1988 GT V8 Swap Oil Pressure Gage (Page 1/1)
V8Steve AUG 18, 08:49 PM
I've (hopefully) read all the threads on this but cannot solve my problem. My V8 swap began in 1998 and ran for 25K miles with no issues until the ZZ4 seized and cracked the block in 2007. Then it sat indoors until 2015. During the rebuild I eliminated the C500 connector and cleaned up all the wiring.

So now, the new V8 is in and I'm having some ECU/EFI electrical problems. One of those is the oil pressure and I'm pretty sure the dash gage worked Ok a few weeks ago when I was cranking the motor and trouble shooting other startup problems. Since the 355 CI V8 was dyno tested (427 HP) I know it has oil pressure. To be sure, I installed a mechanical gage and it showed pressure while cranking.

To make the story short: I checked the single tan wire from the sending unit to the connector on the back of the gage circuit board. There is continuity. I bought a new sending unit but no improvement. I checked both the old and new sending units with an ohm meter and my air compressor set at 30 psi and both showed the same ohms at zero pressure and at 30 psi.

The parallel volt meter gage works and is on the same circuit as the oil pressure.

I'd really appreciate any ideas on this one.

------------------
88GT 355 CI Sequential EFI Bigstuff3 , AFR milled 180, Dyno'd at 427 HP
anderson@gdsconsulting.com

shemdogg AUG 18, 09:44 PM
Im having issues w my new gauges, im planning to run a new wire from the sender to the gauge.

shem
fieroguru AUG 18, 09:49 PM
Which sender are you using (some are for lights, some are for gauges)?
Is the wire going to the center terminal (if there are 3)?
V8Steve AUG 18, 11:06 PM
It's a 3 connector plug but only using the tan center wire. The new sender is a Delco unit and perfect match to what I believe is the original 88 OEM except for the NPTF thread size. Otherwise the plug is the same. To be honest, this startup with new motor and original BigStuff3 SEFI has been problematic with what we believe to be electrical. The oil pressure was actually working and I'm trying to solve this one aspect. Front battery to engine and block and chassis are 2/0 marine cables.
J Gunsett AUG 19, 10:16 AM
With the key on and you pull the connector off the sending unit, does the gauge peg high?
theogre AUG 19, 03:15 PM
Oil Gauge reads resistance, 0-90Ω, on Tan wire to ground.
Dash Gauges often have several problems not just wire from a sender.
Common issues... Gauge itself can be "Dead," Loose connections to sender, power and/or ground, resistor on back of gauge is loose/bad.

Gauge Resistors are only seen when gauge is remove from the dash. When you remove them Do Not tighten to much or can easily damage the resistor element.
Just loosen/tighten the stamp nuts a couple times to wipe away dirt etc often helps.

Clips connect dash back to bolt on gauge often have problems too. If you try to clean and mess up, can damage the dash back "board."
Big plugs on dash back often have same problems. Just removing/installing them can have problems like often copper looses glue to the board then bends and shorts out.

------------------
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)

The Ogre's Fiero Cave

V8Steve AUG 19, 10:12 PM
Good advice. Thank you. For now, I'm leaving it with a mechanical gage and copper tubing while I try to get this to fire up. The engine had over 20 dyno pulls with a carb but now I'm having a lot of trouble with the ignition and getting it to fire.

------------------
88GT 355 CI Sequential EFI Bigstuff3 , AFR milled 180, Dyno'd at 427 HP
anderson@gdsconsulting.com

darbysan AUG 20, 10:19 AM
Just a couple of thoughts that popped into my tired, old brain. I've seen issues where teflon tape is used to install the sensors. The tape can prevent a good ground. Also, if your sensor is 3 wire, one of them may be a ground wire.

------------------
'87 GT , '00 3800 Series II SC, 4t65e, Vue Power Steering. (SOLD)