I bought a roller 1998 Z28 without the engine and trans. I found out yesterday that the harness had plugs on it that connect to the dash and ecu that makes the gauges works. My question is, is there any way to get the instruments to work if I’m not using the factory ecu and engine combination?

 

Has anyone experienced similar issues??

 

This site is not what it used to be - 100,000+ members, but less than 10 who check in regularly and try and help. This is not a question I've seen in the 20+ years on this site.

Let me see if I can get the PCM/electrical engineering wizard to take a look at this.

@GaryDoug

 

Ok thanks I appreciate any info I can get on this topic

 

Your 1998 dash gauges get their data from the PCM using a data protocol called VPW.

What ECU are you using? If it’s just another GM factory PCM from some other Gen3 V8 (any variant of the P01 or P59), I believe those all “speak” VPW and should pretty much just work, although some minor repinning might be necessary depending on which PCM you have now.

On the other hand, if you’re using an aftermarket unit like the Holley Dominator, Fast XFI, Haltech, Motec, etc, then you need something that can translate from whatever outputs you have available to a VPW signal, and I’m not aware of any such commercially available device.

You do have other options, though. Some people keep the factory ECU, feed it data from redundant sensors, and hook it up to the dash. If you don’t mind the redundant hardware and wiring, this is a pretty straightforward option.

Most aftermarket ECUs have a CANbus output that carries all of the data you need, and many also have digital and/or analog outputs you can configure with any data your ECU has access to. Usually there’s an aftermarket digital dash kit (Google for “aftermarket digital dash” — there are lots) that’s compatible with whatever ECU you’re using, or you can get a filler panel like this one from Classic Dash designed to replace your existing gauge cluster, pre-cut with holes for a number of aftermarket gauges.

If you’re so inclined, it should be possible to build a translator box with with an Arduino or Raspberry Pi, paired with a LOT of time spent coding and debugging. I’m not aware of anyone who has even really tried this, let alone actually succeeded, but I believe it would be doable. This is not everyone’s cup of tea, but AFAIK this is the only way to feed your stock gauges from an aftermarket ECU. I’m a software engineer with most of the right skills, and I have friends who could fill in the blanks. I’ve toyed with the idea of someday getting an aftermarket ECU, and this is the option I gravitate towards.

 

The 93-97 cluster gets the following from direct wired sensors - fuel level, oil pressure, coolant temp, voltage. The speedo/odo are driven by the PCM 94-97. I believe 93 may be driven direct from the VSS, with some sort of buffer(?????). Or 94-97 put something like the Dakota Digital speedo calibrator may allow you to convert the VSS pulses to the correct speedo/odo input pulses. 93 tach is driven from the coil with a filter in the circuit. 94-97 gets RPM from PCM. But might be a workaround.

But….. I don’t know if the 93-97 cluster is dimensionally interchangeable with 98-02 cluster.

The factory service manuals for most years, with wiring diagrams and pinouts are available to download (free) courtesy of GaryDoug:

https://www.mediafire.com/?40mfgeoe4ctti

 

I used a Dakota Digital interface to connect my TH400 with a late model GM truck VSS to the stock speedo in my 94 Formula. A much older model than this one:

https://www.dakotadigital.com/index....od/prd1192.htm

But even though I was running the engine with a MoTeC M48 Pro, I kept the factory PCM to pass the speedo signal through (along with a few other data functions).