Falcon350z

iTrader: (6)

I've been battling through an issue with my Evo and I'm at a total loss... hopefully you guys can help me figure this out.

The Problem
Under WOT, around 5500 to 6500 rpms, the car will begin to sputter. Its like it hits a minature fuel cut, and then keeps on accelerating. Sometimes, it will happen three or four times (one sputter right after the other). It sounds *very* much like a hose blowing off an intercooler pipe -- but I've visually inspected the hoses and installed constant torque clamps without remedy.

It never happens below 5000 RPMs (at least, I've never noticed it), but it sometimes does happen under partial throttle at high RPMs. I have tried WOT in 5th gear at 3000 rpms, and held it without issue until 4500 RPMs (full boost). The problem seems to go away after 6500 rpms, and things seem to smooth out.

My car was purchased used, and is equipped only with a Walboro fuel pump. I reflashed the ECU back to the stock map (thanks to Mellon Tuning for providing the ROM!); aside from the fuel pump, wheels, and springs, the car is completely stock. I suspect that the restrictor pill was removed as well.

Data Logging
At first, I thought it was a boost leak issue, but I have data logged three seperate runs (3rd gear, from 2500-7000). Everytime, the boost stays consistent from spool up until the redline.

My Air Flow (Hz) seems kind of wacky. I'm not sure what the graph is supposed to look like, but there are some nasty spikes and tall peaks throughout the power band; these were relatively consistent across the three pulls I ran.

The knock is great -- since I flashed back to the stock map, I'm not seeing any problems with knock.

The Diagnosis
My first guess is that there is an airleak somewhere. Either before or after the turbo... I'm confused because the reading at the MAF sensor is seemingly spiking/dipping erratically exactly where my RPMs start to waver (around 5700+ rpms). But then why wouldn't my boost pressure be dropping as well? Also, why wouldn't I be seeing the same symptoms at lower RPMs (i.e. 60mph in 5th at WOT and full boost)?

Is it possible to have a boost leak that would be sporadic, cause a noticeable loss of power, but NOT cause a loss in boost pressure?

I guess I'm at a loss because I'm seeing the goofy spikes at the MAF -- which is well upstream of the turbo or any potential clamps. I checked to ensure the MAF is plugged in nice and tight, and it is. Could this be a filter issue?

The other potential hypothesis is that the fuel pump is shoddy, and failing to deliver. The injector pulse width on the datalogs seems to go right in-time with the MA reading, but is it possible to tell whether its actually delivering fuel? I feel like if this were the problem, I'd be getting an SES light or something... thoughts?

This is not the boost cut, but I'm wondering if this could have to do with the restrictor pill being removed. Again, my boost remains constant once it spools up; I'm guessing I'd see it spiking in EvoScan if this were an issue. Anyone know for sure? Is there any easy way to test to see if the restrictor pills were removed?

Other than that, I'm open to ideas. I'm at a loss.

I plan on purchasing a BR TBE, and a MBC to go along with the fuel pump, and then get it tuned... but I'd love to figure out what this problem is *before* I start adding power.

Here are some pictures of my three runs with the core parameters shown (there was an upshift after run 3, so just ignore that part). If you want to see anything else/have me log new parameters under different conditions, let me know...

Run #1


Run #2


Run #3

MZP@TeamD

Have you check your ignitonsystem( plugs,coils,plug wires) yet ?

Falcon350z

iTrader: (6)

Aside from pulling the plugs and manually checking the gap, is there anything I should be logging which might point me in the right direction?

subrwho

iTrader: (42)

I had the same problem. changed spark plugs like 5 times, and tried different gaps. That didn't work. . It wound up being my spark plug wires. Go to Mitsubishiparts.net They were 30$ shipped

Falcon350z

iTrader: (6)

I'll check it out... I'm going to grab a gapping tool as well as a new set of OEM wires just to make sure the plugs are gapped correctly, too.


I'm just curious as to why the MAF would fluctuate if the spark was scattering/failing at higher RPMs. Can anyone explain this for me?

I r teh Winnar

The MAF fluctuates because it is either getting too much air or not enough air coming through it at the higher RPM's.

