Engine cranks but will not start
 

SINCE JUNE 23rd approx., HAVE NOT BEEN ABLE TO START THE CAR

Hello guys,

I am writing for help - members of this Forum have unbelievable knowledge and I live in a rural area where Porsche resources are simply nonexistent. I am located 600 miles East of Boston, in the province of New Brunswick, Canada.


CAR INFORMATION
1 Porsche Carrera Coupe, 1986.

2 Mileage is approx.152,000 miles.

3 Bought from BAT in May 2022, from owner for 29 years.

4 During June 2022, I thought there was a bit of misfiring.

5 In early July 2022, I put in NEW – ignition rotor, distributor cap, spark plug wires, spark plugs, and ignition coil.

6 Car ran very well after that, and I drove approximately 7000 miles since then (in 6 months of driving).

7 The only item I would mention that has not been perfect - the car sometimes seems hesitant at low RPM.


CURRENT SITUATION
1 Car out of winter storage in April 2023 – started on the very first turn of the key after 5 months parked.

2 Got new tires, turbo tie rod kit. Big increase in driving pleasure.

3 Car has been running extremely well since May 2023 – a real pleasure to drive, both on the highway, and in my small town (daily driver).

4 Around June 6, I drove the car in heavy rain (on purpose) to test my new wiper setup – I have removed passenger side wiper, and driver wiper now parks on the passenger side. I did this while my gauges where out for new LED bulbs – much simpler than going through the front trunk. I like the result.

5 We have had very unusual wet weather for a few days, so the car was left parked in the garage for a couple of days.

6 When the sun came back, I went to start the car and it started immediately, but it is MISFIRING badly. It is as if there is only 3, 4 or 5 cylinders working, depending on the moment. If I leave it running, it will end up stalling.


THIS IS WHAT I HAVE DONE SO FAR RO TRY AND FIX PROBLEM
1 Checked the resistance of the coil, and it is within specs, clearly.

2 Checked the voltage to the coil with ignition on, and it is at 12.1 volts.

3 Cleaned the connections to the coil, to the distributor cap, and used dielectric grease to improve contact.

4 I have ordered a new DME relay – I should receive it next week.


CONCLUSION
The car was running very well, but after 2 days in wet (damp) weather, it suddenly misfires quite badly. And yet, the car was NOT in the rain, it was parked in my garage. I have done fair amount of research on the Forum and have not found similar situation.

I would like to insist - the car always starts, whatever the problem. It is not a starting problem. It is after having started that one can notice that all cylinders are not firing. Some people mentioned that the plug wires could be the problem – but that would not have happened all of sudden.

Do you guys have any suggestion as to what I could do further to solve the issue ? I am leaning towards faulty relays but I do not know how to proceed.

Thank you a lot.

Jacques



http://forums.pelicanparts.com/uploa...1686755904.jpg

Some basics with my limited experience…I wouldn’t grease the rotor contact (for sake of collecting dirt) but would use a silicone paste around the distributor gasket. Microscopic moisture could be seeping in and since driving is limited there’s no time to sufficiently dry out. Then the same applies to gasoline. Could timing be a bit off or distributor loose, maybe one of wires are mixed up?
Also - check for vacuum leaks and determine if you’re experiencing and over-rich condition with blackened exhaust smoke.

Thanks EC900
Will check those items that I have not already verified.

Spray some WD40 in the dist. cap and see if it helps.

Skipping ?
Remove and clean the inside of the distributor cap
Remove and clean the crank and reference sensor connections.

Possibly replace all ignition wires with new ones
Check all grounds , clean and tighten (all ground on engine)

Thank you r_towle,

I have new ignition wires from July 2022. Can you please say what are the reference sensor connections ? Thanks.

IME, these are often symptoms of a coil going bad. After checking the distributor and cap for any condensation, try swapping the new coil you installed for the old coil you took out. Was there anything wrong with the old coil? Or did you just swap it for the sake of having everything new?

Hello PeteKz, and thank you for your comments.

I did not try swapping coil this time, as specs of the new coil were well within the specs.

Last year, I changed the coil as I was having minor ignition fire problem (nothing like this time).

But I will take your suggestion at heart, and add it to the list of possible solutions (before I start trying them one by one). I am expecting a new DME relay within a week and I will try it on to see if it helps the situation.

Thanks again.

Looking into the engine bay, left side, rear
You will see a short metal bracket with three electrical connectors.
Crank sensor
Reference sensor
Temp sensor

When I had weird behavior I replaced the dme relay, nope
I replaced the reference and crank sensors
The wiring is old, so are the sensors

This is all part of your bonding with your car :)

Thank you again - will look into it for sure.

You must have already done it but if not inspect the cap very carefully for cracks. It might not be visible when cold but expand a little when hot

For my 85, I found condensation was traveling down the wires towards the cap. It found its way in the cap through the top of the boots. My solution was red RTV where the wires meet the boots. It has not happened again.

