Bogging down at point of turbo engagement. Why?

I'll try to keep this short. Bike: 1982 XJ650 Turbo. Mostly stock parts, rearranged. See pictures.

Problem: Under load at high RPM I lose power. My boost gauge never reads boost pressure. It's as if when it is time for the boost to kick in, the engine goes LEAN. Bike runs great other than this. I can cruise in 1st at 7-8000 rpm, no problem. Medium acceleration through gears, no problem.

Ideas?

 

Loss of turbo power at boost could be several things. Spark blow-out from dirty/mis-gapped plugs, fuel enrichment issue or a leak in cold or hot side piping. Not knowing a lot about the fuel setup I would have to say check the plugs first to rule them out. Weak spark and turbos do not play well.

 

First, welcome.....second; with your system as highly modified from stock as it is, I can only give you some "overall" suggestions. It sounds like your engine is running very well, your turbo sys, no so much. I would pay close att to the weak spark issue mentioned above....my stock spark was the weakest I'd ever seen on a running bike. I have Acells now. 28,000% improvement...lol

Your system not making boost- IF YOU ARE POSITIVE OF CORRECT PLMG AND NO LEAKS(& good turbo)---Check actual fuel pump pressure. A failed pump will not overcome atmos press,= no boost. These are the only pressurized carbs made, they operate just a tad differently in this system.

If you are making boost but then it cuts out, look for a disconnected or failed front knock-sensor. At the same time, test the other pneumatic/electric or PE sensor shown in the manual and it WAS located below and to the center of frame from the ICU. Typically, they begin retarding the timing very early.

The guy that everyone recommends for parts, Chacal...is top notch. You are better to get from someone who actually knows this stuff!

Also, the Turbo forum is over here, It's ok...we all share; https://www.tapatalk.com/groups/tmioa22687/yamaha-seca-650-turbo-f10/

jeff

 

Great info. I never considered spark. Recommended plug and gap?

I disassembled the fuel system and checked regulator and check valve. Regulator may have been stuck cant test it because now the dang fuel pump wont operate. Whyyyy

 

I know, right? What you really need is a hotter coil to make sure the spark won't get extinguished. As JeffK mentioned the coils on these bikes are very weak. I would think stock gap would be fine on a small turbo. Only reason I mention the spark is I did a lot of turbo engine tuning work on my Genesis project. People with boosted cars often think the misfiring and detonation are just injector or air flow issues with timing. They don't consider the fact that pressurized air flow can literally blow out a weak flame front or extinguish spark completely if it's not really hot. Racing plugs help with both detonation and bad firing issues by recessing the electrode and ground strap inside the tip. The spark is protected from swirl, the flame front has a better chance of forming on-time and the tip of the plug runs colder by being in the flame only a short period of time instead of through the entire combustion cycle.

 

Mad...., let me know via PM if you need a pdf copy of the Turbo manual...it's actually a supplement for the XJ manual, I've got both if you need them, just pm me a email addy.

jeff

 

Let the process of elimination begin.
1) New plugs - NGK manual spec, gapped .03" from factory.
2) I pressurized the intake, some small leaks buts it did hold pressure.
3) I felt the original fuel pump was working properly, replaced with new pump. Zero noticeable changes.
4) Knock sensor connected. Voltmeter jumps around when I move the sensor. I assume its working properly. All connections tight.
5) Pressure sensor reads 2v when tested per manual which is considered a "pass". There was something strange, 3 wires to sensor - Power, Ground, signal. Both power and ground had continuity to ground. I wired a dedicated wire straight from battery + to "power" on pressure sensor... and got no changes.
6) Checked fuel pressure regulator, it opens and closes when air is applied, sprayed some silicone lube in it, I assume its working.

Whats next? Rode it today after everything, rpm's reach redline in first at slow acceleration, Bike runs great accept about 5-6k under load. then sudden loss of power and "spitting" noise from exhaust. back off throttle and full recovery. I can feel air being pulled into turbo at idle, and if I blip the throttle in neutral I feel a small push of air on the hose to boost guage (air taken from 2nd intake port between carb and motor. Sooo I assume the turbo is working.. well enough. I did get about 2-3 psi ish reading on gauge after one pull. Choke on only makes the bike run worse.

Any other suggestions?

Thanks.

