I should have added that I verified all the grounds that I could find.

New update - AFM tested very well (voltage)
 

AirFlowMeter removed from car this afternoon.

Tested according to Clark's Garage procedure (for a 944, but it is the same AFM model). Bulletin ELECT - 22 Air Flow Meter Operations and Testing.

Voltage readings are good, based on Bulletin data. Barn Door operates well and voltage is linear in its increase / decrease based on door position. I should also add that for a 37 year-old car, the potentiometer mechanism looks awfully clean.

However, I have 0 experience with these. This is the first time I have seen one for real. For those of you that are more experienced, does the very little "debris" along the curved lines warrant a pencil eraser cleaning ? Perhaps, if I did that, the car would not hesitate as much at low RPM . . . ? Even my girlfriend noted that I was having difficulties leaving from a red light.

The prior owner gave me 3 years worth of receipts, so there is no way to know about prior to that.

I am stumped.
I guess I am going to have to go back to the beginning in my diagnostic efforts.


NOTE - I received yesterday two new sensors for flywheel - position and speed sensor. I bought the BMW model from our host at about 1/5 of the cost of the Porsche. Since I have them in hand, I am going to install them. That will be 2 more items that I can remove from my list of possibilities.


http://forums.pelicanparts.com/uploa...1689214054.JPG
http://forums.pelicanparts.com/uploa...1689214054.JPG

The cable on the sensors dries out and and cracks so they don't last forever.

Update July 20
 

JACQUES CF LANTEIGNE ORIGINAL POST – Pelican Parts 911 TECH Forum 14 JUNE 2023

Engine cranks but will not start

SINCE JUNE 23rd approx., HAVE NOT BEEN ABLE TO START THE CAR AT ALL
(June 8 to June 23rd, engine would start and then stumble and then die off)

Porsche Carrera Coupe, 1986, 152,000 miles
Bought May 2022 from owner of 29 years
Ran great until June 7th, and then ooops, runs terrible from June 8th.

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

Early July 2022, put in NEW…
- ignition rotor
- distributor cap
- spark plug wires
- spark plugs
- ignition coil

Car ran very well after that.
Drove approximately 6000 miles since then (in 7 months of driving).
Only item not perfect - the car sometimes seems hesitant at low RPM.


CURRENT SITUATION

- Car been running extremely well from May 1st to June 8th, 2023, real pleasure to drive on the highway and as a daily driver.

- Around June 6, drove the car in heavy rain (on purpose) to test new wiper setup – both wipers now park on the passenger side. I did this while my gauges where out for new LED bulbs – I like the result.

- We had very unusual wet weather for a few days, so car parked in the garage. When the sun came back, June 8, car 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.


JULY 20TH NOTES

I have been trying to start the car with no success. I crank it and it does try to start but can’t.

To try and identify the problem, I have followed the suggestions and advice found on Pelican Part Tech Forum – great resource. Thank you again to all contributors.

While doing the tests and work, I also decided to take the opportunity to rejuvenate the car – it is 37 years-old – but in great shape and I would like to keep it if I can.


THIS IS WHAT I HAVE DONE SO FAR RO TRY AND FIX PROBLEM

1 All Grounds in the car (Bentley page 971-3) have been verified and cleaned.

2 Fuel Pump Pressure (B 201-7)
- has been confirmed at 35 psi while cranking (at left rail shredder valve).
- No can do for engine ON.
- After cranking stops, the fuel pressure is retained (does not drop).

3 Fuel Pump / Main Relay (also called DME relay) has been verified (with 2 methods) is OK.
Excellent article about DME relay from Jazzbass, site admin, on March 24th, 2008.

4 Fuel Delivery (B 240-5)
- has NOT been verified, but there is fuel being supplied.
- After enough cranking, we can smell it generously.

5 Fires to the Injectors (B 240-10) verified using noid light
- nos. 1, 2, 4, and 5 showed good fire.
- Could NOT verify no. 3 and 6 (position).

6 ECM Harness Test (B 240-15) :
- checked the 6 grounds at pins … 2, 4, 5, 16, 17, and 19
- with key ON, pins 18 and 35 have 12.3 volts each
- while cranking, pin 4 is showing 10.5 volts

7 Green Wire Integrity (to coil) was verified to be OK. There is not short.

8 Air Flow Meter was verified (B 240-17) and found to be working fine.
- The method supplied by Clark’s Garage under ELECT-22 was great.
- Opportunity was taken to clean potentiometer with pencil eraser and electric contacts cleaner.

9 Cylinder Head Temperature sensor is still of the old style (1 wire) and reads 2340 ohms – a bit high has specs show 1000 to 2000 ohms.

