Mondial t misfire

Hi 348 / Mondial t afficianados - any initial diagnoses / 'what to check first' ideas for an intermittent but persistent misfire - single cyl I think, not a whole bank

Symptoms : Misfire occasionally clears at high revs but reverts to missing (constantly) at intermediate throttle settings

No CEL lights or anything else untoward showing

Idle is also very lumpy even after reconnecting battery and letting run for 15 mins- typically running at 1000 rpm, nearly dying and then picking up to 1500 before dropping back, every 10 secs or so. Car generally recalcitrant at intermediate throttle settings

Occasionally the rev counter jumps up & down erroneously (not in sympathy with the actual revs) on idle

Finally am I likely to do any damage driving the car in this state - e.g. to the cats ?

Thanks in advance - all ideas accepted. Hopefully something straightforward like a loose connector or dodgy HT line.... (?)

 

The list can get pretty long quickly.
Here's what comes to mind, but isn't complete:
- bad ignition wire
- crossed ignition wires
- faulty ignition coil or wiring to coil
- faulty ECU or ECU wiring
- faulty injector or wires to an injector
- fouled spark plug

You need to find out what it is before driving further. If the cylinder is getting fuel & not igniting it, it's going to get dumped into the catalytic converter & cause it to overheat, might even start a fire back there.

 

First, the tach can get jumpy when your alternator is dying, so stick your voltmeter leads into your cig lighter socket to watch if your voltage is going nuts when your rev counter is jumping. Note your voltage reading when the car is off, when the motor is idling, and when you give the girl some throttle. Post those numbers here.


Second, when your engine is cold and turned off, pull your spark plugs, photograph them, and post the photos here. See my link in my signature below. That can speed up diagnostics of complex problems.

 

Then check the connections for the Mass Air Flow Sensors.

Now if my memory severs me correct, you aren't able to pull the engine codes. I don't think that Mondials cam with On Board Diagnostics. Other wise I would have told you to pull the codes anyway.

 

He has a '93 to he can pull the codes (2.7)...Search the 348 threads on how to get the stored diag. codes. In the t you access the computers by opening the firewall cover in the trunk. I am still learning but wouldn't the jumpy tach also indicate a possible crank sensor problem?

Dave

 

A jumpy tach is usually a sign that the voltage regulator, in the alternator, is going bad.

 

OK thanks all, will get it into garage next w/end & post the diagnosis. Hopefully nothing too painful...

 

My money is on crumbling plastic rpm and tdc sensor connectors and/or the MAF connector grunge...

 

My 328 was doing something very similar -rough idle , stumble in intermediate and no to slight miss at higher RPM . Was a tiny hole in the spark plug extension cap near the plug on #5 allowing a little of the spark to jump to ground @ the valve cover surrounding it .

Found it visually but for $10 you can buy a simple ignition / wire tester at Advance or Auto Zone . It essentially lets you see the spark jump across an air gap you set . I set mine at 2 KeV and checked all 8 wires . I hoped it would not harm the Marelli's and it did not .

 

Mondial is now firing on all 8 glorious cylinders again - HT lead was breaking down at plug end. Both banks OK on compression testing. However going to pull ECU codes & check all connectors as a precaution - watch this space...

THanks for the advice

 

I had simialr problem, I had my MAF rebuilt via rock auto and I when I did the very easy r/r I had a completely different car...I found that these MAF's control your whole ferrari motoring expereince.

 

Just to finalise this thread, all my various woes did indeed seem to come down to one loose HT lead connector to a plug - engine idles & runs like a turbine now. Amazing how such a simple fault can wreak such ECU chaos...

 

Thanks for the update.

 

Can someone post a pic of the faulty part? I would like to check mine as well - I am getting misfires and generally bad running.. and have already gone down the plug / wires / cap route.

Thank you!!