Open downpipe fuel cut/bucking?

[jtimms6]

So today I went ahead and started to make a custom test pipe. Everything else on my exhaust is stock. Cut out the cat and went to weld in a 2.5in pipe in place and then boom welder took a shit. So I had to drive home with the car the way it was till I can finish tomorrow. Figured it wouldn’t Be a big deal since an open downpipe is the same as a exhaust cutout still decided to drive the car like granny to be safe. Well at one point I decided to see how everything ran with a open downpipe so I got on the throttle and around 4-4500 rpm the car poppled and did some sort a fuel cut for a second then caught it self and continued to pull. I’m just wondering why it’s doing that? It does it almost every time mostly in 1, 2 and 3rd gear....I was planning on eventually doing cut outs but if this is what the cars going to do then no thanks. Let me know if this is normal or what it could be...car has a DC cold air intake and ap stage 1+ tune and just did spark plugs and oil change

[Vansquish]

I really hope you have aftermarket HPFP internals. If you don't, you're risking blowing your motor. What you were probably feeling is boost and/or load cut based on your car now exceeding both boost and load limits set on the shitty-ass OTS map you're running.

You need a map that actually accounts for your car's physical modifications, ESPECIALLY when the modifications are airflow and exhaust-flow based.

[Jeff23spl]

A tune for stock exaust can't work with free flowing one. The ecu have to push further to get boost under restriction. If you keep the same tune and remove restriction, you get a spicy torque monster setup for a forged engine on meth/e85 blend lol (Ok not completly...) but you get wastegate duty mapping for above 18-19psi at low rpm and then, the ecu try to protect your engine by cutting the fuel.

Back then in 2009 i made the same, i put a downpipe and drove the car with stage1 ots map thinking it would be less agressive than flashing a stge2 right away. In fact, it is worse...

[jtimms6]

I monitored my fuel pump the entire time never went below 1655 at wot so I had good fuel pressure and good afr also so you’re saying flash the stage 2 map onto my car? I never even got above 14 psi of boost because I’m still trying to figure out a boost leak/wastegate issue

[jtimms6]

I guess what I should ask is for now while driving an open downpipe what tune should I flash to my car with the cold air intake

Then what tune should I flash to my car once I have the test pipe done I still have the first stick car in the car and I have the stock mufflers and exhaust piping on the car. So with that and the cai what tune should I flash?

Also other then the Cobb tunes what are my options to get a tune specific for my car? I know I can go get it dyno tunes but that’s a lot of $$$ so other then that what are my options and do I really even need to do that? I assumed with just an intake and a test pipe that’s not to far from stock where I can still use an ots map from Cobb for my car and be safe?

[jtimms6]

Originally Posted by Jeff23spl A tune for stock exaust can't work with free flowing one. The ecu have to push further to get boost under restriction. If you keep the same tune and remove restriction, you get a spicy torque monster setup for a forged engine on meth/e85 blend lol (Ok not completly...) but you get wastegate duty mapping for above 18-19psi at low rpm and then, the ecu try to protect your engine by cutting the fuel. Back then in 2009 i made the same, i put a downpipe and drove the car with stage1 ots map thinking it would be less agressive than flashing a stge2 right away. In fact, it is worse...

this is what cobb says:

Stage2 93 OCT or 98 RON
Intake Requirements:
COBB SF Intake required
COBB Turbo Inlet Hose (TIH) required
Intercooler Requirements: Stock
Fuel Requirements: 93/94 OCT or 98 RON fuel
Cam Driven Fuel Pump:
Autotech High Volume Fuel Pump (CDFP) required
Exhaust Requirements:
Upgraded Catback exhaust required
Upgraded High Flow Catted Downpipe required
Boost Targets: 18psi peak tapering down to 17psi by redline +/- 1.5psi
All other intake, exhaust, engine related components: Stock

they wouldnt recommend anything to me since im not running the exact set up for these maps but would this sage 2 map be my best bet for now?

