No BOOST leaks, still hitting Fuel Cut @ 12psi!?!

[SnowBird]

I fixed all the boost leaks I had, some major, some minor. I still hit fuel cut/backfire at about 12-13 psi. I use to be able to hold 15psi through all the gears all day long.

The only thing thats changed since that set-up is a different block, different 14B (The old one was blown still holding 15lbs), a N/A head w/exhaust gear retarded one tooth, and my FMIC (which has no leaks). My intake mani, and all lines/electronics are the same.

I understand I shouldnt even get a cut until around 20psi on the 14B. Im leaning towards my Maf or something. Oh, and my FP is rewired too. Is there something Im missing?

Any insite is much appreciated, this is annoying as hell.

 

[GSX93DSM]

The only thing I could think of is the timing. Try putting it back to stock and see what happens.

 

[SnowBird]

You mean the timing on the cam or the base timing?

 

[dsm-onster]

I hit fuel cut at 15psi with the 14b and everything else stock. If you could do a pull with a log, we can tell you for sure if it's not fuel cut. Log grams/rev. The reason why it is possible that it is fuel cut is that you have ALOT of overlap if you have the n/a intake cam and retard either the turbo cam or the n/a cam. The n/a cam has alot of advance. I think this could drastically alter your grams/rev in the mid range. Just a thought.

 

[SnowBird]

I hit fuel cut at 15psi with the 14b and everything else stock. If you could do a pull with a log, we can tell you for sure if it's not fuel cut. Log grams/rev. The reason why it is possible that it is fuel cut is that you have ALOT of overlap if you have the n/a intake cam and retard either the turbo cam or the n/a cam. The n/a cam has alot of advance. I think this could drastically alter your grams/rev in the mid range. Just a thought.

With retarding it a tooth it should only be about 2.5 degrees retarded, still too much? Maybe I should just switch out to turbo cams, its just a straight forward swap right? No clearance issues or anything?

 

[beezwax]

fuel filter?

 

[dsm-onster]

With retarding it a tooth it should only be about 2.5 degrees retarded, still too much? Maybe I should just switch out to turbo cams, its just a straight forward swap right? No clearance issues or anything?

48 teeth on the cam sprocket. 360degrees / 48 = 7.5 degrees per tooth. Crank rotates at 2X cam speed. 7.5degrees X 2 = 15degrees per tooth. . . That's alot. But retarding the exhaust cam one tooth was a common free mod in the early days. You still have too much intake cam advance running an n/a cam, if you left that cam in the head. I don't know if this is causing you to reach maximum g/sec (fuel cut) earlier or not. But it's probably not good for topend power regardless.

Best thing is to log a run when this fuel cut occurs. Have you checked your base timing? You timing could be too advanced and you could be running into massive knock causeing the ecu to yank timing. The ecu will also completely close the boost control solenoid if timing retard doesn't stop the knock. But you're running JUST a MBC correct?

I just looked at your profile you have upgraded to the 7cm^2 turbine housing. Was this done before when you were able to run 15psi without fuel cut? I definately feel alot of overlap and a bigger turbine will encourage fuel cut earlier. Also the temperature and/or elevation will change when fuel cut occurs. Is it colder now than when you were running it at 15psi? Perhaps,a t 15psi in the summer, you were just barely under the fuel cut threshold.

 

[SnowBird]

48 teeth on the cam sprocket. 360degrees / 48 = 7.5 degrees per tooth. Crank rotates at 2X cam speed. 7.5degrees X 2 = 15degrees per tooth. . . That's alot. But retarding the exhaust cam one tooth was a common free mod in the early days. You still have too much intake cam advance running an n/a cam, if you left that cam in the head. I don't know if this is causing you to reach maximum g/sec (fuel cut) earlier or not. But it's probably not good for topend power regardless.

Best thing is to log a run when this fuel cut occurs. Have you checked your base timing? You timing could be too advanced and you could be running into massive knock causeing the ecu to yank timing. The ecu will also completely close the boost control solenoid if timing retard doesn't stop the knock. But you're running JUST a MBC correct?

I just looked at your profile you have upgraded to the 7cm^2 turbine housing. Was this done before when you were able to run 15psi without fuel cut? I definately feel alot of overlap and a bigger turbine will encourage fuel cut earlier. Also the temperature and/or elevation will change when fuel cut occurs. Is it colder now than when you were running it at 15psi? Perhaps,a t 15psi in the summer, you were just barely under the fuel cut threshold.

