The turbo on my '83 280ZXT seems not to be working correctly. Car starts and runs fine otherwise, but does not seem to get the 'oomph' it should with a turbo. In sedate driving, the car behaves fine. But when you punch it or hit high revs, it starts missing and stumbling.

I have done extensive work to this car to bring it back from a long period of sitting and neglect. This includes cleaning all contacts, all new fluids/filters, timing, compression test (within specs), fuel pressure, vacuum test, check cam timing, remove/clean/rebuild hydraulic lifters, replace manifold gasket, test just about everything via FSM and replace a few items from my parts car or buying new. So I'm reasonably sure I've eliminated just about every system BUT the turbo. This is also a replacement turbo I got on eBay, since the one in the car was seized. It spun okay but did have a small amount of axial play. You can hear it spool up when you drive.

In neutral, acclerating slowly, my (stock) boost gauge reads -5 at idle, at 2000rpm and at WOT. It really never changes.
If I punchi it, it will sometimes pop up to -1 or so.
In gear, the engine will occasionally pop up to perhaps +1 or +2 level on the boost gauge.

I don't really know what the boost gauge is supposed to read under these circumstances. That's not in the FSM anywhere I can find.

In fact, the only info I CAN find on the turbo in the FSM (pgs EF/EC 73-75) doesn't tell me a whole lot that makes sense or is testable. For example, the 'Specified supercharging pressure' is P(sub)o. WTF does that mean and how do you test it? Or to test the bypass valve controller, APPLY pressure, but not greater than 19.69 inHg or you can damage the thing.

Anybody have a quicker and dirtier way to test this stuff?

 

Welcome to ZDriver!

An ebay turbo is your first problem.

Sounds normal so far.

Doesn't sound so great.

It is in the FSM. EF&EC-74, top left of page: Pmax is 50.7-53.3 kPa.

Googled a converter, those pressures equal: 7.35psi to 7.73psi of boost.


Did you read the top right paragraph on page 73? It states Psub0 is the specified pressure value for the proper max boost level (now we know it's 7.35psi to 7.73psi). Psub0 is a variable... just like variables used in Algebra & Calculus.

Having said all that, I would first check your waste gate. Make sure it's opening at the proper boost level, and not too soon, or if it's possibly stuck open. If the turbocharger is an aftermarket, does it have an adjustable arm?

Also check your air fuel mix at WOT (full boost). If you are lean, you may have a fuel problem.

 

now is this a turbo you got off a real person on e-bay, or a replacement "new" turbo on e-bay that they mass sell.


also, check the turbo out, pull off the intake boot from the turbo intake and see how the compressor blades rotate (by grabbing the center rod/nut section not the blades) and try to pull that same section in and out and wobble side to side. should feel smooth rotating with no rough spots and have a little tiny bit of resistance since it is an oil/journal bearing setup. and have what feels to be a millimeter or two of play in the side to side deflection and nill in the back and forth (in and out) section. also if its stumbling and popping alot like a very intense miss fire could be your AFM. it will cause it not to boost. had the same problem with mine as well as loose wires in the ECU connectors to wire harness.

 

Sometimes a simple vacuum leak will do just what you are saying. There are all the usual culprits, but make sure to check the brake booster as well.

 

I will check out vacuum again, and also turbo play and wastegate. (How do you check the latter — apply pressure?) AFM is a replacement from my parts car and spec's out properly. Turbo is a stock Nissan 280ZX unit that I bought through eBay. Not a cheapo Chinese clone. Sorry for that confusion.

 

hard to truly check the wastegate. if you can grab the wastegate arm with a vice grip or similar and move it but it is REALLY difficult and it springs back into place it is probably good. but that is all i can say for a generic test.

 

Have you tried checking the emergency pop valve ,As you look at the intake manifold it will be the 2 inch round looking valve next to the EGR ,Lift the cap up a few times to make sure it is closing.If it is stuck open then you will have very little PSI ,You should be able to hear this hissing sound if it is stuck open ,It might also be a lose wire going to the intake valve sensor.

 

pull the safety valve and put a pipe plug in there. at least you eliminate one point of failure. buy a real boost gage. harbor freight has a nice one for around $20.