EDIT: What is your boost at that/those RPM?

tonster

Seems like it could be a few things. Its obvious that the MAF is seeing a decrease in air flow. Which means you could be blowing spark out at that given rpm at a given boost threshold. I would check your plugs first. Gap them to .028, then go to the wires, see if you can borrow a set. Let us know what happens.

Falcon350z

iTrader: (6)

Tonster: Will do. Not sure if I can borrow wires, but I have no problem dropping the 40 bucks to get a new set.

Winnar: I do not have a boost gauge, so I can't give you an exact figure. It is the stock tune, with a stock turbo, and no boost controller. On the graphs, it is the dark green line (very level, appears right below the 50 mark on the y axis).


EDIT: Just picked up a gapping tool and a set of new OEM wires. Probably won't have a chance to install them for a week or two, but I'll update this asap. In the meantime, if you guys come up with anything else, let me know!

Falcon350z

iTrader: (6)

UPDATE


I took some of your advice and picked up a set of OEM wires from Lancershop.com... I put them in as soon as they arrived, but this didn't fix the problem.

A few days later, I pulled the plugs and took a look at them for fouling, checked the gap, etc. Everything looked fine. They were the NGK Iridium's (OEM plugs) with about 15,000 miles.

I did some research on the forums and started reading up on the NGK BPR7ES vs the NGK BR7ES. Essentially the BR's are the equivalent of about a 1/2 step colder. Since I know the car has a Walboro in it, I figured it might be running really rich causing high RPM misfires. I decided to go with the BR7ES's, and the sputtering has pretty much gone away completely.

It only sputters occassionally at around 6500+ rpms in 4th gear. I attribute this to the fuel pump, and hoping that when I get tuned this problem will go away entirely.

I'll update you as I get the car tuned, but it looks like the ignition system was the culprit afterall. I'm still not 100% sure why this would cause a loss of airflow at the MAF, but I guess the car was pulling timing? Not really sure... still have a bit to learn.

Thanks for the help...

Mellon Racing

iTrader: (38)

hey Falcon, what was the gap on the new plugs? they should be ~ .026 out of the box if I remember correctly

Falcon350z

iTrader: (6)

Ooook, so the problem is back. (WTF)


After I get the BR7ES's, I gapped them to ~.027. I did about 4 or 5 pulls in both 3rd and 4th gear to the redline, with no sputtering except around 6500 in 4th (and it was extremely minimal). This weekend, I took a road trip and the problem came back mid-drive. No idea what could have changed.

I pulled the plugs, tried gapping them wider (to ~.029) ... no luck.
I pulled the plugs again and tried gapping them closer (to ~.025) ... still no luck.

I'm at a total loss.

To recap, I'm on a totally stock tune with a Walboro fuel pump. I replaced the wires with a fresh set of OEM's, and I changed the plugs out and regapped them several times (using lancershop.com's gapping tool).

When the car stutters, there is a very (loud) audible popping noise that can be heard from the engine bay. I've checked over all the hoses a million times, and every connection is sealed tight (with constant torque clamps). I haven't done an actually boost leak test, but this is a sudden loss of power... a boost leak wouldn't be so sudden and noticeable unless a hose blew off.

Could it be a faulty fuel pump that can't provide enough gas at higher loads? Any other thoughts? If anyone has a stock Evo VIII fuel pump they want to sell me/lend me let me know...



Mellon: The BR7ES's all came out of their boxes gapped anywhere from .024-.029 as I recall.


Keep the ideas coming... thanks.

Mellon Racing

iTrader: (38)

I'd like to see the raw data in excel .. leading up to the event and during it

Falcon350z

iTrader: (6)

Name the parameters, and I'll log it up tonight.

Mellon Racing

iTrader: (38)

www.mellontuning.com has a list

Falcon350z

iTrader: (6)

Ok, here's the story...

Tonight I went out and tripled checked every coupling to make sure they were tight. I pulled all the plugs and checked the gapping, checked all the wires and coils to make sure they were snug and were making solid contact with the plugs. I scoured the engine for loose vaccum lines -- nothing there.

I took the Evo out for three runs, logged the parameters found on Mellontuning.com, and here are the results. Same problem as before... popping and stuttering persists from around 5500-6500 rpms, but is smooth after 6500 to the 7000 rpm redline.

Here are links to the .csv files for your downloading pleasure

July 23rd, Run #1
July 23rd, Run #2
July 23rd, Run #3