‘90 348- intermittent power loss. Like flipping an on/off switch.

Lots of good stuff done already. One I didn't see, however, is replacing the cam phase sensor, only saw you mention the crank ones. The plugs on all these components get old and brittle, exposing the wires, and can cause shorts. In my experience over 18 years of ownership, most of the "abrupt" and intermittent power issues I've had were due to these. I've had to replace both sets (cam and crank) twice in that time frame, due to connector failure, in a garaged car that is rarely driven.

You can also check the readings on many sensors, like the TPS, by pulling the ECU harness and/or backprobing. The connectors on the ECUs are large, so take your time if you decide to reseat them.

And yes, the relays can and do fail. Usually that is just due to corrosion or pitting on the contacts. If you are careful, you can remove the cover, gently clean the contacts, and test them using a bench power supply.

 

Cam sensor is trivial to replace, but there is only on the back of the 1-4 bank and it infers the other banks timing from the current bank given timing. Doubt that's the issue, you would get a CEL (4112 Cam Phase Sensor) and it will probably throw O2/MAF CEL also, but its pretty cheap if you shop around and very easy to do.

 

It must be a 2.5 if the car is a 1990 model (see topic title). 2.7's didn't come out until late 1993.

A lot of the diagnostic checks on your chart can be done without the breakout box. The resistance checks in the diagnostic procedure can be done at the ECU connector sockets with the connector disconnected. However, I don't think the chart is entirely applicable to the 2.5 car. 2.7 Diagnostic Chart Item/Test Nr. 36 is related to pin 52 (and mentions Slow Down Lights). Pin 52 is related to the TPS on the 2.5 car.

Here is an internal schematic of the 2.5 TPS

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Both brown/white (MB) and brown (M) wires go to the respective pins (53 and 52) on the ECUs. As splicing and interconnect plugs are involved, the check should probably done at both ECU plugs.

Full wiring diagram here:

https://www.dropbox.com/t/tMX16pymSd6m4mqM

The middle wire is a black earth wire.

The internal diagram suggests there are two internal switches in the TPS. Perhaps combinations of these switches represent idle, mid throttle and full throttle.

i.e. continuity across pins 1 and 2 AND no continuity across pins 2 and 3 = idle
no continuity across pins 1 and 2 AND no continuity across pins 2 and 3 = not idle and not full throttle
no continuity across pins 1 and 2 AND continuity across pins 2 and 3 = full throttle.

 

Nah, I have a USA October 90 TS and it's a 2.7. The 2.5 was on the 89 to mid-90.

 

That explains why I could never understand the parts manual. So there are non-GTB/GTS cars with 2.7? Is Wikipedia completely wrong?

https://en.wikipedia.org/wiki/Ferrari_348

In late 1993, the 348 was revised, featuring subtle styling changes (front grille, rear chrome Cavallino and removable seat cushions) and more power, this time 312 hp (233 kW; 316 PS) and 320 PS (235 kW; 316 hp) (Europe) from the same 3.4-litre engine, with an improved engine management system - Bosch Motronic 2.7 and a new exhaust system (single muffler).

The revised cars are called 348 GTB (252 made) and GTS (137 made) and were presented to the public as the 348 GT versions, equipped with the F119H engine (as opposed to the original F119D and US F119G). The F119H engine had an increased 10.8:1 compression ratio as compared to the F119D & F119G's 10.4:1 compression ratio, taller intake plenums, a larger intake compensation valve, fuel pressure raised from 3.4 bar to 3.8 bar, and different camshaft timing.

 

The "improved engine management system - Bosch Motronic 2.7" is the same 2.7 unit from mid 90 but with different timing curves, that was the improvement.

The 2.5: Bosch 0 261 200 190
The 2.7: Bosch 0 261 200 457 (TB/TS) or 0 261 200 489 (Spider & Challenge) or 0 261 203 327 (superseded the 489)

Here is pics of my build Plate and ECU.

 

So Wiki is poorly worded.

Can the 2.5 to 2.7 changeover be linked to vehicle assembly numbers or do you have to use components on the car? i.e. 2 throttle position sensors instead of one?

 

Its linked to assembly number I believe, can probably see it on various online parts diagrams with build numbers like Ricambis tends to have. I have seen it out here somewhere in the past I believe.

 

Thanks. I see Eurospares offer the ability to enter VIN, but I couldn't find a changeover point. Anyway, I've edited Wiki to prevent further confusion. I just put the changeover point as 1990, but I can always modify that at a later date. The VIN number changeover point may vary between markets, so I've kept it simple.

 

Reading the Wikipedia writeup in the link you provided, I find the info to be correct:

First, it states that "In 1990, the Bosch Motronic engine management system was updated from the 2.5 to the 2.7 version."

