my '81 just dies when idling

[JK930]

hey guys

I have this very nice dream car a 81 turbo
trying to figure out why the car just dies when idling

HERE IS THE LONG VERSION OF THE STORY.
ALSO I'M NOT A MECHANIC BY TRADE



I bought it 4 months ago and fixing all the little things before unveiling it.

I did bring it to a Reputable Porsche Mechanic for it ppi and first full service
valve adjustment
fluids and all filters
plugs, cap & rotor
belts
brakes
etc.

he delivered the car back to me .and it sat for 3 weeks

tried taking it for a ride let it warm up and it backfired and stalled many time within a few blocks.
i made a u turn and parked it.

he picked car up

put fuel gauges on to monitor
then cleaned and adjusted the warm up regulator
replaced boost relay
replaced rear fuel pump
replaced fuel relay

car seem to run good and fast on test drive. he was driving

note: oil level gauge jumps
tach jumps when in boost

get the car back car sat for another 2 weeks

the car started right up
a puff of smoke ..cleared up in a few seconds
pulled car out of garage
car idled nicely for about 3 minuets the stalled like:
someone pulled the cord out of the wall

mechanic stopped by to checked it out


it was not a fuel issue (pumps stay running)

also
we do hear the high pitch sound(ignition box?) after the car stalls

I want to thank you all in advance for your input
I am tiring to learn as i go
and get this beauty back on the road with everything working as it should.

[JK930]

update

so it is not a fuel problem.

the mechanic put in a in line spark ignition tester.
it allowed us to view the spark thru the see thru glass.

with engine running for about 12 to 15 minutes it died.

we observed that the spark was the cause.

he plugged in a different cdi box and the same thing happened.

as the car got warmer it died quicker.

put testing light to see the out put of the box and it proved well.

the finger now points to the coil.

we will get another coil and continue the test....

[Jeff NJ]

I hope the parts that the mechanic replaced without cause are going back to him and your money refunded. Reputable or not, replacing parts and hoping it fixes it is not a good sign. Especially when it turns out he replaced a bunch of expensive fuel system parts for an ignition problem.

Why cant he test the coil if he thinks its the coil?

Is it original? They are pretty reliable. The replacement ones available now apparently suck, so if you have a replacement coil, it may be the issue.

[Rawknees'Turbo]

In your first post you mention "tach jumps" - often, a jumping tach needle is an indication of system voltage spikes due to a bad voltage regulator, so use a multimeter to measure charging voltage. High voltage spikes (anything above 14.5) can cause many of the running issues you describe.

[JK930]

Originally Posted by Jeff NJ

I hope the parts that the mechanic replaced without cause are going back to him and your money refunded. Reputable or not, replacing parts and hoping it fixes it is not a good sign. Especially when it turns out he replaced a bunch of expensive fuel system parts for an ignition problem.

Why cant he test the coil if he thinks its the coil?

Is it original? They are pretty reliable. The replacement ones available now apparently suck, so if you have a replacement coil, it may be the issue.

the coil is original. do you recommend any particular brand .
the rear fuel pump was making noise so I thought it would be wise to swap it out.

[JK930]

Originally Posted by Rawknees'Turbo

In your first post you mention "tach jumps" - often, a jumping tach needle is an indication of system voltage spikes due to a bad voltage regulator, so use a multimeter to measure charging voltage. High voltage spikes (anything above 14.5) can cause many of the running issues you describe.

ok i will check it out.
do you see any concern that the battery the previous owner put in this year was just a new but generic small sized battery. or should the car have a long type like originally equipped. porsche must have used them for a reason.

[Rawknees'Turbo]

Small batteries work just fine, and in fact, put less strain on the alternator (less work to keep a low storage battery charged) - I've been using a 15 pound Odyssey 680 for many years without issue, as have countless other 911 owners.

The only reason I can think of that Porsche put that huge battery in (the original weighs about 65 lbs) is to try to lesson the car's poor weight distribution (a different version of the led weights in the front bumpers like found on very early 911s).

