Dw400 issues

[Cyotee]

Anyone ever have a check valve fail in a dw 400 fuel pump? Brand new pump , made sure clamps are all tight twice. Engine is cranking longer than normal to start. Data logs show 0 psi before engine cranks over.

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[Martin5.0sc]

There is no check valve, let me guess auto car?

 

[Angrey]

There is no check valve, let me guess auto car?

The new DW400's have an internal check valve. Either the one he has is the older style or it's failed if it's not maintaining fuel pressure at shutoff.

 

[engineermike]

There is no check valve, let me guess auto car?

I gotta ask....why does the transmission matter?

 

[engineermike]

I believe the check valve actually addresses vapor lock, not priming. And vapor lock only occurs on hot start. If it’s a long crank when cold, then it’s probably not the check valve (or lack of).

 

[Angrey]

I believe the check valve actually addresses vapor lock, not priming. And vapor lock only occurs on hot start. If it’s a long crank when cold, then it’s probably not the check valve (or lack of).

The check valve prevents backflow through the pump. So at shutoff, when the injectors are no longer consuming, there should be residual pressure in the fuel line, which makes starts less laborious and grumpy. Internally checked pumps flow less, so for instance the TI 295 (which has no check valve) flows better than the 285 version, the only difference being you need to run an external in line check valve, or else everytime you shut off the car, the fuel will drain back through the pump and have no line pressure. Once the key on primes the pump(s) and they spool it will re-establish some pressure, but the line will burp and the starts will be grumpy.

It also plays a role if you have multiple pumps staged, you want the secondary pumps to be checked, otherwise the primary pumps will flow back through the second stage pump(s).

 

[80FoxCoupe]

I addition to the above post, if you have a return style fuel system, the regulator will bleed off fuel pressure as soon as pumps shut off.

 

[engineermike]

If the problem was simply loss of pressure, the system would re-pressurize in less than a second because it would take a tiny volume addition to restore pressure. However, the hot start issue takes much longer than that. Also, if it was simply losing system pressure due to backflow the problem would also occur during cold start, but it doesn’t.

In order for a pump to lose prime or for significant backflow to happen, you must get gas (not “gasoline”) into the system. Air can’t enter the fuel system on either end due to the pump’s suction being submerged on one end and the injectors being closed on the other.

I can only come up with one thing that explains the issue and that is vapor lock. The fuel vaporizes in the fuel rails. The vapor must be purged through the injectors before liquid fuel enters, which takes time. This would explain why it only happens during hot start. A check valve would maintain pressure on the fuel system which would increase the boiling point of the fuel dramatically and prevent vapor lock.

 

[Angrey]

If the problem was simply loss of pressure, the system would re-pressurize in less than a second because it would take a tiny volume addition to restore pressure. However, the hot start issue takes much longer than that. Also, if it was simply losing system pressure due to backflow the problem would also occur during cold start, but it doesn’t.

In order for a pump to lose prime or for significant backflow to happen, you must get gas (not “gasoline”) into the system. Air can’t enter the fuel system on either end due to the pump’s suction being submerged on one end and the injectors being closed on the other.

I can only come up with one thing that explains the issue and that is vapor lock. The fuel vaporizes in the fuel rails. The vapor must be purged through the injectors before liquid fuel enters, which takes time. This would explain why it only happens during hot start. A check valve would maintain pressure on the fuel system which would increase the boiling point of the fuel dramatically and prevent vapor lock.

You can do your own research. The biggest reason pump manufacturers started incorporating internal check valves into their assemblies is because of startup issues. There's zillions of threads outlining failed check valves and start up issues. It IS pressure related, if that weren't the case, there'd be no need for check valves in single pump arrangements cause you could just prime and put pressure and would go away.

In reality, the fuel lines gradually lose pressure overnight and bleed back through the pump under suction and there's AIR in the system. Then when the system wakes up and attempt to prime, the injectors aren't OPEN and so it labors to start as it's spitting air/vapor out of the injectors until fresh fuel reaches the rails.

