Looking for help with 1600rpm limit...

[Eiger]

Hi All, I'm trying to get my 16vS engine to run right.

I'm not able to rev above 1600rpm without the revs dropping suddenly and then surging up again.

I double checked the crank - camshaft timing/TDC and it's set correctly.

I sprayed WD40 into the ICV under the manifold through the front aperture after removing the hose that runs to the bottom of the intake, as I've read they can stick. No difference once reconnected and left to idle. When I try increase revs it hunts at 1600 again.

I've also tried running with the TPS disconnected but the symptoms were the same... Still won't rev above 1600rpm before dropping back, then climbing up and so on ...

What else can I check?

Thanks to anyone who can help me get my 944 running again!

 

[Hallsy]

Gut feeling would be AFM, which is easy enough to bench test. I remember I left the AFM disconnected on my 200SX accidentally once, and it wouldn't rev past 3k.

Failing that, is something knocking the timing right back? Faulty knock sensor maybe?

I can't see the ICV effecting anything but idle.

Have metered out the idle switch to make sure it is operating correctly?

The 994S electrical manual has a number of fault finding tips for checking sensors/switches, etc - do you have it?

 

[zcacogp]

I presume the ignition system (plugs, rotor arm, dizzy cap, leads etc) are all in good nick and you are getting a nice fat spark?

Have you re-seated the flywheel sensors in the back of the engine recently?


Oli.

 

[Eiger]

Yes Oli - the whole ignition system is new as is the ignition module.

I've also set the flywheel sensor to the correct gap.

 

[zcacogp]

In which case you need to do the classic diagnostics; is it lacking spark or fuel? Given it happens at a speed other than idle then I doubt it will be TPS or ISV. Have you checked for a spark while it is struggling? A spark gap tester would be a helpful tool as it's pretty easy to see what's going on.

As Andrew said, the AFM would be an obvious port of call but I'd be a bit more methodical if possible. AFM's are also quite pricey, so can you borrow a known-good one from somewhere?


Oli.

 

[Eiger]

Yes I checked spark with an inline tester - they're all good - spark is healthy.

The only other AFM I have is off a 8v - I don't know if I could substitute it for the sake of a test?

 

[zcacogp]

Yours is an 8v engine if it's the lux in your signature. Do you mean that the spare unit you have is off a 16v machine?


Oli.

 

[Eiger]

sig is incorrect - car now has 16v motor

 

[zcacogp]

Have you tried this:

http://www.the944.com/afm.htm


Oli.

 

[Eiger]

I will be as soon as the 9v battery connector arrives from an ebay seller - in the mean time I stripped off the intake, TB, AFM and the crow's nest of larger vacuum hoses...

I'm going to test the ICV using this procedure: ICV test by TexasBlake

 

[zcacogp]

If the problem is at 1600rpm then I very much doubt it will be the ICV. The ICV is only switched on when the throttle is closed. If you have the throttle open then the TPS switch is turned off and the ICV is not in operation.


Oli.

 

[Eiger]

Fair enough Oli but I tested it anyway to be sure - and it works...

A question about the ICV tho' - when closed should the hole be closed completely by the flap or is there a slight opening?

This is mine closed:

and open:

Is this correct operation?

 

[Hallsy]

From memory, when I had my icv off it was partially open when closed - as I remember thinking it was stuck before I cleaned it!!

As mentioned on Tipec, test your AFM on a bench with the 9v supply.

 

[Eiger]

Right....

Popped off the AFM cover, it's been off before, the tracks were deep even the white ceramic was showing through in a couple of places, so I adjusted the slider thingy 'South' to get clear passage...

Started the car and same issue - won't rev higher than 1600rpm before dropping revs and climbing again, then dropping etc etc :evil:

Tested the AFM with 9v battery. Smooth voltage throughout with 8.7v ish at WOT when pushing the flap.

Connected AFM in the car with ignition on and voltage climbed and maxed out at 4.5v output at full flap. Huh?

Pulled off the connector lead and tested the voltage with ignition on; 4.97v across t4 and t3.

Is that the correct? Should that input voltage be 12v?