Jerking

[TurboTuli]

Hey all,I thought installing my o2 sensor would fix the jerking problem I was having, but it hasn't. Basically while applying minimal throttle at a constant speed the car intermittently jerks like I have let of the throttle. It also jerks when I do let off the throttle instead of smoothly decelerating. Someone had said backing off the timing a couple degrees helped them in the cold, but I did that and no change. Possibly my plugs? I got 200sx 1.8l turbo exhaust side plugs, but the part number is BCPR5ES-11, which doesn't match what is in the FAQ(PFR6A-11 ), but does match NGK's website for the 200sx plugs needed. I forgot to check the gap before I installed them, and will do that tonight, but shouldn't they come with 1.1mm gap?

Does anyone have any other ideas?Everything is stock except i'm running an SR t25 with 3 inch exhaust.

Let me know, thanks!

[float_6969]

Have you pulled the codes from the ecu?

What fuel pump are you using?

Try the plugs reccomended in the FAQ's. I used them on my stock CA w/o problems for a long time.

Double check your timing with a timing light. Follow the instructions in the FAQ.

Make sure you're timing belt is installed correctly.

Check your fuel pressure.

Clean the MAFS.

Check the idle control valves.

Check the TPS.

[TurboTuli]

stock fuel pump.

No one seems to carry the part numbers in the FAQ, but I'll look into it more.

I quadruple checked the timing when I set it to about 13* BTDC last week.

I guess I'll start checking all the rest of those things this weekend. Hopefully one of them is suspect.

The car accelerates completely smoothly, its just when I try to maintain a constant speed that it jerks...

[pulsar gtr]

You might have dirty fuel injectors, get some injector cleaner and add it to the fuel tank.

Did it always did that, or it just start doing this problem recently? If recently, how long did you drive the car after the engine swap?Also, set your timing to 15Degrees BTDC.

Check the intake and the vaccum lines for any leaks?When the car is warm, what is it idealing at?

Good luck,RafiPULSAR GTR

[TurboTuli]

Well, I only got it running about 2 months ago and didn't have an o2 sensor a until a month ago and I thought that the o2 sensor would fix this problem, however it didn't. So I changed the plugs, installed the new o2, but the problem is still there. Also, the plugs were quite fouled because it was running very rich with no o2, and now with the o2 my gas mileage has gone way up to a reasonalbe amount, but my plugs are already a bit fouled again...thoughts?

Someone mentioned backing the timing off slightly had helped their similar problem, but it didn't help me. I will set it back though.

If there were leaks, wouldn't the problem be worse under boost/full throttle as opposed to non-existant?

That does remind me. It idles anywhere from about 1k to 1500 rpms...What would that point to?

[pulsar gtr]

If the intake gasket is gone bad or a tiny hole in one of the vaccum lines, the car will ideal a bit higher and since your car drives fine under acceleration but when you let go of gas it jerks, it seems that you have a small vaccum leak which causes a surge when you let the throttle off. Which also explains why you have a higher ideal, you car should ideal no more than 1k, it should be approx 800 rpm -/+ 200 rpm.you said that you retarded your timing to 13degrees, if you do that you car should ideal lower which still points to tiny vaccum leak. Do you have any vaccum hoses that are not hooked up? or any other nipples that are on the intake which arent hooked up?

RafiPULSAR GTR

[burnout 180]

This jerking happened to me before when i was installing a walbro fuel pump into my cousins turbo integra. After draining the fuel in the tank in the integra I put the fuel into my ca18det. That is when it started i figured it was either the old gas or perhaps water or possible impurities that had settled to the bottom of the integras tank that was causing this. So i drained the lines and tank. I then cleaned the injectors and tank and put fresh gas and a new fuel filter.

And then a miracle occurred the problem was gone. wing

[float_6969]

OK, now that I know that it's fine under full boost, and that the plugs are fouled again, I'm going to have to agree with him. It's a probabally a vac/boost leak. Get some carb cleaner and start spraying all of the connections on the intake tract. I'd work from the manifold twords the turbo.

[slipnfall]

Excuse my ignorance, b/c I don't know much about CA's. When you said 'back off the timing', I assume that to mean you have a distributor? If so, take a look at your contact points in the cap. Make sure the spark markings are centered on the contacts. If they're too close to the end or base plastic it can cause similar symptoms from mis-firing.

[float_6969]

No problem, but no, the CA lacks a distributor.

It uses a crank angle sensor, and then 4 coils that sit direcetly on top of the spark plugs, aka no wires.

[slipnfall]

gotcha, ala coil-on-plug...

[float_6969]

exactly.

[biosehnsucht]

I have jerking/power loss issues which I'm sure are due to vacuum leak at the hose from the cold start gizmo to the intake mani..

once heated up doesn't happen (cracked hose at the ends)

what is happening likely is this: small amounts of vacuum, very little leak, gives no real change in power, larger vacuum (pre boost load) sucks in more unmtered air, you run lean, leadingto power spikes as you get momentary lean increase, ECU freaks from o2 readout, throws some more fuel in, power loss from richness, rinse repeat, then when you get in boost it just runs continuously rich (leak vacuum now leak boost, meaning metered air is more than real air and so rich instead of lean) and the ECU just runs continuously rich (but by a stable amount) so it feels normal..

thts my theory anyhow..

[float_6969]

Sehn, you nailed it. That is EXACTLY what happens. And that is why MAFS suck. They're accurate, but you've got to be running a TOTALLY sealed system. There is no room for error.