Thermocouples, slow down lights, related CEL’s, and how to conquer them...

Ian I’m sorry I don’t know how to do the fancy quote thing to respond directly to things.

His response was the tech measured the output and the readings were between .8 and 4.8 depending on the conditions. There are no conditions that are normal that produce 4.8 v. The bias voltage is 5v and the above graph shows the normal range. If he got 4.8 v there is an intermittent short in the sdl system

As for the motronics, I was speaking of the SDL system parameters. I am not aware of any euro or other SDL motronics parameter unique to the 5.2 for 355s. If there is then I am mistaken and will stand as such.

I do know that if the poster or anyone else wants to really know what’s going on with the sdl system, simply tap or back probe or whatever the sdecu output and get a Dvom and drive around like I did in the video I posted. You will know in 5 minutes what your problem is and from where.

 

Ignition / engine ECU's are different for US / non US.

 

Thanks, Bob.. I misread the statement.

4.8 sounds like the bypass cats are on fire... or, as you say.. a fault.

Quoting is just a matter of putting "[ quote ]" before the text and "[ /quote ]" afterwards, but don't put any spaces inside the square brackets.

 

Thanks Bob got my spare thermocouples today.
They are like my American Express "I dont leave home without one"

 

OK. That's the box!!!!!!!!! My car was ok for about 500 miles till it shorted out. That box somehow fools the Motronic 5.2 system. I have asked the mechanic if he can fix the box but nobody can find the guy who was making them.

 

So my options are to find someone who can repair the box, find someone who will sell me a European ECU, replace my cats with OEM if they ever make them, or buy the code reader and clear the CEL when if goes off. Interestingly, as other people have noted, lots of people change the exhaust and don't have this problem. So clearly each car is somewhat different or those cars are set up in such a way that the exhaust temperature is different and compatible with the rest of the car. Think my best and cheapest option for now is to just reset the CEL. But if anyone knows how to fix these boxes, please let me know

 

There is something else going on.
Why dont you just probe the ends like Bob said and if the tc is bad just replace it. I do need t think its your cats from fabspeed. Others have them and they work.
What muffler do you have?

 

So it was a Goth's box? Strange... Goth's stuff is usually top quality.

Does the Goth's box for the bypass valve have a single or dual plug? The ones with the single plug won't be plugged into the thermocouple (temperature probe). They'll only be plugged into the Motronics ECU.
However, I can't see how a Goth's single plug box would work in the bypass position.

 

Ian it puts out a constant voltage, probably 1.5v. Apparently that satisfies the motronics that the BP is functioning.

It doesn’t need the TC port.

I thought that Skipp’s had stopped working which led me to believe as I said that the motronics was looking for a change in voltage at the BP and not just a constant but maybe not.

 

Bob,
Mine is still working. I did get a CEL one time which I had to clear. It has not returned in a year. I’ve got an extra box that I’m holding on to for dear life !
Somebody needs to crack on of these open and put them back into production. They work.

 

Sorry if I missed it but has ehrst posted the code? A CEL without knowing the code is just a light on the dash.

 

If this is the case, it seems to me that the Motronics ECU is looking for a threshold temperature (voltage) when it thinks at the valve is open (i.e. when the ECU has commanded it to open). It probably knows what the likely maximum temperature of the air (after the bypass valve) would be with the valve closed (i.e. on a hot day, perhaps with no cooling airflow, with the engine bay and exhaust components at their hottest) and any temperature above that is a sign that the valve is open. The ECU may also be looking for excessive temperatures when it thinks the valve should be closed (which might be caused by a valve which is stuck open). Perhaps this 1.5v(?) is a value which fits neatly matches both sets of parameters?

I wonder if the Motronics ECU is monitoring other parameters and modifying the threshold values moment to moment. Perhaps the Goth's box doesn't quite have the right voltage for all situations? i.e. Ehrst's box is actually working as designed. It's not actually broken.

Anyway, I'm kind of disappointed that the ECU isn't looking for valve open/closed temperature changes. Perhaps this method had some kind of shortcoming.

I did read on the forums that bypass valves stuck closed are not particularly healthy for the engine. I think you would have to know your car reasonably well before you fitted one of these dummy boxes (i.e. you would have to know what your exhaust sounded like when the bypass valve was operating normally).

 

Skipp is the only one I know who actually worked through the BP location issue with straight pipes so his experience is a data point of one for me.

The fact that it worked then didn’t work and now works leads me to believe that it isn’t just a fixed voltage that does the job. Maybe it does need to see a delta as I said that approximates the levels in my video.

I couldn’t get Skipp to give me an actual voltage reading from his unit . But I’m pretty confident it’s 1.5 v.

We know the BP valve opens above 4000 rpm so the motronics is monitoring rpm and it’s possible it is looking for that 1.8 volts in conjunction with 4000 rpm trigger to identify the working BP. In that case, over time and cycles maybe it says nope to the fixed output and throws a CEL.

This is a CEL not a SDL and other CEL s have pending codes that after so many cycles become stored codes. Maybe we can get Skipp to run his OBD and see if the code is pending ?????

