engine and drivetrain suddenly running as if on 3 cylinders.... but not. Help?!

[ecpreston]

My '02 was restored in '99 and I've been daily driving it for almost 2 years. Runs great every day. It's got a Weber 32/36, pertronix, larger alternator, headers, but other than that the engine is stock, it was new in '99, compression is good, it seems to be in great shape.

Today after a long drive, I got off the highway and suddenly it was barely idling, running really rough. I've never seen it do this. I limped it another hour home, oil pressure and temp were fine, but it flutters on acceleration, idle is low and engine shakes violently, but under load and at medium revs... it seems nearly normal. Strong fuel smell. Backfiring. Sounds like a tractor coming up the neighborhood streets.

I thought I was down a cylinder, maybe ignition.

Pulled the plugs figuring one would appear fouled, and they all are identical. Fairly white though. Inspected cap, rotor, wires, they aren't perfect, but seem ok. Vacuum leak? Couldn't find a loose or even brittle hose. Pulled off air filter, carb butterflies and choke plates appear to be functioning normally.

I figured for it to suddenly turn to crap, I'd find something obvious. What am I missing? Tomorrow I'm going to check the timing, possibly the tensioner failed and it jumped a few teeth?

[Simeon]

Put a timing light on each cylinder in turn to look for misfires. I would tend to blame the Pertronix here. Try substituting it for the points and condensor that you keep handy for random failures.

Rule out the ignition first

[ecpreston]

ok, I'm going to start in the ignition department again this afternoon, I didn't bust out the timing light yet, thanks

[c.d.iesel]

DIRT in the idle jet / circuit

dirt in the float bowl - and in main jets & passageways

fuel pump failing

[beammmer]

Very similar condition happened to me while driving to The Vintage this year. About 20 miles away we hit rush hour traffic, the car was stumbling, backfiring and bucking like crazy. I was thoroughly embarrassed rolling into the hotel parking lot with the car acting this way.

Bottom line, after checking the jets as previously suggested and re attaching my stock air cleaner I learned two of the nuts holding the carburetor to the manifold were very loose, the other two were completely missing.

Everything was better after reassembly, additional nuts were added to hold the carb in place.

HTH

Don

[eurotrash]

If you're thinking its ignition..

At idle:

1.Pull/replace plug wires, one at at time, until you find the one where no change is apparent when its pulled off of the plug.

2.Swap wires from the culprit cylinder with another and see if the misfire travels to the other cylinder.. if so, its the wire. If not..

3. Swap plugs with the other cylinder. If the problem travels, its the plug. If not..

4. Its probably the Pertronix. A very similar sounding problem happened to my car.. Ran like crap until the revs were up. I tested everything from compression to plug. Nothing travelled or changed. I finally swapped in points and the car ran great.

[Timmer]

Check the float as well if all else shows no results; especially if float is brass; I had a brass float of a 32/36 split in half, this on a '74 2002 I had; car ran on 3 clyinders as wel however, you're plugs are showing whitish, mine were black from unburned fuel fouling.

Tim

[Mike Self]

Look for a vacuum leak--loose carb, loose intake manifold, cracked/broken vacuum hose to the distributor, bad vacuum advance on the dizzy, missing plug on one of the vacuum ports on the manifold...

cheers and happy troubleshooting

mike

[ecpreston]

Thanks for the ideas, now I'm really confused.

It IS running on 3 cylinders. When I pull plug #1 with engine running at fast idle, it doesn't change a thing. The other ones clearly do.

But the timing light says spark is going through wire #1.

And when I use my little spark tester, the spark is very much there when cranking, appears just as hot as the others (I made the test gap about double normal and it jumps fine)

Bad plug you say?

I swapped plug 1 and 2 and it's still cyl 1 that's dead per the "pull the wires test while running". And 2 is again working. So plugs are fine.

Compression test on cyl 1 is also fine, pulled valve cover and there's no broken rocker arm or something like that.

And I would guess since 2,3,4 are getting fuel, 1 is too.

Now what?

[roadhog0]

Vac leak on cylinder 1. Been there before... Loose a vacuum cap?

You're doin better than me. My 02 is running full on on 2 cylinders, and the other two are maybe half there... >.<

[TobyB]

Make sure it's not the plug wire- they die, especially the Bosch ones.

Then look at the cap- loose wire connection, connector, or a crack

(even had the stud fall out of one once, but that was when the motor

mount broke and let it hit the strut tower)

Then pull the valve cover, make sure you still have 2 whole rockers.

hth

t

[Guest_anonymous]

Spark.compression.fuel.. you examined the rocker. How about the valve lash. Did the eccentric come loose on the intake rocker. That would explain compression as well as a dry plug and un even running. You have not mentioned valve adjustment as part of your diagnosis.

[ecpreston]

I had to double check my results, so I tried pulling wires while running again, swapped plugs with #3 this time... and you know what, cyl 1 wasn't totally dead. I thought it made no difference when I would pull that wire, but it does, just so much less than the others. And the engine runs smoother without it, and backfire goes away completely! I swapped wires, cap, rotor, none of that helped.

So I found a bag with points and capacitors... I don't know anything about these, I've never messed with points, car came with the Pertronix. Pulled out the pertronix, swapped in the points system and adjusted per manual. Fired right up. Runs like crap. Cyl 1 still barely helping and now the ignition timing is messed up. 2AM so I came up here to post my double failure and go to bed with the intention of checking ignition and cam timing tomorrow and valve lash.

... Loose a vacuum cap?

...missing plug on one of the vacuum ports on the manifold..

A vacuum cap eh? Ran back downstairs. Like the ONE ON THE INTAKE RUNNER TO CYLINDER ONE? Where I see a tiny little test port with no cap on it? Found something to cover it and THAT WAS IT!

That was it all along.

Well that was "fun", I learned a lot. Thanks guys. Maybe I'll even leave the points on. Why do they even call it point(s)? There's one... point. Oh dwell.

[Mike Self]

before it caused some damage. I didn't realize that an in-place cap was leaking on #4 intake runner and eventually l blew a head gasket from the lean running cylinder.

cheers

mike

[Guest Anonymous]

Thought I knew a lot about these cars after 40 years of driving them, but what is this "vacuum cap" of which you speak? (I don't have any experience with tii's or anything after 1971, so I am hoping it is some new-fangled contraption on the modern 2002s that I don't have to worry about....)