Mondial QV won’t rev

There was the equivalent of half a salad bowl of rust flakes in my tanks. After 40 years, whatever can rust (hose unions, fuel sender, tank cap,...) ends up in the tank. Even the body panels next to the tank ended up crusty. Fuel pickups were torn appart by these metal flakes. No wonder I kept on replacing fuses, pumps and k-ket filters...

So yes they are aluminium, but they can be filled with rust flakes. Not sure this is the OP problem, but he'd better have clean pickups.

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Then flow test (easy), and pressure test (requires the gauge but still easy).

 

A few basic things to check first, which would not involve parts costs. Remove ecu electrical connectors, clean with deoxit and reseat the connectors.

(https://www.amazon.ca/DeoxIT-25cc-Precision-Dispenser-100/dp/B0000YH6F8/ref=sr_1_3?crid=1Q39A3A4VW7PW&keywords=deoxit&qid=1679766202&sprefix=deox,aps,396&sr=8-3)

Check the fuel pump fuse box connection for signs of overheating (the white connector will look burned by the connection pin), also clean up with deoxit. Swap/test or replace the fuel pump relay at the fuse box. Since your car starts and runs til things (like the Board connector connection) heats up when under load, this is worth looking at carefully.

Check the spark plug extenders for signs of arcing. I presume the dist cap contacts were not too worn, or you dressed them lightly when you replaced the rotor, that is ok, the caps are designed to last quite a while and the contacts can be cleaned up. Might want to use a timing light to check each spark plug wire while the engine is idling, and see if you are getting the consistent spark, if you removed the cap to replace the rotor, an old wire might have pulled loose in their holes/pin in the dist cap. Alternatively take a few spark plugs out and see if any one is fouling/smells of fuel more than the others.

There could be a coil failure underway, if you check plugs and one bank is fouled while the other is not, that would be an indictator. I am not aware of an easy check for coil integrity, people usually swap one side for the other if it is clear one bank is nmot running well, or just replace the coils, for the qv they are not too costly.

There is a crankshaft angular position sensor that can also cause this type of problem. It can be tested for resistence, which is not definitive as these can to fail intermittently, or just replace it pn 119052 or 115019 depending on the engine number. (I am assuming your qv is the 3.0 litre, sometime the later 3.2 is also referred to as a qv).

My car presented somewhat like yours, and after many checks, and parts replacements in the quest for electrical issues it was the fuel distributor that needed rebuilding. There are rebuild kits on ebay, and it is a meticulous but doable diy job. You need to get the right kit, it is based on the serial number on the specific distributor. Here is an example (Salvox is this kit provider, I also link to the other supplier which includes intructions, you can see if you want to tackle this on your own or not)

https://www.ebay.ca/itm/291660777425?hash=item43e85647d1:g:QFgAAOSweW5VS6DE&amdata=enc:AQAHAAABALkdIdfYKmI5wEORYbgYitRHAex/ercsWSEl999n9E/WWwyr4ZxAqi9gKEL2Trl/lhlGsATdLzcJghf/whwU+msRGVQ4O0iSNz28dirJam4uMb06Jqc535pdIVdfCU2CJFgDCM2EbqR2iNqHK66P04NBIRBjLy8KUZZKbPkMBqTux6z3hAX5E15kQrCEjyBaxOeb2PEtCryx9FiZP5/3v4SE81IBrGSVm9Gi7S9nuDZIWxfca0BIudUDpODVlvjN/HQG6pZFKrTAEGlt/ClBYPlaRBjeQHSdpjEuDBZaiy9iItiLUQgFxWE/cPwxc3HB16OZOSYD7jepcr7JdNqMNX4=|tkp:Bk9SR_Lx6J7jYQ

https://cis-jetronic.com/index.php?rt=product/manufacturer&manufacturer_id=26

Calibrating it for proper flow at idle can be tricky, but there is a reasonable procedure to trial and error this, a rebuilder does this on their bench with flow equipment. As you can see from the kit there are lots of rubber orings and a diaphram that deteriorate with age, so if yours has never been done it needs to be.

This is the go to US rebuilder http://cisflowtech.com/, the owner is a very experienced and nice fellow.

