Hi,

Today something strange happened to my nicely running original L-48. I drove several miles from home just fine, then refueled. After driving about 20 minutes the engine began running rough when adding more gas (accelerating). For example, I had it in 4th gear and when I pushed throttle down half way, the car accelerated in a sloppy manner and the whole car was shaking in the rhythm of the engine.

It happens in every gear. I also pulled over to an empty parking lot and did some testing. When in neutral and pushing throttle down, the engine doesn't rev like it usually did, but the noise is like so that you can hear the cylinder bangs much better than normally. Kind of like "bam-bam-bam-bam". I'd say like an old tractor.

After revving it for some time, I managed to get it back to normal but it went sloppy again after some minutes of driving. The engine noise was different from usual - I could just hear the cylinder bangs much more whenever accelerating.

I also noticed a remarkable power loss compared to usual experience. I didn't notice a remarkable increase in fuel consumption.

I have two explanations to this myself:

1) I re-fueled at a gas station which I've always used and is the cheapest one around here. I've never had problems before, but I've had friends who told that they got bad fuel from there messing up their engine performance. Did this happen to me today? Could it be bad fuel?

2) Something wrong in the ignition, one cylinder not firing or smth. Perhaps bad spark plug, cable or distributor issue? Actually the cables aren't very old at all and I had new spark plugs installed like 1.5 months ago. Maybe bad fuel made a plug dirty?

Thanks for all the help.

 

Sound as if a valve spring broke..........

Easy to check. pull valve covers and see if any valve springs are loose to the touch...

You can also run engine(watch out for oil) with valve covers removed and listen for clatter.

Good Luck

 

or a batch of bad gas and detonation occuring when the engine is under load

 

oops, wrong thread

 

depends on the noise you mentioned.
Could be a lot of things.

 

After sleeping over this, I remember people reporting in this forum that when they got bad fuel, they had detonation on acceleration and they were suggested to use octane boosters to solve it. I wonder if that's the same kind of a thing...

I ran the engine with the hood up and revved also, I didn't really notice any unusual noises. I got it running smooth for a while so perhaps a bad spring wouldn't heal itself. If it is a spring, can it be replaced without removing the cylinder head?

 

Check the simple stuff first. Pull the valve covers and check for a broken spring. It happened to me. Started running rough, on seven cylinders. Simple fix, if that's what it is.

 

Update: Just took some 98 octane best fuel available from the best gas station, the mixture of the old fuel + new fuel was probably around 3:1 (3 being new). Didn't change anything. I drove about 10 miles and that must have certainly used up all the fuel stored in the fuel lines, carb and bottom of the tank.

I'm now waiting for the engine to cool down in the garage and I will pull the valve covers. I just can't understand how something could break in the engine so easily... I mean a physical part. Usually those things happen during heavy engine load or strong accelerations. I didn't do any of that when it happened yesterday. I don't know how to check for one cylinder not firing properly or perhaps I know but I didn't have anybody to help at the moment so I could listen the exhaust myself. As much as I could hear from the inside when giving gas, it felt like it was missing a bit.

Maybe there really is a problem with one of the spark plugs or cables. I've had the engine idling at 500 RPM or even slightly less for some time because that was the best low idle setting I could find on the Q-Jet. Oil pressure has been OK so no worries about that, but is it possible that long time idling (+ I know my carb runs a bit too rich on idle) could mess up the spark plugs?

 

Alright, new update. Removed the valve covers and closely inspected and tapped all the valve assemblies. They were all real tight and nothing seemed broken. The only strange things I found were on two valves - you know the metal bowls which cover the upper part of the springs, they were like broken off on two valves. The springs themselves were nice.

I ran the engine without the covers and I didn't notice any unusual noises. I could barely hear the valves, it was pretty smooth. To my untrained eye all the valves were moving in a proper manner and similar to each other. I remember that usually the pushrods are supposed to be rotating - I found at least two valves where they were not rotating constantly but let's say they were sticking a bit (rotating in steps). This probably doesn't have anything to do with the current issue I have though, even if something is wrong about them.

I took one spark plug out which I could reach easily and took a photo. The edge of the spark plug is covered with black cinder and the tip looks like cement, not like metal.

 

Have you checked your fuel pressure?

 

Nop. I believe I can't do it myself, but perhaps I should have it measured?

 

You can buy a fuel pressure guage at any auto parts store. I had a '95 Bronco that was doing the same thing you are describing, and it was the fuel pump. Kind of hard to tell from the photo, but it looks like you might be running lean, which could be a symptom of a bad fuel pump.

 

Are you sure you are getting spark in all cylinders? I know its an overly simple thing, but have you made sure that none of your spark plug wires happened to touch a header and get burnt through?

Check the basics. Spark plugs/wires are good? Fuel filter is good? Base timing is still set properly?

Another thing, did you fill up with Ethanol 10%? My car HATES the stuff. The difference in power and sound between non ethanol and the up to 10% mix is huge.

 

[QUOTE=Kevins77;1570781598]

Check the basics. Spark plugs/wires are good? Fuel filter is good? Base timing is still set properly?


Sounds like a bad plug wire or burned out boot to me

 

Alrighty, the issue is SOLVED. I had a good friend over who knows these engines inside out and he checked the valves, found nothing problematic, tightened a few and then we closed the valve covers with new gaskets. We replaced the module inside the distributor, didn't help. We also cleaned the contacts inside the distributor. The next day I discovered remarkable vacuum leaks from the brake power assist pipe where it comes out from the carb and also on the intake where the pipe comes out supplying lights + climate. I got rid of the leaks by tightening all the vacuum connections with gasket maker silicone. Then I also replaced the ignition cables which have probably never been replaced within several years.

The issue still didn't go away until today when we removed all the spark plugs and found half of them really black and horrible looking. The other half were quite perfect. We measured compression in all cylinders and we got results between 10-11 in all of them, so it seems pretty tight. We then put new spark plugs in and voila, FIXED!

I must say that the engine has never ran so well in my hands. Perhaps it was the ignition cables or maybe there's some issue with the carb mixing a bit too rich mixture at idle. However, I think that if carb was bad, it would affect all spark plugs. It's more likely still an ignition thing.

Oh, and one of my Cherrybomb glasspacks blew out all the glass. What an AWESOME sound I now have