First thing I would do is pop the cap and check for condensation inside. If the cap is dry inside, then I suspect spark plug wires and/or cap issues. I find this works well:

With the engine running in the darkest outdoor environment you can find, lightly spray the wires with water. If there is a problem, you will see arcing on the offending wires and/cap.

Check plug gaps. Too big a gap and the spark tries another path. I had ngk plugs in mine and after a year the electrode had worn enough to replace coulda just re gapped but…

Has not been consistent in starting. DME Relay ?
 

Hello guys,

Weather around here has been terrible - not a good set up to follow up on your recommandations.

In my starter post, I did mention that the car would always start, although it was stuttering (or misfiring). Well now, it is no longer as keen to always start.

Regarding the DME relay, I read in another thread (much older) that the relay had nothing not to do here. If it works, the car can work. If it does not function, the car will not run. There is no middle ground apparently - a relay would not cause interrupting or misfiring engine... Is that the case ?

Thanks again.

At the risk of sounding obvious, have you checked all the ground connections? I’ve definitely wasted a day chasing an electrical issue only to find a ground that was lousy.

Many tests done - more to go + grounds to clean
 

Hello guys,

To fix my issue of misfiring in damp weather, with issue now gone over to no start in wet weather, I have been following advice received on this thread, and conducted several verifications in last few days. I have also done fair amount of research on the Forums to gather all possible info.

2020 - new fuel pump, new injectors
2021 - new fuel filter
June 2022 - new ignition rotor, distribution cap, spark plug wires, spark plugs and coil

NOW DONE:
- remove and cleaned DME relay, re-installed
- no condensation in distributor cap, has now been cleaned
- no visible cracks in cap (to be reviewed again)
- speed sensor resistance is ok to specs
- reference sensor resistance is ok to specs
- ignition coil resistance is ok to specs
- WD 40 in distributor cap

TO GO
- check and clean all grounds
- plug gap
- plug wires arching
- temp sensor resistance
- sensor connections to be cleaned again

As mentioned before, I am awaiting on a new DME relay but I now doubt it will help me. Thank you all for making some more suggestions / possible avenues to further explore to solve issue.

Your car was inside, but don't forget the CIS intake gaskets on top of the cylinders for those of you that park outside. These are paper and can fail from moisture then allow water into the combustion chambers, which then cause a nice water/fuel mixture and can also pit your cylinders.

1986 model - no CIS. Thanks.

May be worth looking at.... I just got my 3.2 motor for my build and am finding a lot of small things that I need to replace/repair.

One such thing was a broken clamp on the back bottom portion of the airbox, the second I saw that I knew I needed a new unit, I could see water/moisture getting in there on wet drives.

May be worth looking at while you're digging around for solutions.

-Ian

Clean the grounds while you are checking everything else, they may look good, but remove wires and clean connections.

update
 

Hello guys, and thank you for all the suggestions on possible solutions.

I have followed many pieces of your advice and was able to discount these as possible problems:
- coil
- two sensors at crank
- some grounds

With the help of my son, we were also able to establish bad fire in the distribution cap (several black marks) and on the rotor. We were also able to confirm black residue on spark plug (first on the left of engine). This would tend to confirm bad firing...

We were able to establish that DME relay worked fine, on smelling the gaz fume at the back of the engine.

So, I have decided to treat myself to a rebuilt DME unit from Steve Wong c/w performance chip. At the same time, I will also change the rotor and the distributor, and the spark plugs.

Will let you know guys how it turns out...

I think that it’s possible that your plug wires are arcing.Maybe your rotor has been going bad as a result of plug wires arcing.

SNbush67,

I changed the plug wires last July. I Was hoping that they would be ok. If the new/rebuilt DME does not fix the problem, I will check all the plug wires again. Thanks for your input.

How did you discount the coil as a possible problem? Simply measuring the resistance is not sufficient. Since you have a spare coil, swap it out (5 minutes if you are slow) and see if the problem persists. If it doesn't fix your problem, rule it out and then chase more expensive stuff.

But DON'T make lots of changes at the same time. One thing at a time.

It doesn’t matter if you changed the plug wires, brand new wires don’t care, they can arc. Even if the new DME works fine, you still have to check to see if the new wires are arcing.

The rotor could have been damaged by arcing wires, so if you didn’t change the rotor when you changed the wires then the problem would remain. Or as Pete recommends, if your coil is on the fritz then only a different coil will work. You really have to do some serious troubleshooting and determine what exactly is wrong. Without an accurate diagnosis then you’re only risking damaging the new shiny parts you’re throwing at it, it becomes an expensive circle of destructive mechanical and financial frustrations.


Cheers, Shane

I suggest checking the distributor bushing by seeing if you can move the rotor side to side. My nephew's 87 911 distributor upper bushing was worn allowing the rotor to contact the cap. Mine at the same mileage was just fine.

I did verify the distributor bushing - they seem fine.

I also verified the coil, by swapping a new one - but as it was said, perhaps arching was the culprit and damaging the setup.

