930 died

[jlj]

We have done extensive upgrades and restoration to my 1982 911 turbo.
Classic retrofit CDI, new plugs , wires, rotor and cap, new fuel pumps , fuel filters , fuel lines .
Callssic retrofit fusebox , new Turbo , fabspeed airbox, rarlyl8 exhaust
It has run like a champ for 6000 kilometres.
Other day it’s starts a slight hesitation , then gets worse then clears up then starts back firing and dies . Tried to restart it and was just cranking and back firing .
The shop has eliminated the CDI, plugs , wires , distributor and there is fuel.
What else could have caused this?
Thanks for any assistance

[Rawknees'Turbo]

How is the condition of the signal wire that goes from the CDI to the distributor (the infamous "green wire" that often gets baked and cracked near the distributor body)?

Also, I know you said you have fuel, but just for the sake of component elimination troubleshooting, ground the overboost switch wire (remove from switch and attach to a a nearby, suitable ground point - like a manifold stud), and see if it starts then.

[pkabush]

What’s troubling is that your car is at the shop and you’re posting here. While the brain trust here is excellent it shouldn’t be difficult for a competent Porsche mechanic to diagnose your problem.
What’s the story with the shop ? Do they specialize in air cooled Porsche’s ? If not I’d get it to one ASAP. Or better yet, spend some time reading and a bit of money on a set of diagnostic fuel gauges and get up close and personnel with your engine. Also, there’s an excellent “No start” sticky at the top of the page.

[jlj]

Originally Posted by pkabush

What’s troubling is that your car is at the shop and you’re posting here. While the brain trust here is excellent it shouldn’t be difficult for a competent Porsche mechanic to diagnose your problem.
What’s the story with the shop ? Do they specialize in air cooled Porsche’s ? If not I’d get it to one ASAP. Or better yet, spend some time reading and a bit of money on a set of diagnostic fuel gauges and get up close and personnel with your engine. Also, there’s an excellent “No start” sticky at the top of the page.

Thanks, They are excellent and specialize in air cooled. I’m asking on here because they are so busy I want to get a head start on getting my own knowledge of the situation. That way I can know what’s going on when they call me to say what they found. Basically I’m being proactive for my own sake

[pkabush]

I totally get it. But, It’s pretty tough to diagnose based on the info provided. As long as it’s in good hands it’ll get sorted out. Honestly, the best way to get know your car is to wrench on it yourself. Short of that, there’s a ton of great info here. I’d start with the sticky if you haven’t already done so. If nothing else you’ll glean some insight on most if not all of the possible no start scenarios.

[991gts6s]

Sounds like simple plug wire or plug end cap is grounding to me..
happened may times to me in many Porsche and Mercedes cis cars..
CIS systems are fun and most times the easiest fixes..
Either air leaks / grounded ignition / throttle plates stuck
good luck.. keep us posted.

[full quack]

When you say it "Back fires", do you mean it pops back through the intake or do you mean it pops out the exhaust?
Super lean mixture can cause a true back fire through the intake, and then a super rich mixture can backfire through the exhaust.
A backfire through the exhaust simply from a super rich mixture, is most likely going to happen on throttle lift while decelerating, not while cranking from the starter.
I know you said your shop checked the CDI box, but mine did the very same scenario when my CDI box was dying. Although my symptoms where on again/off again for about 2 days before it finally gave up the ghost for good. It would run fine for a long time, then crap out for no rhyme or reason. Let the car sit and cool down, it would fire up and run just fine for a bit, then act up again.
So just because they checked it once, does not mean your CDI box is actually good. Have your shop temporarily swap out the box for another, and see if that solves your problem.

My .02 worth.

Mark

[smurfbus]

Also the rotor inside the distributor can act like this if its bad. I had to DIY myself a resistorless rotor. Also once I had the porcelain on the sparkplug crack and it made similar behavior.

[Rich76_911s]

Where did they check that it was getting fuel?

I only ask because I went through my ignition system trying to figure out a very rough running situation. I then checked that each cylinder was getting fuel just before the injectors. All was good until I actually pulled the injectors and found a clogged one.

Just a reminder to check for fuel all the way to the point of delivery for each cylinder.

[T77911S]

i know the shop has said all this stuff works but people get on here all the time and say "this" works only to find out it does not.

