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Hi, Dave here. Got a fully rebuilt SBC 350 in my hot rod.
-has newish new Edelbrock
-has newish HEI dist.
-newish new shorty plugs
-160lbs every cylinder
-valves well adjusted
-adequately timed
Starts right up but runs poorly, missing on three cylinders: checked with electronic temperature sensor on header tubes.
Spark seems to be getting to all plugs, pulled and observed for spark.
WTF is going on? Totally frustrated by this! Where would you guys go next?
Thanks much for any ideas!!
First thing I'd check is the spark plug wires, Are they Accell as well as the plugs?
Ken, Plugs are ACCEL but the wires are likely not, but fairly new. What cha thinking?
Dave
I've never had any luck with anything that has Accell stamped on it. If you have a decent multimeter Check the resistance of each plug wire. Anything over 500 ohms, IMHO, is too much. How old is the module in the distributor? What kind of cap and rotor bug? The module is solid state and normally they either work or don't. The cap and rotor if they are cheap can ark between contacts. I like something with a high dielectric strength.
I’m not trying to ask a dumb question, but are you SURE that the plug wires are not crossed?
Driver50x, that was not a dumb question!! That would be something I might do :-/! Given that, I have checked the wires for correct location (but now I will do it again :-) ). Maybe those ACCEL plugs are the problem. I only used them because my damn headers are so close regular plugs would not fit or if they did, the wires were touching the header pipes. The distributor is new though I did get it off eBay. It wasn't the cheapest.... :-0.
I'll get some shorty plugs from AC or and let you all know what happened.
Thanks,
Dave
I run E-3's in my 76 Vette and 04 Dakota. In June I drove from Springfield, Mo. to Columbia, SC to attend my grandson's boot camp graduation at Fort Jackson. Round trip is just under 1800 miles and the Dakota averaged a little under 20 mpg which I don't think is too bad.
I tried running the accel plugs back when I had my 72 Camaro and they were garbage. I'd never use them again.
Dave here again (thread starter) about the SBC not firing on several cylinders... so as before I have 160+ per cylinder, new HEI, new carb, good wires and now new Autolite plugs. Same problem... not firing on at least one cylinder!! This is crazy. With my temp sensor #8 for example showing like 250 deg where most all others are around 450 pretty soon after startup. Also again, this is a totally rebuild engine with probably 2 hours or less of operation.
**My carb spacer does not line up the carb and intake manifold all that well. As I recall the vents are kinda offset. Could that effect fuel getting to different cylinders? Or any other ideas??
Thanks again, Dave
Thanks Denny. Plugs were checked and all the same. The valves were adjusted... correctly?, well thats another question :-/, but I believe I got them right this time! Is spraying starter fluid to look for vacuum leaks?
BTW, should I be getting about the same temp on each of the header tubes? Even #8 for example is sorta hot (250) which may suggest it is firing but poorly... yes?
Hold the rpm at a steady 2.000 rpm with no load if it has a steady pop through the intake it has a flat cam. You can have good compression somtimes with a flat cam. With todays oil flat cams happen on start up vary often. Take a magnet and drain the oil over the magnet if it grows hair the cam is gone.
Hey you guys. So I put in new plugs and the same things are happening as above. But in looking around the net for why this could be happening I see that a leaking intake manifold or an unplugged vacuum hose/fitting seems to have all symptoms I am experiencing.
-hesitation when acceleration
-misfiring
-rough idle
-overheating
So I will do what Denny suggested and spray some starter fluid/cleaner around looking for rpm changes. Yes I have a working fire extinguisher just in case and yes it is in the garage!!!!! :-)) BTW a pic of the beast "we" are working on is hopefully attached.
Few things to try run it in total darkness and look for spark plug wires jumping spark--------
take valve covers off and check to see if pushrods are rotating as valves lift/close( Lobe wiped on cam-----lifters should rotate and also will spin pushrods) turn carb around and see if missing cylinders change---plug all vacme lines------
My first "go to" tune up tool when there's nothing obviously wrong with the simple things is a leak down tester. It's also a really goo way to keep track of what the engine has going on internally. JMO
Don't overlook a leak at the inside bottom of the intake at the interface of the cylinder head, where you may or may not find a leak with a sprayed flammable substance. Such a leak will allow oily vapors from the oil pan to be sucked into the intake port, disrupting air/fuel mixture balance and providing a vacuum leak. It will also foul the spark plugs with oil. If you find nothing pointing to a leak, pull the intake and examine the gaskets to insure that they are being pinched with equal force top and bottom, side to side. The manifold could have been mis-machined. If nothing is found there, examine the manifold for cracks. We used to use a Zyglo process back in the day, but there may be better ways today.
.
Have a CO2 extinguisher handy. You don't want to clean up the mess a dry chem will make, don't ask how I know.
Vacuum leaks from the underside of the intake manifold can be found by performing a simple vacuum gauge test.
1. Remove any breathers and plug or cover their holes in the valve covers with tape.
2. Remove the PCV and plug or cover its hole in the valve cover with tape.
3. Remove the oil dip stick and connect a vacuum gauge to the dip stick housing.
4. Start the motor and read the vacuum gauge.
If the vacuum gauge shows vacuum, you have a leak under the intake manifold.
Hi you guys, here is an update on the SBC that won't fire on cyl. 8. Again compression is 160, did leak down and got air out of the valve cover portal when pressurizing #8. Other cylinders leak air through that hole also to some degree but none through exhaust or carb. Oil is clean (shavings etc.)and the rockers appear to be working well so I don't think I have a flat cam. This is crazy... My neighbor, a pretty good home style mechanic even says WTF!?
I think Denny has nailed it, you probably have a damaged reluctance tooth
More good ideas. Here's more:
-all new plugs
-moved plug wires around, still problem with #8
-HEI dist was new 5 years ago with at most 2 hours of use (but yes could still be bad)
-as noted before, seem to be getting good spark to plug
-dist is tight, no play but the reluctance tooth...? Dont know what that is: help!
-yes the rotor does not seem to point directly at the cap #8 point.... but if its off there wouldn't it be off at all the cap points... but its firing on the other cylinders.
M
How (exactly) did you determine the rotor is misaligned only on #8?
That is extremely odd.