K-Jetronic tune-up Part II -- Accumulator and Fuel Pressure Regulator

This how-to is the next step in my attempt to get my '83 400i auto to pass California Smog Check II. (Smog Check II is a sniffer test which puts the car on rollers and samples emissions of the key pollutants -- unburned hydrocarbons, carbon monoxide, and oxides of nitrogen -- at 15 and 25 mph.) I'm calling this installment "Part II." "Part I" would be the thread "Checking system and control pressure on K-Jetronic."

To establish my starting point, here is a tabulation of the results from three Smog Check II runs that the previous owner did earlier this year, followed with three runs that I did last weekend.

------------HC@15--HC@25--CO@15--CO@25--NO@15--NO@25 [=15 and 25 mph]

Max allowed--130-----103-----0.94-----0.74----1106-----936

01/07/2012---200------99-----1.24-----0.91----1332-----979
02/03/2012---174------87-----1.32-----1.51-----100------12
02/08/2012---184-----118-----2.09-----2.49-----126------36
06/23/2013a--498-----303-----3.75-----2.08-----287-----615
06/23/2013b----------288--------------0.11-------------1422

Between the 1st and 2nd tests the P.O. got new catalytic converters installed to replace the ones that were on the car when he bought it in 2007. That caused a big drop in NOx and a slight improvement in HC. But CO got worse! Between the 2nd and 3rd tests the distributor cap was found to be misaligned, which caused the ignition timing to wander. Correcting this condition cured a hunting sensation that had been present at steady cruise -- which is what Smog Check II uses -- but it bumped the car into Gross Polluter status with respect to CO @ 25 mph. The Gross Polluter cutoff for CO @ 25 mph is 2.24%, and the car tested at 2.49%.

I did the June 23 tests after I had discovered that the cold start injector on the passenger side was always on, a condition which would have required a too-lean adjustment of the mixture control plunger in the fuel distributor in order for the car to start and idle. Besides correcting the wiring I also put a Colortune on each cylinder bank and, with the engine running at 2000 rpm, I adjusted the idle mixture adjusting screw to try to achieve a correct air:fuel mixture. I thought I would see a great improvement over the P.O.'s Smog Check II results. But I did not. The owner of the Smog Check shop was kind enough to let me adjust the mixture with the sniffer in operation, to try to improve on the results using the real-time readouts on his system's computer monitor. This is why I have an "a" and a "b" result.

In a long telephone call with Larry Fletcher at CIS Flowtech (www.cisflowtech.com/), Larry gave me a road map for further tune-up techniques. The first step is to set the airflow sensor plate at the correct rest position. We will get to that later. But before we can make that adjustment, first we need to check that the control pressure is holding steady with the engine off. This is because the sensor plate height is controlled, in part, by the mixture control plunger. And the height of the plunger is controlled by the the system pressure and the control pressure.

 

To check the car's ability to maintain system control pressure, you have to check the vent on the "dry" side of the fuel accumulator. This is what I did yesterday. The fuel accumulator consists of a spring loaded diaphragm which is pushed open when the fuel pump is running and which closes up when the fuel pump turns off. In the closed position, system fuel pressure is held in, to make it easy to start the engine the next time.

The "dry" side is vented to the outside world. In the diagram, below, that vent is indicated by a discontinuity in the rear wall of the "dry" side. In the 400i, the vent is a metal tube that comes out the back of the accumulator and takes a 90 degree bend. A rubber fuel line is hose-clamped onto the end of the tube. The other end of the hose vents into the fuel tank.

If the diaphragm has a hole in it, this means two things: that it doesn't work -- it won't maintain system pressure with the fuel pump not running -- and that there's going to be fuel present where it doesn't belong, in the "dry" side.
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Here are some photos of my check of the fuel accumulators on my car.

The first photo in this post shows the driver side of the car jacked up. I didn't jack the car up very high. Jacking it up higher would have made this job easier, and possibly a little less messy.

The second and third photos show the fuel pump and fuel accumulator on the passenger side, then the fuel accumulator on the driver side.

The fourth photo shows the rear of the passenger side accumulator. You can see the 90 degree tube and the rubber hose.
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Yes. What "correcting the wiring" means is that I took the always-on connector that was connected to my cold start injector and plugged it into the auxiliary air valve ("AAV"), and took the on-for-a-few-seconds-when-cranking connector from the AAV and plugged it into the cold start injector.

I'm just following the Larry Fletcher method. He says we need correct control pressure to get correct airflow sensor plate height. That requires the fuel accumulators to be doing their job, even if their ability to hold pressure lasts just one hour or less. I also have a hot start problem, and the most likely cause of that is the fuel accumulator(s).

The routing you describe is not the case in my '83 400i, as I discovered to my gasoline-soaked surprise. Read on.

 

Resuming my fuel accumulator how-to: what we've got to do first is remove that hose from the 90 degree tube. Then we will run the fuel pump and see if any fuel comes out the tube.

