Hi everyone, I got my 308 GTS QV from 84 2 weeks ago that did 1000 miles in the last 12 years, so most of the time sitting. It had misfiring problems, then after 40 miles, I started the car and was running on 4 cylinders only. I switched the coils and still the same 4 cylinders working, so not a coil problem. After reading all the threads on ignition problems, I decided to take a look at the distributor wires and spark plug wires. Few wires had very bad connections, were all hard and the ends, etc... I decided to change the wires and the sparks plugs. I went for ACCEL 7mm spark plug wires and NGK Iridium spark plugs (BPR7EIX). After rewiring both distributor, testing all connections between the coil and distributor, distributor to spark plugs, cleaning the rotor and distributor cap: Nothing anymore, not even 4 cylinders. What should I check now? The wires I installed have less resistance than OEM, can this damage the coils? (in other hand, the spark plug have a resistor when the previous one haven't) I even reinstalled original wires and spark plugs on the 4 cylinders that were working and still nothing. I really don't know what to check now, any idea? Thank you Image Unavailable, Please Login
When you switched the coil, did the problem switch from one bank to the other bank? You also might want to check the Digiplex box in the rear left corner of the trunk. Also, that plug wires is not the correct wires for the car and it can damage the Digiplex
I would install a spark plug on the output of the coil, just lay it on something grounded. Do you have spark from the coil? You should and 4X as often as you'd usually see. That tells you which direction to go hunting.
Just did it, I have spark from one coil only, and when I switch the coil wires, I have spark on the other one. So basically problem should be before coil, what can it be? sensor? Digiplex?
Could be either one of the Digiplex ECUs or one of the flywheel TDC sensors. The easiest thing to do is to swap the connectors on the two Digiplex ECUs (they are mounted on the underside of a panel on the LH side of the rear trunk): Image Unavailable, Please Login If the problem stays on the same bank = good sign that the Digiplex ECUs are OK (as those are expensive), but a bad sign for one of the TDC sensors so those would need investigation. Image Unavailable, Please Login If the problem moves to the other bank = bad sign for one of the Digiplex ECUs (these have the power module with the high-current transistor that actually switches the coil primary current built inside -- they got smarter on the following Microplex ignition and made the power module a separately replaceable component so that the whole ECU would not have to be replaced if that transistor failed).
My money is on the crank position sensors. My 84 lost the one at 11:00 position and ran on half the engine. A new one cured the problem. That was 14 trouble free years ago.
Actually after few tests, I revived the 4 cylinders that were working! When engine running, I plugged a spark plug tester on the other bank, and it works too! When the 4 other cylinders are plugged on the coil, still nothing. I have a Current Clamp so I compared the Coil to Distributor wire, and there is less Amp in the one not working. Can it be a wire problem? I don't think it a sensor now because I have signal at the coil
Mine failed at Road Atlanta - 200 miles from my house. The car ran normally above 2500-3000 rpm. Some where in that area. I drove it home, all 200 highway miles home, keeping the revs up without a problem. The sensor was shot but would work under those circumstances for whatever reason. Would NOT idle on 8 cyl. Period.
Could be -- measure the resistance of each coil wire from the metal terminal that plugs into the coil to the center carbon button of the distributor cap = should be about the same resistance. If not try re-piercing the coil wire in question (the pointed screw securing the coil wire to the dist cap is under the carbon button so just pull it and its spring out to access). I'm also having a vague memory that there was a problem (addressed by Service Bulletin) on some QV dist rotors with arcing from the bottom of distributor rotor (thru the plastic) to the top of the distributor shaft -- so wouldn't hurt to remove the rotors and inspect their underside, and try swapping dist rotors.
You were right!! Switched the rotor and the other 4 cylinders finally started, but of course the other ones stopped. What's wrong with these rotors? Compared them, cleaned as I could and still nothing. What could be wrong on the rotor?
