Major bogging and hesitation when giving throttle

2002wrxpdx · 06-01-2011, 12:22 AM

I have been over all sorts of stuff and I am finally going to post on here and see what feedback you guys might have.
Car: 2002 WRX, 2.5L Sti block, 2.0L heads, stock head gaskets, 900cc injectors, aftermarket fuel rail and regulator (same pressure as stock), VF39 turbo at 15psi, silicone turbo intake tube, short ram intake, AEM cone filter, large billet MAF housing, TGV deletes, custom reflash tune, brand new Walbro 255 pump, brand new fuel filter, brand new Oxygen sensor, brand new OEM ignition coils, good plugs gapped at .028", full catless up/downpipes, 3" exhaust.

Ever since I got the car it has idled poorly, but always ran fine once off of idle. In the process of diagnosing the bad idle, I replace several parts (coils, O2 sensor, etc).
But recently, it has developed a terrible bog when I give it any sort of throttle. major hesitation, and often some popping from the intake (mini back-fires). This has gotten worse over the last week or so, the car is now hardly driveable.

Here is what i have checked:
1. replaced the MAF with a known good MAF
2. replaced the MAP sensor with a known good one
3. checked plugs (tips are clean, no fouling, they look descent).
4. pressure tested inductions system for major leaks, etc, nothing.
5. Cleaned both MAF's with sensor cleaner, re-tried both of them.
6. Flow tested injectors, all flowing at 900cc (de-capped stock injectors) at 3Bar.
7. Installed a fuel pressure gauge, shows exactly specified fuel pressure (3 bar).

Just today I installed a new Walbro fuel pump, problem did not change.
I am not getting any smoke out the tail pipe.

No engine codes (I have the evap, TGV and secondary O2 DTC's turned off).
The only damn thing I have not checked is the throttle position sensor. But I will need to borrow a live-data scan tool to check it, I will do that in a few days.
Any other ideas of what to try???? It is killing me!

bad grocerygetter · 06-01-2011, 07:42 AM

Prob goes without saying but the car is tuned right??

2002wrxpdx · 06-01-2011, 08:52 AM

Yes, the custom reflash tune is in there. Like I said this bogging is relatively new and has gotten gradually worse over the last week.

bad grocerygetter · 06-01-2011, 09:47 AM

Hmm. Anyway to do a compression and or leakdown on it?

pzr2874 · 06-01-2011, 10:41 AM

You clean or replace the IACV lately?

2002wrxpdx · 06-01-2011, 11:32 AM

Did a compression test about a month ago, all was good, since then I have not beat on it at idles.
it starts and idles fine (well, idle has always been somewhat shaky, but for now it seems good.)
i can't give it more than 10% throttle or it lurches, bogsand bucks.it is either pulling timing or getting inaccurate inputs from maf or tps.this sucks.
i about to take it to a shop....which I hate doing.

pzr2874 · 06-01-2011, 12:26 PM

Couple buddies of mine had similar issues that you have and it was 2 different issues, one was the IACV and the other was one injector that had the wiring backwards (DW believe it or not).

You have a way to datalog or monitor anything?

2002wrxpdx · 06-01-2011, 04:12 PM

Isnt idle irrelevant when I am into the throttle? And it idles pretty well too.
Also, since injecors are just solenoids, they dont have polarity.
I honestly do appreciate all the input. Sometimes a suggestion can lead to a solution , even if the suggestion itself is not the solution..

BLAZE2099 · 06-01-2011, 09:44 PM

Quote:

Originally Posted by pzr2874

You clean or replace the IACV lately?

get a new gasket for it and try it, this sounds to be your cause as I was thinking the same thing while reading your list of things done to try and solve.
pretty sure that unabomber over on nasioc has a how to for this as well, maybe its in his manifesto?....GL

....................CHEERS!!!

BLAZE2099 · 06-01-2011, 09:46 PM

oh, and did you check your BPV for leaks?, that would give you those same exact symptoms.