[Jeff23spl]

You need to flash a tune for what you have and none of the ots one will fit correctly.
Especially if you have a boost leak, you just makes things even worse.

Peoples going stage2 do the step1 mods first so you won't find a free tune for your setup.

If you need to temporary run the car with an open exaust, the best is to disconnect the EBCS wire to get on the turbo spring and rule out all the wastegateduty. Yes the car won't be fast but it won't blow either.

The problem isn't just looking once in a while at your fuel pressure, the pump fail under high load at anytime. Your pressure look good when injector IDC is low but if you load it more, the pressure will definitely drop and ecu will try to compensate by increasing afr a lot making other bad issues until a rod get out of the bloc. Then peoples usually blame the car engeneering bashing on engine longevity when the problem is the lack of proper tune and proper supporting mods.

[jtimms6]

Originally Posted by Jeff23spl You need to flash a tune for what you have and none of the ots one will fit correctly. Especially if you have a boost leak, you just makes things even worse. Peoples going stage2 do the step1 mods first so you won't find a free tune for your setup. If you need to temporary run the car with an open exaust, the best is to disconnect the EBCS wire to get on the turbo spring and rule out all the wastegateduty. Yes the car won't be fast but it won't blow either. The problem isn't just looking once in a while at your fuel pressure, the pump fail under high load at anytime. Your pressure look good when injector IDC is low but if you load it more, the pressure will definitely drop and ecu will try to compensate by increasing afr a lot makinother bad issues until a rod get out of the bloc. Then peoples usually blame the car engeneering bashing on engine longevity when the problem is the lack of proper tune and proper supporting mods.

So then when the test pipe is on which will be today with my intake what tune should I run or am I screwed there I didn’t think an intake and test pipe would be such a big deal but with that said can I run a stage 1 or 2 tune with my intake and test pipe on and be fine?

[Thor Hammer]

Originally Posted by jtimms6 So then when the test pipe is on which will be today with my intake what tune should I run or am I screwed there I didn’t think an intake and test pipe would be such a big deal but with that said can I run a stage 1 or 2 tune with my intake and test pipe on and be fine?

You should really listen to what they are saying and not keep asking the same question. These guys know what they are talking about! So do as they say.

Regardless, since you are hell bent on ignoring simple advice....get a set of HPFP internals first and foremost. Then, run the map that is the most similar to the mods you have. Stage xyz it doesn't matter. Pick one that fits your mods and be done.

Will it be ideal? No, but close enough. And as long as you have upgraded internals you will be fine.

The test pipe deletes only the second cat right? If so and your primary cat is still there, you don't have to worry as most of the exhaust restriction is in the primary cat.

If you go with an upgraded DP catted or not, you will get the most benefit and protection for your motor by ordering a custom E-tune from the many tuners on this forum.

When I bought my car from the original owner it came with a Cold Air Intake, Autotech HPFP Internals, and a CPE catted downpipe. He was running the Cobb Stage 2+ map IIRC and no issues. Right away however I got custom tuned after going fully bolted. Best money ever spent.

If you take shortcuts, do mods without properly researching the how, why, and consequences, you risk irreparable damage to your engine.

Exhaust cutouts are installed after the DP and before the mufflers. So when you get to the point you REALLY want everyone to hear your car, you should get a custom tune. I will tell you though, the DISI motor sounds godawful with straight pipe exhaust. Its just not a pleasant sound. Bypassing the mufflers (get high flow ones) will not cause such a great increase in airflow that your tune will need to change.

