328 misfire

Short answer.. it can be the mixture too.

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Single biggest cause is probably spark plug extensions.

 

So take out the 8 spark plugs and post the pictures here

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So who done the last(s) and when ?

 

Spark plug connectors can go bad, hopefully its that simple , if not go back to Kent, they will get it sorted for you, I have heard good reviews about them in the UK car magazines. I believe they also sell Ferraris.

Thank you

 

As other member suggest, do spark plugs and wiring were recently change ?

 

Simon:

Use NGK Iridium DR8EIX (stock #6681) in your 328...they’re about $9 each.

Alan
N.J.

 

Simon:

One other point: there are counterfeit NGK Iridium plugs out there so only buy from a reputable source. Don’t fall for the lowest priced plugs on ebay. There are YouTube videos explaining how to spot the fakes.

These plugs come pre-gapped but you should double-check that they’re at about .025” before you install. Be super careful not to damage the fragile center electrode in the unlikely event you need to adjust the gap.

Alan
N.J.

 

I have installed thousands and never not had to adjust the gap.They are indeed pregapped but not for a Ferrari. Those plugs have many applications.

 

https://www.ngk.com/ngk-6681-dr8eix-iridium-ix-spark-plug

Buy direct for the best price.

 

Kent High Performance would only buy the plugs from a very reputable and trusted supplier - I would seriously doubt it's the plugs.

If you're having problems with the car, I'd let them check it out first - Just in case.

(If you start taking things out/changing things, they might not cover the cost. Chances are you've bought a car on consignment from them, which limits the warranty to a degree, but they're good people, and I'm sure they'll sort it out for you. I bought and sold my 348 TS through them, and was told: "If you should have any issues, don't hesitate to get in touch, and we'll get it sorted for you". I dealt with Dave in sales, and he was great to deal with)

It stands a good chance of being an issue with the ignition side of things, but I wouldn't rule out the possibility of a fuel injector playing up.

 

That's not the failure mode for the plug extenders - even with a bad extender the resistance will test just fine. The problem is the extenders burn through the side insulator wall and short to the cylinder head. You have to look for tiny pinhole burn through marks, inside and outside, along the length of the extender. Hopefully you have the red extenders, not the black ones!

Also examine around the spring clips for the top of the spark plugs - if those don't have a good grip, you'll get corrosion buildup and bad connections to the plug.

Gordon

 

Given the service history, I doubt it is ignition related. Make sure all connections are snug, including those to the ECU, just removing and replacing connections can "clean" the contact surface and solve for things.

I would also check the throttle position sensor. You can't do an "ear check" by having the car turned off in a quiet place, and push the throttle slightly at the throttle body lever and you should hear a click just off the idle position. With a good ear you could hear this from the seat by lightly pressing the throttle. If not the TPS needs adjusting, not hard to do but do report if you indeed hear the click. The TPS is part of what tells the ECU computer the amount of acceleration being requested. There is idle, mid throttle and full throttle as the three positions the TPS is measuring, so it can affect acceleration fueling. You can use an ohm meter to test for the unit internals as well.

 

If they're iridium plugs and you do want to measure the gap, use a proper feeler gauge and not one of those circle gap tools (looks like a metal disc) that can damage the tip.

I use NGK on all my cars and never had to regap them either FWIW.

 

Yep...those are the correct NGK Iridium plugs.

Make sure you get the ones with the screw-off tips (as shown)...they’re the only ones that will fit into the plug extenders.

Alan
N.J.

 

I have been using Deoxit for my electrical contacts, there is a cleaner and a preserver fluid. Others have used Stabilant. Both are contact enhancers, and are used by some OEM's (eg. Lexus).

Do you know if your fuel distributor has been rebuilt? If it is original, there are rubber o rings and a diaphragm inside that perish with time and especially with the alcohol in modern fuels. Many fueling problems can present as if there is a spark issue. The fuel metering device is a very precise device. The internals seem to last a surprisingly long time if the car is used and driven, but if original it is due for a rebuild.

If your spark plug inspection is showing a black fouling rich condition in more than one plug, the distrubutor would be a suspect.

I went extensively through all the electrical items as you are, did a compression test to rule other things out like a head gasket leak or valve wear, and eventually realized it was my fuel distributor.

fyi, here is a test procedure for the fueling ecu, might give you some ideas.
http://ferrari.cdyn.com/carl_rose_docs/Ferrari%20328%20Fuel%20Injection%20ECU%20Testing.pdf

 

Not sure where your based, but I have a pressure test kit for measuring the fuel system pressures and leak down rates. If your interested I'm near Bishops Stortford and happy to help.
I went through all the same niggles when I bought my 328 ( from Maranello!!!) and learnt quite quickly that the workings of these cars (although quite simple) are lost in time to many garages.