I am at my wits end here. I have a 1988 Pontiac Fiero coupe, converted to a lemons racecar. It was originally a really abused 2.5 Tech IV car, but I've replaced it with a L44 2.8 built up like my other lemons Fiero.
It has the correct ECM, correct 1988 V6 wiring harness out of a donor Formula. Everything is running and it's already run one event, but I still can't get power to the speedometer.
I first noticed this after the test drive. The Speedometer was dead. Completely dead. So I replaced the VSS wondering if that would fix the issue. It was still dead. Then I replaced the speedometer with one I knew worked. Still dead. It was then that I noticed there were no instrument lights whatsoever on the left side of the instrument cluster. I checked the connection at the back and everything was clean and secured. Still no power. The grounds on the engine are secured. The grounds in the engine bay are secured. The grounds under the center console are all secured. What am I missing?
I was thinking it was a speedometer ground at first, but now I think it's something else that's preventing power from going to that side of the instrument cluster.
Does anyone have any knowledge or wiring schematics specific to this so I can fix it?
Given I don't really look at the speedometer when I race, but since it works in the other car, I would really like it to work in this car as well.
Thanks
------------------ Owner of:
1985 Pontiac Fiero Sport now with 2.8 liter 4 speed M17 1986 Pontiac Fiero GT 2.8 liter 5 speed Muncie 282 1988 Pontiac Fiero Coupe ... TBA
Unplug all the connectors on the back of the instrument pod, (You remembered there are three plugs... right? One plugs straight in to the bottom of the speedo, from below.) and make sure none of the foil contacts on the printed circuit are bent or shorted. It can happen very easily.
Unplug all the connectors on the back of the instrument pod, (You remembered there are three plugs... right? One plugs straight in to the bottom of the speedo, from below.) and make sure none of the foil contacts on the printed circuit are bent or shorted. It can happen very easily.
Did that twice already. Switched between two different clusters too to rule out a bad cluster. Still no power. None of the dash lights behind the speedometer work, the speedometer gets no power
Checked the 10A Radio fuse back in the beginning. Is there more than one? I mean, there's a fuse missing from one of the slots in the fuse block now that I look again. But everything else seems to be there that's supposed to be there.
Keep in mind I bought this really abused heap for 400 dollars. The previous owner was not good to it.
Also, where exactly are all the grounds for the instrument cluster and speedometer?
Can you unbolt it all, but leave the wiring connected, and make measurements? If you rotate it toward you over the steering wheel, is there any slack there? You might be able to use a meter to check for voltage on the pads that the bulb socket goes into. Be careful not to pierce the plastic with the leads. Can you take the lamps out of left and right, swap them, and put them back in? Are you using LEDs? They have polarity.
Dash lights and other gauges get power from "board" on back of dash. Speedo has nothing to back. Only from connector on bottom.
All guages and some idiot lights get power from same fuse but some still works so fuse is good. Speedo get power from radio fuse
Light connected to dimmer... and some works... then likely a different problem. Loose/bad sockets or bulbs are common issues.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Dash lights and other gauges get power from "board" on back of dash. Speedo has nothing to back. Only from connector on bottom.
All guages and some idiot lights get power from same fuse but some still works so fuse is good. Speedo get power from radio fuse
Light connected to dimmer... and some works... then likely a different problem. Loose/bad sockets or bulbs are common issues.
I messed around with it yesterday once again and it's bizarre. I wiggled the dash bulb on the dead side and the light came on when I loosened the bulb, but went dead again afterwards.
As far as the speedometer is concerned I'm confused with that. When I first got the car, I hooked a battery up to it and the factory radio came on immediately. After ripping the interior out I'm worried that I may have neglected a ground somewhere.
Where specifically is the ground for the Speedometer located? Is there more than one?
speedo and ALDL pin A ground is in engine bay likely on the engine. Speedo Goes thru C203 below ECM on the way.
Speedo display can be dead and still send vss to ECM. If speedo is completely deed the ECM will set DTC 24 at random time while driving and get 0 mph while scanning but have a swap engine then VSS can be wiring in odd ways. Means Is possible VSS may work but Speedo can't see signal after the swap.
Dash lights socket and dash case plastics can deform from heat and contact pressure after 25+ years. Get new socket(s) and wiggle if need to get good connection. Should stay put after.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
speedo and ALDL pin A ground is in engine bay likely on the engine. Speedo Goes thru C203 below ECM on the way.
Speedo display can be dead and still send vss to ECM. If speedo is completely deed the ECM will set DTC 24 at random time while driving and get 0 mph while scanning but have a swap engine then VSS can be wiring in odd ways. Means Is possible VSS may work but Speedo can't see signal after the swap.
Dash lights socket and dash case plastics can deform from heat and contact pressure after 25+ years. Get new socket(s) and wiggle if need to get good connection. Should stay put after.
This is really good information.
The grounds on the engine are on solid. Also, at the last race the engine didn't throw any codes. This helps me narrow it down some more.
The swap is a straight 2.8 using a stock harness out of an 88 Formula. Maybe the donor harness has an issue.
Scan ECM jack a wheel and spin by hand as fast as possible while watch data stream for speed. Should happen in a few seconds.
If you get even 1 mph the speedo meter is bad and get another speedo.
If careful move odo or expect issues every time you get inspected or sell the car. You can change/replace odo legal but must say odo # is not = mileage on the car etc. Example: You title have a box to check basically real miles unknown etc.
[This message has been edited by theogre (edited 08-14-2017).]
Scan ECM jack a wheel and spin by hand as fast as possible while watch data stream for speed. Should happen in a few seconds.
If you get even 1 mph the speedo meter is bad and get another speedo.
If careful move odo or expect issues every time you get inspected or sell the car. You can change/replace odo legal but must say odo # is not = mileage on the car etc. Example: You title have a box to check basically real miles unknown etc.
I'll give it a shot. I don't think it's the speedometer unit itself though because I've already replaced it with a known working one.
I did switch the odometer out when I did that and set it into the new speedometer like I did on my other car.
Really don't need to, because in our state, after the car gets so old, they don't even record it on the title anymore. This car isn't even street legal anymore anyway after caging it and removing the e-brake assembly and other items.
I'll give it a shot. I don't think it's the speedometer unit itself though because I've already replaced it with a known working one.
I did switch the odometer out when I did that and set it into the new speedometer like I did on my other car.
Really don't need to, because in our state, after the car gets so old, they don't even record it on the title anymore. This car isn't even street legal anymore anyway after caging it and removing the e-brake assembly and other items.
UPDATE:
We took the car to the 24 hours of lemons race in Washington this weekend.
Speedometer was still dead. That is until, one of the inexperienced drivers spun the car hard in testing.
But means likely to come back w/o warning. ECM/PCM need speedo data for can set codes and hurt performance. Scan ECM next time to see if it get speed data.
