Resolved 2G Diagnosing no rpm signal

[v8s_are_slow]

No rpm's on the gauge. Had a spare cluster so I swapped out that portion of it. Swapped ptu's and still nothing. Rpm's read in ecmlink.

Not sure what else to check for other than at the ecu. Would I just back probe pin 58 and test for 5 volts, a varying voltage, or what am I looking for exactly? Anything else to test for? Trying to knock out these last few gremlins to get the car track ready. Thanks!

 

[9 T GSX]

Did you test/look at the VSS on the transmission? That could have gone bad, Easy fix if that is what the problem is. Might want to pull it out to make sure the plastic wheel is still in good shape. Perhaps the plug came unplugged a bit?

 

[v8s_are_slow]

Did you test/look at the VSS on the transmission? That could have gone bad, Easy fix if that is what the problem is. Might want to pull it out to make sure the plastic wheel is still in good shape. Perhaps the plug came unplugged a bit?

I did not. Thought that was just for speed???

 

[TSiAWD666]

RPM for the gauge cluster comes from the PTU, and the VSS has nothing to do with it. Perhaps your PTU wiring harness is damaged, not fully seated, or the wiring from it to the gauge cluster is. Maybe check connectivity from the PTU rpm output wire and the connector for the gauge cluster. I can't remember which is what so you'll have to do some digging.

 

[19Eclipse90]

I'm not certain what the signal is supposed to be (5V?) so I would pull the plug from the ECU and check continuity between pin 58 and pin 24 of C-05 (gauge cluster) to ensure the wire is not broken.

 

[v8s_are_slow]

Thanks y'all. I'll be taking a look and report back.

 

[steve]

I think you're on the right path checking the wiring from the PTU to the ECU and Cluster.
The ECU doesn't use the signal from the PTU for RPM, it has the Crank and Cam Angle signals for that. It uses the PTU signal for diagnostic input, like is the coil firing when it tells it to.

 

[v8s_are_slow]

I'm not certain what the signal is supposed to be (5V?) so I would pull the plug from the ECU and check continuity between pin 58 and pin 24 of C-05 (gauge cluster) to ensure the wire is not broken.

Are you meaning E-37 for the Tachometer? I was doing some searching to figure out which pin this is (so I'm not totally being spoon fed) and found the diagram for the back of the cluster. C-24 is for the coolant light.....if that's what you were meaning.

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[steve]

The connector is C-05. Not sure where they got their naming for that diagram as useful as the image is.

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[v8s_are_slow]

Okay, I'm not sure which side connects to the pin at the ecu. Not sure if I have a bad plug or if it's working and I'm just probing the wrong hole out of the two choices I have here.

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[19Eclipse90]

How to identify ECU pin numbers

It looks like the pin that has continuity is the correct one. So, from here, does pin 4 of the PTU have continuity with either of these pins (pin 58 at the ECU or pin 24 on C-05)? Also check that pin 4 on C-04 is providing a good ground.

 

[v8s_are_slow]

I haven't had a chance to check that and would need to get some wiring long enough to reach with a probe or something that could stay in the pin while doing the check so I may have to get back to that. But I'm looking at the back of the cluster and I'm not so sure about the circuit board/paper that they made this thing out of. The arrow to the right is actually a cut about halfway through. I'm wondering if that could be the fault and maybe run a wire with a connector to go under the bolts to make the connection being that there's a split there. There's also a split at the arrow on the left but unsure if that even goes to anything at all. The circle looks like a bit of corrosion or something there. Not sure what that even does. They could've made this a bit more "quality" in this regard, but it is what it is. The cuts might be a bit difficult to see in the picture but they're there. Almost as if the plastic is getting brittle over time and just splitting from the edge and working inwards.

I looked at my other cluster and the board/plastic on that one is absolutely terrible so I can't use that one at all. Right now, I'm leaning towards this being the issue, so I'll have to do something about this and report back I guess. Appreciate the assistance on it though.

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[19Eclipse90]

That's more or less what we're leading up towards. If the wiring ultimately checks out, then you're left with the components in the system. We've simply assumed that it would be unlikely you had two bad clusters.

I'm pretty certain you could check continuity from these two bolt heads. If you don't get it, then the tear could be an issue.

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[v8s_are_slow]

Funny you should mention that. I thought of doing just that after I made that last post. I had continuity there. Just hadn't had time to post back yet because I was working on replacing my door handles with the metal ones I had ordered. So guess I'm back to the drawing board and checking for continuity in the other locations. But if that's good, I'm really not sure what else to check for.

