Fuel cut and boost leak test

[Momar]

Well, I bought this car not running. I repaired head(bent valves) and installed stainless valves. I have installed a 20g, walboro255, 650cc injectors, and a 2g maf. I installed a translator from my friend, but it is not working so back to 2g maf for now.

I am hitting boost cut, but I am not sure if it is just from the flow of the larger turbo, or if I have other problems(I know that the 2g maf is not an exact match to the 650's). I am hitting the cut running only 10lbs of boost. I made a boost leak tester today, and hooked it up. The first leak was major. It was the lower ic hose. I fixed that, and a couple smaller ones. Took it for a test drive and it still cuts but spools much quicker. Now not until almost redline though instead of 5000 rpm. I tried turning the boost up and it hits the fuel cut hard at much lower rpm. Still hardly makes it past 10psi before this happens.

I will say that when I did the boost test I could still hear some air leaking through the engine, but I didnt set the engine at any specific point, so I think I am going to try it again and try to get it set so that valves are not overlaping and see if I can come up with anything else.

I just wonder what you guys think with my mods should I be hitting boost cut at that low of boost? I know that turbo flows pretty good, but I dont even really have it turned up. I plan on getting another translator and wideband eventually as well as other mods, but on a budget. I figured I should be safe to run over 10 pounds of boost though if I can get it to stop fuel cutting.

If this turbo really does flow enough that it is fuel cutting right now with the 2g maf, will adjusting a translator for the 650cc injectors be enough to avoid it?

Thanks
Ben

 

[1995gsx20g]

i never really messed with a MAFT but i can tell you that it is not advised to be messing with injector sizes and MAFT's without a wideband.

Fuelcut occurs because the ecu sees a maf value that is to high. this could be because the turbo is really flowing that or because the MAFT isn't setup properly and changing the actual values higher than what they are or because you still have boost leaks.

the best way to look at it is to look at what would make the maf values exceed the limits in the ecu.

 

[Chicken Patty]

I think what you need to do from here on is try to get a hold of a logger. With a logger you can see your o2 voltage or I think it's called o2 feedback trim. This guide tells you how to tune with a data logger and how to watch your o2 voltages and such.

From there on you can then start to compensate a bit with your MAF-T little by little until you are able to fool the ECU a bit more so that you can run more than 10psi. However, keep an eye on the Timing Advance, too much timing and you'll knock, timing tends to rise when you compensate too much either via a MAFT or a SAFC or a piggyback of some sort.

It would be ideal if you get a wideband for this as it is more precise than o2 voltage, but that'll help you get started at least.

 

[kmj 4g63t]

First off, what is the flow of the turbo. Lbs/min the ecu starts to go omfg at 35-37lbs/min and will cut fuel, if your turbo is flowing over 35lbs/min then yes it's fuel cut. Safc can reduce this airflow reading and prevent the fuel being cut. If you don't have a safc, get one because that will help you A LOT!!!!!

 

[Momar]

I have done more testing, and found a couple more leaks. I will post back with details in a little bit. I do want to get a logger soon. As far as the safc/translator, the translator can lower the airflow that the computer sees like an safc. The translator actually has specific settings for base injector size. Since mine are 650's I would set it to compensate for those which should allow me to flow more air before hitting fuel cut. The problem is that the translator that I have is bad so I will have to get another before I can do that. I also want to get a logger in the near future.

Ok. Anyway, other leaks I found:

First the idle air bleed or whatever it is called was leaking around the threads. I checked how many turns out it was then pulled it out and put thread tape on it and reinstalled to where it was.

Next it had air leaking somewhere under the throttle body. I couldnt tell where it was coming from, but could feel and hear air movement. I think it may have been the egr. I have the throttle body and egr off right now. I have new gaskets for them and will reinstall in the morning and recheck.

I could also hear something else that I hadnt been able to track down yet, but I got to thinking and I bet that it was the pcv valve, so I am going to test it once everything is back together as well. I did use soapy water on the hose connections, throttle body and intake gaskets, and injectors. Didnt find any leaks there. So with any luck the new egr gasket, and a new pcv valve will have most of my problems solved. Then I will be able to see if it is still going to fuel cut.

