85 Mondial QV appears to be running rich

Having worked on many of these cars, I will say it is difficult to pin point one thing. You really need to find a shop that is VERY familiar with this system. It is odd that they replaced only 4 injectors and disabled the cold start without actually repairing the system. As well, the twin ignition systems must be working correctly or it will appear to run rich.
Since it is a "project car" I am guessing it will need more work. Poor spark plug wires will make these cars run really poorly. Check them and make sure they are good. I was told 650 Ohm pre foot is a good number. Over the years, I have found this to be a good place to start. Many cars read zero connection. You can replace the wire and reuse the sleeving and boots most times. The extensions should have no resistance, I rarely find a bad extension as it is just a metal rod. Make sure there are no signs of arcing through the plastic, still not common but it happens.

 

I see you're in Alabama right ?! No need for that cold start injector in your climat. Just disconnect the Bosch connector of it But you have to check if that injector is not leaking even disconnected.

 

The fuel injection system is mostly designed to meet emmissions and to do that is has to run well at low rpm. Once off idle, the car is much less sensitive to fuel mixture, indeed may run very well at higher rpm when rich.

So if it runs well off idle, it is probably not an ignition related issue. That said these cars run like two four cylinder engines strapped together, and the good bank can offset the bad bank to a surprising degree. You could take out a couple of easily accessible spark plugs and see if they are all fuel fouled, if only one/some are that is ignition related.

My wild card suspicion based on the service work described is that the rebuilt fuel distributor is not calibrated correctly. There is very small tolerence for setting the plunger depth in the distributor body. If it is not set correctly fuel will flow at idle greater than it is supposed to. As rpm's rise the problem will abate. Restart is very hard as the car is as you say flooding.

The distributor plunger ideally needs to be calibrated on a flow bench, otherwise it is going to be a guess by the rebuider. Do confirm if you can who rebuilt the distributor. If it was CIS Flowtech, you are good to go. If not, then the issue noted is worth considering. The unit can be rebuilt with a seal kit quite easily, but that plunger set up does require experience to get it right absent bench testing capability.

There is a fairly simple check for whether the dist plunger is set correctly.

You remove one of the gas lines to the top of the fuel distributor that feeds one of the fuel injectors. You then jump the fuel pump relay and cause the fuel pump to activate while the ignition is in the on position but the car is not running. There should be no fuel welling up in the distributor pipe opening when the throttle is closed in its idle position. If the fuel rises and spills out, the plunger is not correctly set. (Of course, if fuel comes out it is helpful to have someone working the relay jumper, and stop the jump immediately so no fuel/fire risk ensues). If no fuel rises in the distributor, the plunger is set up properly.

I would note that setting idle mixture on these cars is not so simple. It is supposed to be done with an exhaust gas analyzer, which is becoming a rare piece of service equipment. It is possible the mixture simply needs to be leaned out. A tiny movement of the mixture screw can solve for things. A 1/16 turn of the mixture screw counter clockwise is leaning the system. Many caution against playing with the mixture screw as the problem may well be elsewhere. But it is worth a try, just reset that screw to where you started if it makes no impact, and continue to diagnose other potentials.

Mechanics who work on Mercedes of the same vintage would understand this injection system.

The fueling system when all is in order is quite reliable and effective.

 

Jarrod, I am always busy and have a number of big projects but I work in smaller tuning and maintenance jobs as they come through. Give us a call and we can schedule you in if you like.

 

If the car has its tool kit, there is a spark plug socket in there.

 

All indications are that plugs for your QV would have the 21mm hex which is 13/16 inches. My 3.2 has a 18mm hex plugs. Maybe you have some usual brand of plug that has a different than typical Hex size.

 

There should be no need to disconnect the cold start injector, it should work as advertised and should be connected. It can have a leak though, so even when disconnected it would over fuel. What is the mileage on your car, you refer to it as a project, but recommisioning a lower miler car can present different issues than restoring a high miler. You might run some Marvel Mystery oil, it will clean up varnish inside a fuel system that has sat too long.

 

You can only do an electrical check without removing it.

With the low mileage, I would not expect that valve to have failed. I just replaced mine when trying to diagnose broader fueling issues rather than try to bench test it.

With the low mileage, I would not expect that valve to have failed.

 

Yes, but it is not soaking with fuel, not as crazy rich as one might have expected. The picture is blurry, that spark plug gap looks a bit too tight?

 

The rubber cover is to add a degree of water resistance in the rain. It is reproduced/available from the usual parts suppliers.

 

Yes, the gaps look correct, you are definitely running rich, and since all the plugs are looking the same we are likely ruling out ignition issues. You will have to change out those plugs if you want to have the car run better, it will be hard to eg. Play with the mixture screw and see what happens when the plugs are now going to cause some hartd start and rough idle. Either that or try the 7,500rpm Italian tuneup to clean them up.

 

https://awitalian.com/product/distributor-cover-118889.html/

 

Hmm, I might have expected that also to be the case on the first plugs you had removed in the rear bank. With one bank wet and the other bank relatively dry (but still showing signs of running rich), that could point to eg. the coil failing on the one bank, or the dist cap/rotor worn, the wires poorly pinned in the cap or the wires being old and failing (as one original poster suggested).

Other items to consider are the crank position sensors. These can also fail, they are magnets and the engine heat and time can degrade them.

My hunch remains on fueling, but as usual there are plenty of other possibilities one can consider.