Another (Another) NO START

[surfdog4]

NOTE: Edited with the Solution at the end

I've seen a lot of posts for no starts where the car has been sitting for a long time, but in my case i drove it into the garage just fine, and then a few days later (less than a week)...it won't start (1987 N/A)

It cranks, cranks, cranks, but no firing..not a sputter.

I first tried the DME relay jumper...the first time it sputtered, but no start...after that nothing.

- the tach bounces upon cranking

Took a look at the battery after i read that the injectors must have >12.5V to fire...battery was 12.2, 11 when cranked....ah ha! the battery was less than a year old, but i charged it, didnt seem to help, so i took it in for a replacement.

Installed the new battery (and a new DME relay just in case)...same result. So i checked the new battery, and it reads 12.5V..so i checked all the batteries in my multi-car fleet (with two voltmeters)..all 12.5V...I thought car batteries were supposed to be >13V?!?

So next disconnected the fuel line at the pressure regulator, installed the Fuel pump jumper, and fuel pump seems to be working. (i don't have fuel pressure meter)

Pulled the distributor cap, didnt see anything that would cause a no start. "rear bolt" is in place) Does anyone ever have problems with the coil going bad?

I want to pull one of the injector wires, but does anyone have a suggestion on how best to do that without breaking those old plastic shells?

Does anyone have a suggestion of what order of things to try next...there's lots of things to still try but i'd like to do them in some kind of order from most likely to least likely. I know the DME is looming....

Thanks!

[cauzomb]

Besides checking actual cranking fuel pressure, and if the injectors are squirting fuel, and if there is spark to number 1,2,3,4 plugs.

The other things to check are the AFM plug "if this is a problem, usually the engine will start, then stop..

DME temp sender in the head, I'm not sure if the car will start with it unplugged, but I've heard that if it's bad, it won't start..

The best way to remove those injector plugs is to get a small mechanics pick, or other slim, poker, a bobby pin broken close to the curve, so it's sort of hook/L shaped at the end works well to sort of rake the ends of the injector plug spring clips.

Once you get the retaining spring clip above the injector retaining tabs (both sides) the plugs slide right off.

[surfdog4]

Thanks for the tip on removing the injector connector..i learned the hard way on the 928 i was working on that old plastic doesn't like to bend much.

I was thinking next to start working the "spark" side of the equation...the cap and rotor had some corrosion, but that doesn't happen all at once...

Thanks!

[surfdog4]

OK, since i was working alone i pulled out my timing light and clamped it onto the main coil wire to the distributor...flashing on crank, so appears spark is there.

Just for fun, i clamped it to one of the spark plug wires...no flash..then another..no flash.

Then pulled the cap and rotor, cleaned all the contacts, ohmed each one out (seems to be a consistent ~1000 ohms between outside and inside contacts and between the center contact and the tip of the rotor.

Put distributor back on, still no flash...so i pulled #1 spark plug and pushed it up against the motor (checked that it was grounded) and now with my wife at the crank, observed NO SPARK..

SO, is this a sign that the coil is "weak"?? I can't see where anything besides the cap and rotor that get between the main coil wire and the spark plugs (since the car was just running i am assuming all the spark plug wires didn't die on the same day)...and just to be sure, there isn't anything about Porsche spark plug wires that would keep an inductive timing light from firing if there were reasonable voltage present, correct? (it works on the coil wire)

Still plugging....thanks!

[cauzomb]

Standard induction timing light works just fine on the 944 stock ignition. When in doubt, connect the induction timing light's +/- power cables straight to the battery +/-.

There should be less than 1 Ohm of resistance between the internal post and external sparkplug wire connector for that post, at the distributor cap. Slightly more between the coil wire terminal and internal carbon/metalic button, but not much difference, they are pretty much straight through conductors.

Are you sure you are getting a good reading with your ohmeter?
Is the battery in your meter OK?
Is the meter adjustable?

