Going in circles - starter issue - suspect wiring.
Discussion
Chaps,
Long story short, an intermittent starting problem which is as of today more... er..... yeah it's a frikkin' paperweight at the moment and it's sunny! boo!
I'm seeking help in identifying which connectors and pins take 12V to the starter solenoid so I can trace back if I have any dodgy joints / any other epiphanies to direct my fault finding.
I *think* I have a dodgy joint between my immobiliser and the engine harness connector in the bonnet. But I'm not 100% sure. I'm really struggling to read the electrical circuit diagrams.
https://tvrtuscan.info/public/resources/TVR_Tuscan...
which is super useful, but I can't really see how to trace the starter solenoid wire. I think It goes through the immobiliser,
in the white/red wires 7&8, or am I incorrect? I've tried measuring resistance from either of the white/red cables to the starter solenoid and I'm not getting sensible readings, I'd have thought one of them went up there? But its maddening as I'm clearly getting some voltage hit the starter, but I can't measure sensible resistance here (it may well be probing error).. as truth be told I'm really struggling to read the table on "Tuscan Speed Six Main harness" around page 80 - the table doesn't actually make sense to me and I can't work out where in the schematics the connectors for the large engine harness are! I'm clearly missing something!
I have proven:
So yeah. Suspected weak drive signal to starter solenoid. Proven not in engine harness,... am I diagnosing correctly here / if so where do I trace to next?
Thank you for any help - I want to go play and bump starting it seems cheating
Long story short, an intermittent starting problem which is as of today more... er..... yeah it's a frikkin' paperweight at the moment and it's sunny! boo!
I'm seeking help in identifying which connectors and pins take 12V to the starter solenoid so I can trace back if I have any dodgy joints / any other epiphanies to direct my fault finding.
I *think* I have a dodgy joint between my immobiliser and the engine harness connector in the bonnet. But I'm not 100% sure. I'm really struggling to read the electrical circuit diagrams.
- I have measured about 8.5Volts at the +ver terminal of the starter solenoid on crank - which I presume should be about 12V if working properly? (The rest of my thesis relies on the assumption I should be getting 12V on the top of the starter solenoid. If I'm wrong there then #idiot )
- I've measured good earthing between starter motor body and engine ground, so I don't think it's an earthing issue.
- I haven't been brave enough to put a jump cable on the starter engeriser to solenoid to prove the starter - should I? Feels fruity thing to do. If I do this, should I do with Ignition on to start it, or leave ignition off and just see if it cranks? I'd rather chase wire resistances first because I'm scared of shorting that for some reason
- Given the above, my working assumption is that it's something on the energise side of the starter solenoid, dry joint / high resistance point somewhere.
https://tvrtuscan.info/public/resources/TVR_Tuscan...
which is super useful, but I can't really see how to trace the starter solenoid wire. I think It goes through the immobiliser,
in the white/red wires 7&8, or am I incorrect? I've tried measuring resistance from either of the white/red cables to the starter solenoid and I'm not getting sensible readings, I'd have thought one of them went up there? But its maddening as I'm clearly getting some voltage hit the starter, but I can't measure sensible resistance here (it may well be probing error).. as truth be told I'm really struggling to read the table on "Tuscan Speed Six Main harness" around page 80 - the table doesn't actually make sense to me and I can't work out where in the schematics the connectors for the large engine harness are! I'm clearly missing something!
I have proven:
- terminal "cc" on the engine harness (I can't find this in the wiring manual, just looking at the connector itself) has 0ohms to the starter solenoid ring terminal.... So I don't think the issue is in the engine bay any more.
- where does "cc" go to? I can't find it in the wiring digram, but I can sure as hell see it exists and I can probe from that to the starter!
- This leads me to suspect something between the immobiliser connector and the engine harness connector in the footwell (joy) - am I on a sensible path or am I getting myself confused here?
So yeah. Suspected weak drive signal to starter solenoid. Proven not in engine harness,... am I diagnosing correctly here / if so where do I trace to next?
Thank you for any help - I want to go play and bump starting it seems cheating
Edited by stuthe
on Friday 29th March 20:02
on Friday 29th March 20:02
Ok so I’ve made some progress and it’s really stumped me but I can now read the electrical diagram.
Connectors by Letter are large connectors that go in the back of the fusebox.
M2.4 is the 4th pin second row of connector M
I believe this connects, via the starter relay 12v via the 30Amp fuse in slot 26 to connector C, pin 4.5.
I’ve shown continuity (well maybe 0.2 ohm) from C4.5 to starter solenoid connector.
I’ve shown 0.2 ohm from immobiliser to M2.4.
I’ve shown about 9V max to the starter solenoid.
I’ve also shown that if I try and short the starter motor solenoid to the large supply there that I’m not able to get a good connection with a screwdriver as it keeps clicking - so in think I’m not making enough current. OR the solenoid on my new (3month) starter is not working.
I tired. But progress. I’ll open up the starter relay tomorrow and see if that’s clean & whether Incan get a couple more volts to the solenoid… I can finally understand the Tuscan wiring manual, but think my starter solenoid is probably needing replacing already
Connectors by Letter are large connectors that go in the back of the fusebox.
M2.4 is the 4th pin second row of connector M
I believe this connects, via the starter relay 12v via the 30Amp fuse in slot 26 to connector C, pin 4.5.
I’ve shown continuity (well maybe 0.2 ohm) from C4.5 to starter solenoid connector.
I’ve shown 0.2 ohm from immobiliser to M2.4.
I’ve shown about 9V max to the starter solenoid.
