Z28 Cluster Calibration? vs Ultraguage OBD2 Tool - Chevy Impala SS Forum
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post #1 of 22 (permalink) Old 04-16-2017, 08:54 PM Thread Starter
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Z28 Cluster Calibration? vs Ultraguage OBD2 Tool

I've installed a Z28 cluster and most of my gauges read different from my Ultrgauge that plugs into the OBD2 port.

Speedometer reads 40mph, but scanner reads 35mph.* Note PCM is modified, and calibrated to a different size wheel/tire combo, but is one of these speeds right? At 65mph the scanner reads about 57mph.

Tachometer reads about 350 at idle in park when the scanner reads 700 (always seem to be about half). At cruising speed of 35mph the cluster reads 700, but scanner reads 1400. Seems like on this one, the scanner reads higher.

Coolant Temp reads about 10-15 degrees warmer on cluster compared to scanner.


I've noticed that my coolant temp and voltage needles seem to get "stuck" sometimes and eventually self adjust, but are they correct? I'd tend to believe the Ultraguage, but would like to use my cluster and only reference the scanner.

Scanner matched the speedometer in my 96 Buick RMS exactly, so I'm wondering if I can recalibrate my Z28 cluster somehow or if I bought a bad one or if it's the wiring harness (I have getting a P1661 code, but I think that's just a bad bulb, because I've never got this code before when I had the digital OEM cluster in my Caprice) and I'm not getting a CEL on the cluster now (I have in past on this cluster, but not anymore).


Ideas?

96 DCM Caprice B4U
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Last edited by k gee; 04-16-2017 at 09:06 PM.
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post #2 of 22 (permalink) Old 04-16-2017, 09:39 PM
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First the easy questions. The temperature and voltage gauge are separate from the PCM.

The voltages can be different. Tell us how different?

The temperature sensors for the PCM and gauge are in very different places. It is well documented on the forum that under different conditions the temps will read different from each other.

Gauges sticking? You are going to have to be very descriptive.

RPM differences did you reprogram the PCM and use a real V8 cluster?

Speed difference: does the scanner agree with a GPS. You need to know which one is wrong to sort out the issue.

MIL lamp error could be a lamp or a open or shorted wire. If it has not worked since the swap you may have a wiring issue. Do you want to wait till the PCM is damaged?

All issues could be a bad cluster grounding problem.

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post #3 of 22 (permalink) Old 04-16-2017, 09:55 PM
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From what I understand the Z28 cluster is not a simple plug n play item as there is a small mod that needs to be done first. Don't know the exact details but have you done anything to it or when you bought it was there claim to have the mod done already?

1996 DGGM Impala SS
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post #4 of 22 (permalink) Old 04-17-2017, 02:19 PM Thread Starter
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First I've heard of that. It was sold under the idea that it was plug and play with the custom harness, even had it changed to the correct odometer reading.

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post #5 of 22 (permalink) Old 04-17-2017, 02:27 PM Thread Starter
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Replied in bold

Quote:
Originally Posted by Z09B4U View Post
First the easy questions. The temperature and voltage gauge are separate from the PCM.

The voltages can be different. Tell us how different?
Ultragauge will read 14V, but cluster shows between 8 and 18, with what I'd expect halfway to be 13, and it's reading closer to in between 18 and 13, so to me it looks like it's reading 15-16V.

The temperature sensors for the PCM and gauge are in very different places. It is well documented on the forum that under different conditions the temps will read different from each other.
That's fine, temp and voltage aren't a huge deal to me right now.

Gauges sticking? You are going to have to be very descriptive.
They will drop to below the range of the gauge, and seem to have trouble popping up when the car is started. I had to take off the clear lense and manually move the temp gauge and make sure it was "popped" on.

RPM differences did you reprogram the PCM and use a real V8 cluster?
I did not reprogram my PCM for this new cluster, did not think I had to, assumed it just took the reading for what it was. It is a V8 cluster.

