AGreen

iTrader: (11)

I have a walbro 255 fuel pump, and at idle I'm getting around 50 psi of fuel pressure. Not sure if that's what it's supposed to be, but if stock is around 34-39 at idle, the walbro should put out more pressure, right?

Now here's the real problem. I started having lean issues. Idle and light cruising is fine, but part to wide open throttle is very very lean. As in it pegs my wideband at 16 AFR. This started happening after the car sat for about 2 weeks. I started by replacing the fuel filter just to verify that's not the issue. The real weird thing is that applying vacuum to the fuel pressure regulator doesn't change anything. Using a vacuum pump with the fuel pump running, it stays at 50 psi no matter what. So is the 50 psi with the FPR failed in the open position, or shut?

Additional info:
88 convertible, TII swap
MegasquirtII v.3 (nothing changed)

misterstyx69

iTrader: (142)

\the Fpr sets the fuel at 50.if it is adjustable.
if you set it at 50 it will keep at 50.The walbro is being controlled by the FPR.

AGreen

iTrader: (11)

Stock FPR. And even if it's adjustable, it should drop the fuel pressure with vacuum applied to it. I know the stock one is obviously stuck, I just want to know in which direction it's stuck?

RXSpeed16

iTrader: (41)

When paired with a Walbro, the stock fpr just can't flow enough volume to drop the fuel pressure back down to stock levels. Applying vacuum causes the fpr to open at lower pressure, not further. Think of it like an undersized wastegate and you are getting boost creep.

I measured the same numbers with a walbro then switched to an FD pump. The idle got noticeably leaner, according to my nose, so I didn't bother confirming the pressure.

As for your actual issue, I do not know MS systems at all. Maybe an air leak to your pressure sensor or tps signal is off? Then move on to physical obstruction and wiring of the secondaries. I'm sure you checked more things than you listed in your post, so just throwing out general ideas.

MMoore4545

iTrader: (7)

doubtful the fpr is stuck closed/open. If it were you'd see some seriously high pressure in the rails/lines.

+1 for it being like an undersized wastegate. although the result is slightly more fuel versus engine explosion.

I am running a megasquirt as well, so I just tuned with that fuel pressure since higher pressure = higher injector capacity.

Did your lean issue JUST start, or did it occur after you installed the Walbro?

Take a log and post it up here (if you can), I'll take a look at it.

AGreen

iTrader: (11)

Actually, a fuel pressure regulator regulates backpressure in the fuel system. It restricts more or less on the return side. So when the engine is at idle, it sees full vacuum and opens the regulator, freely dumping the return to the fuel tank, thus lowering the pressure. When vacuum is lost, i.e. opening the throttle, it shuts the regulator and increases fuel system pressure.

The reason I was asking this question was because it was working just fine before the car sat, but suddenly when I apply any sort of throttle, it goes really lean. So I checked fuel pressure, but I get 50 psi whether I apply vacuum to the regulator or not. And I know that the Walbro is a higher pressure fuel pump, which is why I was asking the question. Is the 50 psi I'm seeing with the FPR stuck wide open (thus dumping fuel pressure and leaning it out) or is it actually stuck in the shut position, giving me full pressure. This really does matter, because if, for instance, I tuned the car with a non-functional FPR, then I not only have a bad FPR, but there's another issue somewhere else. If it worked before and doesn't work now, then the ECU tune doesn't need to get changed and all I have to do is get a new FPR and I'll be on my merry way. I just want to know what fuel pressures people are seeing with a Walbro 255 lph pump, with and without vacuum applied to it.

AGreen

iTrader: (11)

I would take a datalog, but I don't want to go into those 16+ AFR's again until I think the problem is fixed. The engine is a stock S4 TII, stock ports with 550cc primaries and 720cc secondaries. I was even getting a pulse width of 11-12 ms at about 3000 rpm at about 0-2 psi, and still leaning out really bad. I haven't changed anything at all in the past couple months, it just sat for a couple weeks, then suddenly started doing this. I'm thinking fuel restriction (or starvation if the FPR is dumping all my pressure that I had before) because if the injectors are still trying to supply the same amount of fuel, it should still be in the same AFR range as before.

beefhole

iTrader: (29)

Your regulator is broken. It's obvious because with max vacuum at idle, it's not dropping. In fact you're saying varying vacuum/boost levels doesn't change anything.
50PSI is also a lot for idle. Most people run between stock levels up to 43.

I run a 255 pump as well, and my base pressure is around 43. At idle I can see it's a little under the 40 mark. I am running an adjustable aeromotive unit.

