3.6L into '74 911 Conversion - Troubleshooting No Spark

[Tom '74 911]

Hello -

I'm hoping for some trouble shooting help. I am in the final stages (hopefully) of installing a '90 3.6L engine into my '74 911. I tried to start it for the first time yesterday and while it cranks, it will not fire. I checked for spark by pulling a plug wire, inserting a spare plug and grounding it, and watching for a spark when cranking the engine - with the fuel pump relay disconnected. I can hear the DME relay click when I turn the key, but no spark.

A few notes about my install:
I am using the main Patrick Motorsports conversion harness in the passenger compartment that connects to the main wiring harness by the DME. I did not connect the wire in the harness to the fuel pump. In my '74, the fuel pump runs continuously when the key is in the 'on' position - I can hear it running when the relay is live.

In the rear engine compartment, I pulled out the entire stock fuse/relay panel and modified the 14 pin connector on the car side to accommodate the 14 pin connector from the engine. I tried to follow wiring diagrams and match everything up. Here's what I ended up with:

1. Yellow - Starter
2. Blank
3. Blank
4. Green/Red - Oil Pressure
5. Green/Yellow - Back Up Light
6. Grey/Brown - Back Up Light
7. Blank
8. Blank
9. Green/White - Oil Pressure Light
10. Blank
11. Blue - Alt. Light
12. Red - Alt./Batt 12+
13. Blank
14. Blank

When I had everything together and made the battery hot for the first time, the fuel pump was on and a few gauges and lights on the dash were 'on' even though the key was not in the ignition. By disconnecting the Red wire @ the #12 pin above, everything acted normally.

So one of my questions is: does the 'always hot' Red wire on the engine side of the 14 pin connector in the engine compartment need to go through the connector? It seems that if it does run through, it backfeeds power to some things. Since I removed the entire stock rear fuse panel and associated relays, I assumed it is not necessary?

My other questions are all related to starting the troubleshooting process for no spark. After putting a spare plug in an unplugged wire and verifying that there is no spark, how and what should I check next?

Coils, Grounds, the DME itself?

Thanks in advance for your help!

Tom

Notice the trick, highly custom (temporary) overflow/breather tank:

[ischmitz]

The DME relay (part of the Patric harness) is controlled by the DME. Once you crank its second stage supplies power to the fuel pump.

The first stage of that DME relay supplies +12V to the injectors and one side of the coils as soon as you turn the ignition to ON. So you can measure this +12 V on both screw terminals of the coil when the ignition is in the ON position. Once you crank one terminal of the coil is pulled to GND for a very short period of time and then returns to +12V. This creates the spark. It is driven by the ignitor modules which get their signals from the DME itself.

Things to check:
1. Does the first stage of the DME relay turn on when you turn the switch to ON
2. Do you see the +12V with the ignition in ON at both screw terminals of the coils
3. Does the second stage of the DME relay switch on when you crank?

Ingo

[Tom '74 911]

Originally Posted by ischmitz

Things to check:
1. Does the first stage of the DME relay turn on when you turn the switch to ON
2. Do you see the +12V with the ignition in ON at both screw terminals of the coils
3. Does the second stage of the DME relay switch on when you crank?

Ingo -

Firstly, thanks for your help! I feel like I'm so close, but can't quite get to the finish line.

I checked:
1. First stage of DME relay - I can hear a 'click' from it when I turn the ignition ON.
2. I DO see +12V at both screw terminal of the coils with the ignition ON.
3. Second stage of DME relay - I can hear another 'click' when I start to crank.

Is there a way to determine if the DME relay is working other than listening for audible clicks?

Thanks again,
Tom

[ischmitz]

If the Patick Motorsports harness follows the factory wiring the second stage of the DME relay powers the fuel pump and the O2 sensor heater. So if the fuel pump turns on only when you crank this is a very good sign.

Do you get fuel (smell raw fuel in at the tail pipe) after prolonged cranking?
Does the resonance flap actuator click when you turn the ignition to ON?

Both are signes that the DME itself is alive and well.

Ingo

[Tom '74 911]

Originally Posted by ischmitz

If the Patick Motorsports harness follows the factory wiring the second stage of the DME relay powers the fuel pump and the O2 sensor heater. So if the fuel pump turns on only when you crank this is a very good sign.

Do you get fuel (smell raw fuel in at the tail pipe) after prolonged cranking?
Does the resonance flap actuator click when you turn the ignition to ON?

Both are signes that the DME itself is alive and well.

Ingo

Ingo -

I haven't wired the fuel pump portion of the PMS harness. I kept the old fuel pump relay and wiring intact so the pump turns on when the ignition is switched to ON. I can easily wire in the PMS harness fuel pump power wire - I left that wire loose and unterminated by the front fuse box. Strangely, I do not get a raw fuel smell at the tail pipe after cranking even though I can hear the fuel pump running continuously - although I haven't cranked for more than a few seconds at a time.

I have heard a clicking in the engine compartment - I assume it's the resonance flap actuator. It does click when the ignition is turned to ON.

Thanks again for helping.

Tom

[Tom '74 911]

A side thought in regards to not smelling any fuel in the tail pipe: the engine (and injectors) have been sitting for over a year. About a month ago, I pulled the injectors and tapped A LOT of crap out of them from the top. It's possible they are stuck. I remember reading somewhere that it's possible to get them moving/unstuck by using a 9V battery? Do I unplug the electrical connector at the injector and touch the terminals on the injector with some short leads from a 9V batt?