I got a big surprise when I removed the hose from the tube the first time. The first photo, below, shows the rear of the driver side accumulator with the hose still in place. The second shows what happened when I pulled off the hose: gasoline came flowing out the hose at a great rate! With me laying underneath the car and reaching up to jam the hose back onto the tube, quite a bit of gasoline poured into the sleeve of the jumpsuit I was wearing. I discovered that gasoline causes a burning sensation to the inside of your upper arm and to your back, but not so much to the forearm. Funny how that works.

The reason for this mishap is that the hose -- which I thought merely vented into the top of the gas tank and therefore should hold no fuel under normal operation -- in fact is plumbed into a T-junction with the much larger hose which connects the fuel tank to the fuel pump. The third photo, below, shows this junction. The lower hose clamp in the photo is on the hose to the accumulator. The upper hose clamp is on the hose to the fuel filter. (FYI, the flow path goes from the tank to this T-junction. Then, as already mentioned, the main fuel line proceeds to the fuel filter, then to the fuel accumulator, then to the fuel pump, and then to the front of the car.)

Anyone who considers following this how-to must decide how much he or she wants to get a soaking with gasoline. A little bit of contact is inevitable, although if you follow my advice you won't need to experience the multiple soakings that I have enjoyed today.

That advice is, first, to have a drain pan ready to catch the spillage. Second, have at the ready a length of 3/16th fuel line hose, about 7" long. (For you metric types, measuring with my calipers I found that the inside diameter of the original fuel hose is about 5.25 mm.) Have a hose clamp loosely in place and ready to go at one end -- not too tight or the hose won't fit over the nipple on the T-junction -- and at the other end have a 3/16" bolt threaded into the hose and hose-clamped in place. See the photo, below. Third, don't start by removing the hose from the tube on the accumulator. Remove the hose at its other end, at the T-junction with the main line from the tank. You are going to get spillage when you do. But quickly jam the 7" piece of hose onto the T-junction and tighten the hose clamp.

Please try not to ignite the gasoline, because if you do you are going to catch fire and so is any gasoline flowing from the tank, and both of you are going to burn at a rapid rate. The combination is likely to lead to a total loss of one of these precious F-cars, and I would feel personally responsible if that were to happen. I would also regret your burn injuries and disfigurement.
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Now we're ready to check the fuel accumulator. I pulled the Bosch connector off the fuel pump cutoff switch at the airflow sensor plate on the driver side. The first and second photos, below, show the blue plug where this Bosch connector goes. Then I turned the ignition key to the "run" position, position III, and went back to observe the fuel accumulator.

The third photo, below, shows what I saw: a steady flow of fuel. Unless someone tells me otherwise, I believe that this indicates a defect in the fuel accumulator. Specifically, the diaphragm has a tear or a hole in it. This disables it from maintaining system pressure after the fuel pump stops running.

The reader will also notice that my earlier description of the rear half of the fuel accumulator as "the 'dry' side," was mistaken. It would seem that in the '83 400i, at any rate, this rear half is always filled with gasoline, albeit it at atmospheric pressure. So it would be better to describe the rear half as "the spring chamber" or something like that.

OK, so now that we've checked the vent tube for anomalous emissions with the fuel pump running, we shut off the fuel pump. Now it's time for another soaking. Loosen the hose clamp around the bolt at the loose end of the 7" hose that we've previously attached to the T-junction with the main line from the tank, and unscrew the 3/16" bolt. Now jam this end onto the tube at the rear of the fuel accumulator and tighten the hose clamp. The final photo shows the result on the driver side accumulator on my car.
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Oops. I just realized the two photos of the blue plug in the previous post show the cold start injector, not the fuel pump cut-off at the sensor plate. All those gasoline fumes must have left me confused. The correct connector is also blue, and it is located just to the right of the one in the photos.

 

Hi Bruce. I have that Probst book. It is a good one.

The rag technique will not help, when you've got the entire contents of your gas tank ready to exit the T-junction between the time you pull off the hose to the fuel accumulator and jam on the replacement hose with the bolt plug at the other end.

BTW, the reason I recommended to replace the hose from the gun is because I found with my original equipment, fabric-wrapped hose, that when I plugged it with a bolt it split. When I cut off the split portion -- of course with gasoline pouring out of the hose -- I found that it would split all over again when I tried to jam it back onto the nipple on the fuel accumulator. I performed this split end cutting twice, with gasoline raining down, before I gave up, and decided to replace the entire hose from the T-junction forward.

@ Steve: that's interesting that the T-junction on my car is aftermarket. I thought this arrangement looked awfully cobby to be a factory install, with all these hose clamps and rubber hoses.

I wonder if it affects the life of the fuel accumulator to have gasoline continuously present in the spring chamber, if that was not the plan when they were designed and built. In any event, those 400i owners who can check fuel accumulators that don't have the vent plumbed directly to the fuel tank should count themselves as lucky.

My next question is, where do I get a pair of fuel accumulators? Larry Fletcher says they're a Mercedes part as well. Does anyone have a source?

