Pressure Pulsing at Part Throttle, Measurements and a Solution

[jeff97vr4]

Originally Posted by erikgross

One other thought in a possible explanation for this... If the pulses in pressure cause an extremely lean condition (> 16:1 or 17:1), you can get a misfire, and it will actually show up on your O2 sensor as a rich condition. Misfires could certainly cause the bucking. Once the ECU sees the rich readings (even though it's actually LEAN), it may pull even more fuel, which will make for even more lean conditions, more bucking, less fuel, more lean, more bucking, and on and on. This would be essentially a positive feedback operation condition, where once the cycle got started, it would feed on itself until something stops it.

--Erik

Erik,

I think this is a reasonable issue to raise. I have a question about an O2 sensor reading rich if there is a misfire. The O2 sensor responds to the O2 partial pressure in the exhaust stream. If there is a misfire, gas isn't burned and there should be more O2 or a higher partial pressure. This would yield a lower voltage signal and be interpreted as a lean condition. If there is flaw in my logic, I 'd like to understand.

As far as the behavior of my engine there isn't any indication of any misfire. The A/F on the wideband deviates at the slightest pulsing. I'll have to think about this some more, but I think the A/F shift is from the pulsing and not the cause.

I'm going to try just using a straight 6mm hose as a bypass when I go out this weekend. Given the input so far, this seems like a reasonable thing to try.

Jeff

[erikgross]

Originally Posted by jeff97vr4

Erik,
I have a question about an O2 sensor reading rich if there is a misfire. The O2 sensor responds to the O2 partial pressure in the exhaust stream. If there is a misfire, gas isn't burned and there should be more O2 or a higher partial pressure. This would yield a lower voltage signal and be interpreted as a lean condition. If there is flaw in my logic, I 'd like to understand.

No flaw in your logic - you're absolutely correct. I don't think I was fully awake when I wrote that. Doh! I guess that's what I get for allowing the fingers to hit the keyboard without the clutch for the brain being engaged... I'll go sit in the corner for a time-out.

It's a longer shot, but overly rich mixtures can also cause misfires, so the cycle might be able to work that way. My understanding, though, is that it has to be REALLY rich to cause a misfire, and I'd suspect that isn't happening here. Back to the drawing board...

--Erik

[HilbillyHomeboy]

Originally Posted by erikgross

No flaw in your logic - you're absolutely correct. I don't think I was fully awake when I wrote that. Doh! I guess that's what I get for allowing the fingers to hit the keyboard without the clutch for the brain being engaged... I'll go sit in the corner for a time-out.

It's a longer shot, but overly rich mixtures can also cause misfires, so the cycle might be able to work that way. My understanding, though, is that it has to be REALLY rich to cause a misfire, and I'd suspect that isn't happening here. Back to the drawing board...

--Erik

Erik - I missed what you wrote also, so don't feel too bad. Scanned it too fast and thought you were talking about what you are now....rich condition causing a misfire.

That certainly can and does happen. That is what my car was doing. Stupid rich and actually misfired and sent the ECU into limp mode.

However, I agree that is not part of the problem at hand as my car will pulse...rich, lean or indifferent....

Jeremy

[woovr492]

So what do DR or GTPRO or the other big shops do when a car with this problem rolls in?

Tell them that it's unfixable and send them out? They must have a solution - if they don't, I am clearly mislead on their expertise regarding our platform.

This seems to be a fairly common problem among 3s cars. I appreciate all the work jeff is putting in but I'm surprised the big boys haven't stepped in and said anything.

They are always there to give advice on bigger turbos, exhaust, and clutch setups - I would hope that they would at least have more to add on this topic.



More on-topic, I've been messing with this situation for about a year and have found the same results.
Relevant mods:
td04hl 15g's, cc 8inch fmic setup, hks ssq bov in recirc, dejon tool intake pipes

With these mods, the car pulsed like CRAZY. If you weren't WOT, it was pulsing. And yes, I pressure tested the crap out of that thing - it was sealed tightly.

I removed the HKS bov and replaced it with the stocker and the pulsing just got worse.

I tried my Greddy Type S from my 2g awd dsm and it was just as bad - probaly worse.

At this point, I realized that the pulsing was unstoppable and was hoping that it was a drawback of the cc fmic kit. So I sold the kit and went back to stock. With the stock intercoolers and HKS bov, the surging is much more tame. It only occurs during cruising at low rpm at partial throttle. It is the worst on the highway in 5th gear under 2.5k. If I go WOT and drive in bursts, I can avoid it.

