Car runs lean under boost :(

[totaleclipse_05]

Hey guys,

I've done pretty much everything I can think of, but my car still runs lean at anything above 4-5 psi. Once it leans out, it seems very slow on boost so I know something is wrong. I've searched and searched on this subject on many different forums, but can't seem to pinpoint what it is. Here is what I have done:

-New Fuel Filter
-Took off FMU and put on a friend's, but still leans out
-Thought it could have been FCD's, but have tried 2 different kinds and still leans out
-New O2 sensor

I just can't seem to figure out what it can be. I guess it could possibly be the fuel pump, but I don't know if that is a logical choice or not.

Please help me, I don't want to keep spending money on stuff that isn't the culprit.

EDIT:
Guess I should let you know what I have. I have a Walbro 255 and Vortech FMU on stock injectors only running 6 psi tops, but I have lowered the wastegate down to 3 and it stays rich on that boost level at WOT. Anything above 4-5 though and it leans out and is very sluggish feeling.

 

[Blitzeclips]

Check your plugs.
Post what they look like.
Did you check all of your lines for feul leak? Let me say that again: Did you check ALL of your lines for a feul leak? Remember, it will evaporate very quickly when only a couple drops fall, so it can be decieving. As the pressure builds with boost, the FMU should contribute feul accordingly, but if theres a leak somewhere, the higher pressure would allow more feul lost @ 5psi versus 1-2psi. So instead of a few drops being lost, you begin to squirt whereever there MAY be a leak, thus, losing more feul at higher boost levels. Check the barb fittings and your worm clamps.

Also, check the vacuum line running to the FMU. I had the silicone stuff and while tuning my car, we were encountering problems due to these lines collapsing on me. This would cut off the feul delivered by my FMU under boost. Well, it wouldn't cut it off, just give false readings. So check to see if thats pinching somewhere when you close your hood, or if it's anywhere near heat, you can easily ruin the integrity of that tubing. Mine sagged, and eventually turned out flattening from the heat.

What else have you checked? Voltage to the pump?

 

[cs82685]

Do you have the vac line for the fmu run directly to the intake manifold? If not where is it? Also check the vac line for leaks too, it might not be crushing or melted, but it may have a small leak. Oh are you sure the fmu has the 12:1 disc?

If you still can't find the problem with anything blitz said, I would spend the money for a mechanical fp gauge to put on the test port on your fuel rail then use say a small air compressor while the car is at idle to supply positive pressure to the fmu and make sure that your fuel pressure is rising accordingly. I have used this method several times to try and figure out problems, its a good way to test after making changes, much safer than actually boosting and messing up your motor.

 

[totaleclipse_05]

I just replaced the plugs last week along with wires. Plugs seemed alright. I expected them to be fouled out a bit because of my bad O2 sensor. It made it run really really rich at some times before switching to "safe mode" (check engine light, stays at stoich) at startup.

I tried DSMCrazy3's FMU and Fuel pump to weed out those and I had the same results with his stuff, so I am assuming I have a 12:1 FMU. Vacuum line has it's own port on the intake manifold with nothing tee'd off of it.

The fittings on the FMU are very VERY secure on there so I KNOW they aren't leaking. I haven't seen any leaks when I was underneath it last night either.

I figured it get's very sluggish feeling because the ECU is pulling timing because of the lean factor. I will probably try a new vacuum line and just run it alongside the car so it will be away from the heat and pinching possibilities (like from the hood alongside the car and then to underneath where the vacuum port is. Thanks for your quick replies guys. I just have run out of ideas as to what it could be.

 

[TalonESIT]

Are you sure it is leaning out? The car will bog out on you if it is leaning out, which is more than just a sluggish feeling. I can't see why your stock injectors wouldn't work out for your setup unless they are clogged, though doubtful. Do you hear the turbo spool up, but just no torque response (or acceleration)? Can you describe this "lean" condition a little more?

From experience: back when I first turbo'd the car would not build boost, problem was solved by adjusting the internal wastegate flap(was not open completely so boost was not working).