[jtimms6]

Originally Posted by Thor Hammer You should really listen to what they are saying and not keep asking the same question. These guys know what they are talking about! So do as they say. Regardless, since you are hell bent on ignoring simple advice....get a set of HPFP internals first and foremost. Then, run the map that is the most similar to the mods you have. Stage xyz it doesn't matter. Pick one that fits your mods and be done. Will it be ideal? No, but close enough. And as long as you have upgraded internals you will be fine. The test pipe deletes only the second cat right? If so and your primary cat is still there, you don't have to worry as most of the exhaust restriction is in the primary cat. If you go with an upgraded DP catted or not, you will get the most benefit and protection for your motor by ordering a custom E-tune from the many tuners on this forum. When I bought my car from the original owner it came with a Cold Air Intake, Autotech HPFP Internals, and a CPE catted downpipe. He was running the Cobb Stage 2+ map IIRC and no issues. Right away however I got custom tuned after going fully bolted. Best money ever spent. If you take shortcuts, do mods without properly researching the how, why, and consequences, you risk irreparable damage to your engine. Exhaust cutouts are installed after the DP and before the mufflers. So when you get to the point you REALLY want everyone to hear your car, you should get a custom tune. I will tell you though, the DISI motor sounds godawful with straight pipe exhaust. Its just not a pleasant sound. Bypassing the mufflers (get high flow ones) will not cause such a great increase in airflow that your tune will need to change.

They never really answered my question like you did i dont plan on ripping my car around with an open downpipe especially without the proper tune i just wanted to make sure for the little driving ill be doing that ill be okay till i get that test pipe welded in. As far as research ive read a lot on the forums and its hard cause everyone contradicts each other but from what i gathered hpfp internals is the best thing to do HOWEVER as long as your mods are only down to an intake and minimal exhaust work such as a test pipe with stock mufflers or some kind of cat back that still has mufflers to allow some restriction out the back you are fine with the stock internals. Also read that as long as your fuel pressure stays above 1600 at all times at wot you are fine with your set up and ive taken many logs that all show my pressure between 1655-1750 therefore i assume either my set up isnt demanding enough to absolutely need internals now or the previous owner did internals. So now my question is how would i investigate that? Would i need to open up the fuel pump and see whats in there or are there other methods to check what internals i have? Also i havent measured yet but as long as the intake is same size as stock shouldnt it not make a big difference other then bringing in colder and more air? finally where do i go on the forums t find these tuners that can make me a custom tune im most likely going to use the stage 1 or 2 tune for now but when i have money for a custom tune id like to know where to go thanks

[Jeff23spl]

Originally Posted by jtimms6 They never really answered my question...

I know my English isn't good but if you don't like the answer because it doesn't give you a pleasant solution, even if you keep asking, it won't get better. Einsteing said: Insanity is doing the same thing over and over again and expecting different results...

You ask which ots tune to pick with an open exaust and everything else stock...

We all answer that there is no ots tune availaible that will work regardless of how long you run it.....An open exaust is worst than a DP and the pump is required when using a dp or you can blow up the engine...

stage1 are made for a plugged exaust
stage2 are made for DP with an HPFP


The option i gave you is to run any ots map with the ebcs disconnected to keep boost at 10-12psi until it get welded.

With your dp welded, you will be able to pick a stage1 that fit your mods and cai as long as your cai is same id.

At the end, you can do what you want as long as you don't complaint if you blow it up.

[Thor Hammer]

Originally Posted by jtimms6 They never really answered my question like you did i dont plan on ripping my car around with an open downpipe especially without the proper tune i just wanted to make sure for the little driving ill be doing that ill be okay till i get that test pipe welded in. As far as research ive read a lot on the forums and its hard cause everyone contradicts each other but from what i gathered hpfp internals is the best thing to do HOWEVER as long as your mods are only down to an intake and minimal exhaust work such as a test pipe with stock mufflers or some kind of cat back that still has mufflers to allow some restriction out the back you are fine with the stock internals. Also read that as long as your fuel pressure stays above 1600 at all times at wot you are fine with your set up and ive taken many logs that all show my pressure between 1655-1750 therefore i assume either my set up isnt demanding enough to absolutely need internals now or the previous owner did internals. So now my question is how would i investigate that? Would i need to open up the fuel pump and see whats in there or are there other methods to check what internals i have? Also i havent measured yet but as long as the intake is same size as stock shouldnt it not make a big difference other then bringing in colder and more air? finally where do i go on the forums t find these tuners that can make me a custom tune im most likely going to use the stage 1 or 2 tune for now but when i have money for a custom tune id like to know where to go thanks

Hey bro, could you hit the return key a few times on your next post? Makes it easier to read.

