ka-t bucking misfiring under load, throwing weird codes

[spooled240]

So I'm going to try my best to not make this a novel, but include as many details as I can.

Mods?
-'97 s14 with original KA
-JWT '95 OBD1 ECU
-garrett 50 trim
-555cc injectors
-Aeromotive FPR
-Walbro FP
-Z32 mafs

What happened?
-Car ran fine but rich <10 AFR under full boost
-I remove upper intake manifold and fix boost leaks and remove EVAP and some EGR stuff
-Replaced the leaky nismo fpr with aeromotive
-Rebuild throttle body with new seals
-Did a minor tuck with the harness inside the intake manifold as opposed to the stock location on top of the fuel rail
-Performed a boost leak test and passes

Ok cool, Let's drive it!
So then I take the car for a spin. The first couple runs it's fine and pulls hard. Then starts randomly breaking up under load. Wideband reads lean so it's safe to say that its a misfire, since the fuel pressure is perfect.

The car will start up and idle fine and do a decent pull in 1st gear then fall right on its face in second. One time I just let it do its misfiring bullshit in second with the pedal to the metal and it barely wanted to idle after that. After letting it sit for a good hour, it seemed I was able to keep it from dying by feathering the throttle. I pop it in gear and start creeping forward and BAM! a couple violent bucks and it's firing on all 4 again but back to it's original condition. Any moderate load and it feels like the ignition is cut.

Let's pull the codes
I pull the codes and this is what I get:
-83
-87
-93
-132

....and there's no information on these codes in the FSM, google, anywhere. I call JWT and they don't know what's going on there either. Fucking perfect.

Backtracking
So naturally I'm retracing my steps and checking wires, sensors, etc. So far:

I replaced:
-knock sensor (old one was bad)
-coolant temp sensor
-lower mileage distributor

and I checked:
-continuity for all ignition wires to ECU
-ignition coil resistances according to FSM
-resistors in ignition harness
-unplugged mafs on idle and car dies (maf is functioning)
-plugs are white/crispy brown when I pulled them
-plugs new and gapped to .030
-timing is good

Cliff notes:
-car runs fine
-I remove intake manifold to fix boost leaks
-car now misfires under load, but runs fine on idle/light load

Any help is appreciated.

[w0nderbr3ad]

ounds like a fuel related issue to me. It could possibly not be the problem, but it's just something to check anyway.

I'd check that all fuel lines are correctly connected.

I would try checking your fuel injectors to see if resistance is still within spec. Then proceed to check if they are spraying. If everything checks out, move onto the fuel pump.

I had an issue with running a walbro 255 on my ka-t with a t25. After a month of use it would gradually read lean (12.8-13.7) under boost, even after hardwiring it. Coming out of turns and going WOT it would feel like boost would feel flat, as if the motor was waiting for something to happen. I switched to a denso supra FP and problem went away.

[Kingtal0n]

whens the last time it had a tune up? cap rotor wires filters etc..

how does the oil smell?

Do you ever clean the plumbing? Did you clean the intake manifold out while you had it off?

Did you fill the plumbing with 15psi from an air compressor to verify no boost leaks recently? Do it again, & then Do it again.

[Kingtal0n]

The first couple runs it's fine and pulls hard. Then starts randomly breaking up under load.

sounds like a boost leak sprung open at a coupler that got sideways


The car will start up and idle fine and do a decent pull in 1st gear then fall right on its face in second. One time I just let it do its misfiring bullshit in second with the pedal to the metal and it barely wanted to idle after that.

again sounds like a boost leak, as if excessive fuel is pouring into the cylinders. A bad/intermittent ignition component is possible but I would rate that 15% as likely as a fuel related. You should have seen the wideband peg 10:1 and the black smoke pour from the exhaust when it was "barely idling after that" to verify.

On second thought because you have a distributor/wires I will raise chances of an ignition related component to 50% instead of 15%, you may have a wire falling apart if they are old, or burnt up.

[spooled240]

I also had experience with a failing walbro which resulted in bucking and hesistation under boost, but this seems a bit different. It's just too damn consistent of a hesistation on moderate to high load.

