Supercharger bucking

hello everyone, I’m new to Toyotas and superchargers and just bought a 1999 supercharged manual 4wd Tacoma. It has a problem building boost under load, in 1st and 2nd it doesn’t build boost at all, through 3rd to 5th I can get it up to 4lbs but if i floor it the power tapers off and sometimes surges back and forth. I cleaned the iac and throttle body when I got the car because the idle was a bit high and also replaced the pcv and grommet but that’s all I’ve done to the car. Also when coming to a stop it bucks and shakes a bit, I’ve noticed when i brake early and put it in first at the last second it seems to not do it as much but I wonder if they’re related? I’ve also noticed it has the dynamic tensioner on it and I’ve heard that’s worse and slips, could that be it? Also there are no codes showing up. Sorry that was a lot! Just want some help to figure this out.

 

How old are the spark plugs? When the truck is idling does the tachometer needle bounce a little bit or is it steady? Is that vacuum line cracked?

 

Did u clean the maf sensor?
What kind of air filter do you use?

 

No clue how old the spark plugs are, owner didn’t tell me much as I bought the car online. Yes the tachometer bounces a bit, idle has been a little rough but I figured that’s the ecu relearning after I cleaned everything. That hose looks like it is cracked a little at the end too. I did clean the maf sensor aswell. And no idea what air filter is in but i pulled it out and it didn’t look too bad.

 

Let’s get some new plugs into it.

 

Sounds like it can possibly be a dirty or bad bypass valve. I had issues with the MP62 on another vehicle where the car would fall flat on it's face when trying to build boost fast but would drive fine if you build the boost up slow. Turns out that the brass fitting inside one of the bypass valve nipple was clogged due to contamination. The solution is to remove the brass fitting entirely to prevent it from happening ever again. The fitting is just used to slow down the air to make it smoother when going into boost. It's not necessary.

You can test this by disconnecting the hose that goes into it and capping the hose off. Then take it for a drive to see if the vehicle drives fine. Mind you, you will be in boost at all times but a short drive around the block is all you need.

The other issue might actually be the valve itself but the test above will single it out. To test the valve, you need to pull a vacuum on it. It should hold. If you slowly start to lose vacuum, then the rubber inside the valve is done.

The valve looks like the picture below. You can even see the brass fitting on the nipple end.

https://www.jonbondperformance.com/product/bypass-valve-vacuum-actuator-101-va784/

 

Doesn’t look like it has the brass fitting, previous owner probably messed with it. Is there a way to take it apart and clean it?

 

Pulled the vacuum on it and the vac pressure went to 15 and idle dropped to around 600.

 

This bolt on the back was quite loose…maybe it’s supposed to be like that and I’m an idiot

 

I'm not tracking...you mean the idle pressure went from 15psi to 600psi?

That valve would be in multiple pieces at 600psi lol.

You need to use a vaccuum gauge like the one below. Pull a vacuum on it and watch the gauge. It should not move at all. If it does, that BPV is toast. There is no way to open it since it's a sealed unit. I believe autozone might even have the vacuum pump free to rent. It's worth a shot.

 

Sorry the idle dropped to 600rpm, there is a gauge in the truck lol

 

The truck is off when you do the test. You simply hook up the vacuum gauge to the bypass valve and pull a vacuum and then watch the gauge on the vacuum gauge, not the rpm on the truck. The needle shouldn't move at all. If the gauge holds the vacuum, then it's something else. It's just a easy thing to check when you have weird boost behavior.

 

Oh gotcha! Completely misunderstood this.

 

What bolt are you talking about?

 

This one here

 

The nut? That will not come off due to the retainer. Doesn't look abnormally loose to me.

 

This may not be your issue but I highly recommend an AFR gauge if you don't have one. This can help tell if you have a bad AFR sensor or MAF sensor. I'd do spark plugs, make sure you get 1 step colder and probably some new coil packs. Does your boost gauge have vacuum one it too? Whats your hot idle vacuum?

 

Just put new denso ik22’s in, engine is much happier but still have both problems. These were the old ones…

 

Legend has it that with the engine idling tap lightly the maf sensor with the handle of a screwdriver. If the idle fluctuates the maf is bad ( or so I hear). Let’s see if the legend is true.

 

You had the bolts in the previous photos, but the bypass valve actuator is not bolted down.