Then later: "In late 1993, the 348 was revised ... with an improved version of the Bosch Motronic 2.7 Engine Management System"

"Improved version" means improved existing Motronic 2.7 (introduced in 1990). I do not see in the Wikipedia article the part of the sentence you quoted: "with an improved engine management system - Bosch Motronic 2.7 ....

 

That's because I personally changed it today Wiki allows you to do that.

That's why you should never completely trust Wiki.

 

I've been getting the same fault too (1990 car running Motronic 2.5). The car was running like a dream then all of a sudden it's like the engine is being choked and someone had thrown an anchor out the back :-(

All very intermittent and seems to have no logical pattern apart from when it's most inconvenient.


Try unplugging your MAFS one at a time and see if the engine stalls



And after swapping them around the fault follows the MAF ie unplugging the one marked with an 'X' regardless of side makes no difference but unplugging the other MAF regardless of side stalls the engine.



NB The car has had new coils, igniters, plug leads, spark plugs, fuel filters, all the relays changed, crank sensors, and cam sensor. Just had the injectors cleaned and tested this week too. Lots of connectors cleaned with contact cleaner.

 

Will disconnecting the MAF on a 348 (2.7) stall the engine or will engine control switch from the MAF to the Throttle Position Sensor (on the respective bank) like the F355.

Note: I don't think we've determined which engine John has yet.

 

Interesting. Thanks.

 

Here's the quote from the F355 2.7 manual

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I guess there must be a software difference on the 438

It seems unlikely that both TPS sensors are faulty (not being able to take over from the MAFs)

 

You can, of course, do resistance checks on the TPS's.

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The checks are done at idle and various levels of opening defined in the manual. Of course the bypass and plate stops should be set so the 2 sides are the same, I used geometric balance, also in the manual, pic above has the feeler gauge where I did it.

Unlikely it's the tps being intermittent though maybe if it happens at certain throttle opening only like 3/4 or above maybe....

Sent from my SM-G990U using FerrariChat.com mobile app

 

@JOHNCJ8989,@retro.phit, measure the ohms on both MAF's at pins 1 & 6 please with car not running.

 

You can still have 383ohm and the MAF sensor not be working - all my MAFS whether working or not were set to 383ohm

I've managed to borrow a good MAF and notice the difference now. You can unplug either MAF and although the engine stumbles it continues to run so in my mind if you have at least one good maf you can limp home - 2 bad mafs and I think your done :-(

 

No, I am not asking because of 383 (which btw is one of the worst pieces of advice to blindly take a good running car with no issues related to open loop and set them to 383), I am asking because the 2.7 Motoric uses MAF CO adjustment at open loop which happens to come in at 73% or so of throttle, if the MAF is rich enough and the issue happens at 3/4 throttle or more if "could" be that. If the MAF's are way off, then its good advice to start back at 383 as someone messed with it trying to tune the car or something in the past. If they are 378-392 ish range leave them ESPECIALLY if the banks are different which they almost 100% are from the factory.

First thing I'd check at this point if I were these 2 guys is that MAF setting. May be it's fine, but it so easy to rule it out, maybe its not. Have read about cars with settings in the 500's.

Their issue is specific to intermittent cut out that lasts for short periods, would be more akin to a MAF connection being loose as opposed to a straight bad MAF.

 

In messing about with my 348 when I was sorting out its hot idle, I disconnected the MAF's, one at a time whilst engine running, it didn't cut out, the idle increases a bit, but in now way caused the engine to cut out.
If the ECU is not seeing the expected parameters from the MAF, the ECU reverts to TPS and predetermined tables.

 

I have been watching this thread, noticing that as these cars are getting older, they are showing all sorts of random faults like this, even my own 348 with some random stupid faults.

A while ago I was considering fitting an aftermarket ECU to enhance performance and make the car more reliable and maybe even more fuel efficient given the advances in ECU technology.
After having the car on the Dyno and observing it ran quite well, I went off the idea and decided to leave it stock, but then one of my banks would randomly cut out, I replaced the injector relays, and the fuel pump relays, and it hasnt done it since but to be honest, I feel these very old antiquated ECU's and the way they work and the age of them is almost past their usefulness.
These were some of Ferrari's first attempts and running modern ECU's for engine management, the whole "one ECU per bank" is a ridiculous idea and this is evident as they did away with that idea once things started progressing with the 355 and so forth.....
Time to update I feel.

I am now going back to the idea of ripping the Motronic system out of the car and installing a modern ECU, new modern injectors, wideband O2 sensors, map sensor, and get on with making the engine more reliable and also enhance the performance and reliability.

The MAF's will go in the garbage with the narrowband O2 sensors and the old injectors.......things have really advanced and moved on, time to maximize the potential of these cars, I'm done with the old failing electronics.......its becoming more and more common to see these things throwing random faults....