My fuel pressure is a solid 34psi at idle with vacuum (43 psi without vacuum) It's weird you would never know the car had this issue seeing it idle and free rev.

[spooled240]

whens the last time it had a tune up? cap rotor wires filters etc..

how does the oil smell?

Do you ever clean the plumbing? Did you clean the intake manifold out while you had it off?

Did you fill the plumbing with 15psi from an air compressor to verify no boost leaks recently? Do it again, & then Do it again.

I recently did an oil change so the oil smelled fine. It will start smelling like fuel after a while because the AFR's were always in the 10's on full boost.

Intake manifold looked fine when removed.

For the boost leak test, I pressurized the entire system from turbo intake to engine with 15psi and did not hear any hisses or see any bubbles when I sprayed everything down. I must've fixed 5 decently sized boost leaks that didn't allow me to pressurize the system past 1 psi. Pressure at 15psi dropped rather slowly, maybe less than 1 psi a second - which I heard is normal.

sounds like a boost leak sprung open at a coupler that got sideways



again sounds like a boost leak, as if excessive fuel is pouring into the cylinders. A bad/intermittent ignition component is possible but I would rate that 15% as likely as a fuel related. You should have seen the wideband peg 10:1 and the black smoke pour from the exhaust when it was "barely idling after that" to verify.

On second thought because you have a distributor/wires I will raise chances of an ignition related component to 50% instead of 15%, you may have a wire falling apart if they are old, or burnt up.

when it was barely idling the wideband was pegged on lean and there was no black smoke coming out of the exhaust. This is what leads me to believe that this is an ignition misfire of some sort.

It has been a couple years since I did a tune up on it, but I just have a hard time believing that it could have failed that bad, that fast right after I put it all together..

[Kingtal0n]

I recently did an oil change so the oil smelled fine. It will start smelling like fuel after a while because the AFR's were always in the 10's on full boost.

Intake manifold looked fine when removed.

For the boost leak test, I pressurized the entire system from turbo intake to engine with 15psi and did not hear any hisses or see any bubbles when I sprayed everything down. I must've fixed 5 decently sized boost leaks that didn't allow me to pressurize the system past 1 psi. Pressure at 15psi dropped rather slowly, maybe less than 1 psi a second - which I heard is normal.



when it was barely idling the wideband was pegged on lean and there was no black smoke coming out of the exhaust. This is what leads me to believe that this is an ignition misfire of some sort.

It has been a couple years since I did a tune up on it, but I just have a hard time believing that it could have failed that bad, that fast right after I put it all together..

okay. A lean misfire. A super rich WOT. The engine needs tuning, and like you suggest, may have an ignition component gone bad. tough to say from over the internet of course. Pictures might help, how is your pcv routed? It sounds like its misfiring on all cylinders. this may suggest a maf translation issue. This is why I do not like rom tunes. If you had a PFC (a $400 computer) you could just look at the commander and hit a few buttons to dial up or down the fuel / timing within seconds, which would dramatically speed up the diagnosis.

this is the kind of problem that could be something silly like a loose ground, or loose ECU plug, on an sr20 I would say check the coil pack grounds... or some previous wiring gone bad.

[spooled240]

I'll see if I can get some videos up later. It's currently undergoing an oil pan swap..

PCV hose off valve cover goes through radium oil catch can which is hooked up to the turbo inlet.

"Oil separator" PCV check valve was replaced with a straight-though brass fitting then connected to the turbo inlet. The crank case should always see vacuum.

It's definitely misfiring on all cylinders, which is why I suspected the iginition components were failing. But swapping out the distributor didn't change a thing and the wiring all checked out. The ecu always made the car run rich on boost, but the driveability was great before all this happened. Something changed or got effed up during the intake manifold R&R...

[Kingtal0n]

I'll see if I can get some videos up later. It's currently undergoing an oil pan swap..

PCV hose off valve cover goes through radium oil catch can which is hooked up to the turbo inlet.

"Oil separator" PCV check valve was replaced with a straight-though brass fitting then connected to the turbo inlet. The crank case should always see vacuum.