Let the process of elimination begin.
1) New plugs - NGK manual spec, gapped .03" from factory.
2) I pressurized the intake, some small leaks buts it did hold pressure.
3) I felt the original fuel pump was working properly, replaced with new pump. Zero noticeable changes.
4) Knock sensor connected. Voltmeter jumps around when I move the sensor. I assume its working properly. All connections tight.
5) Pressure sensor reads 2v when tested per manual which is considered a "pass". There was something strange, 3 wires to sensor - Power, Ground, signal. Both power and ground had continuity to ground. I wired a dedicated wire straight from battery + to "power" on pressure sensor... and got no changes.
6) Checked fuel pressure regulator, it opens and closes when air is applied, sprayed some silicone lube in it, I assume its working.

What's next? Rode it today after everything, rpm's reach redline in first at slow acceleration, Bike runs great accept about 5-6k under load. then sudden loss of power and "spitting" noise from exhaust. back off throttle and full recovery. I can feel air being pulled into turbo at idle, and if I blip the throttle in neutral I feel a small push of air on the hose to boost gauge (air taken from 2nd intake port between carb and motor. So I assume the turbo is working.. well enough. I did get about 2-3 psi reading on gauge after one pull. Choke on only makes the bike run worse.

Any other suggestions?

Thanks.

 

Looking over your pictures.....can you make a schematic drawing of how you have the exh/intake/turbo/carbs plumbed? I see all those K&N filters and one looks to be mounted to the impeller side of the turbo? If that's the case....it's easy to see what's going on....

jeff

 

I'll explain best I can with text and if illustrations are needed I will make them.
Exhaust: Stock header pipes = stock 4 to 1 manifold = homemade pipe to turbo housing = turbine exhaust to homemade pipe to muffler
Intake: Stock surge tank (BOV shimmed) = homemade pipe = K&N Filter
Turbo 1: K&N filter on turbo compressor IN
Turbo 2: Compressor discharge = homemade pipe = K&N Filter
Carbs: Stock

Motor to surge tank is all stock. What are you thinking, Jeff?

 

TYPO Sorry:
Exhaust: Stock header pipes = stock 4 to 1 manifold = homemade pipe to turbo housing = turbine exhaust to homemade pipe to muffler
Intake: Stock surge tank (BOV shimmed) = homemade pipe = K&N Filter
Turbo 1: K&N filter on turbo compressor IN
Turbo 2: Compressor discharge = homemade pipe = *Surge Tank
Carbs: Stock

Motor to surge tank is all stock. What are you thinking, Jeff?

 

Is the K&N an oil media filter or one of their dry filters?

 

oil

 

Does it bog down with no filter on the compressor inlet?

 

I haven't tried. Anyway, are you suggesting the oiled filter is restrictive? The filter I have is probably large for its application. Got a deal so I bought them.

 

Is the stock boost sensor connected to the port out of the carburetor? The boost sensor must be plumbed after the carbs, as it is used to read the pressure manifold air pressure and retard timing accordingly. Are you running the stock ECU as well? Without the boost sensor functioning (and stock ECU) it won't run right on boost

What exactly are you trying to achieve with your setup? The inlet to the surge tank is there to bypass the turbo when it's not under boost. You've replaced that with another restriction. JeffK can attest to achieving 18psi boost with the stock turbo and plumbing (some other mods necessary). Given the small displacement of the engine, and smaller volume of exhaust gases, it going to be difficult to spin up two turbos without lag, and one turbo can actually provide more boost than the motor can handle.

 

You will get better performance from dry cone media and you don't have to wash them. Try it without the filter to rule it out. With so many mods you should have as much stock as possible and add back changes one-by-one.

 

1) Yes stock boost sensor is connected to port of carburetor which tee's off to boost gauge.
2) Yes stock ECU. I'm wondering if boost sensor internal parts of ECU are damaged, fried wire or something. Rule that out last.
3) "inlet to the surge tank is there to bypass the turbo when it's not under boost. You've replaced that with another restriction"
I do not have issues with not under boost conditions. Anything upstream of the reed valves is not causing my problem (I think).
4) I only have one turbo. I moved the turbo from under the bike to the middle, as kind of a show piece, among many other reasons.

 

Filter can effect performance but do you believe the filter can make the difference between NO boost and 18 psi boost? It would effect efficiency, but not prevent boost conditions (I think).

QUESTION: Suppose I had a 100% stock xj650 turbo. What would happen if the boost sensor malfunctioned? Would the bike exhibit the symptoms I'm having?
QUESTION 2: 100% stock xj650 turbo with seized turbo. does the bike run normal with just less power (b/c no boost)?

Work with me on this logic....
Seized turbo seams equivalent to an induction leak, If the manifold doesn't pressurize no boost is generated, no timing is adjusted...is that right? No turbo, seized turbo, giant gaping hole in turbo, motor *should (I'm speculating) run fine just no boost..So since I'm having issues I am generating boost.... right?
Manifold/carbs are pressurizing, my issue does not lie within the turbo, piping, induction portions but with timing, ignition, fuel.

