CIS-E problem - injectors pulsing

[alaincopter]

Hi all,

Thought I'd run this problem by you folks, hoping someone has seen something similar and can share some good advice. Basically I am having this problem where my injectors are pulsing rather than spraying a continuous flow. Fearing my injectors were dirty, I've replaced them along with the fuel filter - so far, I've tried three different sets of injectors and though the brand new set showed a bit of improvement, the issue remains.

When testing the injectors, they begin spraying a continuous flow when I press a bit on the air plate, but as I press it down further they begin pulsing, and continue to spray in pulses throughout the rest of the air plate travel.

Here's a video showing the spray pattern:



My guess is a bad fuel distributor, since it was replaced (as I'll explain below). But before I get a new one, I thought it would be a good idea to hear your opinions, as I fear finding out the problem is elsewhere - maybe the fuel pump, the fuel accumulator or the pressure regulator

A little background info:

My car is a 1990 VW Fox with a .50 T3 turbo, still running CIS-E. The WOT enrichment circuit is activated via a pressure switch and I have tuned the DPR as per Jonathan's (Longitudinal) guide. Though not relevant to the fueling issue, my ignition retard under boost was taken care of by replacing the stock distributor advance diaphragm module with a advance/retard diaphragm from an old turbo Audi. Here's a link to my 5-year build thread

The car has run well using the stock FD, which later was upgraded to an Audi 5cyl unit with the 5th port blocked off for more fueling capability under boost. It still ran very well, even got it to pass emissions - but I still had to run less boost than I was hoping to, risking it leaning out on the top end. At the time, I was running about 10 psi and the car was making pretty decent power, considering what it is.

In order to provide even more fuel and also to clear out some space in the engine bay to make room for an intercooler, I moved on to a Mercedes V8 fuel distributor which is a downdraft unit. This change was made along with a big tear down of the whole car. Due to this and also due to spending some time overseas, the car stayed parked for well over a year.

I really want to get it back on the road soon, but the funds have nearly ran out and until I begin working again I won't be able to afford to keep replacing parts, so good input would be greatly appreciated!

Pics of the car just because

[ziddey]

Whoa, that is crazy. Can you get a hold of a fuel pressure test kit for CIS? Curious what your system and control pressures are (hell, I'm curious what mine are!!)

I thought the point of going with the MB distributor was to run 4 additional injectors in the intake runners? How far are you pushing the plate before they start pulsing like that?

[alaincopter]

Hey ziddey, thanks for chiming in. I am also curious to test system and control pressure numbers and more specifically to see if it variates, which would help pinpoint the problem. Do you know any good, inexpensive kits to get?

Bigger fuel distributors are capable of providing more fuel even when still running four injectors, as the injectors are not the bottleneck in the system. Sure that remains true up to a certain point and past that point more injectors will increase flow - having the option of running 8 injectors available for the future was a major factor to consider picking out this unit. But the main basic advantage is being able to meter more air (larger diameter air plate) and flow more fuel through the metering head. A factory practical example of this would be the Volvo 240 Turbo fuel distributor, which is essentially a 6-cylinder unit with only 4 ports machined on it. So the plan would be to try out the V8 FD with 4 injectors and seeing what it can fuel up to, then upgrading in the future when necessary One thing I can say is that when testing, it seems that the quantity of fuel coming out of the injectors doesn't seem to stop increasing as I press the plate further and further down, until at about maybe 80% travel and above. When I get things working right, I may run a few cc tests.

The pulses start at what feels like maybe 10% of air plate travel - or in another way of looking at it, at what looks to be just a tad bit more plate travel than I can see when revving it up in neutral.

I really think it may be the FD itself that's faulty since I pulled it from a 450 that probably sat for years at the JY - maybe the ethanol-blend fuel did a number inside it while it sat?

[turbinepowered]

The pulses start at what feels like maybe 10% of air plate travel - or in another way of looking at it, at what looks to be just a tad bit more plate travel than I can see when revving it up in neutral.