If the meter is connected well between the two contacts, and the battery is OK, and it's adjustable, stick the end of one probe into the socket for the other probe, pressing it in firmly to get good contact, "positive to negative" of the ohmeter, then spin the knob till the reading is zero ohms.

If it's a digital, just make sure the battery is good, as this is used to determine the amount of resistance to electrical continuity between the probes/conductor...

Where is the spark going once it leaves the coil wire?

What is the resistance between the coil possitive and negative terminals?

Disconnect the coil wires, all three, then measure the resistance between coil positive and negative terminals 'Clarks-garage says the resistance specs should be between .4 ohms and .6 ohms.

What is the resistance between the coil main output/primary and negative terminal?

While the wires are still disconnected, measure the resistance between the coil main-to-distributor terminal and coil negative terminal. 'Clarks-garage says the resistance specs should be between 5000 and 7200 ohms.

Bench test the coil, and all of the plug/coil wires, if the coil resistance readings are within spec.
With the wires still disconnected, bench test the coil, get yourself some insulated wire, old speaker wire atleast 16 guage, several feet will due, then use one side to jumper power to the coil positive terminal.. "possitive terminal" connected straight to the battery, then connect the other to the coil trigger side, coil negative. You will be tapping the coil negative jumper wire to battery negative.

You should get a spark from the coil main, through a plug wire or coil wire, to ground, each time you tap and release the negative wire at the battery.

You can test the coil wire and each sparkplug wire on the coil this way, to eliminate them as possible issues..

Test the spark gap for each wire, a bright blue spark is a sign of strong spark, red/orange is a sign of weak spark. The gap should be around 12-15mm.. There are spark gap tools, but I use a screwdriver in one end of the wire, with the blade hovering over the shock tower bolt or cam gear housing, or intake manifold.. The rubber boot of the wire end works well as a prop, to hold an air gap between the screwdriver shaft and the back edge of the cam gear housing, or the ridge at the cam gear housing.. Use the screwdriver handle as a support/ resting on the cam tower. A bit of paper towel/shop rag or old newspaper as support between the screwdriver handle and the cam tower, increase/decrease the thickness of stuff under the handle to adjust your gap distance.If the coil doesn't jump a spark from the coil wire to ground at a 10mm gap, it's got weak spark. If you are getting a weak spark but the coil resistance readings are within spec, It could be due to corroded ground terminals, between the chassis/engine ground point and the battery, or bad wires. The wires have their own set of resistance specs that you can check with your ohmeter, if all the resistance specs check out, and your bench test works, you are looking at possible bad wiring to the coil, or bad connection at the DME.

Read through these pages for much of the same info as above.

Ignition System Troubleshooting
Troubleshooting Fuel Supply Problems

[surfdog4]

i thought that was weird too, so i checked it with both a digital and an analog ohmmeter..think next step for me will be to pull the coil and do all the checks ...thanks!

[plyhammer]

Just an off chance that the jboot came off the afm and so it won't get a reading? Had this happen to me once.

[968 GUY]

Is the rotor turning? Maybe the bolt came loose.

[surfdog4]

plyhammer: that one wasn't on my check list so i will check it out

968 guy: I saw that one on Clark's Garage, so i checked, yes the bolt is there and the rotor is turning.

thanks guys!

[earlr85944]

check for 12V at the coil positive terminal with the key on

[surfdog4]

Finally got back to the car today, with new coil, wires, cap, and rotor in hand.

IT RUNS! yea!

I think ultimately it was the coil wire..when i ohmed it out it read very very high...i didn't check it initially because when i clamped a timing light on it it was firing, and i've never experienced a wire electrically just failing all at once...it was perhaps a combination of weak coil and coil wire, but in any case it was due for a tune up, so today it got one.

Carbon on the spark plugs was another clue that i had weak spark.

Thanks for everyone's advice and help, i hope this thread helps someone