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Looking for some insight on an issue that happened last night to my supercharged '79 928 Spyder.
About a mile from home, I downshifted and passed my wife in her 997 in 4th gear with a change to 5th (Z06 trans so tall gears). Probably started the pass at 50 and ended around 100 MPH since she was trying to keep up. After turning into the neighborhood, the car started missing, stuttering, and eventually stalled. It would restart for a second, then die immediately. I tried this a few times with the same result. Popped the hood and also looked underneath - nothing obvious was wrong..
I revved it up pretty high once to try and get it up into the driveway and after that, it continued idling as I pulled it into the garage. Turned it off and tried to restart it and the same thing - ran for a second, then died. During all of these restarts, I could hear the fuel pump buzzing for a few seconds when I turned the key. I took off the relay panel cover and checked all the fuses - all good, pulled the fuel pump relay, turned key - no buzzing, of course. Put in a spare relay and the car started up and ran. Put in the old relay and the car started up and ran.
Any ideas of what might be or might have happened here? I haven't driven it today yet.
Doesn't your car have a 3rd party ECU or still the stock brains with the supercharger?
Sounds like something popped off or loose causing a huge air leak.
Stock K-Jet setup tuned by Carl for the supercharger.
why would it then start working though?
I just remembered that when this was happening, my AFR gauge was going back and forth between normal 10-12) and full lean, which I guess would happen if it stopped getting fuel or had a huge vacuum leak?
I couldn't find any loose vacuum hoses or hear any vacuum leak sucking sounds either?
I start with stupid stuff like making sure there's fuel in the tank. Then move to a fuel pressure check to make sure that there's good flow available. If you have the original CIS intact on the '79, I'd hook up the full gauge set to verify things are OK. CIS is finicky when it comes to even a tiny bit of crud. I'll speculate that the hard higher-RPM pull dislodged something in the system, and that something found its way into a critical spot. The gauges should tell you.
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A SoCal local experienced similar symptoms, and spent days chasing them. Only to find that the fuel gauge was showing him a little gas when the tank was almost empty. Stupid stuff, but only after you find it. Perhaps it's that simple for your car.
Oh, since it's supercharged, look to verify that all the pressurized plumbing is still perfectly connected. A hose or pipe that's just "sitting" together will offer a vacuum leak, and push apart when your manifold is under pressure. So a push-and-pull test may reveal more than the simple visual inspection.
Probably a good idea to get Carl in the discussion, since he's intimately familiar with the specifics of your engine build.
It's a long shot, but it wouldn't be the first time something came loose under boost only to "relax" enough after cooling down to hold a bit of vacuum at idle.
Originally Posted by Petza914
Kevin, I don't think I have a pop-off, blow-off, or pressure relief valve with this Powerdyne setup.
Did some poking around. Could this red hose (see photo below where I'm pointing) being completely closed off cause this.
I rerouted it just now to have a more gradual curve, but when I looked at it after opening the hood, it was pulled down and closed off with probably very little if any flow through it being possible.
If that hose being choked off is the culprit, could the long pull under boost or the off throttle lift that creates vacuum at the end of the straight been what caused it to close up?
This setup can pull a lot of vacuum, in fact I've put a loose very open coil spring inside this black hose to keep it from collapsing as well.
New info. After finding that crimped hose, fired it up - started just like normal and drive it around the neighborhood. Perfect. Figured I had it, then approaching the driveway, it just died again. Restarted and pulled down the driveway, and now it's doing the exact same thing as last night again - starts for a second, then dies.
Behaves like a fuel starvation issue, so I think the first thing I'm going to do is check the fuel filter. Maybe enough gets through for the car to start, but then the flow gets restricted and won't keep it running. It's odd though as I've been through lots of tanks of gas even a round trip from SC to WI and I would have thought any tank junk would have been worked through by now.
That hose your pointing at provides a vacuum signal to the Warm Up Regulator (aka: WUR). Yes, if it was pinched closed it could effect the tune. The WUR is miss-named; it is the K-Jetronic fuel pressure control regulator and operates in all temps and all conditions. Not just during warm-up.
Normally, when the WUR sees a loss of vacuum through that signal line, it richens the mixture because it knows you have your foot in it.
Take a close look at what might have shaken loose or fallen off on that lil' jaunt of yours...
I would have thought any tank junk would have been worked through by now.
Its funny how sometimes a piece of scale inside an old fuel line can flake off and cause a little trouble fore a while as it works through. I'm not saying that's what it is, but it could be.
Are you still adding Sea-Foam to your fuel like I suggested? The light oil in the Sea-Foam helps lubricate the central piston in your fuel distributor so it moves smoothly and doesn't hang up. Not an issue for other cars, just K-Jetronic. Helps the mechanical injectors open and close better, too.
Are you still adding Sea-Foam to your fuel like I suggested? The light oil in the Sea-Foam helps lubricate the central piston in your fuel distributor so it moves smoothly and doesn't hang up. Not an issue for other cars, just K-Jetronic.
Actually forgot all about that recommendation, so no, no SeaFoam has ever been run through it. Guess I need to pick some up and start following directions. How much should be added to a 12 gallon fill- up? I can't completely fill the tank as the vent hose at the top leaks.
02-15-2017, 02:11 PM
After high-speed pass, car died & wouldn't run
