engine shakes under load

[Jakegday]

Good morning all! This problem just started on my 81 ford fairmont. 3.3L in line 6 cylinder, 3 speed automatic. Car has 120,000 miles on it. New carburetor a few years ago, and new fuel and air filters at the beginning of this year. I thought a bad batch of gas may be responsible for this, but have now ruled that out.

The engine shakes/shutters most of the time when driving. (and sounds horrible) The only time the engine doesn't do this is when cruising at a steady speed, or decelerating. And even sometimes while cruising at a steady speed it does it.

Ive linked a video of what im talking about, but the engine may be a little hard to hear in it. The sound is present up until the 0:22 mark.
http://www.youtube.com/watch?v=vGy1ADD5HJo

Any tips on what could be causing this will be greatly appreciated! Thanks

 

[ddtmoto]

Time for a good ole tuneup? Plugs, cap, rotor and wires....

 

[eljefino]

^ +2

 

[ARCOgraphite]

time for a good 'ole 289

IS it a 2 door - these are awesome diggers!

(I cant see viddys at work - they are blocked by the Internet Interpol)

 

[440Magnum]

Ah, old-school (almost). When I took driver's ed (driving section) they had a fleet of '77 Granada's with the old inline six.

Misfire under load is usually related to spark, but sometimes fuel issues can cause it. Yours is such a regular "chug" related to engine speed that its almost certainly one or two cylinders affected. I'd begin with the old cure-all: Cap, rotor, wires, plugs. If the problem persists, then dig deeper- but you have to be sure these parts are 100% before you can find other problems because any question about the integrity of the spark path will confuse other testing.

If its not spark, check compression.

 

[CurtisB]

It's possible you're experiencing a timing issue. A timing issue can be related to anything from the distributor, timing chain and even the camshaft. Don't rule out a simple tune up (plugs, wires, coil) and a distributor adjustment. If it where my vehicle I would start by hooking up a tachometer (The Idle likely to read erratic) and start with a distributor adjustment. Just my two cents.

 

[MolaKule]

Originally Posted By: 440Magnum
Ah, old-school (almost). When I took driver's ed (driving section) they had a fleet of '77 Granada's with the old inline six.

Misfire under load is usually related to spark, but sometimes fuel issues can cause it. Yours is such a regular "chug" related to engine speed that its almost certainly one or two cylinders affected. I'd begin with the old cure-all: Cap, rotor, wires, plugs. If the problem persists, then dig deeper- but you have to be sure these parts are 100% before you can find other problems because any question about the integrity of the spark path will confuse other testing.

If its not spark, check compression.




Good advice for starters.

And as CirtisB stated, after new igniiion components are installed, check for timing issues.

You may have a stretched timing chain with a harmonic showing up at certain RPMs.

In addition, have you checked the valve train to see if some of the rocker arms are loose or floating, or if the hydraulic lifters are filling properly? It may also need a lash adjustment if the above components are ok.

 

[[email protected]]

Ive owned 3 Ford Fairmonts (dont ask).

Great things to check that have been mentioned but do not overlook the ignition module on the fenderwell.

I'd go through them every couple of years. They are cheap enough to keep 1 as a spare anyways.

 

[KB2008X]

You need to start with the basics or you'll just be flailing about guessing what the problem might be.

As others have said check your ignition system first. If you're not sure how to do that then replacing the cap, rotor, plugs and wires is not a bad idea, unless you've replaced them recently and know that they're still good.

 

[nitehawk55]

3.3 6 cyl ?

 

[Jakegday]

thank you for the input everyone. The cap, rotor, plugs, and wires are about 4 years old, and have about 10,000 miles on them. (i replaced them when i bought the car) The cap and rotor looked great, i tested the plug wires for resistance and they all passed with flying colors. The spark plugs looked ok i guess. They certainly didnt look new, but they looked acceptable. I checked the resistances on the ignition coil and it also passed with flying colors.

So i thought i'd mess around with the timing. I advanced the timing just a hair, just enough to raise the idle a bit, and its now running perfectly! i certainly wasnt expecting the fix to be that cheap, but ill take it! Thanks again everyone

 

[KB2008X]

Congrats.

 

[CurtisB]

Hey look at that, a simple cheap fix and that's rare. Good work keeping that old thing alive.

 

[artificialist]

I'm glad it was simple. I figured what was happening was that a vacuum leak happened somewhere which is a huge nightmare with 70s smog devices.

 

[Jakegday]

well, apparently i spoke to soon. That fixed the problem for a little bit, but the problem continues. I checked for vacuum leaks and put new spark plugs and wires on it and still no results. Could a coil pass the resistance test and still be bad? Could a bad ignition control module cause a misfire?

 

[Warstud]

Shakes...like it's about to stall (missing)?

 

[artificialist]

Originally Posted By: Jakegday
well, apparently i spoke to soon. That fixed the problem for a little bit, but the problem continues. I checked for vacuum leaks and put new spark plugs and wires on it and still no results. Could a coil pass the resistance test and still be bad? Could a bad ignition control module cause a misfire?

I have been told that sometimes an old ignition will function properly when cold, but once it gets hot, the expansion causes and open circuit somewhere, and then you get no spark. The last time someone showed me this was on a distributorless ignition, I don't know if it happens to distributor ignitions.

Ignition module failure? It certainly can happen. I am not sure how to test one on your car. You would need a manual for test procedures. Get a real Ford ignition module, some cheap replacement ones don't even function properly when new.

I thought of something else. When you pull the cap off the distributor, did you check for rotor play? When it happens, you get erratic spark timing and random misfires.

 

[Winterpeg]

Absolutely an ignition coil that tests good on dc resistance can be bad.
The coil is subject to high voltage and can break down under this condition.
You could get turn to turn shorts at high voltage that dc resistance will not pick up.

 

[JetStar]

Originally Posted By: Winterpeg
Absolutely an ignition coil that tests good on dc resistance can be bad.
The coil is subject to high voltage and can break down under this condition.
You could get turn to turn shorts at high voltage that dc resistance will not pick up.


+1

 

[Merkava_4]

Does your Fairmont have the 1 barrel Holley carburetor by any chance?