Intermittent stalling

Rich Kruger

Supporter
Ok first a related funny story. Back in the day I worked in a Ford/Lincoln service dept. A turbo Tbird had an intermittent stalling issue. Don our excellent lead tech checked everything related and determined that even though the fuel pump was running (submersed in tank) it was losing fuel pressure. The required removal of the tank ensued and upon removal of the pump there appeared to be a plastic bag floating around in the tank. An expertly configured coat hanger removed the offending object and with that it became even more offensive. The object was a condom that had swelled to about 15 inches long and 6 inches wide (reservoir tip and all). Don displayed the trophy of his superior diagnostic and repair abilities on the wall above his bench for months to come. Many conjured stories were spun by the techs as to its sordid history.

Now my tale of woe. My SLC has a LS3 376/480. My fuel system is as follows: tank to 100 micron filter to Holley 125 low pressure pump to swirl tank. High pressure Bosch 200 (replacement for their 044) out of the bottom of the swirl tank to 10 micron filter to pressure regulator to rail. The pumps are mounted low with minimum lift required. What happens is after about 40 to 45 minutes of driving it appears to lose fuel pressure. I checked the tank vent (from tanks Inc) and its clear, when I open the fuel tank cap there doesn't appear to be any vacuum when the condition happens. If I sit 10 minutes the car will run ok. The condition seems to happen when I am in the throttle aggressively. The high pressure pump seems to be laboring. I have replaced the fuel filters and the high pressure pump (the original Bosch 044- verified OEM was screaming). My thoughts are either the Holley 125 pump failing and the swirl tank runs dry (seems unlikely) or an intermittent restriction in the swirl tank ( Hmmmm maybe a condom! ) like weld slag etc. Any Ideas? I'll be taking it apart this weekend.
 

Mark B.

Supporter
How's your fuel temperature? I noticed after driving mine for similar time the pump sounds labored, but I haven't yet noticed a drop in fuel pressure (I need to check now). I'm thinking the fuel is getting heated up because of the return style setup along with close proximity to the engine. It's possible the fuel temp is getting too high causing the pump to overheat and/or vapor lock?
 

Neil

Supporter
From the curves shown here:


Your pump should be OK but if the wiring is too small and creates a large voltage drop while drawing around 10 amps, it might be a problem at full throttle. Check the voltage AT THE PUMP while driving at full power. This should confirm or eliminate voltage drop as the problem.
 

Rich Kruger

Supporter
Mark the fuel temp is ok. With an electric pump literally 8 inches out of the swirl pot I don’t believe it’s vapor lock.
Neil I did wonder if it could be a wiring concern. I was going to contrive a setup to check that. A cursory check at time of failure didn’t reveal hot wires or even the pump being warmer than the fuel. I’m using a high grade 14 gauge wire about 6 feet long from the infinity box.
 

Kyle

Supporter
Not sure if you’re track riding, but this is a big reason I didn’t do a swirl tank. Creates unnecessary head aches. One pump, one filter, one regulator and done.
 
Those Bosch 044 pumps need a big diameter 13mm fill hose, gravity fed.
That hose must be unrestricted, so no pre filter.
In OEM aplications, these pumps where always below fuel level.
 
Are you 100% sure its a fuel pressure issue? When I had my SLC i had the same experience. However, the issue in the end turned out to be a battery disconnect to the car that was fouled up with gunk and cutting off power to the car as well as losing throttle. The battery disconnects are notorious for causing these issues and making them look like lack of pressure.
 

Rich Kruger

Supporter
The cutoff switch is new and the low pressure pump works with no problem. Also the car cranks over and almost starts. All other elec systems fully powered.
Last night I let both pumps run for over an hour and they didn’t miss a beat. With a volt meter on the high pressure pump it never dropped below 11.1 volts with 12.3 available at the battery.
Now it’s storytime again and a trip down the rabbit hole. If your out there Neil pay attention. Once again back in the day I worked at a Subaru dealership in service. When their Legacy model was brand new we had a customer towed in twice for a stalling condition. The car started and ran fine upon receipt at the shop. One of our techs was an electronics wiz and he was able to determine that because the car was being towed from the exact same place both times there must have been some type of radio wave interference. The old RFI theory. Turns out the area was a construction site and the two way radios were stepping on the unsheilded ECM in the Subie. The tech cobbled a sheild over the ECM and problem solved. A report was sent to Subaru of America. The odd thing is my car is stalling (3x times) in the same spot on the highway at a spot of construction leading into the Tobyhanna Army Depot which is a major military electronics repair site. BUT in my case only the high pressure pump is affected. I can easily switch the power sources and give it another shot. This time if the low pressure shuts off I know it’s related to the Infinity Bus system. Just in case I’m going to fabricate a tin foil helmet for the drive.
 

