Misfire Under Load
 

I recently bought an ERA with a 428, it's 5 years old and has approx 3,000 total miles on it, I understand the engine build is:

Believed to be a 1968 block
Scat 4.250 rotating assembly, 462 ci
Mahle forged Pistons
Edelbrock Performer RPM heads
9.5 to 1 CR
Edelbrock intake
Holley 750
MSD distributor
Howard hydraulic roller cam
Harland Sharp rocker assembly
Canton road race oil pan

I've driven the car approx 500 miles and experienced a progressively worsening oil leak(s) and misfiring under load. The oil leak(s) appear to be coming from the upper front drivers side of the engine, I've replaced the fuel pump gasket and managed to get 1/4 turn by hand on the remote oil filter, both of which appeared to be culprits. I haven't driven it since to know if this has cured the leaks.

The misfire is of greater concern, the engine starts, idles and runs fine at light throttle applications. However when I accelerate harder, say 1/2 throttle and 2500 to 3000 rpm the engine starts to misfire/stumble, it will continue to pull through the misfire. On the few occasions I've accelerated at full throttle, it again misfires/stumbles, then appears to clear itself and when I look in the rear view mirror there is a large blue cloud of smoke in the road. I don't think this is a constant trail of smoke, rather a single cloud that's blown out.

Apologies for the very long post, if you've managed to read this far, do you have any ideas or suggestions as to what's wrong?

Thanks in advance for any assistance.
Regards
Kevin

Have you pulled the spark plugs to look at them? That me give you an idea if you are burning oil, are rich or lean.

Do you have another coil that you can try?

Good suggestion, I'll pull a couple at the weekend.

It doesn't appear to be continuously burning oil (not ruling that out), it the large smoke cloud that is blown out under full throttle hard acceleration, it feels like it's "clearing it's throat" so to speak.

Yes I was given a spare with the car, I'll swap them over.

Thanks
Kevin

Replace the plugs before you do anything else. Start with the consumables.

Grasping at straws here but....I've also ordered a new PCV valve in case that's operating intermittently, my theory being, it sticks and then opens and allows a slug of oil rich vapor into the intake, hence the single large cloud of blue smoke. The over pressurization of the crankcase could also be responsible for the oil leaks.

Unfortunately this doesn't explain the misfire under part throttle, but it's only a $2.99 part, so I may as well change it....

Kevin,

I at one time had a leak coming from the upper front as well that was hard to find. Ended up that my coil, mounted sideways on the top front driver intake area was leaking oil. Inside the wire receptacle the screw that seals the oil in had come loose. If you're coil is in the same area perhaps that's it and perhaps explain the oil leak and related timing/spark issues?

Best of luck. Brent

Don't do anything. First, have somebody trail behind you when you "burp" your oil plume. Have them tell you whether it comes out of one pipe, or two. If it's only coming out of one pipe, then your diagnostics will be different than if you're burping out of both pipes.

When I had similar issues and symptoms on my small block, a good cleaning and carb rebuild fixed the stumbling and hesitation.
If the smoke coming out of the exhaust is blue, that would indicate burning oil, black smoke = rich condition
Just a thought

Brent,

Good suggestion but there's too much oil on my garage floor for it to be coming from the coil, plus there's no oil on the inlet manifold where the coil is mounted.

Thanks for your input.
Kevin

patrickt,

Good suggestion, I'll get my son to follow me.

Thanks
Kevin

Pull all eight plugs keeping them in order. You should see which cylinders are passing the oil. I have a couple sets of cheap quality intake gaskets that got sucked into intake ports hanging on my wall to remind me not to be a dumb ass. Just one possibility...

Until I experienced the burp of blue smoke at full throttle, I was suspecting a carb issue -blocked jet, float height, etc., basically insufficient fuel flow to support higher power outputs. But the burp of blue smoke I experience last weekend made me think again. Although I could have multiple issues.....

Thanks for your input.
Kevin

Make sure your son also looks for any smaller amounts of smoke that you might have missed. Also, in addition to hard acceleration, rev it up nicely and then back off the throttle so it decelerates in gear from a high rev with your foot off the gas. See if that produces smoke/backfires/massive explosions;) etc. Talk to your son on your cell phone as you're doing all of this so he knows exactly what you are doing when he sees the smoke. Being able to replicate a visual, or audible, problem on demand puts you about 75% on the road to a solution.

Will do.

I have noticed the odd minor pop /backfire on over-run from higher revs (say 3500), nothing major. Also last weekend the engine ran-on for a couple of seconds after I turned it off, it was quite hot at the time. It has not done this before.

Thanks
Kevin

That engine should rev smoothly right past 5000. No pops, backfires, smoking, drinking, chasing women, or anything else. It should rev clean and even.:cool:

The first cheapest place I would start is with the magnetic pickup in the distributor. I replaced mine and one on a Backdraft just in the past two years. Intermittent electrical gremlins are a pain. Just my take. You could have multiple items, but I would start ruling out the electrical. Last magnetic pickup would work for exactly 20 minutes and then shut off. It would cool down and then would fire again for another 20 minutes and then shutoff.


Phil

Thanks, I'll add that to the list

Curious if you have vac advance on your distributor?
You mentioned easing into the throttle (vac advance would be pulling max advance still) and it runs fine.
Then you mentioned when throttle up aggressively you get the misfire (vac advance will not be helping the the timing will be retarded quite a bit).

You may have phasing issue in the dizzy where your too much advance or too much timing retard (your rotor is in between spark plug posts). This is a problem more common on small diameter distributors and can cause scatter and crossfire.

https://www.youtube.com/watch?v=aWMlNwGW0tM

Bad phasing and crossfire
https://www.youtube.com/watch?v=zulDzQ5q9TM

Everything You Wanted to Know About Vacuum Advance and Ignition Timing