Airflow mystery on a 4A-GZE swap - ideas?

[ThaChemist]

Well, I finally got my 4A-GZE (1st-gen) swap up and running, mostly. It starts and idles just fine (self-adjusts to 1000 RPM and everything), but it will not rev. The fuel system works just fine, and basically floods it when I hit the gas, though it does self-readjust fairly well.

Everything works just fine up until the throttle body, but the pressure is extremely low going into the engine itself (you can see the connectors suck in, plus if I make my own vacuum leak there, it does rev up), so somewhere between the throttle body and the engine, there's one heck of a blockage. I don't know a lot about the supercharger itself, but I didn't think it could actually stop the system like that. Is there some way to bypass it, or is it a different problem? I don't have a lot of time to work on it right now, so I'm fine running it without the SC for a little while until I could get it rebuilt or whatever is necessary.

[CrUZida]

The pressure is always extremely low after the throttle body at idle. Some might even call it a vacuum!

[ThaChemist]

No kidding. However, the point is that when I hit the throttle, nothing happens - the pressure differential remains exactly the same - even WOT. Isn't the throttle supposed to be the last air-limiter in the intake system?

[wilbo666]

The restriction is the Throttle, which is believe it or not 'Throttling' the engine (Think bart and homer throttle...)



Cheers
Wilbo

[wilbo666]

Oh, well in that case look for something like a sock, or rag etc in one of the pipes

Cheers
Wilbo

[CrUZida]

Timing could also be way out
Is the fuel pump running while the engine is idling ?
Is the AFM flap moving freely ?

Rag is the most likely solution, either a rag or some other form of blockage.

[brett_celicacoupe]

doesnt the bypass service the engine with air between 1000-2000rpm and then once you really punch it the supercharger cuts in?

is the supercharger clutch engaging?

[ThaChemist]

That's a huge relief, actually - I'll start digging asap. The only problem with the timing could be that the distributor might be perfectly 1/2 off, but I'm pretty certain it's ok. The AFM flap moves when the throttle moves, so I think that's all right as well. I know for a fact that the fuel pump goes like a champion, plus I had it idling for a good twenty minutes today.

I can't really tell if the SC engages at all since both the engine and the SC are new to me, but there is an interesting hiss-whine and other noises which went on and off at intervals as I was trying to mess with it. Is there something I could see in the pulley system that would tell me?

About the bypass valve, I don't really know. It looks like a cylinder with a bunch of vacuum lines sticking out, right? Anyway, the car won't really rev past 1400 no matter what I do, so I can't tell what is feeding what, to be honest. Anyway, I'll take a picture in the morning if I can't find the obstruction.

[CrUZida]

Have you checked the plugs ?

Bad plugs or plugs covered in oil can cause similar issues

[TERRA Operative]

The bypass valve sits on the down pipe from the throttlebody to the supercharger and has a single vac line to one end (The subject of the much famed ABV mod) and the other side bolts to the down pipe with another pipe coming from the side which connects to the pipe from the sc to the intercooler.

I doubt it's the problem. Many people remove and blank this valve off to achieve higher boost with little detriment to idle etc.


I would say, check timing and check for obstructions.

[ThaChemist]

Ok, so there was one of two problems. Either the obstruction was the supercharger itself (it was a bit corroded, and it's a bit of a mystery how air could pass through it when it's not running and, in fact, how it runs is also a bit of a mystery to me - I can take a picture if you'd like) or the AFM was somehow screwing up everything.

So... there's a couple problems. First, I'm not precisely sure if the AFM is conflicting with another sensor. The AFM is on the K&N intake which the previous owner had installed (and was big trouble when I made the harness) on the original 4A-GE, so when I did the swap I took it along because the wiring didn't seem to work out otherwise, and there's no other AFM on the intake system.

What I did was take out the supercharger (not easy) and bypass it through creative use of intercooler piping, which was conveniently the same size as the connector from underneath the throttle to the SC.

Here are the results:
Case 1: With the AFM on.
Originally: Idled perfectly at 1000 RPM, but does not rev at all, eventually flooding it.
Now: Idles perfectly at 1000 RPM, dies if I touch the pedal or if I manually move the AFM flap.

Case 2: With AFM off, but still plugged in.
Originally: Idled fine, revs to 1400 and stops, occasionally flooding.
Now: Revs to 2000 exactly. Any higher and it coughs and either drops 1000 or dies altogether, with the same noise as with the AFM on. I think it's getting too lean rather than flooding, since I could smell it the first time.

I also tried disconnecting the AFM, but it understandably it dies pretty quickly.

So is there any solution to this? Can the AFM be tuned or the fuel mix be somehow creatively adjusted? Or is it trying to engage an SC or bypass valve that isn't there, and there's nothing I can do about it? Could this purely be a messed-up wiring problem?

Option B is that I put back the 4A-GE distributor and switch back to the 4A-GE ECU and try to run it like a NA engine. I left enough wiring in to do that, because I'm not enough of an optimist.

Option C is that I get the SC rebuilt or a new, compatible one (prices?). Considering that a new one from Toyota (I wanted a laugh) is $4100 CAD (!!! I'd do it for <$700, maybe, but seriously) and that none of the wreckers around here stock SCs (no clue as to why not), I'm thinking this isn't a terrific option.

Thanks -- I'd really appreciate your help on this.

[Norminator]

have you opened up the AFM to check how it is? pull out the black plastic access panel to check if the spring is still located properly inside the wheel. make sure it all operates smoothly through the full motion of the flap, and make sure the adjustment wheel can't slip.