Thanks,
Tom

[wax105]

Tom,

I assume you're running a PMS conversion flywheel?!?

I had the same type of issue and it turned out to be bad gapping on the crank sensor... Should be .8mm if I remember correctly, had to slightly modify the sensor bracket and she fired right up. If you have no fuel make sure you have crank signal. Good luck

[ischmitz]

If the DME relay clicks when you crank that is a good sign the DME is "seeing" the crank sensor fine. However, you need to confirm whether you have fuel and igntion signal issued by the DME. So your best option is to get an LED test light to verify the fuel injectors are fired. Next, make sure you have proper power and GND to the ignitor modules so the ignition can produce sparks.

ingo

[Tom '74 911]

Originally Posted by wax105

Tom,

I assume you're running a PMS conversion flywheel?!?

I had the same type of issue and it turned out to be bad gapping on the crank sensor... Should be .8mm if I remember correctly, had to slightly modify the sensor bracket and she fired right up. If you have no fuel make sure you have crank signal. Good luck

Wax -

I just checked the gap and it's a hair over .8mm - my .813mm feeler slides in/out, but with slight resistance. I will snug up the gap to see if it makes a difference.

Thanks for the idea!

Originally Posted by ischmitz

If the DME relay clicks when you crank that is a good sign the DME is "seeing" the crank sensor fine. However, you need to confirm whether you have fuel and ignition signal issued by the DME. So your best option is to get an LED test light to verify the fuel injectors are fired. Next, make sure you have proper power and GND to the ignitor modules so the ignition can produce sparks.

ingo

OK, I have a test light.

For the injectors, I'm assuming I unplug one of the electrical connectors, connect the test light to it and then crank the engine? Should I connect the test light to each of the 2 poles or to one pole and then ground the other? Maybe it doesn't matter as one of the poles is probably ground anyway?

For the ignitor modules, I looked and each electrical connector has 5 pins. Looking at the wiring diagram, it looks like pin #2 is ground, pin#1 goes to the respective ignition coils and pin #5 is signal 'IN'. To check for signal in and out of the ignitor, do I simply put the test light in pin #5 and pin #1, ground the other end of the light circuit and crank the motor? If the light flashes during cranking, the signal is good? Would I check the ground pin in he same way?

Sorry for the basic questions. I only know enough about electrical stuff to be dangerous and would rather not make things worse by using bad test methods!

Thanks for the help,
Tom

[CabMike]

Make sure you have the dme hooked to a power source that is hot when cranking. I had similar symptoms with mine and it turned out I just needed to move one wire on the fuse panel.
Good luck!

[Tom '74 911]

Originally Posted by CabMike

Make sure you have the dme hooked to a power source that is hot when cranking. I had similar symptoms with mine and it turned out I just needed to move one wire on the fuse panel.
Good luck!

Mike -

As easy as this sounds. . . this was it!!! I checked the switched +12V wire at the front fuse box at least 10 times over the course of going over all my wiring. The terminal I had connected it to showed 0V with the key 'OFF' and +12V w/the key in the 'ON' position. I assumed it stayed hot in the 'START' position - not so! I did some more testing w/my multimeter while my wife did the cranking and found one that had 0V at 'OFF' and showed +12V at 'START' and that was all it took. (There were a few more steps in there of trial and error including one where the engine continued to run even after I turned the key to 'OFF'!). As complicated as I can make things, the solution is usually a simple one. But now everything is working as it should and I am a happy guy.

I can't tell you how happy I am to hear the motor run. Now it's on to the next set of challenges - exhaust, heat, oil tank overflow etc... it will never end, but at least it runs now!

Ingo & Mike - thank you for your help!

Tom

[CabMike]

Tom,
Glad that worked! My harness came from Timmins and his documentation had it hooked to the wrong fuse, but his troubleshooting tips led to the correct one.

I've had mine running for about 6 weeks and I'm just about to resolve all of the little issues. I drive it a little further each time as I build confidence. My biggest issue was getting the exhaust sound level to where I wanted it.

You will love the extra power!!

[Tom '74 911]

Originally Posted by CabMike

I've had mine running for about 6 weeks and I'm just about to resolve all of the little issues. I drive it a little further each time as I build confidence. My biggest issue was getting the exhaust sound level to where I wanted it.

Mike -

Yes, I expect it to take some time to work out all the bugs. Can I ask you a few more questions about your conversion?

I'm assuming that your exhaust issue is that it's too loud? What have you tried and where are you headed? At the moment I'm planning to use a Magnaflow 2in/2out - seems like a popular and well documented option. I'm planning to use the biggest one that will fit between my Fabspeed headers.

Also, I have a carbon RS heat tube that I tried to make fit but the interference between it and the left side motor mount looked to be too much. I knew I'd have to modify it because it didn't fit properly between the tin and fan shroud to begin with, but when I test-fit the engine, the motor mount interfered as well. How did you solve that issue?

Thanks again,
Tom

[CabMike]

I used Timmins "Happy Crab" muffler with 993 heat exchangers. I installed the car chemistry baffles in each output. The muffler is a flowmaster with the inputs made for the 993 exchangers. It was too loud without the baffles but is not bad right now.

I used a 4 inch long piece of 3.5 inch silicon turbo hose to make the carbon fiber tube work.

[wax105]

Good for you Tom!!

[Tyson Schmidt]

Check to make sure that your power supply to the conversion harness is connected to terminals that have power in both key-on, and crank positions.

There are a number of terminals on the fuse panel that have power in the key-on position, but power off during cranking.


OOPS! Edit.... didn't read all the posts before replying!