I am looking for help understanding if boost and AFR should drop (not stay at the wastegate spring pressure) when the wastegate opens.

Below are some videos that show the boost and AFR gauges during a pull. The wastegate spring is 8 psi. Should the boost drop below 8 psi when the wastegate opens or should it stay at 8 psi?

If the boost should not drop lower than the wastegate spring pressure, what conditions would cause the boost to drop once the wastegate opens? Exhaust restriction?

Also, I do not understand why the AFR drops when the wastegate opens?

Thanks in advance for any help,
Bruce

 

It may spike, and then drop a little, but should stay relatively steady given the combo of parts, and tune is right. What gate, and combo? It could all be a tune, or a fuel supply issue.

 

Mnix, thanks for responding. I don't think it is a fuel supply issue. I am running a Walbro 255 lph pump on 440 injectors. Should keep up.

It really does not seem to spike. The boost goes right to 8 psi and then starts dropping and the AFR drops fast from like 11 to 8.8 once the gate opens.

I feel like when the wastegate opens, it should open just enough to keep the boost right at 8 psi. But for some reason, it opens too far and allows boost to drop. I was wondering if there might be something that causes this to occur?

Thanks,
Bruce

 

I missed the 8.8 part, I assumed it was leaning out. It could be the gate sticking, or possibly, the reference line, but it could easily be in the tune as well, it looks quite rich in boost, which could be killing hp and boost.

 

Hmmm? Had not thought about the gate sticking. That sounds possible. The ECU is a stock 95 Supra A80 TT and so can't do much tuning there as far as AFR.

 

I got a better look at your videos, and your fueling is all out of whack imo. 14:1 afr at 6-7 psi is very lean. What all have you done to this?

 

That's a good question. It was running so good for so long and now all of the sudden it has gone crazy. Before it started going nuts, it would run at around 10.2 at 5-8 psi. Being that it is a stock ecu, it has to be something else in the system. I used a vacuum pump to check my lines and found the vacuum line to my MAP sensor was leaking bad so I replaced it. It is running better now, but still acting a little funny. I am going to check a few other things and then take a couple more videos to see where I am. I will post when done.

 

Check your plugs. You might have fouled them running that rich.

 

first, wastegate spring pressure is based on a known backpressure.
In other words, most gate springs are ASSUMING that your backpressure is EXACTLY some number.

In reality, as the engine flows more air (and exhaust) the backpressure is likely to change over time. Typically it will increase.
As backpressure increases it will further open the gate.
Therefore it is fairly typical for boost to gradually drop as backpressure increases and forces the gate open more and more, for setups with small exhaust or restrictive exhaust systems.

To find out how much the gate will open you would take the diameter of the gate valve exposed to exhaust gas, and use the area and pressure to determine the force. Then do the same thing from the top, area and diameter, PLUS the spring force, and compare the two.

Now, on to your issue with the A/F. It looks to be initially too lean (I see 14's at 0, 1, 2psi) which is not good. Around 0,1,2,3psi you want to drop into the 13's if not 12's already for best torque. Especially if the engine is higher compression (over 9:1 is 'higher')

Once your boost reaching 5psi+ I see the a/f gauge goes to 8.8 or so. This is not very likely since the engine at 8:1 a/f ratio would be very unlikely to run properly, or at all. It should stop like you hit a brick wall with an a/f that rich. It is therefore my opinion that the a/f gauge is inaccurate for some reason. 10.2 sounds much more likely but also too rich. It should be in the 11.5 range (say 11.0 to 11.5 at 5 to 8psi of boost with typical 9:1 compression gasoline engines). Anything in the 10's is too rich for such low boost on any engine in gasoline 93 octane.
It is also likely the plugs are completely fouled which would contribute to lack of power, misfires, and the super-rich reading. It can also cause lean readings, falsely due to excess O2 present. It depends on the gauge and sensor. Furthermore the sensor itself could be coated severely in carbon and this can cause erroneous readings.

I recommend you change the plugs, check the gap of course, and change the Wideband sensor. Check for exhaust leaks and ALSO you absolutely need to perform a PRESSURE TEST on the intake side. Connect an air compressor from the turbocharger inlet (where the air filter goes) and fill the turbo and all the intercooler plumbing with high pressure 'boost' use say 15psi or 20psi to fully test the system, intercooler, lines, fittings, intake manifold, compressor cover, everything. it should hold pressure like a balloon for a reasonable amount of time (at least 5 to 10 seconds or longer).

