No start - conversion to 3.6

[BobTucker]

Hey guys, Need help with no start after installing a 1990 964 in a 1973 T.

This is a conversion to a 3.6, all pieces are supposed to have been tested and were working: brain, harness, engine.

I have checked all I can think of but still no luck. I have a good ground to the DME unit. I have power to the DME relay, when I jump the DME relay I can hear the pump run. I checked the crank sensor while cranking with an o-scope and there is a signal. I would like to make sure the harness is OK but don't have a wiring diagram (manual out of print back ordered Bentley). My plan was to test the signal at the brain while cranking.

Anyone have a pinout diagram for DME? Or full wiring diagram for 1990 C2?

I suspect the brain at this point as it completes the ground when it sees 30 rpms or greater from the crank sensor. Is there some other parameter that needs to be true for engine start? I would like to test this theory with a known good unit but am reluctant to borrow one in fear of toasting it as my harness could be bad.

What's the best process of elimination?

Thanks for any information!!
-bt

[ChrisBennet]

Bob,
I have a the 964 manuals including the wiring diagrams and the engine manual has a test plan. I don't have a car during the day but if Rich is going to your house for something I could give them to him to give you.

Just an idea...
For safety reasons, the DME does not energize the fuel pump unless it knows air is going through the motor. (You don't want to keep pumping fuel if the motor has stopped in a crash.) In order to start the car though, the DME has to ignore that "rule" when you are starting the car (no air going through the motor yet). If the DME doesn't know you're trying to start the motor...

Maybe 30rpm is fast enough to produce the "air through the motor" condition that the DME needs before it energize the fuel pump relay?

-Chris

[BobTucker]

Hey Chris,

Thanks, yes I'll try to send Rich over to grab the manuals, I've ordered a new sensor to try. Not sure if it needs a stronger signal. The wiring harness had some burned parts and was "fixed" and I fixed it better by cutting out all the short circuited stuff and putting in new wiring and then soldering the connections and heat shrinking the connections. The harness and the brain were supposed to have been working OK.

Yeah I know that the DME has a rule that prevents pump running but thought that was keyed to the crank sensor. I got the 30 rpm from the Enthusiast's manual. The E manual does not give quite enough info. In later years there was an alarm interlock as well.

Thanks again, great to see you at the last DE!

[ChrisBennet]

Originally posted by BobTucker
Hey Chris,

Thanks, yes I'll try to send Rich over to grab the manuals, I've ordered a new sensor to try. Not sure if it needs a stronger signal. The wiring harness had some burned parts and was "fixed" and I fixed it better by cutting out all the short circuited stuff and putting in new wiring and then soldering the connections and heat shrinking the connections. The harness and the brain were supposed to have been working OK.

Yeah I know that the DME has a rule that prevents pump running but thought that was keyed to the crank sensor. I got the 30 rpm from the Enthusiast's manual. The E manual does not give quite enough info. In later years there was an alarm interlock as well.

Thanks again, great to see you at the last DE!

Yeah, I think you are right on the "air through the motor" theory. It would make sense to key it to the crank sensor. (In my defense, I wasn't thinking clearly; I was drinking heavily and trying to drive while texting in my post on my PDA/phone. It probably wouldn't have been a problem if I hadn't gotten high before. I have got to lay off the drugs.)

The flywheel sensors on the earlier Motronics can work with a pretty weak signal I know. The heat kills the wiring and they get flakey after a while.
-Chris

[jevvy]

Hi Bob

You dont say what is actually happening when you try to start, does it crank and not fire, crank fire then die or not crank at all. I had the "crank fire then die" issue with mine and it was solved by sourcing an ECU wit ha "123" part number as my "124" nersion was drive blocked.

Heres a usefull thread of another pelican that had this problem:

any 993 3.6 DME gurus out there? Car wont start

[BobTucker]

Hey jevvy,

Right, I was thinking that you could read my mind, eh. It cranks but does not have any spark and the fuel pump does not run. What does drive blocked refer to? the control unit is a 911.618.124.02 (bosch 0.261.200.182) is this the 124 you refer to? I have not tried jumping the DME relay and cranking to see what happens yet...

I'll check out that link-
Thanks

[ChrisBennet]

I think Drive Block is a 993 motor thing not a 964 motor issue.
-Chris

[BobTucker]

dude, I have the 124 DME unit...I also have a new chip but was waiting until I could get it running to change it as it has "tamper" tape on it.

