I’ve received the gaskets today, so it was time to reinstall the parts on the engine. The engine starts perfectly when it is cold (weather temperature at 35°C). I didn’t have time enough to test it when it is hot (the car is not at home and i had to leave). I hope i can do it tomorrow. Next step , I shall rebalance both sides when the vaccum gauges will arrive.
Just a question... The bypasses are used for cold start or for cold and hot starts ? If only cold start, i shall keep the problem for hot start....
The fixed (pre-set) bypasses via the bypass screws are used all the time to provide the air flow (together with the variable bypass flow through the IAC-s) to the engine at idle since the throttle butterflies are practically completely closed at the idle position. The bypass screws are also used to balance the left and right banks. The balancing procedure (for 2.7) as described in the WSM is not totally clear but I understand that it means that the balancing is done with the IAC-s disconnected from the engine looms and connected to a special Ferrari tester which keeps both IAC-s at equal fixed (steady) openings keeping the idle speed at some 850 rpm. Then the vacuum gauges are connected and the banks are balanced using the bypass screws. However, I do not know what procedure is used in the case of the 2.5 mechanical IAC valves. I have just bench tested (works very well) the electronic "IAC Valve Control Device" I built which I intend to use instead of the "Ferrari Tester" to balance the banks on my 348 (2.7). This device connects to both IAC-s and sends equal signals to them which will keep the IAC openings equal left-right and also control the idle speed via a potentiometer by opening the IAC-s more or less. Will inform the forum on how my balancing went in a few weeks from now (busy with my work at the moment).
If the IAC controller I have built works well for the bank balancing, I intend to build more of these and offer them on Ebay.
Still in R&D stage (and under heavy investment) but with already very good bench test results: Image Unavailable, Please Login
Hello 348 fellows. I just want to share my experience with a similar issue. I have had my 348 TS 1992 for 5 years now, with no problems what so ever. I drove it around 14000 km totally. But the last 5-6 weeks I have had similar problems, going on and off. It began an evening some weeks ago, I was on my way home from a classic car meeting. It was a long distance, driving 400 km out in the morning and the same back home in the evening. A big part of the trip was on the danish highways with quite good speed. So the car was up in working temp for many hours that day (thats how it should be). On my way home, the car suddently slow down, seems like one of the cylinder banks was disabled. No warning lights, good oil pressure and temp. The tackometer showed zero, even though I was still doing 80 km/h. I stopped and pulled in, opened the hood, but off course there were nothing to see. After a short break, I could start again and go on. It happend 2-3 times on my way home, and after that, there was nothing. Next morning, no problems. A couple of weeks later, the problem was back, again on and off. This time, it seemed like an ignition problem. The engine slowed down, like it was running one side only. Sometimes it sounded like there was a few ignitions, that blew the unexploded gas mixture off, bang - bang! I checked and cleaned all connectors on MAF, injection port feedback, thermo couples from exhaust, etc. But all connections was clean and like new. Only the thermo couples seems like the wirés inside was short circuited just after the connector, but they must be OK. Because if I disconnect it, the warning light "slow down 5-8" appeared. And this week (just started my summer vacation), the fault is back. Now permanently. I called my workshop (non Ferrari, but they are working with red cars only). He was pretty sure, that it was caused by a bad igniton coil. I took of the covers, and the connections here was a bit dusty, but seemed OK. I cleaned them and put it back together. Now, it runs fine again. But how long? A couple of questions: 1. Does anybody have experience with bad ignition coils? Is that a common problem? 2. What would You guys say is the most common problem on a 348, being used regulary? 3. Does anybody have a tester to read out error codes (I know it can be done with warning lamps and pushbuttons)? If yes, what type of tester? A 348 friend of mine has a "Launch X431", but it doesnt work on pre-OBD systems. 4. If I put in bulbs for the Motronic errors in the dash, will they show errors continhously, og only by pressing the test button on the Motronic unit? My car is Euro, so its not mounted in mine. Thanks for reading Image Unavailable, Please Login
Just a few word from my side... I tested the engine today, cold start ok, hot start ok. I made an ECU reset. I pluged 2 vaccum gauges on the inlet manifolds, right is perfect but on the left side the arrow is shaking, so it is impossible to balance them. I don’t know why. But now, the engine starts correctly.
The left bank crank sensor provides tachometer data and left bank ignition timing. Try cleaning the crank sensor connector first. They often get contaminated with oil. Cheap fix. There’s a message thread about it here: https://www.ferrarichat.com/forum/threads/90s-electronics.578756/#post-146055798 Make sure you identify the right sensor and also make sure that you fit shims if required. Check that the depth of the sensor matches the workshop manual. Search the 348/355 forum for Kia crank sensors. They have the same Bosch sensor as Ferrari.
Note that the left bank crank sensor is on the right hand side of the engine (as seen from the rear of the car, looking forward) Image Unavailable, Please Login The right bank sensor is on the bottom of the crank.
Thanks, Quavin. I checked the connectors, they looks fine. But of course the sensor itself might be bad. Today my car wont start at all. I think I must give up finding the problem myself. I am just a little afraid, that the workshop will start to replace all sensors from and end. It could easily cost a fortune... I am happy to hear that You are running again, Marc556. ☺️
It's a very common problem. I can't think of anything else which would cause engine and tacho problems (other than a failed ECU or wiring). You can do wiring checks. Is it Motronics 2.5? By "won't start", do you mean the engine cranks, but won't fire? Or does it attempt to fire, but just dies? Here's a crank sensor for sale in Europe: https://www.ebay.com/itm/321584056192
Motronics 2.7 Yesterday after cleaning connectors on the ignition parts, It started up fine. I let it run idle for 5 minutes, then it slowed down and stopped. When i try to start it now, it cranks fine, it sounds like its firing but gets no fuel. Weird... Now my vacation is soon finish, so im running out of time...
If the crank sensor is causing timing issues, then it may be firing at the wrong time. Also, if the crank sensor is not showing that the engine is turning at 30rpms, it will not activate the fuel pump.
Fuel pump not activated if not showing min 30 degrees on crank sensor? Thats very good info, could explain a lot. Thanks a lot.
Doesn't your car have two fuel pumps? The Left/Right Motronic ECUs control their respective fuel pumps, so they should use signals from their respective crank sensors. In theory, the two banks are independent (apart from a single cam sensor). However, the Left Hand crank sensor is also used for tachometer information (on the instrument panel). I'm still 90% sure that your "LH" crank sensor or sensor wiring is faulty. With only one bank running, it may be difficult to start the car. Note that some folks have been known to carry a spare sensor around with them. They are not known for their robustness.
Yes, You are right. 2 fuel pumps. And even if the left sensor controls the tack, the fuel pumps are still controlled separately... The sensors are both connected to a small connector block. Can they be replaced separately, or do I have to order a "double set"? No, They can be replaced separately, I see... Another question: Do You know if the same sensor is used on the Testarossa? I beleive they also use the Motronic 2,7 controller. In that case, I might know somebody who has a spare...
They can be replaced separately, but at U$18 each (plus VAT), I would be buying a couple. The 512TR has these sensors. Not sure about the earlier Testarossas.
Now I swapped the two sensors. Again, the car starts up perfect. But for how long this time... Only thing i noticed was that the distance between the left sensor and the toothwheel was quite long, so I removed the shims. I think You are right, it must be a periodic problem on the sensors. I better order new ones. OR it could be a connector/wiring problem. Or a failure in the Motronic box. Or a lot of other things... Quavion, thanks for all Your help on this issue. You have a great knowledge on this car. I hope I can help You some day.
