Mondial Has Stopped Starting

This morning I completed the WSM check for operation of the fuel pump (as noted in post #22). No fuel flowed from the return line outlet exiting the fuel distributor.
Based on the WSM this suggests only a couple of possible causes:

1. Incorrect voltage at the fuel pump (WSM indicates minimum voltage required at the fuel pump is 11.5V). Voltage at my fuel pump is 10.6V (with ignition on, but engine not running).

2. Dirty fuel filter. To be certain this wasn't the issue, I replaced the fuel filter this morning and repeated the test with no difference.

3. Defective fuel pump. With power to the fuel pump I can hear a faint "bubbling" sound, though I almost have to put my ear on the pump to hear this. I also notice that that fuel pump gets very hot - is this normal?

Could someone please advise if my voltage at the pump is still sufficient for adequate functioning? If it is, then I will disconnect the fuel pump outlet and try running the pump to see if there is any fuel flow.

Regarding Mondi Cab's post (#25) - I did try lightly depressing the air meter plate during engine cranking when trying to start the car, with no success.

 

Ok - thank you. I'll advise of the outcome.

 

I disconnected the hose that runs from the fuel pump to the accumulator, disconnected the blue switch at the fuel distributor and turned the key to "on" (not "start"). Immediately I could hear the fuel pump working - while standing beside the driver's door. It was definitely much louder than previously.
I checked the disconnected hose and fuel was flowing at a good pace into my catch bottle.

I turned the key off and reconnected the hose to the accumulator. Then turned the key to the "on" position again (blue switch still disconnected) and could again clearly hear the pump operating.

I reconnected the blue switch and after a couple of attempts to crank the engine, it started and ran fairly well.

I left it running for 5 minutes, then turned it off for 2 minutes. Turned it back on and it started first time.

I now want to go back and retry the fuel pressure tests that previously produced no results.

Is it possible that there was an airlock either in the pump or the accumulator that was preventing fuel flow?

 

Yes, the sound is quite distinct and easy to hear. I didn't realize it was that loud (without the engine running, of course). I took a short video of the fuel pump operating to share here, but unfortunately I can't compress it enough to meet the file size restrictions.

What I can't understand is why the pump would have stopped, and why it only started operating once the pump output hose was removed from the accumulator. Both the pump power & ground electrical connections were secure and the ground chassis connection is nice and clean. I didn't touch anything in the fuse panel or recharge the car battery (which was fine anyway), so I don't think I affected any electrical connections.
If a blockage wouldn't cause the pump to stop, then the only thing I can think of is that there must be something going on with the internal electrical connections of the pump itself.

 

Ah, now I get it ! So my pump was running when I was initially able to hear it faintly - with my ear close enough to it. The reason it wasn't making more noise/it's normal sound, was because fuel wasn't being pushed through continually. This makes sense.
So when I disconnected the fuel line at the accumulator and ran the pump, whatever was blocking the line must have become dislodged and fuel was able flow freely.
I've checked my catch bottle and there are some "black bits" floating around in there - perhaps that was the cause.

I also took another look at the fuel line connecting the pump to the accumulator and realized that it's quite old (perhaps original), so maybe there's some breakdown occurring in that. Luckily I had a spare hose that I'd ordered a while ago, so I've just swapped that one in and it seems to be working well.
The engine starts on first crank and the fuel pump remains cool.

I really appreciate everyone's feedback to help me sort it out - and a huge thanks to Steve for his super-fast responses and his willingness to share his massive wealth of knowledge in an educational way.

 

I replaced the fuel pump and the accumulator in October 2019, so hopefully all is still ok with both of those. In May 2022, I replaced the hose that connects the two fuel tanks and the hose running from the fuel tank to the fuel pump, so I'm confident those are in good condition too. I'm really hoping that the hose from the pump to the accumulator was the source of the problem.

It may be worth my time to drain the fuel tanks and check the tank fuel filter (as mentioned by theunissenguido in post #29), as I didn't do this when I drained the tanks the previous two times. Though now that my fuel pressure checks are back within range and there is good flow from the fuel distributor return port, it would appear as though this might not be necessary.

 

So my saga continues. While the car now starts and seems to idle reasonably well, it struggles when under any load and quickly stalls.
I rechecked my fuel pressures and found the following:

cold pressure (with vacuum): 24psi
warm pressure (with WUR): 49psi

system pressure: 63-65psi (pressure continually fluctuates between these two readings with pressure gauge needle bouncing back & forth)

with pump off, immediate pressure drop to 28 psi
after 5 minutes, pressure has dropped to 22 psi
after 10 minutes, pressure has dropped to 13 psi
after 20 minutes, pressure remaining is 8 psi.

So, as best I can tell, I have two issues to address - low fuel pressure and a fuel pressure leak somewhere. Though maybe the two are related.

I've already checked for blockage in the system (see above posts), but I hadn't checked the fuel filter on the fuel tank. I drained the tanks, unscrewed the filter and found nothing but a long pipe. Given the markings on the pipe, I'm not even certain this was original to the car. I've attached couple of pictures in case anyone recognizes this.

Before I reconnect the pump hose to this "filter" I'd like to install an actual filter to protect the pump from debris, but it seems impossible to find anymore. The original part number was 116404, superseded by 136594. Has anyone crafted a screen of some sort to replace the original filter? Or are people perhaps using a small in-line filter between the tank and pump?

With no blockage at the tank, I am wondering if perhaps the problem lies with the pump. Though I did replace the pump in 2019 (and various other fuel system parts - see my first post here for details), I am thinking that perhaps the pump check valve is no longer functioning properly.
As I understand it, fuel pressure loss with system off could come from leaking injectors, the accumulator, or the fuel pump via the check valve. I have no visible leaking from the accumulator and the injectors were replaced just a couple of years ago. Is there a specific test I could perform to isolate the potential problem source?


