free hit
agk - The Lotus Forums Jump to content


Basic Account
  • Content Count

  • Joined

  • Last visited

Community Reputation

3 Neutral

About agk

  • Rank

More Info

  • Name
  • Car
    1995 Lotus Esprit S4s
  1. I want to thank everyone for your help with this issue! The speedometer finally started working, and I finally had a long enjoyable ride knowing what my speed was Trying to recall what I could have done to fix this issue, I realized that while doing all the measurements and taking the J2 plug from and back into the ECU, I noticed that the very J2-B8 connector pin was a bit shorter that the other pins. I'm not sure what could have caused this: perhaps, once when inserting the connector back in, I pressed a bit too hard on it. So I gently pulled this pin back out - to make it the same length as the others. After that I didn't drive the car immediately and carried on with my measurements. Today I put everything back in and decided to take the car out for a ride. And to my pleasant surprise the speedo started working at last, and I had a very enjoyable ride. Even though your great advice here didn't directly come handy, I will sure keep it in mind should a similar trouble occur in the future, now knowing much more about diagnosing such problems. Thanks very much again!
  2. Derek, thank you, I followed your instructions to check if the orange wire is short to the ground. The reading is infinite, so there is no short.
  3. Barry, yes, that's what I'm trying to come to: confirm I need another ECU, then get it and try it. What's the proper way to check if the Orange (Signal) wire from the speedo is not shorted? Yes, I used Freescan multiple times, and it shows speed reading: as I rotate the rear road wheel, I manage to get up to 4 mph reading. However no speed at the speedometer still... Derek, I in fact did all my measurements first with the speedo wires disconnected from the speedometer. I'll double check reading at B8 (when wheels are stationary); should the other wire (from multimeter) be connected to Ground? When rotating the road wheel by hand, I tried both slow and fast rotations (the best I could anyway). So, as you see, it was enough for Freescan to show speed (and it showed all settings in that range: 1, 2, 3 and 4 mph). But not for the speedometer: none of the wheel rotations produced any noticeable movements of the needle (of course I couldn't be totally sure: maybe there were some tiny movements, but my eyes could see none). Re: Freescan, I even asked Andy W. (Freescan creator) about how his program reads the speed setting / at what points / where from. I thought he would point me for example to B8 pin and another pin, or some internals. But all he said was that Freescan simply reads the data stream from ECU, and said my continuity testing methods may be wrong (that's why I brought up this subject here again). Thanks very much again for all your help. With all this, are we coming to the consensus that I need another ECU?
  4. All, thanks very much for your latest advice! My latest results: Continuity of Signal wire from ECU to the speedo checks OK (my multimeter is in Continuity mode by default). Voltage between Ignition and Ground wires at the speedo is 12V DC. The Ground at the speedo checks OK (against a good ground point). Last puzzling piece (and this is where the problem may be) is: mindful of Derek's and Barry's advice, I tried to measure voltage in the Signal line - by slowly rotating the rear wheel and trying to see if there would be any small fluctuations of voltage (pulses) (as Atwell advised), with ignition On, all speedo wires connected to the speedo: - between Signal and Ground wires at the speedo: regardless of the rear wheel movements (slow this time) it showed 12V DC! I tried to rotate the rear wheel slowly many times, but I couldn't see any discernible movements of the needle; - between Signal wire at the speedo and the wire connected to J2-B8 pin at the ECU; no voltage shows (stays at 0), again - no movements of the needle when rotating the rear wheel. (with the above, I tried different voltage scales, starting with the smallest hoping to see needle movements (if any) 'magnified'). I didn't bother driving the car with the multimeter connected, I thought the above would suffice. Also, Barry implied that multimeter reading on this signal would not give anything meaningful (and I don't have an oscilloscope). Please advise as to what the above indicates (I guess: no pulses are sent from ECU to the speedo, despite that line's continuity), and what else can be done here.
