1986 328 loud engine clicking sound and stalling. Diagnosis?

Unless I missed reading it, I'm surprised no one has suggested the unlit propane torch test to detect vacuum leaks. Follow every line under vacuum and where the intake manifold bolts to the engine. If a leak is causing the low idle, the engine speed will increase when propane enters the intake system at the leak.

 

The symptoms also sound like an ECU issue(s)... You can pull both ECU's to have them tested/checked to see if they're your problem. I think these guys charge around $100 diagnostic fee for each unit.

https://www.ecudoctors.com/#

 

Only one ECU on a 328.

If you are looking for air leaks there is a long vac hose goes from the left side of the plenum to the ECU in the trunk.

If that goes it's a double whammy , you get unmetered air entering the system and you get no vacuum advance on the engine as the revs rise

That line disappears into the wheel well and goes above the arch liner into the trunk. You need to remove the arch liner to get to it though you should be able to check if its leaking without removing that.

I had a hole in that one once , screwed everything up, even more so because someone adjusted the mixture to compensate.....

Took a while to find it.

Another possibility with that is that the diaphragm in the ignition box fails. Effect is the same.

 

You can touch the plate, but be gentle, it has a high lever effect on the fuel distributor plunger. But you are technically on the right track, if you push the plate ever so slightly down, the car would probably stall due to the mixture being too rich, if not that would suggest a vacuum leak.

There are two small vacuum hoses: One goes to the air injection valve which you know about, and one that goes to spark ECU (there is a second ECU for the fuel injection system, so there are two ECU's on your car). Then there is in effect a vacuum line to the Auxiliary Air Valve unit. It is possible to get air leaks at the injection manifold plenum gaskets, they are the thick rubber items. I am leery of propane or starter fluid being sprayed around with a high voltage ignition system near by. I would think you would need a pretty big leak for this type of procedure to work. Shops would use a smoke machine.

You can also get air leaks in the exhaust system, such that air get sucked into the exhaust and the Oxygen sensor will read too lean, and richen the mixture to compensate. Take a close look at the air injection rails where they connect to the exhaust manifolds, and the test port pipes also which connect into the tops of the exhaust manifolds, they tend to corrode and can leak.

But I am still not sure your AAV is ok, it could be sticking and not giving its full range of movement, and sticking is a known issue in these cars.

I was perplexed that your screwing the air bypass valve did not have any effect. Still thinking about what that might mean. When did you last replace your O2 sensor? For greater certainty did you check a spark plug gap? If it is wet, carbonized, or shows signs of lean running, this would be helpful information.

 

What is the failure mode of the AAV that would cause this? If the AAV was stuck open then cold idle speed would be OK and warm speed would be too fast. If the AAV was stuck closed then cold idle would be low, but warm idle would be normal. If it was stuck in the middle then cold idle would be a bit low and warm idle would be a bit high. I don't see that any of these failure modes match the described symptoms of idle is always low.

 

Good question. I think various sensors are also measuring fuel mixture, and engine temperatures affect fuel metering and the fuel ecu responds to all the inputs. For example, the oxygen sensor would also be kicking in after warm up and sensing conflicting signals of a lean mixture that could trigger an inappropriate enrichment which could stall the car. Might be good to disconnect the O2 sensor and see what happens. The O2 sensor is not active at cold start up.

The cold start up fuel injector gets the car started, but once warmed the car is either too rich or lean to run properly. Given the car runs well at speed, this would be more likely if the car was running rich rather than lean. So my thinking is something is singalling and creating a too rich mixture.

Keep in mind we are trying to deal with simple test procedures to get some clues as to what could be the problem.

Although the check valve issue appears ruled out, I find it hard to believe that a 30 year old rubber diaphragm internally exposed to hot exhaust gas has not perished. Must be a very low milage car?

 

When the check valves went bad on my '87 GTS, there was no noticeable effect on the engine idle. When they failed they passed gas in both directions. Another time one rusted through and I could hear a change in the exhaust note but there was no change in engine idle.

 

This thread is certainly interesting and informative. I will just reiterate, as I noted a while back, that I had EXACTLY the same symptoms with my 308QV and it turned out to be an ignition issue. I have since learned that the 328 has only one ignition ECU and two sensors. Still, has the ignition timing been checked? Even though I have two new ones in reserve, I never considered the check valves and also question whether they would cause the symptoms described. I agree it would be a good idea to disconnect the oxygen sensor, which is easy to do, and see the results.

 

There us no way of adjusting the ignition timing on a 328, all done in the ECU. The vac advance is the only thing that changes it.

Sent from my SM-A505FN using Tapatalk

 

Yes, there are no adjustments. With the ignition, it either is working or not. If not, it is coils, plugs, wires/extenders, caps, rotors and crank position sensors that need checking, and related wiring grounds and connections, in the extreme the ecu can fail but that does not seem common at all.

For the 328 (same for 3.2 Mondial), for those interested here is the instructions on how to test from the ignition ecu wiring connector, you have to dismantle the connector to get the probe access to the wires, and make sure you don't short any wires by accident. Even if you don't do the tests, it gives you a sense of all the interacting components in the car's core systems.

I have done these tests, the connector dismantle is easy, and it is all very helpful to rule things out. I also attach the procedures to test at the fuel injection ecu as well. Doing all these tests is what guided me to the need the rebuild the fuel injection distribution unit, by ruling out the many other possibilities along with all the various inspection related things being discussed in the thread.