I really think it may be the FD itself that's faulty since I pulled it from a 450 that probably sat for years at the JY - maybe the ethanol-blend fuel did a number inside it while it sat?

If it's a mercedes part from the 80s, I seriously doubt that would be the case. Old gas would be more the culprit I'd suspect, with its dirt and varnishes that drop out as it ages and evaporates.

When you're idling, are they pulsing? I'm with Ziddey in thinking this is a fuel pressure issue, not a distributor head issue. Those pulses almost look like you're just not flowing enough fuel through the lines to keep the valves in the injectors open, which could indicate a pressure issue.

You're using a very large distributor to run a somewhat small engine, so you might find that you need to mess with system and control pressure to get a smooth fueling curve.

[turbinepowered]

Oh, also, if you guys can't find a CIS pressure kit, I have one I'm willing to rent out, especially to Fox folks I know.

[edit] ZDMAK on E-bay has a CIS kit for sale, but it's $160 shipped. I can't remember how much I bought mine for, but it was MUCH less than that several years ago at a "shop sale."

[WaterWheels]

Want to make it clear up front that this is not a subject I have a lot of information on or experience working with. I really just want to throw out some ideas from looking into this kind of stuff and see where it goes or what it creates. Nothing should be considered “engraved in stone” but rather food for thought and to stir up some possible deeper discussion.

First the action of the injectors, the chattering they do. Although yours do seem very extreme, it is somewhat normal. More often it happens much faster and turns into a squeal kind of sound, like a stuck pig. The injectors are opened via the pressure forced through them and they will open and close based on the pressure/volume the fuel distributor is sending. They will always be trying to close due to the internal spring. As I said, yours do seem to be a slower more defined open-close so there could be a delivery problem to the injectors. Not going to say it is the fuel distributor as I can’t tell from where I am, but pressure could be to low coming out of the distributor.

Next is the concept, yours and others also, that using a fuel distributor from a six cylinder or 8 cylinder car is going to supply more fuel. Take the 5 and six cylinder VW engines for example. Their cylinder displacement is the same as the 4 cylinder engines, they just have one or 2 more cylinders. I don’t know the Merc engine sizes and their cylinder displacement but I am sure they are also about the same. It is my opinion that the fuel distributors are all just about the same and swapping what is thought to be a „more flowing“ one serves no purpose.

I have a chart somewhere which lists air and fuel flow for some of the CIS mixture units. The fuel distributors do vary some but really not a lot and for sure not as much as people seem to believe based on hearing talk about swapping this one for that one. I believe the air cone is a much better place to do „up grading“ if you are looking for more fuel delivery. I have stripped down dozens of different fuel distributors, VW, Porsche, Opel and Mercedes and they all appear the same as far as machining and parts goes. Yeah, there could be a very slight size difference here or there as I did not measure anything, but I didn‘t notice any difference just in looking. Most of what I saw as being different were the position of external things which would vary by manufacture and model.

Here's my take on increasing flow if one determines they have to:
They all run on about the same system pressure so that would not be a place to look. Fuel flow out of the distributor is based on the differential pressure difference and plunger lift. Plunger lift is a function of air cone and how it is machined for a particular engine. So I believe gains could be made by matching a different air cone to whatever fuel distributor you are using. Which will work for what application I can‘t say, but the function of the plate and cone shape is easy to understand and tinker with I think. Heck, years ago I remember some company sold "inserts" which changed the cone shape. The differential pressure, basic CIS anyway, is determined by the spring pressure and the setting made at the factory. I would not suggest trying to use different springs, but if you know what you are doing you can adjust the differential pressure and with it the flow real easy. It is what you would do to balance the injector output if it were off too much, just to a more extreme degree. CIS-e is a little different but the basic idea is the same, alter the differential pressure to increase fuel flow and the balance screws, if it has them, to also increase flow.

