I posted a week or so ago re the wiring in my 328 's ECU area. Anyway I'm sorting thru it slowly but have another related question. I got a new thermocouple from Eurospares in the UK. Part looks good but has 2 spade type connectors on the end instead of a red and yellow wire on the original item. I've double checked the correct part no etc and it all checks out. Can anyone tell me if it makes any difference which way round these wires are connected to the Cat control unit. Cost close to 250 quid so I'm loath to wire it up wrong and fry the thing. Any help much appreciated Cheers Mark Taiwan / UK 1988 328 GTS
Thermocouples produce dc voltage and the wires are polarized + and - The good news is you won't fry anything by connecting them bassackwards. If I were faced with that dilema I would try it one way then reverse it if it doesn't work.
It's usually the thermocouple ECU that goes bad, not the thermocouple itself -- how did you determine that the thermocouple was bad? Also, thermocouples are very rugged gizmos, but they do have polarity so the risk is more for blowing up the thermocouple ECU rather than hurting the thermocouple itself -- did you also buy a new thermocouple ECU? Although, as Paul indicated, it may be that the worst would be (if there is a required polarity) that the system just wouldn't work correctly -- do you know how to measure the O2 sensor output at warm idle to confirm if the system is actually running closed-loop? If not, give a shout... (I know this doesn't help with your predicament, but just curious.)
Thanks for the replies Steve and Paul. Very helpful. I have re-newed the thermocouple ECU and already installed. I stopped at installing the thermocouple as the wiring looks different ie both wire connections to the thermocouple are the same - no coloured wiring. The reason for renewing the thermocouple was simply that I have recently had the Cat removed and replaced with a test pipe and then reverted back to the original cat (for reasons of noise - too much when combined to a new sports exhaust as well) The thermocouple was bent in the cat and its been in and out a couple of times now so thought it best to replace. Also re newing the thermocouple ECU did not improve the intermittent slow down light (from my previous post) making me think its not getting a signal form the thermocouple itself. Incidentaly the new thermocouple is much shorter than the old one so it fits without being "bent" into the cat. All this was started originally to solve a rich running poor hot starting car. Don't seem to be getting much closer to fixing that despite all this... Thanks , any other info or ideas much appreciated. Cheers Mark Taiwan/UK 1988 328 GTS
OK Mark -- understood, but, if your old thermocouple is OK, you might be able to recover some value (even if a little banged up). If the resistance between the two leads is very high/open, or if either lead has a low resistance to the outer (metal) case, either would be a sign that the thermocouple is bad -- but if you pass those tests it might be OK. One thing that is unique to the K-Jet with Lambda systems like yours is that there is an intelligent (electrical) connection between the thermocouple ECU and the injection ECU -- in the jpeg, I've recolored this line to purple. I'm not sure what it should be (and I'd like to know ), but logic dictates that it should be "different" when at cold idle (i.e., thermocouple less than some temp) versus when at warm idle (i.e., thermocouple greater than some temp). Measuring the voltage on this line and detecting a difference for cold idle versus warm idle would be a good sign IMO that the thermocouple system is working correctly -- just a suggestion (but I'd really like to know these voltage values so, if anyone with a K-Jet with Lambda system would/could measure, I would be grateful -- TIA). Image Unavailable, Please Login
Thanks Steve - that makes total sense to me. I've put the new thermocouple on anyway. I eventually noticed that one wire was thicker than the other which seemed to match with the old one where the red wire is slightly thicker than the yellow. Took a risk and fitted it. I'll get the car back this afternoon from the main dealers who are trying to set the mixtures to a sensible level. They reckon any further problems with hot start/mixtures etc must be related to the Bosch fuel distributor being gummed up or otherwise in need of an overhaul. The car has sat for quite some time over the last few years I think. Trouble is their knowledge of the "classic" models is limited so we're shooting in the dark a little. All a bit of a rush as its in the Ferrari 60 year parade here in Taiwan on Thursday. Mines the oldest car involved can you believe (1988 !) and I'd rather get there and back under my own steam if possible... Got 45 others coming though so it should be interesting. Got an Enzo various F50's / F40's, TR, bunch of 430's 360's 355's and 1 348 I think. At the weekend i'll try to get those voltage measurements for you. Once again, thanks for the input. Cheers Mark Taiwan/UK 1988 328 GTS
Although it seems counter-intutive, the red wire is the ground and the yellow lead has the positive voltage. If your thermocouple modules are like the ones on my car, they just light up the "slow down" lamps on the instrument cluster or the "drive to the dealer right now" lamps. So if one is connected backwards, the warning lamps won't function but you won't hurt the thermocouple module. You could take the car on a short drive and compare the thermocouple voltages.....the readings will be in the milivolt range. FWIW. Jeff Pintler 89 348tb, 86TR
Thanks Jeff, Similar to what Steve suggested I guess. I'll try checking the voltages later when I get a chance. Just got the car back from the main dealer. Goes like stink now but still a hard hot start apparently. Not sure any of this will affect the running of the car in any case given the info above. Thanks for the help though Cheers Mark Taiwan/UK 1988 328 GTS
