Weird start issue 95 LT1
03-17-2015, 10:34 PM
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Weird start issue 95 LT1 After power washing the engine months ago, my car started having very slow starts, where before it was crank crank boom like clockwork.
Figured it was the opti getting wet and dying, but that's not the case.
I replaced the opti a couple days ago and the starting problems didn't change at all.
Think it's fuel pump or FPR. I dunno. Need advice.
Car will start great after sitting over night. But after sitting for longer than 15 mins to about 3 or four hours, it'll crank and crank for five seconds before starting. Sometimes it'll sputter at very low rpm for a few seconds, then head up to about 2k for ten seconds or so. I'm certain there's no vacuum leaks, so assuming this is fuel dumping in there?
If I let car sit for a couple hours etc, then put key to on, wait for fuel pump to shut off (3 seconds or so), then crank, it'll fire right up like crank crank boom.
Love some feedback before I go throwing a FPR and fuel pump on.
I've checked for leaking injectors while this has been going on. Two were leaking and I switch them out. I don't think any are leaking now after the last check. Car did run a little better after switching the injectors. LOL
Figured it was the opti getting wet and dying, but that's not the case.
I replaced the opti a couple days ago and the starting problems didn't change at all.
Think it's fuel pump or FPR. I dunno. Need advice.
Car will start great after sitting over night. But after sitting for longer than 15 mins to about 3 or four hours, it'll crank and crank for five seconds before starting. Sometimes it'll sputter at very low rpm for a few seconds, then head up to about 2k for ten seconds or so. I'm certain there's no vacuum leaks, so assuming this is fuel dumping in there?
If I let car sit for a couple hours etc, then put key to on, wait for fuel pump to shut off (3 seconds or so), then crank, it'll fire right up like crank crank boom.
Love some feedback before I go throwing a FPR and fuel pump on.
I've checked for leaking injectors while this has been going on. Two were leaking and I switch them out. I don't think any are leaking now after the last check. Car did run a little better after switching the injectors. LOL
03-18-2015, 03:43 AM
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Pull the vacuum line to the fpr if it smells like fuel replace fpr. If not, it's likely the fuel pump check ball; replace pump.
Put a fuel pressure gauge on it. With the key on engine off it should be around 43psi. If it drops quickly then block the fuel return line. If the drop stops its the pump check ball. If not is a leaking injector(s).
The check for the fpr requires you to drive the car and monitor fuel pressure at different loads and rpms. It should be 43psi at idle and drop a little at higher rpms IIRC.
Put a fuel pressure gauge on it. With the key on engine off it should be around 43psi. If it drops quickly then block the fuel return line. If the drop stops its the pump check ball. If not is a leaking injector(s).
The check for the fpr requires you to drive the car and monitor fuel pressure at different loads and rpms. It should be 43psi at idle and drop a little at higher rpms IIRC.
03-18-2015, 05:28 PM
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03-25-2015, 05:51 PM
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Not the ICM, put one on and no change.
Tested fuel pressure. Think this is where the problem is. Key on, pressure hits 46 psi, then drops to 25 psi in 20 seconds. From my reading, that's too far too quick. Can anyone confirm the drop is too quick? Chiltons isn't ideal in this subject.
So figuring the fuel filter is ok since it's getting to 46 quick with key on. I didn't see any leaks in the injectors last time they were out while this start issue already existed.
So that leaves the FPR and the fuel pump. My fuel return hose is nylon, can't clamp it without breaking it. Any feedback is helpful.
I did get a faint smell of fuel in the FPR vacuum hose.
Tested fuel pressure. Think this is where the problem is. Key on, pressure hits 46 psi, then drops to 25 psi in 20 seconds. From my reading, that's too far too quick. Can anyone confirm the drop is too quick? Chiltons isn't ideal in this subject.
So figuring the fuel filter is ok since it's getting to 46 quick with key on. I didn't see any leaks in the injectors last time they were out while this start issue already existed.
So that leaves the FPR and the fuel pump. My fuel return hose is nylon, can't clamp it without breaking it. Any feedback is helpful.
I did get a faint smell of fuel in the FPR vacuum hose.
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03-26-2015, 01:18 PM
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Looks like fuel pump. Hope this is the starting issue also.
Blocked off the return with a rubber hose and clamps. Pressure still bleeds off quick. Pulled injectors and none are leaking. Ordered a Delphi pump and fuel filter from Rock Auto. Will post up when it's put together.
Blocked off the return with a rubber hose and clamps. Pressure still bleeds off quick. Pulled injectors and none are leaking. Ordered a Delphi pump and fuel filter from Rock Auto. Will post up when it's put together.
03-26-2015, 05:44 PM
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Looks like fuel pump. Hope this is the starting issue also.
Blocked off the return with a rubber hose and clamps. Pressure still bleeds off quick. Pulled injectors and none are leaking. Ordered a Delphi pump and fuel filter from Rock Auto. Will post up when it's put together.
Blocked off the return with a rubber hose and clamps. Pressure still bleeds off quick. Pulled injectors and none are leaking. Ordered a Delphi pump and fuel filter from Rock Auto. Will post up when it's put together.
03-27-2015, 10:38 AM
#10
The LT1 F-body cars have a pump that is inside a plastic fill-bucket. The fill-bucket's inlet and check-valve system in combination with the fuel pump are designed to draw fuel from the bottom of the tank via suction. This keeps the bucket full at all times and the pump fully immersed in fuel regardless of the tank level so that when the tank is low on gas and you are doing some hard cornering or acceleration the pump does not run dry and start aerating (air bubbles) the fuel. This happens as the fuel sloshes from side to side in the tank leaving the center low on fuel. The F-LT1 cars have minimal to no baffling in them. This can cause detonation and possible engine damage. The bucket also allows the car to operate with lower fuel levels in the tank due to its scavenging effect. The bucket can also effect motor cranking time as the priming time is reduced under certain conditions. The return line from the fuel pressure regulator is diverted back into the bucket via a filter sock inside so that the unused fuel also helps keep the bucket full at all times. Keeping the pump constantly immersed in gas within the bucket can extend the pump's life by not allowing it to be exposed to open air. Open air within the tank contains moisture and in time will cause the pump to rust / seize up especially if left to sit for long periods of time without the tank topped-up (i.e. winter storage). The Racetronix pump assembly is modified so that it will seal in the buckets rubber check-valve so that its function is retained.
04-12-2015, 11:40 AM
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^ Thanks for that info.
Think it may have been the pump per se. I went to replace it last night and the return line was off the pump.
Reattached all the hose connections with clamps and the problem hasn't show back up after some good conditions for it to.
Car actually starts like it did when I got it. Kick kick boom 100% of the time since I put the return hose back on the pump.
Fixed the fuel sender, too. Whoever did this fuel pump was a hack. They blocked the sender with one of the hose routings.
Thanks for the help folks
Think it may have been the pump per se. I went to replace it last night and the return line was off the pump.
Reattached all the hose connections with clamps and the problem hasn't show back up after some good conditions for it to.
Car actually starts like it did when I got it. Kick kick boom 100% of the time since I put the return hose back on the pump.
Fixed the fuel sender, too. Whoever did this fuel pump was a hack. They blocked the sender with one of the hose routings.
Thanks for the help folks