Next, I had a sluggish feeling when accelerating my car, would not build boost fast enough. That problem was due to an inadequate fuel setup, 1:1 fpr, SAFC, 275cc injectors.

Check over your vac lines also like blitz suggested. Do you have any monitoring tools? (wideband, datalogger...)

 

[totaleclipse_05]

Turbo spools and builds boost. It would be like if you were on a bike and pedaling hard and you are going faster and faster and then someone grabs your bike seat and starts to pull you back. In my car you can feel the boost pushing you until my A/F gauge reads lean and then it just kinda feels almost like NA. Car doesn't seem to go anywhere.

I tried to get a datalogger to work, but couldn't. I will probably try again on tuesday, the next day I can take a look at it. I am gonna get some vacuum line and run another line to the FMU to see if that changes anything. Also will probably test the voltage at the pump.

It's just frustrating. I've done all this trial and error and have come to nothing. Thanks for all the help so far guys.

 

[Blitzeclips]

Actually, now that you've put it that way, you may want to check for smoke when accelerating. If the power falls off like that I would do a compression test for sure. I may just be on the safe side, but that COULD be something serious. Let us know what voltage the pump check out at...

Also, how do you have your vac lines setup? What i mean is, does your fmu share a vac line with any other components? Maybe this could cause an erratic reading.

 

[totaleclipse_05]

Vacuum line is it's own dedicated line right off the manifold.

Right now, my car goes lean right away at any boost level. I had my FMU lines mixed up (stupid me ), but I fixed that today and now it leans out right away when any boost is built. Maybe the FMU is bad from being hooked up wrong? I am going to try getting a fuel pressure gauge next and see what that is. Then I will re-check my vacuum line for any rips or tears in it going to the FMU.

This just keeps getting better and better

 

[VelocitàPaola]

Are you sure that's a 12:1 disk in there? I don't recall the measurements off hand, but Vortech should be able to tell you the exact diameter of a 12:1 disk. That's the only thing I can think of that would cause this, supposing you checked all the other obvious things (fuel filter, kinked lines, etc.).

 

[BigRand]

Paul get out the diagrams again, .

Your fuel rail should have a test port on the passenger side, if you wanted to see what your fuel pressure is, you could go to a local shop and see if they'd let you use it for a sec.

 

[totaleclipse_05]

Just tried Autozone and they don't have a Fuel Pressure gauge to buy or rent out. Will have to try another auto store tomorrow.

So even like a 10:1 (as an example) would cause my car to run lean right away at the sight of boost? Because I can just be feathering the throttle around 0 and 1 psi and right when it goes into boost, it reads lean on my a/f gauge. Same with WOT

 

[VelocitàPaola]

So even like a 10:1 (as an example) would cause my car to run lean right away at the sight of boost?

Yep. If the 12:1 disk in an FMU gave you a stoichiometric AFR (which it doesn't, but it's the closest we can get) with the stock injectors, then the 10:1 disk will already give you two less pounds of fuel pressure at just 1psi of boost. You can visualize it with this little graph I made.

The effect should pretty much be immediate, but also amplified as you boost more.

By the way, the 12:1 disk is 2.72" in diameter, and it does not require a seating ring.

 

[BigRand]

just to be clear about the air fuel gauge.....are you using a wideband or narrow band?

You really need to find out what your fuel presssure is doing, and make sure that fmu is even turning on and doing what its supposed to do.

 

[DSMcrazy3]

It's a narrowband. Even though they are "worthless" we still feel it's a red flag to see it dive into red like that, even when at WOT. There is no powerloss however from the rich to lean display. I'm beginning to think less and less of the situation.

 

[totaleclipse_05]

No Josh, there is a power loss when it goes into lean. You felt it when I turned up the boost and gave it a quick floor. You even said it didn't feel as fast as it should.

The FMU I have has a seating ring for the disc. Does that mean I DON'T have a 12:1 FMU? I have pics posted up in the other thread asking if my FMU is OK. I'll find the link.

