355 2.7 ECU Help

As I remember its a round red plunger on the ECU it self, got to get up under there to see it. Ignition on, and hold it down for 4 seconds, and the codes if you have them will flash thru the CEL lights. One on each side under the black side covers.

 

Before throwing parts at the problem, I would disconnect the cam sensor from the wiring loom, thoroughly clean the terminals with electrical contact cleaner and a wire brush, reconnect the sensor, reinitialize the ECU's and see if that gets rid of the error. The intermittant nature of your error code leads me to believe it is an electrical signal problem, not a bad sensor.

 

Yup, yup, yup. It's certainly common for that 348 cam sensor electronic cable to get brittle and crack due to age/heat. I suspect that the same could happen for the 355. Cheap and easy replacement, though...even if the problem is more than just that one cable.

 

Guys I know this is an old thread but I'm searching for the life of me for the test button on the 1996 ECU. This is a 2.7 system because of a Challenge car spec so it's the same as a 1995.

I found the ECUs at the back and other than the thick bundle of wires going into them through that large connector it looks pretty sealed in there to have a test button?

Any leads?

Thank you.,

 

Sorry guys -- false alarm -- since my car is an Euro, I don't have the test buttons but have the adapter wire hanging off from the ECU thick connector so I will be making my own wire hopefully.

 

I believe it's my348.com that tells you how to build your own button.

As to the CEL light - taking it out during winter, it tended to flicker on & off a bit. Same with the ABS light
Come Spring, rarely flickered. The ABS would only come on after about 30 minutes of driving.
Now that's it's summer, I haven't seen any light.

Truly, this is a fair-weather car

 

My problem is not the same as the original poster -- I have a slow down light which I'm in the process of debugging by using the swap-a-roo method (O2 sensors left to right and maybe ECUs left to right).

My car doesn't have cats so the sensors are plugged into the straight-pipes -- I have no idea what that does to the system in terms of codes/etc.

 

The slow down light is driven by the cat temp ECU's, not the motronic ECU's or O2 sensors. Swapping the motronic ECU's or O2 sensors won't do anything for your slow down light, you have to swap the cat temp sensors and cat temp ECU's, but since you have no catalytic converters the best thing to do is just unplug and remove them from the car as there's nothing for them to monitor.

The 5.2 cars have a secondary O2 sensor that will be affected by removing cats as they will throw a cat efficiency error, but they don't exist on the 2.7 cars.

 

My '95 turned out to be a bad Temp sensor. Replaced it & it's been right-as-rain since.

 

Thanks Pete -- by now I'm sure you are probably tired of mentioning this over and over but I will try your suggestion tomorrow.

I am just now learning the car (and I figured out today that I don't have the test button on the ECUs since the car is an Euro) and will get to these cat temp ECUs next. For some reason my original thought process had to do with:

Slow Down light = cat issue = what goes into or after the cats = O2 sensors => maybe it's the O2 sensor.

However, you are completely right -- I actually even unplugged the O2 sensors altogether and it had no effect whatsoever on the Slow Down light.

The only other thing that *bugs* me to some extent is why I only have the Slow Down 1-4 and not the 5-8; unplugging both cat ecus will eliminate this as you had mentioned but I am still scratching my head to understand why it only shows up on one right now?

Many thanks for all your on-going help.

 

So I actually did this right now and I'm confused -- the Slow Down 1-4 light stays on solid event after disconnecting the CAT ECUs. You were right in that the 2 CAT ECUs tucked away in the rear fenders were connected only on one side (to the car) and not to any thermocouples.

I also reset the battery connection (disconnected the - cable for about 2 mins) and yet no change?

Could it be maybe some wiring harness issue? Or any other thoughts?

Thanks.

 

It is very possible that the wiring / connections related to the TCU signals going into the main ECU are messed up, corroded, and giving bad information for the ECU which decides to turn on the slow down light.

A temporary solution is to isolate the pins (you have to know which ones to look at) and clean them so that they make better contact. A better solution is to replace those pins with new ones. The mother of all solution is to replace ALL pins with the gold kit from SR. The costs go from free, to a few dollars, to a few thousand dollars.

You decide.