Anyhow, hope this at least stirs the gray matter a little. And again, it is only my thoughts as I have seen almost nothing on the subject written (as of yet).

[alaincopter]

Kurt (turbinepowered), thanks so much for your willingness to help I will try to see if my local Canadian Tire store has a pressure tester to loan - sometimes I loan brake flaring tools, gear pullers, clutch alignment tools from them and I think I remember seeing a FI pressure tester in their catalog. Granted it's most likely not for CIS, hopefully it can be fitted where I need it to and the gauge will go up to around 100psi. If not though, I may very well take you up on the favour, thanks man!

I'm definitely not trying to diss '80s Mercedes quality when believing the FD could have gone bad inside - I recognize Mercedes parts are some of the best quality stuff around - but the fact of the matter is that it's a part made by Bosch just like any other FD, built out of aluminum and thus just as likely to corrode with ethanol-blend gas over time as the fuel distributors from a Fox or a Ferrari would be. Mercedes' reputation doesn't change that. When showing my car on brazilian forums a few years back, a guy who was a mercedes tech for decades quickly identified the CIS-E system and went on to say that brazilian gas (which is by law 24% alcohol) was very tough on the Mercedes they would work on at the dealership and that they had to replace dozens of failed mercedes fuel distributors back in the day costing the owners a fortune. That is probably why CIS and its derivatives were never available in the brazilian domestic market, even though they built cars with the system there for export only. If 24% ethanol can be that harmful on fuel distributors that are flowing daily, 10% can be at least a bit harmful when stored inside one sitting for years. I'm sure you read reddfoxx's turbo wagon thread. There, when Jonathan (Longitudinal) first replaced the stock FD for the Audi 5-cyl unit for greater fueling capability, he came across a faulty FD, and had to replace it for yet another Audi 5-cyl FD. It does happen... I do hope it's the fuel pump though, it would be a much better problem to have!

They are not pulsing at idle; Idle is not great, there's the occasional miss, but it's at little throttle (cruise) where the worst is felt. What you said about running a big FD on a small engine is true, but I wouldn't think that that itself would be the issue. The only things that would "tell" the FD that it's being run on a small engine would be the fuel pump and the fact that only 4 injectors are being used, but I believe the fuel pump is similar or at least flows the same volume and pressure (please correct me if I'm wrong) on Foxes and Mercedes, and about the injectors, other people have run this FD with 4 injectors in the past without this issue.


WaterWheels, thanks for sharing your input. I don't mean to sound rude, I really apreciate you trying to help and invite you to keep the info coming if you'd like - but I just have to say that I agree with little of what you wrote:

Your first point about the behaviour of my injectors in the video being somewhat normal: It's actually anything but normal. Even as the name of the injection system suggests, fuel injection is supposed to be continuous. The valve inside the injector does indeed receive force from the spring that would make it close but in normal operating conditions it does not fully close until the engine stops running and pressure drops below 3.3 bar. What you described (the "singing") is from the mere vibration of the valve, as described on page 7 of the Bosch Manual. This page explains very clearly how the injectors work. Other than that, you can watch any video of cis injector testing, and you'll see none of them ever spray in pulses.

Your next point talks about cylinder displacement being the same between vw models (??) and why you think that bigger fuel distributors won't be able to supply more fuel than smaller ones. It is a known fact that a bigger fuel distributor has a higher fueling capacity, there's no point in arguing that. There's theorical, practical and factory-used real world data proving that and I don't think it's necessary to explain it further, but if you would need me to I can. For now, I'll just leave two simple bits of data in order to try and make this post not longer than it's already going to be:

- A stock Fox makes 81hp and the stock FD is known to fuel up to 170hp, the point at which other provisions (such as opening the CSV, adding more CSVs, etc) have to be made to extract more fuel from the system. This "bottleneck" in the system is not caused by the injectors, as we know there are 4-cylinder cars running similar injectors making more power.