When you start to mod your car with an intake and exhaust I highly recommend upgraded internals. Its your choice. But $250 is cheaper than venting your block. Think of it as insurance.

Lots of threads on how to tell the difference between stock and upgraded internals. The stock piston is the same diameter along its entire length. The upgraded ones have a step up to a larger diameter. There are pics on here if you search.

The E-tuners are in a separate section. Just go to the main page and scroll on down. You'll find them.
Freektune
Stratified
Purple Drank
Tuned By Nishan
etc...

Far as your intake goes the MAF cal will be already done in the applicable map you find on the Cobb AP. Power increases come from turning up the boost, adding more fuel, timing, and spark advance. All are done in concurrence in relation to the level of your mods. Decrease flow restriction and increase boost, you can add more fuel. then timing, spark advance, etc...

[MSMS3]

Originally Posted by jtimms6 I monitored my fuel pump the entire time never went below 1655 at wot so I had good fuel pressure and good afr also so you’re saying flash the stage 2 map onto my car? I never even got above 14 psi of boost because I’m still trying to figure out a boost leak/wastegate issue

You will not see it drop pressure with real time monitoring. A data log will show. I thought I could get away with no fuel pump internals running a catless 3" dp/rp and intake. Fortunately, I was data logging and saw dips down to 1100 that lasted only a tenth of a second or two under WOT. Very much of that will destroy your engine.

Get internals now.

Also, running catless without a proper tune is notorious for dangerous boost spikes up into the 21-22 psi range or higher. Since your map sensor will only produce voltage equivalent to 22.5 psi, if your logs show that, you may be much higher! A manual boost gauge connected to a vacuum/boost line will report true boost

You need a tune compatible with your mods. An OEM stock tune will be dangerous. You need pump internals and a stage 2 tune compatible with your mods.

Another thing that may be happening is that catless will raise boost about 2 psi. You may be getting high boost induced spark blow out from plug gap being too wide. This happens under high load in the 4,000-4,500 rpm range just like boost cut, of which it is, albeit induced by plug gap. With boost probably now in the 17-18 psi range, if not dangerously higher, you need to close plug gap to .026-.028". Assuming you've upgraded the pump and have a compatible tune, closing the gap usually stops the cut.

You probably have primary boost cut because of dangerous boost and a possible induced cut from plug gap.

No, an open exhaust is not safe on a forced induction, MAF controlled direct injection engine without supporting mods and tune. Stay out of it until then you get your shit together and fix these things.

Upgraded internal piston on the left, note larger diameter on tip. Stock is same diameter all the way down.

[jtimms6]

Originally Posted by MSMS3 You will not see it drop pressure with real time monitoring. A data log will show. I thought I could get away with no fuel pump internals running a catless 3" dp/rp and intake. Fortunately, I was data logging and saw dips down to 1100 that lasted only a tenth of a second or two under WOT. Very much of that will destroy your engine. Get internals now. Also, running catless without a proper tune is notorious for dangerous boost spikes up into the 21-22 psi range or higher. Since your map sensor will only produce voltage equivalent to 22.5 psi, if your logs show that, you may be much higher! A manual boost gauge connected to a vacuum/boost line will report true boost You need a tune compatible with your mods. An OEM stock tune will be dangerous. You need pump internals and a stage 2 tune compatible with your mods. Another thing that may be happening is that catless will raise boost about 2 psi. You may be getting high boost induced spark blow out from plug gap being too wide. This happens under high load in the 4,000-4,500 rpm range just like boost cut, of which it is, albeit induced by plug gap. With boost probably now in the 17-18 psi range, if not dangerously higher, you need to close plug gap to .026-.028". Assuming you've upgraded the pump and have a compatible tune, closing the gap usually stops the cut. You probably have primary boost cut because of dangerous boost and a possible induced cut from plug gap. No, an open exhaust is not safe on a forced induction, MAF controlled direct injection engine without supporting mods and tune. Stay out of it until then you get your shit together and fix these things. Upgraded internal piston on the left, not larger diameter on tip. Stock is same diameter all the way down.

