MBC on BOV line - relation to fuel cut?

[j_eclipse96]

Hi. Could having my MBC tee'd to my BOV line cause or relate to me having fuel cut at 16lbs?

 

[CanadianTSi]

Your hitting Fuel Cut at 16lbs because you have a boost leak.

 

[MrBoxx]

But you still shouldn't tee the BOV line for your MBC.

 

[j_eclipse96]

Did an extensive boost leak test today.. tightened all my couplers and everything, and all the common places for boost leaks have been looked at or repaired.. even the throttle body shafts. Still hitting fuel cut at 16 lbs. Forgot to mention that, sorry.

I know I should tee it off of something else, but my j-pipe doesn't have a nipple on it, and everything else is far away. Any ideas?

 

[zippyshoe]

You could drill and tap your j-pipe and install a nipple on it - I don't have any personal experience in doing this, but I'm sure there are forum members that have done this and could give you some guidance.

If you are certain that you have no boost leaks and are still hitting fuel cut at 16psi of boost, then you may need to turn your boost down a bit until you upgrade your injectors and install some type of fuel controller. This will delay the onset of fuel cut until you reach higher airflow numbers, allowing you to increase boost. You may also want to verify the accuracy of your boost gauge, if possible.

 

[j_eclipse96]

Alright, thanks zippy. Next time my j-pipe is off, I'll drill and tap for a nipple on it.

I know that some of my silicone couplers are the cheap ebay brand, and a couple have pinhole leaks in them. But it did not seem like air was leaving my system very fast at all during the test, and my system is sealed better than it ever has been. Could a few pinhole leaks be enough to cause fuel cut this early?

 

[dsm-onster]

CanadianTSi is right. I hit fuel cut at 15 1/2 psi w/ a stock long block, 2.5" free-flowing exhaust, small fmic, and 14b; and 14psi w/ the small 16g.

If you wern't hitting fuel cut before then you were right at the edge. It may be getting a little cooler now in Wisconsin.

Also, your BOV could be venting prematurely because of the bleeding effect of MOST Manual Boost Controllers. This could cause a large boost leak. I've seen BOVs leak on boost when running a "bleeder valve" boost controller, that would seal durring a boost leak test.

 

[zippyshoe]

Alright, thanks zippy. Next time my j-pipe is off, I'll drill and tap for a nipple on it.

I know that some of my silicone couplers are the cheap ebay brand, and a couple have pinhole leaks in them. But it did not seem like air was leaving my system very fast at all during the test, and my system is sealed better than it ever has been. Could a few pinhole leaks be enough to cause fuel cut this early?

Any type of boost leak will inflate your mass airflow numbers to some extent - Like dsm-onster indicated, you may be at the hairy-edge of fuel cut at 16psi on the 14b. A small boost leak may be enough to put you over the threshold for fuel cut. Even after you fix any remaining boost leaks, you may still want to turn down the boost a hair to give yourself a little safety margin - at least until you upgrade your injectors and install a fuel controller. This may minimize your chances of hitting fuel cut in the coldest winter months, when the air is denser.

 

[dsm-onster]

. . . at least until you upgrade your injectors and install a fuel controller. This may minimize your chances of hitting fuel cut in the coldest winter months, when the air is denser.

HAHA! this is when I first felt the symptoms of fuel cut. I tuned well in the summer of 2004 and november rolled around and I played w/ it down a back road. . . BAM! . . . I still have the teeth marks on the steering wheel .

 

[zippyshoe]

HAHA! this is when I first felt the symptoms of fuel cut. I tuned well in the summer of 2004 and november rolled around and I played w/ it down a back road. . . BAM! . . . I still have the teeth marks on the steering wheel .

Yeah, reaching fuel cut sounds like a pretty frightening experience. I've never had a chance to experience it first-hand since I upgraded to DSMLink before I had a chance to turn the boost up high enough to reach fuel cut. Now since DSMLink eliminates fuel cut altogether, I guess I'll never have a chance to experience it.

 

[j_eclipse96]

HAHA! this is when I first felt the symptoms of fuel cut. I tuned well in the summer of 2004 and november rolled around and I played w/ it down a back road. . . BAM! . . . I still have the teeth marks on the steering wheel .

