Strange issue

[FLYONWALL9]

So, I recently did a refresh on my 3.2. I have this posted in my engine drop thread but thought I would post just this one issue in hopes of reaching more people.

Mostly all I did when the engine was out was to replace orings and gaskets along with a valve adjust and new clutch.. After putting the engine back in I had very few issues. The only noted was the RPM bounced, mostly like you would get if voltage or charging was low. I put a few very local miles on the car before putting it on the interstate. On the way to my Dr's apt. when merging onto the interstate I got what can best be described as a stutter. It seemed more like a very fast clutch skip than anything engine related. This little jaunt was about 40 miles total and the car ran like a dream. The RPM issue seemed to improve.

A few days passed and I decided to take the car to run an errand, as per norm I went to start it to warm before blasting off. It fired right off and was running fine for perhaps 15-20 seconds then died off. If I tried to restart it, it would struggle, fire, and die straight away. If I wait perhaps an hour the same scenario occurs. It will start run perfect, then die off after a few seconds. When it does this it doesn't stutter, or fluctuate engine speed, it just dies as if you simply turned the key off.

I have unplugged and plugged the electrical connections back and no change.

Again, the car ran perfect both ways to my appointment and had no issues starting when I headed home after the appointment. Also, no issues the same day when I went to pick up my prescriptions a few hours once I got home.

Any thoughts?

Thanks in advance for your replies and help,
Scott

[99hdtop]

My 85 coupe acted the same way. It was a loose hot wire at the fuse panel. Have a quick look to see if this is a issue with your car.

[timmy2]

Possibly a loose red fuel pump relay. Pull it, spread the pins slightly with a razor blade and put it back in.

[FLYONWALL9]

Originally Posted by 99hdtop

My 85 coupe acted the same way. It was a loose hot wire at the fuse panel. Have a quick look to see if this is a issue with your car.

Could you photo/show, which wire your referring?


Did yours seem to occur not only on initial start but the same delay
in time 15-20 seconds? You can pretty well put a stop watch on it
and count down when it will happen.

Cheers,
Scott

[FLYONWALL9]

Originally Posted by timmy2

Possibly a loose red fuel pump relay. Pull it, spread the pins slightly with a razor blade and put it back in.

TIMMY,

Is this relay located in the front bonnet or engine compartment?


Reason why I ask is because when the engine was removed I could
have sworn the car had a relay in the fuse panel in the engine bay
at the top of that panel and was removed so it would not pump
fuel when the key was turned to accessory. I know I took the pos
battery terminal off before starting the job. And vaguely recall the
guy helping me remove a relay.

Thanks,
SCOTT

[tirwin]

I agree with Dennis (timmy2). My first thought was the fuel pump is cutting out. Not sure about about the later Carreras but the shudder you described sounds like the rev limiter in the SC. The rev limiter works by momentarily shutting off the fuel pump. It can be very harsh.

Were you at high RPM on your merge? If something is loose -- like the fuel pump relay or a wire -- it would have the same type of effect.

The fuel pump relay is usually the big red one on the row of relays above the fuses in the front engine compartment. On my SC it is the one closest to the cabin.

[FLYONWALL9]

Originally Posted by tirwin

I agree with Dennis (timmy2). My first thought was the fuel pump is cutting out. Not sure about about the later Carreras but the shudder you described sounds like the rev limiter in the SC. The rev limiter works by momentarily shutting off the fuel pump. It can be very harsh.

Were you at high RPM on your merge? If something is loose -- like the fuel pump relay or a wire -- it would have the same type of effect.

The fuel pump relay is usually the big red one on the row of relays above the fuses in the front engine compartment. On my SC it is the one closest to the cabin.

Thanks for the reply...

The strange part about this is you being able to nearly time when
it would take place. Start the car for the first time that day and I
can count down and boom it is off. Try to start it back after this
happens and it is pretty difficult. If you wait an hour or so and it
will repeat the same process as the first crank of the day. it will
run for a few seconds and then just stop. You can give it some
gas to extend this time frame but sooner or later it will die off.
The fuel pump relay would be a good starting point.

When I merged onto the interstate I wasn't at high RPM, maybe
3600-4000RPM. I've been trying to keep RPM low due to the new
clutch and breaking it in.

[tirwin]

Originally Posted by FLYONWALL9

Thanks for the reply...