It's definitely misfiring on all cylinders, which is why I suspected the iginition components were failing. But swapping out the distributor didn't change a thing and the wiring all checked out. The ecu always made the car run rich on boost, but the driveability was great before all this happened. Something changed or got effed up during the intake manifold R&R...

Oh I missed that. It ran fine till you pulled the intake off? Well sir, re-trace those steps. did you mess with the injector O-rings or something? maybe plug them in wrong order? Maybe forgot a ground wire? All that wiring you un-hooked and then re-hooked may contain the answer.

otherwise, its a coincidence, and the first thing I would try is a set of new plugs.

[spooled240]

No I didn't touch the injector o-rings, just pulled the whole rail off. All the grounds were reinstalled like they were. I even sanded and cleaned the contact points. I even went as far as adding another ground wire for the hell of it, but it didn't change anything.

shit is weird. I'm starting to think it may be the ecu being that it's throwing out these weird codes..I mean 4 codes that don't exist anywhere on the FSM or Google wtf. I know I'm not tripping either, I quadruple-checked the number of times the light blinked lol

[Kingtal0n]

If you have an internal gate, I would suggest disable it so there is no boost. then drive the car hard and see what happens with 0psi.

If it still has trouble, next quick step is stock computer/injectors/maf and try again. Oh. and, Do a compression test asap.

[spooled240]

The car has started randomly started losing power without boost. One time I was on the freeway and it just randomly started losing power and the wideband was reading lean (misfiring?) After pulls at WOT it will run a lot shittier on lighter loads, then it will seem to smoothen out again and only misfire on higher loads later...

I've pulled the plugs out immediately when the car started acting up after these pulls and the plugs look perfect. This is another reason why I think it's a misfire.

[Kingtal0n]

If you are just driving along and it starts to "forget" to inject fuel, wideband goes lean, and the car slows down, I think fuel pump 79%, maf sensor 14%, fuel filter 6%.

I think you need to verify compression first just for the heck of it. Clean the slate.

Then I think you should verify your fuel pressure isn't falling off intermittently. Thats pretty simple and a very common problem.

From there I feel ECU/Wiring harness is next, go back to stock. If it does the same thing with the stock computer/injectors then you can jump to the ignition components.

[spooled240]

Possibly. The fuel pressure has always been a solid 43psi/34psi on idle even when the car would idle like complete crap.

I wish I had still had the stock parts, they're ruined now that my dumbass left them outside :/

I've been wanting to swap out the ECU for something more customizable, like a nistune. This may be a good time lol

[OnTheChip]

It could be an ignition switch or wiring problem. If the ignition ON signal from the ignition switch is flaky, the ECU will be restarting itself over and over, which could cause the weird DTCs you're seeing. Also check the ECCS relay and wiring as that is what powers the ECU when the ignition switch is turned OFF for an orderly shutdown.

[spooled240]

hm, that's funny you mention that. My car was down for a while with the intake off so the battery ended up dying. When I tried jump-starting it with one of those battery chargers that have the 50 amp "jump start" setting, the dash lights flickered and I heard some relays in the driver and passenger side kick panels buzzing. I heard bad relays can still perform the switch function, but they will act like a resistor and and cause a voltage drop.

I hope I didn't fry anything, but I'll check the fuses and relays...

thanks for all the responses so far.

[spooled240]

Update: Swapped the EGI relay for the a/c relay and there were no changes

Re-did my timing chain and ignition timing and there were no changes (I had previously messed up the timing chain years ago when I rebuilt the motor. I thought now would be a good time to eliminate that issue)

Then I remembered that I had the intake pipe in this vertical position while I was working on the intake manifold. I also remembered a decent amount of oil inside the intake pipe from blow by....oil that might have dripped down towards the maf sensor when it was in that vertical position. So I decided to take it apart and check it out. Sprayed a good amount of air sensor cleaner in there and put it back together. Fired it up and the car ran perfect. Drove it around the block and there were no issues, well for the most part. There are still some issues that need to be sorted out but the car's improvement is night and day. Pretty stoked.