 

I’m happy to help decipher things where I can.
I’ve checked for codes many times. There aren’t any pending codes. The BP box from goth has a switch that toggles allowing you to choose BP or Main Cats to “fool”, so the signal is different for those two different tasks. When I got that random CEL, I toggled the switch back and forth to make sure it was set to BP. The CEL hasn’t returned since then. My car just got a huge major and was turned off for 3.5 months. The CEL has not returned following that down time either.
I also think the issue running test pipes and how it effects the BP is too LOW temperature. Things flow cooler without the cats and the TC becomes unhappy with that.
The reason I never tapped the wires to check the voltage readings is because I don’t know how ! I’m no electronics expert. Stock Market investing, I’m good at. Electronics, just enough understanding to be very dangerous.

Goth’s boxes are floating around out there. Someone needs to obtain one, cut it open, and reverse engineer the thing. Think Area 51

 

There may be a difference between a 2.7 and a 5.2 but I would question the idea that test pipes yield a too low temp and trigger a CEL. I say this because I have run hollow cats on my car, a 2.7, and never got a CEL or SDL which would be associated with the TCs in the cats or test pipes. Second, as I stated before, the split in the exhaust going to the bypass comes before the main cats, so the main cats or test pipe have no influence in the temp in the bypass circuit. Perhaps if the secondary cats in the bypass pipe are deleted, but the problem I see is that ehrst has stated that the CEL comes on at idle, when you would expect the bypass TC to see a lower temperature and goes out when it is driving at higher RPM. I still think the problem lies with the bypass valve. But, for me, it isn't even clear from what has been posted which TC box ehrst has in the bypass circuit. I'm just confused about what is on the car, test pipes and Capistro bypass valve, but what TCUs are where?

The other problem I have is that it is not at all clear how the main ECU processes temperature data from the bypass circuit. The algorithm for the cats temperature circuits are pretty well documented in the WSM, but I haven't seen anything about the bypass circuit algorithm.

 

more data points:

Capristo BP + stock headers+ stock cats= NO CEL

Capristo BP + Tubi Headers+test pipes = CEL

Once CEL comes on, it doesn’t go away on its own. It must be cleared with scanner.

Too Low temperature is purely an uneducated guess on my part. It’s just a thought.

Capristo technician stated via phone that their BP valve would trigger a CEL if used without cats.

It would be interesting to see if a car with
Tubi headers + test pipes + OEM BP valve = CEL. That would rule out the BP valve itself.

 

Skipp, like I said, a CEL is just a light on the dash. What is the associated code? Does the CEL come on if you just idle the car for a while, or must you dive it to the point where the BP valve should open?

One other thing. Lot's of talk about temperature here, but perhaps more significantly, removing the cats reduces back pressure. Changing the back pressure would change the pressure at the split where the bypass pipes come off the headers. This could impact the flow through the BP pipes/valve.

If Capristo know that the CEL will come on with their valve and test pipes, do they have an explanation as to why?

Lastly, you last sentence is crucial. If there is no CEL with the OEM BP valve then it's a problem with the Capristo valve. I have read here that it operates differently. maybe time to search for an alternative.

 

It's normally open, not closed like the OEM.

 

Just reading about the Capristo valve. I note that it says if there is a vacuum failure the valve defaults to the open position. If I read ehrst's posts correctly, he gets a CEL at idle. Perhaps the problem is a vacuum leak somewhere that results in too little vacuum at idle and the valve, sensing a vacuum failure, then opens, resulting in the CEL. Juts guessing here. Hate to guess, but got to throw the idea out there for consideration.

P.S. Dave, didn't see your post before I posted, but thinking along those lines.

 

John,
The CEL doesn’t come on just idling that know of. Once reset, you go drive and get CEL either while driving, at a stop light, or once returning home and idling in the driveway.

The OEM BP was never run with Tubi headers and test pipes, so we don’t know what the result would be. Capristo BP worked fine when run with OEM Headers and OEM CATS. In other words, I changed the BP to Capristo first with no issues and later added Tubi Headers and removed CATS for test pipes.

Capristo BP has been pressure tested to rule out leaks !!!

Capristo BP working properly.

The flow differential is definitely possibility. I can’t remember whether Capristo mentioned this or not as a issue since it’s been two years. I do know my very competent mechanic thought that may be the case.

P1448

Here’s my thread from the time:

https://www.ferrarichat.com/forum/threads/tubi-headers-tubi-test-pipes-bigg-daddies-catted-o2-extenders-p1448-code.526547/

 

I'm trying to address ehrnst's problem. Form post 198

But that may be irrelevant because I just read he has the FabSpeed valve and I don't even see one listed for a 355 on their web site. So, I give up. Hard to make any useful suggestions when it's not clear what's on the car.

 

Don’t feel bad. I gave up too and bought Goth’s box. This whole system is garbage, imho.

 

Glad my car is a 95. No bypass TC, not to mention no immobilizer, and no OBD II nonsense.

You should measure the output of Goth's box and post it.

 

Skipp, respectfully - it's not. It was designed to work with a set of original components and when you start changing all the original parts, all bets are off. The system has purpose. Yes, the integrity of some of the components is lacking that is for sure.

 

That OBDII nonsense has led me directly to the source of problems on several model cars - just saying