EDIT:
OK here it is:
http://www.dsmtuners.com/forums/showthread.php?t=242704

Also, on my way home I went WOT to see a little better what it does. At WOT it will boost about 2-3 psi before going lean. It doesn't gradually go lean, it dives into the lean. If I just give it gas to get into boost levels (like 1 or 2 psi) it will go lean too right away, no delay. Kinda hard to explain I know.

 

[BigRand]

The narrow band is going to react about 300-500rpms behind what is actually happening.

Get that fuel pressure gauge, you might consider buying one from jegs.com (1-2day shipping), but one that you can plug into the test port and rig it under your hood so you can see it at WOT.

Possibly get it on the dyno, and check the air fuels in numbers.

 

[Talon ESI-T]

You are at WOT correct? If you arent then that is your problem. The ECU will shoot for stoich until it sees WOT.

Now go one step farther, if your TPS is bad and the ECU never sees the TPS in WOT position then it will continue to pull fuel out to achieve stoich.

You will need a datalogger to verify this.

Next is to get a pressure gauge and make sure you are rising fuel pressure with boost. at 5psi you should have 110psi.

Terry

 

[VelocitàPaola]

The FMU I have has a seating ring for the disc. Does that mean I DON'T have a 12:1 FMU? I have pics posted up in the other thread asking if my FMU is OK. I'll find the link.

According to Vortech, the 12:1 disk has no seating ring. I'd pop the cover off and measure the disk just to be sure it's 2.72". If not, then I'd bet that's your problem right there...

All this talk about the proper disk is making me wonder if I have the correct disk in my FMU. I remember measuring it to see if it was 2.72", but I also vaguely remember having a seating ring in there too. Hmm... between my shot wastegate, and breaking in this new block, I never really had a chance to go past 4-5psi anyway. Something to check into when I get home...

 

[totaleclipse_05]

Do you measure it from end to end of the disk or something?

I've also noticed (not sure if it has anything to do with it), but when I first start it up cold sometimes it smokes out of the exhaust and smells like burnt oil kinda. Also if I try to hold the throttle down to like 2,000rpm, it sputters and doesn't hold it. Kinda fluctuates and doesn't stay at a constant rpm. Once I start driving though, it goes away and doesn't come back until just start from being sitting. ALSO, haha, when I am cruising at like just a steady 55 or so it feels like the car hesitates for just a moment. Not long at all, but I can feel it when just cruising on a flat road.

After you put down TPS sensor Terry, I began thinking maybe that could be a problem. If I feather the throttle between vacuum and boost, under boost it goes lean, but once I let off a bit to get it right around 0 and vacuum, it goes full rich. I can just barely be tapping the throttle around here and it will jump from full rich to pretty much full lean. Bad TPS? More input please. Also, how do you test something like that? Which wires to read (I believe there is 3) and what should the voltage be? Can you test it when the car is off or does it have to be running to get a voltage?

 

[BigRand]

I think you need to stop paying attention to the narrow band AF gauge, as its only useful at wide open throttle, The ECU is doing to much checking and recalibrating for it to be acurate under closed loop operation.

 

[totaleclipse_05]

Ok, well it should cycle then not under WOT right? It doesn't do that. At idle, it stays at right around stoich and rich, more into the rich though. Under WOT, it leans almost all the way.

 

[totaleclipse_05]

OK, I'm guessing this is no bueno?

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[Blitzeclips]

OK, I'm guessing this is no bueno?

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I spy your problem.

 

[selmerguy]

You will need a fuel pressure gauge to make sure your fmu works. Terry is right about the 110 psi. I had an adaptor made to go from the -4an on the test port to the 1/8 npt needed for the fp gauge. Napa can make a short hydrolic hose with both these fittings, one on each end of course. Also if the car runs good at 3 psi and then when you bump the psi to 5 or 6 it leans out you might be close to maxing out those 195cc injectors. Some cars dont do well with the fmu and stock injectors. Hope this helps

 

[DSMcrazy3]

We're pretty sure the problem is solved.. The disk was supposed to be 2.72" for a 12:1 FMU and obviously it isn't. Doesn't even reach 2.00". Tomorrow we're picking up a true 12:1 and we'll see how things go.