I am by no means a pro/expert, just a motivated home hobby mechanic who has and will tackle pretty much anything - I sure have learned a lot how the car functions by doing all these diagnostics. If nothing else it takes the mystery out of things and makes you respect the original design and engineering, and also respect the mechanics who work on these cars as while there is nothing exotic there is time and curiosity required to solve for these cars needs.

http://ferrari.cdyn.com/carl_rose_docs/Ferrari 328%2

https://ferrari.cdyn.com/carl_rose_docs/Ferrari 328 Fuel Injection ECU Testing.pdf

 

The O2 sensor is not active until the car warms up a bit. At cold start there is the separate fuel injector that squirts fuel to get get things going (that is what is sticking out of the right side of the plenum on your car with the blue connector). Sometimes this injector does not shut off or dribbles and leaks, and you get over fueling. You could try disconnecting the wire connection, and see if it starts and runs any better. It is this injector, plus the AAV (and the computer and WUR) that gets the car going with an extra rich mixture. These cars in proper tune can run just fine with no O2 sensor, but the O2 sensor does add new information and allows the computer to optimize fueling and emissions as various throttle openings, and it also helps the computer compensate for something else out of adjustment. Once warmed up a bit, the O2 kicks in and the computer takes its signals and alters the mixture accordingly. It is not as quick a response system as in some modern cars, that is why some experience a minor surging at idle or while cruising as the computer is iterates the signals it receives. If your O2 sensor is original, it is probably carbonized and can give the wrong signals. If the plugs are new then that is not an issue, but if you take a look you might get a clue as to the fueling situation.

Yes, I am obsessed with the check valves. They rot out inside, not necessarily outside as the prior attached thread suggests. Your test seems to have ruled this out. Just surprised the old units are still working.

 

Totally agree with the previous post. I previously suggested disconnecting the coldstart injector and oxygen sensor just to see if either seems to have an ameliorative effect.
I realize there are no adjustments on the ignition ECUs. Although my sensors and the two Digiplex ECUs in my 308 tested okay on the bench, I am quite sure that it was an intermittent sensor or Digiplex issue that caused my problem. "Experts" have told me that they don't necessarily fail totally or all at once. My 308 has two boxes and I noticed erratic timing movement on one bank of cylinders, even though that bank was still "operating." A quick check with a timing light can rule this out. I ran new grounds to the boxes and cleaned all grounds and contacts to the coils as well. Of course it is possible that that's where my problem lay, but I tend to doubt it.
Interesting information on the check valves. I've only owned my 308 for a little over a year but purchased two new check valves for insurance. I will install them soon.

 

Good luck. I'm anxious to hear the resolution.

 

The idle droping in 20 seconds sounds about right, the internal heater in the Aav kicks in fairly quickly. Then the mixture is not correct, after the air valve closes. Since the car is idling a bit differently this go round it takes me back to the sticky aav theory. Still stumped why the idle adjustment air bypass screw had no effect, that should have had the effect of raising the idle. I would unscrew it by three quarters of a turn before starting the car, start it up and see what happens. It should make a difference, I can't see how it would have no effect, that is how the car idle is adjusted.

 

Ok, so if you turn the idle screw in until the rpm decreases at a steady rate, then pushing the throttle slightly, does the rpm rise at a steady rate while pushing more and more?

 

Does it drop slowly over that whole 10-15 seconds, or does it drop suddenly like a switch (maybe in a second or two).

 

I don't follow your logic. The AAV shouldn't have an impact on mixture, it uses metered air.

 

FYI, the idle air screw affects the fuel mixture through the entire range of the rpm band of the engine , whereas the throttle plate position does not affect mixture. That is why setting the correct mixture for emissions testing iterates the mixture screw on the fuel distributor with the air bypass screw, you adjust one, then the other until get both the correct emissions and idle speed. That is the dark arts part of these bosch systems!

Because your unscrewing the air screw had little effect, that would suggest leaning out the idle mixture had no effect, which suggests....maybe a very rich mixture further being tempered by the O2 sensor, computer, etc.? Not sure, maybe others can chime in on other causes of the air bypass screw not affecting things the way it would be expected to?

I know you are likely off to a mechanic to solve this, but maybe we get lucky with a few more ideas.

 

The aav has no mixture effect, but the extra aav air and fuel from the cold start injector stop when the aav closes, and if the car is not idling properly after that start up phase, there is a fuel mixture problem, or some other problem but the air idle screw not giving the expected effect suggests a fuel mixture issue, probably too rich.

 

Are you sure? That's not how I think it works. I don't think there is any link, mechanical or electric, between the AAV and the cold start injector.

 

Yes, the cold start valve is only a thermally controlled switch with delay. If the engine is cold, the switch is closed and injects fuel for some time. I looked into it some time ago, and also verified by looking at the spray pattern.

Depending on engine temp as a starting point, the fuel spray is longer or shorter but it is also heated electrically to open up the switch after a few seconds. If this opening does not work, the engine would get too much fuel.

When the engine is warm, the switch opens also by the same mechanism (bi-metal contact or later by built-in electronics).

To sum it up, the switch opens by two things, the electric heater or the coolant temperature.