RB25det jerking problem. please help!

[bkos90]

I have a RB25det in my s13 and the car recently started to jerk under acceleration, its drivable only if you keep the boost gauge below 10-vac... The jerking feels like you just kick the accelerator pedal nonstop and the car backfires if you give it half throttle or more(when it goes into boost)
this issue started happening after i changed the water temp sensor to the KA one so that i can read the temp on the cluster.
I have checked for vac leaks all over the place and didnt find any.

[Acecool]

What rpm does it do it. all?

It could be a timing issue. Did you rotate the CAS on the front of your engine when you got it?

[bkos90]

it starts doing after 2k rpm, but if i go really light throttle on it it drives ok with small hiccups...
the CAS was never moved or adjusted, the car ran fine before but started messing up after i changed the water temp sensor to the KA one, im not sure if that has anything to do with it... the car also starts to heat up when it starts jerking.

[Kevin.A]

question: do you have a afr gauge. mine did this(Rb20) until i got the mixture correct. it's very possible that your running very rich.

Kevin A

[bkos90]

I do have one and i start running rich when the jerking starts...
did your rb20 jerk or run too rich?

[bkos90]

Im also not getting a Check engine light... does that mean that the ecu is not throwing any codes? I have the light hooked up and working when you turn the key to ON position it lights up and then after i start the car it goes away...
It also shakes when cold (like its running on 5cyl only)

[Joe]

so. right after you changed your temp sensor all these problems started?

ever think that the temp sensor might be the cause?

[Carl H]

is the maf still connected to the intake track?
sounds like something intake related has seperated some.

[RustspecS13]

You changed the single wire sensor to the KA sensor right, because all it does is send a signal to your gauge in the dash.

The two wire sensor must match the ecu, IE SR to SR KA to KA and RB to RB.

~Alex

[Acecool]

Leak in your intercooler piping could also cause that..

[Kevin.A]

I do have one and i start running rich when the jerking starts...
did your rb20 jerk or run too rich?

I was running a drawthrew maf and an open air blowoff. it was really rich, and it jerked and wiggled and overall misbehaved until i converted to map

[bkos90]

I only changed the one that gives the signal to the dash(1 wire) and i really think that its a leak in the i/c piping because i hear the leak when i accelerate just before it starts to backfire and jerk

[bkos90]

can it be the fpr? im running really rich after all and i still have the stock fpr
im also thinking its the maf sensor... would a bad maf sensor cause the car to run rich?
i cleaned it like 3 times and still nothing

[Kevin.A]

rich is too much fuel, so i doubt it's your FPR is too restrictive.

if your maf is reading too high, then it's very possible it's the cause of the problem.
Also, check for leaks in your IC and IC piping, if your loosing pressure, that could cause you to run rich also

[stevespeed]

One thing to check if you ever had it start happening after you ran out of gas, clean your fuel strainer on the actual fuel pump in the tank, I seriously doubt this is your problem, but it could be low fuel pressure. My car would get one SOLID pull then just start dying down after that into limp mode because of that.

[bkos90]

Alright. last night i found a ic piping leak on a coupler, after that my car doesn't run rich anymore while cruising (10.0 on the wideband) now its more like 14-16 cruising. I also changed the plugs because mine were completely wasted from running so rich. Now i got NGK BKR6E gapped to .28
my idle is too rich though, the wideband reads around 11-13 when the car idles.

I also noticed one trick, if i accelerate the car half throttle it pulls nice with very few hiccups thats in 3rd,4th and 5th gear
but in 1st and 2nd it backfires and jerks, but if i go really light throttle, i can take it to like 7k

Very weird, i have no idea what to do now

[bkos90]

Alright. last night i found a ic piping leak on a coupler, after that my car doesn't run rich anymore while cruising (10.0 on the wideband) now its more like 14-16 cruising. I also changed the plugs because mine were completely wasted from running so rich. Now i got NGK BKR6E gapped to .28
my idle is too rich though, the wideband reads around 11-13 when the car idles.

I also noticed one trick, if i accelerate the car half throttle it pulls nice with very few hiccups thats in 3rd,4th and 5th gear
but in 1st and 2nd it backfires and jerks, but if i go really light throttle, i can take it to like 7k

Very weird, i have no idea what to do now

[Acecool]

Told you leak would do that :-P

Next up for the other jerks... Take off all of your coilpacks. Dremel the insides to be clean, and replace the springs inside.

Should clear up most of the jerks around 4k to 5k - if not, warm up car, and unplug coilpacks 1 at a time, see if it gets worse, or stays same.. if car stays same - you have a bad coil!

[bkos90]

im pretty sure that its not the coils because it revs free till redline, but it only does the jerk under load...
I also found out today while reving the car that i can hit full boost in neutral by just free reving it.
i also found out that after i unplug the O2 sensor the car runs a lot leaner on idle(16-17 on wideband) just like it used to when the problem didnt exist. and after unplugging the O2 i still dont get a check engine light... i dont even know if the light works, it light up when you turn the ignition to on but then goes away after you start the car.

