VG30DETT warm crank issues after injectors swap

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RomChip200
Posts: 393
Joined: Mon May 11, 2009 7:58 pm
Location: FRANCE

VG30DETT warm crank issues after injectors swap

Post by RomChip200 » Fri Oct 08, 2021 2:50 am

BEFORE:
740cc Deatschwerks (370cc redrilled)
E85 for 8 years
Never had crank issues in all engine conditions from very cold (-10°C) to very hot (100°C) 
CRANK_ENRICH 120 120 75 65 50 40 22 12 10 8 8 8 8 8 8 8
AFTER_START_ENRICH 200 200 200 140 125 110 90 70 55 45 35 30 30 30 30 30 (yes, 30 when high temp to counteract evaporation)
CRANK_TIMING 30 30 30 30 28 25 25 25 25 25 25 25 25 25 25 25 (yes 25° !)
K was in the range from 208 to 240 (auto adaptation) depending on ethanol % (from ~62 to ~76%)
Latency 1120us

NOW:
750cc 12 holes
Had to adapt:
_the fuel map a bit
_K is in the range from 184 to 196 at the moment (78% ethanol)_auto-adapt
CRANK_ENRICH deeply decreased (the old values prevented me from starting ...). These injectors throw out more more fuel when cranking compared to the previous ones.I suspect a vaporization issue.
Runs perfectly fine (cruising, WOT, etc ...)
At the moment:
CRANK_ENRICH 60 60 48 34 24 16 10 9 8 8 7 6 6 5 5 5
AFTER_START_ENRICH 160 160 140 115 100 85 70 60 50 40 30 20 10 10 10 10
CRANK_TIMING 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5
I decreased a lot CRANK_TIMING to be in a better condition when cranking
Latency from 850 to 1120us, makes no change in warm cranking

Symptoms:
Cold crank from 10°C to 50°C: no problem (1second starter @10°C, 2seconds @50°C)
Mid warm crank from 30°C to 60°C: no problem (2s starter)
Warm crank @80°C or @90°C (even after having stopped 5mins): no problem
Warm crank from 60°C to 90°C after sitting half an hour ==> does not start. Here, this is hit&miss behaviour. Eventually, on the second attempt, it may start, or pumping the throttle will make it start after a while.


Cold crank phase 1 (perfect): crank pulse OK
image.png
image.png (47.13 KiB) Viewed 89 times

Cold crank phase 2 (perfect): after start OK
image (1).png
image (1).png (47.62 KiB) Viewed 89 times

Warm crank phase 1: crank pulse OK
image (2).png
image (2).png (46.88 KiB) Viewed 89 times


To sum-up, the quick switch to the TP-based fuel map is a nightmare for me, the pulse is so big that it kills the RPM. I don't remember what controls the duration of the use of CRANK_ENRICH table (RPM threshold ? Time based ?), one way would be to use the crank table longer to delay the switch to the fuel map. Hope you got my concerns.
Last edited by RomChip200 on Fri Oct 08, 2021 5:54 am, edited 4 times in total.

RomChip200
Posts: 393
Joined: Mon May 11, 2009 7:58 pm
Location: FRANCE

Re: VG30DETT warm crank issues after injectors swap

Post by RomChip200 » Fri Oct 08, 2021 2:51 am

Warm crank phase 2: switch to TP-based injection map, 5.76ms injector pulse, RPM die !!! unable to start ( 2 attempts)
image (3).png
image (3).png (48.09 KiB) Viewed 88 times

RomChip200
Posts: 393
Joined: Mon May 11, 2009 7:58 pm
Location: FRANCE

Re: VG30DETT warm crank issues after injectors swap

Post by RomChip200 » Fri Oct 08, 2021 5:53 am

RAM2:1432 warmup_counter: rmb 1 ; ...

Starts to count from 0 as soon you kick in the starter.

Matt
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Re: VG30DETT warm crank issues after injectors swap

Post by Matt » Fri Oct 08, 2021 9:20 am

Crank enrich used whilst start key on, but IIRC then it starts adding more fuel the longer the crank time (hence the crank timer used)

After crank, the after start table is used and quickly dissipates (about 5 seconds with a quick decline) whilst at the same time switching to reading the fuel map

See page 6 of the attached documents from GMH for the VL RB30 (better documentation than Nissan) for a general description how the crank tables work. Should be similar for Z32

The issue with after half an hour is strange. Like one of the injectors is leaking into the cylinder making it hard to start? You could put a endo camera into the spark holes to see if that is the case?
Attachments
RB30E description.pdf
(959.17 KiB) Downloaded 12 times

RomChip200
Posts: 393
Joined: Mon May 11, 2009 7:58 pm
Location: FRANCE

Re: VG30DETT warm crank issues after injectors swap

Post by RomChip200 » Sat Oct 09, 2021 1:01 am

Not exactly.

When start key on, the initial crank pulse is used (according to engine temp initial) and then decreased stepwise.
If you start with 12ms and RPM don’t rise, the ECU will decrease it stepwise, 12 10 8 6 …. till a certain point.
When warm and big injectors (my case), I start with 2ms pulse (that is enough to start a warm engine with 750cc injectors) but there’s no room to decrease.
This corresponds to Equation 2 in document.

Probably I meet quickly the conditions (rotational speed) to switch to TP-based fuel map (I’m still in start phase with start key on !). This corresponds to Equation 1 in document.
Then, the injector pulse keeps increasing (related to TP) and this is definitively too rich and this kills my rotational speed.
This is too rich probably because the enrichment value/tables are adequate for 370cc OEM injectors, but not for my bigger injectors.
I’m pretty sure a 370cc redrilled and flowing about 740cc @3bars will not flow the same (quantity and spray pattern) compared to a 750cc from factory, when triggered by the same 4ms pulse (= warm start conditions). This is the source of my problem, when engine is warm.

All what I describe is aligned with the document and the switch from Equation 2 to Equation 1 while cranking (while keeping start key on)

I attached some screenshots below, with successive attempts to start, I focused on the second attempt:
First is crank pulse 2ms (Equation 2)
Second is TP based (Equation 1)
Third is final pulse when RPM dies (too much fuel, engine dies)

No leaky injector, I have a pressure gauge that shows steady pressure and whatever, the fuel pump primes each time the key is put IGN on.
Crank1.png
Crank1.png (143.92 KiB) Viewed 63 times
Crank2.png
Crank2.png (144.55 KiB) Viewed 63 times
Crank3.png
Crank3.png (145.09 KiB) Viewed 63 times
Crank3.png
Crank3.png (145.09 KiB) Viewed 63 times

Matt
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Re: VG30DETT warm crank issues after injectors swap

Post by Matt » Fri Oct 15, 2021 8:59 am

Thanks for the clarification. I've never looked into the ECU code and counters too closely, beyond that document.

We have adjustments for initial crank (by ethanol FP1.0, and now by voltage in FP1.1) but that is as far as I took it. R34 has quite a few different crank tables, to complicate things even further
I’m pretty sure a 370cc redrilled and flowing about 740cc @3bars will not flow the same (quantity and spray pattern) compared to a 750cc
This is the reason why I would go proper 740CC (I ran Nismos on my S14) rather than drilled

This is worth a read
http://injectordynamics.com/articles/dr ... d-dipshits

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