 

[Chicken Patty]

I have done more testing, and found a couple more leaks. I will post back with details in a little bit. I do want to get a logger soon. As far as the safc/translator, the translator can lower the airflow that the computer sees like an safc. The translator actually has specific settings for base injector size. Since mine are 650's I would set it to compensate for those which should allow me to flow more air before hitting fuel cut. The problem is that the translator that I have is bad so I will have to get another before I can do that. I also want to get a logger in the near future.

Ok. Anyway, other leaks I found:

First the idle air bleed or whatever it is called was leaking around the threads. I checked how many turns out it was then pulled it out and put thread tape on it and reinstalled to where it was.

Next it had air leaking somewhere under the throttle body. I couldnt tell where it was coming from, but could feel and hear air movement. I think it may have been the egr. I have the throttle body and egr off right now. I have new gaskets for them and will reinstall in the morning and recheck.

I could also hear something else that I hadnt been able to track down yet, but I got to thinking and I bet that it was the pcv valve, so I am going to test it once everything is back together as well. I did use soapy water on the hose connections, throttle body and intake gaskets, and injectors. Didnt find any leaks there. So with any luck the new egr gasket, and a new pcv valve will have most of my problems solved. Then I will be able to see if it is still going to fuel cut.

Keep in mind, setting it to 650's might be too much compensation, you'll have to get a logger or preferably a wideband to make sure you are not leaning out the car too much when compensating. That's why before you proceed even if yours worked or you got a new one, you need AT LEAST a data logger.

As far as leaks, remember if you have a boost controller, they leak, that's what they are supposed to do. They bleed off just like if you ran a "T". So you have to cap off the boost controller, that may be the air you hear escaping that you can't track down because you probably didn't look there, if you haven't that is.

For the TB, you might want to replace the gaskets and put a touch of silicone on them as well, just for a bit of extra sealing.

 

[Momar]

Keep in mind, setting it to 650's might be too much compensation, you'll have to get a logger or preferably a wideband to make sure you are not leaning out the car too much when compensating. That's why before you proceed even if yours worked or you got a new one, you need AT LEAST a data logger.

As far as leaks, remember if you have a boost controller, they leak, that's what they are supposed to do. They bleed off just like if you ran a "T". So you have to cap off the boost controller, that may be the air you hear escaping that you can't track down because you probably didn't look there, if you haven't that is.

For the TB, you might want to replace the gaskets and put a touch of silicone on them as well, just for a bit of extra sealing.

Ok, well a wideband is in the plans. I have one on my bike, and have been tempted to swap it over temporarily. . I ordered a palm, datalogging cable and software. I should have that all by friday hopefully. I dont believe my engine has the timing marks anymore. Were they on the lower timing belt cover? I know that if I pull balancer off there is the tdc marker, or I can look at cam sprockets and line up tdc. Where is it that I need to line up to avoid having valve overlap? I think that may be what I have going on. I think I may just. I replaced egr and throttle body gaskets since I already had them laying around. Didnt find anything that seemed like it was leaking there other than the idle air bleed and I already fixed that.

Oh, as far as the boost controller I just have the lines connected straight from the wg actuator to the fitting on the compressor housing while I am testing.

 

[spyderturbo007]

The first thing you need to do is a thorough boost leak test, and I mean thorough. What are you pressurizing the system to and how long does it take to bleed down?

You shouldn't be messing with injector sizes and compensation without a logger especially when you said yourself that they don't match. That's just asking for trouble. So, until you get the logger, put the airflow and fuel system back to stock. If you do those two things, I'm convinced she will run just fine.

 

[LiquidX]

I agree, minute adjustments could make or break running fine but you have no idea what is going on. Any boost or vacuum leaks will completely throw off your tune as well.

Get a logger and then start messing with the trims.