MMoore4545

iTrader: (7)

Agreed on the backpressure, what I was commenting on is that the factory FPR is a too small to handle the increased flow. I think the idea we were trying to convey with the wastegate comment is that the proverbial "flapper door" is too small to bleed off the excess fuel pressure from the rails back to the tank. So the FPR just gets slapped open based on the extra 60-70lph from our new pump. And since the fuel can't leave the rail fast enough the the rail pressure goes up because of the bottle neck created at the fpr. Beefhole has an aftermarket one so his keeps up with the 255 better.

It could be stuck totally open, I had a SARD fpr fail closed on my Starion, blew a fuel hose off the rail around 100psi, car caught fire for a very brief period.

How old is the gas? You are totally right on that it does matter. Our stock FPR "rarely fails," but if anything yours has failed open. How are you checking fuel pressure? Don't take that datalog, better not to risk it.

If it is an inline tester from the autoparts store then you may want to do the FSM fuel pump check. Key on, let your megasquirt prime the lines, key off, and see how long the system pressure holds. If it does hold 40psi for 30 minutes (IIRC) your fpr is fine. If it drops immediately to 0, get a new fpr.

RXSpeed16

iTrader: (41)

Your understanding of how the sytem should operate is correct. Problem is stock fpr is undersized with a walbro. It's like when you reeeeeeeeeaaallly need to pee after getting that 128oz big gulp from 7-11. It seems to take forever to relieve the pressure. The stock fpr also expects the pump to have an internal bypass limiting the application-specific max fuel pressure. Problem is the Walbro is a generic part set to err on the side of performance, which is much higher than most stock applications.

I'm pretty sure the fpr isn't stuck open, it's just always completely open. The vac source is also like a boost controller trying to lower your boost pressure with an undersized wastegate. You can get it it to open earlier, but not more.
I also checked pressures a while ago with a walbro 255 and stock fpr. My numbers are hazy but behavior is the same. Walbro w/stock fpr. Head pressure was ~65 (<-Should be the same as a stuck closed fpr). Pump jumpered, engine off was ~55. Idle w/vac ~52. Idle w/o vac ~52. I suspect the small drop between off and idle was because the fuel had another 'bypass' around the fpr via the injectors.

AGreen

iTrader: (11)

I didn't check the hold pressure for that long. It held 35psi for a couple minutes, but I didn't go too far with the check because I don't know what the pressure should be for a walbro. Without these known pressures, I'm just shooting in the dark. What if the walbro overpowers the stock FPR at all times? Then in that situation, I'd have tuned the car like that and it's not even the problem I'm having! I like to have hard evidence before throwing parts

AGreen

iTrader: (11)

I think I'm smellin what you're shittin here. We're all on the same page it seems. So what you're saying is that all along the FPR wouldn't be able to drop pressure anyways because the Walbro flowed so much more than stock that even with full vacuum applied, it still wouldn't lower the pressure any because of the remaining restriction in the return system. Sort of like I was saying, the Walbro probably overpowered the FPR the whole time, and the ECU was tuned like that. So there has to be some other reason as to why it's suddenly lean. I need to look elsewhere then (and eventually get an adjustable FPR and some larger fuel lines).

When I worked at a shop, one of the guys had an invaluable tool used for checking injectors. It sent a set amount of pulses at a predetermined pulse width to each injector. I think the Megasquirt has that feature. Using that tool, you would pressurize the fuel system and watch fuel pressure drop for each injector. If one injector dropped less pressure, that was the one that got replaced. If this turns out to work, I'll just send them all out to get cleaned

Thanks for the input everyone!

RXSpeed16

iTrader: (41)

We're definitely in the same room! That's the only way I could make sense of my numbers with the walbro. Agreed with everything else you said. Good luck!

sharingan 19

iTrader: (16)

Sounds like crud in the fuel system. You said you replaced the fuel filter, what about the sock in the tank? I would not be surprised if this lean issue manifested itself around the secondary staging point, which might suggest that your secondaries have been compromised. If you have already verified that they click when activated it may be time to poul them and check the baskets for sediment.

Oh, and get rid of that POS stock fpr

AGreen

iTrader: (11)

I agree. I'm going to try and do a rudimentary flow balance test here in a little bit. Unfortunately, I cant do them one at a time, so I think I'll have to pull the UIM anyways to pull the injector clips to do the test. I did find the feature that allows me to do the injector pulsing, but I'm pretty sure you have to pulse all of them at the same time. That won't tell me a whole lot, so I'm going to unhook all but one, test, repeat on the next.

I'll get right on that. Just slip me about $200 and it's as good as done

sharingan 19

iTrader: (16)

Actually w/ a mechanics stethoscope you can listen to the injectors one at a time regardless of how many injectors are pulsing. But thats only half the battle, because if there is crap in the basket they will still click but won't flow properly.