I don't want to sound like a know it all expert. I'm a mechanically inclined noob. I'm just explaining my problem solving direction here.

THANK YOU to anyone trying to help. I always try to solve a problem myself before I resort to getting spoon fed ideas/solutions.

 

Yes, compressor inlet restrictions reduce intake flow, which reduces outflow which kills the turbine speed. It is not a supercharger, it's a turbo so it has to have intake air to provide turbine flow. Cold-side leaks = poor boost. A bad intake filter is just as bad.

 

I follow you on this. I agree completely. but, I feel pressure from carburetor pressure/vac hose (hose to boost pressure) when I blimp the throttle in neutral. I know the turbo builds boost under load, so if I'm getting some positive air pressure just in neutral the turbo should be breathing healthy? again, I make assumptions.

It's just strange I'm not getting poor performance I'm getting zero performance at boost. Bike should make more power but it makes less power.

 

If the boost is there (shows on a pressure gauge correctly) and the fuel isn't then it's a fuel management problem.

 

Any easy way to test this? I'm lead to believe I'm not emptying my bowls because bike fully recovers immediately every time. Could it be leaning out? hmm so many variables. If I apply the choke during boost attempt it runs even worse, I thought this would richen the mixture a little and I'd see an improvement... not the case. Am I too rich??

 

Look at the plugs. They'll be wet and really dark if you're running too rich. I'm used to using a wideband AFR to monitor stuff like that when tuning a car turbo. Fuel smoke is black if it's blowing any. Oil is typically light grey to white.

 

I will check. If it leans out when I'm having the issue (white plugs) and running rich at idle or normal driving conditions, will the plugs turn black again? Do I need to lean it out and shut it off immediately?

 

Eagerly waiting for your response lol.

 

Easy? Not without a boost gauge and a port on the manifold for it. The MAP sensor in the manifold should be able to tell you if it's sensing boost or anything at all. That will affect the fuel ratio.

 

​

replace that paper fuel filter with a sintered bronze filter

 

Yes i think? Timing needs to be retarded when on boost. Without that signal, the ECU will stick with ambient air pressure settings. Make sure the wiring is good with the sensor.

 

Sensor checked out according to service manual inspection. Any other testing procedures I could try? Voltage = 2v at ambient, voltage = ?? At 8psi.
What's out there in a way of replacement sensors?

 

Or eliminate it. The bowls will settle stuff out.

 

I appreciate all the advice. I'm noting everything as future improvement opportunities, but I'm hard pressed to believe the fuel filter, or dry vs oiled air filter is causing my current problems.

Annnyyoonnee wanna chime in with a countermeasure? Even if it doesnt work I can cross it off as the issue. Bring on the ideas!

 

Hmmm... Interesting.
Asks for advice.
Gets advice.
Ignores advice.
Asks for advice again.

 

By "noting" advice, one might assume I am making a note to myself NOT to ignore the advice. If advice was given to check tire pressure, i would note this but i wouldn't go inflate the tires than try a hard pull on a motor that is running incorrectly.

 

The tires are not part of the fueling system. The filters are.
Small things do matter in the correct function of systems.
Things that are both easy and cheap to change should not be ignored just for the sake of thinking that they do not matter.

For example: Using a replacement foam air filter (K&N or Uni) on a non-turbo XJ instead of an OEM-spec paper filter. One causes a poor running condition, and the other does not.

You've been given two potential "countermeasures".
You've stated that you're willing to try things that might not work just so you can cross them off the list.
Why not try those first?

 

Absolutely agree. I'm trying to rule out the LARGE things before the small things. Most likely first to least likely. Filters, I believe, would effect efficiency/poor performance. I am getting zero turbo performance.
Like I said,noting all suggestions to my list, no advise is wasted.

 

Fair enough.
Do you happen to know what small item causes a very noticeable mid-range bog on a non-turbo XJ?

First rule of thumb in the industrial maintenance world: eliminate the easy things first. You'll get better raises that way.

 

many little things can add up.

if your not getting fuel at boost what happens?


Problem: Under load at high RPM I lose power. My boost gauge never reads boost pressure. It's as if when it is time for the boost to kick in, the engine goes LEAN

lean by to much air or lean by to little fuel Hmmmmmmmmmmmmmmm think about it

 

No, I do not own that bike. My research is centered about the motorcycle I own.

Although our conversation is going on undesirable tangent which may draw attention from the original post intend. You have my curiosity?

 

Changing from a paper air filter to a foam one (drop-in filter with factory airbox).
Every XJ of the era was delivered running on the lean side in order to meet U.S. emissions regulations.
When combustion is already running on the edge of being too lean, every little thing in the fuel system matters.