  5. Hi Barrykearley, Re: your post: "Signal I believe is a pulsed signal. You would need an oscilloscope to make sense of this signal. You should be seeing 12v on the on other pin and GND on the remaining one." I measured voltage between Green (Ignition) wire and Black (Ground) wire at the speedo to be 12V DV consistently (the wires temp. disconnected from the speedo, ignition On). Is it what you meant by "the other pin"? Measuring voltage between Orange (Signal) wire and Ground didn't make sense, but you already said it can be properly measured only with an oscilloscope. Would it be the only way to test that Signal wire?
  6. Hi All, I'm questioning whether I properly checked continuity of all 3 wires that go to the speedo. Can somebody please advise on a proper procedure? I used a new multimeter for my continuity testing. Part of the trick is that it's a 3-wire-speedo, - but only 1 output port on the ECU?. 1 direct connection - between ECU's output J2-B8 and the speedo's Orange wire (Signal) - can be tested directly (I still hope using a multimeter for this purpose in Ohm mode is right). I'm more concerned about the other 2 wires - Green (Ignition) and Black (ground): they don't go to the ECU: I thought checking the Ground would be as simple as testing continuity between the Black wire (at the speedo) and a known ground point, say, at the engine block or intake manifold. I'm not sure how to check continuity of the remaining wire - Ignition. The wire from the speedo goes to Splice A... Last but not least, I suppose all continuity testing is done with Ignition Off. Please kindly advise, thank you.
  7. Thank you all for your helpful answers, for confirming what each wire is for. I believe that's what they used at the speedo repair shop - an oscilloscope - to check the gauge. It's kind of funny: I wrote to Caerbont earlier, back when I thought my speedo was faulty, asked them, they said they have a new one. Then my speedo checked out to be working, so I didn't pursue getting a new one. I suppose I'll write to them again, asking more details about how this 3-contact Caerbont speedo works... On a separate note, and this may be a dumb question (apologies for that), but: what would happen if I connect the correct wire (one of the 2 that lead from VSS to ECU), bypassing the ECU, to the output J2-B8? I wonder if the speedo would work in that case. I realize this may be naive, only based on the assumption that the ECU simply passes the signal through and does nothing to it inside. Does anybody know what happens inside the ECU between inputs J3-C2, J3-C8 and output J2-B8?
  8. Hi All, I have a question on a slightly different note: this Caerbont speedometer has 3 connectors. Generally they should be Signal, Ignition and Ground (or so I read). On the schematic/diagram in the Service manual/Electric section (Eearly cars, sheet S3, or Revised harness cars, sheet 14), I see the speedometer has 3 wires coming to it: 1) ON (Orange?) - goes to the ECU (terminal J2-B8) (that's the connectivity that I measured). So it's only 1 wire - ON - that connects the speedo with the ECU. 2) G (Green?) - goes to Binnacle splice A. 3) B (Black?) - goes to Binnacle splice D (earlier cars) or G (revised cars); I believe this one goes to the ground (negative post). Can somebody please explain how these 3 wires work / the function of each? I take it ON would be Signal, B would be Ground, so that makes G to be Ignition. And are there any additional continuity tests that should be performed on G and B? They go to the splices that unite wires from other circuits/components all of which seem to work OK.
  9. Atwell, thank you very much for providing more details, and thanks to everyone else for your help here. Alas, I can't attend the Lotus meet this weekend. The odometer (being a part of the speedometer) doesn't receive the signal either. However, when the speedo shop tested the instrument, both the speed needle and the odometer worked. So the least I can and will do for now is - I'll try to get the ECU out, open it and inspect it for any damage signs.
  10. I tried both combinations advised - with a paper clip: 1) connected B8 to B14; 2) connected B8 to B16 (I've put the paper clip on the smooth - female - side of the connector, bent it to reach for both pin holes, cut it to the right length in both cases, gently re-installed the connector/plug back into its place). In both cases Freescan showed the speed, but the speedometer still didn't. So what does that indicate and what should I try next: take out the ECU and open it? Please let me know your thoughts, thank you.
