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View Full Version : Bucking under Acceleration, not fuel pump/filter



modulation
08-19-2009, 10:22 PM
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
08-20-2009, 11:21 AM
Well I ordered a new FPR today for $99..
Really hope that's the problem.

r20crazy
08-21-2009, 01:42 AM
did you check for a vac leak? compression test? spark plugs and gaps ok? ground wires have good contact? [I'm ASSuming you have checked these since you have resorted to other drastic measures but figured I'd ask anyway]

modulation
08-21-2009, 01:59 AM
did you check for a vac leak? compression test? spark plugs and gaps ok? ground wires have good contact? [I'm ASSuming you have checked these since you have resorted to other drastic measures but figured I'd ask anyway]

Replaced 3/4 plugs and set to minimum gap, same problem.
Replaced MAF and ECU same problem.

Ground wires look good. Vacum leak is a possibility but to be this big of a problem it would probably need to be large enough to cause problems at idle.

I'm sure my compression isn't great, but since it happened a few times intermittently I doubt I blew a cylinder and the it went back togather cool for 200+ miles and then broke again.

Thanks for suggestions though keep em coming.

duncan351
08-21-2009, 09:23 AM
Check your acutal "O2 sensor voltage" readings while driving down the road. Also check your maf voltage readings too, make sure they're linear. You can simply put a pair of vice grips on the return fuel line to rule out an FPR problem.

modulation
08-21-2009, 12:52 PM
Check your acutal "O2 sensor voltage" readings while driving down the road. Also check your maf voltage readings too, make sure they're linear. You can simply put a pair of vice grips on the return fuel line to rule out an FPR problem.

Yeah I have nistune so I can see all the logs.
The o2 sensor voltage doesn't matter under WOT and I even tried unplugging the o2 sensor but no difference.

I swapped out MAF sensors, and the same problem.
When I see the maf voltage on logs in nistune it's perfect and stable under WOT. It moves up and down with the TPS and everything so it looks great.

I've been logging for the past year, and from a electric stand-point all sensors are reading as they always have been.

I like the vice-grip idea. Wish I would have asked you guys before I got the FPR cause that would have saved me some time/money. Now that I have one I guess I'll just swap it..

You guys are awesome though thanks for the tips. I've searched lots of forums and these are some good tips I haven't seen elsewhere.

modulation
08-22-2009, 08:19 PM
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..

modulation
08-23-2009, 12:33 PM
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
08-23-2009, 04:33 PM
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.

a_ahmed
08-25-2009, 08:23 AM
I'm really curious to see what it is when you find out

HybridAndy
08-25-2009, 01:25 PM
I've got a similar issue with my car, not sure if it's the same thing.

Redtop SR20DET in a '90 S13. Motor runs fine and pulls strong from startup and usually for about 20 minutes but then sometimes, it will start to run poorly under boost. Bucking, lack of power, car can barely pull itself up hills in 3rd gear. It doesn't do it consistently (I tend to notice more often when driving home rather than in the morning) and the motor seems to run fine at low revs/off boost. Oil pressure is solid and boost stays consistent at .6 BAR, just no power. I have a Greddy EGT gauge plumbed into cylinder 1 (closest to the CAS) and the temps climb rapidly when it's doing this.

Strangest thing is, if I shut the car off, pull the key and restart, it will run fine again for a time (usually much less than 20 minutes). I'm starting to think my factory ECU is running Windows 98 and just needs to be rebooted all the time.

Chasing an idle issue right after the swap, I pulled and cleaned the IACV and replaced all the intake manifold gaskets (head to manifold, lower to upper manifold and IACV) and sent the injectors to Deashwerks (probably spelled wrong) and had them cleaned and flow tested. Turned out to be the fuel rail bolted down wrong (motor came with weird spacers between the rail and manifold).

I was still running the OE pump so I thought the issue was the 160k mile pump just getting tired and running the motor lean after it was forced to run for a while (and the ECU was pulling timing) but I recently upgraded to a Warboro 255 pump and I'm still having the issue. I'm running a Z32 fuel filter and all factory SR20 FRP setup.

Pulled the plugs the other day and they looked good (NGK Iridiums). Compression was 165-175 and I pulled the valve cover and the timing chain, rockers, shims/guides all look good. Checked the timing right after the swap and was at 15 degree at idle.

I'm starting to think maybe my o2 sensor is going south. Maybe when shutting the car off and restarted, the ECU ignores o2 sensor data (thinking it's still heating up) and that's why it runs fine again for a time. I also have a replacement ECU water temp sensor I'm going to install but I have a HKS fan controller running off the factory ECU temp sensor and it seems to be getting good data. Otherwise I'm thinking either a failing FPR or coilpack but I can't think of why a shutdown and restart would affect either of those systems.

modulation
08-26-2009, 01:34 AM
I'm really curious to see what it is when you find out

Well I hope it's sooner then later.
I won't really have much time to dedicate to it until Saturday.

Today I noticed my fuel pump doesn't prime anymore, but I think that's cause I've tried starting it so many times my battery voltage is like 11volts and I think the ecu won't turn the fuel pump relay on unless it the voltage is higher so I gotta buy a battery charger now.

I have a fuel pressure gauge ordered so I can be 100% it's not fuel. I double checked spark today and everything looks good.

