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Fri Feb 20, 2004 9:53 am

Hey everyone,

So here's the deal. I'm looking for some vindication of my theory here, or some other thoughts if this sounds bogus. I've had a nagging problem for the year I've owned my bus that I'd like to correct. When I start up the bus for the first time of the day, it fires up like a champ with no hesitation. Then, say, I shut it down, walk into a store for a bit and come back. And the bus just doesn't want to start. The only way it will (and it always does thankfully) is to keep the gas pegged to the floor while cranking it for about 15 seconds. Keep in mind, 1979 FI federal. Now some time ago I raised a post about my rotted off EGR pipe. My theory is that when I start the engine cold, the egr has yet to open up. (It is thermostatically controlled, right?) Then, when I shut it down, the engine being hot for a while keeps the egr open. Hence, when I try to start it up, it is sucking so much false air in through the egr pipe that it leans out the mixture too much. Therefore, I have to give it loads of gas to get it going. When I finally block off the EGR this spring, I hope the hot start problem will go away. Am I on the right track here? Or does the problem lurk elsewhere? :?: :(

Fri Feb 20, 2004 10:05 am

Have you checked your auxillary air valve? It is opposite the cold start valve and performs much the same function as you discussed.

Fri Feb 20, 2004 10:09 am

1979westie wrote: Keep in mind, 1979 FI federal. Now some time ago I raised a post about my rotted off EGR pipe. My theory is that when I start the engine cold, the egr has yet to open up. (It is thermostatically controlled, right?)
The early 75-76 1/2 EGR's were electro-vacuum. Yours is mechanical unless it's not stock. When the throttle is closed the mechanical linkage is supposed to keep the valve closed. If the adjustment is wrong then some exhaust (or air is you have leaks) will get in.

Quote: Then, when I shut it down, the engine being hot for a while keeps the egr open.
It doesn't work that way. Read the description in Bentley brief as it is.

85% of the time, problems blamed on FI turn out to be igntion/fuel/electical. You can diagnose the whole thing with a VOM, fuel pressure gauge, vacuum gauge, some containers and time so there's no guessing.

Fri Feb 20, 2004 10:31 am

Yes, Richard, you are right, now that I think about it I see how the throttle also controls the openning and closing of the egr. So what would be the most likely problem in this case? It's had a complete tune up, and runs great with the exception of this hot start issue. What would be the most logical path to follow to trace the problem? Thanks again,
Eric

Fri Feb 20, 2004 10:59 am

If you don't feel like doing the EGR adjustment (a tach and vacuum gauge are needed for fine tuning) go to the hardware store that has good prices on materials and buy a strip of metal that is the approximate thickness of the flange on the EGR tube (in case the threads for the screws aren't deep enough) to make a block off plate. Cut a piece, drill two holes in the same place that pipe has screw holes, re-use the gasket under the pipe and bolt it tight. Also make sure the screws that hold the valve on are tight.

That should eliminate the leaks and help you diagnose the remaining problem if it exists.

If the bus was running lean you'd have trouble starting when cold. I'm not sure how rich the FI system can be made before you exihibit starting problem when warm. Check your plugs first thing in the morning before you start next time you have the time. They should have a greyish look to them like this. That will tell you how the mixture is set and you can rule that out.

If the timing is right, the dwell is right, the plugs are gapped right, etc and the battery is charged then you may simply need the $8 hot start relay. I don't buy the theory that a worn starter bushing causes the problem over time (it would make for a labor intensive experiment to prove it).

It's hard to mention FI problems in the same sentence without blaming the temp sensor screwed into the head behind intake runner #3. When the electrical connection is poor starting is a problem but more often than not it's erratic rather than predictable like the problem you are experiencing.

You can double check it but checking the resistance at room temp (68F) and when the engine is still hot after you've shut it off. An infrared temp gun helps to figure out the head temp if you have one otherwise you'll have to do a little guestimation. If the resistance valves aren't in the ballpark for operation, replacing it for $20 is worthwhile.

Fri Feb 20, 2004 11:11 am

1979westie wrote:
So what would be the most likely problem in this case? Eric

Your fuel pressure regulator has two functions.
1) It regulates the running fuel pressure. Duh.
2) It maintains static pressure in the fuel rail to prevent boiling off during warm/hot soaks when you are running into the store. No duh.

