R34 GTT RB rough idle problem with weird RPM gauge fluctuations

[Joni Boi]

Thanks everyone for the replies/suggestions on my issue here. I'm still trying to diagnose the root cause of this.

Things I have done so far:

A week ago, I disconnected my 12v constant relay mod and returned it to the stock FPCM wiring: I could hear the sound of the fuel priming was different because of the FPCM limiting the amount of volts going to the fuel pump. From memory I think it also primed to 43psi. It was very hard to start it. I don't think from memory I could start it at all. I had to then ground the fuel pump to the chassie and then it could start after a couple of cranks. Fuel pressure did drop a bit to about 45psi (i think). It was idling even worse than before. 🤔 It was also doing the same weird RPM tacho thing. So I've returned it back to the constant 12v relay mod for now as I investigate more.

Right now, I'm in the process of deleting my aftermarket immobilizer, an old Japanese turbo timer, and another aftermarket transponder immobilizer that the previous owners put in years ago (from sexspec days). 

Just curious to see if this whole bird nest would cause some weird electrical problems. The Viper 5900 immobilizer stopped working a few years ago, and I pulled out the main fuse on it years ago to stop it from being a parasitic battery drain and I haven't bothered to clean up the mess there, so now is a good time to. There was a RPM signal wire that spliced into the RPM tacho signal from the ECU harness. I've taken it out.

I've already pulled out the Viper immobilizer and returned all the joints wires/splices back to factory. I let the car idle and it's still the same idle and RPM tacho idle issue.

Now I'm going to delete the turbo timer and the other key transponder immobilizer (autowatch) and return splicing/wiring back to factory setup. Just to see if this might be causing some electrical issues. It might not, but I just want to get rid of it anyway.

On 16/10/2024 at 6:26 PM, luke gtr said:

TL;DR

Not sure if checked, but confirm no blockage in the vac/boost reference line to the ecu. 

Have had rich and fluctuating idle from a blocked line and ecu could read that it was under vacuum(no MAF).

True!, I was actually thinking this the other day. I will check with another new vac line to make sure this is not the issue.

 

On 17/10/2024 at 9:48 AM, MBS206 said:

Go get some fresh gas from a totally different servo, jerry rig a fuel pump, and run the new tank supply to the fuel input at the motor.

 

There's every possibility you've got really shit fuel, thats possibly full of water etc.

This is actually on my to-do list, and you might be right, this might be a shit batch of fuel because I filled the tank up to 3/4 full from near empty, then I went to the shops and it happened straight after that. I've always filled up from this servo for years with no problems, but yeah might be my first batch ever batch of shit fuel from them. Will be doing this next when I get my hands on a container/jerry can. I just didn't think to do this straight away because it doesn't really explain why the tacho RPM thing is happening. Maybe I'll chuck some injector cleaner in the new batch too?

[Dose Pipe Sutututu]

Post up your data logs, might help provide insight to what is going on.

[Joni Boi]

Update on this situation:

(Forgot to put in my previous post that I bought another brand new pressure gauge and fuel shows the same 50psi)

I've deleted all the aftermarket immobilizers and turbo timer shyt and placed all factory wiring back to normal. The problem is still the same and nothing changed, but atleast it's a bit more tidier under the steering wheel.

I've also siphoned out all the old fuel and then poured new batch of BP98 fuel (about 15L) into the tank. Nothing changed. Still the same idle. I also changed out the MAP vac line with a new one and, still the same. 

So 2 days ago, I thought fk it. I'll just change out the fuel rail and injectors with another set that I know worked well in my brother's R34 a while back. That other fuel rail has the exact same Xspurt 640cc as what I have right now. So I changed it out to that other fuel rail and injectors (new O-rings) and injector harness. Put everything back together, started the engine,

 

and yeah... still the same 50psi and idle problem. 🫠

I can also hear each of injector's solenoids running when I put a screw driver to it and have the other end to my ear. I might get a noid light just to confirm pulsasion but yeah, very strange that both fuel rails and injectors put out 50psi. 

On 23/10/2024 at 7:56 AM, Dose Pipe Sutututu said:

Post up your data logs, might help provide insight to what is going on.

31-10-2024.csv

I've attached it here. I started recording, then started the engine and let it idle with no throttle, then at the end I applied a little throttle and then stopped recording. 

 

So, now idk. I'm going to see if swapping out the brand new R35 coils to my old splits fires will change anything.

🤷‍♂️

Edited November 1, 2024 by Joni Boi

[Dose Pipe Sutututu]

Data looks rock solid?

I'm assuming you jabbed the throttle twice OR once? the TPS voltage moves up and down twice, however you've mentioned you did it once.