If you are speaking literally, maybe I'm not hitting fuel cut then. Mine doesn't jerk nearly that hard. Or at least it doesn't seem like it anyways. The engine just sounds like it misses hard, and jerks the car firmly. I can even keep on the gas and the RPMs will keep rising after it cuts. It always happens around 5k though.

But I've never had my head come anywhere near the steering wheel.

 

[oldman]

CanadianTSi is right. I hit fuel cut at 15 1/2 psi w/ a stock long block, 2.5" free-flowing exhaust, small fmic, and 14b; and 14psi w/ the small 16g.

Matt, that is way too early for fuel cut, my old 16G use to creep up to 23+psi before fuel cutting, sounds like you HAD some serious boost leaks.

 

[dsm-onster]

Matt, that is way too early for fuel cut, my old 16G use to creep up to 23+psi before fuel cutting, sounds like you HAD some serious boost leaks.

That is entirely possible. This was before I had built my own boost leak tester. I would just ensure the clamps were tight . . .

j_eclipse96, fuel cut feels very drastic. It you have to let off the gas to go over the rpm that you reach fuel cut. . . At least in my case.

 

[j_eclipse96]

Alright, thanks guys. I'm going to put a barb fitting on my j-pipe this week, and hopefully that eliminates my final boost leak. I have a ball-and-spring type MBC, but I've read they can cause boost leaks when tee'd to the BOV line as well.

Just to verify: To my understanding, having my MBC tee'd to my BOV line is basically a boost leak, as the air going to the MBC will open up the BOV before I want it to. Correct?

 

[oldman]

Just to verify: To my understanding, having my MBC tee'd to my BOV line is basically a boost leak, as the air going to the MBC will open up the BOV before I want it to. Correct?

Correct. On a side note,

1. What was the air compressor regulator set to during the test?

2. How many PSI were you able to register on the BOOST GAUGE during the test?

3. Is your 2G mas hacked?

j_eclipse96, fuel cut feels very drastic. It you have to let off the gas to go over the rpm that you reach fuel cut. . . At least in my case.

Anyone who (hitting fuel cut for the first time) kept their foot on the gas pedal after hitting fuel cut instead of slowing down while checking the rear view mirror for scattered engine parts is either not hitting fuel cut OR crazy.

 

[j_eclipse96]

1. I'm not sure, it's a little cheap one from a hardware store, so I either push air in until it either hits where I want it to, or until the tank runs out of breath. The compressor on there is worthless; it takes roughly 10 minutes to fill a small tank. So I just fill up the tank with air and then push it into the system.

2. No one was home to watch for me on the last test, but I know before I replaced my 14b (which had bad oil seals, and leaked a ton of air into the crankcase via the return line) I could get up to ~16lbs before it started to drop off. The system is much more tightly sealed now, though, since I just upgraded to a like new b16g.

3. No. I personally haven't touched it, but the previous owner was a tard. I'm pretty sure all the honey combs are still in there though. Isn't it a bad idea to hack the 2g MAS anyway?

About the fuel cut: I've been fixing boost leaks for awhile now, and every time I've fixed one, I'd take her out for a whirl with the boost up to see if I still had cut. And every time, I did. So maybe I've just gotten kind of numb to the shock of it. I remember the first time I hit it, though, I screamed "HOLY SH*T! So THATS what they were talking about."

 

[dsm-onster]

Anyone who (hitting fuel cut for the first time) kept their foot on the gas pedal after hitting fuel cut instead of slowing down while checking the rear view mirror for scattered engine parts is either not hitting fuel cut OR crazy.

Well, I wouldn't classify myself as crazy. . . very foolish. But, a DSM will grow up any joe. I bought the car from a guy who took me in it to show me what fuel cut feels like. So I wasn't exactly surprised when I hit it while driving myself. . . Well, I was surprised and shaking a little, but then I did it again to see what else would happen. Very childish!

The car was a mess when I bought it. The timing belt had been replaced, but not the BS belt(which later broke). The cam timing was off just enough to give it a he!!ish lope and a scary quick spool but no top end. The ignition timing was consequently way advanced and the stock maf was being overrun, so there was knock everywhere . . . So likely a boostleak was present .

