LT1 No Start - Not Optispark
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Joined: Dec 2005
Posts: 98
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From: Titusville Florida
LT1 No Start - Not Optispark
Working on a 1993 LT1 that a friend owns. The car has been sitting for 4 years. The last time he drove it, the engine was running rough, and he determined it needed an optispark. So the car sat as he had other projects. About 4 months ago he started it and drove it around the driveway. The next day it would not start. We put in a new optispark and water pump. Engine turns over but will not start. We have power and spark at the coil, and plugs. We have no fuel pressure at the Schrader valve using gauge. We changed the fuel pump relay as two terminal were discolored, no start. Checked fuses in cabin and behind battery. Still no fuel pressure and no start. Changed fuel filter, no pressure. Found no power to fuel pump at the connection. We have power to fuel gauge in "run mode but no power to fuel pump wire.
I am using '95 service manuals and cannot find much to help. Also there are not diag codes (checked with Master Tech). The manual mentions an oil pressure sensor/fuel pump switch and a fuel pump module however, no locations.
Does anyone have any thoughts as to what we have missed or where to go from here.
Thanks
I am using '95 service manuals and cannot find much to help. Also there are not diag codes (checked with Master Tech). The manual mentions an oil pressure sensor/fuel pump switch and a fuel pump module however, no locations.
Does anyone have any thoughts as to what we have missed or where to go from here.
Thanks
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
There is a oil pressure activated switch that can act as a back up if the FP relay fails. When the system builds ~4 PSI, the switch should close and send power to the fuel pump.
Safety Car
Joined: Jan 2004
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OP switch is located at rear of the intake ( the larger 3 wire unit , not the 1 wire gauge unit circled in pic)
Should have 12V on one wire continuous ( ref your FSM , usually red or org wire )
Jumpering the two pump wires there should make the pump run assuming pump circuit supply fuses is good
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
On early cars, the power to the relay was from the same ( fusible link ) source as the OP switch.
IIRC ,
on later cars like yours the pump supply was split to give extra redundancy.
In any case you need a confirmed 12V ( key off ) supply into both the relay and the OP switch. With that , jumpering either unit should
make the pump run assuming everything else correct and working.
Have you tried power direct to the pump to confirm it builds pressure at the rail ?
You have confirmed the pump fuse is good ?
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Joined: Dec 2005
Posts: 98
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From: Titusville Florida
I have not applied 12 Volt power to pump yet, as I still do not have 12 Volt power coming to pump when key is in run or start positions. Need to find out why no power to pump. Have checked the fuse in panel behind battery and it is good.
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Joined: Dec 2005
Posts: 98
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From: Titusville Florida
I am not sure how to check for power to fuel pump relay as it is located under the glove box on the front facing side of the upper instrument panel just below the A/C duct. It is just above the curve in the dash so getting behind it will be difficult and must remove seat to get under dash to pull relay out to insert probe. I guess it could be done, but difficult. If relay is removed there is limited room to get test light probe and will be operating blind since you can not see the plug-in for the relay.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
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From: H-Town Texas
Need to remove the lower dash panel on the passenger side. However, as has been said, there is the OP switch that should override the relay if you have 4+ oil pressure. I would take out the pump and inspect the connections. Sitting in aging gas for four years cannot be good for it. JMHO.
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Thread Starter
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Joined: Dec 2005
Posts: 98
Likes: 1
From: Titusville Florida
Found problem with no power to pump. There was a chaffed power wire from the fuel pump fuse behind the battery. Wiring harness lays on sharp edge of frame gusset. it had rubbed thru the plastic loom and worn a hole in the wire and chaffed two others. All repaired and now power to pump. Pump was also dead. Replaced pump and car now runs. We encountered a problem getting it to take coolant. difficult to burp. After much effort now have coolant flow at upper radiator hose and steady stream at bleed valve. Engine idling fair but backfires and coughs when accelerator depressed. Thinking still may have fuel issue. Or possible that new OPti is bad. Will check tomorrow.
Thanks for all the responses.
Thanks for all the responses.