10 Intake Air Temperature sensor showed resistance a bit low at 940 ohms, but this would not stop the car from starting.

11 Oxygen sensor was not tested, as car could not operate.

12 TDC Reference sensor (B 280-5, 11)
- has been verified at ECU harness, pin 25 and 26.
- Resistance of 998 ohms and with dynamic testing, 0.1 volt.
- Both results are within specs.

13 RPM Speed sensor (B 280-5,11)
- has been verified at pins 8 and 27.
- Resistance is 1013 ohms and dynamic testing yields 2.4 volts.
- Both results are within specs.

NOTE – both TDC and RPM sensors are new from this month. They were installed using the excellent guidance of tom.stiller on PP Forum, in his text of July 9th, 2010.

14 Throttle Position Switches (B 240-18) – Tested as described in Bentley and results are OK.

15 Idle Position Switches (B 240-20) – same and result OK.

16 Idle Control Speed valve (B 240-22) – checked by the “feel or hear” method – OK.

17 Altitude Correction Switch, Oxygen Sensor system – NA

18 Spark Plugs (Bentley 280-9)
- are new from this month.
- Gap is OK.
- Become dark (carbonized) after that much cranking without start, and they smell of gas.

19 Spark Plug Wires (B 280-9) are new from Juy 2022.
- Verified using the “ water mist “ method in the darkness, confirmed that there is NO spark lost.
- All wires are shown to have 3000 ohms resistance. They are new from July 2022.

20 Distributor Cap (B 280-8)
- There is (no longer) any humidity in the cap.
- New from July 2023.
- Previous one was showing black carbon marks (sign of sparks looking for where to go ?)
- No crack present.

21 Ignition Coil (B 280-9) tested re. Clark’s Garage IGN-04.
- New from July 2023.
- Primary Terminals resistance was 0.6 ohms.
- Secondary Terminals resistance was 6200 ohms.
- Ignition switch ON = 12 volts DC from black wire to ground
- Ignition switch ON = 12 volts DC from neg terminal (green wire) to ground.

22 Ignition Rotor (B 280-10) tested for a resistance of 1067 ohms. OK.

23 My DME unit (ECU) is a rebuilt unit from Steve Wong complete w. performance chip. It was installed AFTER the problem started. Although I would have preferred a 2024 purchase, it was definitely in my list of must do eventual purchases.

24 Along the test conducted, Compression was verified.
- cyl 2 165 psi
- cyl 3 160 psi
- cyl 4 165 psi
- cyl 5 165 psi
- Unfortunately, cylinders 1 and 6 were not verified, nor leak down numbers on all cylinders.


Thank you for reading guys.
What am I missing ?
Any new suggestions ?


Jacques, in Caraquet, NB, 600 miles East of Boston.

Nice detailed recap.
After all that’s done so far, it seemed weather related might not have been the problem.

Perhaps it’s time to check on the individual injectors themselves being either leaky or clogged, you didn’t mention if tank was low to maybe pickup some debris or filled up stirred some up.

CHT.

If you are good with electronics, unplug it, Hotwire it so it sees COLD ohms, within range, forever.

Use a resistor or three in your Hotwire kit, or ground out the wiring which is max ohms on a cht.

I’m suspicious of your wiring harness.
I re-read the story line and I believe it ran great, then heavy rain, then no start.

Is that correct?

Thank you for the question Rich.

The proper way to describe the issue goes like this:

1) car ran fine, for 10 months
2) car ran fine in heavy rain (to check new wiper set up), 90 minutes drive
3) parked car for 2/3 days, in enclosed garage.

4) then in humid but no rain weather, car started at only 4 or 5 cylinders
5) then, the next day, the car would not start - it cranks but does not start.
6) I am having a mechanic will electronic expertise come by next week.

It seems to me that the harness would not fail " all of a sudden "

Wish me luck, and thank you sincerely for your input.

Jacques

It’s not a failing harness but if you bend any wire it’s likely the outer insulation cracks and/or falls off.
We are at 40?years now.

You have checked everything.
Moisture and cracked wiring….

Rich

This morning, I verified injector plug connector located behind heater blower motor. This was suggested to me by a well respected member of this board.

I unplugged and then plugged back the connector several times, and I also cleaned the connector using electrical contacts cleaner. No impact the no start situation.

I also took the time to run the Ignition Switch Test - it has been suggested and described to me by Ingo Schmitz.

I ran a jumper wire from battery Pos +12 to fuse 7 or 8, in fuse box no 1. Those are fuses that get powered when ignition switch is turned ON. Car would still not start - if it would have, it is because we had bypassed a bad switch.

It sounds like you've been quite thorough and detailed with your testing.

I'd focus back on the basics if it were me at this point: air, fuel, spark. What's missing? Pull each spark plug out and test for spark, pull each injector out and test if and how it's spraying when cranking, etc.

