Pull #1 plug out. Find TDC firing. Mark new TDC on pulley. Plan to replace pulley immediately if the original mark is somewhere else!

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3 hours ago, GTSBoy said:

Yes, because the outer part of the pulley can slip on the rubber so that it no longer bears any relationship to the inner part (and therefore the rest of the engine).

Pull #1 plug out. Find TDC firing. Mark new TDC on pulley. Plan to replace pulley immediately if the original mark is somewhere else!

That makes sense. Thanks so much for that.  I was baffled on why I couldn’t see the marks. 
 

I’ll definitely start shopping around for a new balancer. I’m thinking if I’m gonna pull the balancer might as well get a new timing belt and tensioner. It looks like the hardest part about getting to the timing belt is getting that pulley off. 

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