2. No one was home to watch for me on the last test, but I know before I replaced my 14b (which had bad oil seals, and leaked a ton of air into the crankcase via the return line) I could get up to ~16lbs before it started to drop off. The system is much more tightly sealed now, though, since I just upgraded to a like new b16g.

A 10 gallon air tank at 60 or so psi should fill her up good and have plenty left over. Set the crank for about 30 after TDC (a tip from Bruce). It should take 15-20 seconds to bleed back to zero.

I can't believe that I nor anyone else has asked: do you have a logger?

 

[j_eclipse96]

Yes, I do. When I log though (I haven't done one yet with the b16g, as I'm trying to solve the FC issue, and my PDA has been acting funky), I always got really low ignition timing advance. I'm talking 15 or 16 at the top of third and fourth at 15 psi. I never saw more than a degree or two of timing being pulled, though, and that would usually be in the lower end. I just assumed it was because I was running pig rich do to boost leaks. Could my base timing maybe be off as well?

 

[dsm-onster]

Yes, I do. When I log though (I haven't done one yet with the b16g, as I'm trying to solve the FC issue, and my PDA has been acting funky), I always got really low ignition timing advance. I'm talking 15 or 16 at the top of third and fourth at 15 psi. I never saw more than a degree or two of timing being pulled, though, and that would usually be in the lower end. I just assumed it was because I was running pig rich do to boost leaks. Could my base timing maybe be off as well?

Well, look at your % injector dutycycle. This is an indicator of whether or not you are having fuel cut issues. If you're running into 100% IDCs, then fuel cut is likely.

Log your maf hertz as well. I can't remember where the approximate hertz count is that activates fuel cut (you'll have to research), But if you're hitting this wall at the same hertz level everytime then that is another clue that supports fuel cut.

If your ecu is dropping the rpm reading at the same rpm everytime this may lead to a fuel-cut-like symptom. So look at your logged rpm curve. Also, can you ease it to red line and not hit this wall?

16 degrees at the top of 3rd/4th is dead nuts factory for a 2g, not 'really low'.

 

[j_eclipse96]

I have a 2g; I can't log IDC. Good idea though.

I'll try and log my MAF hertz next time I'm in my car. I believe its 2.55 or something close to that, but I'll look it up first.

Yeah, I can ease it to redline and not hit fuel cut.

Alright haha, good to know about the timing. My bad.

 

[dsm-onster]

I have a 2g; I can't log IDC. Good idea though.

Thanks. I don't work on many 2g DSMs. I spaced on that one .

If you can ease it to redline w/ no "hicups", then it is not rpm based. It is so much looking like fuel cut. I'm SURE you have more boost leaks with which to content. You just need to find them!

 

[oldman]

1. I'm not sure, it's a little cheap one from a hardware store, so I either push air in until it either hits where I want it to, or until the tank runs out of breath. The compressor on there is worthless; it takes roughly 10 minutes to fill a small tank. So I just fill up the tank with air and then push it into the system.

That is what I call cheating. You have to be able to regulate output to about 20-25psi, a 3 year old can pressurize the intake tract to 15psi even with huge leaks when the tank output is at 60psi.

2. No one was home to watch for me on the last test, but I know before I replaced my 14b (which had bad oil seals, and leaked a ton of air into the crankcase via the return line) I could get up to ~16lbs before it started to drop off. The system is much more tightly sealed now, though, since I just upgraded to a like new b16g.

What was has nothing to do with what is, especially because you have installed a turbo since. You need to repeat the test and have a friend watch your boost gauge, with the tank output set to 25 psi, you're looking for no less than 20psi on the boost gauge while taking no less than 30 seconds to bleed down to 0. Just to give you an example, I just did a leak test last weekend on my 90', with the compressor regulator set to 30psi, I was able to pressurize to 25psi and it took about 4-5mins before it bled down to 0. I don't expect everyone to achieve this but you have to come close.

Until condition 1 & 2 is satisfied and verified, your previous leak tests are basically meaningless.

3. No. I personally haven't touched it, but the previous owner was a tard. I'm pretty sure all the honey combs are still in there though. Isn't it a bad idea to hack the 2g MAS anyway?

It is a terrible idea indeed, my question was not to encourage hacking, quite the opposite.

