Wiring harness for the Speed Six engine
Discussion
Hi, I'm thinking of replacing the wiring harness on the Speed Six engine in my 2002 Tuscan Mk 1, as the wires have become brittle and unreliable. Does anyone have any experience of the quality of available replacement harnesses? I'm thinking of buying one from TVR-parts (cat no M1668). Hopefully the insulation on the new wires will last for some time before degrading (which I suspect is what is causing my current engine problems!)
Mike
Mike
Edited by RMS5 on Thursday 21st September 11:51
s6boy said:
Interested to hear what your engine problems are and what other work has been done to discount the causes?
Thinking of doing the same btw.
Hi there,Thinking of doing the same btw.
The most obvious problem I've had recently was a misfire which (after a lot of detective work) I tracked down to low voltage supply to pin 1 of the electrical connector to the fuel injector for cylinder 6 of the engine. I found out that all six of the fuel injectors take their pin 1 voltage from a common connection to the fuse box, and I also noticed that a previous owner or garage had solved a similar problem by soldering in a piggyback wire between the plugs for injectors 3 and 4. I soldered in a piggyback wire from pin 1 of the plug for injector 5 to pin 1 of injector 6 and all was well for 24 hours, when cylinders 3 and 4 started misfiring. Evidently my examination of these plugs had disturbed the wire which had been supplying both of them. I added an extra piggyback wire which now connects pin 1 of injector 2 to those for injectors 3 and 4 and the car is back to running on all cylinders. Clearly, though, I'm on borrowed time with this solution as the three elderly wires that originally supplied plugs 1, 2 and 5 are carrying between them the current for all six injectors.
As well as the immediate problem of the fuel injectors, I'm aware that the entire engine harness is of similar age and whenever I've looked at the wiring leading to other plugs (for example, the air temperature sensor connector on top of the airbox) I've found the insulation brittle and cracked to the point where the two wires may be shorting, at least within the rubber boot that covers the connector. I've also had problems with the engine in the past which have been solved by replacing the water temperature sensor that informs the ECU but which, in retrospect, may have been simply temporarily resettling a defective connection in the wiring (I'm sure the sensors should last longer than six months, after all). Whether or not that is the case, the need for new wiring at least to the injectors is clear enough, and I feel I may as well get the benefit of (hopefully) more reliable wiring throughout the engine by replacing the entire harness.
I gather that an experienced mechanic can swap the old harness for the new in a matter of a couple of hours without taking the engine out of its bay. I feel that I would like to watch someone else do it first before I take on the task by myself, rather in the same way as you'd want to watch someone else do a triple heart bypass before your own first attempt. Of course, if you're thinking of doing the job in the comfort of your own garage, you could post a wire-by-wire account on here or on YouTube! Which model do you have and what problems have you been encountering?
RMS5 said:
Penelope Stopit said:
The question you need to be asking suppliers. Is the loom made with Thinwall Cable?
Thinwall cable has tougher insulation
Many thanks for that advice! I shall enquire when their office is open.Thinwall cable has tougher insulation
RMS5 said:
No conclusive information on this from TVR-Parts, though they tell me the harness is made up by the OE supplier. I've bought one anyway, so I'll find out how reliable it is in due course
You have a new job as harness testerThanks for posting back your findings or in this case lack of findings
Penelope Stopit said:
RMS5 said:
No conclusive information on this from TVR-Parts, though they tell me the harness is made up by the OE supplier. I've bought one anyway, so I'll find out how reliable it is in due course
You have a new job as harness testerThanks for posting back your findings or in this case lack of findings
ninetynine said:
i had all sorts of problems with my wiring harness it turned out to be an earth connection about 400mm fron the multi plug where all the earths are crimped together to one main earth and had corroded
Presumably that had some far-reaching effects on the engine's performance 
Was the car running at all? I suppose a partial/intermittent connection would still allow some function…did you re-solder the earth connection or go for my more radical (read: expensive) solution?Gassing Station | Speed Six Engine | Top of Page | What's New | My Stuff