This is a serious problem and deserves more attention than it has recieved imo. I KNOW that a lot of people w/ upgraded intake/intercooler systems have this problem and just let it go and drive with the pulsing. I'm really interested in what the big shops do when someone comes in with this problem.

I appreciate your R&D Jeff - I'm going to be giving the modified HKS BOV a try when it warms up. I just hope it isn't detrimental to the overall power output of the car

[jeff97vr4]

Weekend report, this is what I tried on Saturday, Jan 22.

1. Straight 6mm hose from y-pipe to intake elbow. This seemed worse than the hose with the solenoid, which is a restriction. I thought this would be better because more air could bleed off. The pulsing would continue until the pressure in the y-pipe dropped to about 2.5psi.
2. If 6mm couldn’t release enough air, 8mm should be better. Silver soldered a 5/16 fitting in the y-pipe and the copper el adapter and ran an 8mm hose. This was about the same as with the 6mm hose, except it threw PO0170 andPO0173 error codes, front and back fuel trims. I’m not sure why the codes were thrown, the engine ran fine and the A/F was in the normal range. It was probably some transient from all of the air that was being bypassed.
3. Loosened the BOV spring pressure with the 8mm hose to see if there was an effect. No change.
4. Went back to the 6mm hose with the Hobbs switch controlled solenoid. This seemed to be the best setup. There is some pulsing but it seems to damp out faster than the straight hose. I want to try this setup earlier in the day when it is colder to make sure that warmer temperatures in the afternoon aren’t the reason for the improved behavior.

I still want to try the bigger solenoid on order to see if that is an improvement over the smaller, more restrictive one in use now. I won’t know until it arrives, but I suspect it will be more restrictive than a straight hose. The Hobbs switch will control the opening and closing of the bigger valve. I may not try it before I go to Phoenix next weekend since the present setup seems to work very well.

I am guessing that the larger opening was bypassing too much air and the throttle had to be held open more which in turn pushes the turbos to make more boost. Having the right sized leak is the goal. I wonder how the bypass will work with a Greddy s type push BOV. At some time I will convert my modified HKS valve back to the stock configuration and see how it behaves. Right now I am getting tired of this. Each trial drive takes about 35 minutes if I have to return home and about 20 minutes if I can make the change at the side of the road. If the weather is decent next weekend, I will drive the car to Phoenix and will have a chance to observe behavior over an extended time with different load conditions. I will adjust the Hobbs switch pressure turn-on and the BOV spring pressure to get some feel for the sensitivity of those parameters on the pulsing.

If anyone were interested in doing this mod, I would strongly urge monitoring y-pipe pressure and O2 readings, either factory ND or WB. A simple pressure gauge teed at the y-pipe nipple in front of the throttle body is all that is needed, vacuum reading aren’t needed. You will be able to observe the pressure in the y-pipe when the pulsing occurs and compare that to the plenum pressure from your standard boost gauge. You can get some idea of how fast the pressure drops when the BOV opens. I also hooked up a DVM to the front factory NB O2 sensor. When the WB indicated the A/F dropped to 12.5-13 from 14.7(dithering), the NB went from dithering to a steady reading around 0.9V. Either a WB or NB could be used.

Jeff

[jeff97vr4]

Originally Posted by woovr492

So what do DR or GTPRO or the other big shops do when a car with this problem rolls in?

I've talked to Matt at DR and he has only seen this on one or two cars. It seems to be a random problem that most end up accepting for the performance upgrades that precipitated the problem. Don't know why anyone else has added their knowledge oor opinions.

More on-topic, I've been messing with this situation for about a year and have found the same results.
Relevant mods:
td04hl 15g's, cc 8inch fmic setup, hks ssq bov in recirc, dejon tool intake pipes

What are you using for a MAF/MAS, aftermarket or factory?

I removed the HKS bov and replaced it with the stocker and the pulsing just got worse.

You are the first one that has reported this with a stock BPV. Do you know if yours is one of the rare ones that doesn't leak? Are you sure your cams are all corrrectly timed to the crank?

At this point, I realized that the pulsing was unstoppable and was hoping that it was a drawback of the cc fmic kit. So I sold the kit and went back to stock. With the stock intercoolers and HKS bov, the surging is much more tame. It only occurs during cruising at low rpm at partial throttle. It is the worst on the highway in 5th gear under 2.5k. If I go WOT and drive in bursts, I can avoid it.

