Surging/Thrusting Problem Under Acceleration
 

Greetings YotaTech!!!

Long time lurker, first time poster and hoping someone might be able to help me out with a problem I'm having with my truck. First off, I've got a 2004 Tacoma with the 5vz v6 and manual transmission. It used to have a TRD supercharger and URD AIC and 7th injector kit. Both have since been removed in trying to troubleshoot the problem.

So...symptoms. It feels very similar to a misfire, but without the sound a misfire normally makes and it's not consistent. Its more of a thrusting/surging feeling as if it is accelerating normally, and is if i for a second lifted off the accelerator pedal, and then mashed on the pedal again, and then repeats several times like a rocking chair. Only happens under load (moderate acceleration and is much more noticeable going uphill). Only happens between 2000-3000 rpm and mostly only noticeable in 2nd to 4th gear.

I tried starting with the basics and working from there, but I'm really out of ideas at this point.
I have absolutely no check engine fault codes or any previous stored codes.
Brand new factory NGK spark plugs (Old plugs looked like normal wear, greyish/brownish color. If anything there's a minor amount of carbon soot deposits and minimal electrode wear).
Brand new air filter.
Brand new fuel filter.
I've inspected the coil boots thoroughly and they look absolutely fine.
I changed both the fuel pump when I did the URD 7th injector kit for the supercharger less than 20k miles ago. Fuel pump is actually a larger 190 lph pump.

As far as cleaning goes, I seafoamed, cleaned the MAF, and cleaned the throttle body.

I've inspected and measured according to the Factory Service Manual (resistance, voltage, etc):
1) Plug wires
2) Coils
3) Camshaft position sensor
4) Crankshaft position sensor
5) Air/Fuel Meter (AFM) sensor (Pre-cat O2 sensor)
6) Post-cat O2 sensor
7) Mass air flow (MAF) sensor
8) Throttle position sensor
9) Throttle control motor (both motor and clutch resistance)
10) Pedal position sensor

As part of eliminating possibilities, I've completely disabled the URD 7th injector kit and pulled the supercharger off completely and back to factory intake manifold.

I measured fuel pressure at idle with the vacuum sensing hose disconnected from fuel pressure regulator and measured 48 psi. I connected the fuel pressure regulator to a vacuum port on the intake with a brand new vacuum line, and the fuel pressure dropped to 44 psi. Turned off the truck and let it sit for 5 minutes. Fuel pressure only dropped to 40 psi.

I also left the fuel pressure regulator disconnected from vacuum and snaked the fuel pressure test kit into the cab of the truck and went for a test drive to see what happens while I'm experiencing the problem. Fuel pressure is consistently at 48 psi EXCEPT when the surging happens. When the surging happens the hardest, the fuel pressure gauge flutters ridiculously fast between 42-48 psi. I mean so fast I almost didn't notice it at first. I did 4 passes up and over the hill in third gear and every time the truck surged at its strongest, the fuel pressure gauge fluttered at light speed. http://i.cdn2.tacomaworld.com/forum/...as/notsure.gif
If I lift off the throttle or go WOT, it goes steady back to 48.

Also along the lines of fuel and as part of eliminating possibilities with what I had, I still had 4 old fuel injectors from a previous 5vz engine. I swapped 3 injectors out at a time and test drove in between, same exact symptoms, no change.

On the next hunch I disconnected the A/F sensor (upstream 02) completely from the truck. Took it for a test drive, of course thru a check engine light....but no more surging problem!!!! This leads me to believe the problem has to due with fuel management in closed loop.

That said, I've replaced the A/F sensor and the MAF sensor, but with no positive results and I'm at a complete loss as to where the problem is now or what other sensors come into play with fuel management.

Thanks in advanced for any thoughts!

The good news is, I found my pliers I lost a year and a half ago when I swapped the supercharger on this engine http://i.cdn2.tacomaworld.com/forum/.../anonymous.gif



http://i1014.photobucket.com/albums/...871104ACB0.jpg

So you are supercharged? It sounds like it is cutting fuel for some reason. It is possible that you reached the limits of the MAF sensor but seems unlikely sicne I was running a 2.0 pulley with meth injection and didn't have a problem.

Something is causing the fuel injectors to stop flowing though, either a short or most like the ECU if when you disconnect the O2 it works fine.

Is your speed sensor working right? If it thinks it is over 110mph it will cause fuel cut.

Unless I missed it, have you replaced the fuel filter? I had a surge/stumble issue a few years ago and it was due to a restrictive fuel filter.

As mentioned, I WAS supercharged. In troubleshooting this problem, I'm back to natural aspiration with the factory intake manifold and still experiencing the problem.

Speed sensor is just fine. I swapped out the gear in the transfer case years ago, my speedo is dead nuts on. The problem is not speed specific, but rather load specific.

Yep, also mentioned in the OP. Fuel filter is brand new along with plugs, air filter, MAF, and A/F sensor.

Well it sounds like some sensor is out of whack causing the ECU to go into fuel cut mode or a short someplace.

I would start by logging the OBDII outputs and watching for anything that matches up with the surging. Might get lucky and notice a sensor is shorting out or something.

Yeah I'm waiting for my TIS Techstream cable to get here.....

Swapped coils, plug wires, AFM, and MAF from a buddies truck. No change in my problem.
May have to break down and take the truck to a mechanic.

Check the OBDII stream first, sounds electrical and is most likely a sensor or short.

