@tshih914 .
cal tech man. i'm impressed.
and driving a 914 back then. man of taste.
my business partner is a chemical engineer.
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ok i spoke to mike finally.
here is what you do.
now that we have discovered the AAV and decel issue they must now be taken 100% out of the mix for further trouble shooting.
pinching the hoses is not adequate. thats merely a initial test to note that you can lower the revs closing them.
1. pull decel hoses as previous test. plug them at the ports with 100% sealing plugs.
the decel valve is not to be hooked up again while the trouble shooting work is being done. it is not required for this work.
you can reinstall it later if you succeed in adjusting it properly. at the end of everything else. we know this drops the revs 400-500 going off your video.
2. pull and plug the AAV hoses. mike did not think that the huge drop in revs you were getting at times by clamping it was out of order. cold it is wide open. and since we know its stays wide open the warmer the engine gets the faster it can run on the fuel being made available to it.
3. in consideration of the hard starting you could start the engine and warm it with the AAV connected if this helps to start it. then stop the engine. disconnect and plug the AAV at the ports and the hose. probably most convenient where it connects to intake duct.
4. ensure the timing is correct. this can be done statically. it is surpsingly accurate if set this way. so long as you know what you are doing. if the timing is out, setting it statically will get it closer to where it ought to be than where it is now.
5. check the points gap. it is essential that the points are clean and set precisely.
6. check that the accelerator cable is not pulling the throttle plate even open slightly when you have it connected up. ensure that throttle plate is completely back at rest on its stop and not being even cracked open a little bit.
7. what you are going to be doing is manipulating the AFM flap by hand with your fingertips while the engine is running. in the case of a 914 due to the air cleaner design and AFM location you will find it best to unbolt the AFM from the upper aircleaner it is attached to but still connected to the air intake boot. you need to be able to get your hand in a comfortable position to be able to gently manipulate the AFM Flap for what is ahead. it will probably be necessary to get the rest of the air cleaner out of the way/
8. it is essential that the idle is lowered as far as possible for this exercise.
there seemed to be promise that with those hoses effectively plugged and engine fully warmed it might drop as low as 1200 rpm. if its still to high - say 2000 rpm try and bring it down by adjusting the idle screw on the throttle body. do it in small amounts.
and give it time to settle between each small adjustment.
9. play with the throttle in the engine bay. get used to finding a comfortable position where you can manipulate it very gently opening it small amounts and opening it slowly.
do this with out the engine running. just find out how you can position yourself.
what you are going to be doing is manipulating the AFM flap with your left hand and the throttle with the right hand while leaning into the engine bay. so you need to work out where to position the AFM and prop it and where to position yourself and do all this.
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A after timing is set, points checked, decel definitely out and plugged. start the car with the AAV still connected if you think this will help. let the engine warm for at least 5 minutes. if you want to control it a bit and lower revs pinch the AAV hose shut and just let it run as low as you can get it until its warm. you will feel the engine heat and know its hot enough.
B. switch off. disconnect AAV and plug the hose and port 100%
restart. hopefully it can without AAV assistance once its warm.
if necessary lower the idle further if its still high at say 2000. get it down as low as you can. it might go unstable due to further air leaks we haven't found yet. ie it will lean out. just back it back off again if it does. go for as low as you can get it to be.
C. once its idling at whatever you can it to. hopefully somewhere down there between 1200 and 1500 its time to play with the AFM. push it in very gently and very slowly very small amounts. what you are doing is tricking the ECU to deliver more fuel.
you are changing the mixture. we want to see if the ECU is getting the AFM signal.
the throttle will still be closed and we will have taken the major air leak routes out, so the revs and tone of the engine should change if the AFM is working and also communicating.
remember very small manipulations. you will get the hang of it and can play around a bit with it.
if it does respond we go to D.
i have always been uncertain about this bit as i believed the throttle position switch controls the mixture at idle. and it does. but mike says, like Van, that if the AFM flap moves far enough it will provide info too. usually it does not at idle because it is not being pulled far enough to override the idle circuit in the ECU.
D this is where you are going to crack open the throttle and play with the AFM at the same time. now you don't want to open the throttle wide and suddenly. you want to crack it open and hold it open a little bit. and then if it falters push the air flow flap a small amount as well. see if you are able to keep it running. if you can keep working up the scale. a little more throttle - a little more AFM flap.
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why are we doing this.
its to see if in fact
@Van B is right.
Van is basically saying this thing has a mixture problem in very crude terms.
its not getting anything like enough fuel out of the injectors once the full pressure comes on. EDIT - more properly Van is saying its not getting its fuel delivered in the correct way as an atomized mist pointed in the right direction as well as possibly not giving the full flow rate at throttle open fuel pressure. but you can trick it to prove this.
mike agrees with Van. he is not saying this is necessarily the cause but the above test will certainly tell you whether it is or not and it will also affirm the AFM is working and communicating.
the problem you have got is you are way up there in revs at the moment at "idle"
and then you are wanting to open the throttle and the AFM is actually at a point lower down the rev mountain (in terms of fuel and air). so we need to be doing this test from a point where we climb the rev mountain if possible with the throttle rather than fall off the cliff if that makes sense.
anyway this test is going to tell you a lot.
it might take you a few attempts to master this given the fickle state of its idle and its cold start problem.
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as to cold start difficulty.
timing. timing. timing. points gap. points gap. points gap.
and is the cold start injector working.
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as to badly spraying injectors.
not just flow rate.
i got a lecture on where the injectors might be pointing whatever spray pattern they make. correctly functioning injectors are pointed directly at the back of the valve where it seats. vaporization in a warmed engine completes the job atomization has done.
if they are spraying anywhere else at other surfaces fuel won't vaporize effectively.
etc etc. unhealthy injectors can produce a whole series of difficulties of which Van B is only hinting at because he knows what it all means just like mike does.
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see how you go with this.
at least you will be able to feel confident with your AFM after this if it works.
and also your AFM to ECU connections.
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As an aside L jet is as reliable as D Jet and far simpler.
Its just a matter of making sure all the components are working to spec.
running well an L jet is real sweet in my humble opinion.
not that there is anything wrong with a D Jet 2.0 either.