85 3.2 Rebuild - Starts then Stalls immediately

[nagromike911]

Hi Everyone. Just got through my rebuild and have been having real problems getting this 3.2 to light up and stay lit! I've read through all the posts about idle issues but this seems strange and would appreciate some help.

Basic symptom is car now fires very quickly with key turn and then struggles to keep running and stalls almost immediately, after a few seconds.

Checked, Spark is good on all cylinders, fuel pressure is 35 psi when starter motor is turning engine over. Checked inputs from speed and ref sensors on a scope and all look very strong. Injectors are clicking during turn-over and scope shows injector pulses going out.

I'm suspecting the AirFlowMeter (AFM) or the Idle Control Valve (ICV). I checked the voltage fed back to the DME from the AFM at idle and I'm seeing 238mV; not sure what this should be.

ICV is buzzing and I've removed and cleaned and valve seems to move when I shake the thing. Does anyone know of a way to check ICV other than feeling the buzz and shaking it to hear the clunk?

Here's the strange thing, which I'm hoping is also the clue. I partially opened up the AFM flap (don't tell anyone but I used a wooden hammer handle) and when I get 2V or more into the DME from the AFM, it starts and runs but hunts up and down in revs and eventually just dies on it's own after 30 seconds or so, or if I pull out the object. I would say the revs go between 1K and 2K while it's running. I'm thinking that's because the DME is confused about the mixture etc.

I've pulled the AFM and added the soldered wire mod, moved the pick-up points on the carbon track but I'm wondering if I messed up the calibration of the AFM in the process.

Just wondered if anyone could point me in the right direction as to what I should try next.

Thanks from a sunny and cool Dallas

Mike

[Peter M]

Mike,
I frankly have no idea.

But assuming it ran OK before you rebuilt it, you could be forgiven for assuming that all the sensors are OK. So could it be something as simple as the two reference and speed sensor connections on the LHS of the engine bay being mixed up?

[proporsche]

you said the fuel press is 35?? it has has to be 2,5bar 35 system pressure if you are testing the pump.When cranking or engine starts 2,3-2,7 ..
Did you plug some of the fuel lines when you had the engine out?Double check that..

One more thing ...just in case ..you have the distributor on number one cyl not on number 4 ..try that...

Ivan

[MBEngineering]

HI Mike

check the White head temp' connection on the L/H side is ok, also the throttle is closing onto the mico switch,

have a look through this, it may help?







if you need any more info' let me know

regards mike
(sorry the photos are side ways on)

[Tippy]

My 3.2 died every now and then when I first rebuilt it.

Over time, as it broke in and loosened, wasn't a problem.

Mind you, this "tight" time frame was pretty short. Maybe like a few days of driving.

Motor just maybe a little tight.

[prschmn]

Vacuum leak? Fits the symptoms.

[nagromike911]

Thanks Everyone for the swift replies and help. Will look into some of these and report back. I scoped out the ref and speed sensors and they appear good and in the right place. Also they are making it through that first bosch chip on the DME and I am getting injector pulses (neg going) at pins 14 and 15. I double-checked the vacuum lines and I did previously have the ones on the throttle body swapped but now that's OK. Getting strong spark to all 6.

Proporsche, you mentioned the fuel pressure and I didn't quite understand this statement 'When cranking or engine starts 2,3-2,7 ..' Would you mind clarifying please. I will recheck the fuel pressure; I need to get a new gauge as I'm not sure I trust the one I have.

Thanks again

[proporsche]

about the fuel pressure..here is some reading.
What i meant is this..sometimes when people remove the engine they plug the fuel line with some kind of plugs. Then when the fuel is connected the plug stays - or is forgotten that will create to big of a fuel pressure ,symptoms car starts and then dies.

Also did you recheck position of your TDC distributor rotor facing no.1 cylinder.

And one more thing the ground strap on cyl number 1 intake.

Ivan

https://www.porscherepair.us/porsche-911-1984-1989/fuel-supply.html

[nagromike911]

Thanks Ivan. Now I understand your point about the fuel but I drained the tank and so did not need to plug anything. I went over and cleaned the ground straps everywhere and re-attached, so think they are good. I will recheck TDC and distributor rotor, just in case.

Mike