[Joni Boi]

11 minutes ago, Dose Pipe Sutututu said:

Data looks rock solid?

I'm assuming you jabbed the throttle twice OR once? the TPS voltage moves up and down twice, however you've mentioned you did it once.

Yeah I think i did jab it twice.

[Dose Pipe Sutututu]

1 hour ago, Joni Boi said:

Yeah I think i did jab it twice.

From a data perspective, nothing really is out of the ordinary 

[Dose Pipe Sutututu]

On 09/10/2024 at 2:45 PM, Joni Boi said:

Checked TPS sensor on haltech and it reads correcly. 0.45v no throttle and 4v WOT.

Did you calibrate the throttle in the Haltech?

It might be falling in and out of the closed loop strategy, especially if the car has been tuned on different TPS voltages.

[Joni Boi]

2 hours ago, Dose Pipe Sutututu said:

Did you calibrate the throttle in the Haltech?

It might be falling in and out of the closed loop strategy, especially if the car has been tuned on different TPS voltages.

Yeah, after my first post i did notice that my tps wasn't calibrated exactly to the tee. So I did calibrate it:

applied the settings, rebooted ecu and it's still the same.

[Dose Pipe Sutututu]

Can you pull logs of the actual idle fluctuations?

The previous logs you posted didn't show any idle issues.

Also if you can log idle duty cycle, idle state, injector duty cycle 

[tylink720]

Any chance the zero demand ignition table is messed up? Or possibly the minimum tps for it to engage zero demand?

[Kinkstaah]

Yea - From what I have seen from the video, the car idles like any R34 lol

50PSI of fuel pressure is hardly super abnormal, the regulator is working because the pressure remains static when the throttle gets revved, i.e pressure remains the same when manifold vaccuum changes.

Bigger pumps on stock rails always bumped the pressure in the rail without using an aftermarket regulator to change that.
Do you know what your IAC is actually doing? Has there been any data showing the stepper motor % etc?

There's no way your idle is actually moving around the way the cluster(s) are indicating. You would hear the difference with the engine RPM flying to 3k and 1k in mere seconds.

I'd be checking the wiring to the tacho. What the tacho is telling you and what the engine/ecu is telling you are different things. I assume your ECU doesn't display the spike. So whatever is telling the tacho to be at X rpm is doing something weird.

When the going gets insane, you're on the wrong path. You've ruled out plenty of things that are working correctly/aren't the issue.

Your idle isn't doing what the tacho is indicating. You have two seperate issues, I don't think they are linked, and the idle seems reasonably okay unless it's stalling which.. well, it hasn't. Troubleshoot the stall if it occurs by figuring out what your IAC is doing vs what it is being told to do.

[tsuokun]

Throwing my spoon to the soup here a bit. 

When I installed a 044 back in 2012, along with the direct power mod, the car became very difficult to start. To a point I burned one starter motor as I was late for work and tried to get the thing going. With some tuning and careful use of gas pedal when cranking it became bearable.

Trying to make this short as possible, but the 044 died after 2-3 years, after which I went with an AEM 320lph pump, which also died after about 4 years to my dismay. After that I went with a Nismo pump, and while trying diagnose an emissions problem, I noticed for the first time that my fuel pressure was 5bar/72psi on idle, and that removing the vacuum line did nothing.

After monitoring the situation, and removing the direct power feed and going back to FPCM in attempts to remedy it, I noticed there was fuel in the pressure regulator vac line. Kept the FPCM, installed AEM external regu and the car became sooo much better in every way, including starting. And I had driven it like it was for 11 years..

Anyway, I agree these are likely two different problems, and the FP problem you just haven't noticed before. I do not know much about haltecs, but what first came to mind was the CAS, which probably is not there any more. So how is the wiring from haltec to gauge cluster? How is the battery voltage and alternator?

Edited January 7 by tsuokun

[Joni Boi]

Bit of a late reply here as me and my wife have been really busy with new born twins.

I finally got these issues fixed and it was something really stupid that caused all of this 🤦‍♂️...

After alot of mucking around with trying to figure out what is causing these issues, I back probed one of the R35 coils on the power 12v supply, with the engine running it got 25v! And I thought, hang on..., this isn't normal. Measured my battery with the engine running to check for over charge from the alternator and it wasn't that. So then I dissconnected the R35 PRP coil harness and backprobed the power supply on the engine loom where the ignition coil harness connects, with the key on ignition (engine off) it measured 30v! So then I had to trace where that high voltage was coming from and it lead me to the brown relay "ECM & IGN coil relay" inside the cabin next to the ECU on the passanger wall. This relay feeds power to the ECM and ignition coils. Tried swapping it with another same relay. nah still 30v.. coming from the 2 green/white wires in the brown relay. So then I set my multi meter to the beep continuity mode and probed every fuse on the fuse box inside the cabin to try and find this high voltage power source. Wasn't any of the fuses inside the cabin. Then probed all the fuses in the engine bay and BAM, got my power source that was a 10AMP fuse called "ENG CONT".

