Itermittent Start/No Start on 3.2 Conversion Car.... Please help.

[crashr]

I have a 87 3.2 Euro engine in my 1975 car which I can't get to start consistently. After we dropped the engine in the car the engine would start every time. Earlier this year the car was in at the body/paint shop and for the first time the car would turn over but appeared to have no spark. We went down to the shop and checked to make sure none of our wires in the trunk had come loose, it looked ok. We went to start the car up and it fired up. The car didn't exhibit this behavior again until two days ago after I got it out for my first drive in several years. The car ran fine. When I got home and turned it off a few minutes later I couldn't get the car to start. For the last few days the car doesn't appear to have any spark, but occasionaly it will fire up when we try it. When it starts up it runs perfect. You could turn the engine off after that and once again it won't start.

We have checked all our wiring from the conversion and it appears to be correct. The black wire at the coil has a constant 12 V however we get no spark. I checked to make sure there was 12 V at the DME relay pin on the security system (my car doesn't have one) and it appears to be there. I even took the DME relay out of a funcitoning 88 3.2 and tried it in my car and it still wouldn't start (so I ruled out the DME relay).

I am running out of ideas on what the issue is and how to isolate it. I am open to sugestions to what it could be.

[ossiblue]

Does the CDI box "whine?" Even if it does, it may be going south. Also, check the notorious "green wire" (do a search) from the CDI to the distributor.

[JeremyD]

What does the reference sensor look like? Was it installed correctly as in the correct distance from the flywheel?

[crashr]

I didn't think there was a CDI unit on the 3.2? I thought that came out with my 2.7. Am I wront here.

JeremyD, I will check the distance on the reference sensor. I guess I should probably check out to make sure it is sending the apropriate signal.

[kach22i]

Have you checked all of your fuses in both the front and back of the car? Sometimes they look fine, but take them out and they fall apart in your hand.

I may have a similar problem, can't tell yet:

No start last night - starts up this morning
No start last night - starts up this morning

[sbrown.nw]

From what I can tell from your description, my car reproduced similar or the same behavior, espeically with hot starts (fuel pump would buzz, plenty of juice and car would not turn over some of the times, then she would sit overnight and start fine). Tried 3 new (rebuilt) starters and it did not fix the issue. Installed the Starter Relay Kit Starter Relay Kit and now she fires up every time without problem (she is a 72T with an 85 Euro 915 and 3.2). Our host seems to be out of stock for this item but web searches should find you one for purchase...

Also, at the same time, I had my mechanic remove a "Mickey Mouse" detuning box on the Euro 3.2 from the wiring harness, restored the wiring harness to factory and put in a Steve Wong Euro chip and she starts the first time without stalls hot or cold and idles much better.

Scott

[Formerly Steve Wilkinson]

The green signal wire to the distributor is an item that most serious maintainers routinely replace every so often, it's that prone to failure.

[crashr]

Hi Steve,

I thought the only wire going to the distributor is the center coil wire which feeds the spark plug wires. Do you mean the green wire on the coil which goes back to the DME?

[Formerly Steve Wilkinson]

Well, my SC has carbs and no DME, so I don't know where it goes on yours. It's the short green wire that has a special connector on it and goes to a small plug on the back (toward the front of the car) of the distributor body, not the cap. It's actually a fairly delicate coax that often fails. Car will crank, everything else works, but no start.

[3.2 CAB]

It appears that some are getting the wrong impression about the type of system that you have, and the symptoms it has.

You state it is NOW a DME controlled 3.2 engine.
It did crank and run.
Now it does not start, but does turn over.
It will sometime start, other times not.

I don't see mention of a no cranking condition.
I would check the crank reference sensors and the wiring connectors to them.
The speed and reference sensors are hard to get a true idea testing, without a scope, in order to check the sine wave.

From what you have stated, I am in agreement about the cause could be the reference sensors. In order to check the distance, the holder would have to be removed, and the sensors removed, then reinstalled, using a 0.08mm washer temp. glued to the bottom of the correct sensor, and the the holder bracket installed, and adjusted and tightened. the the sensor with the washer removed, to have the washer removed, the reinstalled. The other sensor, will be adjusted correctly, because the sensor the has the washer, is actually adjusting the depth of the holder, this will allow the sensors to be held at the proper setting. Good luck!! Tony.

[crashr]

3.2 Cab you are correct it is NOW a DME controlled 3.2 engine. Also you have restated my symptons correctly.

I checked the reference sensor resistance and between pin 1 and pin 2 it was 1024ohms; which is within spec based off of Bently.
I also checked the resistance between 2/3 and 1/3 however they showed up as Infinite and not 100kohm. I know 100kohm is a high resistance but it is still different than an infinite resistance(open circuit). Does this mean that my reference sensor is bad?

I am picking up some probes for my osciliscope this week and will take a look at the AC signal. In the meantime can someone comment on the DC infinite resistance I am seeing?

Also I tried to use the 5mm Allen key to get the sensors off, but the bolts seem very coroded, any suggest on how to best get them out without stripping or destroying them in the process?

Just to add an extra kick in the pants, my car started up tonight, however after we shut it off and tried to turn it on a minute later it wouldnt start again. When it did start however it seemed to have to crank over for a few seconds as if it was still looking for that reference pin. Thoughts?

[crashr]

I was just reading through the archives. Although I don't think it is related but I thought I might mention that I believe my fuel pump may be wired to always be on when the key is in the on position. From what I have read it should wait to turn on until the engine is cranking over. Would this effect me in any way? If left for to long in the on position will the engine flood? I just thought it was odd that I can get it to start when I leave it for a few hours.

