Engine missed at load while cruising

[gr_diver]

Last drove the car at 19:30, mixed driving and all were fine. Then I used it at 23:30, city driving at first, highway afterwards. While cruising I came to an uphill part, and the engine started missing interminently. When the hill was over it stopped missing. Followed 10 mins of city driving all normal.

Parked for 10 mins, and took exactly opposite route. 10mins city no problem, a couple of GOOD uphills in second gear, no problem. Took the highway, after 5 mins approached slight uphill, the miss came again interminent. Once uphill part was over miss was gone. Exited the highway, followed nice 5 mins. nice uphill driving in second gear, no missing.

What could be happening in there? It is night, so I can't pretty much do anything now, but my mind can't rest!

A week ago I set my valves, the motor is running very good. If it was due to valves, shouldn't it NOT be interminent, but rather like running on 3 cyls until the hill was over?
Also shouldn't the lower gear uphills would make it appear again (as my engine runs a little lean at idle to 2500 rpms (city), while it runs just a tad rich while cruising (>3000rpms))? The higher temps of lean should make the problem more obvious, right?

Maybe it is just something simple like dirty spark plugs or pitted points (as tune-up time approaches), but having adjusted valves last week keeps bothering my thougths! The weather is rather cold these days, now it was 0 celsious, and after I set the valves for a couple of days it was like 15 celsious; shouldn't it have been obvious then?

[Dmcbrass]

Almost all misses are ignition related. An electrical miss is always more likely and more pronounced under a load. Could be coming from lots of sources. Wires, point pitting, timing, dwell, plugs, cap, rotor, condenser, coil)
1. Start by making sure the dwell is 50 + or - 2. (don't assume that your dwell meter is correct. Check with at least two different meters and never rely on point gap unless you have no choice. i.e. no meter available.
2. Set the timing next. Make sure the engine idle is low enough so that the centrifugal advance is not affecting timing and that the vacuum advance hose is disconnected from the distributor and plugged.
3. Check the plugs make sure that the gap is correct and that there are no hairline cracks in the porcelein. I had this problem with a 4 cyl boat engine one time. It took me forever to find the cracked plugs. I blamed it on everything else first.
4. Check the cap and rotor. Look for cracks in the cap and wear on the posts. replace if anything looks suspicious.
5. Check the spark plug wires. If you have any doubt as to their condition and nothing else has cured the miss. Replace them. I had a Chevy truck that had the same symptoms from bad plug wires. None of the usual tests found them.
6. At last resort you can swap the condenser and/or coil.
Good luck

[john4856]

Mine did the same thing. Intermittant skip, mostly when the engine was under a load such as going uphill. It was the points, they had wore down and had no gap at all. Good luck, John.

[dcm013]

Don't forget about the possibility of a plugged fuel filter. The engine needs more fuel to climb hills. Remember to check the simple things first.

[mykolvet]

My car did the same thing fuel filter only let the amount gas for noload driving

[tekenaar]

"Under load" missing is almost always a sign of carburetor fuel starvation of some sort, especially in our 30- to 40-year old Opels. Over the years a fine rust powder forms in the tank and accelerates the rate at which fuel filters plug up . . . you need to change them more often. The carbed fuel systems only run at ~3.25psi in the first place and the stock 8mm(5/16") fuel line provides adequate fuel volume unless restricted. Fuel availablity (volume) in the carb is most critical under load and any irregularities will always be most noticeable under load . . . 3rd or 4th gear uphill for instance.

If you have two filters installed, one close to the tank and the other between the pump and the carb, get in the habit of checking the one at the tank regularly as that's the one that will plug up the quickest . . . ask Gene Smith about this. Also remember that fuel pumps are designed as 'pressure' devices, not 'suction' devices. For any fuel pump to operate correctly, inlet fuel flow must not be impeded (plugged inlet filter) in any way.

Another thing overlooked on Weber carbs is that they also have a fuel strainer right at the entry to the fuel bowl . . . ever wonder what that big nut under the fuel bowl inlet is for? Loosen it and you will find a small mesh fuel strainer inside it!

[gr_diver]

Thank you guys ALL!

You verified my thought that it is not propably due to valves, but rather like an electrical or fuel problem...

I will check EVERYTHING today, starting from ignition, carb next (I have a feeling I will find garbage in the fuel-bolw)...

[gr_diver]

I didn't have to go much far! I removed spark plugs, and #4 plug was contaminated with ash deposits like in the pic below, a solid deposit between the electrode's insulation and the circle gap to ground/threaded part.

My plus tend to get contaminated like this, but I clean them every 3.000km, and never had such problems so far. I have changed to very good oil quality (ARAL Elastic 15w40 for the winter, and ARAL Elastic 20w50 summer, both mineral) the past two years, but I still get ash on the plugs, so it must be the LRP fuel that we use here...

Once again thank you all for your suggestions...

[opelnut10]

Next time you change plugs, increase the gap about .003 and road time you engine (take it out and run it under driving conditions, advance the timeing about 2 degrees at a time until you get it to kick back on the starter or spark knock) then back it up (retard) until you don't get that. Unless the cam was degreed in when the engine was assembled, and the timing marked on the flywheel at that time timing marks are not always accurate. You can also static time it by getting #1 to firing TPC and then loosen the distributor hold-down, take the coil wire out of the top of the coil, turn on the switch and hold the end of the coil wire over a ground (with a rag, don't get zapped then with the other hand move the distributor forward or backward slowly until you get a spark from the coil wire that is true TDC, then lock it down and turn off the switch and re-install the coil wire.

[gr_diver]

So you are saying this is an indication of maladjusted timing? Since 2004 I am timing with the timing light I bought, and after a few days I checked the plugs for the color change on the electrode. It has always been exactly at the middle of the bend, as it should...

In a few weeks time it is "tune-up" time, and I will time it by the vacuum gauge first, then make corrections by the "drive-and-feel" method you describe. I will not do it now, because an other carb will be fitted in a few days, so all will be done after everything is there "to stay"...

Will try it, thanks!...