In fact, the FIRST thing any wrench head is gonna ask you if you have problematic starts is..."have you checked the check valve." It's one of the symptoms of a bad check valve (laborious and grumpy start ups).

 

[Cyotee]

There is no check valve, let me guess auto car?

There is a check valve and it’s a auto car for what it’s worth.

 

[Cyotee]

Once the car sits for a half hour or so it cranks for 3-5 seconds and starts every time. This only started once I installed the dw400. In fact when I unhooked the discharge line from the fuel hat with the stock pump there was a good amount of pressure that bled off. When I unhooked again with the dw no pressure at all which raised a eyebrow. All logs were fine up to 7600 rpm so it not a cracked line or loose clamp.

 

[engineermike]

You can do your own research. The biggest reason pump manufacturers started incorporating internal check valves into their assemblies is because of startup issues. There's zillions of threads outlining failed check valves and start up issues. It IS pressure related, if that weren't the case, there'd be no need for check valves in single pump arrangements cause you could just prime and put pressure and would go away.

In reality, the fuel lines gradually lose pressure overnight and bleed back through the pump under suction and there's AIR in the system. Then when the system wakes up and attempt to prime, the injectors aren't OPEN and so it labors to start as it's spitting air/vapor out of the injectors until fresh fuel reaches the rails.

In fact, the FIRST thing any wrench head is gonna ask you if you have problematic starts is..."have you checked the check valve." It's one of the symptoms of a bad check valve (laborious and grumpy start ups).

I’m not saying it isn’t pressure related. It’s absolutely pressure related but it’s also temperature related. Vapor lock is when there isn’t enough pressure on the fuel system to keep the fuel in liquid form when it heats up after shut-down. Simply pressuring up the system will not re-condense the fuel into liquid form, so the vapor must be purged through the injectors during the 3-5 seconds of cranking.

What I am saying is that it’s not AIR in the system that’s causing the issue. There is no way for air to get into the fuel system because the pump suction is submerged and the injectors are closed. Also, after sitting overnight it starts fine. If it were air then this wouldn’t be the case. If it were pressure alone then it wouldn’t be the case either.

I had the issue myself for months because I had an early DW400 without a check valve. The ONLY time I had the problem was during hot restart after soak time. Cold start was never an issue and neither was immediate re-start. The only explanation that fits all of the symptoms is vapor lock. Swapping to a DW400 with a check valve completely fixed it.

 

[Burkey]

I’m not saying it isn’t pressure related. It’s absolutely pressure related but it’s also temperature related. Vapor lock is when there isn’t enough pressure on the fuel system to keep the fuel in liquid form when it heats up after shut-down. Simply pressuring up the system will not re-condense the fuel into liquid form, so the vapor must be purged through the injectors during the 3-5 seconds of cranking.

What I am saying is that it’s not AIR in the system that’s causing the issue. There is no way for air to get into the fuel system because the pump suction is submerged and the injectors are closed. Also, after sitting overnight it starts fine. If it were air then this wouldn’t be the case. If it were pressure alone then it wouldn’t be the case either.

I had the issue myself for months because I had an early DW400 without a check valve. The ONLY time I had the problem was during hot restart after soak time. Cold start was never an issue and neither was immediate re-start. The only explanation that fits all of the symptoms is vapor lock. Swapping to a DW400 with a check valve completely fixed it.

I think they’re missing the bit where the boiling point of gasoline rises as pressure is applied.
The addition of phenolic spacers to my vehicle (and others) has reduced the hot start times significantly. Makes sense that the rails aren’t as hot, less vapour, faster starts.

 

[Cyotee]

Just a follow up. Whipple sent a new pump under warranty/ installed and no more starting issues.

with the bad pump out I lightly blew into the discharge port of the pump, went right through. Tried on the new pump, all good. Check valve did the job

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