[TT Oversteer]

I have a '89 3.2 in a '77 911S. My fuel pump is on all the time when the key is on. I've never had any flooding or starting problems.

[crashr]

Ok good to know about the fuel pump.

Back to my question on the sensor. Does testing the resistance mean that the impulse sensor is working properly or can you get a proper resistance measurement from it and it still be malfunctioning? It appears that the car will start up when cold, but once warm I get no spark.

[3.2 CAB]

Hi Nick, don't replace the TDC sensor, that is only a diagnostic sensor, it has nothing to do with the engine running, it is test device only. You can try to test the, Ref/Speed sensors, but usually they will test ok with a meter, but the only real way to test is with a scope and check the sine. When it does die, have you checked to see if you have spark or not, if you do and it does not want to start, you might have a fuel problem, maybe a stopped up filter or strainer, or even a pump starting to seize up. Could also be the CHT sensor, even though you have a fairly new one, test it, it does not affect starting persay, it controls fuel, not spark, but it will make it run like crap. Another thing to check is the large vacuum line connection behind the heater blower, the one that tee's off from the metal pipe, it also has the little vacuum line for your cruise, on the y fitting, and the big vacuum hose for your brake booster, a lot of times these hoses at the fittings will crack, and cause a large enough vacuum leak and really screw up the way the engine runs.
As Ron said, I had a ref/speed sensor problem, if the outside temp was below about 70 degrees outside, the car would not start, no spark condition, checked everything, popped in a new DME relay, nothing... this went on for a few days, but after the car sat in the closed up garage all day and it got warm in there, it would fire right up, wouldn't turn over twice and it would start. That went for a couple of days, everytime I would try to start it after it sat getting warm in the garage all day, it would start right up, so then I decided to warm up the components, using a blow dryer, to see if it made a difference, first I warmed the DME unit, then the relay, no spark still, then the ref sensors wire connections, no spark still, rolled under the car and warmed the ref/speed sensors for about 10 seconds, rolled out from under, hit the key, it fired right up, ran perfect. Could turn it off and try it again, and it would start right up again and again..... So I left it till the next morning, was about 50 degrees outside and in the garage, tried starting it, would not start, NO SPARK, rolled under it with the blow dryer, heated the ref/speed sensors a little, rolled out, tried to start it, fired right up!!!! Went in and ordered 2 ref/speed sensors!! Replaced them, have not had a problem with the DME system since. I tried to find out what it could be that the temp would affect, before I discovered what was wrong with mine, but no one had an answer, kept being told nothing could be temp related to this problem. A Porsche tech helped me a lot, but he is over a hundred miles from me, but I would go there and he would help me trace the DME circuits and everything else that would control the running of these engines. He even had a colored DME circuit wiring diagram that was huge, like 2'x4' you could trace everything. I learned a lot from him about the DME system. Hope I was able to give you some ideas. Good luck.
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Last edited by 3.2 CAB; 12-01-2004 at 09:21 AM.

[crashr]

Thanks that does help. I am going to test the sensors with a scope and will report back on my findings.

[crashr]

So my car started all week when cold. You can start it, turn it off, start it again no problem.

I had to bring my car to the body shop to have the fender lips cut back. Its about a 30 min drive. Car ran great. As soon as I got to the shop I turned off the car and as expected the car would just turn over and over with no spark.

I did find this thread ( Motronic control unit problem ) from a member who seemed to experience the exact same problem. I emailed him to ask if he resolved the issue and he told me that once he had the flywheel sensors replaced the problem disappeared.

The only difference between the problem you had 3.2cab vs my issue and tastytel's issue is that our cars would start fine when cold but not once warm. I believe your issue was the opposite in regard to ambient outside temperatue.

3.2cab as you mentioned earlier it does seem that when these parts fail or begin to fail they may be affected by temperature. Could it be the position to the pin somehow changes ever so slightly across temp or just the sensor itself?

Anyway, I have put in an order for my impulse sensor and will update everyone with the results once I install it.

[CliffBrown]

Dennis

There are a lot of threads on the Forum regarding problems with bad solder joints in the Motronic DME.

[crashr]

Hi Cliff,

I have seen a bunch of these threads as well. My thought is if the Impulse sensor replacement does not fix the issue then the DME box must be the culprit and I will open it up and take a look at the solder joints.

[crashr]

Ok I'm really getting frustrated now. The car was cold and I started it up ran great. Took off the sensor cable for the reference sensor and saw my 2V peak to peak voltage. So then we let the car warm up for 10 minutes. Turn the car off and as usual it just turns over. At that point I checked the Ref sensor at the engine again and I still see the 2V peak to peak voltage as it is cranking over. I thought this would eliminate the reference sensor from being defective.

Next I moved to the DME. I swapped out my DME with a known working DME and it still wouldn't start in my car. Put my DME in the other car and the other car fired right up. This should rule out the DME.

I have done the same swap with the DME relay. Same result.

I started checking ground locations and them seem to read close to 0.5ohms. One caveat is that my engine ground location thread (on fuel air input area) is somewhat stripped and the bolt won't tighen right down however we are getting .4ohms resistance from that bolt to the body.

I am running out of ideas. Could it be the alarm? I don't have one as this was a conversion car. Is there any way to test if this is what is causing the problem? Also any other suggestions on what I should be looking for?