KA24E, occasionally down on power...?

[orion]

Hey guys...need some brainstorming help.

I posted an "intro", but in case you missed it: I have a used ITA S13, with a SOHC KA that has required a headgasket, new bearings, new injectors, and many cleaned up plugs (for sensors).

It never felt like it made power above ~5000...it pulled great until thereabouts, but then just stayed flat.

It's taken a lot of work, but I got it running *perfect* a couple weeks back - I did a "redneck dyno" (quarter mile), and it trapped 84.4mph...which would estimate 130RWHP given a weight of ~2800 with me in it.

It ran it's best that night. Pulled hard and strong until redline.

Took it to the semi-local short road course (Gainesville Raceway), and it was flat again? I thought maybe it was the heat, but the data shows a max speed of ~68mph on the back straight - I should be doing around 74-75mph, easy...even in 100F weather. And again, it had no pull over 4500-5000rpm.

This was 2 days after it ran perfect.

I have to think it's a sensor, or wiring: MAF, TPS, Coolant temp...one of the ones the ECU would use to determine load and timing advance.

Maybe fuel pressure, but I don't think so...it's got a fuel cell with a Bosch pump.

I think it's a poor connection, or intermittent short.

Here where you come in:

Have you ever been to the track, and had your KA24E feel down on power...only to find the CTS plug had come loose?

Ever had a bad TPS, and the car ran...but felt slow?

I've tested all these sensors at idle, and they all check out. CTS resistance is good, within spec for the ambient temperature. TPS shows ~0.5v with the throttle closed (idle), and +4v with it WOT.

Base timing has been checked and checked again, and it dead-on at 15 BDTC.

Maybe a bad distributor, or more specifically...a bad crank position senor within the dizzy?

Give me some ideas, please.

I feel like I've checked and double-checked everything...this is my 11th 240SX, and I had to do my fair share of troubleshooting over the years.

But on this one, I'm stumped.

Thanks for any suggestions.

- Brian

[orion]

Still looking for ideas.

Coolant temp sensor has been triple-checked, and it A-OK.

1.6k Ohms at ~80 F, .547k Ohms at ~150F...within spec.

The hard starting makes me thing base timing is off - I might just try some random advance/retard to see if that helps (that's actually an FSM-approved diagnostic tool...hehe)...and go from there.

Then, I guess I'll start tracing wires and checking continuity.

??? - Brian

[Tristan Smith]

Brian, I'd also double check that the timing chain/cam gear are properly aligned. What's your distrubuter cam gear look like? They are notorious for wearing out, especially the way we twist these motors.

[orion]

Thanks for the reply...

Cam timing is dead-on...like I said, it ran great ONE afternoon. Dont think these motors could skip a tooth.

I will check the dizzy gear...

- Brian

[Tristan Smith]

Sorry, to clarify, not just the gear on the distributer. The gear on the crank that drives it. Nismo use to make a gear of alternative material (I want to say a bronze silicate or something like that) because of that issue. I don't believe they are still made and are hard to find now a days. Good luck.

[DavidM]

I had issues with the injector wires. The rubber boots get hard with age and can rub through the wires causing a short. Had this happen a couple times. Dr. Tristan helped me find it at the track once. Showed up as a miss in the motor. Sounds like you've gone through and checked all the connectors, though.

You said the motor is hard to start? Mine fires right up once the fuel rail is primed. Have you checked the fuel pressure just to be sure the pump is ok? Maybe a faulty fp regulator? Might replace the dist with a known good one just to rule it out. I've read of some issues with the dist having problems when hot, but I've never experienced it.

As an aside, I have no idea how my car ran with the wiring harness it had. That thing was so rigged I'm surprised the car even started. The harness in the new tub is near perfect.

David