3.2 cranking but no spark
 

So I've been using the search function excesively all day but am a bit of wits end.

My car ran great yesterday I had an awesome day out at the track, and this morning I did some work on the instrument cluster, fixing the speedometer to use a proper harness (I'm installing 964 gauges). I went to take it for a drive to make sure that speedo was working. The car cranked but will not start.

I pulled the speedo cable off just in case but no change

The car is a 1971 with a fuel injected 3.2 from a 1989 vehicle in it.

I have done the following

1) Jumpered the DME relay with a 3 wire jumper and no change, DME Relay also clicks when I put my hand on it.
2) Replaced the DME with a second one I've had for several years, no change
3) It appears as if there is no spark, I'm not seeing one with a spark tester or when I pull a spark plug and lay it on the block.
4) The flywheel position sensors test with expected resistance at both the 35 pin connector and the engine connector
5) The coil has 12 volts and appropriate resistance
6) The distributor cap and rotor seem to have appropriate resistance.

I'm about ready to have it flat bedded to my local mechanic but any other thoughts would be appreciated.

Check the voltage going out of the DME relay. Make sure it is 12+ volts. I just had a similar problem and it ended up being a bad ground strap at the transmission.

Where would I check that voltage? Is there a good spot for it?

Pop the cover off the DME relay plug and check it on the backside of the connectors

Have you checked the voltage from key to spark plug? When I had the same problem I researched on here and with some local help. While I was very frustrated with the problem I learned a ton about my car and was successful in finding my problem by tracing the voltage.

Have you checked that you are getting proper voltage out of the fuse box?
Have you checked voltage on both sides of the coil? If yes, I would check at the end of the cable out of the coil to the distributor.
You have confirmed that some of the major components are OK (DME, DME relay, Coil, distributor, etc.) If it is a problem with no spark, it will be along that path way that you will find the problem (ground, bad wire, etc.)

Hope that helps.

I just had a similar problem with my '86 Carrera. Car ran great, then stalled and wouldn't restart one day (actually, it happened intermittently a couple of times before dying out completely)

I changed my DME relay out with my spare but no joy. I had no spark, according to a timing light and it ended up being a bad solder joint inside the DME computer for the ignition. I re-soldered it and it's running fine now.

You can do a search for 3.2 no-start and tons of results will come up. A quick diagnosis is to watch your tach as you crank, it will bounce as you're cranking if the ignition transistor is good in the DME computer.

The DME relay has two stages. Does it click once when you turn the ignition to RUN and a second time when you crank?

Does the ICV vibrate with the key in RUN position (DME is powered)?
Do you get fuel pulses (smell of gas after prolonged cranking, NOID light)?

Ingo

Well today I tried a second DME computer with no joy. I don't know what the NOID light is, and maybe I don't have it as I have older gauges in my car (although I'm working on the 964 upgrade now).

As I said in my original post I did a lot of searching and a lot of reading, unfortunately many of the post say things like

1) Check that the DME relay is working
2) Check that you have spark
3) check the fuel pump
4) blah blah blah

without telling you what to do if it fails a step. No complaints the info here is fantastic, but I finally worked out the built in search here kinda sucks, I found that putting in 3.2 no spark got me nothing, but another set of terms found me a post entitled "3.2 no spark" it seems using site specific search on bing might be a better choice just to try and help folks out in the future.

Anyway thank you all for the further suggestions, I finally gave up today as I'm heading out of town tomorrow for a bit and wanted the car to be working when I came back so I had it flat towed to my mechanic (Sigh) I so wanted the satisfaction of nailing this one myself!

2nd DME no joy.

Hmmmm, it is time to check the OHMs on the Ref and Speed sensors.

Next time please check your DME in another 3.2 engined 911, if your car as a fault, it could damage the new/donor DME.