You blew my mind with all those numbers I was told retarding the exhaust gear would knock off 5 degrees dropping the 7.5 to the 2.5, but yes the intake cam is still in there, I got scared about swapping over to my turbo cams because I didnt know how the head would like it. Yes I did run the old setup with the 7cm housing with no problems, my old 6cm was so ported so heavily it probably was close to the 7cm.

I just switched to a FMIC, but the car acted this way with the sidemount, it seems the head may be the problem. Another tuner around here told me I was hitting cut because of the FMIC, but I told him how it did it with the sidemount. I just pulled out my MBC and ran a line from the wastegate to the j pipe nipple and it actually holds close to 10lbs now all the way to redline without cutting, but thats no fun. As far as logging I dont have one so I cant help you help me that way (I need to get one, just didnt make it a priority with Stage 0 mods). Ill check my base timing again, maybe it got thrown off somehow. With everything being identical to the old cars setup except for the N/A cams you are probably right about it. It definetly feels weak up top and the turbo just doesnt scream like it use to.

Im gonna throw another BOV in it on Monday and do yet another BLT, then Ill pop out the cams, it is just a direct bolt in easy swap right? Thanks for your input, this is driving me crazy.

 

[MaNGiNa24]

You might be overlooking the simple things like a failing fuel pump or a poor connection from the rewire.

Have you already logged the car?

 

[beezwax]

You might be overlooking the simple things like a failing fuel pump or a poor connection from the rewire.

Have you already logged the car?

thats kinda what Im thinking as well... if its an actual "FUEL CUT" then he needs to pay attention to the fuel system....


lookup the simple stuff first.... then pull your hair out

 

[kottyking]

If you are running a 255 fp do you have an FPR?

 

[MaNGiNa24]

If you are running a 255 fp do you have an FPR?

+1

Also, what are you using to tune/log? I dealt with an EVO recently that had similar low boost symptoms due to a sloppy tune.

 

[64_Frankenstein]

Check o2 sensor and wiring harness. That may be the problem.

 

[dsm-onster]

Beezwax, though I agree that he should look over his fuel system for another problem that may have a similar symptom as fuel cut, real "fuel cut" done by the computer has nothing to do with the fuel system malfunctioning. I don't see how checking over anything in the fuel system could find the cause of fuel cut. Fuel cut is caused by the ecu calculating over 2.21g/rev airflow from the maf hertz input, baro input, and IAT input. You can take a stock fuel system and alter the maf hertz and bring on fuel cut at lower boost or push it back a little and make it occur at a higher boost. . . I could be totally misunderstanding your post.

You blew my mind with all those numbers I was told retarding the exhaust gear would knock off 5 degrees dropping the 7.5 to the 2.5, but yes the intake cam is still in there, I got scared about swapping over to my turbo cams because I didnt know how the head would like it. Yes I did run the old setup with the 7cm housing with no problems, my old 6cm was so ported so heavily it probably was close to the 7cm.

I just switched to a FMIC, but the car acted this way with the sidemount, it seems the head may be the problem. Another tuner around here told me I was hitting cut because of the FMIC, but I told him how it did it with the sidemount. I just pulled out my MBC and ran a line from the wastegate to the j pipe nipple and it actually holds close to 10lbs now all the way to redline without cutting, but thats no fun. As far as logging I dont have one so I cant help you help me that way (I need to get one, just didnt make it a priority with Stage 0 mods). Ill check my base timing again, maybe it got thrown off somehow. With everything being identical to the old cars setup except for the N/A cams you are probably right about it. It definetly feels weak up top and the turbo just doesnt scream like it use to.

Im gonna throw another BOV in it on Monday and do yet another BLT, then Ill pop out the cams, it is just a direct bolt in easy swap right? Thanks for your input, this is driving me crazy.

Do a hard run, stop the car immediately, and pull the plugs. Describe their color. Take a pic if you have a camra, if at all possible.

Porting out a 6cm2 turbine housing inlet to match a 7cm^2 turbine housing hole does not make the scroll (cone that raps around the turbine wheel) largr. The larger the cone, the more flow. Enlarging the inlet alone is not going to make any noticeable difference in flow. So I am to understand you correctly that you did run the 7cm^2 housing before with the stock intercooler and had no issue like this. And then suddenly the issue cropped up. You switched to a FMIC and the problem persisted.

