User 52121

Ok... posting this up for the collective since I am out of ideas. Been having lots of help from John @ Vitesse already and I think he's starting to run out of ideas too.

Issue is the car is running lean at WOT. To the point where the car stumbles when you first hit WOT and bogs until you lift off of WOT.

What's on the car:
- Vitesse MAF (stealth) and injectors with appropriate Vitesse chip
- Wired for piggyback w/Vitesse MAP and Boost Solenoid but currently all disconnected, chip running in straight MAF mode (non-V-Flex)
- 3" Exhaust, no cat
- TiAL 38mm, .8 spring, no boost control at the moment (just running the spring.)
- Lindsey braided fuel lines
- 3bar FPR
- Hyperboost DV (fresh about a year ago, I replaced it when the stock BOV was leaking. All metal construction.)
- Venturi delete
- Stock CV delete

New (*brand* new, changed just this week):
- Fuel pump
- Fuel filter
- 3 bar FPR
- Injectors
- Plugs and wires

Checked:
- Fuel pickup sock in tank. Clean.
- Fuel pressure @ idle: 44.5-45.0psi w/o vac line on FPR. 39psi w/vac line.
- Pressure tested intake system, from big end of J-boot, through J-boot, through turbo, through intercooler. No leaks (once I plugged the AOS line.)
- My personal DME, KLR, and MAF all checked out by Vitesse (I overnighted them down to him, he tested on his personal car, came back A-ok.)
- TPS. Smooth operation across pins @ DME. Idle switch verified A-ok as well, tested @ DME pins. Both done per Clark's Garage procedure.
- "Full Load" signal verified @ DME when going WOT as well.
- Ohm'd out wiring to injectors from DME. 0.3 ohms - looks good.
- Piggyback wiring has been checked over about a dozen times now. All wires are as they should be. As mentioned earlier, currently the shorting plugs are in place and the chip is running on Map 1, which is non-V-Flex, non-PB, etc.
- All vacuum lines are updated to silicone. Mityvac'd the entire system, it all holds fine.

Waiting to be checked:
- Injectors. En route to Vitesse now.


Symptoms:
- Right as you hit WOT, there is a stumble/bog. Stumble/bog is independent of boost level or RPM. Does it at 1500rpm, does it at 4500rpm. To me (former engine software engineer), my dad (current engine software engineer), and another buddy of mine (owns a speed shop) it feels like a "hole" in the map. Like a multiplier or something is off in a table and it goes lean when you hit WOT and it goes to that table. But as already mentioned, John plugged my entire DME and KLR into his car and it ran 100% perfect, nice and rich under WOT. So it's NOT a map issue. (Or even an issue with anything to do with my physical DME, KLR, or MAF sensor itself.)
- Watching the O2 sensor w/a volt meter, it's around .78v @ WOT. VERY lean.
- If I set the FQS to position 3, stumble/bog goes away, O2 sensor reads .89v @ WOT. Still lean but better. I *should* be blowing diesel-levels of black smoke out the tail pipe @ FQS 3 though.


If the injectors aren't the culprit... then I have NO idea. John @ Vitesse has been super diligent about following up with me, working with me to figure out what the heck is going on. This has been going on for a few weeks (I was out of town, then had family stuff... so it's been a slow-ish process.) We're starting to test the stuff that's "out there" and are still coming up empty. It's obviously something to do with my car and not the Vitesse stuff (or the interaction between the two... but definitely not the direct fault of the Vitesse stuff as it works perfectly fine on another car.) But I'm kind of at the point where, since my car ran fine previously (stock AFM + Welt chip) I'm just going to go back to that and abort the whole MAF conversion project. That or see if I can sucker some other Chicago-based Rennlister into loaning me their truck and trailer so I can drag my car down to Atlanta so John can look @ it himself. Otherwise I'm just not sure what else to do here.

*sigh*

Anybody got any wacky ideas that they think might be the culprit?

mudbuddha

How about cap and rotors? Also check your DV/BOV valve- if stock, rubber diaphram maybe torn/blown.

User 52121

Updated my list. Car has an updated DV/BOV on it. Holds vacuum fine on the diaphragm side. Pressure test from J-boot (DV was installed) held pressure fine, no leaks there.

Did not check cap and rotor. I suppose I can... though I'd expect that if that were the problem, I'd go rich, not lean, since it wouldn't be burning all the fuel in the chamber and a lot of unburnt fuel would be passing by the O2 sensor.

mudbuddha

Try to recall if you did anything differently to the car right before this symptom started...ie. running it harder, more boost, change refueling location etc...When did this started, maybe bad tank of gas? I am just thinking it through and perhaps you can fill us in if anything occurred that is outside of the norm.

CPR

Jim,

Went through this EXACT same thing with a VERY similiar set-up.

Did two things tht cleared the problem right up....problem is I did them both at the same time, so I am not sure if both were an issue or just one.

~Installed new TPS
~Installed new main ground (battery to block) and thoroughly sanded/cleaned block contact patches & installed new gold ring terminals on smaller (#8awg) grounds at same location and adjacent location.