I'm inclined to agree. Unfortunately I don't have a scope to test to the TPS (which is my new suspect) and still waiting on my cable for Techstream.
I did read loads of crap specific to the 2003-2004 tacomas specific to the throttle bodies especially those that were supercharged + 7th apparently due to heat. I believe the 3rd gen runners adopted the same throttle body earlier (2001?). The throttle body itself is completely drive by wire. There's only a mechanical linkage between the pedal itself and the accelerator pedal position sensor mounted on the front of the throttle body. Toyota in all it's wisdom does not sell the TPS or the APPS separately. You have to buy the entire effing throttle body for a meager $1000, which is still $700 my cost. I think I'd rather let a pro sweep the sensor and tell me its bad before dropping that kind of money.

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Relative links:

http://www.ttora.com/forum/showthread.php?t=140995
http://www.ttora.com/forum/showthread.php?t=13283
http://www.ttora.com/forum/showthread.php?t=16753

Dead on to my symptoms:
http://ttora.com/forum/showthread.ph...81#post2206381

Sounds like you're having fun with this... looks like you've covered the fuel supply thoroughly... by chance have you checked for vacuum leaks? Any unmetered air will cause all sorts of problems with a MAF system... make sure your PCV system is hooked up correctly too... it is quite possible that you're right about the throttle body, although I would think it would throw a code... good luck hope you figure it out with a scan tool

Vacuum leaks:
I emptied two bottles of carb cleaner and a bottle propane searching for any. If there's a vacuum leak, I'll be damn surprised.

PCV:
I tested it per the FSM and it tested fine. Also as a test I pulled the PCV out completed, vented the valve cover to atmosphere and capped the vacuum port to the intake and went for a spin. Same symptoms.

The most compelling thing I've found so far is I go WOT, my symptoms are gone. ECM goes into open loop. If I disconnect the A/F meter, I of course get a MIL, but my symptoms also go away. Disconnecting the A/F forces the EMC into open loop due to connection malfunction with A/F.

a TB issue doesn't jump out at me as being the cause if what you said about the fuel pressure is true. A video would help a lot to see what exactly is going on.

If the fuel pressure is bouncing around like that in time with the stuttering then that indicates that the injectors are ceasing to fire as that is about the only thing that could cause that kind of fluctuation. Why it suddenly goes into fuel cut? That I don't know.

Techstream software is actually nice. Lots of features and graphing functionality, but didn't help me one damn bit. Swept the TPS with Techstream and swept the TPS with a voltmeter. It swept fine, but the refresh rate is slow. Still need a graphing meter or oscilloscope to see if there are any small blips but I went as slow as I could and numbers were completely consistent.

As for the fuel pressure bouncing, ya got me.

Video below.
Skip till after I shift into third around 5 second mark. Around 15 second mark is where you can hear the problem most noticeably if you're listening to the sound of the intake. The back and forth of the camera is from the thrusting the truck is making. Don't have a video of the Fuel Pressure as that was just a rental tool.

Hmm, well that doesn't sound like what you were describing. That seems a lot more gentle unless I am hearing it wrong. I heard it breakup with what sounded like a misfire once or twice.

With the OBDII scanner try turning everything off except the item you are wanting to log, that generally speeds up the refresh rate. Then just watch them all and see if anything jumps outs.

If not then it gets a bit more complicated. That video does make it sound like it could be the TB afterall, I was expecting sharp misfire style stuttering which would be too fast for the TB to be the cause. But that much slower response could be it I guess if it is a known problem.

Maybe some kind of malfunctioning traction control system?

What happens if you go WOT?

Thankfully I don't have any traction control or vsc crap with my truck, so that's certainly not the problem.

As for going WOT, problem goes away. Any time I go to open loop, surging stops, whether it's induced by throttle, or forced induced by disconnecting sensors.

Too bad you don't have a wideband that might help a lot.

Goddamnit. I'm out of ideas.
I swapped throttle bodies complete with TPS and APPS sensors and put in my old fuel pump and still the same damn problem.


By the way, thanks for your help and ideas thus far Texas_Ace. I certainly appreciate it!

Ok so, on a separate hunch, I unbolted my exhaust after the first cat and slid it to the side. I unbolted here rather than before the first cat because it's only two bolts and the first cat also has the AF sensor bung as part of the same piece. This bypassed the secondary cat completely and the downstream O2. Aside from it being mind numbingly loud, my truck is running like an effing raped ape and I'm not feeling any surging. Granted it's difficult to feel anything with the exhaust as it is now, but holy piss it is pulling with more power than I've felt in a long time.

Can a plugged cat cause this?

Mystery solved!

The second cat was plugged up tighter than an asian virgian's ass. Pix below are all taken from the direction of exhaust flow. Notice the last picture which shows some light barely shining though. That was the brightest damn flashlight I have and you can barely see it.

After the test drive without the second cat I just gutted it completely and bolted it all back up. Truck ran fantastic after that and no more surging. Got back a ton of power that I thought I may of lost but was sure it was all in my head. Put my supercharger back on and it's running like a bat out of hell again. When I get some time tomorrow I'll drop the tank, but the larger fuel pump back in and go back to a smaller pulley, piggyback and 7th injector and be happy as a pig in shiet again.

Thanks for everyone's input, especially Texas_Ace.

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Yep, that would do it.

That most likely happened due to skyrocketing EGT's due to either no extra fueling with the supercharger or a bad tune on the 7th injector.

Get a wideband and check the tune ASAP. EGT's that high are not good at all for anything.

You want AFR's in the 11's (11.8 being about ideal) the ENTIRE powerband at WOT. The tune that came with my URD was completely wrong and I had to start over from scratch to make it work.