I agree to double check your pump rewire. Don't forget to check base timing. Yes, triple check for boost leaks.

 

[MaNGiNa24]

Beezwax, though I agree that he should look over his fuel system for another problem that may have a similar symptom as fuel cut, real "fuel cut" done by the computer has nothing to do with the fuel system malfunctioning. I don't see how checking over anything in the fuel system could find the cause of fuel cut. Fuel cut is caused by the ecu calculating over 2.21g/rev airflow from the maf hertz input, baro input, and IAT input. You can take a stock fuel system and alter the maf hertz and bring on fuel cut at lower boost or push it back a little and make it occur at a higher boost. . . I could be totally misunderstanding your post.



Do a hard run, stop the car immediately, and pull the plugs. Describe their color. Take a pic if you have a camra, if at all possible.

Porting out a 6cm2 turbine housing inlet to match a 7cm^2 turbine housing hole does not make the scroll (cone that raps around the turbine wheel) largr. The larger the cone, the more flow. Enlarging the inlet alone is not going to make any noticeable difference in flow. So I am to understand you correctly that you did run the 7cm^2 housing before with the stock intercooler and had no issue like this. And then suddenly the issue cropped up. You switched to a FMIC and the problem persisted.

I agree to double check your pump rewire. Don't forget to check base timing. Yes, triple check for boost leaks.

+1

And then check again. Everytime I had fuel cut issues, even on the stock turbo it'd be because of a boost leak I overlooked while quickly checking for leaks.

 

[beezwax]

Beezwax, though I agree that he should look over his fuel system for another problem that may have a similar symptom as fuel cut, real "fuel cut" done by the computer has nothing to do with the fuel system malfunctioning. I don't see how checking over anything in the fuel system could find the cause of fuel cut. Fuel cut is caused by the ecu calculating over 2.21g/rev airflow from the maf hertz input, baro input, and IAT input. You can take a stock fuel system and alter the maf hertz and bring on fuel cut at lower boost or push it back a little and make it occur at a higher boost. . . I could be totally misunderstanding your post..

just tryng to think of anything that comes to mind that MAY have something to do with his issue. Thats all. I dont understand a thing you said with all the caculations but you sound for more qualified to give advice than me.


good luck

 

[SnowBird]

Ok, my O2 sensor is brand new. My plugs are a light tan color, but I put new plugs in them for the hell of it, I think they are gapped at .032 which may be too much. I will get a pic of the plugs if I can. Again, I have no logger since I was only running stage 0 mods.

As for the fuel pump rewire, it also did it before I swapped over the rewire, so I did it and it persisted. As for the 7cm housing, I see what you mean, but I thought I would get massive boost spike off it if anything, but again, YES, I ran that housing on the old setup also. A lot of people are saying its my FMIC, but Id like to believe its as easy as the cams.

UPDATE: My Bov kept leaking so I just tried to tighten the bolts even tighter as a last attempt, and heard something go SNAP! I thought I broke the bolt but it was actually the flange on the BOV. I noticed that when the flange was welded on my pipe last week the damn thing wasnt flat, creating a massive gap that was so big it had enough play to snap half the BOV flange when I tried to pull it tighter. This will also be fixed Monday.

2 questions. As far as the N/A cams, do you guys think I should make it a priorty to get them out anyways? It seems like they could only be hurting me, robbing power.
Also, when I do my BLT I havent really been paying attention as to how close I am to 30* TDC, could my valves both be open everytime I test not letting the gauge in my car build?

I will try to get some pics of the plugs DSMONSTER, Just give me till tomorrow when I flatten the flange and put the new BOV on, I dont think I can get an accurate reading on them with BOV cracked, I actually will try to get video of it cutting also, since My buddy can arrange that. Thanks again guys, this problem is killing me, I have to keep making excuses why I cant run my car hard to everyone.

 

[SnowBird]

I couldnt get with my buddy to try and tape the problem, but today I picked up a set of EVO1 cams for $20, so Im gonna try them out, even if its not the problem I feel its better to get the N/A cams out. From what Ive heard the EVO1 cams should be a slight upgrade equaling to almost 256's.

