greddy32 Posted April 22 Report Share Posted April 22 hey guys so im having an issue starting my car. its been down for about a year getting a full rotisserie resto. the only thing ive changed is the hot side, i went from single gtx3582 back to twins.. the car ran totally fine before the restoration and i figured it would at last fire up seeing how ive only changed turbos (clearly i was wrong)... the car cranks and "chugs" a little while cranking oh and the surprise ear piercing backfire from time to time, but will not show signs of life . ive ran tests on the coils and injectors and they fire when commanded to, ive hooked a ht lead on cyl 1 and i def have spark. my assumption is, the problem is timing based.... im half dumb though so idk lol. ill attach the tune file that im trying to use from before my car when under the knife... and if someone can walk me through logging a trigger scope that would be awesome, ive tried but the prompt that pops up says shows no ecu connection. thank you in advance.... ill be over here pulling my hair out r32 gtr rb26 single throttle body oem rebuilt twins greddy suction kit greddy 264 cams (unknown specs) g4+ e85 twin walbro 450 in tank -8 feed -8 return radium fpr with built in pulse damper 1300 id inj. gm flex fuel sensor r35 coils stock cam angle sensor link can lambda link 3 port boost solenoid internal map sensor Iacv and everything under the plenum has been removed Wallewein UMS Dyno 2.pclr Quote Link to comment Share on other sites More sharing options...
Vaughan Posted April 22 Report Share Posted April 22 can you attach a PCLog of an attempted start and a Trigger scope taken while cranking please. Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 22 Author Report Share Posted April 22 i cant at the moment its too late and my kid is asleep. i tried to catch a log earlier of it cranking but while i crank it seems to stop any activity on my laptop... like the ecu disconnects while cranking or something... should i start a log, crank it, stop the log, save and send? im afraid ill be sending an empty log also when i bring up the trigger scope screen and start cranking then press start on the scope it says there isnt any connection to my ecu Quote Link to comment Share on other sites More sharing options...
Vaughan Posted April 22 Report Share Posted April 22 If the ECU disconnects while cranking then start checking what happens to the voltages to the ECU while cranking. For the gtr plugin the ignition switch signal comes in on pin 45 which when powered grounds pin 16 which triggers the ECCS relay which supplies power to the ECU through pin 49. The ECU Power grounds are on pins 10, 20, 107, 108 & 116. Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 22 Author Report Share Posted April 22 so check 45 for power while cranking? if it drops low whats the next step? godzillamf had a similar problem a few years ago, should i try grounding pin 16? Quote Link to comment Share on other sites More sharing options...
Vaughan Posted April 22 Report Share Posted April 22 Pin 49 is the ECU power, pin 45 is just part of a circuit that turns on the ECCS relay so start with pin 49 power with your ground probe on one of the ECU power grounds. Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 22 Author Report Share Posted April 22 the car needs to be cranking to test this im assuming? or just the on position? Quote Link to comment Share on other sites More sharing options...
Vaughan Posted April 22 Report Share Posted April 22 cranking, coils and injectors can most likely be unplugged. you are trying to see why the ECU disconnects when you crank and so you need to see if there is a massive voltage drop on cranking that would turn the ECU off. Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 22 Author Report Share Posted April 22 okay sounds good, ill have to do this tomorrow afternoon ill report back. thank you! Vaughan 1 Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 22 Author Report Share Posted April 22 Hey Vaughn are you available in about 1.5 hours? Gonna head out to the garage when the baby wakes up Quote Link to comment Share on other sites More sharing options...
Vaughan Posted April 22 Report Share Posted April 22 I am around yes Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 23 Author Report Share Posted April 23 Hey Vaughn, the wifey got a flat tonight I'll have to get with you tomorrow if you're available. Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 23 Author Report Share Posted April 23 Hey Vaughn this is what I came up with 49 grounded to frame key on is 13v then drops to 9.48 while cranking 49 to 10 cranking is 8.75 49 to 20 8.87 49 to 107 8.72 49 to 108 8.68 49 to 116 8.63 Quote Link to comment Share on other sites More sharing options...