- A stock Mercedes 450 SEL had a 6.9 liter engine making over 280 horsepower. A fair guess would be that given the tolerances used in the vehicle, the fueling system is capable of providing fuel for more than just a bit more power than that.

The chart about fuel and air flow would be interesting info to have on hand, please share it if you can But also please note that air cone "upgrading" serves little to no purpose with CIS-E, as all it would do would be to change how much the plunger is being pushed up for a given amount of air plate travel. Effectively, this would force a richer (or leaner depending on the change, but we're clearing talking richer in this context) condition for certain amounts of air flow, which is undesirable when the car needs to be able to pass emissions tests (mine does). This practice was valid on older CIS cars (I remember reading about that on old Saabs a while back) but cars equipped with CIS-E have the ability of "choosing" to run either stoich mixture or richer mixture, with the aid of the differential pressure regulator and the WOT circuit . Also worth mentioning that changes to the air cone will not affect the maximum amount that the plunger can be pushed, and as a result will not increase maximum fueling capability of the system; it will merely affect how "soon" the plunger is pushed for a given amount of air plate travel.

Maybe I should have mentioned earlier that I am not having any issues whatsoever with fuel enrichment or my system's fueling capability on the top-end: the car is making very good power, and I do notice that this current FD, even with the issues on the low end, is able to provide adequate fuel for higher turbo pressures (and by consequence more power) than the Audi 5-cyl unit did - which was already more than the Fox stock FD did. This is not what's being tested in this thread, but since the subject was touched: I'm still going to dyno test my car and I have no doubt that you can make at least 200hp still running 4 injectors.

Anyway, moving back to the problem I'm facing - I removed and inspected the little filter inside the bolt where the fuel inlet connects to the FD. That filter was nearly plugged, I could barely blow air through it. Removing this filter didn't change anything though and I'm still getting the pulsing behaviour. Knowing that my FD has at least 9 more filters INSIDE IT, my theory that something inside the FD is causing this on-off pressure drop at the injectors seems more and more possible. Stay tuned and please continue to share thoughts, folks!

[turbinepowered]

Kurt (turbinepowered), thanks so much for your willingness to help I will try to see if my local Canadian Tire store has a pressure tester to loan - sometimes I loan brake flaring tools, gear pullers, clutch alignment tools from them and I think I remember seeing a FI pressure tester in their catalog. Granted it's most likely not for CIS, hopefully it can be fitted where I need it to and the gauge will go up to around 100psi. If not though, I may very well take you up on the favour, thanks man!

I'm definitely not trying to diss '80s Mercedes quality when believing the FD could have gone bad inside - I recognize Mercedes parts are some of the best quality stuff around - but the fact of the matter is that it's a part made by Bosch just like any other FD, built out of aluminum and thus just as likely to corrode with ethanol-blend gas over time as the fuel distributors from a Fox or a Ferrari would be. Mercedes' reputation doesn't change that. When showing my car on brazilian forums a few years back, a guy who was a mercedes tech for decades quickly identified the CIS-E system and went on to say that brazilian gas (which is by law 24% alcohol) was very tough on the Mercedes they would work on at the dealership and that they had to replace dozens of failed mercedes fuel distributors back in the day costing the owners a fortune. That is probably why CIS and its derivatives were never available in the brazilian domestic market, even though they built cars with the system there for export only. If 24% ethanol can be that harmful on fuel distributors that are flowing daily, 10% can be at least a bit harmful when stored inside one sitting for years. I'm sure you read reddfoxx's turbo wagon thread. There, when Jonathan (Longitudinal) first replaced the stock FD for the Audi 5-cyl unit for greater fueling capability, he came across a faulty FD, and had to replace it for yet another Audi 5-cyl FD. It does happen... I do hope it's the fuel pump though, it would be a much better problem to have!

I'm not doubting Mercedes quality either, or that there were troubles early on with adapting them to ethanol added fuels. I don't think that it was nearly as much the ethanol having bad reactions with the aluminum (unless they weren't using anodized materials, in which case sure they were having problems) so much as seal materials, especially in the 70s and early 80s. If aluminum has a protective oxide layer, ETHANOL is no problem; methanol, like "race fuel," would still cause problems.