Cheers

[jevvy]

Hey bob

Sounds like you do have a 993 engine ECU with part number ending in 124 that is drive blocked, most of what I know is in the other thread but here are the important bits: (it may be worth trying the chip you have as that might have the driveblock bypassed)

As far as I remember with a 124 part number ECU is is matched to the imobiliser on the car and you would need all of that to get it to work with the current ECU.

You have 3 options:
Buy a new 123 ECU (this is what I did)
Get the ECU unlocked (As Ian says Steve is the man for this but you might also get him to 'chip' it at the same time as I think it costs very little more)
Buy a 'chip' for your ECU - Steve Timmins cyntex(sp) chips for example.

As an off the wall idea when I spoke to Robbie at Ninemeister in the UK he was sure that on 1 conversion he got round the drive block by connecting one for the black wires that come out from under the drivers seat in a 3.2 to one of the pins on the ECU but he couldnt remember exactly which one - might be worth looking into.

Good luck sorting it out - I know I was sooo frustrated when I found this out on mine as everything else was in place and the car would hav fired up first time after the conversion had I had a 123 ECU.

Chris I think you are right about driveblock being a 993 'feature' however it sounds like bob has that ECU and not a 964 one.

[ChrisBennet]

Jevvy, Bob,
The 964 shouldn't have a drive block problem.
Note that there are "124" 964 ECU's and 993 ECU part #'s but they are different animals:
1990 964 ECU part# 911.618.124.04
1995 993 ECU part# 993.618.124.06
-Chris

[jevvy]

thanks chris, sounds like you know more than me about this so I will bow out gracefully.

Good luck sorting it out Bob, you will have a blast once its running!

[DW SD]

Bob,
Did you try adjusting the crank position sensor? I know you said you could read the signal with an o-scope, but does that mean it is in the right range for the computer to read? On the 993 conversion, the cps is set at .8mm, I think. I'm quite sure on the 993 the computer must read that the crank is spinning to energize the fuel pump relay. I bet the 964 is the same.

I'd also assume the same conditions would be met before the computer generates spark or opens the injectors.

Doug

[BobTucker]

Thanks Doug,

Yes I have modified the 915 trans so that the larger sensor fits in there. I was told by Steve Timmins that the gap should be less than 3 mm. I have the sensor as close as it will go without modifing the sensor housing itself. I have a new sensor that I will try tonight and see what happens. I don't have a manual yet so I am going by the 964 Enthusiast's manual (Bentley) which states that once the DME "sees" 30 rpm or greater then ground is provided to the relay.

Thanks again
-bt

[DW SD]

I know Steve knows his stuff.

I used Patrick Motorsports flywheel in my 993 to '71 conversion. It has specific instructions which require modification to the bell housing + some potential grinding on the crank position sensor mount. The distance between sensor "teeth" and sensor is only .8mm in the 993 application. ***Please note, I'll double check this spec by digging out the instructions - .8mm is from memory.***

I could send you a PDF via email or fax you the directions sheet, if you are interested.

Let me know.

Good luck,

Doug

[ChrisBennet]

964 gap is 1.0mm +/-.2
Jerry Peligrino (EPE) told me closer is NOT necessarily better. Your scope should show you that though.
-Chris

[BobTucker]

IT RUNS !!!!!!!!!!!!!!

I should have read the manual more than twice !

Thanks for all the support on this one guys. It came down to a missing ground. I replaced the crank sensor and it still wouldn't start so I jumped the relay and it fired up. In Steve's manual it states to connect the brown wire to ground. In my defense I was wondering what to do with the orange wire...I didn't put it together until I noticed the color of the wire at terminal 85 of the DME relay and then the light came on...or the ground was compeleted.

Thanks again very much!
Cheers
-bt

[jevvy]

excellent - so whats it run and go like or do you have other stuff to finnish before you can go for a spin?

[BobTucker]

Hey Jevvy,

I don't have brakes right now and it's a race car so I can't drive it down the road..or at least legally. I may have to get some temporary brakes on it so I can check out the trans and give it a shake down. Just replaced the rear arms with aluminum ones so I need to do a quick align as well.

I put the chip in late last night after confirming it ran and noticed the difference in how quickly it revs. It has great oil pressure and sounds strong. Can't wait to get it to the track!

Thanks and cheers

****************
Tucker
73 911 T 3.6 now with retsyn and more power

[jevvy]

cool, I will keep my eye out for you first track report!