help the new guy with engine miss

[garycox]

Guys

I recently purchase a 68 911. The car underwent a nut, bolt restoration a couple of years ago. Yesterday I took the car on a trip of some distance for the first time, when I got about 45 minutes from home it began to misfire and pop and this quickly deteriorated to the point where the car would not rev past about 3000rpm and would only run in 3rd gear or lower. Any higher gear the engine just bogged down and did not respond at all to the throttle, except to make the bogging sound louder. I stopped to check things out, but of course I had no tools, eveything looked fine on inspection. When I stopped, the car would idle ok, and it would accelerate through first gear ok, but would start to miss in second and above. I managed to limp home in second and third gear, even in third gear the engine would not rev past about 3000rpm, it would just miss and pop and bog down.

Today I get in the car and on a short trip around the block it ran fine. I think it probably has some sort of ignition problem, but I welcome any insight and opinions on how to troubleshoot this problem.

I know the engine is a 68 2L case built up to 2.7RS specs with webers. The distributor has points, they appear like new and clean. I have not yet checked the dwell. The blue box in the photo is mounted on the firewall. Is this a CDI type of unit? I am not familiar with this. It has no labels. As the photo shows, it has a new bosch blue coil. The other thought that came to mind is the small aftermarket fuel pump shown, but I am not sure how a fuel pump could cause an intermittent failure?

I just removed the spark plugs, they are a sooty tan color. Not carbon fouled but certainly not white.

Any help would be appreciated.

Thanks

Gary Cox

[edmayo]

I just love intermittent problems that require you to get 45 minutes from home before they appear One of the possibilities is the intank filter is clogged and should be removed and cleaned just so it can be eliminated as a possible cause since you have almost all the right symptoms, except usually the engine dies entirely but will restart after 15 minutes or so. Another possibility is the Permatune CD box and/or the coil which could get weak when hot but then be okay again when cooled down. But the more I think about this it may just have been vapor lock. I see you're in Baton Rouge, I know it was hot there yesterday, the fuel pump is mounted in the worst possible place (I know, that's where Porsche put it) but I also see that the fuel lines are routed unnecessarily high which serves to allow a high point for fuel bubbles to occur. I would shorten and reroute the fuel lines to keep them as low and short in length as possible. You could install a TEE in the fuel line and run about 5 ft. of line into the car to a fuel pressure gauge. Repeat your 45 minute drive and see what the fuel pressure is when (or if) it goes into its stumbling act again. If the pressure remains constant then you probably have the previously mentioned bad coil or CD box.

[Flieger]

Permatune ignition boxes (the blue box) have aquired a reputation for failing at the worst times, often being intermittent before going completely dead. Try swapping in a known good box from a friend's car?

[John Z Goriup]

It's been my experience (and that of a lot of my friends with 911s) that the new Brazilian-made blue coils are garbage. They are usually good for about a year maximum. I would buy two old, black, tested coils (so you'll always have a spare), check the primary wiring, and install. They are much more powerful and reliable. Then get the correct, tested Porsche CD box, install & and see what happens.

I'm quite sure just those two items will improve things noticably.

A lot of commonly used Porsche "Original Teile" that are sold nowadays by Porsche but which are not made in Germany by the factory are really not very good.....but the prices sure would make you think otherwise.

PS: an experienced, respected, professional mechanic/ builder locally, swears by Champion spark plugs,...... says they're good for at least 2-3HP. PM me for the plug # and info if interested.

JZG

[garycox]

Thanks for the sugggestions.

I will reroute the fuel lines, and may go to a bendix type of pump as well.

I will get a bosch CD unit and go from there.

Thanks for the help.

[karlusmagnus]

Gary, welcome to the board. How about some nice pics of your car ....?
Always looking to see new members cars

Karl.

[CamBiscuit]

Gary

Just noticed the top wire on the connector panel is not screwed to anything....

I doubt it is related but it seems a bit odd.

Cheers

[Rich Lambert]

Check the points gap.

[Mudi]

My vote is the fuel filter is getting plugged.. Drain the tank, put some filters on the line and go for a long drive... Have fun..

[Neil '67 911S]

Hi Gary,

In the event that it might be vapor lock, bring a soaking wet wash cloth with you in a ziplock baggie. if the car craps out, wrap the wash cloth around the fuel pump for a few minutes. the evaporation will cool the pump off and then it should restart if that's the problem.

The fuel filter should be on the outlet side of the pump. Since it's on the inlet side, the extra energy required to pull the fuel through it versus pushing the fuel. This exacerbates the fact that the fuel pump, as it is placed now, acts as a suction pump versus a pressure pump, which is what it would be if it was mounted below the outlet level of the tank. As you reduce the fuel pressure on the inlet side, the boiling temperature of the fuel drops, which is what vapor lock is. Ever see those glass "love meters?" It's color water under a vacuum.