I have spent numerous hours reading many postings here related to rough idle and it seems I am in for the big ticket fuel distributor. Please give me your opinion before I replace it.

The car is a 1989 420 SEL (W126) , 221K KM. I have a rough idle, both warm and cold, sometimes. It seems one, possibly 2, cylinders may be missing, sometimes. It will idle for 20 secs. perfectly and then it will start to miss-fire, and the engine rocks, missing for 30 secs, and then run perfectly again, the cycles are not consistent, sometime 45/15 sec. and other periods. At non-idle the car does not seem to miss fire.

It has been scope tested, there seems to be no electrical problems. The dist. cap was opened, the cap was clean, no arcing or deposits. Pulled wire to cyl. #8, tip was loose, and was replaced. Replaced the injectors and holders, flushed the injectors before installation. Gas line from the tank has been replaced, gas filter has been replaced, filter at the fuel distributor has been replaced, Plugs have only 4k KM, and are the Bosch copper, W8DC. O2 sensor replaced 2K KM ago. A compression test showed all cylinders 180 PSI, except #8, which was 140 PSI. Performed vacuum and air leak test, no leaks detected. Both cams replaced, all rockers replaced. Chain replaced 4K KM ago. Checked both cam timing marks, on the shaft compared to the line on the side of the engine, both left and right sides lined-up, the timing is 0 degrees.

While idling hot, opened cylinder #8 fuel injector line at the fuel distributor, no change in engine performance. Took the line off the distributor and no fuel bubbling out. Tried the same thing for cylinder #4 injector line, engine starting rocking more, a noticable difference. So it seems cyl. #8 is not getting fuel at idle. Loosened #1 cyl. injector line and the fuel looked dark but then cleared-up, but did affect engine performance too. I am trying a bottle or two of fuel system cleaner.

Does the fuel distributor need to be changed? What should I check or do next?

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1989 420 SEL

Couple of thoughts:
Did the scope test actually say you have a dead cylinder?
I'm trying to understand the low compression on #8. Has anyone done a leak down test on that cylinder? What did the compression do with the wet test in the compression check? Did the presure come back up to the same as the rest of the cylinders? Low compression has to pretty much be gasket, valves or rings. If you have been running real lean on that cylinder, you could have a burned valve. (btw, has the engine had valve seals done?) What did the plug look like that came out of there?
Have you tried running a few cans of Chevron Techron thru your tank? I would double or triple the dosage just to see if it will help. Can you switch the lines for #7 and #8 at the fuel distributor without damaging the lines? Might be interesting to see what that does. Just don't leave it that way.
Another thing to try: Be careful on this one. May want to have friend on hand with fire-extinguisher. With engine not running but fuel pump on, remove the fuel line from the injector and point it into a small container. Press down on the sensor plate for just a second. See if any fuel comes out. Note: there will be fuel running in all injectors so the rest is going into other cylinders and eventually the oil. You may get some fuel out this way, but maybe less than the other cylinders.
Finally, if you do have to replace the distributor (and does kinda look that way) maybe get one used from a salvage yard? Those things normally go for a very long time and I would expect one from a recent arrival at a yard to be fine. and maybe a lot cheaper

You might also want to check for vacuum leaks, like those 8 rubber hoses between the intake manifold halves, manifold gaskets and other hoses.

A junkyard fuel distributor sounds good.

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Thanks guys, I appreciate your recommendations.

The scope test did not show any dead cylinders, all cylinders are firing. The spike on #8, at hot idle, is a little lower that the rest of the cylinders, but if you rev-up the engine, to 1500, everything looks perfectly normal. I am hoping the valves are not burned and that I have found this fuel starvation problem before the valves get burned.

No leak down test done.

The valve seals have been done at 207K KM. All plugs looked the same, slightly dark grey dusty. The plugs had been gapped to .032 inches but were re-gapped to 1MM, about .040 inches to get a bigger spark. I know the book says .032.