 

Thanks -- do you have some links handy? I'll search for this...

However, what confuses me is the following -- the car does not have cats but a straight-pipe exhaust; I am pretty sure the only sensors going anywhere after the headers are one O2 sensor in each of the two exhaust pipes.

The CAT ECUs were connected to the car/main system but with no input from the thermocouplers (since they do not exist).

Upon starting the car, the CEL lights go on and then off; the Slow Down 1-4 light goes ON but then stays ON solid. Car starts up around 1000 RPM, then within ~30 seconds jumps to 1500 RPM for about 1-min then drops back down and idles at close to 1000 RPM.

Does the Slow Down lights go on as part of the starting procedure? In that case along with the problem I am having I may also have a burned Slow Down 5-8 light? Since the problem should manifest itself the same way?

I will look into the wiring issues; is there a wiring diagram detailing the pin-outs?

Thanks.

 

I have the same issue on my 96 F355 for a few weeks now and what I have done is to remove all three TCU from the car, check their operation with a battery and a Volt meter amnd they all seem to work. Wiggling the connectors did not result in any funny signals so all I can conclude is the TCUs are OK. I just cleaned the connectors really well and then put them back. That seems to have make the slow down light go away. This leads me to believe that I have some corrosion in the connector pins.

If it comes back for me, I would eventually chase down the ECU pins and clean or replace those. Sorry, I do not have a wiring diagram to tell you which pins those are.

Since you still have the TCU in the car, connected to the main wiring harness, I suggest you take them out and clean the connectors, and hope for the best.

 

On a 2.7 the slow down lights will come on solid if the thermocouples are unplugged. I can't explain why you only have the 1-4 light on. There are three solutions if you have test pipes..

1. Install thermocouples and zip tie them somewhere safe with the probe hanging in the breeze.

2. Short the two wires together so the system sees a complete circuit

3. Remove the bulbs from the dash.

If you have a CEL it is probably not related to the missing Thermocouples.

 

Thanks -- the CEL is both 1-4 and 5-8 only for a split second when cranking; there's the battery and brake light that flash for about 1 second then everything goes off *except* for the Slow Down 1-4.

Based on what you're describing above it probably means my Slow Down 5-8 is actually burned out?

Finally -- for the solution (2) mentioned above, where would I short the wires; can I take the CAT ECUs out of the loop and deal with the wire that goes out from the CAT ECUs?

Thanks.

 

Honestly, since you have no cats, I would just pull the slow down 1-4 bulb out and remove the cat ecu's from the car completely. I thought if you unplugged the cat ecus that the slow down lights would not come on at all, but I guess they just come on solid. My car has the cat ecus and thermocouples plugged in but just dangling free and the slow down lights come on and then shut off once the car is running along with the CEL lights (and all of the other dash lights). The Brake and ABS light take 5 seconds or so to shut off, but the others all shut off as soon as the car starts.

The Cat ecu's actually provide a voltage signal to the motronic based on the cat temp, so if you wanted to remove them from the car but still have the motronic get the proper signal, you'd need to create a circuit that provides the correct voltage. It'd be easier to just short the thermocouple wires together (with a resistor maybe to get the right resistance?) or, as I said, just pull the bulbs out since you have no cats to monitor and keep all the parts in case you need to install cats again at some point - and worry about getting it all working right then. That would probably just involve plugging thermocouples in and installing a new 5-8 bulb in the dash.

I can measure the resistance of a thermocouple at room temp if you wanted to go that route and fool the cat ecu's by just putting a resistor in-line.

 

If you could do this, I would appreciate it. I'm thinking I'd like to try the resistor route before taking lights out of the dash...

Thanks a lot.

 

I should be out in the garage tomorrow or Tuesday and I'll get a reading for you.

 

Does anybody have any links or pointers regarding the test button on a 348 or an early/Euro F355? I've been searching and for the life of me I can't find this info on building my own. All suppliers seem to be out of stock of the test cable itself...

One alternative was to try things out with a paper clip or some form of 'shorting' wire since I would assume that's what the push button itself does, but I'd rather not experiment unless I have to.

Also -- has anybody ever listed the connectors that are on our vehicles' harnesses?

Thank you.