Mondial 3.2 fuel smell, backfire, rough idle all when warm

Ok,
this has been discussed like 30 times on a lot of threads, so started from cheap to expensive.

first, checked all valves, and did a lot of work there (a few admision where under .20) but problem did not disappear (but noted better response in general).

then changed both coil modules with new ones, the thermal paste was shot dead... but problems are still there

next week will change the 10o'clock crank sensor....

plugs, extenders, wires, all are under 3000 miles and very new.

WUR was checked (3000 miles ago) and was ok, could check it again just in case....

will update if it was the crank sensor, but let me know if you know it can be something else...

BTW: its almost ok until about 1 hour of running (like 100kms) then the problems starts.

 

Overload protection relay (next to the ECU)?

That can cause the poor running symptoms that you describe, although they should always be there cold or hot if there's an issue with the relay.

If the CIS frequency valve isn't buzzing, then it's probably the relay and/or the fuse on the top of the relay.

 

Interested to know if CGPT could help, I came up with the following. Helpful?

Suspect Areas & Ideas to Explore:
1. Crank or TDC Sensor (as you're about to replace)

• Likely culprit, especially if the issue appears once the engine is hot. Heat can cause marginal sensors to fail.
  
  
• If the 10 o'clock sensor doesn’t help, also check the 2 o’clock and 7 o’clock sensors (Ferrari typically used three crank sensors on these engines).
  

2. Fuel System / Mixture
Even though the WUR (Warm-Up Regulator) tested OK 3000 miles ago:

• Check system and control pressures again when hot.
  
  • WURs can drift or degrade.
    
    
  • You want to verify pressure values at full operating temperature.
    
• Check for vacuum leaks—especially ones that open up more when warm due to expansion.
  
  • Intake manifold gaskets, injector seals, etc.
    

3. Oxygen Sensor / Lambda Feedback

• If your Mondial has a Lambda (O2) sensor and an ECU that manages closed-loop mixture:
  
  • A bad O2 sensor can cause mixture instability when hot and in closed-loop mode.
    
    
  • Try disconnecting the O2 sensor temporarily and see if backfire improves (forcing open-loop).
    

4. Ignition Timing Drift or ECU Ignition Maps

• Since you've swapped coils and extenders:
  
  • Consider if timing is shifting incorrectly when warm—due to a faulty sensor, or timing advance circuit in the ignition ECU.
    
    
  • Use a timing light to check advance progression cold vs hot.
    

5. Fuel Injectors / Delivery Problems

• Possible that one or more injectors leak or dribble when hot, causing unburned fuel to ignite in the exhaust.
  
  
• Look for:
  
  • Uneven plug coloration
    
    
  • Cylinder-specific backfire
    
    
  • Injector spray pattern testing
    

6. Exhaust Leaks

• Minor exhaust leaks before or near the O2 sensor or at the manifolds can create false lean readings, prompting over-fueling.
  
  
• Also, leaks allow cold air in—can combust with unburnt fuel and cause backfiring.
  

Suggested Diagnostics:

• Timing Light Test (cold vs. hot): Ensure stable ignition advance.
  
  
• Fuel Pressure Test (WUR): Again, hot values especially.
  
  
• Smoke Test: Check for vacuum/intake leaks.
  
  
• Try unplugging O2 sensor (test open-loop mode).
  
  
• IR thermometer / cylinder balance test: Detect lean/rich cylinders.
  
  
• Injector flow test, especially hot rest pressure behavior.
  

Let me know how the crank sensor swap goes. If that doesn’t solve it, the next best bet might be WUR drifting hot or Lambda/ignition timing issues when warm. You've done excellent groundwork already—you're close to solving it.

Would you like a detailed test checklist or pressure spec sheet for the Bosch K-Jetronic system (if that’s what your Mondial uses)?

You said:
yes
ChatGPT said:
Great — here's a detailed diagnostic checklist and pressure spec sheet for the Bosch K-Jetronic (CIS) system, which is used on most Ferrari Mondial 8 and QV models.

✅ K-Jetronic (CIS) Diagnostic Checklist
Tools Needed:

• CIS fuel pressure test kit
  
  
• Multimeter
  
  
• Smoke machine (optional, for vacuum leaks)
  
  
• Infrared thermometer or cylinder drop tester
  
  
• Timing light
  
  
• Vacuum gauge (optional)
  

1. ✅ Fuel Pressure Testing
Test when cold and then hot (after the issue appears).