Vaughan Posted April 23 Report Share Posted April 23 Voltages don't seem low enough to turn the ECU off but it definitely sounds like you have an ECU grounding issue if the ECU earths are 1v higher than the chassis. Can you also see if the blue lights on the ECU PCB turn off when cranking? Also if that was done with coils and injectors unplugged then it may be even worse with those connected Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 23 Author Report Share Posted April 23 so sorta strange... the car starts now... ill attach everything i collected the car is just idling on my lift with a few revs. i also grounded pin 16 and got 1 log of it cranking then that didnt work anymore for some reason, but the car runs both with with pin 16 grounded and not grounded. the ecu also looses connection both ways too, ill tripple check that in like 30 min to confirm. also with pin 16 grounded when i turn the car off the ecu starys on im assuming this is normal if pin 16 in grounded? Trigger Scope Log 2024-04-23 1;58;17 pm crank no start.llg Trigger Scope Log 2024-04-23 2;15;45 pm 2.llg random start.llg running 2.llg running.llg Quote Link to comment Share on other sites More sharing options...
Vaughan Posted April 23 Report Share Posted April 23 Grounding Pin 16 will power the ECU and engine loom, if the ECU powers up and runs with pin 16 not connected to anything that would suggest a backfeed issue, can you confirm whether your pin 16 not being grounded test was with the pin removed from the header or the pin left in the header? Have you altered any of the factory wiring or added any extra wiring to the ECU like adding a boost solenoid etc? Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 24 Author Report Share Posted April 24 Pin 16 was left in the header I used a piece of welding wire to poke through the back of the header and touch the terminal, from there I ran a jumper from chassis to pin 16, this left the ecu on even when the car was off when I removed the jumper the ecu powered down. The harness has had unused connectors removed i.e. no power steering, no abs, no ac, no heater No wipers, no defrost it's bare bones essentially. The car was just on a rotisserie for the past year too.. can you see much from the logs? Or scope? Quote Link to comment Share on other sites More sharing options...
Vaughan Posted April 24 Report Share Posted April 24 logs and scope won't show me anything, if you left the wire in then ECU still running after removing your ground pin will be because the ignition switch input would have been active pulling that pin to ground. In terms of ground issues make sure that the ECU power grounds on the engine are securely bolted to an unpainted surface Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 24 Author Report Share Posted April 24 so from the header should i run each ground to its own location or can i use a batt neg. stud i have on the firewall? Quote Link to comment Share on other sites More sharing options...
Vaughan Posted April 24 Report Share Posted April 24 All ECU power grounds should go to the same location on the engine, usually on RBs that's at the front of the intake manifold. greddy32 1 Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 24 Author Report Share Posted April 24 okay thank you Quote Link to comment Share on other sites More sharing options...
Adamw Posted April 24 Report Share Posted April 24 I would also check voltage on pin 45 during cranking, if this drops below about 7.5V the ECCS relay can drop out. Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 24 Author Report Share Posted April 24 Hey Adam, my g4+ is from 2019 do you think that it's possible my mosfet is bad? I was reading a thread between you or Simon and godzillamf, he seemed to be having the same issue that he solved by running a relay to pin 16. Quote Link to comment Share on other sites More sharing options...
Adamw Posted April 24 Report Share Posted April 24 It sounds like your ECU is powering up ok initially but dropping out when cranking. This suggests the FET is ok. What is the voltage on pin 45 when cranking? Quote Link to comment Share on other sites More sharing options...
greddy32 Posted April 25 Author Report Share Posted April 25 It doesn't show any voltage on 45 while cranking or ever for that matter. 1 lead on 49 the other on 45 while testing Quote Link to comment Share on other sites More sharing options...
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