So i got my test pipe welded on today not well but its welded with no leaks JUST a test pipe so still have the first cat and the stock mufflers and then i have my intake which i measured the diameter and its the same as stock 2.75 or so.

Im running stage 1+ tune on the car and everything seems fine also did a log or two and they showed no problems. Only other thing to figure out is why i only get 13.5-14 psi of boost

[Jeff23spl]

You may let it learn with your mods for a while now. Flashing a tune reset the fuel trims too...

You mentioned boost leak at first so it could be why you just get 13-14. Make a boost test and see. If you solve something, reset the fuel trim again, it will settle faster.
Check boost in third and 4th gear as it won't load enough in 1 and 2 to see real thing.

With upgraded pump internals, you would usually see higher pressure in the 17xx. But this is part of the commended pressure from the tune + the pump size. I don't know the behavior of an upgraded one on stock tune...Physically checking it, is probably the best option as long as you take care of o-ring and gaskets or put new one. Imo the chances to have one are very small...

2.75id isn't bad, i measured 2.64 from my oem3. It is still 8.5% off but nothing compared to an open exhaust...

[jtimms6]

Originally Posted by Jeff23spl You may let it learn with your mods for a while now. Flashing a tune reset the fuel trims too... You mentioned boost leak at first so it could be why you just get 13-14. Make a boost test and see. If you solve something, reset the fuel trim again, it will settle faster. Check boost in third and 4th gear as it won't load enough in 1 and 2 to see real thing. With upgraded pump internals, you would usually see higher pressure in the 17xx. But this is part of the commended pressure from the tune + the pump size. I don't know the behavior of an upgraded one on stock tune...Physically checking it, is probably the best option as long as you take care of o-ring and gaskets or put new one. Imo the chances to have one are very small... 2.75id isn't bad, i measured 2.64 from my oem3. It is still 8.5% off but nothing compared to an open exhaust...

2.75 was the measurement of the intake sorry i don't think i said that was just throwing that in because people in another thread were saying my intake is messing up my maf and that's why i have low boost.

How do i reset the fuel trims? just by reflashing the car?

[Jeff23spl]

reflash or, disconnect car battery and apply brakes to discharge capacitors

Fuel trim adapt the afr thru the o2 feedback when the maf reading isn't accurate. It do it at least up to 25% error, than throw a cell
That's great but maf reading also drive load values that affect which column of the table is used for other stuff.

A larger maf pipe than expected by ecu will read less voltage for the same flow so ECU will try to push a little more to compensate and could lead to knock, overboost etc...
The reverse for a smaller one.

And OTS maps are suppose to discard the load control function that originally drive the boost controler...So it shouldn't affect your boost that much...

[jtimms6]

Originally Posted by Jeff23spl reflash or, disconnect car battery and apply brakes to discharge capacitors Fuel trim adapt the afr thru the o2 feedback when the maf reading isn't accurate. It do it at least up to 25% error, than throw a cell That's great but maf reading also drive load values that affect which column of the table is used for other stuff. A larger maf pipe than expected by ecu will read less voltage for the same flow so ECU will try to push a little more to compensate and could lead to knock, overboost etc... The reverse for a smaller one. And OTS maps are suppose to discard the load control function that originally drive the boost controler...So it shouldn't affect your boost that much...