 

[v8s_are_slow]

I'm not real sure what pin 4 at C-04 is but I'm assuming it's the one I'm pointing to. I only say this because I tested a few and this is the one that made my meter beep when testing for ground. Other than that I just need to test the wires for ptu. I'll get on that asap.

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[v8s_are_slow]

So I have continuity at pin 58 at the ecu, to pin 4 at the ptu. Guess that rules that out. And have continuity at pin 58 to the pin here in the picture if that's correct. 4th one down. Assuming there's really nothing else to check other than just getting a new cluster all together???

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[DSSA]

Check the wiring/fuse continuity at the fuse block inside the car as well. I seem to remember we had a car in at one point with a similar issue and there was an issue with the fuse block as well.

 

[v8s_are_slow]

I purchased another gauge cluster today just for the heck of it. Should be here tomorrow so if that doesn't fix it, guess I'm back to square one again. Not sure what the odds are of the ecu being the cause of this. I've been searching and searching but haven't seen any mention of this being the issue anywhere. Everything has been checking out so far though.

Not sure what to really be checking for at the fuse block but I'll take any suggestions. This is the only thing that'll keep me from the track right now.

 

[19Eclipse90]

There's the PTU and the wiring on the "feed" side of the PTU that could still be suspect. Assuming an operating coil, you should see continuity between pin 3 of the coil (black w/ white) and pin 6 of the PTU (also black w/ white). That's probably the easiest check. I don't believe the noise condensor / capacitor missing would cause this but it is on that circuit so it might be something to check.

The 2G PTU is acting the same as the 1991-1994 PTU, the test procedure for it is below. It leaves out pin 4 in any of its steps which is a bit concerning as that would be the pin directly tied to the tach. But it's something...

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Past that, I don't see anything in the manual suggesting test procedures for the tachometer itself. Many of the other gauges have some procedure laid out, this one simply says check at the speed detection connector in the engine bay which does nothing other than to say that if you can read it there, the tachometer might be bad.

 

[v8s_are_slow]

So I tried the new cluster that came in today. Still nothing. $80 wasted but at least I feel better about that not being the issue.

I'll test that ptu test when I get a free moment. But as for testing those wires at the ptu, I wanna make sure I'm testing the right ones. I didn't get any continuity there. Also, I have coil on plug. No stock coils if this makes a different.

Can't wait for the day I blow a tire and I can see that it's flat. It'll be the only and only issue with this car that'll be easy to diagnose.

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[steve]

Did it ever work with the COP? I assumed that the tach was working and then stopped.
There is no guarantee that the PTU's internal circuit to generate the tach signal would work with anything other than the stock coils.

Are the ends of the PTU connector broken off?

The PTU connector (A-92) pins are:
1 Blue/Black Coil B (Coil pin 1)
2 Brown/Red ECU Coil B (ECU pin 23)
3 Black Ground (#3)
4 White Tach Signal (ECU pin 58, C-04 pin 24) * This one *
5 NA
6 Black/White +12 (Larger wire)
7 Black/Blue ECU Coil A (ECU pin 10)
8 Black/White Coil A (Coil pin 2, A-59 pin 1 Blue/Red at Coil)

 

[v8s_are_slow]

It was working. But then started getting lazy and so I had to take the clear cover off and hit the needle and it would bounce up and start working. But now it's just dead. I'll have to check the continuity of all the wires from the ptu plug to the ecu and report back....again.

P.S. The car runs just fine. Just no tach. That's my only issue.

 

[TSiAWD666]

The PTU will generate the tach signal for the dash even when connected to other non-oem coils.

 

[v8s_are_slow]

The PTU will generate the tach signal for the dash even when connected to other non-oem coils.

Right. Just not sure where to be checking in that regard. I just know to check wires for continuity from the ptu plug to the ecu and that's about all I know. I HATE trying to figure out electrical issues.

Wondering what role the ecu plays in this and if it could be an issue or not. Just trying to think of all possibilities.

 

[19Eclipse90]

As mentioned, the FSM does not provide a test for the tach generation signal, only what is shown above. I'm not certain what the ECU does with the tach signal but it would reason to say it shouldn't matter since the signal is coming from the PTU.

Checking the "feed-side" wiring is a little cumbersome and time-consuming, but it is free. Pin 6 (black w/ white) of the PTU should have continuity with pin 3 of the stock coil connector (also a black w/ white) but should also have continuity with the noise capacitor connector if it is still there. I realize you said C.O.P. ignition but also that it worked before. But somehow that is using the same "source" wires as the stock coil, are they not? Since it was working at some point, verifying this leg of wiring from PTU to coil would be enough to rule out the rest of the "feed-side" and point at the PTU, assuming I'm correct about the ECU. --- Edit: I see that this matches with what Steve said above in post # 7.