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Tech Talk Technical Discussion About The Nissan 240SX and Nissan Z Cars


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Old 12-06-2017, 11:16 PM   #1
Jkrb25s14
 
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Rb25 s14 shuts off after 15 minutes of driving (read whole post)

Ok guys so heres whatsup, this is a long post fair warning.
i have a series 1 rb25det in my 95 s14. I got it a year ago tuned it on a z32 MAF and a z32 na ecu with nismotronics, found out it had a bad turbo, but it was reliable, no hiccups at all.
So i pull motor and trans, planned on building it but didnt, just inspected block without pulling everything out, it had compression. I lapped the valves, new head gasket, rear main seal, thermostat, oil pan, arp head studs, water pump, oil pump, timing belt, cxracing exhaust manifold, freddy intake, q45 throttle body, wiring specialties oem main harness, precision 5858bb, id1050x injectors, precision 38mm wastegate, radium fuel rail, SARD FPR, warlboro 255 wired on its own relay, new fuel return and supply from tank to engine bay, fuel filter, battery in trunk, oem z32 MAF since the original was a knock off replacement.

So with all that said i get it tuned it makes 470whp 350tq. Runs damn good, until its warm.
Once its warmed up it stalls out, on the data log everything looks good with the ecu, the only thing that happens is the MAF voltage drops and the rpms just drop even when throttle is still applied.
You can start it back up and its a 50/50 shot if its running super fat with afr at 9 at idle, or its normal. So i can take back off and lay into it and it does a normal healthy pull and then again it hiccups again. And it constantly will do it.

Ive tested the MAF already its good, TPS is good, VCT is working, ecu is getting VSS signal.

The only thing that drops out on the log is the MAF voltage and rpm like i said. Guys im so lost at this point
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Old 12-06-2017, 11:40 PM   #2
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is there anyway to monitor the water temp? its possible that the sensor for could be faulty at higher temperatures. Ive seen it happen with a Land Rover where once it crawled up to 90c that it opened the circuit making the computer think its massively hot and shutting itself off. Water temp sensors can affect the computer a lot.
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Old 12-07-2017, 12:15 AM   #3
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Yeah i can data log on my laptop and see what the ecu is doing. Ill monitor that next, from what i remember, and what my tuner told me, that temp was fine. But im still going to confirm that real time for myself
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Old 12-07-2017, 08:55 AM   #4
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Who tuned it? If Je I'd bet that's the problem.
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Old 12-07-2017, 08:58 AM   #5
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Sounds like an ECU limit/failsafe is set or you are coming up the upper limit of the MAF sensor.
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Old 12-07-2017, 10:44 AM   #6
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John kerr of jk tuning did it. He had it on dyno but didnt drive it around.
I am pushing the limits of the maf im at 470 its good till 480 500. But it does it when im just cruising.
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Old 12-07-2017, 11:41 AM   #7
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Look at your overboost table in the nemu
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Old 12-07-2017, 01:49 PM   #8
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What will the over boost table show me? And how do i get to it?
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Old 12-07-2017, 01:59 PM   #9
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Overboost or MAF limit table. Basically its a failsafe that if MAF hits a certain voltage, it shuts everything down.

Look up on the nismotronic website for the manual........or just ask John to look at your logs.
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Old 12-07-2017, 03:35 PM   #10
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John has been looking at my logs and he says he doesnt see anything out of the ordinary besides the MAF voltage drop and the rpms drop even though im still giving throttle. He hasnt been able to find anything.
Last words from john to me were "check the fuse box and relays" idk how the fuse box or relays would cause this issue though
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Old 12-07-2017, 05:45 PM   #11
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Rpm loss would be from your cam angle sensor, where is the maf located? Is it on the cold side? Maybe a ecu issue
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Old 12-07-2017, 06:28 PM   #12
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Would a bad cam angle sensor come up in the datalog? And my MAF is still on intake before turbo
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Old 12-08-2017, 10:59 AM   #13
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I don’t think it will show up, it will just drop rpm. Unless you can use a scope and read the signal and physically see it drop. Have you always had your maf on the intake before the turbo? I once had a issue I forgot the symptom and moved my maf from that location to the cold side. Someone called it a blow through maf set up.
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