Also, I'd rather work with something that had E10 in it for a decade sitting than E0; at least the relatively nonvolatile ethanol component would help keep the crap in the gasoline in suspension, rather than it all drying out.

They are not pulsing at idle; Idle is not great, there's the occasional miss, but it's at little throttle (cruise) where the worst is felt. What you said about running a big FD on a small engine is true, but I wouldn't think that that itself would be the issue. The only things that would "tell" the FD that it's being run on a small engine would be the fuel pump and the fact that only 4 injectors are being used, but I believe the fuel pump is similar or at least flows the same volume and pressure (please correct me if I'm wrong) on Foxes and Mercedes, and about the injectors, other people have run this FD with 4 injectors in the past without this issue.

There is also the air plate movement at low engine speeds and off boost that will "tell" the distributor that it's on a smaller engine. The fueling curves aren't linear, and are influenced by the fuel pressures.

Anyway, moving back to the problem I'm facing - I removed and inspected the little filter inside the bolt where the fuel inlet connects to the FD. That filter was nearly plugged, I could barely blow air through it. Removing this filter didn't change anything though and I'm still getting the pulsing behaviour. Knowing that my FD has at least 9 more filters INSIDE IT, my theory that something inside the FD is causing this on-off pressure drop at the injectors seems more and more possible. Stay tuned and please continue to share thoughts, folks!

I'd suspect this more than fuel-related corrosion.

[ziddey]

I know EL DRIFTO had a writeup on running E85 with CIS. IIRC, it was more the rubber causing problems than anything else?

[turbinepowered]

I know EL DRIFTO had a writeup on running E85 with CIS. IIRC, it was more the rubber causing problems than anything else?

Yep.

[alaincopter]

Found the E85 thread, thanks for sharing ziddey, it's a good read (or decipher lol). From there, it seems common fuel filters (paper) also dislike ethanol.

I don't think that it was nearly as much the ethanol having bad reactions with the aluminum

Some good points you shared, thanks Kurt - I will discard the possibility of Ethanol having corroded any aluminum, and stick with clogged mini filters inside the FD as the probable cause for now.

There is also the air plate movement at low engine speeds and off boost that will "tell" the distributor that it's on a smaller engine. The fueling curves aren't linear, and are influenced by the fuel pressures.

I am pressing the plate down on the plate with my fingers... definitely not the issue.

Again, the problem is not with the air flow being metered correctly, or with the quantity of the fuel sprayed. It is solely with the fuel spray being intermittent.

Gonna run a few more tests today but may very well IM you about that pressure tester - they didn't have one in their catalog for borrowing after all.

Thanks, Alain

[alaincopter]

Ok, I've got a new theory - I think this is it!

Today I tested two things with the fuel pump.

I've been testing it so much that my battery voltage dropped below 11 volts - so I had an idea. I hooked up a battery charger to the battery on the 50 amp engine start setting, and used a power bar to be able to switch the battery charger on when I wanted. Then I proceeded with the injector spray test - you could tell there was a pretty noticeable difference in the sound the fuel pump made when turning on the battery charger, but there was no change at all in the spray pattern.

I then proceeded to test the fuel pump output. This was still with the battery at around 10.5 - 11 volts. I read that it should be at or above 0.5 gallons per minute; I did a 10-second test and it overflowed a 341ml container (), which equals rough estimate of output being over 0.55 gpm.

ANYWAY; I am certain that the fuel pump output and pressure were higher when the 50amp were supplied to the run-down battery; I should have been able to see at least SOME change in the spray pattern behaviour. It should have gone from terrible to "just bad", perhaps.

So the new theory is: the custom made fuel lines to each injector!! I made them with metal brake lines (not a problem there) and high-pressure fuel injection rubber hose. This hose, though high-pressure rated, expands under pressure and absorbs some of the pressure that should go to the injectors instead! This would explain everything!