I would ask how do they know these things work. what did they do to test them.

spark, check for spark, remove a wire and put a plug on it and crank it.
a bad coil can do this. happened to me. acted like it wanted to crank but would not.

fuel. does it have gas in the tank.
look in it if you have to.
do both pumps run.
remove the plug from the rear of the AFM and turn the key on.
both pumps should run. - try cranking it like this.
with pumps running, push down on the mixture adjuster on top of the AFM. you should hear the injectors squeal. try cranking again. this will "bypass" the CSV.

put some gauges on it and check fuel pressure and control pressure. could be that the inlet screen to the WUR is clogged and your CP is very high.


air leaks. if your IC is not bolted down it WILL pop off. check all the plumbing.


if you really want to get into the fuel supply, remove the return hose from the FD and do a fuel supply test,. I think it is 1500ml for 30sec.
or you could do the supply to the WUR. 225cc(?) for 1 minute.

[jlj]

Got the car back after going thru everything, new over boost relay, rebuilt distributor , new green wire , checked all wiring , sensors , did valve adjust ....Car ran perfect on Wednesday for 150 kms and then hesitated and back fired. Didn’t die and cleared up . Today went for a drive , all good for about 20 kms, pulled hard no hesitating and then just backfired and shut down. Cranks over but will not fire or even try to fire .
I’m at a total loss as this makes no sense how it runs perfect and then just dies.
Any suggestions please ?

[gsxrken]

You need to observe spark at the end of a spark plug wire when it’s cranking. Then check the sticky thread on top of this forum for the reasons why it might be interrupted. It’ll get expensive if you rely on a parts-swapping shop as you may have begun to find out.

[jlj]

Originally Posted by gsxrken

You need to observe spark at the end of a spark plug wire when it’s cranking. Then check the sticky thread on top of this forum for the reasons why it might be interrupted. It’ll get expensive if you rely on a parts-swapping shop as you may have begun to find out.

We did all that and more before changing or replacing anything . As I said car ran perfect for 150 plus kms and then did the same problem again.

[s5uewf]

Check alternator and make sure you have enough spark to fire the engine with the plugs in the cylinders/under compression. Perhaps not enough voltage (could be bad or weak grounding too).

I have had backfiring in the past related to low voltage/not enough amps to fire the plugs under load...

[JK930]

Originally Posted by s5uewf

Check alternator and make sure you have enough spark to fire the engine with the plugs in the cylinders/under compression. Perhaps not enough voltage (could be bad or weak grounding too).

I have had backfiring in the past related to low voltage/not enough amps to fire the plugs under load...

I had the same problem. in the end it was a bad alternator.

[jlj]

So we bypassed the fuel cutoff safety switch on the CIS and the pumps started running . But no spark now.
So strange.
Went through all the electrical we could and are going to try a new coil tomorrow ( although the coil is only 1 year old)
Classic retrofit cdi has a green light that comes on when it gets a signal ( its working) and the newly rebuilt distributor is turning but no spark at plug or coil
So annoying to fix one problem and have
another right away

[full quack]

I have a pick-up coil in the dizzy go south on me a few years back, everything else worked as it should but no spark to plugs.

Initially it was a little hit-n-miss, hard starts both hot and cold. Then finally no start at all. Easy fix, not too expensive, our host had the part. Not sure if Pelican still carries that part of not.

Mark

[T77911S]

so you are getting the light on the CD saying you have signal from dist?
if so and still no spark look at coil or rotor.

intermittent electrical issues can be the fuses. they make poor contact. spinning them helps.
one other thing I would do is remove each wire from the fuse block and clean the ends with a wire brush and clean the ends of the screws.

check the sockets for all the relays including the delayed action relay. make sure the socket pins are not stretched open too much.

[jlj]

Originally Posted by full quack

I have a pick-up coil in the dizzy go south on me a few years back, everything else worked as it should but no spark to plugs.

Initially it was a little hit-n-miss, hard starts both hot and cold. Then finally no start at all. Easy fix, not too expensive, our host had the part. Not sure if Pelican still carries that part of not.

Mark

just rebuilt the distributor and put a new pick up coil

[jlj]

Originally Posted by T77911S

so you are getting the light on the CD saying you have signal from dist?
if so and still no spark look at coil or rotor.

intermittent electrical issues can be the fuses. they make poor contact. spinning them helps.
one other thing I would do is remove each wire from the fuse block and clean the ends with a wire brush and clean the ends of the screws.

check the sockets for all the relays including the delayed action relay. make sure the socket pins are not stretched open too much.

yes green light is coming on
we replaced the fuses with the classic retrofit kit that uses all modern fuses.
thanks for the other advice will check that too if the new coil doesn't work