Engine Problem... Advise?

digginfool · #1 (**permalink**) 03-05-2011, 10:19 AM

Last night took the BDR out for a spin. I drove to Miami and back, about 48 miles each way. Was cruising at 3,000 RPM for most of the trip. Half way back, the engine dropped a cylinder. I know it's not fuel related because it was popping and backfiring intermittently (unburned fuel igniting in the exhaust). The engine is a Ford Racing 392, MSD ignition and 4 - 48 IDA Webers. Oil pressure excellent but oil and coolant temps a bit low (coolant 185, oil 150). I've checked the cap and wires. Haven't checked plugs because I can't get to them with the tools I have at the house. Aside from a seriously fouled plug, any ideas?

blykins · #2 (**permalink**) 03-05-2011, 10:44 AM

Did it seem like it was down on power, or did you just hear a lot of racket?

One quick thing to check would be to pull the valve covers and take a quick look around.

Cashburn · #3 (**permalink**) 03-05-2011, 11:11 AM

Welcome to Weber ownership??? Have to dig some more...

digginfool · #4 (**permalink**) 03-05-2011, 11:40 AM

Definitely down on power and running rougher. It was running a smooth as could be, wasn't accelerating just started running rough, RPMs dropped a couple hundred and started to pop and sputter. Would backfire when I let off the gas. Checking the plugs now. The popping was limited to only the driver side. The back two were a little dark for my taste but still brown. I've got one of the front two and it's a little lean, if anything; perfect tan with a hint of white on the grounding (side) electrode. Pulling the last plug next.

digginfool · #5 (**permalink**) 03-05-2011, 12:06 PM

I think I found the problem. When I pulled the front plug on the driver's side, the insulator had shattered. I've never seen that before. It was an NGK Iridium plug. Anybody else ever see that before? I've got to run to the auto parts store and get a new plug. Hopefully, that was the problem.

blykins · #6 (**permalink**) 03-05-2011, 12:08 PM

I hope so too....

madmaxx · #7 (**permalink**) 03-05-2011, 01:23 PM

I chased a cracked spark plug ceramic for two weeks. What a complete circuis. I had convinced myself of everything from a leaking valve, defective lifters, lifters pumping up (even though physics proved it impossilbe) and in the end after compression test, leak down test, valve spring test it was a bad spark plug. I did determine the engine was in perfect condition though, LOL!!

digginfool · #8 (**permalink**) 03-05-2011, 03:06 PM

That would have been too easy. Replaced all the plugs on that side of the engine and the problem persists, if not gotten worse. I don't have an infrared thermometer so I guess I need to go pick one up to see if I can narrow it down to which cylinder is running cooler. Any other thoughts on what my gremlin might be?

bobcowan · #9 (**permalink**) 03-05-2011, 04:06 PM

Check the balance again. If one of your linkage rods cam a little bit loose - even a little bit - it will run just like you described. Individual runners are very sensative to balance.

mln385 · #10 (**permalink**) 03-05-2011, 04:10 PM

WHy did the plug shatter would be the question? You say the insulator shattered was it from a collision with the piston? Did you vacuum out the cylinder to get the pieces out if any?

Might want to perform a compression check next. Good luck hope it isn't anything major...

digginfool · #11 (**permalink**) 03-05-2011, 04:35 PM

Okay. Went and purchased an infrared thermometer. The rear cylinder, driver's side, is 150 - 170 degrees cooler than the other three (220 compared to 368 - 388 for the other three). Thankfully, that's not the cylinder with the shattered spark plug, although it was only the external portion of the insulator that broke. I don't see how linkage could affect only half the carb and the popping suggests that fuel is still flowing through that half of the carb and into the cylinder, where it's not burning, and dumping raw into the exhaust. The plug that came out of that cylinder was one of the ones that I thought was a bit dark but still brown, so I don't see how it could be a burnt valve from leaning out, which if anything would cause that cylinder to be hotter than the rest as well as a different color. I'm officially stumped. I'm going to look at the cap again to see if I missed something.

digginfool · #12 (**permalink**) 03-05-2011, 04:44 PM

Cap is good. Nothing strange going on there. Ideas anyone?