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Thanks for the hint about searching for fuel "sock" - I would never have thought to use that word. Amazing how many posts come up with that small change!
And, it seems like it's fairly straightforward to attach a new sock onto the pipe, so I'll track one down.

I hadn't considered the possibility of the fuel distributor o-ring being the problem. I would have expected that CIS Flowtech would have looked at all of these parts when I sent the distributor and WUR to them for a refurbishment/recalibration last year, but I suppose that same thinking could apply to the fairly new pump, accumulator, etc. Theoretically it should all be fine, but obviously there's an issue somewhere. Checking the o-ring is easy enough with all the fuel out of the system right now. Fingers crossed I have a new o-ring in one of my many parts bins....

Will keep everyone posted on the progress.

 

Ok, so after a small delay I'm back with the promised update. I removed the fuel pressure plunger (as noted in post #39 above) and the smaller o-ring (identified by the red arrow in post #39) was damaged. I've attached a photo of the offending part. I ordered a rebuild kit from the CIS-Jetronic website and installed the new o-ring. I also replaced the green o-ring with a new one.

I re-tested the fuel pressure. Warm pressure (with WUR on for about 3 mins) was 49 psi. System pressure was 61 psi. With engine off the pressure immediately drops to 40 psi and holds steady, dropping to 39 psi after 20 mins.
So, the o-ring solved the lack of holding pressure.

Thinking all my problems were solved (I really should know better!), I tried taking the car out for a test drive. My driveway is about 35 ft long and goes slightly downhill from the garage to the road. By the time I had reversed from the garage to the edge of the road, the car had stalled. It struggled to restart and would then stall as soon as I tried to give it a little gas. Over three separate attempts I was able to briefly start the car, rev the engine fairly high and move the car a few feet in 1st gear before the engine cut out again. Thankfully on the third time I was able to have the car roll into the garage and stop.

I rechecked the fuel pressure and got the same readings as noted here. I also checked the fuel flow via the return feed line, as per the WSM (D33 in the Mondial 8 WSM) and it produced almost exactly 1 L of fuel in 30s. Although I have the euro Mondial QV cabriolet, I'm assuming the required values are fairly consistent across the Mondial family. If that's the case, then 1L is the target amount and all is good.

I've compared my fuel pressure readings to the WSM (page D40). For my euro version, the chart suggests I should have warm pressure readings of 3.5 - 3.9 bar, which is approx. 51 - 56 psi. My actual test reading was 49 psi, so definitely on the low end. For clarity, my WUR is 0438 140 116.

According to the WSM (D41), my system pressure should be 5.0 - 5.6 bar (72.5 - 81 psi). My actual system pressure is 61 psi, well below the minimum.

My first questions are:

Is it possible that the lower system pressure and lower warm pressure may be causing the engine to stall under load?
Does is make sense for me to purchase some additional shims for the fuel distributor plunger to try and bring those pressures back up to the target range?


My second issue/question is this:

In previous, uneducated efforts to adjust idle speed I have played with both the throttle screw and the by-pass screw (refer to D53, fig. 41). Unfortunately, before making adjustments, I didn't bother to note the original position of these screws. I am now wondering if my changes might also be impacting the engine response.

According to section 11 on page D52, the idle speed (target is 900 - 1100 RPM) should be adjusted using only the throttle screw. The WSM states that the by-pass screw would normally remain fully closed (i.e. turned clockwise as far as possible).
Can someone please confirm if this is in fact the way it should be done? I seem to recall having read elsewhere on the forum that some people have opened up the by-pass screw quite far.

Thanks to all who read through all this!
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I'm fairly certain I didn't ever measure any of the fuel pressures prior to the problems starting. Of course in retrospect, this would have given a very nice baseline....oh well.

I will try to look closer at the distributor tomorrow and make sure it's completely clean.

While waiting for the CIS rebuild kit to arrive I did install a new fuel pump and run a new ground from the fuel pump to the chassis. I now have approx. 12.4V at the pump.

The information regarding the idle speed adjustment is really helpful - thanks! I'll see if there's anything unusual with distributor first and then reset the idle according to these directions.

 

No misunderstanding - but thank you for making sure everything was clear

 

I did order that same one but couldn’t get it to fit over that “shoulder” that’s about 2” up from the end of the pipe. So, I ended up going with a different style:

https://a.co/d/5r21zwi

I cut the metal end off the sock so that the sock would slide up over the tank tube and then used a stainless steel zip tie to secure the sock to the tube just above the tube’s shoulder. This way I’m fairly confident it won’t slide off.
Of course I didn’t think to take any pictures at the time to share

 

I removed the fuel distributor today, removed the primary pressure regulator/plunger and looked inside that chamber - it was completely clean. I did carefully wipe a Q-Tip around the chamber and then used some clean compressed air to be sure the chamber was completely clear.
While the primary regulator was out I took a moment to compare the new green o-ring that I had installed yesterday (from the rebuild kit sent by CIS Jetronic) with a brand new one I had in a kit I’d ordered from Salvox. I noticed they both had a similar inside diameter, but that the Salvox o-ring had a larger outside diameter.
I replaced the CIS version with Salvox version and reassembled everything.
The system pressure is now up to 67 psi (from 61 psi).
Warm pressure seems to have increased by 1 psi from 49psi yesterday to 50psi.

Although the new pressure readings are moving closer to the lower end of their respective target ranges, the system pressure still needs to increase quite a bit.

 

Wow - that's gorgeous!