If fuel pressure pressure turns out to be good, I know compression and spark are good so I guess that leaves an intake manifold leak.

duncan351
08-26-2009, 03:32 AM
Yea, check fuel pressure. See if you can find a shop in your local area that has an EVAP smoker device. I have one at my shop and we use this to check ever customer car when its complete to check for vaccum leaks. Works great. Simply cap off the intake of the turbo and put the smoker in one of the vaccum lines. Then you'll know the truth. I've personally had a few cars that had vac. leaks and didn't respond to carb cleaner being sprayed everywhere for what ever the reason but the smoker always tells the truth.

modulation
08-30-2009, 08:37 PM
Yea, check fuel pressure. See if you can find a shop in your local area that has an EVAP smoker device. I have one at my shop and we use this to check ever customer car when its complete to check for vaccum leaks. Works great. Simply cap off the intake of the turbo and put the smoker in one of the vaccum lines. Then you'll know the truth. I've personally had a few cars that had vac. leaks and didn't respond to carb cleaner being sprayed everywhere for what ever the reason but the smoker always tells the truth.

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?

slows14a
08-31-2009, 11:31 AM
What is the idle vacuum?
Definitely try the smoker or even try to pressurise your intake manifold and listen for leaks.

Some less obvious things to check are that the EGR and EGR-BPT valves and associated plumbing are ok.
Main points:
1. Check that the EGR valve operates smoothly and springs shut properly. Carbon can build up and prevent it from closing 100%.
2. Check the signal pipe which goes from the EGR tube to the bottom of the EGR-BPT valve. This has a small orifice at one end ~ 2 mm, and may need unblocking.
3. Check the hose which attaches the above signal pipe to the bottom port of the EGR-BPT valve. This hose is not great quality as mine was split on a vehicle with only 100 000 km (albeit with an SR20DET).

modulation
09-05-2009, 08:02 PM
As I said earlier right now it won't even really idle.

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.

modulation
09-13-2009, 08:45 PM
#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.

steve shadows
09-16-2009, 12:39 AM
Now that you mentioned you have Nistune you are worrying me.

What are the settings in the ECU?

100% stock? or did your nistune have a pre-loaded map on it, etc

Make sure of this also I would check your

1. Ignitor
2. Dist condition, maybe water got in there or something else
3. Spark plug wires, try to diagnose which cylinders are mis-firing more, chances are one is bad and therest are fine.

My guess is you have bad spark on one cyl and you need to just replace your spark plug wires because the connection sucks.

Make sure you are using BKRE6XI these have better tips to make contact with your wires on the inside as wellq

alan-n
09-16-2009, 01:40 AM
Another thing is do you happen to be running a SAFC, there is nothing wrong with having one provided you know what it does and not what the hype says it does. SAFC complicates things especially when improperly wired, grounded or configured.

modulation
09-16-2009, 12:51 PM
I've tried 2 different ECU's. 1 with the nistune, and 1 totally stock ECU.
On the totally stock ecu I can still use nistune as a consult cable to read and error codes and see the sensor values that stock ECU sees.

My nistune setup was running fine for 1.5+ years before this happened.
BUT I did try a 100% stock ECU too and no difference..

I'm starting to think I have a compression leak in the head gasket between cylinders.

modulation
09-16-2009, 12:55 PM
Make sure of this also I would check your

1. Ignitor
2. Dist condition, maybe water got in there or something else
3. Spark plug wires, try to diagnose which cylinders are mis-firing more, chances are one is bad and therest are fine.

My guess is you have bad spark on one cyl and you need to just replace your spark plug wires because the connection sucks.


I've pulled/replaced plugs numerous times. They look the same on all cylinders (fouled). No one spark plug is lighter then the others or anything. I know they are getting spark too though, but it's on more then just one cylinder.

The wires are less ~1 year old and are NGK's..

My friend and I pulled the dizzy and he even looked at the CAS and said it's damn clean.

When the car would run, but badly i'd pull the spark plug wire for each cylinder 1 at a time, and all of them made a difference when I pulled them, so it's not just one cylinder.

The igniter is the chip mounted on the same metal bracket as the coil right?
I will check it according to the FSM specs tonight with a volt-ohm-meter, but if it was bad wouldn't I get no spark? I've pulled the wires 1 by 1 and made sure each one gets spark.

AlligatorMan
09-16-2009, 06:34 PM
My first impression without reading the saga was MAFS/wiring. My MAF wiring started rubbing on the ps pulley and wore through...causing bad signal.

Next idea was vacuum leak...

Either that or the tune is f'd. Do you still have coolant leak?

modulation
09-17-2009, 01:43 AM
My first impression without reading the saga was MAFS/wiring. My MAF wiring started rubbing on the ps pulley and wore through...causing bad signal.

Next idea was vacuum leak...

Either that or the tune is f'd. Do you still have coolant leak?

No SAFC, No aftermarket MAF wiring.
No "tune". This happens with Stock ECU.

Only vacuum hoses I have are to FPR and brake booster, checked both of those. All new intake gaskets.

Cooling leak no, but I can't get it running so it might not leak cause of that.

I'm really starting to think it's head gasket.

modulation
09-18-2009, 09:08 PM
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..

I had changed plugs a while ago too.
When I took them out to do compression test, cylinder #2's porcelain was black, all the other cylinders porcelain was still fairly white.

modulation
09-26-2009, 07:42 PM
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 like 1 month.

modulation
09-26-2009, 07:43 PM
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.)

a_ahmed
10-13-2009, 02:03 PM
So it was headgasket ey?

modulation
10-27-2009, 12:25 AM
So it was headgasket ey?

Yep. I've driven easily over 300 miles since, flooring it all the way and all is well again.

I changed so much at once (no more emissions, no cat, no swirl control valves and new head gasket) that I can't really tell you how big of difference it made. I had the head machined too (resurfaced.)

Without the scv's I lost alot of low end torque but above 3.5K it's a whole different animal. Lots more HP up high.