[Jeff NJ]

Originally Posted by JK930

the coil is original. do you recommend any particular brand .
the rear fuel pump was making noise so I thought it would be wise to swap it out.

Sounds to me like he is guessing that it's the coil. Have him test it or find a test one to swap out without buying a new one. If he cant or wont, find another mechanic. I don't have a replacement coil to recommend. I have just read here numerous times about new silver colored Bosch coils failing immediately.

The pump should be tested to see the amperage draw and flow rate to determine if it's failing. A noisy pump isn't necessarily bad.

Try Ronnies suggestion first, then test the parts instead of having the mechanic replacing parts until he stumbles into the issue while on your dime.

[Alan L]

There was a recent posting where weird things happened to a 930. Turned out the boost gauge wire and Over boost switch wired were swapped. They are close together behind the intercooler (LHS). The wire to the o/boost sw is white and the sw is in the back of the IC - assuming all stock. The effects would be a bit like the bad voltage regulator - screwy voltage to your fuel pump relay and WUR.
You should be able to peer over the back and check.
And there is a rule on this forum. You need to post a pic of the beast, we never get tired of looking at them.
Alan

[Rawknees'Turbo]

^^^^

Ha ha, Alan, that was Jeff with the wires switcharoo!

[Jeff NJ]

See? I speak from experience!

[Alan L]

Well then .., anything is possible.
I nailed it then - but only in 20/20 hindsight. Now he got some other problem..
Just odd with the tach jumping when hits boost. I'm struggling to see where the connection would be. Like you say, the tach bounce is almost always a voltage spike.
Alan

[Rawknees'Turbo]

Originally Posted by Jeff NJ

See? I speak from experience!

Truff!

Originally Posted by Alan L

I nailed it then - . . .

[mark houghton]

Anyone can swap out parts....it takes a true mechanic to diagnose each part individually, which would require intimate knowledge. Tell your wrench dude you want back all the parts he removed, since you have paid dearly for new replacements. What he took off may very well still be good, so hang on to them as spares for future "just in case" use.

Jeff's suggestion is right on regarding the coil:

"find a test one to swap out without buying a new one. If he cant or wont, find another mechanic".

Unfortunately not all mechanics are equal. Some know Porsches, some don't, and some just rely on their customer's deep pockets.

[Alan L]

Sorry - wasn't paying attention to who was posting what.
But to the OP, are you saying, to be clear, there is no spark when the engine dies?
And this takes place quicker when the engine is warm?
Alan

[T77911S]

I am interested in the this spark tester that he used.

[T77911S]

oh, your problem. the coil can heat up and cause it to stop running, I would look into the mixture and fuel pressures.
that seems pretty fast for a coil to heat up and quit.

[klefroid]

Well I had the same with a beetle few years ago. My money goes to the coil... Because the car dies without driving it so no movements in electrics. Check the green wire that goes to the distributor (small chance but easy to check)

[JK930]

Originally Posted by Jeff NJ

Sounds to me like he is guessing that it's the coil. Have him test it or find a test one to swap out without buying a new one. If he cant or wont, find another mechanic. I don't have a replacement coil to recommend. I have just read here numerous times about new silver colored Bosch coils failing immediately.

The pump should be tested to see the amperage draw and flow rate to determine if it's failing. A noisy pump isn't necessarily bad.

Try Ronnies suggestion first, then test the parts instead of having the mechanic replacing parts until he stumbles into the issue while on your dime.

UPDATE:

We tried a brand new Bosch coil car started right up and smooth
ran for 6 minutes and then died.

[JK930]

Originally Posted by Alan L

Sorry - wasn't paying attention to who was posting what.
But to the OP, are you saying, to be clear, there is no spark when the engine dies?
And this takes place quicker when the engine is warm?
Alan

correct.

start car
runs smooth
let warm up
after several minutes (6min this time) you will hear 1 miss
about 30 seconds to a minute later 1 more miss
then a few seconds later it cuts off.
you will hear the high pitch noise from cdi box