Since it appears you are in the UK, here is a firm in Germany that does the same service, maybe there is someone local in the UK, Mercedes of the period used the similar Bosch system so rebuilders for that community might be more common.

https://www.mengenteiler.eu/index.php?name=0438100055 | 0438100055 Fuel Distributor REPAIR | FERRARI TESTAROSSA &artikel_id=30043672&seite=kmt_details&language=eng&nr=8a10d767fcbac1ac29d0655d4620e266&ArtNr1=0438100055&KModNr=1406&KHerNr=700&KTypNr=

 

Raemins posts reminded me of a 328 I had a very similar problem with. I had checked the in tank filter and it looked OK but I was driving the car with a variety of diagnostic stuff hooked up. When I accelerated hard enough to cause it to fall on its face the only anomaly I saw was a small drop in fuel system pressure, maybe 10 Lbs. I couldn't imagine that would cause it but I had nothing else so I perused it. I drained the fuel and pulled out the in tank filter and with a bore scope looked in the tanks. There was so much dirt in it, it looked like a garden but there was really nothing in the filter. I did notice it was piled up around the filter. I pulled and cleaned the tank and the problem was gone. What I think was happening was the debris under high flow would get sucked up and restrict flow enough it dropped some but not all pressure. It was a surprise to me CIS operation could be so disrupted by a quick but only moderate drop in system pressure.

CIS really does not like dirt. After cleaning, replace main filter and test control pressure. Warm up regulators really do not like debris.

 

1) Quite agree with @moysiuan, and to play it even safer, once the connectors are clean, I would add silver conductive grease (MG Chemicals 8463A). You should chase all possible contacts: connectors in the harness, fuse tab, relay tabs, etc.

While you are there, just use a fuse that is half the required rating and see if it blows up. Normally the pump should draw 7.5A, so the fuse is sized for twice as much. Needless to say that if your pump can burn the regular fuse you have quite a clogged plulmbing, a clean system should make it do with twice as less, a so-so system will be just in between, hence my suggestion to put a fuse that can only sustain the bare minimum and see how it goes.


2) Once everything is clean, and the electrical gremlins are out, if the pressures are not correct, you may rebuild k-jet on your own, that's quite straightforward as long as you do not try to mess with the individual injectors set-screws (leave it to the pros).

Distributor : Savox kit is the only one quoted as ethanol compliant, so it's the one I use. But beware that these kits were made for German cars, and they are a few holes of the diaphragm that do not line up (the one for the WUR actually). I had to punch the diaphragm... Not really Savox fault as my car has two distributors, and only one had the issue! See pics here : https://www.ferrarichat.com/forum/threads/ferrari-400-412-k-jetronic-metering-head-rebuild-myths-and-advice.653663/#post-148310988

WUR : when the engine gets hot, the WUR adjusts (leans) the mixture, so your issue could well be that the WUR is not properly setup. The main problem here is that they are tons of (internet) tutorials on how to adjust the WUR pressure. It is indeed easy to adjust the cold pressure, but much more delicate to adjust the hot pressure. These tutorials only show how to "knock" the WUR (cold pressure adjustment) which will make the WUR properly adjusted when cold but way to lean when hot. Many cars were "adjusted" that way by careless mechanics. Also the WUR has a built-in electric heating system that speeds up the transition from cold pressure to hot pressure. This feature could explain why when you cut the engine you can restart again: no electricity for a while allows to cool the WUR bimetallic strip and revert to "cold" enrichment.

 

When the fuel distributor is rebuilt, there is a very delicate calibration of the plunger depth. It is possible the rebuilder has not gotten this quite right. Hopefully they bench tested for the proper plunger depth, but the may have just set it at a "factory" spec, that may or may not be correct for a specific used distributor.

The problem is that at idle, there should be no fuel flowing through the fuel distributor individual cylinder ports. If the plunger depth is literally a hair off, there will be too much fuel at idle, and the car will be running too rich. Off idle, the car would likely run ok.

Call you rebuilder and ask if they bench tested the fuel distributor flow to ensure the plunger nut and depth at rest was set up correctly.

Another way to check this is with the engine off, you can remove one of the fuel lines fittings on the top of the distributor. Then jump the fuel pump relay and see if when the system pressurizes, the fuel should not move in the port, ie. Not rise up or start filling the port up at all. If the fuel is filling up, then the plunger depth is not set correctly.

 

Did you put a clean air filter ?

 

Good reminder to double check some simple things, it is easy to go down intriguing technical diagnostic paths when many problems are indeed very simple and basic things.

Maybe you can post some pictures of the engine bay, distributor area, etc. as people on this board have good track record of spotting things that might look unusual.

 

Does your car have a frequency valve near the fuel distributor? It looks like an injector.