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View Full Version : Primary Fuel Pump, Pump Relay and Pump test lead. (Long Post)


rebelz
10-14-2012, 02:24 AM
After getting my '92 ZR-1 car on the road on August 27th for the first time this summer, all went well for 2,599 miles. Then 88 miles from home on a Corvette club outing at 63 mph the engine just died. I was able to get it started and to move about 20 feet at a time, to get it into a nearby driveway. I'm sure glad it was only about 50 feet away. Once I was off the road I lifted the hood and started the car and waited for it to die while other club members stood at the both sides of the engine.
The reason I got her on the road so late this is because of $12,000 worth of upgrades. If anyone is interested in what all I did, just ask, or PM me. It took me longer to get them done than I thought it would. Not as young as I once was.
Along with all the other upgrades, I installed a new OEM fuel sender /w fuel pumps, a Specialized Racing Products inline fuel filter and under hood fuel pressure gauge. Because of that pressure gauge we were quickly able to determine that loss of fuel pressure was at fault. I knew that both fuel pumps come on at startup and then the secondary pump shuts off, unless the "full power key" is on and proper fuel demand, so I was pretty sure that the primary fuel pump on the NEW OEM ACDelco fuel sending unit was most likely the culprit. The pressure gauge was installed because I think all performance cars should have one and this one looks like it belongs on the car.
We were able to get the car back home safely. The flat bed/ramp truck driver knew his job very well, and was extremely careful with our car. I pulled the primary pump fuse but it was ok. I started the car and it ran fine. I let it run for about five minutes, shut her down and went upstairs for the night. Perhaps the fuse had stopped making good contact? Not all that compelling to me.
I started it again the next morning and it ran fine again. In the back of my mind something just didn't seem right though. I did some more research here and elsewhere and discovered I hadn't remembered everything about the fuel system on the car. The secondary pump stays on until the water temperature reaches 176° F. then shuts off. When started at normal operating temperature the secondary shuts off immediately. I started the car, switched the display to the digital water temp. and let her run. At 189° F indicated the fuel pressure started dropping and when it reached 10 psi I shut the car off. Problem verified, primary fuel pump failure. Fuel pressure with key on 40 psi.
I picked up a '96 Suburban 2500/454 fuel pump came home took a couple of hours to put it in, Started the car let it heat up to 198° and run for 20 minutes. Problem solved!! Fuel pressure at key on 42 psi.
We took it out to the store, a restaurant, back home everything worked fine. The next morning I took the car to the eye doctor. Temp in the normal range 198°-200° F same problem, Engine stops, fuel pressure low.
Now the questions- I've ordered a primary fuel pump relay and I'm going to replace that, what else could be causing this? The last question is can I use the fuel pump test wire to cripple the car home if changing the relay acts like it is working as a fix? It gets expensive getting trucked home. I did use my road assistance for the 88 mile trip!!
Rich 'REBel' Ballou

scottfab
10-14-2012, 02:54 AM
....snip....
Now the questions- I've ordered a primary fuel pump relay and I'm going to replace that, what else could be causing this? The last question is can I use the fuel pump test wire to cripple the car home if changing the relay acts like it is working as a fix? It gets expensive getting trucked home. I did use my road assistance for the 88 mile trip!!
Rich 'REBel' Ballou

I have had the same issue and used the few seconds of run time on each start up to limp home 4miles away .... 1/2 mile at a time.
As for what else can cause this? I can only think of fuel pump #1 or relay.
If these pumps are run AT ALL outside the tank for any reason it compromises them. As for the test lead use as power to #2 pump that won't work.
The way the test lead is wired into the relays as soon as you put the key in the on position the test lead is out of the circuit.
I ended up putting in two emergency switches.
One to put power to the test lead for a pressure test and
one to the FP #2 at the relay for a way to get pressure if #1 fails.
See this post:
(link to my Fuel Pump Bypass switch tread) (http://zr1.net/forum/showthread.php?t=18224&highlight=fuel)

rebelz
10-14-2012, 10:43 PM
Scott-
I read your post on the bypass switch. Great post by the way! Where did you pull the power to feed the #2 pump, and is there anything I need to know about connecting it to the secondary relay? I can envision needing to make sure the power key remains off if the bypass is ever needed.
Rich 'REBel' Ballou