 

[Momar]

Cant put it back to stock. The car had the 650cc injectors when I bought it. I also bought it not running with bent valves. I didnt even recieve a mass airflow sensor with the car. My buddy had a 2g laying around so I wired it up. It is whats on the car now. I have a translator and a 3"gm maf but it is not being used because the translator is bad. I do want to get another at some point, but I dont have it yet, and I will have my logger by then. Like I said in my previous post, I did buy a logger, and it should be here tomorrow.

As far as the boost leak test, if you read my last post, you would see that I was asking about where to set the motor so that it wont have overlap and flow through the motor. I have fixed all the boost leaks I find but I still hear air flowing through the motor. The only leak I found that I could not fix, is that it leaks around the throttle body shaft a little. Other than that I have no boost leaks between the turbo, and the throttle body. Just need to get engine turned right so that it doesnt have overlap so that I can time how long it takes to leak down. I have it hooked to a compressor and an adjustable regulator, so it doesnt leak down unless I close the regulator because the tank keeps it presurized even with the air flowing through the engine.

And by the way guys I am not new to tuning. I just got this car running though, and am on a budget. I was just trying to work some bugs out before I get a wideband so that I could get it running at least around stock boost pressure. I am anxious to get the datalogger so I can see whats going on with my fuel trims and such. I have tuned my grand national in the past. Had some slight tuning experience with megasquirt on a friends camaro, and I totally tuned my 08 hayabusa. The busa has a flashable ecu though, and I set up my wide band logger to have the same tables as my flashing program though, so it was super easy.

 

[spyderturbo007]

30 degrees ATDC is a good place. I would hold off running the car until your logger arrives tomorrow and we can see what the ECU sees. That's going to make this much easier. You'll want to fix the leak at the TB because any leak is going to play games with your tune.

 

[Momar]

Ok. So basically I am just looking at replacing the throttle body right? I wouldnt know any other way to fix the leak on the tb shaft.

 

[1995gsx20g]

Throttle Body Seals

 

[Momar]

Thanks for the link to those seals. I went ahead and ordered them. The car alreay runs better, and think/hope that is my last leak. The price was not bad, but they charged 8.95 for shipping. Damn.

I changed the plugs today. They were the ones that were in the car when I got it. It had 1 autolite plug, 1 bosch plug, and 2 ngk factory style plugs. I gapped the new ones(ngk) to .028. 2 of the ones I pulled out were smashed real tight, and 2 were real loose on the .028 feeler gauge. Just getting good plugs in it made it run better. Supprisingly though, all of the plugs had a nice tan color to them like the afr was realitively close.

I did a compression test while I had them out and it shows 140 across the board.

I cant wait for the data logger to come. Now got to wait for those seals and get that fixed. I hate waiting for stuff.

 

[spyderturbo007]

Sounds like you are on the "road to recovery". What we are suggesting might not make things perfect, but it's much easier to start with the small things first. Either way, we'll all hang in here until you get things worked out. Well, maybe not me because I go on vacation in a week.

 

[Chicken Patty]

Looking much better! 140 was with the engine cold right? If so I believe that's good.

 

[JayRolla]

The 2g maf can make over 400whp easy and I have personally ran over 32psi on one with no fuel cut. Meaning it has to be a boost leak issue.

 

[Momar]

The 2g maf can make over 400whp easy and I have personally ran over 32psi on one with no fuel cut. Meaning it has to be a boost leak issue.

Ya, but when you were running 32psi what injectors were you using and im guessing you were using a safc? If so that will definately allow you some more room. I do have a boost leak still at the trottle body shaft. I ordered the seals, but cant do anything with it till they show up.

My logging stuff didnt show up today. Hopefully tomorrow. I am anxious to use it and see what it says. I know that my numbers will be kind of off until I get those throttle body seals changed, but still cant wait to hook it up.

 

[Momar]

My datalogger came yesterday. I guess I only got enough drive time to show any change on my low fuel trim, but it dropped down to 87.5% I figure that in the low fuel trim that if anything that throttle body seal is a vacuum leak, not a boost leak which would make it run leaner, and it is still pulling fuel. Under boost, I was reading in the .8x range on the 02 sensor when it first hits boost and shoots to the .9x range. It actually was hitting around .97v under boost. So it is definately running rich. I am going to wait and see how it acts after I fix the boost leak on my throttle body. Once I get my translator repaired, I will use it to see about taking out some fuel.