Once you eliminate boost leaks, exhaust leaks, and use new plugs and new wideband sensor, THEN the engine needs to be properly tuned. Make the a/f drop into the 12's and finally 11's mid 11.5~ for the 8psi you are running if using gasoline 93 octane. Don't let it ever go to the 10's unless using much higher boost (12 to 15 maybe 18psi of boost ranges) and even then only 10.8 or 10.6:1 at most.
Also as an aside make sure the engine stays at 14.7 to 15.2:1 a/f ratio during all idle/cruise situations to preserve the condition of the plugs. ONLY use richer a/f ratios near 0psi or in the boost regions. It's okay to drop to 13's as you approach boost. But NEVER 13's 12's 11' etc... when in idle or cruising as it will coat everything, plugs, pistons, valves, exhaust, everything will get sooty carbon buildup.

 

F4K, Thank you for taking the time to write up the comprehensive response. I appreciate it.

Some background on the car. It is a 95 SC300 with 2JZ NA-T. I have done a complete engine overhaul including studs, rings, bearings, valves, etc. I installed a .080" head gasket to drop compression to 8.5:1, 440 cc injectors, and a Walbro 255 fuel pump.

The ECU is from a 95 JDM Supra TT.

Pics of NA-T here: https://drive.google.com/drive/folders/1WJv6SgOxw4gKYD6JXaImftB_-aJqteF2?usp=sharing

Prior to posting this thread, I had already done a 10 psi pressure test on the intercooler plumbing. No leaks. This was my first thought as far as a possible problem.
No exhaust leaks either.

I checked the timing and things look good.

After finding a leak in the vacuum line to the MAP sensor, I fixed that and things got much better.

One new piece of information is that the idle is a bit high at about 1,000 rpm. It might be my TPS being a little out of adjustment.

Or, maybe the idle being high is due to fouled plugs and WB sensor. I will pull a couple plugs and see if they are fouled. I will also pull the WB sensor and check it.

There is really no tuning to be done as this is a stock ECU from a Toyota Supra. I get the maps the Toyota engineers gave me.

Prior to the recent problems, I would get like 10.5 MFR at 8 psi. Probably rich, but also safe. Likely what the engineers wanted.

After I check the plugs and WB sensor, I will post the results.

Thanks again,
Bruce

 

If the engine was truly going to 8 afr on gasoline, it would have stumbled rich and struggle to rev with what some call "shooting ducks" in the exhaust along with black smoke from unburnt fuel.

Your boost drop off seems like it might be a boost leak or an inlet restriction. Ive seen several times when peeps had rubber couplers on the inlet system of the turbo. It would roll into boost and then collapse the coupler , restricting inlet air.

 

F4K, Thank you for taking the time to write up the comprehensive response. I appreciate it.

Some background on the car. It is a 95 SC300 with 2JZ NA-T. I have done a complete engine overhaul including studs, rings, bearings, valves, etc. I installed a .080" head gasket to drop compression to 8.5:1, 440 cc injectors, and a Walbro 255 fuel pump.

The ECU is from a 95 JDM Supra TT.

Prior to posting this thread, I had already done a 10 psi pressure test on the intercooler plumbing. No leaks. This was my first thought as far as a possible problem.
No exhaust leaks either.

I checked the timing and things look good.

After finding a leak in the vacuum line to the MAP sensor, I fixed that and things got much better.

One new piece of information is that the idle is a bit high at about 1,000 rpm. It might be my TPS being a little out of adjustment.

Or, maybe the idle being high is due to fouled plugs and WB sensor. I will pull a couple plugs and see if they are fouled. I will also pull the WB sensor and check it.

There is really no tuning to be done as this is a stock ECU from a Toyota Supra. I get the maps the Toyota engineers gave me.

Prior to the recent problems, I would get like 10.5 MFR at 8 psi. Probably rich, but also safe. Likely what the engineers wanted.

After I check the plugs and WB sensor, I will post the results.

Thanks again,
Bruce

 

I know you said it has a MAP sensor, but does it also have an AMM? Boost leaks cause rich mixture on systems that measure intake air flow.

 

Gruntguru, Tanks for responding. No, no AMM in the system.

Bruce

 

My biggest concern would be the fuel, if the engine isn't running right the boost will drop.

Lean AFR = hot = more boost.
Rich AFR = cold = less boost

I would start by checking fuel pressure through the rev range, then get the injectors flow tested.

Once I had confirmed the fuel supply and pressure didn't have a mechanical fault I'd check that the electronic control of it was ok by changing the tune.

Once that was done I'd check everything for leaks as if a sensor was getting the wrong pressure like your MAP sensor it could throw things out.

Failing that I would do a run with the wastegate disconnected and rev control boost... but be very careful rich is safe lean is dangerous.

If the problem is still present you have eliminated fuel and boost control, I'd look into the ignition. Check all plug electrodes, this can tell you a lot, as well as checking the timing manually not through the ECU to ensure you're getting the correct timing and advance. If it's retarding ignition it can run rich.

Please keep us posted.