What I have observed is the pulsing starts after the the throttle is closed partially after being under a moderate load. Once the pulsing as started, it can continue at a steady throttle and then get worse if the throttle is opened. The pulsing can be stopped by further closing the throttle, of course to be started all over again with the right load and partial closing of the throttle. If you open the throttle from fully closed and hold it steady or continue to open it further, does the pulsing start. Remember that just the slightest closing can start the pulsing.

I appreciate your R&D Jeff - I'm going to be giving the modified HKS BOV a try when it warms up. I just hope it isn't detrimental to the overall power output of the car

Thanks. I've had the boost set at about 10.5 psi while I've been doing all of this so I don't know how the modified HKS will be at higher pressures. It can be converted back to stock with a pipe plug, so it isn't a being irreparably modified. I did test it at at about 20 psi in the garage and it didn't leak then. But that isn't real world driving conditions. I don't plan on going over 15 psi, so I don't think it will be a problem for me. I will report how this work progresses.

Jeff

[jeff97vr4]

Drove the car this morning, it was only about 20 degrees cooler than yesterday afternoon, but the car was also cold to start. The pulsing was about the same as yesterday afternoon. This is with the 6mm hose, small solenoid valve, Hobbs set at 4 psi, and BOV spring backed off.

Something I had misinterpreted was the pressure measurement across the throttle body, from the y-pipe to the plenum. The differential pressure measurement would also pulse. Thinking about this, it became obvious that the pulsing was being influenced by the throttle body. I hooked up the 3.6-psi differential gauge across the throttle body. The pulsing seems to start there. The pulses start as the throttle is partially closed and can increase in magnitude. I am suspicious that the pulsing that has to be occurring in the plenum is the cause. As the airflow is slightly interrupted at part throttle with some positive pressure in the y-pipe, the pulsing in the plenum becomes unstable and is driving the whole process.

I need to observe this for a while to see if the plenum pressure is about the same when the pulsing starts. It is possible that there is a resonance in the plenum design that is driving this phenomenon. More data is needed. Since I have an idea now of what to look for, the perfect opportunity comes up next weekend during my drive to Phoenix. The reason for the trip is to watch NHRA Top Fuel Dragsters and Funny Cars make tuning passes. I can’t wait, the chance to drive the car on a road trip and watch real horsepower be produced.

Jeff

[Bret Brinkmann]

Hey cool NHRA! If the opertunity comes up maybe you could talk to a guys there about this situation and see what they think?

I have been following this problem for a while now and I noticed some people don't quit have the same symptoms and some have found numerous solutions. I was brain storming (okay more like a light drizzle), and thought maybe for some of you it's the hard pipes that are causing this problem?

woovr492 - You mentioned you had the CC FMIC kit. It can be bought with a hard pipe kit. Could you try switching as many of those hard pipes over to a soft pipe to see what the results are? My thinking behind this was if the soft pipes could expand with the pressure pulsing it would dampen the pulses and maybe even eliminate them completely.

[VR4swoosh]

I have been following this problem for a while too. I have all stock intercoolers and pipes and I still have the problem. I never had it with the stock BPV, but it started when I installed my Greddy BOV. I have stock turbos and my upgrades include a HKS intake, HKS boost controller, and exhaust. Other than that, my car is pretty much stock. I am meeting with VR4neophyte this weekend to swap ECUs. Before we do that I will reproduce the problem in my car for him to see if it feels the same as what he is experiencing with his car with upgraded intercooler pipes. I know Erik Gross and I have the same problem because he has sat in my car and seen what I am talking about. He had the same symptoms with his Greddy BOV when it was installed.

-Mike

Originally Posted by Bret Brinkmann

Hey cool NHRA! If the opertunity comes up maybe you could talk to a guys there about this situation and see what they think?

I have been following this problem for a while now and I noticed some people don't quit have the same symptoms and some have found numerous solutions. I was brain storming (okay more like a light drizzle), and thought maybe for some of you it's the hard pipes that are causing this problem?

woovr492 - You mentioned you had the CC FMIC kit. It can be bought with a hard pipe kit. Could you try switching as many of those hard pipes over to a soft pipe to see what the results are? My thinking behind this was if the soft pipes could expand with the pressure pulsing it would dampen the pulses and maybe even eliminate them completely.

[badass3000]

Originally Posted by Bret Brinkmann

... and thought maybe for some of you it's the hard pipes that are causing this problem?

woovr492 - You mentioned you had the CC FMIC kit. It can be bought with a hard pipe kit. Could you try switching as many of those hard pipes over to a soft pipe to see what the results are? My thinking behind this was if the soft pipes could expand with the pressure pulsing it would dampen the pulses and maybe even eliminate them completely.

Im certain thats whats going on with mine. We think alke Bret