348GTB TPS reference power

If memory serves correctly, pins 8 and 19 are the TPS on the 2.7...I am quoting the 355 twin TPS for the earliest 2.7 variant (dont trust my memory), might be the same on the late 348 2.7.

The plastic innards of the TPS are wearing out and no longer have a tight fit on the flat of the throttle shaft and in turn do not follow its finite movements. I have found this on a number of cars now. Try removing the switch and shim the flat of the shaft with thin paper to test the theory, I had to use photo paper on the last one as it was so worn. Reinstall and set to 1Kohm at rest and look for a seamless travel to 2.4K at full throttle. Verify it matches the numbers of the other bank as a cross check. Test drive and then order a replacement TPS pair, they are cheap and if one is bad the other is likely near. Seems the 1-4 bank is the first to go for some reason.

Reading the numbers at the ECU will require perfect condition contacts at the TPS plugs, make sure you have that as well. Contacts at the MAF have to be perfect as well as the ECU is looking for verification data from those that supports the TPS readings. On the 2.7 the ECU's will look for corrupted data and ignore that it doesn't like and run on data it does.....make sure the data from the other sensors is making it to the ECU's with no added resistance from the plug contacts, they are looking for cross check data. ECU knows its running, looks for a reading from the MAF that matches the TPS that is verified by the crank and cam sensors.... high resistance due to corrosion on any of the plug contacts greatly affects the whole package, it doesn't take much and is usually not visually identifiable! For the MAF sensors to give matching data with good contacts at the plug the throttle plates need to match as well, check that with a manometer. It only takes one weak link in the whole chain....

I am sure I still have my "H" harness and TPS from my IMSA 348 Race car in the storage trailer, I converted the entire system to a programmable EFI system due to the Motronics inability to deal with the cams I was using. Cant say as I remember anything out of the norm on that harness or TPS.

 

Sounds like you are well ahead of what I was pointing out.

Signal or referance? One cup of coffee further into the day has me thinking I just told you the pin numbers for the cam sensor....bad data from my end I think. I am currently chasing a cam sensor problem on one, TPS issues on another and contact problems on a third. I should learn to check before I post, they all melt into one this early in the morn... I will look and see if I have the H diagram, seems I remember looking at one when my harness was still being used.

 

Take a look at the 512 diagram.

When the multi-wire connections are done in this fashion when new.....
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Whoa doggie !! Gotta lova it.

 

And they say we Brits have bad wiring! Actually, much Rover wiring is WORSE!

 

'love' maybe not the word I would choose.

 

Not quite what I was in hopes of finding when I was searching for that 348 Motronic problem.... that said, they have lasted quite reliably to date unless someone forgets to pull the ECU plugs on engine removal.

Sounds like we are looking at 2 different variations of wiring diagram's....I will recheck mine this AM but I thought those 3 had different termination points than you just listed. Big surprise! Try following the cam angle sensor wires for a 355 2.7 in the factory diagram....both go to grounds for the 5-8 bank.

 

I show 3 to be an AC signal to both ECU's, 39 to be a ground and 54 to be a Ground on the 348 and open on the 512.

 

No question about that, its SOP for them. When it comes to the end of the line for a model they are just burning up parts inventory on hand. When one runs low they find a way to implement the new parts with no mention what so ever in print.

Take the Diagnosis sheets with a grain of salt, I have many of the steps redlined on mine because they are not correct any more so than the wiring diagrams. The photo'ed connection is that of a late 348 when chasing exactly what you are dealing with. In that case I tagged the harness as NFG and replaced it with one from a box of spares I have from the race cars. Never did waste any more time searching for the fault on that one, not cost effective as a replacement was at hand.

The reason I suggected you look at the 512 and in turn 2.7 355 and Mondial T is the true wiring of a late production model is often a mixture of different models. When the diagnostic sheets disagree with the diagram you need to look further in other models for answers and identify a constant that makes sense with what you are dealing with. Often sister models provides that data. Trust a Ferrari publication regarding specific data or wiring diagrams? PLEASE, not even on a dare!

Set your VOM to a viewable position, review all of the wiiring diagrams and predict where they might have put a splice in the harness for a given circuit and start twisting and pulling and watch for a resistance change. It is seldom found that multi wire splices are at the termination points, they are usually burried in the harness as photo'ed. It has also been found that if there is one common failure point, it is where the harnesses attach to the front belt covers and wire tensile strength was tested when removing an engine without disconnecting the bulkhead plugs, dealing with a 5.2 example of that test now. A delightful experiance, I wondered why the harness was as stiff as a broomstick when the engine was coming out.

 

At the risk of double posting, here again is the connector from the 348 Workshop Manual
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Creatures of habit, the factory has been doing this type of thing with the wiring diagrams since the 250's were in warranty. I have notes on some of my wiring diagrams where it was found they ran out of a wire color and changed but then a few serial numbers later changed back when it was restocked. When ever I make a noted change to the diagrams I note the chassis number of the car with the variation....until I ran out of clean paper on the sheet and gave up. The variations of colors that are being found and noted in the Motronic system is stunning. When folks are installing the Gold Connector Kit I am making I have them write down the colors of the wire prior to the plug removal....with this it really high lights the number of variations as we are all looking at this very closely when doing the install's.

Upside here is you know exactly what you are looking for. That knowledge did not come easy to you, nor will the fix but using logic and tenacity you will get it. Attention to the smallest details is what these systems require to operate properly..... that .5 volt or .5 ohm variation makes a big difference in the end product. I just finished a 2.7 355 where every screw in the throttle assembly was turned and mis adjusted, the holes in the TPS's were slotted, one Cat was empty...... all this RE-work of a system by someone trying to adjust around a connection problem, the hours spent to do this must have been staggering...... I know the hours spent to fix it properly sure were. End result is a dead smooth idle with the O2's off, .06 ohm difference in TPS's and .2 CFM difference in MAF readings.

Stick with it, no fancy equipment will make the job you have to do any easier. Disconnect EVERYTHING on the harness and work backwards, often a multi wire splice in the harness will give you feed back resistance on a wire being chased and lead you in the wrong direction. Often when doing what you are, an accurate analog type VOM is required to see small variations in resistance as you twist and tug on wires. We are so use to the digital VOM's "hunting a little" we miss the minute tell tale signs that we are close to the problem area. My father passed on to me an old analog Triplett VOM.... wont hold a zero between scale changes due to resistance on the contacts internally but when that fine sweep needle twitches you KNOW you are close and with the scale zero'ed you KNOW you can trust the meter reading. Build in the 40's, uses special batteries that cost more than a new digital VOM......couldnt live without it, I use it every day for this type of thing.

 

I have seen this low ref supply caused by another sensor partially shorted within itself pulling down the vref supply. I know you checked the vref at the tps but have you unplugged the other sensors common to the vref to see if one of them is pulling down the supply voltage. Temp sensors are notorious for this.

 

Totally agree with Dave on the VOM. Pro Instrument Techs and Electricians often swear by Simpson analog meters. Not only bulletproof meters, but you can see the needle vibrating, etc. which can tell you something else is there. Kind of a poor man's Oscilloscope, although o-scopes are getting very portable and cheaper now.

 

Exactly, and the diagrams do not show each and every connection in the harness. It is incredible how much stray voltage that dielectric goo will pass when it has absorbed moisture yet some continue to use it and swear by it. Those that do simply have not had to deal with this type of problem, in time they will learn.

 

Sorry, I have lots of Ferrari pdf's but none with electrical info for the 355. The 355 owners manual have no schematic in the "L" section at all. Does anyone have the 355 Workshop pdf?