4af won't start - Toyota Nation Forum : Toyota Car and Truck Forums

nz92 · 07-15-2011, 03:41 AM

Hello,

This is my first post.

I have a ae92 with the 4af engine. It runs ok, has done close to 300,000 kms. Was going yesterday now it is not. It has spark, fuel (I think) and compression is okay (180,180,190,190 psi) actually I'm not sure if that's ok? Turns over freely. The plugs seem to have fuel on them. If I push the throttle to the floor it seems to almost start. The carb seems to be a bit average in general.

Has anybody had a similar experience?

Any help would be most appreciated.

Cheers

Dave

90 GP · 07-15-2011, 04:33 AM

Have you removed timing belt cover to see if broke. Can also verify by removing distributor cap and have someone crank engine while checking to see if distribution rotor turns. By the fuel on plugs you could have a flooding issue with a stuck float in the carb and/or lack of ignition due to faulty ignition item such as cap/rotor/plugs/wires /ignitor/ignition coil.

nz92 · 07-15-2011, 05:22 PM

Hi

Thanks for that. I got it to start, all be it a bit ruff. Held my foot to the floor and cranked it over, eventually it started but sounded like a tractor. Once it warmed up a bit it was running good. Perhaps it has something to do with the cold start thing on the carb? Because until it was up to operating temp it still was a bit reluctant to start.

Is there anyway to adjust the cold start thing? I think it is not delivering enough fuel when cold.

Thanks

Dave

90 GP · 07-15-2011, 06:54 PM

I had to to re read your post to see if you had fuel injection or a carb. On the carb check to see that choke plate is closing when engine is cold. They can get gummed up and need carb cleaner spray to unstick them. Also check float level. There is a clear plastic gauge built into bowl that you can view on right side of carb. Fuel level should be in middle of gauge. If higher you need a new float or needle valve.There is also a diaphragm (Auxillary Accelerator Pump valve) that is vacuum operated. Have heard of the diaphram leaking and causing issues as well.If vac hose is removed and gas is present the diaphram is shot. Here's a writeup on AAP:

Auxiliary Accelerator Pump Diaphragm (AAP)

The auxiliary accelerator pump diaphragm (AAP) is located at the front base of the driver's side of the carb. It has three screws and one vacuum line.

To check if it is bad, simply pull off the vacuum line and look and smell for fuel. If there is gas in the line, the diaphragm is punctured or cracked and should be replaced. I have heard of people simply plugging the vacuum port and being fine, although your idle/take off may stumble a little when cold.

All the AAP does is squirt a little extra fuel into the mixture when the engine is cold. It has no effect on the engine when warm - even when not working properly. The AAP is vacuum operated - when vacuum is applied the diaphragm opens which then adds a little extra fuel. The vacuum is applied by the BVSV which is screwed into a water jacket on the head. This senses the temperature of the coolant and applies or does not apply vacuum to the AAP.

A new diaphragm comes with any rebuild kit or can be purchased from the dealer and maybe from some aftermarket parts stores.

nz92 · 07-15-2011, 07:53 PM

Hi,

Yes the choke plate is closing when cold. The float level is about middle of the glass.

Is the AAP that black thing on the side of the carb?

Cheers

Dave

90 GP · 07-16-2011, 03:59 AM

Here is a diagram of an Aisin carb. Not the same exact one as your's but it shows the AAP which is part 75-78 in the diagram.

http://www.carburetorfactory.com/expvw28.html