engine dies while driving

[Craig Stevens]

I'm Having an intermittent problem with my 80SC. the engine randomly dies when driving, alt. light comes on & engine will not start right away. It will start & run fine after sitting for 5 minutes. I have checked the MSD box , connections & coil, the fuel pump & check valve are a year old. I changed relay, checked fuses & grounds. Has any one experienced this problem & what was the solution I don't want to just start swapping parts . any help is appreciated. Craig

[twistoffat]

You have tested the old reliable´s. Can you hear the fuel pump when you turn the key. If its fine and considering you have changed the relay I´m not 100% certain but I think it could be your ignition switch.If your engine stops the voltage drops through the range which lights the Alternator which may seem like an alternator problem but is not...its the ignition. I´m sure someone more knowledgeable here will have more info

[kidrock]

I once had a fuel pump do exactly what you describe. I initially tried to isolate it as the problem, but could hear it whirr (ever so slightly). It started as an intermittent problem and gradually became worse, to the point where the car would no longer start...even after waiting several minutes. I wound up just replacing the pump out of desperation, and the problem was solved.

[scarceller]

When it dies if it dies stone cold, meaning it does not sputter and the tach drops like a rock to 0RPM then you most likely have ign failure not fuel. Fuel will usually sputter before it dies and the tach will not drop like a rock.

[Vincent Hill]

Please do not think this is a Crazy Question, But are you using or Just Switched to "Shell" Gasoline?

[enjefriy]

Wen u replaced your fuel pump a year ago, did u have a good look at the fuel hose which hooks up from the tank to the pump. The hose is a dual layer rubber construction, with a canvas like carcass in-between. Mine was dying intermittently as u mentioned, & long story short, wat had happened to me was that a chunk on the inner diameter of the hose had peeled off. At certain fuel flow it would peel against the fuel flow, and acted as a check valve which stop any fuel getting thru.
Replaced all sorts before realizing all it needed was a $7 fix.

[Craig Stevens]

Thanks for all the replies. I have not used Shell gas lately. I have learned over the years to not rule any thing out when thying to fix an intermittent problem, The tach does drop when the engine quits, so I believe it could be electrical, but I will check the pump & fuel line hose to be sure. Craig

[scarceller]

If the tach drops like a rock my bet is you have spark loss. What is the ignition system? Stock CDI or aftermarket? Could be the pickup in the distributor affected by heat?

You stated that engine does not re-start for 5 minutes so during this time test for spark and check the ignition system has power and is functional.

[Craig Stevens]

Sal, when the engine stalls there is power. the ac still runs, lights, radio, ect and the engine turns over but will not start. after five minutes of sitting it will start & run fine. I have a MSD Box & coil I will take a second look at the distributor & check the spark. Thanks again,
Craig

[scarceller]

Originally Posted by Craig Stevens

Sal, when the engine stalls there is power. the ac still runs, lights, radio, ect and the engine turns over but will not start. after five minutes of sitting it will start & run fine. I have a MSD Box & coil I will take a second look at the distributor & check the spark. Thanks again,
Craig

Craig,
I suspect your issue could be spark. The MSD is easy to test out, I'd start by verifying you don't have spark in that 5 minute time. Simply remove center wire from distributor attach a test plug and ground it tight with vise grips to a solid ground. Have someone turn motor (try starting) do you have spark? If not I'd then disconnect the trigger wire on the MSD (on my Pro MSD6 it's the white wire) then with key in run (but do not crank the starter) the MSD should be live and have power. If you then touch the trigger wire to a good ground and then remove it from ground the MSD must produce a spark. This is a quick test to see if the MSD can produce spark.

My next question is how are you triggering the MSD? Points, optical, ?? I ask because it could be the trigger that's not functioning. I have seen some solid state trigger components fail because of heat or heat soak when engine is shutdown.

[Bob Kontak]

+1 on Sal's comment. I would go on a ride with a pal and wait for failure to test.

The trigger is probably the standard Bosch distributor with reluctor and stator. Assuming stock.

Just did some searching on Google and there is discussion (somewhat limited) of heat soak related problems that are similar to yours but in cars other than Porsche. Some talk of relocating the box to a cooler spot. Some put bags of ice on the MSD box. Two posters disconnected the battery (after fail) and re-connected and it fired - their feedback was that the box needed repair since power disconnection reset the box.

MSD also has a tech forum.

[Craig Stevens]

Sal,
I am using the MSD 2 pin magnetic pickup
I suspect heat could be a a factor, because the problem happens at around 190o
I'll do some testing on the msd & coil. Thanks again for your help
Craig

[Craig Stevens]

Bob,
Thanks for the info. I love intermittent electrical problems. Google is a wonderful thing!
I'll check out the MSD site
Craig

[scarceller]

Craig, where are components mounted? Left side of engine bay near rear fuse block is good choice. The engine compartment in these cars does not get much above ambient temps when engine is running because that huge mechanical fan exchanges tons of air in the compartment. I know because I monitor IntakeAirTemps on my 84 Carrera and I was pleasantly surprised to see that they run almost the same as outside ambient temps!

But if you shut these engines down the compartment heats up quickly and can easily double the ambient temps on a hot day within a few minutes.

I suggest the coil and MSD unit be mounted on the left side away from the motor.

But keep in mind the trigger components are in the distributor and here temps are hot my bet >200F

[Craig Stevens]

Sal,
The MSD is mounted in the stock cdi space on the left hand side & coil is in the stock location.
I also removed the condenser from the deck lid to improve air flow in the engine compartment
This has been the hottest summer in Florida that I can remember.
Thanks again, Craig

[scarceller]

Originally Posted by Craig Stevens

Sal,
The MSD is mounted in the stock cdi space on the left hand side & coil is in the stock location.
I also removed the condenser from the deck lid to improve air flow in the engine compartment
This has been the hottest summer in Florida that I can remember.
Thanks again, Craig

Can't recall 100% but if the coil is on the main engine fan housing I'd relocate it to the left side as well. Get the coil off the engine as heat and vibration will cause them to fail early. Plus some aftermarket coils like to be installed standing up.

[Craig Stevens]

the coil is a blaster & is mounted upside down on the fan housing. the research I did on this coil said the orientation did not matter. you are probabably right on relocating to the west side. Craig

[edgemar]

Changing to a new fuel pump relay worked for me...with similar symptoms. When the fuel pump stops the engine dies instantly. I thought for sure it was electrical but is was the fuel pump relay in the end... is that the relay you replaced?

[Craig Stevens]

I changed the fuel pump relay yesterday