How do I determine if

tweet66 · May 1, 2008

a cam has a wiped lobe? Lately the 302 in my 68 Cougar has been running like absolute crap. AFAIK it's pretty much stock with long tune headers, a Performer manifold, Durapspark dizzy and MSD (installed last summer) and a Street Demon Jr 525 cfm carb. Timings set at 14 deg btdc with a total of 32 deg total advance. New plugs last week (Champions-possibly crap?)The past week she's been missing/popping through the exhaust really bad at idle but not under load. If I "fattened up" the idle mixture screws the popping went away but so did idle quality and mileage. The past two days I've seen surging while driving (jets too big?) and it won't hold an idle. I tried tuning and re-tuning the Demon and finally just swapped a Holley 1850 on to see if the carb was at fault and the missing got worse I haven't tried to dirve it with the Holeey yet. It's difficult to start when cold (have to pump the pedal while cranking and hold the throttle open), when it would normally just fire up and idle beautifully with a turn of the key. HELP????

Fast63 · May 2, 2008

take off the coil wire going to your distributor so the car does not start, then take off your valve covers and turn the engine over. If you notice that some rocker arms do not move or do not move as much as others, then you have a wiped cam lobe.

woodsnake · May 2, 2008

From what you've described, nothing indicates a bad cam lobe.
It sounds more like you are having timing gear set issues.
Have you opened the front end of the motor since you've had it? If you put a timing light on it, and snap the throttle, how quickly do the marks come back into place?

tweet66 · May 2, 2008

Woodsnake, I just replace the timing chain set two weeks ago when my simple oil change turned into a three day ordeal. The pan plug was stripped so I swapped a new pan on, while there I noticed two freeze plugs leaking so I changed them and since I could see stretch in the chain I put a new timing set on. Of course that lead to re-painting some of the accessories and the engine block, etc, etc... "While I'm at it" syndrome..... I reset the timing yesterday as well. I had set it at 14 deg with the old chain and when I checked it it was closer to 20 deg. so I backed it off. Yes I did align the dots on the timing set and put it in straight up.

woodsnake · May 2, 2008

Well, then the gear set is out. However, if it's backfiring, it's a timing issue. Got any vacuum leaks from the dist? Hoses are good and not cracked?
Did it start having trouble immediatley after the timing gear change? Or was there something else?
*usually* a single lobe won't fail on it's own, out of the blue.
Lobes will fail if you put in a new cam, and don't have the geometry correct. I've done that.....\

You did install a "302" gear set, VS a 5.0, right?

Actually, after a re-read, I'd say double check (again) the firing order, sounds like you have a pair of wires backwards...

tweet66 · May 2, 2008

It is a 302 gearset not 5.0L, I made sure of that when I bought it. The hoses are new, I replaced them when I bought the car last year. Prior to swapping the timing chain I rotated the engine to TDC and lined up the exisiting dots on the chain. I left the dist. in and swapped the gears and chain. My only thought there is that the position I stabbed the dist. in originally might have been off due to chain slop? I did check the wires but another look won't kill me. She ran fine last week after the plug swap, it just started this on Monday. I did drive it to work this morning and as long as I was under load/accelerating she ran fine with no noticable miss. When I let up or idled the popping/miss fire was there.

D.Hearne · May 2, 2008

302 and 5.0's use the same timing sets. Check the vacuum advance and see if it's operating. Pull the vacuum hose from the carb, remove the distributor cap, suck on hose and look for movement in the breaker plate. Recheck the firing order.

woodsnake · May 3, 2008

I had the exact same problem once when I was installing a set of headers on my 69 Coug. WHen I got frustrated and decided to take it some where, it popped and sputtered. I didn't change any of the wires on the dist, I just had two wires, (I think I actually had #'s 3&4 switched) on the wrong cylinders.
I think that is what is getting you.
I could be wrong, I can't "see it" from here....

tweet66 · May 3, 2008

Alright update time. Checked and rechecked the wires, but they're where they're supposed to be. Vaccum advance is working. I did find one of my header collector gaskets was leaking, not sure that would have an effect. Still lookin'......

D.Hearne · May 3, 2008

Are you running the right coil with the Duraspark ? My Comet was doing pretty close to the same thing a few months ago, till I replaced the coil with one known to be correct for it.

tweet66 · May 3, 2008

MSD with MSD Blaster 2 coil. What annoys me the most is the fact that she ran well before the damn oil change and other associated crap it involved. I remeber it poping once or twice before the plug change (which is why I did the change) but this is getting rediculous.

How do I determine if

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