Boiling off causes vapor which, although it doesn't cause a "lock", is more difficult for the pump to bleed out. Even the hot start relay cannot get rid of vapor in the little legs to the injectors, it will cleanse the rail only, the vapor has to slowly bleed through the tiny orifices before you getta-the-gas you need to actually start.
You may have a regulator bleed-off. Hook up your pressure tester on a warm/hot engine and see how well the pressure holds. Your fuel pump may have a check valve that also prevents fuel pressure from draining away at the pump end of the loop. That check valve is intrinsic to the pump in most cases.
How do you distinguish between the regulator and the fuel pump?
Pinch the return fuel line closed when you go into the store.
If it starts up properly when you come back, it is the regulator.
If it starts hard as always, it's the pump check valve.
Test at least three discreet times to be sure.
Colin

Fri Feb 20, 2004 12:43 pm

The FI system isn't prone to vapor locks or trapped air because of the return line back to the tank. At least in the bus design the air raises and flows in the direction of the fuel flow, which is why the pressure regulator is mounted higher than the fuel rail on the breast tin.

The pump has far more capacity that the mere 28-35psi required to operated the fuel injectors. The fuel rail pressurizes almost instantly and the excess air and fuel is pumped into the tank via the return line.

Like you say the check valve in the pump keeps the system primed although there is a still some bleed down as evidenced on the fuel pressure gauge.

1979westie, next time you stop the engine and think you're going to have a starting problem do this to rule out the FI system:

- remove the air filter
- turn on the ingition with the key
- deflect the flap in the AFM with a wooden stick for 5-10 seconds
- turn off the key
- return the air filter and cover then try to start the engine

Fri Feb 20, 2004 1:48 pm

Perhaps I should have mentioned this little tidbit. probably 90 percent of the time I am able to get the engine to start up right away when hot by depressing the gas pedal just about a quarter inch as I turn it over, and then quickly let off the gas. Then it roars to life. What might this indicate? Everyone has their little things only they know how to do to get an old bus to run, but I'd prefer not having to do this little proceedure. Kinda like crossing your fingers and hitting the dashboard at a certain spot will make your headlights work :wink:
Thanks again for all the help guys.

Fri Feb 20, 2004 2:36 pm

1979westie wrote: Kinda like crossing your fingers and hitting the dashboard at a certain spot will make your headlights work
Only if you say, Aaaaaaa afterwards.

Fri Feb 20, 2004 4:44 pm

ratwell wrote: The FI system isn't prone to vapor locks or trapped air because of the return line back to the tank. The fuel rail pressurizes almost instantly and the excess air and fuel is pumped into the tank via the return line. Like you say the check valve in the pump keeps the system primed although there is a still some bleed down as evidenced on the fuel pressure gauge.

I suggested that he try my little diagnostic to help narrow down potential causes. A leaky cold start valve is the other possibility. In that case, pull it out and see if it is wet after you come out of the store. Some of the diagnostics are coming from my BMW/Mercedes fuel injection history. VW air-cooled heads get damn good and hot in a hurry when you shut the engine off. Fuel will boil if the rail pressure drops. This is a known issue and it does not have anything to do with return lines to the tank. As mentioned, the hot start relay you suggested ( no different than sticking sticks in the AFM ) will clean out the rail in a hurry, but the injector legs will none-the-less require a bit of cranking when the engine is hot. Pressing down on the accelerator, as he mentioned, will get rid of that vapor more quickly with extended injection pulse times. Now that I think about it, what about the possibility of a leaky cold start injector???? You'd HAVE to depress the accelerator while cranking to get enough air to overcome the dumped fuel.
Colin

Fri Feb 20, 2004 4:55 pm

Amskeptic wrote: Some of the diagnostics are coming from my BMW/Mercedes fuel injection history. VW air-cooled heads get damn good and hot in a hurry when you shut the engine off. Fuel will boil if the rail pressure drops. This is a known issue and it does not have anything to do with return lines to the tank.
If this was the case and the fuel pressure from the next start didn't evacuate the trapped air via the pressure regulator then all busses in all running conditions would have this problem.

Hot soak isn't good for the injectors but they seem to be able to take it year after year and still perform. Gasoline is made up of several compounds that boils at varying temperatures from 100F - 300F. Everytime you shut off some it is going to turn to gas but the heat doesn't transfer to the entire fuel rail. Give it a touch next time 5 minutes after shutoff.

Now, the baking of fuel into varnish inside the injector is a problem that proper injector cleaning will cure.