Unfortunately, I have been unable to find Chevron Techron up here in Canada. I added Canadian Tire (CT) Ultra fuel system treatment (C$14) just before filling the tank yesterday, and 200 km ago I added a bottle of Duralube advanced fuel system treatment (C$16). So now the full tank has about 1.5 bottles of the expensive cleaners. Both of these expensive cleaners say the bottle treats up to 70 litres of gas, the tank contains 90 litres. I bought 4 more bottles of CT brand normal injector cleaner (C$4) and I also have 2 bottles of STP injector cleaner(C$4). I wonder if the more expensive stuff works better than the lower price stuff?

I'll be taking her for a 500 KM run later this week. I didn't want to over do it with the cleaner. What is the maximum number of bottles recommended for a 1/2 tank fill-up? The cleaners never say what is the minimum amount of gas the bottle should be used in, they only say the maximum amount of gas it will treat.


I am now hunting for a used FD, estimated cost C$500. Estimated cost for a new one C$1,500, ouch!!

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1989 420 SEL

Someone has suggested that it could be idle speed controller. Would the idle speed controller control the fuel to the injectors and perhaps, consequently not supply fuel to #8 cylinder at idle all of the time?

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1989 420 SEL

It's easy to point to a fuel distributor and say 'there's my problem', I know cause I did it. After paying $350 for a used fuel distributor/eha/ fuel pressure regulator my problem didn't go away. New injectors didn't help either. Turned out the cat was clogged. I'd be careful about throwing parts at an apparent fuel system problem. Take it from one who knows!

C H,

I got quoted $350 for a used one from a junkyard, with 30day warranty. Checked the price here and at Rusty's, it's more than $1500 for a new one - final check with germanstar.net; a rebuilt/re-manufactured one cost less than $500 buck with 1yr warranty - guess which one I ended up with ?

Cheers,
Frank.

PS: In my case, no fuel came out of fuel line#3 - thus the replacement of the FD (fixed it). Had thought it's the injectors.

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'86 560SEL | Silver Ext. / Blue Int. | 201K miles (Apr. 05) | 204K miles (Feb. 06)

I replaced the fuel distributor with a rebuilt one today. Had a tough time starting her after that replacement! I have been running injector cleaner, two bottles per fill-up, for the last 700 KM. The rough idle is still there!!!

Sometimes the engine idles perfectly, and then it starts to miss for 15 sec. sometimes continues for 2 min. maybe more. When running above idle, no sense of missing! Driving around I come to a stop idles perfectly, 30 sec. later starts to miss. After a 30 min city drive, the idle seems to be about 800 rpm in neutral, isn't that little high?

Checked cylinder #8 again, 150 PSI on compression test. Dropped in a new plug W9DC on #8. I let hang outside and saw it firing, then put it back in. Did a leak down test on #, 5 & #8. #5 about 12 psi, #8 about 40psi. With the stethoscope, listened in the exhaust pipe, nothing, listened in the air intake very little hissing, listened in the valve body, loudest of the three locations.

Could it be the intake valve or the rings? Could it be a valve guide? Could it be a sticky valve? Am I going in the right direction?

What is the next recommended step? Pull the head?

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1989 420 SEL

If you have 180 in all but#8 the bad spark plug wire may well have caused a burnt exaust valve or worn rings from incomplete combustion .........

William Rogers..........

Do you have any idea how long would it take for the rings or valve to burn if the plug was not firing? I don't really understand why they would burn if there is no ignition?

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1989 420 SEL

Have similar symptoms with my 1989 420 SEL with the similar mileage.

Cigar - Was wondering what it took to fix it?

So far I have new plugs, wires, fuel pumps, coil, used Techron type stuff to no avail.

All that I am left to try are the Air Flow Meter and the Fuel Distributor - both very expensive. One shop thinks it is one and the other thinks it is the other.

Has anyone come to a solution to this inconsistent idle and running.
Is the the fuel distributor or the air flow sensor? I had this issue with an Infinity so I tend to think is the latest but would love to se what Cigar Havana or Mattsuzi found!

This is a 20 year old thread, and most of the posters have not been here for some time.

Duke