Speed difference: does the scanner agree with a GPS. You need to know which one is wrong to sort out the issue.
Don't have a GPS, but was going to have a stock vehicle drive next to me at 40 on cruise control and match that in my car

MIL lamp error could be a lamp or a open or shorted wire. If it has not worked since the swap you may have a wiring issue. Do you want to wait till the PCM is damaged?
Definitely don't want the PCM damaged. This thing has been a nightmare ever since I bought it from Billy Miller. Avoid him at all costs. And this morning I got a "Check Engine Soon" light that went off after 15 seconds after starting car.

All issues could be a bad cluster grounding problem.
Any help on how to best check this?

96 DCM Caprice B4U
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post #6 of 22 (permalink) Old 04-17-2017, 02:33 PM Thread Starter
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Pic for reference.
Note RPM on Ultragauge shows 626 and cluster reads about 300 in Drive and foot on brake.
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Last edited by k gee; 04-17-2017 at 02:37 PM.
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post #7 of 22 (permalink) Old 04-17-2017, 02:49 PM
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From a professional vendor a Z28 cluster for a B-body will have these features:

Custom wire cables pined for a 94-96 Caprice OR a 96 Impala.
The cluster will be selected to work with the B-body.
There will be modifications made to the cluster's circuit board.

The installer will have to reprogram the PCM's RPM output or a extra circuit will have to be patched into the new RPM line from the PCM.

This is from memory so anyone is free to correct me.

Any scan tool reads values from the PCM. It does not always read what it sends out.
You have taken the gauges from a different type of car and as a result the oil pressure and temperature gauges may vary as they depend on the car's sensors and wiring.(not the PCM's sensors and wiring)

Most forum members like this mod.

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post #8 of 22 (permalink) Old 04-17-2017, 04:04 PM
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I am going to take the questions out of order again.

The 4 cylinder tachometer issues is only with the 96 Impala SS's. The 96 Caprice's PCM tach output is a standard 8 cylinder output. If the issue was dues to that the tachometer would read double of the actual speed. I would double check to make sure you ran the wire to the correct position. It could also be a problem with the cluster itself. - Peter(pcordes1979)

So if you have a stock 96 Caprice PCM Peter says it is plug and play.I found that Gary Melier says the same and he made many.

Voltmeter from a cold start could go up to 15V. Running warm the gauge is about the same as my car.

Quote:
Gauges sticking? You are going to have to be very descriptive.
They will drop to below the range of the gauge, and seem to have trouble popping up when the car is started. I had to take off the clear lense and manually move the temp gauge and make sure it was "popped" on.
I can only say what I know about most gauges. The Caprice cluster does not Drop to Zero when the key turns off. It usually stays close to the position it was last at. When you do a "cold start" and just turn the key to run the oil pressure should return to zero (engine not running) and temp should go cold (Cold start right!). Volts will read and Fuel should read.

If the temp/oil/fuel gauge is unplugged from it's sensor it will "pin" high and off scale.
If a gauge has it's ground removed it will "pin" below zero. This should not be possible if the gauge reads a value when running. As a guess you have a grounding problem. I think the gauges are getting a "feedback ground through another circuit" (I do not have time to explain this sorry). It would explain why the gauges zero. It may explain the tach as well.

First thing would be to pop the old cluster in and see if the gauges work normally.
I bet they will if they worked before.

If the old works, the next move is to get the factory book out and track down A6 in the right cluster plug(C2). Also B4(C2) and B3(C1 left plug)
The A6C2 is the suspect one and you will have to sort out for yourself if it is getting to the right place on the Z28 cluster.

See pics, thanks to the person that posted these! (I have not checked them for correctness).

I do not want to get between a buyer and seller!
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post #9 of 22 (permalink) Old 04-17-2017, 05:17 PM Thread Starter
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Thanks for the help.

I did follow Bob's 1FineCaprice write up for the install and put the tach wire into A13, so that should be good.

Oh the joys of a project car.

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post #10 of 22 (permalink) Old 04-17-2017, 11:13 PM
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Quote:
Z09B4U
Is the Caprice and Impala the same pin-out for the cluster and more specifically is there a difference between 94-95 versus 96?

1996 DGGM Impala SS
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