Got my while fuel setup (including fpr) for that, look harder

AGreen

iTrader: (11)

Well, between all the crap I had to do today, I just got time to go out into the bug-infested sauna outside to do the flow test. Apparently I can pulse them 2 at a time, but not one at a time. So the first thing I noticed is that the fuel pressure is STILL sitting at 35 psi. The car sat for 6 or 7 hours since I last turned the key, and fuel pressure was holding great at 35 psi. Now I know I don't have any leaky injectors at least Just for good measure, I primed the fuel system again, and still got 35 psi of hold pressure. I pulsed the primaries first, so with fuel pressure holding rock solid at 35, and 10 injection events at 10ms, it dropped down to 21psi. So that's a 14 psi drop for 2 550cc injectors. I then re-primed the fuel system, got to the same 35 psi, and pulsed the secondary injectors the same 10 injections at 10ms. This time, it dropped to 15 psi, so a total drop of 20 psi for the secondaries. Well, I guess that makes sense, since the secondaries are 720cc each. I didn't do the math, but it sounds right at least.

I'll keep poking and prodding around and eventually find this lean issue, but now I'm not so sure it's even a fuel starvation issue any more. I guess for the hell of it, I'll take the UIM off and pulse the injectors one at a time, and while I'm at it, I'll pop the injectors out to look in the strainers. Hopefully my back won't hurt so bad tomorrow so I can do this.

AGreen

iTrader: (11)

It hit me early this morning. It was a revelation really. I woke up and the first thought in my mind was "The last thing I did before parking the car for 2 weeks was adjust the timing and replace the spark plugs".

It was off pretty good too. I advanced it an unknown number of degrees. I don't know why I forgot about that! So all I had to do was take all the bins above 100kPa and increase them by 25%. Almost got it dead nuts on! Advanced timing makes for more complete burn, thus giving me the lean condition!

Sometimes... I amaze myself with the things I can forget

I'll still be upgrading the rest of the fuel system.

RotaryEvolution

iTrader: (30)

or the smog pump activating(ACV). timing actually shouldn't make that much of a difference with AFRs.

AGreen

iTrader: (11)

OOoohh... a shiny new name there Karack!

I don't have any emissions at all. I live in Georgia. 95 percent of the people couldn't pass smog here anyways. It wasn't just reading lean, it was actually lean. Popping, backfiring, the works. Didn't experience any detonation that I know of, but everything seems fine. I advanced the timing pretty good.

The problem is that I set the timing properly a few years back, but didn't do that with the installation of the Megasquirt for some reason. So the timing had been pretty retarded for some time, and even tuned in pretty decently that way. Something clicked in my brain a few weeks ago to set the timing, but it didn't click the right relay to remember that I had. Stupid brain.

Now that it's all figured out, I actually gained some decent power, as noticeable by the trusty old butt dyno.

RotaryEvolution

iTrader: (30)

well i suppose that would do it if it was really that retarded. but to clarify the issue isn't that the combustion is causing the lean issue it is the lower vacuum reading caused by the retarded ignition causing the ECU to use different map cells.

i figured it was about time if i am going to be pushing things to the next level, most people still don't even know the name of my shop that has been named the same for almost 10 years now.

anyways, good it was a simple fix. every EMS has different timing setup procedures.

AGreen

iTrader: (11)

A little embarrassed now

Well, turns out Karack was right. I guess it wasn't the timing after all. I added all that fuel and it worked great. Until today when it got straight up ***** hot outside. The car started running lean again. I then went to look at the MAT correction and found out that for whatever reason as the IAT increased, it took fuel out. Might be some kind of default setting or something. I changed it to a slight increase, and everything worked out great! Now I need to go back and take out the fuel I added, because the car did run fine, up until it got really hot outside.

My clue was pointing that way->
Now it's this way <-

Mystery solved.

beefhole

iTrader: (29)

Fuel usually is taken out when the air temps increase. Hotter air is less dense, and requires less fuel to maintain a ratio. However, it's probably only small percentages, and most of our maps take out too much fuel. I had that problem myself.

AGreen

iTrader: (11)

I'm not too sure, but it seems to work a whole hell of a lot better adding fuel. I searched MAT corrections on Google and got some conflicting answers. I thought the same thing too. Less dense air means you need to lower PW to maintain the same ratio. I'm shooting in the dark here, but what I have now seems to work.

beefhole

iTrader: (29)

I've also seen a lot of maps just leave it alone (everything zero). If air gets too hot, you should probably keep the fuel in there and run rich(er) to prevent knock. I just leave mine at zero now.