Hi All, I was out enjoying the car this weekend and as I pulled into a parking lot, it backfired... and began to vibrate a bit, kind of like one cylinder not firing. So tonight I decided to take out all spark plugs, gapped them to .025" and re-installed. Problem still there. I did notice that cyl 1/4 plugs are all light brown in color while plugs in 5/8 are a lot darker (bank 5/8 running too rich??) I then looked for any hoses I might have disconnected and didn't find any. I wanted to run through the ECU error codes as outlined in various posts but this car is a euro spec car and I couldn't find the "button" beside either ECU... is there an alternate method to checking error codes with the euro-spec cars? Tomorrow I plan on checking compression in each cylinder and if anyone has other ideas of other things I should check, I would appreciate hearing about it. Thanks JQP
Backfires are usually caused when the car is running too lean, so check your air filter to see if it is clogged. Another prime cause of backfires is an exhaust leak where fresh air is entering the exhaust. ...As for checking error codes, you can order the Ferrari 348 cable and button. They snap right on to your existing Euro ECU harness.
Hey ND, I did find out what the problem was... I replaced the plugs on the 5/8 side (the one where the plugs were black) and the problem went away... I assume then that the 5/8 side is running too rich. Is there an easy way to adjust this? JQP
Sure. There is an adjustment screw on each MAF (under a small circular cap cover that is usually blue). With the engine off, disconnect the black MAF data cable on your left (i.e. 5/8) side. You'll see some electronic pins on the MAF. The pins on the extreme left and right sides are pins #1 and #6. Put an ohmmeter on those two pins and read the resistance. Post that number here. To make the mixture less rich, simply turn the MAF screw to increase the resistance between pins #1 and #6 (or pin #5, they go to the same place). But make certain that you measure the origingal resistance value **before** you start adjusting that screw!
FYI, changing plugs is always a good idea...but running too rich is seldom the cause of a backfire. Glad to learn that your problem went away, though.
Hi ND, OK I checked the resistance on both MAF sensors and the 1-4 side is at 250 ohms and the 5-8 side is at 200 ohms. Based on searches in this forum, I gather this number should be closer to 383 ohms, correct? My multimeter is not accurate enough but I increased the resistance to around 375ohms... let me know if this is good enough or if I need a more accurate reading, I'll go buy a better multimeter. Thanks JQP
Good man. Yes, your MAFs were making your car *way* too rich. Your change to 375 is a pretty good number, but you probably want to be within +/- 3 ohms, say 380 to 386 ohms on each side. You should have almost identical MAF ohm measurements on both banks of your engine, too. ...and 200 ohms was ridiculously rich! I bet you saw plenty of black smoke coming from your exhaust!
I am curious to know , why do the MAF's go out of range (i.e., the resistance). Is there something inharently wrong with the MAF itself? Or do they go out of range over time?
Hey ND, I finally did order the ferrari harness and button you referred to but I found nowhere on the ECU to plug it in... and nowhere on the harness either. I even unbolted the ECU on both sides to find this plug and couldn't find anything. Is it possible some 348s do not have this feature? Do you have a pic of where it's supposed plug into? JQP
Ok, finally had time to look for it and I discovered I have a 348 with the Motronic 2.5 ecu... doesn't have the little connector as shown in the diag below which is for the motronic 2.7... There must be a way to pull codes from an M2.5 ECU? JQP Image Unavailable, Please Login