Rich Kruger

Supporter
Just another RFI tidbit. I was assistant Service manager at a Mercedes dealer. A customer was complaining the AC in his new Mercedes SL would just go the full heat for no reason on a hot day. We checked everything with the climate control to no avail. The customer actually figured out that when he put his bag phone (remember those ?) next to his left leg on the floor while driving and he was on a call the AC acted up. By putting the phone on the passenger seat he fixed his own problem.
 
I would re-torque your intake manifold bolts. I believe they are 89 inch. pounds. When the engine heats up a small leak can occur that can cause your symptoms. The leak may be small enough to not throw a code.
 

Ian Anderson

Lifetime Supporter
Supporter
Your fuel is getting hot from heat soak from surrounding items, exhaust, engine block etc.

Hot fuel Does not work as well as cold fuel.

Duct some cold air to blow over the pump and swirl pot.

Ian
 

Johan

Supporter
Ok first a related funny story. Back in the day I worked in a Ford/Lincoln service dept. A turbo Tbird had an intermittent stalling issue. Don our excellent lead tech checked everything related and determined that even though the fuel pump was running (submersed in tank) it was losing fuel pressure. The required removal of the tank ensued and upon removal of the pump there appeared to be a plastic bag floating around in the tank. An expertly configured coat hanger removed the offending object and with that it became even more offensive. The object was a condom that had swelled to about 15 inches long and 6 inches wide (reservoir tip and all). Don displayed the trophy of his superior diagnostic and repair abilities on the wall above his bench for months to come. Many conjured stories were spun by the techs as to its sordid history.

Now my tale of woe. My SLC has a LS3 376/480. My fuel system is as follows: tank to 100 micron filter to Holley 125 low pressure pump to swirl tank. High pressure Bosch 200 (replacement for their 044) out of the bottom of the swirl tank to 10 micron filter to pressure regulator to rail. The pumps are mounted low with minimum lift required. What happens is after about 40 to 45 minutes of driving it appears to lose fuel pressure. I checked the tank vent (from tanks Inc) and its clear, when I open the fuel tank cap there doesn't appear to be any vacuum when the condition happens. If I sit 10 minutes the car will run ok. The condition seems to happen when I am in the throttle aggressively. The high pressure pump seems to be laboring. I have replaced the fuel filters and the high pressure pump (the original Bosch 044- verified OEM was screaming). My thoughts are either the Holley 125 pump failing and the swirl tank runs dry (seems unlikely) or an intermittent restriction in the swirl tank ( Hmmmm maybe a condom! ) like weld slag etc. Any Ideas? I'll be taking it apart this weekend.
Rich, best routing would be: Tank(swirl or not)-100micron-Pump(if not in-tank)-10micron-Fuel rails-Regulator-Tank. That way you get the desired pressure into injectors and a constant flow through the system. (No vaporlock)
 
possibly vapor lock. Needs a return to tank system.

It would be nice if you had a fuel pressure reading at the fuel rails.
 

Rich Kruger

Supporter
Whew…. OK. The fuel pumps, swirl pot and filters are effectively insulated from heat. Vapor lock is usually a situation where the fuel is being drawn over a long distance ie rear tank~front engine/ fuel pump. It usually doesn’t happen with elec pumps located at or in the fuel tank. This is a loop style system where the regulator returns to the swirl pot. Mike I’m at the point where I need to retorque everything. You are correct the LS is susceptible to intake leaks. In my experience that shouldn’t affect the driveability under loads. I have some more things to check as well. Johan that is basically the system I’m using , just also using a low pressure pump to fill the swirl pot. I’m suspicious the low pressure pump might be not supplying enough to the swirl pot. Back to the drawing board. Hey Neil because this system is a looped system the high pressure pump over provides fuel which normally returns the unused amount to the swirl pot. As far as stressing the high pressure pump under a load wouldn’t the pump be effectively under less stress because it supplies the same volume but less is restricted by the regulator as more is used by the engine. What effect on its load/ draw be?
 

Ian Anderson

Lifetime Supporter
Supporter
And the heat generated by the HP pump continuously circulating the fuel heats it up too.

Modern diesels have an air fuel cooler in the return line for this reason

Ian
 
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