 

[dsm-onster]

You should get some nice gains with those cams. . . vs. your current pair for sure.

 

[1992GSX]

You should get some nice gains with those cams. . . vs. your current pair for sure.

Agreed.

This guy is the man by the way. I have searched for SO many different problems and I am always finding his helpful answers for everything. Oh yes, I have given you rep points

All I could add is that when I was having a very similar problem to you it was as simple as my plugs. I had put in brand new BPR6ES's, thinking that was it and still kept doing it. Mine were gapped at .032 also, like you said, which is what they come at out of the box. I brought mine down to .028 and it was a night and day difference immediately. You may want to look into that as well.

 

[SnowBird]

Agreed.

This guy is the man by the way. I have searched for SO many different problems and I am always finding his helpful answers for everything. Oh yes, I have given you rep points

All I could add is that when I was having a very similar problem to you it was as simple as my plugs. I had put in brand new BPR6ES's, thinking that was it and still kept doing it. Mine were gapped at .032 also, like you said, which is what they come at out of the box. I brought mine down to .028 and it was a night and day difference immediately. You may want to look into that as well.

Yeah, I dropped the gap down to .028 earlier today but it still did it......

PROBLEM SOLVED! I put in that set of EVO1 cams and like magic I can boost away, the power through the RPM range is super smooth. I only got up to about 12lbs, but that is more than Ive been able to get to. I will crank it up to 15lbs tomorrow and see how she reacts, I didnt want the cold air of the night interfere and shoot me down. It took forever for my lifters to fill back up with oil though, the ticking was killing me.

So let me answer my own question. CAN YOU RUN N/A CAMS IN A TURBO? Yes. But why?

I'll revisit this tomorrow afternoon when I crank up the boost.

 

[dsm-onster]

You can. But you will push alot of airflow past the the exhaust valve and cause premature fuel cut (fuel cut from high airflow that you arn't really using). You could have bought one adjustable cam gear and turned your stock n/t cams into stock 1Ga turbo m/t cams. By retarding the intake cam a few crank degrees.

But $20 for a decent cam upgrade is a much better route . Hope it all works out for you. I'd like to see some results with these evo cams.

 

[SnowBird]

Yeah, I retracted my statement about runing the N/A's. I turned the boost up today and it still pops at about 14lbs at about 6K. Im guessing this could be the FMIC, I have a slight leak outta the biss, but thats it. I have the MBC turned down to about 11lbs and it feels good, just as strong as the sidemount at 15lbs. I have a better idle and the power is smooth and strong. Once I get money to play with Ill get on board and start slow with a logger, wideband, SAFCII, 550's, and use my 2G MAS that is collecting dust, that should remedy any airflow problems I might have on stock fuel. Thanks for all the help, right now it just is what it is.

 

[dsm-onster]

Cooler weather, a decent frontmount with better cooling and flow, a better flowing turbine, better flowing cams, open 3" exhaust = fuel cut at 14psi.

The fmic put you over the limit. Are you sure you're not getting boost creep? Are you looking at the boost gauge at the point where the motor breaks up? It is entirely likely that your boost creeping. The td05h turbine housings are famous for boost creep with open exhaust and your other mods, especially the 7cm^2 housing.

The 2g maf, 550s, safc, and logger should be enough to get the most out of a 7cm^2 td05h 14b. You most definately need a fuel pump upgrade. Even rewired, a stock fuel pump will not push enough fuel for a 7cm^2 14b at 15+ psi and other supporting mods.

 

[SnowBird]

Huge FMIC, the XS POWER core. Yeah, Im watching the boost guage the whole time until it cuts then I glance at the tach. Ive never expierienced any boost creep with either of my DSM's. But then again maybe I didnt know it was creeping. I couldnt tell you if it was creeping, it will get up to my desired PSI low in the RPM's and its when I get into the upper range it will stumble once or twice for a split second and then cut out.

Thought about it. When I pull off the MBC and run off the wastegate I can get up to 10-11 psi, so that would make me believe I am creeping a little bit, but at the same time when I set my MBC it pretty much stays set where its at. I appreciate all your help, you are pretty patient, I know I could be a lot more help if I at least had a logger or some better common knowledge of these types of problems. I got lucky with my old talon, it just ran like I wanted it to so I never had to trouble shoot anything.