Got a good puzzle....

[relaxamigo]

I've been battling this issue for a little over a month now. I was on track and the car all of a sudden lost power. The engine would rev smoothly, but it wouldn't "go." I know it's just a KA, but the power loss was absolutely noticeable. The alt also died that day, and was replaced the next morning.

If I shut the car off, wait a little, and go drive again, the car can get one or two strong pulls before it loses power again, the engine didn't cool down all the way, it was still warm. Stock KA with emissions deleted, walbro 255 and tomei FPR.

Here's what I've tested:

Fixed 3 vac leaks
Fuel pressure in and out 35 at itle and 42 at WOT
Stethoscope and voltage tests on injectors
Swapped a new walbro 255 (thinking it got hot under load)
MAF tested
TPS tested .49 volts at idle and 4.21 at WOT
leakdown/compression tests all solid 175 psi on all 4 and a 3% leak
coolant temp sensor tested in three different temps of boiling water according to FSM
swapped ECU
plug wires/cap/rotor/ignition coil/plugs all checked and gapped
AFRs are 11s at WOT and low 14s cruising
Only known issue is my IDLE afrs are crazy rich at mid 12s
replaced CAT with test pipe
replaced o2 sensor

This issue is driving me totally insane. Keeping the car sideways on track requires some seriously aggressive driving and I want it back to normal. Like I said, it revs freely with no sputtering but it just doesn't go. I've read tons of threads on similar issues all to no avail. I don't understand how I can get good AFRs at wot and the car still doesn't get power.

If you took the time to read this, I appreciate you, hopefully someone can help!

Thanks

[Ilya]

Possibly a bad clutch

[relaxamigo]

Interesting theory, although when I clutch kick mid drift the thing grabs pretty good. That would mean the clutch is slipping at all times when I'm on it?

[Ilya]

Just all depends on how bad the clutch is. Sounds like your engine is healthy but not transferring the power to the ground which the weakest link in that path is the clutch. When I had a slipping clutch, it would drive fine in third gear all the way up to around 4K rpm and then the rpms would shoot up with out me feeling any acceleration. But some say putting a car in 5th gear while stopped and letting the clutch out and seeing if your rpms dip or the engine stalls is a good way to see if your clutch is good. If you let your clutch out in fifth gear while stopped and rpms only drop a bit or the engine still manages to stumble but stay on, you may have clutch problems.

Another useful item I like to have nearr by is the eBay Nissan data scan tool that plugs in and let you read out every sensor of your car to your computer.

[relaxamigo]

Thanks for the information, I'll try that test tonight! It's definitely a possibility. The clutch has less than 2k on it, but could very well be the case,

[relaxamigo]

In fifth gear, the car quickly stalled out when I let it out. Don't think the clutch is an issue! Any other ideas? I've also swapped distributors

[bmaddock]

Only known issue is my IDLE afrs are crazy rich at mid 12s


Hey Juan! Good diagnosing skills, sounds like you've got your bases covered. I feel like there's something going on there with the rich idle though. Have you had a chance to pull each injector and inspect the o-rings for leaks? You could also pull the rail with the injectors installed and prime the fuel system to see if it leaks. Or pull all your spark plugs, prime the system and listen/look for fuel mist coming out of the cylinder. Another symptom of this would be occasional hard starts and oil that smells a bit like fuel.

My car had a leaky fuel injector and I still saw somewhat normal AFRs and would start most of the time. Might be worth swapping them out with some known good ones. You should also change your oil if it turns out to be a leaky injector.

[relaxamigo]

Sup ben, thanks for your input! Yeah I forgot to mention I've done that test too. I set a paper towel under the rail with full pressure and pump primed and they weren't leaking. The weird thing about the idle is that if I rev it up to 1500 RPM and keep it there, the AFRs drop to low 14s.. So bizarre.

If my diagnosing skills were good the damn thing would be running properly! I had to camber the hell out of my rear wheels to keep them spinning last weekend. :facepalm:

[relaxamigo]

Just swapped the entire fuel rail with a known good from my coupe, still
slow as hell, and still idling rich. any other ideas??

[bmaddock]

Have you checked your timing? Although unlikely with the chain driven KA, a weak tensioner could possibly result in jumped timing.


I guess that would contradict your statement about it sometimes running good for a brief pull or two. Have you read codes? Pretty easy to do on S13. Maybe your knock sensor harness is messing up... typically you'll see Code 34 (or whatever knock was) and assume it's the knock sensor but actually its the subharness is where the problem is.

[relaxamigo]

Ben-

Yup, I've checked timing with a timing light, and ensured the cams are all in the right direction.