Awesome i will reflash the fuel trims ect. when i head out later. As for my boost issue im going to do a leak test and robably go and replace the normal hose clamps with t bolt clamps however if i dont have a boost leak what is my next plan of atack? Where and what should i look for for whats cusing my low boost

Also must of missed a spot or two when i welded the new pipe on my car cause i can hear the exhaust leak "sputter" when i shut the car off im going to fix it tomorrow but will that having any major effects on the car? Performance or driveability wise?

thanks for all the advice i will be ordering a full exhaust probably a turbo back as well as hpfp internals and a custom tune in the next month the test pipe was just a temporary patch for the huge leak i had before since my second cat was falling apart all over the place.

[Jeff23spl]

Cant hit boost target

[Vansquish]

Originally Posted by jtimms6 Awesome i will reflash the fuel trims ect. when i head out later. As for my boost issue im going to do a leak test and robably go and replace the normal hose clamps with t bolt clamps however if i dont have a boost leak what is my next plan of atack? Where and what should i look for for whats cusing my low boost Also must of missed a spot or two when i welded the new pipe on my car cause i can hear the exhaust leak "sputter" when i shut the car off im going to fix it tomorrow but will that having any major effects on the car? Performance or driveability wise? thanks for all the advice i will be ordering a full exhaust probably a turbo back as well as hpfp internals and a custom tune in the next month the test pipe was just a temporary patch for the huge leak i had before since my second cat was falling apart all over the place.

Why not pull the pump apart and look to see if the internals have been upgraded before ordering parts? It literally takes 10 minutes.

[Solarsurge]

Originally Posted by Thor Hammer I will tell you though, the DISI motor sounds godawful with straight pipe exhaust.

WAAAAAAAWWWWW BRRAPPAPAP-POP!! WAAAAAAAWWWWW P-POP! lol

Personally, I went with the Cobb turbo back because it just makes a deep, evil roar. All the other exhausts out there I've heard sound tinny like Honda fart cans. Even length headers sound a billion times better, though. Stock manifold is what makes it sound like ass, imo.

[BuddySpeed3]

Originally Posted by jtimms6 Also read that as long as your fuel pressure stays above 1600 at all times at wot you are fine with your set up and ive taken many logs that all show my pressure between 1655-1750 therefore i assume either my set up isnt demanding enough to absolutely need internals now or the previous owner did internals. So now my question is how would i investigate that? Would i need to open up the fuel pump and see whats in there or are there other methods to check what internals i have? Also i havent measured yet but as long as the intake is same size as stock shouldnt it not make a big difference other then bringing in colder and more air?

Hey man, the only way to know for sure is to take the pump apart. There are several how to's online that take you through this process in detail.

Fuel pressure may be good now in the summer heat, but as soon as winter comes around, the colder more dense air will put a much higher demand on the fueling needs.

The last thing you want to do is leave it up to chance. It's so important that I urge you not to do another pull until you know for sure

Start with ensuring you have upgraded hpfp internals.

Verify that you have no boost or exhaust leaks (Try a smoke machine and upgrade to T-bolt clamps).

Make sure you have no oil or fluid leaks, and that oil is clean, and at max on the dip stick.

Change transmission fluid for peace of mind.

Listen for any potential abnormal engine noises.

Remove oil filler cap and check the timing chain for excessive slack.

Make sure spark plugs are in good shape and gaped correctly (In your case 0.026-0.028").

Check for oil coming out of the valve cover breather and pray that there isn't.

Do a compression and leak down test to ensure your engine is healthy.

Contact an E-tuner and get a tune specific to your parts.

As far as the intake goes, search up MAF CALIBRATION. If you go with an E-tune, the MAF CAL will be taken care of.

No offence but take the modification process slowly. Read and understand as much as you can about this platform. You will enjoy the car that much more because you'll know and understand what you are doing Welcome to the raw beast that is the Mazdaspeed