kacperbeski

Hey guys,

2 days ago I changed the distributor cap & rotor in my 1982 Porsche 928. After trying to start her I heard a loud 'popping' noise and saw an explosion under the hood in one of the cylinders (the hood was open, had my friend look at it while I was giving her a go). I made sure to check if everything was put together in the right way and discovered that the rotor itself wasn't really fitted snuggly.

Potentially worth mentioning is that the new distributor cap had different numbering, but I traced all the wires and put them in the same pins (basically mirroring the original setup). I have also read that different numbering on the rotor cap should not be an issue provided that all the wires are in the same spots (please correct me if I am wrong).

After that, I tried replacing the distributor cap & rotor with the 'old' setup (they were working before that job, but the engine used to misfire quite a bit & required long cranking before starting - that's why I thought of replacing these two in the first place).

Now here is the problem. Whenever I start the car it fires right away (which would be a great improvement...), goes all the way to above 2000 RPMS and then dies after a second. If I give it a little gas it will hold those RPMs for a while, go down, struggle, bring them up again, go down etc. never really attaining anything stable (used to idle at around 900 RPMS before). Basically, she is currently not driveable.

See the video below showing what's happening after I turn her on. After the first RPM drop she dies, then later I give her a little gas after the drop & then release completely - she struggles to build and sustain anything remotely close to being stable.

You Tube

My initial thought was that I blew one of the intake manifold to head gaskets (hence the backfire & visible explosion in one of the cylinders). Already ordered all 8 to replace them on Wednesday when they arrive.

Any ideas about what the problem could be? What would be the best course of action to pinpoint / solve the issue?

Thanks!

Uploading pictures of my engine bay and wiring setup below:

Schocki

Did you remove the complete distributor assembly?
What's the position of the rotor at TDC for cylinder #1?

Petza914

Check this first. There's a scribe mark on the top lip of the distributor once the cap is removed as the TDC reference.

It looks to me like the car is starting with the fuel from the cold start injector (if it has one) but not getting regular fuel and why it dies. The CSI only fires when the starter is engaged so it gets some fuel from that olbut once the key is returned to the run position it stops getting gas. I'd jumper the fuel pump relay (contacts 30 and 87) and see if it does the same thing of it it runs. Only connect the wires when you're ready to run then ar and don't leave them jumpered as it will flood the engine with fuel - better even to put an on/off toggle switch on it and have the wires long enough to reach from the driver's seat.

How did you see a visible explosion? Are the intake runners and gaskets not properly sealed and tightened? At the spider bod, some of the connecting rubber sleeves don't look exactly positioned so maybe the other ends of the legs aren't secured properly?

hwyengr

That caught my eye, too. If none of the intake system blew apart, I'm betting more on a stray ignition spark igniting a fuel leak mist.

BRB-83-911SC

Check to see if the intake plenum became dislodged from the air guide/throttle body as a result of the backfire. This would create a large source of unmetered air.

kacperbeski

I only removed the cap. Pic below of the position - seems a little off, pointing somewhere in the middle of cylinder 1 & 3. Could that be a culprit?

Mrmerlin

You should recheck the timing and verify what direction the rotor is turning while the engine runs.
NOTE the engine runs CW as viewed while facing the front of the engine.

Then verify that you have plug wire 1 at the hash mark on the distributor body.
then the next corresponding wires
the engine cylinder layout is based on 1 2 3 4 on the right hand cylinder or passenger side,
then 5 6 7 8 on the left hand or driver side. this for USA machines

kacperbeski

thanks! Is it possible that by not fitting the rotor in the right way I threw the timing off?

Mrmerlin

yes though you might have damaged the cap as the rotor will sit quite a bit higher if its not in its groove

kacperbeski

neither the cap nor the rotor look damaged. How do I adjust the position of the rotor? I can only turn it clockwise a tiny bit. Sorry for newbie questions - I am trying to fix it with a help of a friend since my specialist is not available now.

thanks!

Petza914

That tiny bit is the spring inside. If it's off, has to be by at least a full tooth. You have to actually remove the securing bolt that's used to adjust the timing in the groove and then pull the whole thing out. The gear teeth are angled so it will rotate counterclockwise as it comes out and why you also can't align the rotor with the mark when installing as it will end up too far clockwise. You have to install it a bit retarded so as it rotates into position it's in the right place. If the crank and cams are aligned on their marks, looks like you're 1 or 2 teeth incorrect.

GregBBRD

If there was a visible flame, when the car backfired, you have an intake leak.
There's no other way for this to occur.
Locate and repair the intake leak/leaks.

If your picture of the rotor is when the crankshaft is at TDC, it is off one tooth.
That would explain why the firing order numbers on your cap are off.
While technically, this isn't a real problem, since it is probable that whoever did this, also moved the spark plug wires one or more locations. to compensate, but if you want it to be correct:
Assuming that the plug wires are off one position (It's possible that they are off almost 180 degrees...depending on how bad someone messed this up. If this is the case, hold on for further instructions.)
Relax. This is not difficult to do correctly.
Remove the distributor hold down bolt, lift up the distributor, and turn the rotor (this may take a couple of attempts) until the rotor points to the mark on the distributor housing, when the distributor is fully seated.
Re-install the hold down bolt in a the same location, for now (you will want to check and correct the ignition timing after you get the engine running.)
Remove and rotate the spark plug wires to the proper position.

ZEUS+

The rotor should be tight on the shaft. You said it "wasn't fitted snuggly" and you "can only turn it clockwise a tiny bit". Turning it clockwise will retard the spark. The rotor position in the pic will fire the cylinders late/retarded if that's at TDC. It seems to run like it needs to be advanced in the video. Do you have a known good proper fitting cap and rotor ? Unless the distributor was incorrectly installed as previously mentioned. A loose rotor can cause crossfire. Rotor must be be on #1 location with engine at TDC on compression stroke. Firing order 1-3-7-2-6-5-4-8.

kacperbeski

Correct. After trying to replace the old cap and rotor I made a mistake not fitting the rotor in the right way. Then there was that ‘pop’ sound (like an explosion of compressed air + there was a visible light). I went back to the original ‘old’ cap & rotor making sure all the wires are positioned correctly. The thing is that the rotor does not point to the hash mark on the distributor body - it’s slightly off and I can rotate it a tiny bit clockwise.

Today I tried to eliminate the vacuum leak issue and checked the intake runners & replaced all the gaskets. All of them were fine. After I gave her another go today & tried to fire her up, I took off the distributor cap to have another look at it, and the rotor now points to a completely different position then before (it turned roughly 180 degrees).

Does that mean that the timing is completely off? What is the best course of action from here?

Thank you all, I appreciate your help! Will get into the next steps tomorrow early morning.

ZEUS+

TDC on exhaust stroke rotor will be 180 out.