Fri Feb 20, 2004 11:01 pm

Too much information......head starting to hurt.
Quote: A leaky cold start valve is the other possibility. In that case, pull it out and see if it is wet after you come out of the store.

I didn't even know I had a cold start valve...I can just see pulling it out in the Shoprite parking lot, with all these audis and hummer h2's around, soccer moms filling their trunks with low-carb foodstuffs and gawking at me in my garage suit with my head in the rear end of a VW bus. :lol:

Thanks for all the info, Colin and Richard. I'll take it under advisement, but ultimately I think I'm gonna leave this to my mechanic. I only have so much tolerance for troubleshooting. Sometimes it's nice to just pay someone else to figure it out.
Eric

Sat Feb 21, 2004 12:49 pm

ratwell wrote: Amskeptic wrote: Some of the diagnostics are coming from my BMW/Mercedes fuel injection history. VW air-cooled heads get damn good and hot in a hurry when you shut the engine off. Fuel will boil if the rail pressure drops. This is a known issue and it does not have anything to do with return lines to the tank.

If this was the case and the fuel pressure from the next start didn't evacuate the trapped air via the pressure regulator then all busses in all running conditions would have this problem.

"then all busses in all running conditions would have this problem"
Not if the fuel rail maintains pressure! There is no vaporization of fuel under pressure.
I am going to research this further, Ratwell, but in most cases, the fuel rail is able to hold residual pressure for the duration of hot soak. If, in fifteen minutes, the temperature of the engine has dropped below 150* let's say, then the slow pressure bleed-off will be un-noticeable to starting performance. MB requires maintenance of 2.0 bar (28psi) for 30 minutes.
Colin

Sun Feb 22, 2004 12:07 am

I'm sorry but I'm totally confused as to the point you are trying to make or the symptom 1979westie is experiencing that you are trying to diagnose.

What research are you proposing? Getting a FI bus? Retrofitting L-Jet to an old Mercedes? I think you've dug yourself into a bit of a theoretical hole. I'll grant you FI systems vary little in basic design, at least many of the components are there but there's little point to testing the residual pressure of the fuel rail when the bus starts so well first thing in the morning and has neglible fuel rail pressure. The ability to start so easily is one of the strengths of the FI system.

Sun Feb 22, 2004 1:11 am

i like carbs [-o<

Sun Feb 22, 2004 8:52 am

I would start by replacing the fuel line that goes between the regulator to the fuel injectors and double clamp them. For a couple of bucks you could see if that helps.

Sun Feb 22, 2004 10:24 am

ratwell wrote:
I'm sorry but I'm totally confused as to the point you are trying to make or the symptom 1979westie is experiencing that you are trying to diagnose.

"When I start up the bus for the first time of the day, it fires up like a champ with no hesitation. Then, say, I shut it down, walk into a store for a bit and come back. And the bus just doesn't want to start."
There are his symptoms in his words. Possible causes seem very limited with such a limited window of misbehavior. 8)

ratwell wrote:
What research are you proposing? Getting a FI bus? Retrofitting L-Jet to an old Mercedes? I think you've dug yourself into a bit of a theoretical hole. There's little point to testing the residual pressure of the fuel rail when the bus starts so well first thing in the morning and has neglible fuel rail pressure.

Residual fuel rail pressure is only important when the engine is hot. It prevents localized boiling of fuel that starves the injectors at hot start-up.
A cold engine will prime easily. Your jab about retro-fitting an old Mercedes with L-Jet is disingenuous although correct ( D-Jet or some derivitive having been oem on 1971-6 Mercedes V8s) and indicative of a certain juxtaposition of perfunctory ostreporousness coupled with obfuscatory nonsense, do I make myself clear? Because I sure can't tell.
Colin 8)