This Forum is unbelievable - thank you again all, for these helpful suggestions.

Run the engine in a very dark room and give the wires a spritz with a spray bottle of water. If they're arcing you'll get a great light show. Many cases of bad, new wires out there.

Did change rotor when changed wires
 

Hello Shane, and thanks for the comments.

In June 2022, I changed spark plug, spark plug wires, cap, rotor and coil. This June 2023, I changed the plugs, the cap, the rotor, and I checked the rotor.

Unfortunately, my knowledge of mechanics is such that I having a very hard time doing diagnostic. I HAVE BEEN doing troubleshooting, but I am unable to get the car to go.

I had the same problem and it was an almost new cracked distributer cap

Hello guys,

Today, I have done the water " mist " test in the dark, and no, the plug wires do not arc. I am glad that this issue has now been discounted as a possible source of the issue with my car. There was no arching anywhere in the engine bay.


I am now going to start the clean up of the grounds.

My son was just reminding me in a phone call that when we did check the coil, it was barely getting voltage upon cranking the engine over. It would light up a testlight, but very dimly, to sometime not at all.

And therefore, the coil itself could then not produce enough voltage for the distributor cap. We then tried to connect the positive terminal of the coil directly to a good power source with a jumper cable - getting the same sesults.

My son believes that this might indicate a bad ground linked to the DME unit. I am going to start checking those first, but I am not sure where I should be looking.

Does anyone out there has an image of ground points that would be linked to DME ?

Thanks.

DME Relay test with jumpers
 

Today, I performed the DME relay test, by using jumpers in the relay socket.

I removed the relay from it's socket and connected a wire between pins 30 and 87 to turn on the DME and between pins 30 and 87b to turn on the fuel pump. Although the car was cranking, and trying to start, it did not.

As said in my previous post, it really does seem as if the coil is unable to produce enough power to all spark plugs. And yet it is a new coil, after another new coil last July.

I have now started to clean the grounds.

So, I have a new:
- rebuilt DME with Steve Wong performance chip
- 6 new spark plugs
- a new coil
- new rotor
- new cap
- 6 new plug wires from last July, tested for arching with water

Any suggestions guy ? I have a new DME relay on order, but based on my jumper test this morning, the relay is not at fault . . .

Thanks

Jacques

Try the old chip?

Gone to supplier as part of the deal to buy rebuilt DME unit.

And the problem started with the old chip in (the original DME).

It’s happening when wet.
You still have not tested nor replaced the crank/reference sensors.
You have not swapped in the old coil to test.

When mine died in a parking lot, mild weather, no rain. It was the crank and reference sensors.

Also I would consider testing the head temp sensor, another key to the ECU setting the proper mixture.

Lastly, or firstly…
Pull the gauges back out and verify and validate all wiring is in place still. Something may be loose.
What you did last…..the wiper project.
Some (temp) and pressure gauges route via the gauge to the ECU possibly, and a loose connection or one that fell off might do it

Thank you very much Rich - your are very generous of ideas and possible solutions. I will follow up on your suggestions - the 3 sensors are 329 $, which will be about 500 $CAN with shipping. Herk !

You can use the BMW crankshaft sensors which are half the price of the Porsche one. Exact same sensor.

BMW part number 12141708619 / Bosch 0-261-210-002 $55.43 each on Pelican

For cylinder head temperature sensor make sure you get the updated one that's 2 wire, part number 93060691500

Thank you Skunk,
Order is placed - yes to BMW crankshaft sensors.

Update - failure to start in wet weather
 

Hello guys,

I have been doing some more searching on the Forum, and also following up on the advice and suggestions received. Notably, Rich reminded me about the important 3 items for running the engine: 1) there must be FUEL, 2) there must be SPARK, and 3) there must be AIR. I have also recruited a neighborhood mechanic to give me a hand in identifying the problem.

ITEM 1)
We have confirmed that the fuel pump is working ok, and that there is fuel going to the engine. I did the bypass of the DME relay test (when we hear the pump operate), and I also have been cranking the engine. It tries hard to start, but it fails. And then we get this strong fuel odour as well - so yes there is fuel.

ITEM 2)
We have also confirmed that there is spark. My friend and I have tested the coil, the distributor cap, the rotor, and also the plug wires (for spark in the dark caused by water mist testing).

ITEM 3)
In testing the Air Flow Meter, we found resistance measures that were not up to par. I will be detaching the Air Flow Meter from the engine later today, along with air filter. We will then test the AFM more precisely.

NOTE
I have new DME relay, new (rebuilt) DME, new plugs, coil, rotor and distributor cap. So does it seem plausible that the AFM is causing the car not to start. Again, it does crank well, and we hear it trying hard to start, but just not able to.

We also tested 1) the speed sensor, 2) the position sensor and 3) the cylinder head temperature sensor. All three are showing the appropriate resistance levels, per the Bentley book, as well as info found on this Forum.

Any other suggestions. Thank you.

Jacques