RB26 Infinity 508h Hot Start Issue | AEM
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Joshuadehaven
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RB26 Infinity 508h Hot Start Issue

Hello everyone. This is my first ever forum post so please let me know if I’m posting correctly or not. I was unable to find an answer from searching through the forums.

I have a 1990 Nissan Skyline GTR with a single turbo running on Infinity 508h. I have most supporting sensors (MAP, IAT, UEGO O2, Flex Fuel, Oil and Fuel Pressure) as well at the stock coolant, throttle position, CAS, ect.

The issue I’m having is that the car will not hot start. I’ve noticed that all the 5v sensors on the AUX harness have a ton of “noise” on them when the engine is cranking. I’ve had this setup for about 2 years.

I did just have the engine out to be rebuilt and the engine bay was painted. I’m fairly certain that I sanded all the grounds well and checked them with an digital multimeter.

I did find an issue when going over the wiring; the ground for the 12v Flex Fuel Sensor was going to the 5v sensor ground, but that did not make a difference when I grounded that sensor to chassis ground. I’ve removed each sensor, one at a time, to try and isolate a faulty sensor with no luck. I’ve added jumper cables from the engine to the chassis and from the chassis to the battery to ensure proper ground. I measured 5.07V across the 5V and sensor ground terminals when I unplug the AUX harness. I’ve tested every ground I can find in the engine bay and under the dash.
 
When the engine is cranking, the coolant temp shoots from 188F to 260F to -198F then settles back out at 176F. The fuel pressure goes from 55psig to 0psig (I installed a gauge in place of the sensor to confirm that fuel pressure was not dropping to 0). The MAP sensor goes from -.9 to -14.
 
Has anyone had a similar issue to this and can point me in a general direction of where to start troubleshooting? I cannot take a data log at this time.