sudden severe knocking, poor running (240)

[steve roche]

Hello everyone-

Does the following sound like a bad AMM? Or worse?

I had just finally got my 85 240 running smoothly... (I spent the last few months fixing the vacuum leaks which were lying about unnoticed, replacing the flame trap which was all melted, and turing the distributor cap slightly, making the engine start-up right away instead of cranking over twelve times first. Also, I had fixed the cold-starting problem,
only to have hot-starting problems, but I have figured out how to balance it all out).

Until today.
I was driving back from the grocer's, and suddenly the engine began pinging (like bad gas or incorrect timing),
and shortly thereafter began knocking (or a louder version of pinging).. and then knocking VERY loud upon acceleration.
Then, at idle, all hell breaks loose, it lopes and shakes, and the whole car shakes, and I feel it is going to just die, so I gun it to keep it running. And NO acceleration when the red light changes to green.

You do NOT want to stall in Los Angeles traffic, because they will eat you for breakfast.

So anyway, I limp home, basically, and check the AMM, because that is what I have been suspicious of, lately.
(several times, the engine has gotten real shaky, and I wiggle the connector, and it magically improves, after about
seven seconds). This time, no change, and no real difference plugged in or unplugged (although a SLIGHT improvement
in the engine, and much less of the loud "knocking" noise when it's unplugged).

Idle is extremely rough, but the terribly loud knocking begins at any acceleration. It is so loud in the engine that I no longer think it is knocking and I am Googling "throwing a rod" and other engine conditions. It isn't driveable at all, but I got it to be able to start up and I can move it around (it is parked on the street).

This engine noise is the worst engine noise I have heard since I began working on old cars, in 1987.

I am seeing some mention that a bad AMM can causing knocking and all sorts of other fuel starvation issues, and it makes the computer retard or advance the timing and everything goes to hell. Or, it is the timing belt, which got changed a few years ago.

What's the worst that a bad AMM can do? I'm starting with that, since there isn't any money to have anyone diagnose this,
except me. Like I said, I had noticed it had a lousy connection a week ago, but I thought I got it cleaned up.

So far, everything wrong with this car (I got it a few months ago) has been related to the fuel and or air mixture, (the AMM),
or vacuum leaks, or crusty wiring to the fuel/air sensors and regulating devices. So I am going to try to stick with this,
and not go believing that I have thrown a rod.... it's only noisy when you rev it--- wouldn't a thrown rod be noisy at idle?

So I have talked myself in to the idea that it is the AMM (or MAF or whatever).
Also, I cleaned it, but no difference. And the wiring in the next thing I will go through.
I was hesitant to just go buy another AMM awhile ago, because it seems that is a really "oversold" part,
and none of us want to go buy a part which... makes no difference in the long run. For me, there are 'more pressing
issues like putting food on the table, unfortunately.


Ok, well either it's this, or I have a very unhappy engine which will have to go.

steve



1985 Volvo, 240,
flat black,
275,000 miles,
not original engine,
was going to be a cool car, but It spends more time 'not running' than it spends on the road..

[billofdurham]

"more pressing issues like putting food on the table." How much does a Volvo 240 eat?

A bad AMM can cause all sorts of running and idle problems but before dashing out and buying one there are other things to check:

Air intake system leakage. If air leaks from the point where the AMM is mounted on the engine the air-fuel mixture will be lean.
The inlet system between the AMM and the intake manifold. Check all hoses and connections on the intake manifold. Make sure there are no small splits in any hose.
The connectors for good fit on the AMM, air control valve, knock sensor and coolant temp sensor.
The wires for poor insulation.
The coolant temp sensor.

Bill.

[steve roche]

Thank you-- I am checking these things. But I have found that the number one cylinder is not firing at all.
I pulled the wire, and the car runs just as poorly without the #1 cylinder as it does with it. (The other cylinders,
if I pull the wire, the car dies). So I removed the plug, and it's not fouled or melted or even very wet (fuel).
Maybe a little. I swapped it with cylinder #3, and the car ran the same, and number one cylinder was still
not making a difference in the idle. So I switched the plugs back to the way they were.
Then I switched the fuel injector clips between #1 and #2, and the car ran the same, so I switched those back.

So now, I am looking more at a loss of a cylinder than a vacuum leak or a faulty AMM.

What is the next step? pull a fuel injector and swap it with another cylinder?
I have never laid hands on fuel injectors before. Perhaps first I should clean the plug dry with solvent, put it back,
run the car some more, and pull it again to see if it is wet with fuel. This may tell me that the injector
is at least partially functioning.

Compression check?
Coil? (it can't be the coil if the other cylinders run fine!)

The car will start up, most of the time, but I had to turn the distributor a little to get it to do this.
Inside the cap isn't too bad, but the 4 contacts are a little grooved. I could replace it but I have the feeling that
the number one cylinder will still be dead. If the car has severe engine problems I do not want to be buying
new distributor caps.

I also tested for spark, and it is pretty strong coming out of the wire.

I failed to swap wires with another cylinder;
I'll go do that later. Maybe I am lucky and it is only the wire. But they all look new.
I will run it at night.

The loud knocking or rapping noise in the engine that I hear when I rev it (and a little at idle)... that combined with a cylinder
which isn't firing... points to... what?

all advice and even wild guesses are appreciated.

Everyone said not to take this car, and I guess they were right.

[steve roche]

thanks-
I haven't done the compression test yet; I must have loaned out my tester years ago.

I checked the knocking sound against You Tube videos of engine knock sounds. I think I found it, under Rod Knock.


If I were me, I'd be telling me to get rid of the car.

[steve roche]

Before I make the decision to let go of the car, I wanted to pull the fuel injectors and switch out
the one over the bad cylinder, to see if that may be the issue. I pulled the #4 and #6 fuses and
ran the car until it would stall (from no fuel). But it ran for twenty minutes, and it never did stall.
So I pulled ALL the fuses, and it kept running. So I never did get the pressure down in the fuel injector
rail, and I gave up for the day.

This morning, I was going to start it to move it for street-cleaning, and the battery was totally dead.
I jumped it for an hour, and finally I got it started, and I was able to move it. So there seems to
be some bad luck associated with this car! I can't drive it around the block to charge the battery because it will
not drive, it will just stall under any load.

I still want to switch out the fuel injector from the #1 cylinder; maybe it's the reason for the misfire,
though the cylinder still may have poor compression also.

And- the idle is SO bad, that pulling the MAF actually makes things a little better. But there is slightly
more acceleration (0-5mph) with the MAF attached; there is no acceleration (really, none at all) with the MAF unpluged.

I'm looking for a single solution to all three of these problems. Call me an optimist.

sr