- This topic has 32 replies, 4 voices, and was last updated 12 years, 7 months ago by
.
-
Topic
-
I just registered to the forum, and I’d like to start by asking for some help 🙂
I have a Nissan Primera (also known as Infiniti G20). Originally it had a standard SR20DE but I’ve done couple of mods to it, Neo VVL head swap, high performance 4-2-1 extractor, Fujitsubo High flow exhaust and a JWT Pop charger.
Bellow are some pictures of the head swap process, which my mechanic did.
My issue is that acceleration acts weird, specially when cold. Just pushing gently on the gas pedal it starts accelerating and then it decelerates (no matter if I push it further down).
The problem is reduced when the engine gains temperature (harder to notice), and it only seems to disappears when going WOT.
I’ve looked for vacuum issues but found nothing. I’m thinking it may be a problem with my injectors being dirty or not mounted correctly, but that’s just guessing on my part (I’m a car newbie).
Any ideas on what
-
Replies
-
First welcome to the ETCG forums.
I about crapped myself when I saw the ‘hand grinding’ of the pistons. You do realize that those have a specific weight and the methods shown can cause that weight to be off thus creating an ‘unbalanced’ engine right out of the box. An unbalanced engine can cause all kinds of problems, ALL cylinders need to produce equal power and have the same reciprocating mass in order for an engine to run smoothly.
Quoted From EricTheCarGuy:
First welcome to the ETCG forums.
I about crapped myself when I saw the ‘hand grinding’ of the pistons. You do realize that those have a specific weight and the methods shown can cause that weight to be off thus creating an ‘unbalanced’ engine right out of the box. An unbalanced engine can cause all kinds of problems, ALL cylinders need to produce equal power and have the same reciprocating mass in order for an engine to run smoothly.
ouch! didn’t know that was such a sensitive matter.. the problem is that you can’t find any replacement SR20VE pistons here in Chile 🙁 (importing would mean 600-700 USD just for the pistons..)
So what are the symptoms of an unbalanced engine? Is there any way to diagnose it? (we measured compression and it was close to 180 PSI for all 4 pistons) I mean the acceleration is the only issue it has, idle is good and no vibration in the whole rpm range 1000-7000 BTW.
Letting the piston disaster aside, what else could be the problem? faulty sensor?
Thanks for the quick response, I’ve learned a lot from your videos!! Hopefully other members can help me too 🙂
Is the check engine light on?
With all the mods, do you have the right amount of flow from the fuel pump?
Its hard to diagnose issues with vehicles with these types of mods. I usual stay away from them.
Quoted From dreamer2355:
Is the check engine light on?
With all the mods, do you have the right amount of flow from the fuel pump?
Its hard to diagnose issues with vehicles with these types of mods. I usual stay away from them.
no check engine light on or any warning light whatsoever.
About the fuel, I would say highly unlikely given that the problem almost disappears when temperature raises and gone when going over 4.000 at full throttle (no performance issues there).
Lastly, what specific mods are you talking about? and why would it be difficult to diagnose?
Thanks for your response!
Anything thats aftermarket and has a problem, its usually difficult to use the OEM flow charts of diagnostics for some situations.
If there is no check engine light, then the PCM does not think there is an issue. I would still do a fuel pressure test to see if your within specs, as well as stress testing the ignition system to see if its ignition related.
Do you have a scan tool that shows live data so you can view the fuel trims and ECT readings? Any signs of vacuum leaks? If the engine correctly in time?
Quoted From dreamer2355:
Anything thats aftermarket and has a problem, its usually difficult to use the OEM flow charts of diagnostics for some situations.
If there is no check engine light, then the PCM does not think there is an issue. I would still do a fuel pressure test to see if your within specs, as well as stress testing the ignition system to see if its ignition related.
Do you have a scan tool that shows live data so you can view the fuel trims and ECT readings? Any signs of vacuum leaks? If the engine correctly in time?
I don’t have a scan tool myself but I can get one. About vacuum leaks, I checked and found nothing.
I’ll try your other suggestions, thanks!
The way to determine if the piston weight is throwing things off is to weigh them with a VERY accurate scale to make sure they are the same. Without a check engine light and setting aside the possible piston issue as suggested a vacuum leak is a good possibility but I often find that vibrations or missing under load is caused by the ignition system. Here are some videos on checking for vacuum leaks as well as one on checking for voltage leaks.
Vacuum leaks
http://www.youtube.com/watch?v=9CPqbaSgcok
Voltage leaks
Quoted From EricTheCarGuy:
The way to determine if the piston weight is throwing things off is to weigh them with a VERY accurate scale to make sure they are the same. Without a check engine light and setting aside the possible piston issue as suggested a vacuum leak is a good possibility but I often find that vibrations or missing under load is caused by the ignition system. Here are some videos on checking for vacuum leaks as well as one on checking for voltage leaks.
Vacuum leaks
http://www.youtube.com/watch?v=9CPqbaSgcok
Voltage leaks
Well, to measure piston weight we would have to unmount the whole engine, open it, replace gaskets right? probably not going to do it right now as it’s a huge effort (for me at least). I’ll surely do it (me and my mechanic) if I get SR16VE N1 cams, as it will rev higher and that probably means that weight difference is going to matter even more.
BTW, I had already seen both videos 🙂 great material!
I’m taking the car on Monday for a battery of tests, adding the ones you have suggested and maybe redo vacuum test just to double check.
PS: can you recommend any book that I could use to start on?
Quoted From dreamer2355:
The best way to find vacuum leaks is with a smoke machine C8-)
I think I saw somewhere on youtube a guy that did the test with a cigar, it was pretty hilarious haha
It has been a while! happy new year!!! 😀
After trying many things I have a new theory. I’ll start with the symptoms.
Symptoms
Apart from my hesitation I have issues with my fuel line (the one that goes from the filter to the fuel rail), it keeps loosing or braking..
One day I started feeling a huge gas smell while driving I found that the fuel hose was massively leaking (it was broken).
I replaced it and though I just had a faulty hose. Some days later I felt a gas smell again, this time no broken hose, it just got loose and was leaking through the end of it (I thought, maybe I didn’t tighten the hose clamp enough). So I went ahead and tighten it.
After a few days the smell came back again, the hose was leaking again.
Theory
And this is were I began to think that my hesitation issue could be related to fuel pressure. Why? because if pressure is going up and down causing my acceleration to stall and go up again that could translate into some kind of pulling of that fuel hose leading to the issues mentioned above.
I don’t have any startup issues, performance and fuel consumption seems good. I don’t know where else to look for…
Would a fuel pressure regulator fix my problem (assuming that my theory is right)?
Absolutely, if you’re loosing fuel pressure it WILL effect engine performance so fix that first and then recheck for the symptom. Fuel pressure needs to be exact and constant for a fuel injected engine to run correctly, if not it will starve the engine.
OK, I installed a fuel pressure regulator, it alleviated the issue but it’s still there :/ maybe my fuel pump is failing?
I’m getting a wideband to see that kind of A/F ratio I’m getting.
Thanks for helping!!
Using a fuel pressure gage and checking for specifications KOEO and KOER will be good evidence of a fault fuel pump.
I would also advice doing an injector leak down test also.
The last fuel pump i serviced that was at fault, i used a lab scope to check the wave forums and current leaving the pump.
- You must be logged in to reply to this topic.