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30 seconds later, no residual fuel pressure....

3K views 32 replies 12 participants last post by  ToddA1 
#1 ·
As the title states, this makes for some very hard hot starts. I'll give some background, now.....
The 81 1.7 Rabbit was put on the road about 1 month ago and it got a new Bosch pump and check valve. A new accumulator was also installed, because the old one had staining around the weep screw. One week ago, the problem started.
The problem is worse during the day, when it's hot and vaporlocks. It isn't as bad at night when it's cooler. Once you get the car started, (seems to respond favorably to starting fluid) it runs perfectly. Turn the car off and within 5 seconds the pressure drops to 10lbs; 20 seconds later, it's at 0. Pressing the bleed button on the gauge (and getting no fuel spray) verifies it's not a faulty gauge.
- Dwell is perfect between 40/50
- frequency valve impedance reads within spec @ 2.7 ohms
- warm control pressure is @ 52 lbs.
- warm system pressure is @ 78 lbs.
- injectors and CSV are not leaking
- hot start relay is working, and by the short spurts of life, I can tell the CSV is firing
- Fuel dizzy plunger moves freely
- No leaks that I can see or smell from the rear of the car, to the front
- the tank is definitely holding pressure.... releasing the cap gives the telltale hiss. I even lowered the tank to verify all the vent lines were attached and tight.
Now, the Bentley tells you if the mixture goes way lean when checking system pressure, the pump check valve is probably bad. My dwell bounced between 55/65 lbs., so I replaced the new check valve with another check valve. No change and still the same dwell reading with the swapped check valve. I pulled the new accumulator and replaced it with another nonstained accumulator. Same deal.
The fuel dizzy has a pressure relief valve, but I thought it's only for maintaining system pressure, not residual pressure. Could that be the culprit, or any other ideas.... I'm stumped.
-Todd
 
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#27 ·
Re: 30 seconds later, no residual fuel pressure.... (bunicula)

If the CSV is firing and not leaking, then it is good. Since it's a hot start issue, I'd start at the hot start pulse relay, then the thermo time switch. All you need is a testlight or voltmeter.
Another function of the tts is to stop the CSV from firing if the starter is continually cranking. It could flood the engine.
By grounding the wire, you're bypassing everything. By doing this, then having the engine start, I'm sure it's running rough until all of the air is purged from the lines?
-Todd
*** I just reread your post and you mentioned a bad accumulator.... did you replace that? That would be step 1.
 
#28 ·
Re: 30 seconds later, no residual fuel pressure.... (ToddA1)

as of right now its both a hot start issue and what im assuming is a bad accumulator.. could just be the check valve though. same as your car though once the car is running its perfect.. upon initial start up i have a very strange reoccurnace in that i can crank the car over and it will fire right up and then completely cut out.. this litterally happens 5 times in a row EVERY TIME and on the 5th try it will stay running while it works the air out of the fuel system.. that is what im assuming is my check valve and or accumulator problem...
the hot start issue is basically if i dont have the green wire grounded on my TTS the car just wont start period.. i had done some searching on the hot pulse relay and couldnt find any solid info on where the heck it is.. is it buried behind the dash somwhere?
 
#29 ·
Re: 30 seconds later, no residual fuel pressure.... (bunicula)

I wouldn't assume anything, I'd verify. Do you own a Bentley?
The accumulator is pretty pricey @ about $145... the check valve is about $19. I'd do the free stuff first and check the valve. I mentioned how I checked mine, in an earlier post. The diagram that WWR posted is somewhat wrong. When you pull it out, you'll figure out what should be happening. Don't go by the spring return only.
Looking at the rear of your accumulator, is it stained with fuel by the screw/rivet? This is free check, also.
When you mention initial start, is that when cold? Cold start issues require a slightly different troubleshooting procedure.
Other than grounding the green wire, how far have you gone into diagnosing the problem?
Is the green wire grounded all of the time? If so, I'd imagine that you're running incredibly rich... the CSV will always be spraying.
What year is your car? 1981 was the year they started using them... I think 1980 in CA.. Mine is in the fusebox and as per the Bentley, the # is 813 906 064. I verified mine was good with a meter and the short spurts of life. IIRC, it has 3 pins.... I didn't pull it.
If you don't have a Bentley, get one.
-Todd
 
#30 ·
Re: 30 seconds later, no residual fuel pressure.... (ToddA1)

I have the same problem described by Todd's first post. I quickly lose residual pressure then no chance of a hot start. I have:
- new accumulator
- 2 or 3 new pump check valves
- new pump
- new metering valve o rings (did cure the problem initially but it returned)
- tank has been cleaned thoroughly, new tank filter and in line filter
Any other ideas? I suspect a few dodgy check valves but is there a way to test them?
 
#31 ·
FV-QR

Quote, originally posted by ToddA1 »
On the new valve I couldn't blow air from the pump side out, and if I covered the fuel holes from the other side of the nut, I couldn't get air to flow backwards, either. My lungs weren't generating enough pressure. Seems like I found my problem.


-Todd
 
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