 

[JayRolla]

My datalogger came yesterday. I guess I only got enough drive time to show any change on my low fuel trim, but it dropped down to 87.5% I figure that in the low fuel trim that if anything that throttle body seal is a vacuum leak, not a boost leak which would make it run leaner, and it is still pulling fuel. Under boost, I was reading in the .8x range on the 02 sensor when it first hits boost and shoots to the .9x range. It actually was hitting around .97v under boost. So it is definately running rich. I am going to wait and see how it acts after I fix the boost leak on my throttle body. Once I get my translator repaired, I will use it to see about taking out some fuel.

Ive ran the 2g maf with no fuel management, safc, maf-t and with dsmlink. I never had a fuel cut issue. I also ran a 1g maf at over 18psi on a 16g. Its got to be caused by the boost leak all together.

 

[Momar]

Ive ran the 2g maf with no fuel management, safc, maf-t and with dsmlink. I never had a fuel cut issue. I also ran a 1g maf at over 18psi on a 16g. Its got to be caused by the boost leak all together.

I hope thats right. I cant wait for these damn seals to come in, and all usps shipping says is that they recieved shipping info friday. Ready to get rid of this anoying fuel cut. . The logger shows the maf at 1599 hz when the fuel cut happens. That must be the highest frequency that the ecu will accpet I am guessing.

 

[JoshJosh]

Good luck

 

[Momar]

Well, I got the seals replaced today. Now that boost leak is fixed. It still didnt really change how the fuel cut acted. idle seems a bit more stable. I went ahead and removed outer screens on the 2g maf. My fuel trim had previously read around 87.5. Now with the screens removed the trims went to 98.4 or something like that. I didnt drive far so it was only my ftrl that changed. With the screens removed it seemed that I might have got a few hundred rpm more before fuel cut.

After I replaced the throttle shaft seals I did another boost leak test. It kind of worrys me. The throttle body leak is fixed. I can still hear air flowing through the system. I dont find any external leaks. I did however find that it seems to be leaking into the crank case some how. I am not sure what to do exactly from here?

 

[Momar]

Well, upon doing some more searching and thinking about the air flowing out of my crank case, I ended up reading about pcv systems. I understand how they work under vacuum, but I guess from what I read that the fresh air tube is also supposed to vent excess crank case pressure when the engine under boost. The line from the factory runs to the intake tube inbetween the turbo and maf. Well, I did not have any fitting on my intake tube to hook up the line too. I decided to fix that. So now, my fresh air side of my pcv is hooked to the post maf intake tube. This actually seemed to make a difference. I only took the car on about a half mile ride, but it seemed to help. I still hit fuel cut, but it seems to let me rev farther before it hits. I will have to get some more drive time to see whats going on.

Any other suggestions welcome.

 

[NOSLO2PT0]

I just came across this thread. I'll try to add my $.02 in here since I've read some bad info already.

I dont believe my engine has the timing marks anymore. Were they on the lower timing belt cover? I know that if I pull balancer off there is the tdc marker, or I can look at cam sprockets and line up tdc. Where is it that I need to line up to avoid having valve overlap?

The lower timing belt cover has the marks to set base timing. If you didn't replace that when you put the timing components back on....I suggest ya do so, unless you want to just guess where your base timing is. Not a good idea on a boosted motor. Personally, I grab a paint pen, white-out, whatever I can find that marks white, and put a mark on that tic mark on the crank pulley (balancer) and re-install the lower timing cover so you can set base timing to 5* BTDC. Don't need to worry about valve overlap when setting ignition timing. It's when you set mechanical timing with adjustable cam gears that you worry about valve overlap and valve-to-valve contact.

