View Full Version : Very Odd Engine Issue, Not An Easy One
Ok, I bought my 69 Camaro 2 years ago with a crate 350 in it. Not the best crate motor ever but it does have 4 bolt mains. Anyway, on rare occcasions, about every 4 to 6 months (weekend driving only) during warm up <150* I will hear a small back fire. When it does the engine drops about 4 or 5 cylinders and barely stays alive with half throttle. Most times it will stall out. When I go to restart it the engine sounds diffrent while trying to crank it. It starts constantly backfiring and running on just a few cylinders.
If I can keep it running it takes about one or two minutes of spitting and backfiring and everything comes back online and runs perfect. I smell alot of fuel in the exhaust during that time for obvious reasons. While she is hot the engine never backfires or does anything like this. Only on occasion when its cold. I think the amount of time I allow it to warm up has alot to do with it but it seems like an odd thing to happen. I know that if I try and feed it alot of fuel cold it will most likely happen every time.
It did it to me just a few minutes ago and I didnt allow a warm up. Since having this car I have replaced/added the following
Weind 144 blower (12 lbs boost)
Headers/exhaust
Demon Carb
MSD Pro billet dist
MSD 6AL
MSD coil
New Mechanical Fuel Pump
I thought it might be a ignition issue but since replacing almost every engine bolt on that there is I am left scratching my head.
Any ideas?
paul67
10-22-2005, 12:56 PM
Could be plugs.
paul67
OHCbird
10-22-2005, 06:42 PM
Have you checked for vacuum leaks? How much did you torque down the blower? IIRC, they are only supposed to have like 12-15lbs on the blower bolts. More than that, and you'll warp the case (creating a vac/boost leak). What I'm thinking is that when your engine is cold, you have a gap or leak somewhere, then when it warms up- it closes up the gap.
As far as plugs- you say it runs fine after this horrible warmup? Define fine...
Do you have any type of boost / timing device besides the 6AL? ex: a Boost Timing Master that will yank out some timing under boost and during start? I'm assuming you're using a 'double-pumper' style carb, and not a vac secondary?
weird, maybe you are getting trash in the floats, and gas is pouring out of carb, woudln't make it backfire though, could be the mechanical advance in dist? maybe have your ign. system checked out my MSD, check grounds?? should be ground straps from engine to frame, and body to frame. Next time it happens, check for fuel delivery, maybe the pump is acting up. Unfortunately it could be many things, sounds like you need to look at it when it actually is happening.
EDIT, read again, sounds like an ignition problem, i would check all the connections on your MSD system.
Have you checked for vacuum leaks? How much did you torque down the blower? IIRC, they are only supposed to have like 12-15lbs on the blower bolts. More than that, and you'll warp the case (creating a vac/boost leak). What I'm thinking is that when your engine is cold, you have a gap or leak somewhere, then when it warms up- it closes up the gap.
As far as plugs- you say it runs fine after this horrible warmup? Define fine...
Do you have any type of boost / timing device besides the 6AL? ex: a Boost Timing Master that will yank out some timing under boost and during start? I'm assuming you're using a 'double-pumper' style carb, and not a vac secondary?
I was very careful when I torqued my blower on, 12 ft lbs. I have no other timing device. I am running a Demon with vac secondaries. Why?
When I say it runs fine after an occasional bad warm up I mean fine. Totally normal, you can romp on it, idle, cruise etc with nothing abnormal happining. Runs like a champ.
Could be plugs.
paul67
:idea: Its funny you mention spark plugs. When I put in my new ignition system it was late on a Sunday and I forgot to pick up new plugs. I wanted new plugs in it so I was stuck with AC Delco cheapos at the local parts place. I totally forgot that I had done that.
You know, that also might be the issue with another problem. Recently after driving and shutting the key off I have about 3 to 5 seconds of run on. Ive been messing with my timing trying to fix that.
Edit:
I went and bought a set of NGK "V-Power" PN:6630.
I will install tomorrow and post up results.
I just wanted to thank you Paul. It looks like that was the problem. This morning (very cold outside) with no warm up I intentially gave it a stab coming out of my neighborhood and it started to act up, I gave it a little more gas and instead of repeating the problem I hapily entered traffic sideways!
I knew I had junky plugs in there but who would have thought it would make that kind of problem or diffrence. Guess I learned a lesson in spark plugs this week.:)
Thanks Again.
Well, she did it again today while cold. I will look for vacuum leaks. Today it dropped a couple cyl's but it never died and ran badly for about 30 seconds. It seems with the new plugs it helped keep it running and this time it didnt back fire at all. Just ran like crap, I pushed the clutch in and let it sputter and after 30 seconds all was good.
Any other ideas?
BTW, she has been running super rich for a good while now and I just had that resolved yesterday with a good tune.
paul67
10-28-2005, 12:21 AM
Try this when its dark when car is stood in drive way start engine up and lift hood and see if there are any flashes of light, also check plugs again as its been posted you can get faulty new plugs.Also this might be a choke fault .
I you split fires and are very happy with them.
paul67
I will give that a shot. Wouldnt be a choke issue as I have my choke flap removed, its warm enough in Florida most of the time.
Thanks Paul
paul67
10-28-2005, 11:53 AM
I live in the UK and I wish I did not have to use the choke even in the summer.What about humidity causing a tracking fault then when the engines warm the moisture burnt away ?.
paul67
paul67
10-29-2005, 02:11 AM
What I call a tracking fault is where the spark takes the least line of resistance , ie flash from say the plug wire to the block or disy to the block or if you held the wire to you .
paul67
Very interesting concept, I noticed when I changed my plugs that there were small water droplets on the electrode. It sounds like you could be right about this.
If that is the case, the only fix is to make sure I give it time to warm up when I drive it. As is I usually do let it idle in the garage for a minute and then take it very easy through my nieghborhood and on down the street till she comes up to at least 170* but every now and then I have to goose it coming out of my nieghborhood to get into traffic, and thats when Ive had the problem.
Thanks alot for your time Paul
blazer4corners
10-31-2005, 04:52 PM
What heat range plugs are you running and what is your plug gap?MSD recomends a .060 gap with their ign. And if my memory serves me right when upping compression...ie blower.You need to go to a step or two COLDER plug than before.I might be wrong its been know to happen before.
Trying to remember what heat range I bought, I know I did make it a step colder. I gapped at 47 and I am using NGK plugs.
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