  11. Derek, thank you, but, sorry, how do I swap/invert pins on the ECU?
  12. Hi Filip et al, thank you for your advice. I just found - by rotating the r.h.s. rear wheel by hand (and blocking the l.h.s.) - that Freescan registers the speed up to 3 or 4 mph! So I guess that means that the ECU 'sees' the signal, but - doesn't transmit it to the speedometer. (and BTW the VSS on my car is new). The speedo itself is original, it's a Caerbont unit. I made sure (multiple times) the wiring is connected correctly (both in sync in how it was on the car before the speedo started misbehaving, and in sync with the schematic in S3 chart). So what do you think the problem may be now, and how can I diagnose it further? I was advised to take the ECU out and inspect it - for bad soldering, mini-cracks... Could it be that the ECU itself is faulty (and if so, in what sense? it's just the speedo that isn't working; the rest of the car systems seem to be working OK), and if so, what can be done about that? Please advise, thanks very much for your help.
  13. Filip, thank you. Well, first, I checked continuity between VSS (speed sensor) and the ECU. Now, how do I exactly check what you are suggesting - that the ECU sees the signal (from VSS)? It sounds like you are implying I should run Freescan when the wheels are rotating? That could be achieved by either 1) driving the car and having a laptop with Freescan hooked up (unfortunately I can't do that since I don't have a laptop), or 2) as Derek suggested, jacking up the car and running the engine in 1st gear (that I can do since I have a stationary PC with Freescan). I still don't feel comfortable enough to do the latter, but perhaps I'll finally get to doing it - or trying to rotate the wheel by hand - to see if the speedo in Freescan reacts to that. I tried the latter only to check that there is some small voltage on the VSS contacts (that's 'the beginning of the line'). I also know there is no signal at 'the end of the line': the speedo doesn't receive the signal (even though I had the speedo itself checked by a speedo shop so I know it's working). And also there is continuity between the ECU and the speedo. So it feels like something inside the ECU is either not getting the signal from VSS, or getting it but not passing through to the speedo. Anticipating the outcome, what would be the causes in each case: 1) if Freescan doesn't register speed? 2) if it does? Please advise.
  14. Barry, exactly that happened to me - the VSS threw the code 24. So I ended up replacing the VSS with a new one. No code 24 anymore so far; I guess the old sensor was somehow bad. Derek, yes, I thought about that and actually, with the wheel taken out, tried to rotate the brake disk and saw a multimeter register some small voltage upon rotation. However I measured it only on the VSS contacts. So the next question is: where should I measure the same voltage (when rotating the wheel) on the ECU? The input contacts there are J3-C2, J3-C8. The continuity between them and VSS checked out. The output contact of ECU (towards the speedo) is J2-B8, the continuity between that and the speedo checks out as well. However, as I come to think of if, I never measured the voltage between the output contact (J2-B8) - and the ground, I guess (when rotating the wheel); is that what I should try next? BTW, thanks very much for replying.
  15. Hi Derek, thank you for replying. I thought that too, but the S3 sheet diagram may have some inaccuracies (in general) re: S4s, for example it has a tachometer amplifier that S4s doesn't have, as far as I know... I checked the signal continuity everywhere I possibly could - in the speedo-related wiring/circuits. I guess what you are saying is that I should try to run Freescan while driving (that is, when the rear wheels are rotating) to see if it it 'registers' the speedo, that is, the latter shows non-zero speed; is that what you meant? I'd like to be able to do that, but it may be a problem at the moment: I don't have a laptop, only an old PC with a serial port (via which I connect Freescan), hence I can run it only when the car is stationary. I was advised to try to run the wheels (with the car's rear being up on the stands) with the engine on and at low speed, but I don't feel comfortable doing that yet. Are there any other ways to diagnose this kind of problem? I was told I should get out and open the ECU to try to see if there is any soldering going bad, any (microscopic) cracks etc.
  • Create New...