Hopefully that'll narrow it down rather than performing every test under the sun.

Back to the basics...
 

Thank you Skunk and yes to the basics - air, fuel and spark,

Done some testing today, notably with carburator cleaner sprayed directly into the air filter opening. Got the engine going, finally, after 7 weeks dormant.

When spraying carb cleaner continuously into air chamber, then the car ran continuously. I confirmed this statement with an engine run of about one minute long, of using the carb cleaner to keep the engine running.

Wow, the engine ran with a nice whirr.
Not quite like the purr of a cat but almost, for a good minute.
That is, as long as we sprayed carb cleaner into air chamber.
This would seem to confirm that...
- we have good air
- we have good spark


So what is wrong ? Fuel Supply ? ... Fuel Quality ? ... Fuel Pressure ?
--- I confirm fuel quality is NOT an issue in my parts, and I am using relatively new fuel filter...
--- I also re-submit that the engine floods with fuel after about 5-7 seconds of cranking...


Is there a problem with injectors ? I am here, back to the basics, exactly as suggested by SkunkWorks...

1) Pull each spark plug out and test for spark...
--- The carb cleaner test mentioned above would seem to confirm that we have good spark and good air when fuel is sprayed directly and continuously into air chamber.
--- It seems to me that the nice and smooth running of the engine says we have good air and we have good spark.

2) Pull each injector out and test if and how it's spraying when cranking, etc.
- that is exactly my next step, along with getting an oscilloscope to examine the PVM signal.

Thank you SkunkWorks for the reminder about the basics.

Jacques

I have to say I am impressed with your detailed attack to this problem.
I'd guess it is something common to all cylinders and not individual like injectors or it would start.
Fuel line?

Thank you Rod.
Will do some more testing today on fuel injectors.
Will report back here.

Jacques

Update - tests on injectors and their connectors. 1986 Carrera no-start
 

Hello guys,

Today I ran some test on the injectors, and their connectors, on my 1986 Carrera with a no start condition.

ITEM I
Power to the injectors, per Bentley page 240-10+.
Ignition Key ON
Excellent results.
All at " battery voltage ".

Injector connectors:
No. 1. 12.6 volts
No. 2. 12.4
No. 3 12.5
No. 4. 12.6
No. 5. 12.5
No. 6. 12.5


ITEM 2
Injector terminals resistance, at about 30 'C (about 86 'F).
Per Bentley, excellent results.
Ignition Key OFF
Injector Terminal R should be 2 to 3 ohms.

No. 1. 2.5 ohms
No. 2 2.5
No. 3. 2.6
No. 4. 2.3
No. 5. 2.3
No. 6. 2.5


ITEM 3
Fuel injector control test. Per Bentley.
Ignition Key ON.
Injectors 1 to 6 checked individually by " feel ".
Injectors on Rail 1 to 3, and then 4 to 6, checked by sound.
Injector must click when terminal 14 equivalent (brown wire) is touched to ground.
(Connected the harness, and backed up the shrink tube to access brown wire, reached with paper clip contraption)

Individual injector must "click" which can be felt.
No. 1. ok
No. 2 ok
No. 3. ok
No. 4. ok
No. 5. ok
No. 6 ok

Rails can be heard when tested.
Rail Left side ok
Rail Right side ok


ITEM 4
I will have access shortly to an oscilloscope to verify the pulsed voltage signal.
I am quite curious to see what these PWM signal look like.


ITEM 5
I am examining how I will manage the fuel flow test - that is how to collect the spitting fuel.
When I remove each fuel rail.
My garage is small and there is not much room to operate.


I will report back on these results.
I hope I am not being too optimistic - feel I am getting somewhere.
Especially since being able to run the car with carb cleaner into the air box.

Cheers.

Jacques

I’m still a fan of wiring.
It got wet, it stopped starting.

You have fuel pressure when cranking
You don’t have fuel getting into the cylinders.

Add starter fluid, it runs.
Ignition works

Wiring harness could be compromised somewhere, or some sensor is not sending signal to the ECU.

It got wet

Hello Rich, and thanks for the comments,

Upon careful review of the exact circumstances (from memory) of the eventual no start condition, I am keeping the wet factor in play.
As you suggest.

However, the idea that one sensor is not sending, or is not sending correct, signal to the ECU is also very present in my mind.
Car cranks...turns...
5 seconds and it floods...
Grrr...

Can't wait to get the oscilloscope results.

I don't remember seeing this. So it is getting fuel, just not regulated?

Rod,

No, I do not think it is getting fuel, otherwise it would run, at least rough.

Engine will start on carb cleaner.
Engine will run continuously if we continue to spray car cleaner.
Engine stalls once we stop the spraying.

Engine will not react to throttle stimuli.