I did my lines this way for a few reasons, the first one being that the ports on the MB FD are larger than on the VW FD, so the Fox lines can't be used unless a banjo bolt adapter is used, which I'll probably need to source soon. The original MB lines are hard steel similar to brake lines, but of course the FD on the benz sits on top of the engine, so the lines don't need to flex. I made my lines with steel brake line but added the piece of rubber FI hose so that they could flex, and that's where my problem most likely lies.

I first thought that since Deloreans used rubber hose going to the injectors, and CIS-Motronic cars had some sort of rubber hose for that too, it should be fine, but at the time I didn't know that those are actually nylon lines coated with rubber. Live and learn!

So now I am left with two options - either get some nylon CIS-specific lines from here, or try to find some banjo bolt adapters similar to the one pictured below in order to be able to use the stock stainless-steel braided VW lines.



Anyone knows where I could find this sort of adapter?

[alaincopter]

(M10 x 1.00 male, M8 x 1.00 female)

[turbinepowered]

Not sure where to get those adapters; I once could have told you, but the hydraulic supply place nearby closed up two years ago.

That would be my first suggestion, actually. Hunt up an industrial supplier that does hydraulic parts, then call them up and ask if they have your M10 to M8 adapter available. The banjo bolt fuel setups are basically derivatives of high pressure hydraulic line designs.

[edit] If nothing else, this page has something, search for FA-1023M for an M8 female to M10 male adapter. $13.50 US apiece, though.

[ziddey]

http://www.trico-oilers.com/Adapter-...M-FA-1023M.htm
different website but I'm assuming same company. lists it there for $11.40

still a bit pricey. checked mcmaster-carr and they don't have it

[turbinepowered]

http://www.trico-oilers.com/Adapter-...M-FA-1023M.htm
different website but I'm assuming same company. lists it there for $11.40

still a bit pricey. checked mcmaster-carr and they don't have it

Grainger might. They have more lubrication stuff.

[alaincopter]

Thank you for the help guys!

I've spent most of the day calling hydraulic fitting places and scouring the internet, the Trico adapter you found may be the best solution. True, it's pricey, but so far it seems to be the best bet.

I spoke to Trico and they have three of these in stock , and it'd be a couple of weeks to get more. I called around their distributors here in Canada, but no one keeps them in stock; the other sites mentioned probably have them (Stanios sells for $10.23 each) but when I get to check out, the cheapest shipping to Canada is over $60. If I can't find anything else, I may try ordering them and channel the shipping through the States, but will see if there is another solution first:

Adapt-all seems to carry an adapter too (9638-10X1.0-08X1.0, second down the list) and being that it's made in regular carbon steel and they are Canadian, I may be able to get it for cheaper than from Trico. I'll give them a call tomorrow

Thanks!!

[alaincopter]

Noticed I haven't touched this thread since solving the problem, and thought I'd post the solution for any folks reading this that may have similar problems.

The problem was completely solved by using stock Fox injector lines.

Due to the near-unavailability and price of commercially made adapters, I ended up making my own adapters by tapping and shortening brake line fittings - they are basically threaded sleeves, M10x1 outside, M8x1 inside, which allow the smaller bolts from the Fox to fit the larger ports on the Merc FD:



Commercially-made adapters like the ones pictured higher up in this thread would also have made the line fittings sit a bit too high in the end. With the adapters I made, everything works and looks close to stock:





I spent some time tuning it for emissions since solving the problem and I have to say I love what this FD can do. It has no problem running on a smaller engine and half the injectors it originally was meant for - mixture is stoich at idle and part throttle, fuel delivery is constant and smooth, throttle response is great, and it gets nice and rich when in boost. I've taken the car on a 1200km road trip since and it behaved very well and delivered great fuel economy, close to that of a stock Fox.

For more info, check out my thread