As far as the boost leak test, if you read my last post, you would see that I was asking about where to set the motor so that it wont have overlap and flow through the motor. I have fixed all the boost leaks I find but I still hear air flowing through the motor. The only leak I found that I could not fix, is that it leaks around the throttle body shaft a little. Other than that I have no boost leaks between the turbo, and the throttle body. Just need to get engine turned right so that it doesnt have overlap so that I can time how long it takes to leak down. I have it hooked to a compressor and an adjustable regulator, so it doesnt leak down unless I close the regulator because the tank keeps it presurized even with the air flowing through the engine.

No way to close ALL the valves during a boost leak test, unless you pull the cams out. And that's way more work than most are willing to do. This is best way to boost leak test the car. Set your regulator on the air compressor to a STEADY 40psi (with the trigger on the airgun pulled). Pressurize the intake system and start spraying soapy water onto every single square inch of any piece or part that has to do with the turbo, intercooler piping, fmic, couplers, vacuum lines, throttle body, intake manifold, etc. Spray everything ALL WHILE YOU ARE HOLDING the trigger on the airgun. Then start looking for bubbles. The bubbles will tell you where the leaks are.

I changed the plugs today. They were the ones that were in the car when I got it. It had 1 autolite plug, 1 bosch plug, and 2 ngk factory style plugs.

Gap is good. What brand and part number plugs did you go with? I would stcck with BPR7ES's for your setup. If your local store doesn't have the BPR7ES, you can safely use the BR7ES plug as well.

I figure that in the low fuel trim that if anything that throttle body seal is a vacuum leak, not a boost leak which would make it run leaner, and it is still pulling fuel. Under boost, I was reading in the .8x range on the 02 sensor when it first hits boost and shoots to the .9x range. It actually was hitting around .97v under boost. So it is definately running rich. I am going to wait and see how it acts after I fix the boost leak on my throttle body. Once I get my translator repaired, I will use it to see about taking out some fuel.

Boost leaks WILL make the car run pig rich, even more so than what the factory ECU is programmed to run. These cars are set to run around 9.8:1 at WOT in the heaviest load cells. Still, anything in the low 10.x:1 range is way too rich, and any boost leak will add to that rich state. .90-.92V is a good, safe pump gas tune for a narrowband.

I The logger shows the maf at 1599 hz when the fuel cut happens. That must be the highest frequency that the ecu will accpet I am guessing.

1606Hz is the limit of a regular datalogger in terms of actual measured airflow.

Well, upon doing some more searching and thinking about the air flowing out of my crank case, I ended up reading about pcv systems. I understand how they work under vacuum, but I guess from what I read that the fresh air tube is also supposed to vent excess crank case pressure when the engine under boost. The line from the factory runs to the intake tube inbetween the turbo and maf. Well, I did not have any fitting on my intake tube to hook up the line too. I decided to fix that. So now, my fresh air side of my pcv is hooked to the post maf intake tube. This actually seemed to make a difference. I only took the car on about a half mile ride, but it seemed to help. I still hit fuel cut, but it seems to let me rev farther before it hits. I will have to get some more drive time to see whats going on.

Any other suggestions welcome.

That doesn't do anything for your fuel cut issue. It just creates another vacuum source to suck out any excess oil vapors that build up in the head/valve cover area. A stock 1G MAF will hit fuel cut around 15-16psi on a 14b turbo. That 20G flowing 10psi is probably close to what a stock turbo will flow at 15-16psi. Boost leaks will always make you hit fuel cut faster. The ECU sees a certain airflow limit and cuts spark. Boost leaks inflate that airflow amt. Lets say you are seeing 10psi on the gauge, but have 8psi worth of leaks. Your MAF is showing the ecu 18psi worth of airflow, so it's going to fuel cut.

Cheapest way to get around this. Grab an AFC (Apex'i Air Fuel Controller. Get em as cheap as $100 used) and pull out about 22% of fuel. The 650's are about 44% larger than stock. The 2G maf flows approx. 22% more air than a 1G does while metering the same amt. The AFC adjusts fuel compensation by altering the airflow levels the ECU sees. You set the AFC to -22% and it will pull out 22% of air, which results in a 22% decrease in fuel. When the ECU sees the 22% less airflow, it doesn't fuel cut, AND you bring the injectors somewhat back in line to where they are supposed to be.