Uneven Mixture Across Cylinders

[Pawel66]

I am looking for your kind advise on this, did some tests.

Symptoms
1. Spark plugs 5 and 6  - fairly dark brown (NGK 7ES, but same was with Bosch 7)
2. Spark plugs 3 and 4 as should be
3. spark plugs 1 and 2 insulator matt white, ground electrode light grey
4. CO level in the left exhaust 0.5% higher than in the right pipe at ca 4.5 - 5% in the right pipe

Looks like 5 and 6 are too rich or 1 and 2 too lean.

What i checked:
1. Compression is pretty even across cylinders (could not find the data sheet, but I remember there were no big differences)
2. I have no leaks of air to the inlet (checked with e-cigarette and washer pump)
3. FIP is giving equal amount of fuel across cylinders with no pressure, meaning measured form the lines before injectors

but

4. Amount of fuel given to 5 and 6 higher than in other cylinders, particularly 1 and 2 (ca 30%) when measured from injectors. This does not depend on injectors - after swapping injectors there is consistently more fuel for 5 and 6.

Shall I move now on to check valves?

I would imagine a weakened check valve would allow more fuel so that the pressure above the valve, at the injector  is built up faster. When no injector is there, there is no pressure above the valve, they all open anyway. When pressure above the valve is there, weaker valve opens easier and more. Weaker check valves are in 5 and 6.

Am I right?

[Benz Dr.]

I would check the injectors to see if you have even spray patterns and breaking pressures.

[Pawel66]

Thank you!

Particularly form 5 and 6.
Did that. Built my tester, took a Coke bottle and checked - they are all fine. Chirping and spraying nice cones. The opening pressures were slightly off, but within the range I found on the forum.

Also - when measuring the fuel amounts I swapped them. The effect stayed, did not move with the injector.

[Benz Dr.]

OK, how are your compression readings?

[Pawel66]

I lost the page with the data, I remember, however, that there was nothing alarming and differences between the cylinders were within ca10%.

[Benz Dr.]

It's possible that some of your valve guides are leaking oil into the combustion chambers making your spark plugs look a bit darker. Whatever it is, I don't think it's critical.

[Pawel66]

Thank you, I ,obviously, have not thought of that...

[Pawel66]

Having Benz Dr. idea in the back of my mind, I did some checks:

1. Checked compression again and, even though the values are pathetic (140psi, I thought it would be higher, so this was disappointing, I need to check it again on some more professional gauge), they are very even across cylinders to the point I could not tell the difference form reading the gauge.

2. Tested  the check valves (as per BBB) and none of them is leaking even a drop.

By adding fraction of the main adjuster turn each time I checked the plugs, I got to the point where I have cylinder 1 and 2 light brown, 3 and 4 medium brown and 5 and 6 dark brown. I need longer run now to see how would they look like - I do not think I will damage anything due to too lean mixture.

I have idle at 4% on the right hand side pipe and 4.5% on the left hand side pipe.

I will now test the warm up cycle. The car stalls at 70 degrees, I think I need to add round shim for the WRD to cut off a bit later.

The car starts immediately cold or hot, runs very well, no blue smoke nor white nor black smoke whatsoever from the tail pipes. Coolant clean, oil clean.

[mrfatboy]

I will now test the warm up cycle. The car stalls at 70 degrees, I think I need to add round shim for the WRD to cut off a bit later.

I think you are too lean during the “lean dip” during warm up. I would try adding oval shims under the WRD.

I will be updating FIPi soon that will  show updated CO curve and how the “lean dip” most likely stalling you out.

[Pawel66]

Yes, it can be the case, i will run your test.

Last time I did it, however, I was 10-11% for most part of the warm up, which, I think, was too high.

[mrfatboy]

Also, adding round shims to the upper stage WRD will make the WRD cut off sooner not later.

[Pawel66]

ooops.. got it the other way around...

Thank you!

I would revert to the magnificent tool made recently available in the Tech Manual before doing this anyway - it is all there! Fantastic aid. 

[Shvegel]

I think what you must be seeing is the FIP out of adjustment.  It seems almost impossible that the pump lost the “balance” between the cylinders but somehow it seems true.  Because fuel is non-compressible even if the check valves leaked this would result in very little reversion of fuel. I don’t think the elements in the pump (pistons) are worn as that would result in the pump leaking fuel into the oil. Hopefully someone near you can check the calibration for you.

[Benz Dr.]

You could always try two hotter plugs on the darker cylinders.

[Pawel66]

Thank you for your kind attention!

Shvegel, this was my key suspicion. I had that 3 years ago (clearly diagnosed with 6 syringes test) and I re-send FIP to Bosch who re-calibrated it. Now, when I fit 6 syringes to the ends of fuel lines on the injectors side, the amounts of fuel are even.

