RB25DET wont idle for more than 10 seconds. Stalls out without giving it some gas.

[Joey J]

Thread #2

Thank you all for the valuable information in the last thread I posted. the motor cranks on just fine now. 

I'm trying to work out my new issue. The car turns on and and idles for 10 seconds before it stalls out. If I give it some gas through the throttle body. Just rotating it a tad keeps the motor running. I let it go it starts to lower RPMS to the point of stalling out. 

Even giving it some gas it feels pretty rough. The motor is in a Datsun 280z so i don't have a tachometer so I cant check where the RPM is at. Sounds really high when I give it enough gas to stay on

I cleaned out the IAC just incase. Tomorrow I'm going to check the voltage for the TPS and make sure that's set up correctly. Then I'll set the ignition timing hopefully. I don't have the loop behind the motor. I have bought an inline spark tester so I'll use that on cylinder one. 

Also fuel the fuel pressure is confusing me. I had lowered it significantly to about 30 psi and that's what allows the car to run. Today i tried to raise it back up to 42 while it was idling and didn't make much of a difference. Once it stalled out. It only would crank and no start. I disconnected the injectors. It started up for a few seconds. Lowered the fuel pressure back down to 30 and the car started up. 

I looked at my emails from the shop and they used 330cc injectors from a 370z and bumped up the fuel pressure from 42 to 48. They said at the time that worked.

I'm wondering if the injectors are the issue. Since the motor will only start up with low pressure maybe they're soaking the plugs at the regular pressure? From what i understand I cant upgrade injectors without getting a standalone ECU. 

Any ideas and tips are much appreciated! If i cant work it out I'll take a video, upload to youtube and post a link here. I'm sure that would provide more information than what I'm trying to say here. 

 

[GTSBoy]

44 minutes ago, Joey J said:

From what i understand I cant upgrade injectors without getting a standalone ECU.

Yeah. You can't just throw wrong sized injectors in an change the base pressure and have it work on the stock ECU. It will be wrong everywhere else.

And what drugs were those f**kers on, putting 330cc injectors in? The stock 25DET injectors are ~370!

[Joey J]

1 hour ago, GTSBoy said:

Yeah. You can't just throw wrong sized injectors in an change the base pressure and have it work on the stock ECU. It will be wrong everywhere else.

And what drugs were those f**kers on, putting 330cc injectors in? The stock 25DET injectors are ~370!

It is on a z32 rom tuned ECU. I was just looking up what the stock injectors are supposed to be and I saw it was 370cc. I'm not really sure what my next steps would be with the fuel system. If I get 370cc injectors I'm not sure how that would interact with the rom tune. Also, that will pump more gas into the cylinders which seems to be my problem. I've lowered the pressure in the rails considerably through the FPR and that's helped the car run. 

The only thing I'm thinking is get a standalone ECU and get upgraded injectors. I planned to go with Haltech eventually but not so soon. 

[GTSBoy]

I think it is very likely that there is a significant problem with the ripped up Z32 ECU. That whole approach is so substandard these days that you should just abandon it unless you have the gear required to try to work out what it is doing. (Which is fairly basic workshop gear, a wideband, decent timing light and/or CRO, etc. Hell, if it was properly Nistuned, at least you could look at it in software.)

Bin it. Put in some modern injectors that are big enough to be useful (like, EV14 based 1000cc from a reputable source), and start again.

[Joey J]

14 hours ago, GTSBoy said:

I think it is very likely that there is a significant problem with the ripped up Z32 ECU. That whole approach is so substandard these days that you should just abandon it unless you have the gear required to try to work out what it is doing. (Which is fairly basic workshop gear, a wideband, decent timing light and/or CRO, etc. Hell, if it was properly Nistuned, at least you could look at it in software.)

Bin it. Put in some modern injectors that are big enough to be useful (like, EV14 based 1000cc from a reputable source), and start again.

I just came across this on a guide how to set up a z32 ecu for an RB25 motor.

“Z32 ECU uses a fuel temperature sensor and R33 RB25 does not. A Diagnostic Trouble Code (DTC) will be raised by the Z32 ECU if it senses that the Fuel Temperature voltage is out of range”

I checked and I do have this fault code on the z32 ecu. Supposedly when you have this code the ecu makes that car run rich and rough idle because it doesn’t know the temp. Maybe that’s why I was forced to drop the the fuel pressure so much?

GTSBoy, any other option I may have other than just biting the bullet and getting a haltech ecu and new injectors?

 

[GTSBoy]

Well you could try fitting a fuel temp sensor or faking it with an appropriate resistor value and hoping that that is the only cause of the trouble.

If it were me and I wanted to spend the least, I would buy an RB20DET ECU with Nistune fitted and use that.....except that if I was at that stage I'd now just buy a Haltech or a Link.

[Joey J]

Gotcha. Yea I’ll probably just go with a stand alone. Ughhhh, didnt want to spend all that right now but w.e. 
 

On the bright side I messed with the ignition timing again and the car idles pretty good. No need to give it gas or anything. Kept it idling for a good 5 minutes. I moved it like 10 degrees clockwise at the CAS. Last time I moved it about 10 degrees as well and that fixed my no start issue. 
 

From my last post someone suggested that the harmonic balancer went bad and I need to set a new tdc mark to set timing. I checked it and the tdc mark is correct. I tried to use the timing light and marks are no where to be found again. I adjust the timing on the light and it shows up as I increase it. I moved it to 60 and it shows the tdc mark now. I’m super confused. I feel like it’s impossible the ignition timing is at 60 degrees and the car turns on at all. 
 

I attached a pic of the CAs. It’s pretty far clockwise. It’s idling significantly better. The engine doesn’t shake much either. 

[Joey J]

i uploaded a video to YouTube. I have the dial set to 60 and the timing marks show up. In the video it’s a bit off. In person having it at 60 is almost dead on tdc. It fluctuates 5 degrees while idling. 
 

it’s idling rough but significantly better than before. You can also see my fuel pressure at the end of the video. It’s at 25 ish. 

Edited November 16, 2020 by Joey J
Typo

[robbo_rb180]

if its all a standard loom, engine and turbo setup just use a factory rb25 ecu  & injectors for now to get it sorted?
If going to upgrade a link plugin would be the way to go if you don't want to make a complete new loom.