240sx Motor Trouble

I have a KA24DE that was professionally rebuilt, but not re-dynoed after it grenaded on me a while ago. I have the car completely back together now, but it has some issues.

1) The idle will hunt from almost stalling at 500 rpms and then will shoot up to 2500 rpms then back down, etc. I unplugged the TPS, tried adjusting idle screw, but it did absolutely nothing. I also tried replacing the O2 sensor with a used (but thought to be good) unit.

2) The motor rocks a LOT from side to side no matter what the idle is.

When I hit the throttle, it revs and pulls nicely, but the low RPM issues and motor shaking scares me.
Fuel pressure is around 43lbs at idle, oil pressure is 50lbs, everything else is fine.
Bad sensor somewhere?

Cam timing off a tooth or something?
CAS/distributor bad? (my timing light died, so I couldn't check timing today)

Thanks for any help!
Tim

Quote:

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Originally posted by TBreu007@Nov 10 2005, 05:00 PM
I have a KA24DE that was professionally rebuilt, but not re-dynoed after it grenaded on me a while ago. I have the car completely back together now, but it has some issues.

1) The idle will hunt from almost stalling at 500 rpms and then will shoot up to 2500 rpms then back down, etc. I unplugged the TPS, tried adjusting idle screw, but it did absolutely nothing. I also tried replacing the O2 sensor with a used (but thought to be good) unit.

2) The motor rocks a LOT from side to side no matter what the idle is.

When I hit the throttle, it revs and pulls nicely, but the low RPM issues and motor shaking scares me.
Fuel pressure is around 43lbs at idle, oil pressure is 50lbs, everything else is fine.
Bad sensor somewhere?

Cam timing off a tooth or something?
CAS/distributor bad? (my timing light died, so I couldn't check timing today)


Thanks for any help!
Tim

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Big vacuum leak. Check around injectors and check the gasket around the first intake port to head surface.

I'll take off early from work tomorrow tomorrow and check it out (I have to sort this out...it's killing me)

It's been so long since I had it off...is that a real gasket or a liquid (bluegoo) gasket on the manifold?

I'm not sure if the injector o-rings were replaced on the rebuild, but they look okay. Any tips on getting them to seal?

Thank you,
Tim

Quote:

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Originally posted by TBreu007@Nov 10 2005, 07:12 PM
I'll take off early from work tomorrow tomorrow and check it out (I have to sort this out...it's killing me)

It's been so long since I had it off...is that a real gasket or a liquid (bluegoo) gasket on the manifold?

I'm not sure if the injector o-rings were replaced on the rebuild, but they look okay. Any tips on getting them to seal?

Thank you,
Tim

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There are gaskets between the intake and head and also between the manifold halves. Make sure you have new seals for the injectors.

Update on the motor saga:

I bought a new timing light and after some messing around, I got the idle to stay where it needs to be and not hunt.
The timing would stay at 20 degrees BTDC then shoot up to 40 degreed BTDC when the idle went up.
It looks like my timing was off by quite a bit. After I got the timing close, the idle steadied, and I could get the exact timing set.

Since the motor actually stayed in one place and wasn't shaking around violently, I checked around for air leaks. The WD40 method didn't produce any results, so I listened. I found a hissing around the front of the motor by the intake manifold...the rubber boot around injector #1 was bound and didn't seat properly. I pulled off the fuel rail, reseated the injector boots and reinstalled the fuel rail. No more hissing, and it actually idles! :023:

Quote:

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Originally posted by TBreu007@Nov 12 2005, 07:39 PM
Update on the motor saga:

I bought a new timing light and after some messing around, I got the idle to stay where it needs to be and not hunt.
The timing would stay at 20 degrees BTDC then shoot up to 40 degreed BTDC when the idle went up.
It looks like my timing was off by quite a bit. After I got the timing close, the idle steadied, and I could get the exact timing set.

Since the motor actually stayed in one place and wasn't shaking around violently, I checked around for air leaks. The WD40 method didn't produce any results, so I listened. I found a hissing around the front of the motor by the intake manifold...the rubber boot around injector #1 was bound and didn't seat properly. I pulled off the fuel rail, reseated the injector boots and reinstalled the fuel rail. No more hissing, and it actually idles! :023:

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Hey I broke my arm patting myself on the back..... :happy204:

Something else I found out is the timing jumps all over the place if the distributor isn't snugged up. If the bolts are loose while checking timing, the timing will not hold in one place. I have to snug them, check timing, loosen, readjust, tighten bolts, fry my fingers on the header, etc.

Off to Sebring for testing...woohoo. :fingerscrossed: