Bucking under Acceleration, not fuel pump/filter

[modulation]

S13 Ka24de

One day when I tried to drive my car, when I give it 20-30% throttle it starts bucking and refuses to accelerate. It had hiccuped a couple of times now and then a few days before but now it just refuses to accelerate.

I have a wideband and I can see that it leans out really bad >16:1-20:1 and up when I try to accelerate so it's fuel not spark.

I have a diagnostic scanner so I know it isn't:
MAF, TPS. CAS, Temp sensor.

I got done replacing the original fuel pump today with a Walbro and a new fuel filter but the same problem is going on.

Any ideas? Don't bad FPR's normally cause a car to run rich?

[modulation]

I didn't believe myself so I swapped out to another MAF and ECU I have and the same problem persist.

[garagelu]

check the wiring from your ecu to the injectors. You may have a short or a corroded wire.

[modulation]

check the wiring from your ecu to the injectors. You may have a short or a corroded wire.

Thanks for the advice. I looked around and all looks well.
Like I said it's definitely happening on all cylinders, and each cylinder has it's own wire to the ECU so thats not it.

I'm thinking like bad FPR, or bad IACV or something along the mechanical lines.

[garagelu]

Thanks for the advice. I looked around and all looks well.
Like I said it's definitely happening on all cylinders, and each cylinder has it's own wire to the ECU so thats not it.

I'm thinking like bad FPR, or bad IACV or something along the mechanical lines.

thats not entirely true. Each cylinder does not have its own power wire to the ECU. Each cylinder has its own wire till about the firewall. From there to the ecu, its one wire. On the ground side, each wire has its own wire to the ecu. I would check continuity on the power side.

[modulation]

thats not entirely true. Each cylinder does not have its own power wire to the ECU. Each cylinder has its own wire till about the firewall. From there to the ecu, its one wire. On the ground side, each wire has its own wire to the ecu. I would check continuity on the power side.

Dude the ECU has 1 wire to every injector.
Look at the FSM.
It has to be able to open each injector independently.

[garagelu]

Dude the ECU has 1 wire to every injector.
Look at the FSM.
It has to be able to open each injector independently.

dude, I know. Did you not read my post. The injector pulses the ground side to open and close the injector.....NOT THE POWER SIDE. So the injectors all have one source for 12v power. And each injector has its on ground.

[modulation]

Dude the ECU has 1 wire to every injector.
Look at the FSM.
It has to be able to open each injector independently.

dude, I know. Did you not read my post. The injector pulses the ground side to open and close the injector.....NOT THE POWER SIDE. So the injectors all have one source for 12v power. And each injector has its on ground.

Yeah I guess we just misunderstood each other.
Its not a electrical problem. Everything was working fine for months and I hadn't touched anything. Drove 70 miles to autocross, and it bucked once on the way there going up a hill. Then drove 70 miles home, 30 miles to another place, 30 miles home, 13 miles to work and then the next time I start the car it bucks like crazy when I try to accel.

The injectors are opening they just aren't getting enough fuel pressure it seems. Or other things are opening which shouldn't be under WOT and are allowing too much air to come in the engine.

I'd think it would be the FPR but I've never heard of them failing in the way that I have my problem.

[steve shadows]

Step1: Use a Fuel Pressure Gauge to check it under load.

Run it inside the car with a long hose so you can watch it

Make sure your fuel pump is not dieing.

Step2: make sure you do not have a vacuum leak or boost leak that isl etting air into the engine after the MAF.

[SidewaysGts]

Have you checked for any vac leaks before? In particular check your lines and any couplers youve got.

[modulation]

I've looked around for vacum leaks and haven't found any.
Idle is awesome and it starts fine cold etc.. it's just under acceleration I've having problems.

I already replace the fuel filter and pump. I bought a new FPU today for $99.
I tried a different MAF and a different ECU, I've verified the TPS voltages are being seen correctly by the ECU and there are no flat spots on the TPS.

If replacing the FPR doesn't work then I'll spend the $50 on a fuel pressure meter and verify that's the problem.

I found a post on the internet where some guy was having the same problems and it was his FPU so that gave me a little hope.

Also I'm NA so no boost leaks. I didn't mess with the engine, and the car drove 200+ miles in 2 days, and then to work the next day, and then the next day it start having problems so I don't think it's a vacum leak since I wasn't under the hood.

[steve shadows]

I've looked around for vacum leaks and haven't found any.
Idle is awesome and it starts fine cold etc.. it's just under acceleration I've having problems.

I already replace the fuel filter and pump. I bought a new FPU today for $99.
I tried a different MAF and a different ECU, I've verified the TPS voltages are being seen correctly by the ECU and there are no flat spots on the TPS.

If replacing the FPR doesn't work then I'll spend the $50 on a fuel pressure meter and verify that's the problem.

I found a post on the internet where some guy was having the same problems and it was his FPU so that gave me a little hope.

Also I'm NA so no boost leaks. I didn't mess with the engine, and the car drove 200+ miles in 2 days, and then to work the next day, and then the next day it start having problems so I don't think it's a vacum leak since I wasn't under the hood.

Just stop where you are ahead, you should be able to find a cheap fuel pressure gauge for less than 10-20 bucks online.

I would check your Spark Plug gap as well...also your Coil Pack Harness Ground, may be getting lose with certain RPM/Vibration in egine.

To check your Vacuum system you really need to use a Smoke Tester (like a smoke machine vacuum tester)

[Blues13]

Is it misfiring? If the mixture doesn't spark, the unburned oxygen will show up as lean on a wideband...

Check your plugs when it's happening and see if its black or wet..

[modulation]

Just stop where you are ahead, you should be able to find a cheap fuel pressure gauge for less than 10-20 bucks online.


If you can find one that cheap let me know where. Any of the ones I can find that cheap only do like up to Carb. Fuel pressure PSI (up to 20 or so.) They all seem around $50.

Also it's a time thing. I have a track day the 28th.
I got the FPR I ordered same day, it would take me a couple of days to get a fuel pressure gauge. If the FPR works sweet. If I got the pressure gauge then found out my fuel pressure was low whats the next step? Buy a new FPR I would think...

I really don't think it's spark related. I would think it would do it when rev'ving not in gear too if it was spark. Also my friends have watched me try to accelerate and no black smoke or any smells of fuel. It smells like it's running lean when it bucks.

[modulation]

Is it misfiring? If the mixture doesn't spark, the unburned oxygen will show up as lean on a wideband...


I actually didn't know that and honestly didn't believe you until I looked that up and what you say seems to be correct.
I still think it's a fuel problem not a spark problem but I will definitely keep that in mind.

I've checked and swapped my plugs out with new ones and same problem. The old ones look to be running lean. The last cylinder (#4) closest to the FPR looked the leanest of all..

I'll have time to swap the FPR tomorrow, I'll let everyone know. If I was wrong well then you can all make fun of me that I wasted $99. ;-)

[modulation]

I would check your Spark Plug gap as well...also your Coil Pack Harness Ground, may be getting lose with certain RPM/Vibration in egine.

To check your Vacuum system you really need to use a Smoke Tester (like a smoke machine vacuum tester)

Yeah I replaced the plugs with new ones gapped to the minimum. I don't have coil-packs just a normal coil and spark plug wires.

As far as Vacuum leaks go wouldn't that affect idle too?
I seriously doubt it would cause such horrible bucking under accel unless it was so big you could hear it.
I drove 200+ miles including doing autocross runs and no problem. Then like 2 days and 100+ miles it suddenly develops a vacuum leak? That doesn't sit right to me.

[garagelu]

ive got a cheap autometer fuel pressure gauge that I used when I was doing my turbo setup. I have since went to a different gauge. I can send you that cheap autometer one for 25 dollars shipped. Let me know if you need it. PM me.

[modulation]

Well those telling me not to throw parts at it were right and you can say "told you so" now..

Well it isn't fuel.
I clamped the return line and I'm having the same problems.
Friend and I checked out spark and everything is cool.

Engine is running really lean now and doesn't even like to idle.
We are pretty sure there is a massive vacuum link in the intake area some where, but we've sprayed carb cleaner everywhere and can't get the idle to raise.

The problem has gotten worse..

We pulled the fuel line and it's spraying perfectly and everything.
All the injectors resistance test out well, and after pulling numerous spark plugs it still doesn't seem to just be one cylinder..

We check and double checked vacum hoses we could see and we can't find any leaks but with the crazy intake of the ka24de who knows...

[abunai the drifter]

i say dubble check your tps Back probe it with a volt meter and slowly open the throttle and wach the volt meter and if you see 0.00 at any time then thats the problem

[modulation]

i say dubble check your tps Back probe it with a volt meter and slowly open the throttle and wach the volt meter and if you see 0.00 at any time then thats the problem

Yeah I have nistune so I can watch TPS voltage.
I've slowly pressed down on the "gas" and I can see the tps increasing from like 0.5v to 4.3v..

I'll double check it with a volt-ohm-meter tomorrow though.
It's so bad though it does it at idle now.

[modulation]

Well I found some coolant on the floor this morning where there shouldn't be any. Its on the side of the engine with no coolant lines at all.

I'm thinking headgasket, got a friend coming over with a compression tester soon.

[modulation]

Did a compression test today.
All cylinders are within spec and no real compression difference between then.

I'm thinking a intake manifold gasket is leaking.
The intake manifold is 2 parts on my car so there are two gaskets that could be leaking.

Car idles fine when cold, but when it warms up it runs worse and worse.
If I touch the gas pedal when the car is warming up and idling ok it'll start having problems and not return to a normal idle.
If you let the car cool down then start it again it'll run find until it warms up.

Not the CTS I've checked that numerous times.

[Ceepo]

I had this same problem on my s14(ka24de obd1 automatic) to fix it i did new plugs, cap, rotor(or clean the probes on the rotor and cap with a wire brush or sand paper) and that fixed it, there was rust on the cap/rotor probes and it wasnt firing on a few cyliders all the time... also have you reset the ecu? unplug the battery and press the brake peddle down for about 30seconds to a 1 minute and plug it back up and see if that helps? i did read the posts above im just trying to think outside the box...

[modulation]

We used a known good spark plug, pulled the wire from each cylinder 1 at a time, and made sure all wires were giving spark. We'd even accelerate the engine and make sure the wire was still getting spark.

My friend is a510 guy andwe took apart the distributor/rotor and CAS. We cleaned it all and he said it looks really good.

I've tried 2 different ECU's but "resting" the ECU doesn't really do anything on OBDI. I have nistune and a consult cable and can reset the ECU via laptop too, but it doesn't do anything.

It's not spark. It's not fuel, it's not compression.

[RPS13nutt]

Have you put on a fuel pressure reader yet?
I have had that same problem due to the damaged rubber ring on the gas tank.
See if that are any tears on that ring.
It caused my fuel pressure to be off because of little to no vacuum from the tank due to the gasket not sealing.

Could be something to look into.

[modulation]

WAIT!

I replaced the fuel pump and I thought the problem "got worse," but if what you are saying is true then maybe I didn't set the o ring right?

I thought if I didn't have that sealed it would just smell like gas, but you're saying the pump doesn't work properly if it's not air tight? How is that?

Thanks.

[modulation]

Have you put on a fuel pressure reader yet?
I have had that same problem due to the damaged rubber ring on the gas tank.
See if that are any tears on that ring.
It caused my fuel pressure to be off because of little to no vacuum from the tank due to the gasket not sealing.

Could be something to look into.

I don't understand this? A car will run with no gas-tank cap, but you're saying it won't run without the gas tank being sealed?

Please educate me. You had this same problem and it turned out to be a leak on the round O ring for the fuel pump panel?

[osal]

if u have a buddy wit the same car, swap distributors. i had this buckin until i tried changing distributors. buckin stopped

[RPS13nutt]

Not saying it would not run, but saying my problem was the same with too much fuel.

I was having fuel pump fuse problems at first, and when all was fixed it drove like it was getting too much fuel .
I removed fuel pump again to check and thats when i found the gas tank ring was ripped. replaced and the problem went away.