When I put 6 syringes on injectors - there was more fuel in cylinders 5 and 6. This was a difficult test as amount of fuel dispensed is very small, but i think there were patterns there. So indeed FIP may be giving different amount of fuel to cylinders when pressure created by injector is there. Check valves, as I wrote, are not leaking.

So yes, FIP would have to go out to be checked and fixed - I would have to send it to Germany, nobody near can do it, the Bosch service I used are apparently not good enough...

No, there is no fuel leaking to oil. Oil looked and looks very nice, sticky, not smelling gas, level not raising.

Benz Dr., if I can do it like this - I will definitely try! I was not sure if you can do things like that, but if it is acceptable - worth trying indeed!

[Shvegel]

A couple other oddball things to check.  If your car is an automatic transmission see if there is a change? Especially if you have had to add transmission fluid. The vacuum diaphragm in the transmission can rip and allow trans fluid to be sucked into the engine.  The other thing I would check is the power brake booster or servo.  If it is leaking internally it can cause the issues you describe.  You should be able to run the engine, turn it off And still have a soft brake pedal a minute later.

[Pawel66]

It is an automatic, yes.

Thank you, you mean:

1. Check the transmission oil level? Never seen a white smoke, but will check, certainly.
2. Will do, thank you.

[Pawel66]

I did the checks.

1. Transmission fluid was at max when replaced some time ago, it is still at max, I do not see any change. No smoke on start up, no smoke at all.
2. The booster holds the pressure for some time. Almost no change of revs on idle when pedal pressed, maybe 20-30rpms for a fraction of a second.

What I think i will do is to remove the CSV and see what happens there, check visually if it is not leaking. I did the leak test several times and I did not see a drop coming out, but better take a look. I have come across a picture of how CSV looks inside - the nozzle looks like the one for windshield washer, spraying fuel left and right to the cylinder groups. If the left part of the nozzle leaks (or both leak, just the right hand side one is clogged), I will be getting more fuel to cylinders 4-6. I will also be able to take a look inside the inlet manifold - maybe something got stuck there, obstructing air flow. Both ideas are science-fiction, but I do not have any better ones.

[Peter h]

I think that the injection pump does not deliver evenly.
I have known some of the problem and it is usually a poor fuel injector setting. It costs a lot and you should know a professional.
Peter

[Pawel66]

The FIP not delivering evenly is my main suspicion. Before removing it and sending to a specialist (most likely on Germany or the UK, as I do not trust the Bosch service here any more) I wanted to check all other potential topics...

So you say you have come across similar symptoms?

[Peter h]

How else should it be when the cylinders are filled with a difference of over 10%. The ESP is the heart, if after 50 years it no longer works properly you have to do something.
Peter

[Pawel66]

Yes, the FIP (ESP) comes first to mind. It was at the service twice. One time it was because it delivered uneven amounts of fuel to cylinders. It was calibrated and with injectors removed it does deliver equal amounts.

But apparently it does not when injectors are on the line and pressure is built up.

There may also be other reasons for uneven mixture - I wanted to eliminate them first.

[Peter h]

If you have a 70s us pagoda, a 24y will be built in.
It's hard to adjust, it's always too bold. Get an r 20y or better an r24w and remove the us exhaust gas cleaning system.
Peter

[Pawel66]

Peter, thank you. It is a Euro car with R25.
It used to deliver unevenly to cylinders - I could test it with syringes at the end of fuel lines. It was sent again to Bosch service who overhauled it before. It does deliver evenly to all cylinders now when measured at the end of pipelines without injectors. When you fit injectors and measure then more fuel is delivered to cylinders 5 and 6. Difficult measurement, very little fuel comes through. But this indicates FIP is not adjusted.

Still I wanted to make sure it is not an issue with something else.

[Pawel66]

I removed and checked the CSV for leaking - it is not leaking. Nothing in the inlet manifold that would obstruct the air flow to cylinders 5 and 6, looked with an endoscope.

Either it is the oil Benz Dr. was mentioning or the FIP is out of adjustment.

I ran out of ideas what else it might be...

[Pawel66]

I am moving on on this topic. I found a place in Warsaw that seemed to know what they are talking about as far as FIPs are concerned. I took a risk and asked them to check and adjust fuel dosing for each cylinder.

They did and I found out the span I had was 20-25% between the cylinders. As I spotted by difference in colours of the spark plugs, different CO in left and right exhaust pipes, etc. The car was telling me what was wrong with her...

I am enclosing the results and spark plugs picture for comparison.

I will fit the FIP to car this weekend, see how it works.

[stickandrudderman]

Good data.
Didn't you alreaday have the pump looked at before?

[Pawel66]

I did. Twice. By Bosch service specializing in those FIPs. One of the complaints was uneven fuel dosing between cylinders...