Technical difficulties, erratic and inconsistent behavior

DDA

Hey guys! Thanks for going over this post! I went over a large part of the forum, but wasn't able to find anything helpful. Hopefully someone can help me out, or point me to a post I overlooked, because I went to two garages already and they don't seem to find the cause of the following problem(s).

I'm frequently having one or a combination of ALL of the following abnormalities with my car:

- Rough idle, rpm's go lower every ten seconds or so, sometimes to the extent that the engine is stalling; restarting the car doesn't improve it, stalls five times in a row in less than a few minutes. Is often accompanied by some rattling noise, but that might be normal. It's only after some random driving or a night in the garage that the idling improves, only to turn up again at random.
- Power loss or gain at specific and non specific moments. A reoccurring moment when I have a very noticeable loss would be at the exact moment when the engine coolant light reaches its "ideal operating temperature" position, one led left of middle. Happens every time, specially after a cold start. It's a little less noticeable when the engine's still partially at operating temperature and then reaches the ideal position.
- Inconsistent gas pedal reaction. Example one, linked to previously mentioned problem, I hold my foot FIXED on the gas pedal, driving 90kph continuously, while suddenly the car slows down by 1-2kph. Will happen only once per trip. Later on the opposite might happen. Or example two, I slowly take off in first gear, very gentle, and the moment my rpm's are around 2k suddenly the acceleration starts to go exponentially faster, as if I was pushing the pedal 3/4 in, yet I'm not!
- Brute and jolted re-acceleration, often after taking a turn (ESP light even blinks because of it being so harsh), but also on a straight street, for example when catching up with the car in front of you. Feels like engine is responding couple of milliseconds too late, then tries to catch up in panic.
- When in diagnostics mode (after pedal dance), with the engine running, the engine failure light blinks irregularly. More frequent at idle and when revving slowly, less or even not when revving fast, and never when rpm's go down. Combustion problem? No errors show up on connected laptop from garage though!
- Acceleration feels flooded/limited for a minute or so. Happens suddenly, temporary, briefly, like engine is getting wrong mixture of air/fuel.
- Engine refuses to pass 3500 rpm, no warning, no engine light (dangerous when overtaking!), could it be a factory programmed safety reaction in response to some out of gauge values?
- After resetting engine ecu via pedal dance, it takes on average two to three days until engine failure light comes on permanently, error codes 0420 and 0430 catalyst, plus error code oil pressure low have been found stored in memory. Garage says these two things have nothing to do with each other and rarely a catalyst is faulty; they say they looked into the composition of the exhaust gasses and all seemed normal so I didn't have any of the catalytic convertors changed yet. However, car not constantly giving problems, so maybe they checked exhaust gasses at the moment when things were operating normal.
- During these two to three days, the car has moments where it drives PERFECTLY, with not one of the aforementioned problems. I think ecu is trying different modes or calibrating, but doesn't seem to get it right or stick to the right one. If a part is broken or a hose has a tear or whatever, car would NEVER drive normal, right?
- Next it usually takes another two to three days before car limits revs to 2.5k, factory safe mode, forcing me to shift super early. At first I visited the garage to get a reset, but fortunately I learned there's a way to do it myself. Have been resetting my car weekly for over two months now, to no avail :-/
- when decelerating while in gear, I can hear thumping sounds coming from below my car, coming from the exhaust.

I think that about describes all of the problems, all probably linked to one and the same issue. But which?! To give you guys all the information, I should add that I have a unique 370z, not because it's a 40th anniversary, but rather because I installed a liquified gas installation in it. It's a common thing to do in Belgium, price of LPG only one third of regular fuel. I did this in all five of my previous cars (including SLK and 350z) and although I must admit that while the engines obviously don't run better on it compared to what they were designed for, I never had any serious problems with the newer systems with direct injection that have been available for the past 10 years or so. They run the original ecu's software I'm told and hence should perform just as well. Of course, first thing Nissan dealer tells me, it's that system what's causing the problem... While LPG install guy says his system is working just fine... I personally tend to believe him, because when driving on 98 fuel all of these problems still persist!

