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Z28 Cluster Calibration? vs Ultraguage OBD2 Tool

5K views 21 replies 6 participants last post by  k gee 
#1 · (Edited)
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?
 
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#2 ·
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.
 
#5 ·
Replied in bold

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?
 
#3 ·
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?
 
#7 ·
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.
 
#8 ·
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.

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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#11 ·
Is the Caprice and Impala the same pin-out for the cluster and more specifically is there a difference between 94-95 versus 96?
Look at it this way. 96 Impala had a non standard (not digital) speedometer cluster. The car wiring and the cluster are wired different that 96-94 Caprices and 95-94 Impala.

This went with the 96 only column and floor shifter.

Any time you work on a 96 Impala cluster you need different plug diagrams.

I expect the guys making the Z28 kits hated a 96 Impala order as the wires in the left/right plugs were all different.
 
#15 ·
96 PCM vs 96 Impala PCM

I can only quote Gary. 96 Impala PCM was the only one programed for 4 cylinders.
Your PCM may have been copied from one?

Gary Meier was nice enough to get right back to me with this reply:

The factory tach signal output of the '96 Roadmaster is an 8-cyl output from the PCM. The '96 Impala SS is the odd-ball with the 4-cyl tach output from its PCM.

I have seen two issues over 10+ years of building Z28 Clusters regarding tach signal output from PCMs.

The 3rd Z28 Cluster I ever built and installed went into a '96 caprice 9C1. It should have had an 8-cyl tach output (being a non-'96 Impala SS). We found the PCM in this '96 9C1 had its PCM reprogrammed (improperly) sometime earlier using the base code from a '96 Impala SS (resulting in a 4-cyl tach output from the PCM…and the Z28 Cluster's tach needle looking way off). We had the PCM programmer correct the tach output back to 8-cyl.

I did have one recent occurrence of this in a '96 Roadmaster, and that was also due to his PCM programmer using the '96 Impala SS base code. He elected to install a tach divider to solve his issue (that was way cheaper than paying his programmer another $250 to reprogram his tach output).

Gary

81X11 Posted
The Link:

http://www.impalassforum.com/vBulletin/26-electrical/244602-z28-camaro-cluster-2.html

Post #12

The gauge problems should be resolved before chasing programing if you do not have a programmer.
 
#16 ·
#17 · (Edited)
Alex at PCMPerformance may have used a 96 Impala SS as a base for my 96 Caprice PCM.

Good thing I'm getting my PCM redone soon, hopefully this fixes the problem with the tach and mph.

I feel a little better about that, now to just figure out the potential grounding issue so I can stop the CEL code and be able to pass Cali smog without swapping out the cluster every 2 years.

I have a feeling the plugs aren't staying into the connector firmly enough, I wish I could screw them in from the sides. Maybe I can zip tie it somehow.
 
#19 · (Edited)
I've installed 3 Z28 clusters and have never had to modify anything on the circuit board on back of the Z cluster. I run a Z cluster in my 94 Caprice.Only mods outside of having a correct cluster harness made are the oil pressure sending unit,picking the tach signal from red plug/pin A13 @ pcm,and removal of the inline resistor for oil press gauge to read true.

I've installed a Z cluster in a 95 Impala SS and a 96 Impala SS. As Z09B4U stated,the 96 SS uses a 4 cyl tach signal which the pcm needs to be programmed to an 8 cyl signal. Also for 96 SS,there is no inline reisistor to remove above the glove box.For these 2 installs I did,the owners supplied the cluster conversion harnesses.
I made my own harness when I did this mod on my 94 Caprice.

In all 3 installs,the gauges all worked well and were reading what we could call normal and or accurate.Excluding the 96 SS tach of course.

I really like this mod in my 94 Caprice.I've put approx 2,500 miles on her since doing this mod no issues at all.

Jim
 
#21 ·
I ended up figuring that out last week....tried it and now I have 3 different speeds lol. Now I'm wondering if Alex put me in at 3.08 gears (I have 2.93, but going to 3.73 when I swap to disc), so my PCM just needs reprogrammed I hope.
 
#22 · (Edited)
Here are some pictures of the harness. My PCM always triggers a code, but the CEL only comes on sometimes....but I notice it depends on how the left side (shortest harness) is laying, because when I move the wires, the light will come come on and stay on in a certain position.

Does anything look obviously miswired?
The 4th and 5th pics are of the left side plug, C1. I suspect B3 because the Service Engine Soon light goes on/off when I move it.


Also found out the speed on the Z28 cluster is correct and it's the Ultraguage that's off. Can't figure out why, so oh well.
 

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