Agreed there are a lot of posts out there and it's kind of hard to find the good ones. However, by the end of the day the DME needs three things to produce spark and I asked you a couple of posts ago to check for each. Not seen any response:

- Power to the DME
- speed signal from the sensor
- reference signal from the sensor

Check for each. Power is checked easily by confirming the ICV is vibrating. Did you do that??
Next, the speed signal can be verified by disconnecting DME, hooking up a digital voltmeter in AC mode to the correct pins inside the 35 pin connector and measuring while cranking. Verify you see a >2V AC signal.

Then, checking for reference signal requires an o-scope. With a voltmeter it's a little more difficult but you will see a small signal, too. An O-scope is better though.

If you don't have that alternatively, check if the DME produces a fuel signal either directly (NOID light plugged into the harness instead of an injector) or indirectly by confirming long cranking leads to strong fuel smell out of the exhaust.

A NOID light is an LED. Use Google as your friend and eBay to by it cheap for under 20$.

Based on your findings (still outstanding) you decide where to look for a fault: If you get a fuel signal but no spark its either the DME or the coil/distributor downstream. If you don't get fuel and spark it might be the reference sensor or the DME. In your case you swapped the DME and if you are reasonably confident the other DME is healthy I would look at either the coil or the reference sensor.

Testing the coil is described: Measure primary resistance and secondary resistance and verify it has +12 V on the primary.

Good luck,
Ingo

Any Update
 

My '87 suddenly will not start after sitting for a few weeks. Ran great up until then and then suddenly "no start." I changed the DME, all the fuses, put a fresh 5 gallons in and now have to dive in deeper.

Thanks

Any Update
 

My '87 suddenly will not start after sitting for a few weeks. Ran great up until then and then suddenly "no start." I changed the DME, all the fuses, put a fresh 5 gallons in and now have to dive in deeper.

Thanks

You must have done something while you were working on the inst cluster. retrace your steps.

follow up as I just realized I never closed this, it was one of the sensors on the flywheel the one which causes this, I had inadvertently checked the other one so I didn't find it. Car ran great (well until it just did the same thing again last sunday, but I don't know yet if it has spark even as I've not had time :))

Today I've found I have spark and I can hear the fuel pump running loosening a fitting and we get fuel coming out so what's next? What can cause injectors to not fire?

Simple answer:

-Bad DME
-Bad harness
-Bad injectors

How did you determine that the injectors didn't fire? Best use the NOID light or test light.

How did you determine you have spark at the right time?

Just want to make sure you're not jumping to conclusions.

Which type of noid light will work on Amazon there are ones like this http://www.amazon.com/OTC-3054E-Noid-Lite-Test/dp/B0071JJYLO/ref=sr_1_1?ie=UTF8&qid=1444606186&sr=8-1&keywords=Noid+Light will that work?

For spark I used an in line spark tester and it flashes so I know I'm getting spark at the right time? No way to know, but it's sparking, and it ran great until it just quit while I was driving it so I think that's all good

Tried jumping the dime relay after replacement didn't change anything and no dice, haven't checked fuel pressure yet not sure how to do that, advice welcome. Bad dme? I have a spare but want to isolate anything that might have roached it before I try, fuses are intact

In my case, similar symptoms, it was the reference sensor (IIRC) checked at the suggestion if ischmitz. What was odd was it would occasionally check out fine then later it would show bizarre, out of spec, readings. At first I thought I was just checking it wrong. Replaced it and it's worked perfectly ever since. Just waiting for the other one to fail...or something else to go wrong. Moronic no start issues are a complete PITA!!!

My understanding was that the reference sensor going bad would mean no spark. That happened last summer and it was replaced then.

Correct: If one of the sensors doesn't work there will be no fuel and no spark. If you have proper spark the sensor are fine. During cranking the frequency of sparks is low enough that you can see each event with a tester. Better yet get a timing light.

Let's see what the NOID light will tell you. The one on Amazon is fine. Here is an even better deal on evil bay: 9pc Electronic Fuel Injection Signal Noid Lite Tester Light Set GM Ford Bosch | eBay

They all work just fine

Ingo