My problems were sounding almost exact to yours so i posted up to see if thats what you could check and see if that is the same problem.

I have no wide band to show the ratio, just NDS to show i was rich all the time. and under load you can tell as well.
But changed the ring and my problem was gone with too much fuel.

Sill could be a different problem than mine, but sounded simular.

[modulation]

Well I undid the fuel tank access panel, and I got done with a couple of bolts and heard a "hiss" so the gasket was sealing.
Of course then fucking o ring expanded the second I opened the thing and I had to cut it to resize it to get it back in that thing..

Any other thoughts? I'm gonna wait a couple of days before I pull the manifold. Maybe I'll check fuel pressure just to be 100% sure.

It makes no sense that fuel pressure is fine cold idle, but not when the engine is hot idle though. That points to something expanding and causing a leak.

[modulation]

Not saying it would not run, but saying my problem was the same with too much fuel.

I was having fuel pump fuse problems at first, and when all was fixed it drove like it was getting too much fuel .
I removed fuel pump again to check and thats when i found the gas tank ring was ripped. replaced and the problem went away.

My problems were sounding almost exact to yours so i posted up to see if thats what you could check and see if that is the same problem.

I have no wide band to show the ratio, just NDS to show i was rich all the time. and under load you can tell as well.
But changed the ring and my problem was gone with too much fuel.

Sill could be a different problem than mine, but sounded simular.

Mines running way lean not rich.
Thanks for the ideas though keep 'em coming.

[burnsauto]

really sounds like a vacuum leak like steve suggested. I've had that before when i've forgotten to hook up the large vacuum tube running from the cold intercooler pipe to the manifold (i know you're still stock ka, but the principle is the same.)

[modulation]

really sounds like a vacuum leak like steve suggested. I've had that before when i've forgotten to hook up the large vacuum tube running from the cold intercooler pipe to the manifold (i know you're still stock ka, but the principle is the same.)

Yeah. It's gotta be a massive vacuum leak though so that's why I'm thinking intake manifold gasket.

My friend and I sprayed carb cleaner around the engine bay trying to get idle to rise but we couldn't.
We even plugged the tube on the manifold where the vacuum lines go out, but nothing.

I guess it might be time to pull the intake manifold.

[modulation]

I was out of town at a track day at Thunderhill (in my VW R32 since my 240sx is down.) When I got back, my fuel pressure gauge was waiting for me.

I got a new battery today, and all the proper fittings to hook up the fuel pressure gauge to the line. Fuel pressure checked out, 44 PSI. Removed plugs one by one, and put them against strut tower. Tried to start engine and all of them are getting spark. All plugs were fouled a bit and smelled like gasoline (probably because mixture isn't igniting.)

I'm going to check compression again but I've ordered the two intake manifold gaskets (got the thermal one to the head) and I guess I'll be doing a intake manifold gasket job.

I also have a coolant leak, and I'm worried that's coming from the timing cover (it's on the driver side of the engine.) The timing cover couldn't cause a vacuum leak could it?

[Rabboni]

If your fuel pressure doesn't check out then i would check for vacuum leaks again, only this time use propane. If you have a small torch laying around just attach a hose to it (unlit, obviously) and wave that around any suspected leaking areas. This will work alot better than carb cleaner because the gas is more easily sucked through a small hole.

[modulation]

I finally got the manifold off today.
There were some spots on the intake-> head gasket that indeed looked like they had fluids all the way though the gasket, as well as the fact that the coolant part of the gasket came off in two pieces.

The lower intake manifold gasket also looked like it might have been leaking but I'm not sure about that. The top one I'm 90% sure had a good leak, and might have even been letting coolant into the intake manifold. I'll find out when I get all the gaskets in, and put everything back together, probably late next week.

[jspaeth]

I finally got the manifold off today.
There were some spots on the intake-> head gasket that indeed looked like they had fluids all the way though the gasket, as well as the fact that the coolant part of the gasket came off in two pieces.

The lower intake manifold gasket also looked like it might have been leaking but I'm not sure about that. The top one I'm 90% sure had a good leak, and might have even been letting coolant into the intake manifold. I'll find out when I get all the gaskets in, and put everything back together, probably late next week.

