Rev bouncing/surging around 4200rpm - NB8a
Posted: Wed Sep 23, 2015 10:50 pm
Hey guys,
Not sure where to post this really; I have no idea where the problem is so I'll just post it here.
Feel free to skim through the underlined parts if you don't want to read a great wall of text
First up- the car has 7000km old spark plugs and rocker-cover gasket, along with fuel filter, air filter, oil filter and oil.
It also has more aggressive cams, slightly advanced timing (neither of which has caused no problems for many tens of thousands of kilometers) and a brand new alternator (immediately after which the problem began to get worse.)
Before the alternator the car would surge down and stall occasionally at idle, especially while braking at a red light, at low speed, in the last 30m when I would slip into neutral after shedding 90% of my speed. It would also skip a little, with a short little rev drop at about 5800-6200, like a cylinder missing, which I first noticed while I was thrasher her a little at Sandown.
I adjusted my idle using the screw on the side of the air intake where the rubber meets the manifold, up to about 1050-1100 to stop the surge from stalling the car. I had it like this for for about 3 weeks till the battery died (turned out to actually be the alternator). After I got the alternator replaced the problems started. The mechanic said that the idle screw I had adjusted shouldn't be messed with, and the mechanic 'reset' something, but didn't specify what, and it wasn't just the idle screw by the look of it. After this the car began to do the surging thing at 4200rpm, almost as if my rev limiter were set at 4200.
A few times the car has "stalled", mostly at 4500rpm-ish when I go onto a freeway. Despite the engine still rolling at 95-100kmph in 5th or 4th gear, the revs say zero and I cannot in any manner accelerate. It basically acts as if the car is turned off. This always follows a "rev bounce session". I will add that the rev limit of 4200 doesn't happen ALL the time, only 80% of the time, particularly at higher speeds. It should also be noted that this number shifts to about 30% of the time if I rev the car in neutral and parked.
When I got the alternator changed the mechanic mentioned that my little engine miss every now and then at over 6400rpm, along with my surge-y idle was probably caused by an "electronics or ECU problem" and that I should bring it in for them to check up for me. I may be seriously paranoid and totally wrong, but it almost feels like he tweaked something to play up so he could charge me for an expensive ECU replacement or something, and not really need to replace anything, just untweak it. It just doesn't make sense that I would change my alternator over, and fix the idle issue while causing the redline to shift to 4200rpm.
If anyone has had this before I would seriously appreciate knowing what ended up causing the issue.
Not sure where to post this really; I have no idea where the problem is so I'll just post it here.
Feel free to skim through the underlined parts if you don't want to read a great wall of text
First up- the car has 7000km old spark plugs and rocker-cover gasket, along with fuel filter, air filter, oil filter and oil.
It also has more aggressive cams, slightly advanced timing (neither of which has caused no problems for many tens of thousands of kilometers) and a brand new alternator (immediately after which the problem began to get worse.)
Before the alternator the car would surge down and stall occasionally at idle, especially while braking at a red light, at low speed, in the last 30m when I would slip into neutral after shedding 90% of my speed. It would also skip a little, with a short little rev drop at about 5800-6200, like a cylinder missing, which I first noticed while I was thrasher her a little at Sandown.
I adjusted my idle using the screw on the side of the air intake where the rubber meets the manifold, up to about 1050-1100 to stop the surge from stalling the car. I had it like this for for about 3 weeks till the battery died (turned out to actually be the alternator). After I got the alternator replaced the problems started. The mechanic said that the idle screw I had adjusted shouldn't be messed with, and the mechanic 'reset' something, but didn't specify what, and it wasn't just the idle screw by the look of it. After this the car began to do the surging thing at 4200rpm, almost as if my rev limiter were set at 4200.
A few times the car has "stalled", mostly at 4500rpm-ish when I go onto a freeway. Despite the engine still rolling at 95-100kmph in 5th or 4th gear, the revs say zero and I cannot in any manner accelerate. It basically acts as if the car is turned off. This always follows a "rev bounce session". I will add that the rev limit of 4200 doesn't happen ALL the time, only 80% of the time, particularly at higher speeds. It should also be noted that this number shifts to about 30% of the time if I rev the car in neutral and parked.
When I got the alternator changed the mechanic mentioned that my little engine miss every now and then at over 6400rpm, along with my surge-y idle was probably caused by an "electronics or ECU problem" and that I should bring it in for them to check up for me. I may be seriously paranoid and totally wrong, but it almost feels like he tweaked something to play up so he could charge me for an expensive ECU replacement or something, and not really need to replace anything, just untweak it. It just doesn't make sense that I would change my alternator over, and fix the idle issue while causing the redline to shift to 4200rpm.
If anyone has had this before I would seriously appreciate knowing what ended up causing the issue.