 

[dsm-onster]

What was has nothing to do with what is, especially because you have installed a turbo since. You need to repeat the test and have a friend watch your boost gauge, with the tank output set to 25 psi, you're looking for no less than 20psi on the boost gauge while taking no less than 30 seconds to bleed down to 0. Just to give you an example, I just did a leak test last weekend on my 90', with the compressor regulator set to 30psi, I was able to pressurize to 25psi and it took about 4-5mins before it bled down to 0. I don't expect everyone to achieve this but you have to come close.

Well your excellent results could be from running a larger compressor tank than someone elses, right?

The regulator set for 30 psi means that it will allow air from the presurized tank to rush in to the line (and consequently the intake tract of your car) until 30 psi is reached. A large tank w/ high psi will take MUCH longer to bleed down than a small tank. So what size tank are you running? That would give me a good estimate on how "tight" my system is. I have a 33 gallon compressor. Back w/a 10 gallon airtank that I filled at a gas station (before I got this compressor), I could hold positive pressure for 20 or so seconds w/ tank pressure starting at 30 psi . . . W/ this 33 gallon tank I can hold 30 psi for well over 10 minutes! The tank is pressurizes to 140 psi by default. The regulator has a separate gauge, of course, to regulate it to whatever psi I want. I hated using the airtank to test for leaks because I only had abotu 5 or so seconds to really hear any boost leaks.

If my larger tank bled down to zero (consequently the intake bleeds to zero) in 30 seconds, wouldn't that mean I had a HUGE boost leak?

 

[oldman]

Well your excellent results could be from running a larger compressor tank than someone elses, right?

The regulator set for 30 psi means that it will allow air from the presurized tank to rush in to the line (and consequently the intake tract of your car) until 30 psi is reached. A large tank w/ high psi will take MUCH longer to bleed down than a small tank. So what size tank are you running? That would give me a good estimate on how "tight" my system is. I have a 33 gallon compressor. Back w/a 10 gallon airtank that I filled at a gas station (before I got this compressor), I could hold positive pressure for 20 or so seconds w/ tank pressure starting at 30 psi . . . W/ this 33 gallon tank I can hold 30 psi for well over 10 minutes! The tank is pressurizes to 140 psi by default. The regulator has a separate gauge, of course, to regulate it to whatever psi I want. I hated using the airtank to test for leaks because I only had abotu 5 or so seconds to really hear any boost leaks.

If my larger tank bled down to zero (consequently the intake bleeds to zero) in 30 seconds, wouldn't that mean I had a HUGE boost leak?

I have an 8 gallon 120psi tank. The size of the tank should have no bearing on how quickly the system bleeds down since the bleed down time starts after the compressor/tank is removed from the system. My last test was done with a cold motor so I suspect most of my bleed down is coming from the piston rings. My 1G bov starts to bleed at about 17psi, reason why I was only able to achieve 25psi although the compressor regulator was set to 30psi. My 25psi bleeds down to 17psi relatively quickly, in about 30 seconds, then about 1psi per 20 seconds to about 5psi and kinda lingers there for a while. I'm certain with a better holding BOV and a fully warmed up motor, the results will be even better.

BTW my tests starts at the beginning of the LICP since some pressure will always be lost through the turbo seal into the crankcase during a static intake pressure test, I did however test from the turbo inlet as well to make sure the well known compressor cover backplate was leak free.

 

[dsm-onster]

I have an 8 gallon 120psi tank. The size of the tank should have no bearing on how quickly the system bleeds down since the bleed down time starts after the compressor/tank is removed from the system. My last test was done with a cold motor so I suspect most of my bleed down is coming from the piston rings. My 1G bov starts to bleed at about 17psi, reason why I was only able to achieve 25psi although the compressor regulator was set to 30psi. My 25psi bleeds down to 17psi relatively quickly, in about 30 seconds, then about 1psi per 20 seconds to about 5psi and kinda lingers there for a while. I'm certain with a better holding BOV and a fully warmed up motor, the results will be even better.

BTW my tests starts at the beginning of the LICP since some pressure will always be lost through the turbo seal into the crankcase during a static intake pressure test, I did however test from the turbo inlet as well to make sure the well known compressor cover backplate was leak free.

AH! I built my pressure tester w/ a male compressor line quick release fitting. I'll have to disconnect the line from the compressor tank since that end has the self-sealing female quick release. . . Thanx