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for all you 3.6 conversion peeps...

so i have a newly transplanted 3.6 in my 71. it was running and checked out ok when i bought the motor 2 years ago so i wasn't expecting this much trouble from it. what i read about 964 motors (ISV, DME, etc) even perfectly running motors can be finicky so trouble shooting i go...

here's what's happening:
1) car fires up after a few cranks (shouldn't it fire right up on first crank?)
2) runs for a couple seconds then quits

i cleaned out the ISV and noticed there is a sleeve or something inside that doesn't seem to slide. is it supposed to or is this stuck?

there's also what looks like a vacuum port not connected to anything and i feel a lot of air being pushed thru when it stalls.

any ideas?

Old 09-09-2018, 06:10 PM
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TAV TAV is offline
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Hi G50

Does the car even idle properly before it stalls?
The iSV does have a sliding valve inside that you can feel mivung about if you chive a little shake.

Sounds like you could possibly have a vacuum leak somewhere?
Old 09-09-2018, 06:24 PM
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i removed the ISV and noticed the sliding valve is stuck partially open. is it supposed to be able to move freely without power?
Old 09-09-2018, 06:50 PM
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That port you’re pointing to 100% needs to be plugged or hooked up to something. Mine takes a couple seconds to crank if it’s sat for a week or so and bled down fuel pressure. Should crank right up on a restart
Old 09-09-2018, 06:55 PM
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thanks smokintr6. i’ll plig it up tomorrow and see what happens.

i also cleaned out the ISV again and this time got the valve to open and close. it was stuck with carbon build up. i tried firing it up after cleaning and it runs a little longer but still stalls out.

i saw a mod where people are tapping a set screw directly into the ISV. looks hacky but seems there are some reputable shops doing this mod. anyone heard of this?
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1971 911 (PTS Black) - Built 3.6 Sleeper
1989 911 (Grand Prix White) - Cabriolet Bone Stock
Old 09-09-2018, 08:19 PM
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I think if you do the ISV mod, it no longer works as an ISV, you're basically limiting its travel, and it can never clamp down again. I would like to have a couple hundred more RPM at idle, so i briefly looked at ISV trickery. I didn't see one that seemed appealing. Admittedly, I didn't look very hard.
Old 09-10-2018, 05:52 AM
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not sure if this is of any help, but try looking at the ISV to check out the percentage opening (with the one side boot removed) as you are cranking the motor or as the car is idling. you might be able to see if it's working properly or not that way.

on my car, i'm using a different aftermarket ECU but i had to program the ISV (with some help) and i can visually see the % opening of the gate i had it set to thru the ECU tuning software. with car off, the metal gate rests around the 40-45% opening position and wiggles around freely(almost spring like) when gently moving it with a q-tip. i had to experiment with it on my build as well but that's mostly due to the aftermarket ECU and getting that to talk with the various sensors and switches on my motor.

here are couple photos of mine:


Old 09-10-2018, 09:52 AM
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The symptoms you mention can be caused by a bad connection to
the Cylinder head temp sensor, here's a post I put up when I had
a similar problem, good luck:

964 hard/no start problem
Went to start my '80SC with 964 3.6 transplant yesterday and had
a starting problem. Motor would crank and fire off but would not keep running. Found if I modulate the throttle, I could keep it running and after taking it for a drive it would start AOK, but the idle was a bit up and
down i.e. not steady.

First thought was a bad cylinder head temp sender, so I pulled the
plug at the engine and the ohm reading was right on for a warm engine.
I then let the motor cool over night and checked the temp sensor reading at the motor. It read right in spec at 3.6K ohms. So the sensor seemed OK.
I then used the trouble shooting chart below and pulled the
DME cable connector off the ECU and tested the test points at the connector. Everything tested again at the correct 3.6K ohms.

I then got out my can of DeoxIT D5 connector cleaner and sprayed
the test points. Hooked it all back up and VOILA she fired up just like normal.Everything is now working perfect!

According to the trouble chart, if the ECU doesn't see the correct
resistance it enters "limp home" mode and will run, just not correctly.
It seems that was the problem I was experiencing. So a little DeoxIT
D5 performed like magic and fixed it. I have never experienced any
connection problems with the DME/ECU connection before, but I now think I will pull the connector off again and spray all the connections.
Thank god I had the service manual or I still would be scratching my head!



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'68 911 Coupe Orange, '68 911L Soft Window Targa
Old 09-10-2018, 11:49 AM
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so after tinkering a bit i realized something... my problem isn’t exactly the run-of-the-mill engine stalling issue that i’ve read. seems like my engine cuts out at roughly 5-7 seconds of running. it’s almost like the fuel pump’s power cuts off and it dies. could also be the dme?

does this ring a bell to anyone?
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Old 09-10-2018, 08:16 PM
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Have you tried bypassing the DME relay just to make sure it isn't flukey? Should be pretty easy to check if the power to the fuel pump is going away. Also make sure that all the wiring dealing with the ignition switch is sorted & the switch itself. You could have power to things when its in the crank position that goes away when you let the key relax to the run position.
Old 09-11-2018, 05:55 AM
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Quote:
Originally Posted by smokintr6 View Post
Have you tried bypassing the DME relay just to make sure it isn't flukey? Should be pretty easy to check if the power to the fuel pump is going away. Also make sure that all the wiring dealing with the ignition switch is sorted & the switch itself. You could have power to things when its in the crank position that goes away when you let the key relax to the run position.
thatís exactly what i was thinking. iím going to check the power to the fuel pump when i get home later.

i have a new regulator coming in today also so hopefuly one of the two does tbe trick!
Old 09-11-2018, 06:56 AM
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Have you checked your DME ground? Not uncommon in these 3.6 conversions with splicing harnesses together to not have a good ground.
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Old 09-11-2018, 07:24 AM
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Quote:
Originally Posted by 175K911 View Post
Have you checked your DME ground? Not uncommon in these 3.6 conversions with splicing harnesses together to not have a good ground.
i checked but havenít double checked. iíll pull the seat and maybe grind the contact points in case it wasnít done.
Old 09-11-2018, 07:51 AM
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quick question... the DME relay i have has the round contact points vs. the blade type. every reference i see for 964 show the blade type. do i have a carrera DME and not a 964? are they compatible?
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1971 911 (PTS Black) - Built 3.6 Sleeper
1989 911 (Grand Prix White) - Cabriolet Bone Stock
Old 09-12-2018, 12:54 PM
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Most conversions use the earlier Carrera relay with the round plugs.
The reason is the 964 flat blade relay plugged into a relay board in the 964 chassis, not very adaptable. The round plug version could be used with
the earlier Carrera standalone plug receptacle. The relay functions identically.
And yes, you have a Carrera DME relay.
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'80SC Widebody 3.6 transplant Anthracite "The Rocket"
Long gone but still miss them all:
'77 911 Targa, '72 BMW 3.0CS Coupe(finest car I ever had!)
'71 911T Coupe White, '70 911T Coupe Blue
'68 911 Coupe Orange, '68 911L Soft Window Targa

Last edited by uwanna; 09-12-2018 at 01:10 PM..
Old 09-12-2018, 01:06 PM
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