My 355 won't rev past 3k rpm ?

96 355 manual.

Was running fine, started it up yesterday and started to take it out for a run.

As soon as i hit the 2300-3500rpm power band the throttle just bounces off as if its hit a rev limiter

I was previously looking for the engine number in the back end of the block and moved a couple of wires for better access. Had a look and play around with connectors yesterday and back at that end of the block are both connectors for the Phase sensor, knock sensor (both connectors plastic have perished but pins still fine) and the throttle position sensor (TPS). I reseated all 3 connections but no difference.

I have another 355 (f1) so swopped over the phase sensor as it was easy to access = no change so have ruled that out. TPS is different between manual and f1. What about the knock sensor, could this cause such a problem ?

Has anyone seen this before ?

Any other ideas ? Speed sensor or ECU worth checking

 

Just had a dig a little deeper looking at both knock sensors both the connect block end plastic is perished and also the actual sensor end. I’m going to replace both anyway as the have definitely seen better days

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Did you check for codes yet?


Sent from my iPhone using FerrariChat

 

Yes Ive got lots
previous owner pulled the dash bulb, I will make a note and list them here asap

 

I have concerns about posting this because I have no idea if it is your problem or not, but I had a similar situation with my 355 last summer. It would break up badly, always at 4k. Like it hit a rev limiter. Turned out to be related to the crank TDC sensor signal.

 

I had the same issue with my knock sensors man that was not a fun job replacing them. There isn't much room in there!!!!!

 

So you car also had the wall at 4000 or did you mean your sensors were just deteriorating?

 

Just deterioration of the knock sensors. No dramas with rpm.

 

One thing I will add is that it's very important if your going to change the crank ref sensor make sure you measure the air gap before you remove the old one and make the new sensor air gap the same. My new sensor that showed up was 10thou shorter from tip to mount face and when I put the shim that was originally there it made the air gap outside the clearance limits!! Which means Starting problems

 

Pretty big tolerance on the air gap. WSM specs 0.35 to 0.90 mm.

 

very good tip, thank you for this

 

Scott,

Before you go replacing the crank sensor, which is a real pain in the butt because the AC compressor is in the way, check the connections and wires. Ultimately the problem on my car, which had similar symptoms, was that the signal wire in the engine harness was broken internally just where it was crimped to the pin in the connector (sensor end). It was making intermittent contact and for some reason the car would run perfectly up to 4k, then , as I said, it was like it hit a rev limiter. It was a pain to find the problem until I removed the pins from the connector and tugged a little on each wire. Sure enough, when I put tension on the signal wire the insulation stretched indicating a broken wire inside. There was no CEL or error codes.

Also, if you can, measure the impedance of the sensor between the ground (not the shield) and signal wire. It should be around 900 ohm as I recall. It's a passive sensor, so if the impedance is good the sensor should be good.

The other thing is you might wan to check the wires that you were messing with for continuity too.

 

Also check the battery/alternator output. When my alternator was going bad, the car would break up at 3K rpm and would not go over.

 

That's .021" John. Not all that big and he mentioned the body was .01" different. I've seen shims in the mounting.

 

.013 to .035 thou!!!! I think if you get to .030 thou you will have issues due to harness age?

 

That is an alternator issue but also could be a Battery issue

 

Dave, the tolerance is 0.55 mm. That is the mean (.35+.9)/2 = 0.625mm +/- 0.275mm, or Mean +/- 44%. 44% is a BIG tolerance. No? Does it matter whether it's inches or mm?

But yes, you need to check the spacing. If you can't get a 0.014" feeler in there the gap is too small. If a 0.035" feeler is loose it's to too big.

Actually, I think the shim you are referring to is really more of a separator so the plastic casing of the sensor is not in direct contact with the block. I have them on both of my sensors. They are about 0.001" or 0.002" thick. Just a piece of foil.

Don't argue with the old man!

 

Typical Italians. I read the value as a range from .35mm to 9mm, so a .021" inch spread. I convert all numbers to SI coz I live in the US

 

So, contacted an aluminum block is different than aluminum foil?