digginfool · #13 (**permalink**) 03-05-2011, 05:00 PM

Just brainstorming here but could it be I have a clogged jet, causing that cylinder to run so lean that the fuel doesn't ignite in the cylinder but ignites in the exhaust? That might explain why the symptoms occurred so suddenly during cruise speed. The color of the plug is probably just a result of the last 600 miles running at a proper, albeit slightly rich, mixture rather than the last 20 miles to the house.

vector1 · #14 (**permalink**) 03-05-2011, 05:53 PM

leakdown test on a few of the cylinders would give you a good indication of a bad cylinder if there is one.

blykins · #15 (**permalink**) 03-05-2011, 06:07 PM

Did you yank the valve covers just to make sure you don't have a broken valve spring, polylock, bent pushrod, etc?

digginfool · #16 (**permalink**) 03-05-2011, 08:24 PM

I'm not sure about a broken valve spring and certainly not a bent pushrod. I was literally cruising down the interstate at 75 MPH (~3,000 RPM) when the symptoms popped up. I hadn't had the engine over 3,500 RPM all night. The motor only has 600 miles on it and I've put the last 200 on it. I'm fairly certain the person who put the first 400 on it didn't abuse it, nor have I. That's why I'm now leaning more towards a clogged jet on that half of the Weber carb that feeds the rear two cylinders. If I clear the Weber as the culprit, then I'll start considering engine internals.

Rick Parker · #17 (**permalink**) 03-05-2011, 10:22 PM

If you have an electric fuel pump, turn it on (with engine not running) and look down both throats of the suspect carb, is any fuel dripping out of the Auxiliary venturis onto the throttle plates? If so the floats need to be adjusted or the needle & seat checked, are you using the small cone filter near the fuel banjo (?) it IS a good idea. Webers are more suceptable to foreign material in the fuel than a Holley. Pull the idle jet and holder and check it for blockage. Do the same for the main jet and holder. Carefully screw the idle mixture screw all the way in, noting how far it was open, then remove it entirely. Drain the fuel bowl (don't spill any) Blow compressed air in the mixture screw orfice and in the hole where the jet packs were removed. Reinstall, adjust and start it and recheck things. Hold you hand over the top to prevent fuel from being blown all over. This assumes the ignition system and spark plug is not compromised.

vector1 · #18 (**permalink**) 03-06-2011, 02:41 AM

oops, missed the webers, that is what i would look at also.

RICK LAKE · #19 (**permalink**) 03-06-2011, 05:13 AM

digginfool Start with the basics, make sure the ign system is ok
Swap plugs first to other bank and road test, see if problem is in the same side of the motor, if yes
Swap spark plug wires to other side and retest. I would install new cap and rotor. What make of cap and rotor are you running?? Have had alot of trouble with MSD cap and rotors over the years. Only takes a couple hundred miles to kill the center contact terminal in the cap and it still looks ok. if problem still there
Compression test
Leakdown test these 2 will give you a good indication about the motor's soundness.
Now to the tuffer stuff
Pull the valve cover on the bad side and have some one crank the motor
check for a full range of motion on the rockers. Make sure you have the right valve lash. You didn't say if the motor was a solid lifter one. Check and do the lash on the whole side. If the popping is still going on, I would be looking at lifters if they are hydros or sticking valve or out of round seat in the head. You will get good compression and the leakdown test will not show a problem. This is because the valve spins when the motor is running and hits the sealing parts more times than the bad spot. Been there, Had this happen.
Does the oil smell like gas?? or have a funny feeling to like?
Use a sparkplug socket with a rubber insert. This will stop chances of cracking the plug. Also if you use anti seize, it is possible that the heat range of the plug can drop 1-2 ranges because of the paste on the threads. Rick L.

digginfool · #20 (**permalink**) 03-06-2011, 08:06 AM

Rick, I think you're on to something. I just read an article about troubleshooting the Weber 48 IDA. It said the idle circuit handles all operation up to ~3,000 RPM, after that, the main circuit takes over and the idle circuit is inoperative. The popping occurs from idle up to about 3,000 RPM and clears up, although I need to road test to confirm under load. The article said if that's the case (where the problem exists RPM-wise) start with the idle circuit. Looking at a schematic of the carb, it appears that the jets are in the bottom half of the carb. Is there anything I need to be aware of as I lift the top half off (e.g. surprise springs or loose items that can fall into the bore)?