Sun Feb 22, 2004 12:28 pm

Allright Rattie and Skeptik, quit beating each other up. We're losing Westie's original problem with all of them thar big words. :D He said that the bus starts right up hot if he gets the throttle pedal in just the right position. EVERYONE knows that if you've experienced vapour- lock or fuel pressure bleed- off in a Djet , AFC, or CIS system, the only way to get it to start is cranking the hell out of it or cycling the key to run the pump and re- build pressure. It doesn't sound to me like this bus is experiencing that, so I think that while the discussion of Bosch systems and the symptoms they have in common is beneficial, it isn't helping Westie right now. In reviewing the evidence, I'd say that the following are the MOST LIKELY suspects:
I'll start with the simple and go to the worst:
1) Timing off, likely too advanced, or dwell angle off.
2) Spark plugs old and very worn.
3) Air filter dirty/ plugged.
4) Cyl. head temp sensor out of specs.
5)Throttle position sensor maladjusted, loose, or not functioning.
6)Worn valves.
I'd start by having someone stand behind the Bus while you start it under these conditions and look for smoke from the tailpipe. A puff of black smoke is too rich. White is too lean. Greyish blue is oil.
BEFORE you diagnose, or attemt to diagnose, a hard failure, PLEASE make sure all of the basic settings- Timing, idle speed, plug gap, CO value, etc. are correct. You can throw expensive parts at a problem till the cows come home, but if the basic reqirements for the engine to do what it was designed to do are lacking, you'll STILL have a problem no matter what you do. :wink:

Sun Feb 22, 2004 2:15 pm

Here's your research experiment:

- run the engine for 30 minutes and shut off
- clamp fuel line after pump
- attach vacuum hand pump to pressure regulator
- apply increasing vacuum until fuel pressure is half normal
- let engine hotsoak for gas to accumulate
- block return line to tank and divert from PR to gas can
- wait 10 minutes and try to start bus with all fuel lines unclamped and manifold vacuum attached to PR as normal

I guarantee the fuel pump will overpower and trapped gas vapor, the fuel fail pressure will jump to normal and the gas can will start to fill up extremely quickly.

The books say one of the pressure regulator's function is for improved hot start. In practice the strong pump overwhelms that ability. Improved in this context just means the injectors aren't pumping air for the first couple of seconds and the bus starts instantly. The fact the bus fails to start easily when hot doesn't support your theory unless the pump was also weak and didn't let the bus start easily when cold.

Stomping on the gas doesn't do anything for the pressure regulator when starting. The fuel pressure is a function of the engine vacuum and an engine turning over has a low vacuum level so the maxium fuel rail pressure will be around 35psi.

I stabd by my original couple of posts wrt the FI system not being at fault in the first place.

Sun Feb 22, 2004 4:12 pm

ratwell wrote:
I guarantee the fuel pump will overpower any trapped gas vapor,

The function of the pressure regulator and check valve is to prevent any vapor in the first place.

ratwell wrote:
the fuel fail pressure will jump to normal extremely quickly.

That is true, no question there, the fuel rail will almost instantly prime. but the difficulty is *getting the vapor out of the little legs to the injectors*, vapor that should not be there in the first place, there is nothing that pressure can do to get rid of it, only bleeding will get rid of it, and that is where prolonged cranking is the only way to get rid of that vapor. It's sort of like spongy brake pedal, you can only get rid of the air by bleeding not by stomping on the brake extra hard.

ratwell wrote:
The books say one of the pressure regulator's function is for improved hot start. In practice the strong pump overwhelms that ability.

The regulator *holds* pressure only when the pump is off. When the pump is running, then of course it is regulating via engine vacuum. It is sort of like the one-way valve in your brake booster.

ratwell wrote:
The fact the bus fails to start easily when hot doesn't support your theory unless the pump was also weak and didn't let the bus start easily when cold.

Again, this does not relate to the pump's ability to initiate pressure. Fuel rail pressure can be likened to a radiator cap's role in preventing boiling of coolant. We don't want any boiling in the fuel lines/injectors when the engine is off. It does not relate to the *water pump* to have a radiator cap. The radiator cap prevents boiling which can cause vapor locks in cylinder heads (not to mention damaging hot spots and gushers)
It does not relate to the *fuel pump* to have a pressurized fuel system when the engine is off. It relates to having columns of vapor in the legs to the injectors not to mention vapor in the injectors themselves (which promotes hard starting). I have these very same issues in hydronic heating systems. The circulator pump is fine, but the one of the loops doesn't heat due to vaporization from too low of a system pressure causing an air lock.

ratwell wrote:
Stomping on the gas doesn't do anything for the pressure regulator when starting.

Correct. But it does help the injectors bleed the vapor off because the injection pulse times will be greater. Just like opening a radiator bleed valve in the heating system will cause the loop to begin heating because circulation is restored.

ratwell wrote:
I stabd by my original couple of posts wrt the FI system not being at fault in the first place.

I hope my radiator cap analogy breaks this theoretical log-jam. No matter how frustrating it may seem, this is good exercise for our understanding of what is actually happening in our beloved cars.
Colin