I’ve also shown that if I try and short the starter motor solenoid to the large supply there that I’m not able to get a good connection with a screwdriver as it keeps clicking - so in think I’m not making enough current. OR the solenoid on my new (3month) starter is not working.
I tired. But progress. I’ll open up the starter relay tomorrow and see if that’s clean & whether Incan get a couple more volts to the solenoid… I can finally understand the Tuscan wiring manual, but think my starter solenoid is probably needing replacing already
Edited by stuthe on Saturday 30th March 21:42
on Saturday 30th March 21:42OK FINALLY sorted.
Embarrassing this one - but I’ll leave my shame up here in case it helps anyone in the future
I replaced the battery the other week and felt that was secure, hence focusing my efforts and assumption that the solenoid wasn’t firing fully.
After checking and cleaning the contacts on the starter relay, dropping and probing the fuse box, I went back to double checking my assumptions in the engine bay. Cleaning contacts and relay netted me another 0.5V on the solenoid (nearer 9.5V now), but still no crank. In even tried a gentle mallet tap to see if the solenoid was stuck. No.
So I then rechecked my voltages. As I say 9.5V to the solenoid. Good earth to the starter (0v between it and engine or chassis as I’d cleaned the earth points up too). 12V to the alternator, great. 0.5V to alt when cranking.
Whoa. What?!
Re-check. 12V -> 0.5v when cranking.
FFS. The solenoid is fine, but something very weird with my main power cable to starter, huge resistance such that the volts are collapsing and so low that I couldn’t even hear it try to crack.
Back to battery. Probe on a few places and it shows the voltage drop was across the starter/alt wire into the terminal… took it apart and very corroded inside. Drilled it out, reconnected, cranked, BOOM!
Such an idiot I could have found this so much faster but a few things sent me on a goose chase. Especially when I used a screwdriver to short the solenoid and it started clicking (on/off/on/off) it should have been enough for me to work it out - but I thought not enough current to solenoid again, my assumption of what the problem was was blinding me to the facts.
What was happening with screwdriver test was the main supply was collapsing voltage when the solenoid engaged and the starter tried to draw current, which then let go of the solenoid, and then repeated the cycle again as it re energised when the solenoid was open again. GRR! This didn’t happen cranking from the ignition as it took 12v from the starter relay via fusebox, which didn’t have high resistance, so could hold the solenoid energised!
So yeah, of anyone needs help reading the circuit diagram or fuse box checking, I’m you’re man now- but if your starter not working , check your volts on both solenoid and main drive when cranking. I really thought I was weak solenoid, totally wrong. Goon. But done now
Embarrassing this one - but I’ll leave my shame up here in case it helps anyone in the future
I replaced the battery the other week and felt that was secure, hence focusing my efforts and assumption that the solenoid wasn’t firing fully.
After checking and cleaning the contacts on the starter relay, dropping and probing the fuse box, I went back to double checking my assumptions in the engine bay. Cleaning contacts and relay netted me another 0.5V on the solenoid (nearer 9.5V now), but still no crank. In even tried a gentle mallet tap to see if the solenoid was stuck. No.
So I then rechecked my voltages. As I say 9.5V to the solenoid. Good earth to the starter (0v between it and engine or chassis as I’d cleaned the earth points up too). 12V to the alternator, great. 0.5V to alt when cranking.
Whoa. What?!
Re-check. 12V -> 0.5v when cranking.
FFS. The solenoid is fine, but something very weird with my main power cable to starter, huge resistance such that the volts are collapsing and so low that I couldn’t even hear it try to crack.
Back to battery. Probe on a few places and it shows the voltage drop was across the starter/alt wire into the terminal… took it apart and very corroded inside. Drilled it out, reconnected, cranked, BOOM!
Such an idiot I could have found this so much faster but a few things sent me on a goose chase. Especially when I used a screwdriver to short the solenoid and it started clicking (on/off/on/off) it should have been enough for me to work it out - but I thought not enough current to solenoid again, my assumption of what the problem was was blinding me to the facts.
What was happening with screwdriver test was the main supply was collapsing voltage when the solenoid engaged and the starter tried to draw current, which then let go of the solenoid, and then repeated the cycle again as it re energised when the solenoid was open again. GRR! This didn’t happen cranking from the ignition as it took 12v from the starter relay via fusebox, which didn’t have high resistance, so could hold the solenoid energised!
So yeah, of anyone needs help reading the circuit diagram or fuse box checking, I’m you’re man now- but if your starter not working , check your volts on both solenoid and main drive when cranking. I really thought I was weak solenoid, totally wrong. Goon. But done now
Edited by stuthe on Sunday 31st March 22:55
on Sunday 31st March 22:55Well done! I was trained using multimeters (AVOs back then in the 1980s) and have used them regularly since, but they can't find out everything. They only draw a small current (by design) when measuring a voltage so if there is a weak part of a circuit that causes a collapse in supply, It can't be replicated by the meter alone.
Similarly, only a small current is suppled (I use a digital Fluke these day) to check circuit resistances, so only by investigated an entire current path can sort it, which can be tiresome. But rewarding when you suss it. 
Similarly, only a small current is suppled (I use a digital Fluke these day) to check circuit resistances, so only by investigated an entire current path can sort it, which can be tiresome.
But rewarding when you suss it. stuthe said:
said: Back to battery. Probe on a few places and it shows the voltage drop was across the starter/alt wire into the terminal… took it apart and very corroded inside. Drilled it out, reconnected, cranked, BOOM!
Would you mind expanding on this bit to make it clearer where and what you are doing please? My Tuscan was getting sluggish on the standard starter, so I upgraded to the 1.7kW starter and now all is good, but if this area needs possibly checking on mine, then it's worth looking into.
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