If you are saying that you get spark from both coils but no spark to the plugs on one bank, it could well be a bad rotor. They are known to crack where they mount to the cam shaft and this shorts the coil output to ground.
Might not even be a crack - could be a carbon-tracked rotor which will do the same thing but at a glance, the rotor may look OK, especially if it's black since carbon tracks are also dark grey/black.
For a few years they were known to just break down the insulation value of the plastic between the upper contact and the end of the cam. Marelli changed the plastic compound without telling Ferrari. Instead of holding Marelli to a standard on the plastic they went to the flanged screw on rotors on the 3.2 motors and TR. That led to another whole host of problems/fixes/redesigns/warranty claims.
I had a rotor fail once on my Alfa Spider. Couple of years ago. I had a backfire that scared the hell out of me (top was down and sounded like a gun when you don't know what the hell is going on) and the car just shut down. It happens. They do break sometimes.
"...that led to another whole host of problems/fixes/redesigns/warranty claims." I'm always amused to read about Ferrari's production and parts sourcing. The company clearly had (has) a serious understanding of engine building in the sense of the major parts of the engines. But it seems that the ancillary parts were often the cheapest thing they could find to function for the (very short) warranty period! Given Enzo's view of the street cars, that's no surprise, I guess but it does REALLY make me think when folks remove or modify parts and justify it using the phrase "as Enzo intended." If you really modified these cars as Enzo intended, they probably wouldn't have lasted a year on the road! Luckily, Fiat wouldn't let him do that!
Post #1 in this thread has some good photos showing how a rotor was arcing from the metal contact on the top (where the carbon button rides) thru the plastic and onto the metal spring clip that contacts the flat on the distributor shaft: https://www.ferrarichat.com/forum/threads/have-you-lost-power-in-one-bank-of-cylinders.525461/#post-144754234 In addition to maybe a base material problem that Brian mentioned, if in the molding process there are voids, cracks, an unbonded knit line, etc. in that area, it will just have the (low) dielectric constant of air (rather than the higher dielectric constant of the plastic material) so, in addition to using a plastic with a better dielectric property, it is also important to use a plastic with good molding/knitting properties. I thought I had a copy of the related Service Bulletin, but I can't seem to find it (or I never had one ).
Here is a picture of a bad rotor from my old thread. If you pull the spring clip out you can see the carbon.
Papa (Gianni) Agnelli owned Fiat/Ferrari. He also owned Magnetti Marelli. Kind of like why GM uses Delco products. Not only that but in those days the Italian government really leaned on companies to use Italian subcontractors. Nowdays all of the EU is in one great big group hug. It really comes down to a single issue. If it is made in house it is almost certainly going to be of very high quality. If it is from a subcontractor Ferrari typically uses low bidder. In the case of engine management and safety systems, Bosch, and the other suppliers get system approvals from TUV, EPA, DOT ect so streamlining the overall approval of the car you cannot afford not to use them.
Thats the issue. Ferrari used those same Magnetti Marelli rotors since the early 50's until 1985. Suddenly one day in 84 or so we had trouble. The subcontractors for GM that made some of the oil seals for the Corvair engines did the same thing. It lead to massive lawsuits for oil vapors getting into the heater air supply system and causing permanent brain damage to some owners. If I recall it was just one of Ralph Naders big campaigns against the Corvair. GM was never notified the contractor changed the specifications.
1000 miles in 12 years and all you need is a rotor. Probably not. Seriously, when was any service done to the car. Not to be a nudge, but get yourself some wire holders that engine compartment is not winning any concours. Good luck and hope she sees alot more than 1000 the next 12 years. Probably will now that the odo was reconnected ;-)
Never the less, that one was 33 years old and the replacement cost $12. The other side is now 36, so I ain't complaining (85 GTB QV).
The ones we were having trouble with were doing it in just a couple of thousand miles. That is the weak link even in the ones with good plastic. We were fixing lots of them before the 85s were built. The fix was in production on the 85 TR.