Problem immediately went away and has not returned (8months).

gt37vgt

I assume with such a beast you fitted an 044 or 090 pump ?
have you ruled out running out of pump ? although it seems a bit drastic for just a pump..installing a clear return line for a bit is the way to check ..
it also does seem very TPS if the DME sees closed throttle above 1500 or 1800 (can't recall) it kills the injectors .. so a crook TPS or posibly crook TPS loom can cause havik..

tjbreen

I had similar issues and ended up buying second Vitesse MAF, 044 pump, and replacing a lot of good sensors and vacuum lines. You and I are lucky, majority of cars go rich on boost due to air leaks.

Check or replace ground and power cables with Ice Shark kit from Robby.
Check fuel pressure while under boost, difficult to do safely but will eliminate fuel as an issue.
Check for leaks in the exhaust manifold, cracks may let scavenged fresh air into the system.

I had/did all these things and now run in the 11.5 region with two track events done.

Do you have a SMT-8 (not SMT-6)? Is this a Vitesse unit?

User 52121

In reverse order...

@gt37vgt - "Beast"? Aside from the mods referenced, the car is stock. Stock 26/6. The new fuel pump... not at home, not sure what the Bosch P/N is, but it was a new Bosch pump from my local foreign car parts place.

@CPR - Ok I cleaned all the grounds, and added a 2nd battery-block cable a few months ago when I was trying to clear up a low voltage issue (which eventually turned out to just be a missing alternator cooling duct.) TPS.... John has said this too. I've verified everything on the TPS to be within spec. Idle switch engages and disengages as it should. Resistance on the potentiometer is also within spec (per Clark's Garage anyways.) In the case you ran in to - did the TPS measure out to be within spec? I just replaced the TPS a year ago, but can be convinced to fork out the $$$ to try a new one if it's likely that the TPS is bad even though all the tests seem to say the TPS is good.

@mudbuddha - Same fuel I always run. And am actually running LESS boost now than I was before the swap of parts (haven't had time to configure/calibrate the boost solenoid yet.)

Thanks for helping with the brainstorm guys. Once I get it sorted I will definitely post up the cause.

JohnKoaWood

Have you checked your Fuel Damper? How old is it? I know what it is SUPPOSED to do, but...

ALSO are you data logging when you drive? If so can you post the logs, or pictures of them, when you go into your WOT / lean stumble?

Have you leak checked your exhaust?

ALSO what SIZE injectors are you running? I see you mention the injectors, but not the SIZE of the injectors.... BSFC of .6 @32 lb injector should be yielding 215 HP (stock FPR, 245ish at 3 bar) at 100% duty cycle, or there abouts, variation based on FP... you could be hitting the upper limit on your injectors....

FWIW, most injectors are not happy being run at 100% DC, rather it is a good idea to have a safety margin of 10-20% DC, meaning you should be running at 80-90% DC MAX...

Have you tried running larger injectors? 55lbs would give you more room... 72s would give you even MORE room, but might be close to under driving them....

Check out the injector calculators @ whitchhunter...
http://www.witchhunter.com/injectorcalc1.php4

User 52121

Fuel damper was replaced at the same time as the TPS, about a year ago, has maybe 5-6k on it.

Size injectors is a good question. I bought 'em from John @ Vitesse at the same time as I bought the MAF, etc. on his recommendation so I would assume they are the correct size for the software. (Though I shipped them back to John Saturday so he could test them out himself on his own car and verify there wasn't some kind of mix-up and I wound up getting the wrong size injectors.)

I have a log I took from when the SMT-8 was still hooked up but it didn't show much other than AFR saying it was lean (John also reviewed the log and didn't see anything jumping out at him.) I could post it up but it's on my machine at home though. (Usually I work from home... just not today.)

tjbreen

As far as fuel pressure, have you tried a new or different FPR? If you had a sticky FPR it could cause fluctuations if it sticks while rising or falling. FPR varies fuel pressure on boost and vacuum, so when I said boost, I really meant non-steady state fuel pressure (positive and negative boost). I used my Motive brake bleeder and a Mity Vac to feed pressure and vacuum to the FPR while the engine was running and charted output pressure using a Lindsey pressure gauge that screwed onto the end of the fuel rail.

I have a spare 3bar Bosch and a Lindsey fuel pressure gauge I could send you to test.

User 52121

Low fuel pressure theories is what caused me to replace the FPR, fuel pump, and filter last week. Long story short - I had a local mechanic test the fuel pressure for me since I didn't have a fitting for the end of the rail. I didn't write the numbers down but remembered them as 29 w/vac line connected, 39 w/o vac line.... which is low. Now I could have remembered the numbers wrong, but the mechanic is 70 miles away, I didn't want to drive back down there. So I just swapped out everything to new stuff (FPR was new but a year old, sitting in my toolbox... fuel pump was of unknown age so I figured I might as well change it.) After swapping everything out, the behavior didn't change. So I had a friend of mine make me an adapter to fit the fuel rail, and retested the fuel pressure myself. That's how I got the 44.5-45.0psi numbers. Most likely I mis-remembered the numbers the mechanic gave me. The old FPR I took off the car was new.

minho78

Jim those are the same readings I get on my car. 29 with vacumm connected 39 with vaccum disconnected after I started the car.

2bridges

replace tps and try again. Have had intermittent issue myself with an ocasionally possesed TPS.
Next check would be wiring issues, injector harness/connectors, etc.

User 52121

You are running the stock 2.5bar FPR, correct? If so, that is the correct pressure for a stock FPR.

My car has the 3bar FPR, so I am expected to run a little higher pressure than with the stock 2.5bar.