 

Thanks for the tip. I Googled "1983 ferrari 308 fuel accumulator" and "1983 ferrari mondial fuel accumulator" and the top hit on each is Rockauto.com's page for Bosch pn 0438170004, with a price of $96. http://www.rockauto.com/dbphp/x,carcode,1299427,parttype,6048,d,1983_FERRARI_MONDIAL_8_3.0L_2927cc_V8_FI_Fuel_Accumulator.html

I have done a lot of business with Rockauto.com over the years, and have always been happy with them.

 

This information from my post of July 1 is all wrong. The fuel goes from the tank to the fuel pump, then to the accumulator, then to the fuel filter, and then forward to the engine. I wish this forum allowed editing, to eliminate stupid misinformation like this.

To return to our story so far: we have seen fuel flowing from the vent tubes on both my fuel accumulators and have taken this as proof that the diaphragms in the accumulators were leaking. I ordered two new Bosch accumulators at $96 apiece. The first attached photo shows the parts, including the part number visible on the unopened box. The other photos show a new unit next to the old one from the driver side. I thought it interesting that the green color has not changed, as evidenced by the 1" segment of the vent tube (on the unit to the left of the fourth photo) that was covered up by the hose which, in my car, leads to the T-junction with the main fuel line.

The final photo in this post shows the old bracket wrapped around the new accumulator.
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These photos show the new parts installed. The driver side swap went smoothly. But the passenger side was a disaster. The work space around the T-junction in the fuel line is more cramped on the passenger side. When I pulled the existing hose off the T-junction, with the new hose at the ready with one end plugged with a bolt, I could not get the new hose to go onto the nipple on the T-junction. Also, a little bit of the escaping gasoline was flowing along the undercarriage and onto my head. Because I am right-handed, I was laying on my left side to access these parts. With my head laying sideways, some of the gasoline got into my ear. No big deal, I thought, I've almost got the hose on the nipple and then the flow will stop.

But here's what I learned, and pretty quickly: that putting gasoline in your ear is a bad idea. I've had worse ideas, but not many. It will start to hurt a little bit, then a little more, then A LOT! If you've ever had a bad ear infection, it's like that, but worse. I was soon under the faucet at the kitchen sink running warm water into my ear. That relieved most of the pain, but luckily I also had a Vicodin left over from a wisdom tooth extraction or something, a pill probably ten years old or more, but still effective. With the drugs I felt good enough to finish up the job and take the two pictures attached to this post, showing the new units in place, driver side and passenger side.

So there you go, next time you find yourself with gasoline in you ear: lots of water and a little Vicodin.

Also, I discovered a new trick which would have saved me a lot of trouble if I had thought of it earlier, and that was to use a needle nose Vice Grips pliers like a hemostatic clamp on the fuel line. Those of you with cars whose EPA federalization did not include this idiotic plumbing of the fuel accumulators into the main fuel line will not have to deal with all this drama. But if you're not so lucky, this trick will save you some trouble.

Also be advised that if you do have this oddball plumbing, on the passenger side you are going to have to unbolt the mounting bracket that holds the fuel accumulator and the fuel pump in place. This is because the vent tube on the fuel accumulator points upwards on this side, such that routing the fuel line from the vent tube to the T-junction requires dismantling the whole assembly in order to do this accumulator and hose swap.

The good news is that this swap seems to have eliminated my hot start problem. Indeed the engine now restarts with barely a touch of the starter motor.
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I'm thinking you all are taking it easy on the newb.

 

Moving along with this K-Jetronic tune-up Part II -- the Larry Fletcher way: recall that the fussing with the fuel accumulators was a preliminary to checking, and possibly correcting, the at-rest position of the airflow sensor plate. In order to do that step, first we need to check that the control pressure is holding steady with the engine off. Verifying that the fuel accumulators are holding system pressure was part of that preliminary work. The other part is verifying that the fuel pressure regulator is holding control pressure.

To check the operation of the fuel pressure regulator, first you run the engine so that the WUR has warmed up to its normal operating temperature. When I performed my pressure checks I found that this takes between four and five minutes. Then you remove the fuel return line from the base of the fuel distributor. It's the biggest banjo fitting. If you're standing at the driver's side of the engine bay, it's located at 6:00 on the driver's side fuel distributor. In the first photo below I have put a box wrench on the correct banjo fitting.

After you've removed the return line, what you're looking for is fuel dripping from the return line's hole in the base of the fuel distributor. The second and third photos show a bit of this fuel escaping out the hole and adhering to the base of the fuel distributor. What you want to do is count how many drips fall from the fuel distributor. There should be at least five seconds between drips. If the drips are falling more often than that, then the fuel pressure regulator is not sealing properly and the system isn't holding control pressure.

In my case, there were no drips at all. The accumulation you see in the photos never increased to the point where there were drips.

The fourth and fifth photos show the passenger side. The fitting on this side faces toward the center of the engine, so that it's at 12:00 if you're standing at the passenger side of the engine bay. The story was the same over here: a little fuel came out at first, but the accumulation did not increase and there were no drips at all.

I conclude that both my fuel pressure regulators are working.
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