I pull ECU codes after every drive I take, I've replaced the knock sensor and torqued it to make sure I didn't get a faulty reading from it being too tight.

I'm thinking I'm just going to have to deal with this at events :ugh:

[bkg775]

Sup Juan,

Might seem stupid but check the Throttle body to see if it's opening all the way or if the cable or pulley on the throttle body is messed up.

Spray some carb/choke cleaner on the Throttle body, IACV and Intake manifold to see if it has any really small leaks or someting.

Last thing I can think of is to make sure the distributor is tight and not moving.

Sorry if you've tried all this already but I wanted to chime in just in case bro.

[relaxamigo]

Hey man! yeah I've pressurized the intake and checked for leaks. Fixed the few that came up. It's bizarre I did another compression test yesterday and got 180 across all 4. This has me stumped so good!

Thanks for your input!

[jedi03]

How's your differential?

[relaxamigo]

How's your differential?

I'd presume it's okay? I haven't checked it. It's a stock welded

[bmaddock]

I sent this thread to a group chat I'm in and don't know if you've met Josh yet but he's saying your tank is rusty..

You could check fuel filter, fuel sock and look around in the tank? I would look high as mid-drift you could be splashing fuel up and pulling the rust down into the mix.

[pacotaco345]

Have you checked your wiring harness? You might have rubbed through something

[Kingtal0n]

Usually when someone says their engine suddenly lost power for no reason but still drives fine and sounds fine, its related to the knock sensor circuit or fuel pump.

[relaxamigo]

Usually when someone says their engine suddenly lost power for no reason but still drives fine and sounds fine, its related to the knock sensor circuit or fuel pump.

Thanks for the reply gents, I've replaced both the pump and knock sensor. I'll go ahead and check the wiring to both

[Kingtal0n]

wot at 11:1, is this naturally aspirated? are you saying this is by design or symptom? N/A KA24 at wot should be what, 13:1 or something with 22* of timing to start. Then try 26* also, using a dyno and if there is little difference try 18* also and make a graph of output comparing them. If you have EGT data also put that right beneath each one, and you will see the safest timing with acceptably low EGT is minimal, and some number Y.

So thats an a/f of 13:1, perhaps 13.4:1 on 93 with 9:1 compression and [email protected], 24* by 3200rpm and 26-31* from 3200-6000rpm timing. I would have it 18* of timing in the peak torque region if using a stock cam, that would be my 13:1 spot. It would trail off to some leaner 13.[2-8] So if you are going slow at 2200rpm and stab the pedal the first place the engine goes will be 2000rpm 13:1 and 17*. This is exceptionally safe and if we don't care about the engine as much, we could be adjusted to something like 13.8 and 27*. At 2300rpm this is a LOT of timing and not a whole lot of fuel but it could be done if we are trying to squeeze the engine for every last ounce, The compression and fuel will tell whether it works or not, at 12:1 compression this setting might be possible with ethanol when the engine is naturally aspirated. But I would not trust 13.8 at 2200rpm with 27* of timing on 93 octane, that looks like engine explosion to me if the engine is very hot and the fuel is low and also hot, and you are tracking the car it will pop a piston.

All thats left is compression, you should have 140psi+ on each cylinder unless its extremely high mileage. make these values occur and it runs fine if you are controlling all the oiling features of the engine with it.
All thats left is compression = piston/rings, headgasket, valves. Each of these may allow combustion gasses to escape and lower compression. You have to be seeing that number in each cylinder as even as possible, write it down with extreme precision, my 200k miles engine 4-cylinder has: 129.4, 129.8, 130.0, 129.5

Do a compression test every season and compare them for knowledge of the engine's vital statistic data.

[relaxamigo]

Hey man, thanks for taking the time to write that. I'm getting high 11s low 12s at WOT, I don't know if it's a symptom but that's what I'm getting. it idles high at 900 RPM at 12.9, but if I rev it in neutral at 1500 rpm, It idles almost normally at 14.1-13.9.

I don't have access to a dyno, but my compression numbers are at 180 even across all 4 warm. The longblock itself seems healthy, so it's gonna be something silly like you said. I have it timed to the stock value of 20 as per fsm

[relaxamigo]

Gentlemen-

Thank you all for your help. Looks like the culprit was the wiring to the knock sensor. I bypassed the sensor at the ECU with a ghetto rigged 560k ohm resistor pack, and the car runs better.

It still does some weird shit, but I'd imagine it's because I tampered with a vital component of the harness. I'll rewire the knock sensor properly shortly and keep mashing on!

Thanks again for your time! Hope this helps future searchers.