If I didn't know any better, I would say there's probably a virus in the ECU software, but I never heard about such a thing, so highly unlikely. Next guess would be a faulty EGR-valve, but I'm not even sure the 370z has one! I have a few short video clips on my phone, one from the erratic idle and one from the irregular engine light blinking, but I think I described these problems to such an extent that it's not really necessary to upload them.

Looking forward to any and all reactions!

Thanks in advance

DDA

Shawa

idk man, kinda sounds like you answered your own question. if the car had rough idle, and sudden power loss or weak acc. and isn't revving as smooth it's probably the mod you did. good luck with it, I haven't seen any other forum members with that type of install or at least haven't heard anything.

SouthArk370Z

I suspect an Air/Fuel Ratio problem. You should be able to check using the O2 sensors and an OBD/CAN monitor *to log O2s while driving.
You have a lot less energy/volume with LPG than you do with gasoline which means you will have less power. But, when properly adjusted, it should run and rev up smoothly (if not quite as fast as with gasoline).

*edit

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Infiniti370z

FYI, 370z has no egr valve, egr is done with valve overlap by ecu.

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Infiniti370z

Did you install a open loop or closed loop system? Also if you had any air/fuel ratio problems at any time due to the LPG kit you installed it could have over fuelled the cat and burnt it out causing it to melt and fall apart clogging the exhaust system, the pieces can jump around and make clunk noises while clogging and unclogging. Need to check a/f sensor readings.

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DEpointfive0

Sell the fuckin thing and move on

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DEpointfive0

LOL, LPG... Should slow the car down a LOT. And the car isn't direct injected.

Also, do you never change your oil? I ask because LPG cars don't dirty up oil.
Can we see pics of the setup?

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Infiniti370z

Lol yep ^^, also I don't think it lubricates the cylinder walls and causes ring wear so I've read...

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Jordo!

Gasoline Stoichiometric air-to-fuel ratio = 14.7 : 1

Propane (LPG) Stoichiometric air-to-fuel ratio = 15.67 : 1

ECU is tuned for Gasoline, so you are running verrrrry rich, and the ECU cannot compensate.

Assuming the LPG isn't killing the sensors (and the cats, or the injectors, or the pump), you need the car to be retuned for the fuel you are using.

Also, your spark plugs are probably pretty badly fouled... good luck.

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juld0zer

combustion temps of LPG are higher than that of petrol isnt it? that could've led to a melted catalyst. you'd need to remove them and inspect but these cats hold up ok with forced induction so i dont think LPG wouldve burnt them out.

plugs should be chosen to suit LPG too, to avoid misfire and preignition issues.

i'm speculating a fuel supply problem. some of the aussie cop cars that ran on LPG were known to backfire or stall, esp under heavy acceleration or when the engine was cold.
but you say the problem persists with petrol too? after you fill up with petrol, have you tried resetting the ecu (battery or pedal dance method), resetting the learnt mixture settings (disconnect a maf sensor with engine running to trigger a fault then clear it) and also driving a few tanks of petrol so it readjusts?

there are some faults you mentioned which rings a bell. have a browse around the forums here and you might find some leads

1slow370

Lpg uses high pressure injectors so i have no idea how you are using standard gas injectors and holding them closed. I know there are conversions on direct injection engines but running vaporized lpg through a 100 psi injector shouldnt work. Is there an evaporator/regulator on your kit?

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Spooler

Take the LPG system off the car and start from there. The stumbling and idle issues sounds like dirty throttle bodies. The codes are more than likely due to burnt out cats. Hope you have changed the oil at regular mileage intervals. These engines are hard on oil as it is. Ton's of threads about this on here. Most have lead to engine troubles due to blow bye.