So, this just happened. Damned electricals...

I don’t think a fuel pump can respond that fast, especially because of the fuel pressure accumulator. I’m still thinking ignition dripping out.

Aaron

 

Have you replaced the crank position sensor on the XDI system?

 

The fuel delivery seems like a good culprit based on that video. If you managed to pressurize the accumulator during startup (i.e. fuel pump works initially), and then the fuel pump stops pumping, then the accumulator will continue to feed the engine until it is depleted. And you'd expect it to exhibit that "running out of fuel" behavior of dying, not dying, dying, not dying...dead.

Did you ever get a chance to check out the air flow meter theory? I still feel like that's got a shot--if your airflow meter is somehow dying once the engine heats up, it could kill power to the fuel pump but only after the engine is started. This is basically what you're experiencing. Easy check: just disconnect the blue connector to the air flow meter when you have this problem and see if the problem goes away. Here's a an old thread on the location of the air flow meter connection (also called a "safety switch").
https://www.ferrarichat.com/forum/threads/fuel-pump-sound-with-ignition-on-308-qv.159112/#post-136895202

Also, glad to hear at least the car is running smoother with a rebuild of the XDI wiring harness. Some progress

 

The pump moves gas into a fairly large pressure accumulator, so even if the pump suddenly stopped when the engine was running, the accumulator would keep the pressure up for a while, I’d bet about 15 seconds. But that’s just a guess.

The other side of that coin is that when the pump starts again it has to recharge that accumulator before it would get full pressure to the fuel meter.

Your video looks on/off/on/off too quickly to be fuel pressure to me. (A fuel pressure gauge on the inlet line would be helpful though).

Aaron

 

Exactly. It shouldn't take long for the fuel pump to pressurize the accumulator--maybe 3-5 seconds. If the fuel pump died in the middle of running, the accumulator will drain based on the engine demands--let's assume 15-20 seconds for a moderately loaded engine.

So, for instance, if the pump were only energized while the engine was cranking or died short after starting, the engine would run for 15-20 seconds. As the accumulator drains/de-pressurizes, it's unlikely that the engine just dies...It'll choke and sputter a few times before it dies.

In the video above, the car starts, runs for 20 seconds and then sputters and dies. If the fuel pump was only on at the very beginning, I'd expect *exactly* what happens in that video.

 

I'm pretty certain that's ignition cutout. Fuel delivery on a 308 CIS setup can't cut out instantly like that - exactly as Aaron says. The way the cutout interval shortens almost suggests some sort of feedback buildup loop when it starts to cut out. It would be interesting to go super slow-mo playback on the recording and note the timing intervals of cut/resume/cut from when it starts to when it dies.

 

Looks to me like the tach drop out is not only too fast to be a fuel problem, but the the tachometer leads the engine speed - the tach drops before the engine does and much more quickly. The needle bounces off the peg while the engine is still spinning. This has to be an electrical/ignition issue.

 

@thorn To simulate the fuel pump / accumulator interaction, you could simply start the car, and then pull the fuel pump wire at the fuseblock. Even hold the throttle pedal to keep the engine at 2500rpm so it matches your vid.

That should at least tell how the vehicle behaves when the fuel pump completely dies while it's running.

 

Well, at least it tells you (and the rest of us) that the accumulator doesn't keep the car running. Fuel pump dies, car dies. Immediate.

But it does mean a flakey connection to the fuel pump OR an intermittent pump could cause the behavior.

Might still be worthwhile just disconnecting the air flow sensor next time you drive the car (I thought that blue connector is outside the airbox?). If it's disconnected, the pump should run whenever the key is on regardless of the state of the engine. When the car dies, listen for the fuel pump. If you still hear it and it's not cycling on/off, then it's fine.

And then you're back to even higher confidence that it's something in the ignition system.

 

To my ear (and I am just a punter), it sounds like all cylinders fire enthusiastically for briefer and briefer periods of time. Something is telling the engine to stop running then letting it go again. Frequency valve? O2 sensor?

 

If it's fuel related hooking up the CIS gauges to monitor fuel pressures would be the fastest way to figure out where in the system the problem is.

I still lean that it's ignition related. Replace the mag sensor with the hall unit. Mag sensors are absolute junk in these applications.

Trying to recall if the QV has this....
Other thing to look at is the relay and fuses in the trunk... Passenger side under the antenna... There's an over voltage relay sitting in there, tied into the fuel system. I think the QV has this...I know the 328 does... If not disregard.

 

A clogged fuel filter....inside your fuel tank or that after the fuel pump.

 

Hmmm, interesting video that sounded very familiar...

When I changed the injectors on my 328 it acted exactly like your video until the air was purged from the fuel lines. Took several restarts until it cleared up and ran normally. I realize that you didn't change injectors or otherwise open a fuel line but the similarity to the reaction of the engine to new/injectors/air in the fuel lines is striking! I'm wondering if a hose or fitting could be leaking so as to allow air into the fuel lines.

 

It's the roughly 30 mins of runtime that is odd and yet narrows down where to look. If there was a leak then it would be consistent. I'm thinking the time factor points to a thermal sensor or a sensor effected by heat, I'm just not recalling at the moment if the QV has the same CIS setup as the 328, frequency valve and secondary ecu on the passenger side.

I'd still look at the ignition system, mag sensors have given me nothing but grief on the 3x8's, that's why I won't use them. Hall effect fixes a plethora of problems.

 

Hi John,
did you meanwhile check/by-pass the ignition switch, like I suggested further above?

Best from Germany
Martin

 

"It's the roughly 30 mins of runtime that is odd and yet narrows down where to look. If there was a leak then it would be consistent.'

I agree and at first I was totally convinced it was ignition/electrical but that video made me lean toward fuel because that's what it sounds like to me - running out of gas! It seems unlikely that air could be getting into the fuel lines only after 30 minutes so now I'm wondering if it's not the opposite problem - fuel tank venting. If the tank is not venting properly, after a period of running time, the pump can't pull any more fuel so the engine is "out of gas."

It could explain why it takes 30 minutes to happen. Then, after a period of sitting, the pressure slowly equalizes and the engine will be normal until, once again, the pump creates a vacuum in the fuel tank. The running time would depend on how the car was driven - aggressively and it would 'run out of gas' relatively quickly. Low speed/idling, it would take quite a long time.

 

Excellent point... Something to look at, easy enough, remove fuel cap. I will say though, it'd be a first for me that a 308/328 has an air tight fuel system! Fuel systems tend to build pressure, 308/328 esp so with the saddle tanks in the engine bay, all nice and toasty.

I had a Mercedes amg that did a very similar thing, ran for 30 min or so then died... Cool down, run again. Now that monster had diagnostic codes so easy to track the problem. Turned out the crank sensor that sat right next to the exhaust, once it got hot... It failed. That stupid sensor will forever be a failure point in need of replacement... Stupid design.

 

Have you tried starter spray into the air flow when it’s dying? At least it would indicate fuel or spark.

 

Something about this is tickling my memory.... I'm going to ponder this.... Hopefully it comes to mind....
What was the first change you made after getting back from Florida?
You mention fuel hoses... All of them, as in even the cross over and vent lines? Charcoal canister?

Under load only...hmmmm... WUR function tested? Main distributor body filter clean? When fuel systems are disturbed lots of crap gets moved about.