Bill Ball

I was driving along and hit a rather broken up section of the street, but not a whole lot worse than a lot of the old roads around here, when all of the sudden the car lost most (but not all) power and started making a loud, rapid clatter after hitting one nasty hole. I thought I had possible broken the TT shaft, but I still had some power and the noise wasn't exactly metallic.

I have wideband O2 installed as well as the stock O2 in separate arms of my X-pipe and the WB readings have always been good. During this incident I noticed the wideband showed AFR ~27 - SUPER lean.

I pulled over quickly and turned off the ignition. Fortunately, the car immediately restarted and ran perfectly the rest of the way home, even over some rough sections, like it always has.

I puzzled over what the heck happened. I have never heard of or seen anything like this happen before. One guess - the noise may have been one of the relays fluttering on/off. Say, the fuel pump or LH relay. So, the fuel pump was barely pumping fuel. I really have no idea what happened. I know those relays are simple 53s, so it's hard for me to postulate a mechnism for this, but it appears I lost most/all fuel and the situation corrected after killing the power.

Note I do have the ignition monitoring system bypassed.

danglerb

Maybe a short in one of the wires, injector, fuel pump, etc?

Partial power may be key to sorting it out.

Fogey1

Checked your grounds? Big jolts sometimes make marginally loose grounds detach momentarily.

If you didn't lose instruments, lights, etc., perhaps it was a fuel injection ground. Maybe making the injectors stutter or shut off momentarily, leaning it out.

Bill Ball

I would expect a short to KILL the injectors. The loud buzz or whatever it was is a clue. It was so loud my first thought was a mechanical problem, but the relays are right down in the footwell, so could be rather loud. And I don't know why it "fixed itself" on restart. I will get down and poke around the grounds and relays.

Bizarre.

dprantl

Fuel pump itself? Although I have seen relays fail and start to click like crazy. Maybe your fuel pump relay is beginning to bite the dust.

Dan
'91 928GT S/C 475hp/460lb.ft

AO

Let me see if I can say this without mixing things up... the O2 sensor is going to tell you how much oxygen is in the exhaust stream. Lean = more oxygen. The cause for more oxygen in the exhaust stream can be the result of lack of fuel or the lack of ignition of the air fuel mixture. (I think that's right)

The real question is which one did you experience.

Hitting a severe bump may have caused any number of faults. A loose/poor relay is a good place to suspect. A loose ground strap, loose battery that shorted on the cover, ignition lead, ground point, loose chip in the LH, loose ignition switch... All of them possible suspects. Unfortunately, intermittent faults like this are difficult to reproduce. If it were me, I would have (if my ***** felt large) driven over the same patch to try and recreate the event.

Spun

A similar thing happened to me once. I posted, but got no response. Has not happened since and it was 5K miles ago.

Speedtoys

Bill:

Remember my "car dies when I hit a certain type of bump" problem on the way to SF11?

Was a bad FP relay.

I say that..because the ONLY change I made once I GOT there finally (four fuses later) was buying NEW relays for everything.

Yours isnt blowing a fuse..but..Id say its -a- connector that didnt like being hammered, which is 99% relay and pump internals itself.

Ive been trouble free since swapping that relay.

karl ruiter

Even a perfectly good relay will bounce into the wrong state if you hit it hard enough. And it does not really take that much. A drop to the floor from desk height will do it for almost any relay. That does not explain why it did not recover until you turned it off, though.

IcemanG17

Sharky had an odd cut out issue...only when hitting hard bumps or when going downhill (think T5 at thunderhill)...it would loose all power for a second, but ZERO warning lights.......then at most a second later it would fire and run fine...like nothing happened....

Ended up being a bad fuel pump!!!!! I figured it out by measuring resistance of the fuel pump...when it ran crappy or not at all it would spike to 15-20 ohms.....normal is low like 2-3 at most....

the flyin' scotsman

I was cruising down a hwy when after hitting a bump, not that large, the car lost all power, the engine quit like a light switch and wouldnt restart.

After the one and only flat bed home (touch wood) it started.

I posted here and did some research and even though the car continued to start I didnt trust it again so replaced the fuel pump.

Never had a similar issue since........many fast and furious miles

Bill Ball

I'm going to swap out the 3 key relays (EZK, LH, FP). They are all simple 53 and I think original. I carry spares in the glovebox, but never had cause to use them. The only thing that was really odd, other than it fixed itself, was the LOUD noise. Never heard a relay that loud. More than any buzz I would think a relay could produce. I really thought something major mechanical had failed. And AFR of 27, which I'm pretty sure about, is not compatible with running at all, but I believe the motor was still turning, although very weakly, until I killed the ignition. I was sure I was in deep doo doo; flatbed territory. So when it restarted perfectly fine, I was so stunned that I drove through a red light. Very strange.

Bill Ball

Was there a loud noise as well as the loss of power? Did it fix itself after turning off the ignition like my case?

Jfrahm

Fuel pump wear can cause metal bits to get stuck in the works. This is from an A8 but it might happen in other cars:

http://forums.audiworld.com/picture....ctureid=222881

One of the tricks to get going again when this happens is to temporarily reverse the polarity to the pump to try to get it to spin again. A good bump might do likewise.

Bill Ball

Yeah, that old trick can work. The noise I had was far louder than any stuck fuel pump and more a rapid ratatatat than the constant hum of a stuck pump.