The strange part about this is you being able to nearly time when
it would take place. Start the car for the first time that day and I
can count down and boom it is off. Try to start it back after this
happens and it is pretty difficult. If you wait an hour or so and it
will repeat the same process as the first crank of the day.

When you say that you try to start it back after this happens it is difficult. Do you mean it is difficult to start the car again or it is difficult to reproduce the problem the second time? If it only does this on cold starts, that is a clue. It sounds like you're getting fuel delivery at start-up and then not a few seconds later. Unfortunately I'm not going to be any help on the Carrera though.

[FLYONWALL9]

Originally Posted by tirwin

When you say that you try to start it back after this happens it is difficult. Do you mean it is difficult to start the car again or it is difficult to reproduce the problem the second time? If it only does this on cold starts, that is a clue. It sounds like you're getting fuel delivery at start-up and then not a few seconds later. Unfortunately I'm not going to be any help on the Carrera though.

Meaning it only does it on cold starts.

When it runs after the cold start for 15-20 seconds and dies off, it is
difficult to get it started again but it will start. When it starts then it
only runs for a second or two then dies. Even if you try and give it
gas it will die.

[E Sully]

Earlier cars had the red fuel pump relay. On the Carreras, the DME relay under the seat is also the fuel pump relay. From the DME relay, the red wire goes to a 25a fuse on the fuse block, and then a red wire to the fuel pump. The DME relays have problems with poor solder connections, you may want to get a replacement and see if it still has the problem. It is always a good idea to have one of these relays in the glove box as a spare. Check the fuse and wire connections for corrosion.
If the problem still persists, then it is time to look at other components.

[sled9146]

Had about the same with my 87. Checked relay, replaced fuel filter, checked all connections, would fire on starting fluid . Ended up being the fuel pump which seemed to be gradually going out.

[theiceman]

jumper out your cylinder heat temp sensor first. When it warms up it may not be leaning out the mixture. May not be it but is an easy test .

[wwest]

My 6 HP Tecumseh rototiller engine did that just yesterday.

Ah, Spring!


Oil ingestion via the crankcase check valve stuck open.

[kidrock]

Originally Posted by theiceman

jumper out your cylinder heat temp sensor first. When it warms up it may not be leaning out the mixture. May not be it but is an easy test .

+1. Take a paper clip, bend it into a "U" shape, and insert it into the female portion of the CHT plug (white head connector).

If not, then I'm betting that the fuel pump is going south in a hurry.

[Sboxin]

Originally Posted by 99hdtop

My 85 coupe acted the same way. It was a loose hot wire at the fuse panel. Have a quick look to see if this is a issue with your car.

We had this on our race car - loose power wire at fuse box - - these old screws get loose somehow

Regards,

[AdamFritsch]

E Sully is spot on about the DME.

[FLYONWALL9]

This is great!

Thanks everyone for your reply.

I just got off the phone with our fine host and ordered both the DME relay
and fuel pump relay. If it doesn't turn out to be either, it cant hurt to have
them on hand. I'll give a shot to the jumper, I have a boat load of resistors
that I was given. Just have to find the magnifying glass so I can read the
values.

One great thing about PIA troubleshooting is the amount of info you learn
the hard way.

GREAT STUFF GUYS, again, thank you all and have a blessed weekend.
Scott

[FLYONWALL9]

I do have a question for the 3.2ltr owners....

When I did the engine drop I had a helper. He was great help but the problem
is I'm not 100% sure of the things he may have unplugged or wrenched on.
This brings a question that has been bothering me.

The panel that covers the fuses and relays in the engine compartment. It appears
as if one relay is either missing or was never plugged in? Circular in shape to the
top of that panel and towards the firewall. What is this, what should be in its place?
I cant seem to find any photo's of this part of the car either of my own before the
drop or from others..... The crap books I have do not show this panel, I really need
to invest in a proper shop book....

Thanks

[aus911]

Hi,
That sounds like your test/diagnostics port, b and c is shorted to adj your base idle setting, a is for porsche diag use only.

I hope this helps
Ray

/

[FLYONWALL9]

RAY,

THANK YOU!!

That is exactly it! I had a feeling it wasn't for a relay because of the
pin placement. Thanks for that photo.

Could you tell me what book you took the photo from? This looks just
like the type of shop book I am in need of.