Manbot's advice shouldn't be ignored either, because more oftten than not there are multiple issues that contribute to a single problem with any old machine.

 

Thank you for the reply. Thinking about it
.. turbo purpose to ADD air so lean by little fuel is culprit.
Okay, what havnt I already checked, tested, or replaced as part of fuel system? Suggestion for next root cause?

 

Thank you k-moe for helping me with this. I have some 3/4 and 1" ball valves I may couple to filters to restrict airflow and test. I'll share results when I do this.

 

You could save a bit of time (maybe) and use masking tape and cereal boxes to restrict airflow at the filters.

Keep in mind that I could be flat-ass wrong, but the easy things really should come first when diagnosing a problem.

 

I run a mostly stock turbo seca with a stock airbox and foam filter. I know all the grief that gets passed around for normally aspirated XJs, but I don't think that applies to Turbo Seca, since it runs on boost, and you're using the surge tank as well, which should smooth the flow just fine.

I would say that you haven't actually verified boost unless you have a boost gauge on the compressor outlet (I have one installed on my surge tank, which is the same line that connects to the waste gate). If you added a manual boost controller you'll need a boost gauge to set preload on the boost controller check valve.

Even if you have boost, you aren't guaranteed to have ignition at the right time. The wiring diagram shows splices from the boost sensor that feeds both the dash gauge and the TCI box. You should at least verify continuity between the B/R and B/Y wires from the boost sensor plug to the TCI and Boost Gauge. The manual also shows a linear voltage curve with pressure. Get some low pressure air (less than 20 psi) and test it. A bike pump can work well for this.

Finally, you need fuel. First is fuel pressure. I also installed an aftermarket fuel pressure sensor to always keep an eye on the health of the fuel pump and pressure regulator. Unfortunately, the cheapest ones are $100+, but that's how you "know." Unlike a boost gauge, you need an electronic sensor, you can't/shouldn't run a pressurized fuel line up to a gauge cluster. After that you need to guarantee that the fuel fills the bowls. If the carbs leak the "bowl" pressure to atmosphere that won't happen on boost.

Finally, having the turbo up by your legs is risky, that thing gets very hot! Furthermore, the exhaust gases are going to lose a lot of energy through all that plumbing (one reason why the turbo is on the bottom amid other design trade-offs). If this continues to be a problem, returning the plumbing to stock, working out the bugs, then modifying might be the best way to sort this out.

 

I may still have an AEM boost gauge out in the shop with all the boost controller stuff. I have a small dial inline NX fuel gauge as well but dunno if it will work.

 

Thanks ManBot, very helpful.
I have 2 boost gauges plumbed from turbo and intake. its difficult to read 1 or 2 psi on a dial gauge whilst full open throttle on a bike I'm still learning to ride, so I can't confirm I'm not getting absolutely no boost. Oh, and I do not use stock boost gauge.
I removed boost controller as part of problem elimination for now.
I WILL check for this continuity, good call.
I WILL check pressure sensor at varying pressures and cross reference voltage to manual spec.
I do not believe it is pump issue. I've tried stock & aftermarket with no impact on issue.
Where did you plumb your fuel pressure in at? Incase I need to do this?
I believe my bowls are full, If I emptied the bowls wouldn't the motor die? or atleast show symptoms of fuel starvation? After i let off throttle bike returns to normal INSTANTLY.
I need to wrap my exhaust... indeed.

Will post update when I perform the two checks.

Thanks again.

 

Just tested Boost Sensor, anyone take one of these apart and "fix" them? output voltage is low.

 

Well that would def cause a major lean condition.

 

Many of them are peizo elements and you can't "fix" them, but I've never seen a MAP sensor from a bike. Pics?

 

For the boost sensor, ebay is your best bet unfortunately. Means you have to take a chance. How did you test the sensor and how accurate are the tools you used to test? That does seem linear, so it's no like it's stuck at 2V. If that's the actual output it will have an impact on timing (the MAP isn't used for fuel delivery only timing advance). Just want to eliminate possible testing error.

For the fuel gauge you can splice in the sensor between the pump and check valve. From the stock setup, there was a 90 degree bend that I could exploit using a 3 way brass tap (home depot) that I screwed two barbed ends for the fuel lines and could screw on the sensor on the back. IIRC I also got some fuel proof loctite for the threads. This was the cheapest electronic gauge I could find: https://www.glowshiftdirect.com/tinted-7-color-30-psi-fuel-pressure-gauge/

 

Wow, so it only retards spark? I would expect there to be some amount of fuel enrichment.