Stay tuned for the calculation from John

 

Great info guys thank you.

Im on a roll today, just had a major breakthrough on my Testarossa Spider build project thats been literally bugging me for months

https://www.ferrarichat.com/forum/threads/the-ratarossa-the-testarossa-spider-rebuild-project.499875/


Maybe its a good day to dig a bit deeper into the 355 problem

 

A little history. When I first had the problem with my car I though it was the sensor and I replaced it. I had not noticed that the "shim" fell off the new sensor. I checked the gap and it was within the spec range. Then I found the shim under the car. Since the car ran fine and it was a PITA to install the sensor I just left it that way. My moving the wires around must have restored good continuity, for the time being. 8 months later the same problem occurred. That is when I found the broken wire. In the process I removed and reinstalled the sensor with the shim. Car runs fine.

Now, consider the effect of the shim. Assume normal installation is with 1 shim. Given the min and max allowable gap it would make sense for the shim to be about 0.01" thick. I say this because if the gap was just under the minimum spec, adding a 2nd 0.01" shim would place it right in the middle. If the gap was 0.01" too tight a 2nd 0.01" shim would make the gap min spec and adding a 3rd shim would make it right in the middle. On the other hand, if the gap was just greater than the max spec, removing the shim would place it in the middle of the spec. But, if the gap is more than 0.01" too wide there is nothing left to remove. The sensor would have to be modified. I could be wrong as I didn't measure the thickness of the shim, but it sure didn't seem like it was 0.01" thick. Anyway, both my sensors (95 2.7 has 2) have a single shim. Coincidence? I think not. I think the spec tolerance is little more than an allowance to account for manufacturing tolerances on the sensor. And I think it is there simply to provide and Al to Al interface between block and sensor so that the possibility of the sensor bonding to the block is eliminated. FYI this little piece if foil is listed as a $43 part at Ricambi. WTF! Now, I will admit this is a lot of speculation on my part so get out in the garage and see how many shims are on your 95 project car, and measure the thickness. I may be in an alternate universe on this one. This is your big chance, Dave.

 

John, both those sensors have been removed years ago, you know, when I had a life and used to work on my cars....

Anyway, they are at my shop but I seen to recall a shim on one but not the other. Of course the car was worked on by a few that were pretty sloppy so I would not use it as a data point.

 

Thats what I thought i didnt think 10 though should have made a diff

 

I always like to conclude these thread issues to help others in the future

Today I managed to fix the issue.

To add a little more information to the issue. Over the past week I have been tinkering with various parts of the engine trying to find the fault then driving the car to test it. Basically what was happening is the FALSE RPM rev limiter would fluctuate from anywhere between 1500rpm - 6000rpm (that was the max I got on one drive) but it would never change mid journey, once I had shut the car down and left it, the next time I started it the power band would max out at a different position. Every time if I had the new rev limit it would bounce off and behave as if I was hitting the normal rev limiter around 9000rpm. Again this was exactly the same in all 6 gears, yesterday I limped the car home with just 1500rpm and managed 40mph in 6th gear, rather embarrassing in a Ferrari .

My issue had always been the 'red herring' thinking I had damaged the wiring or possibly one of the sensors in the top engine area when I had pushed some aside trying to read the engine number on the car.

I then started fearing the worse that it was the engine ECU = $$$$$$

I had put off doing the crank sensor as it is a pig to get to and change no room and the AC compressor is in the way. Took a couple of hours and a few cuts and bruises getting the 10mm bolt loose.

Anyway as John had mentioned the final thing I changed today was the 'Crank Sensor' (Angolar speed sensor) Part number 162916 ......number 22 on the parts diagram (5.2 engine)
There is only one the 5.2 engine and 2 of them on the earlier 2.7 cars.

On inspection mine was shot to bits, the plastic had disintegrated and the wires were all bare and touching, which must have been causing the fault

Ferrari charge £98.68 plus Vat for it but its just a Bosch part and I managed to get one off Ebay new for less that £30 delivered.

Thanks for all your help and hope this thread helps someone in the future.

A few pics attached

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