It sounds like there was quite a bit of coolant.....but then why didn't any of your friends see white smoke coming out the back?

[modulation]

It sounds like there was quite a bit of coolant.....but then why didn't any of your friends see white smoke coming out the back?

In the beginning the problem was that bad, but in the end I couldn't even keep it running. Probably by the time it got to the point where one could see white smoke the car just wouldn't run.

[steve shadows]

I was out of town at a track day at Thunderhill (in my VW R32 since my 240sx is down.) When I got back, my fuel pressure gauge was waiting for me.

I got a new battery today, and all the proper fittings to hook up the fuel pressure gauge to the line. Fuel pressure checked out, 44 PSI. Removed plugs one by one, and put them against strut tower. Tried to start engine and all of them are getting spark. All plugs were fouled a bit and smelled like gasoline (probably because mixture isn't igniting.)


You need to check it UNDER LOAD

you need to run the gauge into a location where you can watch Fuel Pressure AS YOU ACCELERATE UP TO SPEED>

This is how you will know if your fuel pump is dying. You will not learn anything by just checking your base fuel pressure at idle.

If your fuel pump is in good shape you will see a ROCK SOLID increase 1:1 PSI of FP to boost as you accelerate and it will match the boost.

If you boost pressure is rock solid your fuel pressure is rock solid and if you boost is say 12 psi then your fuel pressure should be 44 +12 = 56 PSI of Fuel Pressure accordingly

This will tell you for sure if your fuel system is robust and working properly under load

[modulation]

The problem got worse and worse, and the car wouldn't even idle or keep running after a while.

Obviously if the car won't run or idle, but the fuel pressure is at spec according to the FSM then it's not fuel system related. That suggestion would've been great early on, but Your info's usefulness has long since expired.

How am I gonna check fuel pressure under load when my car won't even stay running?

[modulation]

#1. I used a Fuel pressure gauge. Fuel Pressure is at factory Spec.
44PSI when fuel pump is primed, and 44PSI while cranking. Still won't start.

#2. I got extra intake manifold off craigslist. Blocked off all emissions stuff.
Use idle set screw to set idle. All new gasket, used torque wrench and FSM specs/directions to put intake manifold on.

Same problem as before I redid the intake manifold.
Can a leaking timing cover cause a vacuum leak?

[k_love4life]

after you get all of those fixed that u think is the problem...try replacing the coil..or distributor if possible...it might just work..i've had the same problem..but on a different car...they really should make coil on plugs like the newer cars...dont really like these distributor and wire type especially when the coil is inside the distributor..they go out alot.-mainly becuase of the heat---u know sometimes...u see spark doesnt necessarily means your kilo-volts are up to spec to spark your fuel.

[modulation]

after you get all of those fixed that u think is the problem...try replacing the coil..or distributor if possible...it might just work..i've had the same problem..but on a different car...they really should make coil on plugs like the newer cars...dont really like these distributor and wire type especially when the coil is inside the distributor..they go out alot.-mainly becuase of the heat---u know sometimes...u see spark doesnt necessarily means your kilo-volts are up to spec to spark your fuel.

I have a spare coil so I'll try that.
I have far more time then money, so I'd almost rather do a head gasket then spend $300 on a new distributor..

[modulation]

I tried my spare coil.
No change, still doesn't work.
I still get nice blue spark.

[modulation]

The last time I did a compression test the car would idle, just buck under acceleration.

I did a compression test again and looks like I need a new head gasket..

Cylinders 1,3 and 4 were all ~180psi.
Cylinder 2 was at 150 psi..

[modulation]

My friend and I finished the head-gasket job today. Didn't fire up at first, but after he messed with the dizzy for 10-20 minute, and then it fired up and ran great.

Still gotta get the timing 100% correct, and need to buy a timing light, but at least it's running again, first time in a month or so.

I'm also a moron cause if I would've changed my oil like 3 weeks ago when I first started having problems then I would have seen coolant in it and wouldn't have spent time troubleshooting stuff that wasn't bad.
(FPR, fuel pump, and intake manifold.)