[GSDKinked]

Change the plugs to BKR7EIXs and it will stop. gap to .023

[bkos90]

also just ran the ecu codes, got code 21 which is the cam angle sensor.
does anyone know on how to check the CAS?

P.S. thanks to everyone that tried to help, i really appreciate your help guys

[RustspecS13]

Also look at replacing your ignitor with a z32/j30 one soon. Mine did something close to that and the ignitor was bad. The smoother I was with the throttle the higher rpms I could reach, and if i just went WOT, it would studder and act like a revlimter around 4K. It made cool backfiring noises and flames but obviously not good.

Pull your cas off the car and turn it by hand and make sure its not rough or anything. There really isn't a good way to test them.

~Alex

[bkos90]

mine is a S2 rb25 so my ignitor is in the ecu.
and im gonna check the CAS wiring and then if no problems found then ill take it off and see

[bkos90]

EDIT: Code 21 is not actually the CAS, i made a mistake
Its ignition signal system... according to the manual it means "Ignition signal is not generated even through the crank angle sensor signal is entered"

any ideas?

[Acecool]

Did you hook up that one wire (S13 it should be red, or orange) to the proper ECU plug?

[bkos90]

i did everything according to the diagram on rbforums.org
It ran fine for a month or so after i swapped it and now recently it started acting up.
Could this be due to a low current/bad connection from the battery to the body harness?
It makes me wonder because all the ecu stuff and the sensors run through that ka body harness connector that usually bolts on to the battery terminal.
I wanted to go and check it this morning but we got hit with a big storm and looks like the whole day is going to waste.

[RBSilvia]

Did you ever figure this out? I've got a very similar problem with my S2 RB25.

Code 21, rough idle, cyl # 5 isn't working even though it's getting spark and fuel...

let me know

[Darius]

EDIT: Code 21 is not actually the CAS, i made a mistake
Its ignition signal system... according to the manual it means "Ignition signal is not generated even through the crank angle sensor signal is entered"

any ideas?

The ECU generates the ignition signal but if the engine runs most of the time, then it is likely to be the CAS hiccuping. BTW, the ignitors are built into the coils on the S2, not the ECU.

[bkos90]

Did you ever figure this out? I've got a very similar problem with my S2 RB25.

Code 21, rough idle, cyl # 5 isn't working even though it's getting spark and fuel...

let me know

It recently went away after a nice rev till like 7k rpm, I had to put some ricer in an integra in his place.

I never had a cylinder not firing or anything like that though, in the beginning i had a leaking injector and one of the cylinders was flooding in fuel. the rubber o-ring was bad. i changed it thinking it went away but the same thing was still happening except for the rough idle.

In my case i think it was clogged injectors and some wiring that gives power to the fuel pump.
the very first thing i did was, i got a Aeromotive fuel pressure regulator with gauge. Set the right fuel pressure and the problem was still there.
Then i checked the voltage going to the fuel pump and found out that it was only 4v on idle, so i just installed a relay so it has 12v constant when the ignition is on, the regulator would do its job no matter how much fuel goes in.
Later on I put some Chevron fuel injector cleaner when i had only like a 1/4 tank of fuel (i put the whole bottle that is supposed to be for 20 gallons) so its was more concentrated and then went through like 1.5 tanks of fuel, After like a week one time a dude in integra pulled up and was thinking he was all that, all he had was body kits and intake prob. So i revved my motor till like 7k, since the misfire would only happen on load. After i revved it the problem almost went away, it would still be there sometimes though. so the next day i put some more and it basically went away.

You should take off your fuel rail with injectors, and have some one crank the car while you have the injectors in sight to see if they all spray the same.
It can also be that the ecu is not getting enough current from the battery and the alternator, i have my battery relocated to the trunk and a thick 4 gauge cable running all the way to the front, then that cable is joined with the starter wire, the alternator and the chassis. They are connected with a big bolt from home depot that tightens and is made for wires. I really dont like that idea but thats all i can do for now, i will solder them all when i have to take off the intake manifold.
The reason im saying this is because i think it could be a solution. one day i noticed that my battery wasnt charging so i measured the alternator output voltage and it was 14v so i knew that it was that link with the bolt that failed.
So make sure you get a good contact from the battery to the chassis and the alternator... also check the alternator terminal and sand it with some sand paper for good contact.
code 21 is still there and never goes away, i reset the ecu and it goes away and then comes back, but it souldnt be a problem because my car runs good now i just have some overheating problems after driving for a while and after accelerating a few times when its hot outside. Maybe you can help me with that.
Hope this helps, keep me posted. i would really like to know if this solves the problem