Test Expected Value
System Pressure 5.0–5.4 bar (73–78 psi)
Cold Control Pressure ~1.2–1.7 bar (17–25 psi)
Warm Control Pressure ~3.4–3.8 bar (49–55 psi)
Residual Pressure (10 min) >2.0 bar (29+ psi)
WUR electrical plug voltage ~12V key ON
Notes:

• If cold pressure is too high → hard cold start.
  
  
• If warm pressure is too low → rich mix → backfiring possible.
  
  
• If residual pressure drops too fast → check for leaking injectors, check valve, accumulator.
  

2. ✅ Warm-Up Regulator (WUR)

• Plug in and measure control pressure during warm-up.
  
  
• Should smoothly rise to warm spec in 2–4 minutes.
  
  
• Check resistance across WUR heater (20–30 ohms typically).
  
  
• Look for rich/lean symptoms when warm: idle too rich = possible WUR failure or vacuum loss to WUR.
  

3. ✅ Vacuum Leak Inspection

• Use a smoke test or carb cleaner spray at idle:
  
  • Intake manifold gaskets
    
    
  • Injector seals
    
    
  • WUR vacuum line
    
    
  • Brake booster line
    
• Unmetered air causes lean mixture → ECU (or mechanical CIS metering plate) compensates with more fuel → rich backfire when warm.
  

4. ✅ Injector Test (Spray + Leakdown)

• Remove and check injector spray pattern.
  
  
• Check for dribbling or dripping after shut-off (especially hot).
  
  
• Listen with stethoscope for clicking when firing.
  

5. ✅ Oxygen Sensor / Lambda ECU (if equipped)

• Temporarily unplug O2 sensor:
  
  • If backfire disappears → mixture is unstable in closed-loop mode.
    
    
  • Bad sensor can cause overcorrection.
    
• Check O2 sensor voltage at warm idle:
  
  • Should cycle between 0.1V – 0.9V
    
    
  • Flatline = bad sensor or wiring
    

6. ✅ Ignition Timing Check

• Use a timing light at idle and ~3000 rpm, cold and hot.
  
  
• Look for timing drift or jump once hot (suggests bad TDC/crank sensor or ECU issue).
  

 

Is the sump coming up or any sign of fuel in the sump oil

 

sump is at normal level, normal oil smell, no fuel on sump.

 

frequency valve is buzzing all the time, cold and warm

 

Fuel distributor needs a rebuild? Too much fuel when warm could be leaking internal O rings in the distributor. When was it last re built?

Take a couple of spark plugs out and see if both banks are fouling with gas, or just one.

 

fuel distributor rebuild like 1 year ago, all spark plug looks very very good

 

That was my point about looking for a rise in sump oil, one i saw was backfiring and pouring fuel into the sump. He does not have that.

 

for me it looks like a advance issue... but i dont have a ligth timming gun, nor know how to do the test (and at where.... in the flywheel window under the oil filter?

 

There is no adjustment to advance, it is all controlled by an ecu.

Even though the caps/rotor/wires were replaced, I would double check these components first by taking plugs out and seeing if it is all the plugs fouling with gas - if so that points to the fuel distributor - if one bank that points to the distcap or the coil - if only a few plugs that points to distcap/wires/extenders.

The dist cap carbon button and spring can get wedged and stuck when installed, or the wires may not have pierced correctly as on some dist caps the wires can be hard to push in fully. You can also get a dist seal leak, and oil flings inside the distcap causing misfirings.

If the fuel dist has never been rebuilt, that would be suspect, the rubber inside deteriorates and causes all kinds of misfueling outcomes.

 

Bad fuel ?

 

The problem starts like 45 minutes after normal driving, when the engine gets fully warm

 

I would do a full CIS fuel pressure test, only takes a few minutes. Warm control pressure could be off, or cold start injector dumping fuel.

A rebuilt fuel distributor is no guarantee. When I had my fuel distributor rebuilt by a well respected CIS specialist, I assumed they had checked fuel pressure in their lab….nope. System pressure was wrong, solved by a $10 shim kit. My rebuilt WUR from a different well known shop also came back with wrong warm control pressure which I had to take apart to raise to spec. Cold start injector could also have misbehaving electrical, or injector itself leaking when warm.

 

I can't imagine how it can take 45 to be warm... For me it's eléctrical, WUR do not change pressure after 5/6 mins max

 

just to finish... looks it was the crank sensor (at 10 oclock)
anyway its very cold these days here, so will need to wait at least a few weeks to confirm

 

500 miles after: it was the crank sensor!!

its amazing how it degrades, after the change I ended in a full re-setup of COMIX and Air ByPass to make it idle back to 1000... as its burns different now.