Pulled the fuse out, and what do you know... it was blown. 🤦‍♂️ 

So then I quickly replaced it with a new 10AMP fuse, started the car and yeah haha [insert extreme face palm]... The RPM blimping thing went away, car idles smoothly now like what it was before.

I swear! I checked all my fuses with my test light twice before I created this forum thread. I think, maybe because one side of that faulty 10A fuse lit up on my test light, I must have thought it was still ok and not blown. But now I know to have both sides light up on the test light when checking fuses...

I hate diagnosing electricals.... I'd take mechanical problems over electrical problems any day🤣.

Drove the car around my suburb with the engine up to operating temp and it runs fine like before.

However, I notice that my fuel pressure is still at 49psi. So I'm thinking this must be normal for my system as I've upgraded the stock fuel pump to a Walbro 255L/h with a constant 12v mod. 

But anyway, I'm just glad to have my daily back on the road! Thanks everyone for the replies on this thread, all sorted now!

One thing I want to ask you tuner guys, my base fuel pressure on the haltech main settings are set to 43.5psi from default (my tuner must have not checked the fuel pressure maybe when tuning my car?). Do I set it to what it actually is idling on at 49psi? Or just leave it ("if it aint broke, don't fix it/leave it")?

 

[GTSBoy]

3 minutes ago, Joni Boi said:

I finally got these issues fixed and it was something really stupid that caused all of this 🤦‍♂️...

This is typically the case with such threads.

What I cannot quite get my head around is where a reading above 12V (or 13.8 or 14.x or whatever the maximum achievable voltage might actually be in that specific car) comes from. 25V or 30V should be completely impossible. There's no way to create it.

5 minutes ago, Joni Boi said:

One thing I want to ask you tuner guys, my base fuel pressure on the haltech main settings are set to 43.5psi from default (my tuner must have not checked the fuel pressure maybe when tuning my car?). Do I set it to what it actually is idling on at 49psi? Or just leave it ("if it aint broke, don't fix it/leave it")?

Hard to answer that question. It will literally depend on whether the current tune relies on the values as set. I'd guess it probably does. ie, the real base pressure being 49 means that the flowrate through the injectors will be higher than if it was 43.5. The Haltech's modelling should be handling that, but because it thinks the pressure is only 43.5, then..... I dunno. It should be thinking that it will be injecting less fuel with each pulse duration than is actually happening. So, something is definitely not-as-it-should-be, but specifically what that is is beyond my abilities to imagine. Someone like Dose who spends more time with Haltechs might have a better thought.

[MBS206]

12 minutes ago, GTSBoy said:

This is typically the case with such threads.

What I cannot quite get my head around is where a reading above 12V (or 13.8 or 14.x or whatever the maximum achievable voltage might actually be in that specific car) comes from. 25V or 30V should be completely impossible. There's no way to create it.

Hard to answer that question. It will literally depend on whether the current tune relies on the values as set. I'd guess it probably does. ie, the real base pressure being 49 means that the flowrate through the injectors will be higher than if it was 43.5. The Haltech's modelling should be handling that, but because it thinks the pressure is only 43.5, then..... I dunno. It should be thinking that it will be injecting less fuel with each pulse duration than is actually happening. So, something is definitely not-as-it-should-be, but specifically what that is is beyond my abilities to imagine. Someone like Dose who spends more time with Haltechs might have a better thought.

Add to this... What blew the fuse too?

If a circuit feeding power to the coils was blown, how were the coils even functioning to let the car start?

 

There is some seriously wrong wiring in that car for certain, and I'm betting there is some melted cables somewhere, but I can't explain the 30v either, unless there is something back feeding on that power line that has a dodgy power system and the electronics are giving it hell.

[Duncan]

Really good point about checking fuses - a test light is not reliable because you might get the voltage from the wrong side of the fuse (my guess is some diode has failed somewhere). You need to check both test tabs of the fuse for continuity.

With the fuel pressure mis match, I wouldn't touch it. The car was tuned with the incorrect setting so changing it is more likely to cause a problem (lean out in this case). If/when the car is next tuned get it fixed then.

Thanks for the update, it is always good to add to the knowledge base