I know you stated you checked for leaks, but that just sounds too dead on.

pzr2874 · 06-02-2011, 05:51 AM

Quote:

Originally Posted by 2002wrxpdx

Isnt idle irrelevant when I am into the throttle? And it idles pretty well too.
Also, since injecors are just solenoids, they dont have polarity.
I honestly do appreciate all the input. Sometimes a suggestion can lead to a solution , even if the suggestion itself is not the solution..

It was something "backwards" on it... Maybe the pins. Engine rocked like it had no motor mounts but acceleration was "ok" till the gas was released and afterfired like a MF.

Not to be a stickler, but who did the pump install? Did you play with the intake manifold or the fuel lines at all ?

2002wrxpdx · 06-02-2011, 11:45 AM

I have cleaned the idle valve, back when I was diagnosing a poor idle a month or so ago. I reinstalled with a brand-new idle valve gasket from the dealer.

I installed the pump a few days ago as an effort to diagnose the surging/stumbling/seizure it has.
It did not effect the problem (not better, not worse). But It was good because I wanted a Walbro in there anyway, and this gave me an excuse to get it done.

Yes I have had the intake manifold off, reinstalled with all new gaskets, same problem. The fuel rails are plumbed up with -6AN hose and fittings.

As for the BPV, it is recirculating back to the turbo inlet tube (as it should be).
Here is how I check for leaks:
I take off the cone air filter from the intake and put a plastic cap with an air fitting into the coupler and tighten the coupler clamp down.
I dial down my air compressor to 15 psi and hook it up to the fitting on the intake. Then I listen and look for leaks. I also spray questionable areas with soapy water and look for bubbles. This method works pretty well, I can hear even the smallest leaks. It is all solid and leak free.

Last night I pulled out all the injectors. In the #1, there were some very small metal chips in the inlet on the injector. Luckily each injector has a small screen on the inlet, this is where the chips were. Maybe this is from the IXIZ Concept fuel rails. I cleaned it all out blew air through the injector while activating it with a battery and reinstalled all the injectors (I cleaned all of them out). I also celaned out the fuel rails and lines, but nothing came out of them.
I also swapped in my other MAF sensor, just for the hell of it. I have been alternating between the 2, but usually it doesnt help.

The first couple minutes of a test drive and it seemed better. Then as I got down the road a mile or two, it all came back. I swore out loud and wanted to drive off a cliff.

Here is the deal, it is pretty much OK up to 2500RPM, then it bucks violently and stumbles, I can rev through it and stops bucking at 3500RPM. I dont want to rev it up becuase of this problem, so I am stuck driving around under 2500RPM.

$25 Paypal to anyone who solves this!

pzr2874 · 06-02-2011, 11:54 AM

AHHAHAA... ^^ Better be no fees... j/k

Did you have the issue B4 the fuel rails went in ?

Another question... I like Ming as much as the next person.... But why did you get new rails ? Are you running a Garrett 40R ?

Just an idea but put the stock rails back on and see if it does it...

2002wrxpdx · 06-02-2011, 01:43 PM

Quote:

Originally Posted by pzr2874

AHHAHAA... ^^ Better be no fees... j/k

Did you have the issue B4 the fuel rails went in ?

Another question... I like Ming as much as the next person.... But why did you get new rails ? Are you running a Garrett 40R ?

Just an idea but put the stock rails back on and see if it does it...

I got new rails because I was swapping injectors in and out diagnosing the bad idle, The stock rails made it a pain in the ass. Way easier to pull ou the injectors with these rails. Also, my stock fuel rails were rusted all over the outside, and the regulator was all seriously rusty too. this used to be an east coast car.
The stock rails were corroded so bad, one of the mouting tabs broke off. They are long gone in the trash.

Yes, it has run fine with the new fuel rails and regulator. I am running the exact same fuel pressure as stock. I checked before and after the install.

2002wrxpdx · 06-02-2011, 07:06 PM

Here is a new clue. I borrowed an OBD2 scan tool that lets me watch live data. During the bogging/bucking event short term fuel trims shoot up to +25% which means the computer is trying desparately to add fuel. So I am thinking it is a fuel delivery problem.
I am going to take it all apart tonight and test everything.

I have another set of injectors to put in, but they are 600cc. I am currently tuned for 900cc. ANyone know how to rescale injectors with ECU Flash software?
thanks