Complete loss of power

[myslateblue911]

I was driving my 1983SC 911 today. Something happened I’ve never encountered before. I was accelerating in third gear and had a complete loss of power. Stepped on the accelerator and the car felt like it started to die. I downshifted to second gear hit the gas and had power again. Drove the car for another 15 miles or so with no problems. Same thing happened. Starting to accelerate and experienced a complete loss of power. I downshifted. Regained power drove for a little while, then lost power etc. Was able to nurse the car to get it home. But there’s something definitely wrong. Based upon the experience in this forum. What might be some initial steps I should take to look at for the culprit of this problem. Thanks

[Jeff Higgins]

I would start by looking at fuel delivery. Maybe as simple as a plugged filter. Under power, the motor is using more fuel than can be delivered, when you let off and the demand lessens, supply catches back up for a moment. Then, running under power again, it can no longer supply enough fuel to meet demand and the cycle starts anew. Classic plugged filter symptoms. If it's not that, maybe the tank vent is plugged. Start there, and if you don't find a problem, then start digging deeper.

[GaryR]

Good advice ^^^, it's likely fuel but I would also look at swapping out your CDI box for a known good one as an easy test if yours hasn't been rebuilt or replaced.. Old elec boards in a hot environment can get "flaky".

[faapgar]

Watch your tach.If the needle drops with power loss then it may be a CD.

[myslateblue911]

Originally Posted by Jeff Higgins

I would start by looking at fuel delivery. Maybe as simple as a plugged filter. Under power, the motor is using more fuel than can be delivered, when you let off and the demand lessens, supply catches back up for a moment. Then, running under power again, it can no longer supply enough fuel to meet demand and the cycle starts anew. Classic plugged filter symptoms. If it's not that, maybe the tank vent is plugged. Start there, and if you don't find a problem, then start digging deeper.

One thing I failed to mention. The first time that it "lost power" on acceleration, I let of the gas and the car backfired. It has never done that before. It also did not do that again on subsequent occasions when it lost power. Just that first time, it let off a deafening backfire. Not sure if that additional symptom helps narrow down the source of the loss of power.

[Nditiz1]

This has happened to me as well. I am still trying to diagnose the issue. I had my CDI rebuilt by Bob Ashlock. It looks excellent and definitely fixed the 15 minute run time issue I had initially. Last year I had a long 2hr drive to meet with Tony (CIS wizard/Eng Builder) On the way back, the same symptoms you experienced I had as well. Car totally shut down, I believe tach dropped, it eventually came back with a backfire. Then, I found if I take it out of gear and wait for the idle to come back up as though everything was ok, back in gear and driving with no backfire. I had to do this 4 or 5 more times on the hour drive back.

Fast forward to earlier this year. When the temps got warmer I was on another long drive and the same thing happened. I temporarily swapped out the CDI for a unknown condition used one I picked up. The CDI worked fine and I have not seen the issue since, but my data is not yet conclusive. The temps have dropped down significantly. I believe something is going on internally with my refurbed unit. I will be sending it back out to Bob to see if he can do more stress testing on it. I picked up a new green wire, but haven't installed it yet. I haven't experienced this when temps were below 80 on long drives.

[JSV798]

Backfire suggests unburnt fuel so suspect momentary ignition failure; classic green wire problem: had it happen on my 1978SC.