Hi chaps I've got a peculiar issue on the 355. Its misfiring on cylinders 4 and 5. I've pulled the plugs and both a dirty (the other 6 look fine). Plug leads are new (and resistance check seems fine). Plugs are also new and seem OK with a resistance check. This leads me to think there's either a sensor issue (although I'd think that would knock out a bank rather than individual cylinders) or something else? Injectors all show around 15.6 ohm impedance as well. Any thoughts? Got me stumped.
It would be helpful to know when the misfire is occurring such as under load (possible secondary ignition) or all the time possible leaking injectors. Being that your plugs are showing signs of fouling, leaking injectors move up the list but I would do some more looking and do a compression check as well.
Looking for commonalities of cylinder 4 and 5... they are on opposite banks so suggests not likely a sensor or leak because they are effectively on separate circuits. A total longshot, but if you have an M2.7 check the condition of the rear sparkplugs, the very early cars have no rubber grommet to seal the plug wire entry into the valve cover, and on mine the rear plugs had quite a bit of corrosion. There was no problem, but something that was "common" to cylinder 4 and 5.
It’s a 5.2 and I’ve literally just rebuilt the top ends with new valve guides and oil stem seals. Leaky injector may well be it although as I said, it’s showing ok on the impedance test. as I don’t want to drop the engine again, is it possible to remove the injectors and fuel rail without removing the intake plenums? Getting them back on is hard enough with the engine out...
The plenums can be put on with the engine in, you just have to get your "technique" What works for me is: *everything spotlessly clean *assemble the half shells and the clamp onto the intake runners on the engine *leave the clamps open as wide as possible (less than one turn of thread engagement) *apply light grease on the inside of the rubber coupler *apply light grease on the couplers on the plenum *set the plenum on the couplers, and "wiggle" it into place. It does take a bit of pushing from the top, but it does go eventually. I've done this several times, so it is a repeatable process. Just make sure that the clamps stay "round" and not bent, and also the rubber couplers can't have an edge folded in, otherwise it won't fit.
Well, I double checked and swapped leads today and it’s not that. Will try some plugs just in case and (assuming that’s not the issue) then I’ll get the injectors out and tested. It’s bloody annoying though
After a chat with a (more knowledgeable) friend last night, and looking at the plugs again, the dirty pair aren't wet (and there's no hydraulic lock of any sort) so I'm leaning away from leaky injectors (although I'll still send them away for testing and cleaning). What he did suggest was combustion problem (as plug is black and dry). So, assuming the mixture is OK then its likely to be a cylinder sealing problem, which made me realise I never checked the state of the lifters. A stuck / locked lifter would likely prevent sealing so I'm going to pull the engine (again) and cams and then check all the lifters. Sound plausible?
A bit more diagnosis like throttle vacuum & balance, compression test & leak down would be the way I would go before dropping the engine. Maybe get an inductive oscilloscope on the plug leads and main sensors. It always pays in the long run to diagnose the root cause before jumping in.
Thinking out loud again. Lifter problem would affect compression, but its even across all cylinders. So, possibly not the lifters. Justwondering, what triggers the spark? Is it crank angle sensor?
When I first read "2" plugs, I immediately thought coil pack since they are linked. But then realizing on separate banks.. scratch that idea. Good to verify injector operation.. and then there's always the what did I last touch approach. Was recently apart correct? Neither are fun options.
Just a thought —- IIRC the 355 has a wasted spark coil (fires 2 plugs at the same time). You do have the HT leads hooked up correctly? You may have it so that 3 cylinders are getting spark at the right time, but the 4th cylinder of each bank is not? Just a thought. Be cautious when running the engine if this turns out to be case (out of phase spark, but injector firing) because you can end up melting the exhaust cats
actually, thinking about it, I don’t think what I have described is possible without the engine running badly, if at all. It does run wasted spark, here’s the page from the WSM.
Well, partly solved. One bent pin on the larger white connector from the engine loom next to the ECU pin. Any ideas what they do? Engine now doesn't sound like a misfire but still slightly mechanical sound. More digging required...
Another thought — those last spark plug boots need a very good shove to make sure they are fully seated on the plugs. The reason is they need to accommodate the three plug wires alongside the boot in the channel which can be quite tight. So might be worth just double checking the boot is fully home on the plug connector. You should feel a “click” when it’s fully home, I know it’s a bit simplistic (not trying to offend) but worth a check... If I’m thinking of the right connector you’re referring to it brings power to the engine cradle, and signals out to the rest of the vehicle eg. speed/temp
By larger connector, do you mean the one with most pins? Any clues on wire colour? Image Unavailable, Please Login On the 9 pin plug, the yellow and yellow-black pins send power to the coilpacks.
It was either 7 or 14 above. My guess is pin 7 (afraid I forgot to check.) My suspicion now is some sticky lifters. Anyone had any success with lifter additive like the marvel mystery oil etc? Otherwise its engine back out and cams off. Again.
Further updates. Pulled the engine (again). Took 4 hours including a stop for lunch! Sadly I'm getting the hang of it now... Anyway. Did compression test (with a better gauge) and they're all between 175 and 190, so that's fine. Also, re-checked timing and that's also spot on. Which tells me that its not a mechanical issue. Oil smells a bit like petrol, so I'm now leaning towards leaky injectors causing oil pollution and misfiring on the wasted spark, as the engine idle makes the car vibrate a little, so its not smooth like it should be. Going to send injectors away for a rebuild.
This definitely sounds like injectors. The ohm value will tell you nothing on the injector operation or spray pattern. It will only tell you the coil is ok or not. I had a similar issue on my Murcielago and 2 injectors were not atomizing the fuel properly. Got all 12 injectors serviced with new pintels, seals and filters and car run better than it had ever done in my ownership. For me I always now get the injectors and their spray pattern checked at every major service. Just had this done on my F355 even though I had no problems. These cars often sit for weeks or months at a time and this can really effect the spray patterns on the injectors. Sent from my iPad using FerrariChat.com mobile app
Well, got the injectors rebuilt. Report before and after showed they were working pretty much spot on beforehand, no leaks, good spray pattern etc. Had them rebuilt anyway, but still no closer to solving things
Did you check whether the injectors 4 & 5 are actually firing/pulsing? If they are not firing (or firing intermittently), their connections to the ECU may be bad, possibly in the injector connectors or in the large ECU connector; or there might be a problem in the ECU?