348GTB TPS reference power

A few months ago I posted a thread in regards to a burnt valve in my 348 and have been pointing the finger at bad injectors, cam timing and a few other things.

Well I think I have NOW found the culprit.

I have all 8 cylinders running and cam timing right, I noticed it seemed to be cutting out on 1 bank with only just a slight throttle opening. There were no warning lights CEL or slow down etc.

Have checked the 1-4 throttle position sensor (TPS) and reference voltage is only 1.06v and signal voltage goes from 0.2v to 0.9v at full throttle, this seems wrong.
Reference voltage on 5-8 TPS is spot on 5v and signal runs from .5v to 4.8v at full throttle this seems about right.

So effectively at anything above idle the 1-4 ECU thought it was idling and delivering enough fuel for that, along with some bad injectors led to a lean out and burnt valve.

I have swapped the ECU’s over and the problem remains on the 1-4 side so I can rule out the ECU’s.

My theory would be a broken or damaged wire in the harness to the ECU as this takes a bit of pushing and prodding to reinstall after an engine out.

The problem I have is that I have a 348GTB with a F119 “H” engine.

This has 2.7 Motronic (#0 261 203 327) and all my diagnosis and wiring diagrams are for the F119 “D” engine with 2.7 Motronic (#0 261 200 489) and all the wires look to be in different positions to the wiring diagram.

Would someone out there have a diagnosis sheet and/or wiring diagram for the 348GTB/S with a F119 “H” engine 2.7 Motronic (#0 261 203 327)? Or any help identifying other areas to look would be appreciated.
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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.

 

Hello Dave,

Thank you very much for your reply, I really appreciate it.

I am pretty sure the actual TPS’s are ok I checked the reference voltage with the plugs removed and 5-8 definitely has exactly 5v coming IN to the TPS and 1-4 only has 1.06v coming IN to the TPS.

As a test I ran a wire from the 5v in on the 5-8 TPS to the 1-4 TPS and disconnected the 1.06v in power, so effectively powering both TPS’s from the 5-8 ECU reference 5v.

Then both TPS’s registered 0.5v to 4.8v on the signal, I took it for a short test run and preformed perfectly.

The 1-4 TPS (according to my “D” engine wiring diagram) reference power comes from 22 and the signal goes to 4, I have checked them for continuity and colours &…. no match, this makes me think the diagram I have may be for a different system.

You mention 8 & 19 as the TPS pins on the 2.7 355, are they the signal pins or reference power pins?

With regards to the harness and ECU, as far as I see the “H” engine does not have 3, 39 or 54 pin.

I don’t have a manometer or oscilloscope, but know someone that does and will get it down to him early next week to check the other sensors.

I have been careful to use contact cleaner and air with all the plugs but they seem remarkably good in comparison with some of the nasty things I have seen posted on F-Chat. That isn’t to say that there isn’t a bad one somewhere.

 

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.

 

No problems Dave it must be very difficult with all the different vehicles you are working on at any given time to remember all the numbers of all the ECU’s and sensors etc.

I know you are extremely busy and apreciate your help.

If you (or anyone else out there) does have a diagram or a diagnosis sheet for an “H” engine it would be incredibly helpful.

If not I will be sitting there for a couple of days with a multi meter playing detective…..

 

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.

 

EEWW,

Well I guess it must work (for a while) but gee it looks ugly.

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Have been going through the standard diagnosis sheet one item at a time and got up to test 20 of 39 before my back gave out grovelling behind the seat....

I blame that date on my brith certificate for that

All of the tests are all coming up with the corect values so far, the 3 missing pins relate "No: 3" to the fuel pump and "No's: 39 & 54" to "memory selection pin", not sure why they should be missing?

Will just keep keep going through one at a time and see what I can find.

 

Don't forget Daniel works for a company that sells to us to "FIX" problems in Ferraris.... I am sure he "Loves" to see things like this....

 

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.

 

Just been going over the diagram I have and think we have the same “diagram” mine shows 39&54 to ground and 3 to A/c.

Where I got the numbers previous was going through "Diagnosis Sheet 13 Mondial T - 348 Engine F 119 D.040" this was on the previous page to the wiring diagram.

Test 6 is to check between 3(+) and 14 (-) for 11-13v, and the notation is "Fuel Pump Control relay winding and harness check" ?????

Even though (as you have correctly said) the wiring diagram shows it as the pressure switch for the A/C system????

On the same wiring diagram pin 1 on the TPS (the reference power) shows it going back to 22 on the ECU plug I have no continuity there but I do have between 12 & 18 which should be the phase sensor and the idle control. The diagnostics sheet refers to test 33 as 37(+) 22(-) as a test for the idle speed actuator so this seems right.Another thing is that 19 is shown to ground in the wiring diagram and the diagnosis sheet but BOTH my ECU’s show no continuity to ground?

You mentioned “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.”

Got me thinking….

Because the this car has a Bosch #0 261 203 327 ECU, this is different to the listed version of the 348 ECU… Do you think Ferrari may have been doing a few different things on the last of the 348’s in preparation for the 355, and if so could this be a 355 2.7 ECU?

 

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.

 

Once Dave again thank you for your help on this.

That just peachey….. I thought as much…..

I will try and track down the sister car wiring diagrams to see where they lead me, I believe that only 14 RHD 348 GTB’s were made, so I guess the chance of the factory writing down what they have done let alone publishing it are pretty slim… So I guess it is back to the detective work.

I have booked the car in with a friend of mine that works with engine management systems and has all the equipment we need. We are going to go through everything one by one and see where it leads us.

I agree that the problem is more than likely in the harness attached to the ECU’s as it is a bit of S**T fight to get them out while removing the engine and a great deal of care needs to be taken.

Unfortunately after looking over this car, all the servicing has been done Ferrari Dealerships and the level of workmanship & care taken is abysmal.

So it would not surprise me if at some stage my engine was hanging from the harness with some turkey wondering why it won’t come 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.

 

Thank you very much Paul, I have a wiring diagram for the 348 but not one with the colours listed this will be a great help, you wouldn't by any chance have a connector diagram for a 355 2.7?

 

That's great advice Dave I have a analogue multi meter (VOM) that I was going to toss out because I have a new digital meter that I find easier to read, I will dust it off and give it a go.

 

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?

 

Thanks Paul for your efforts I appreciate it.

Have had a long list of chores around the house from "She who must be obeyed" so have not had a chance to do more important things like get out in the garage as much as I would like.

Spent a hour or so this morning and have tracked it down a bit more and am getting closer, followed all your advice and hooked up the analogue meter and started shaking wires and plugs looking for a reaction.

Eventually I started pulling plugs apart and found that disconnecting the phase sensor had the TPS Ref volts up to 5v. getting somewhere….

Checked 3 pins “to” phase sensor and had 2 pins at 5v and 1 earth just need to work out if this is correct??? The wiring digram shows the phase sensor having 1 wire to earth and 2 to the ECU.

If this is correct...... excellent I know the phase sensor is RS....... if it is “not” correct ….well more tracking….