????SBC engine problem

My SBC has developed a case of the "I ain't gonna run this year" blues.

It ran great all last season. When I fired it up this year, it would idle, but would pop back thru the carb and fall on it's face when I tried to accelerate.

I went thru all the normal checks. I even swapped out the entire carb and distributor, still same problem.

Finally I fired it up long enough to check the exhaust temps. # 5 & #6 exhaust temps started approaching 900F.

I re-adjusted the valves, but no change. I now have the top of the engine open to check lift on #5 and #6 lifters. All the valve springs look OK. I figure I will leak check each cylinder tomorrow.

Any suggestions????

Justice

 

Check your fuel pump as a weak one will act as you described.
Max

 

Has it still got last years gas ??

Throw some fresh gas in it before you do much more parts swapping !

 

Already put in fresh gas and swapped out the fuel pump just in case.
No Cigar

Thanks for the suggestions though.

Justice

 

Ignition.
Check or replace the coil.
Cosmo

 

check engine ground, and wire to coil, mine was acting up last weekend, and it was a bad-missing engine ground...Toqwik

 

Yep, that is what I thought.
That's why I tried a whole new distributor. I had one on hand, complete with cap & coil.
No Cigar

 

I tried runnning a new 12V supply to the distributor.
No Cigar.

I checked my ground, but I may need to re-visit that one.

Thanks

Justice

 

Fit new plugs?
Fit some more new plugs!
I once had a set of six that had three bad ones in. Misfiring, popping, farting like a motherfeckler

 

Massive intake leak somewhere? Super lean mixture somehow.
Try some water around the intake and see if she sucks it in.

 

vacuum hoses are all connected and in good shape?


its not missing and just backfires on acceleration?

 

I am on my fourth set of plugs.

No cigar

Thanks

Keep the ideas coming. We are bound to get it sooner or later.

Justice

 

I sprayed brake cleaner all around the edges of the intake
and carb flange. The idle never changed.

Justice

 

[ QUOTE ]
vacuum hoses are all connected and in good shape?


its not missing and just backfires on acceleration?

[/ QUOTE ]

There is only one vacuum line to the advance canister. It is new.
You are right. It doesn't really miss. When I would try to accelerate, it would just bog and start popping back through the carb.
Remember, I have tried replacing the carb and the whole distributor with new ones. Still, No Cigar.

Justice

 

your getting good fuel flow where it bolts to the carb? no plugged inline filter(s),kinks in the line?

the second carbuerator you tried it was known to be good?

your timing isn't to far retarded?

 

maybe the exhaust is blocked up somewhere? that would explain the high temperature you're seeing.i would also go back over the valves to make sure they're not sticking open,try squirting some penetrating oil at the valve stems and give each valve a smack on the top with a plastic or rubber or rawhide mallet-george BTW did you ever do a compression or leakdown test?

 

Still have points? Adjust them. I had a problem like that. Adjusted the points 1/4 turn in and it was like new.

 

The second carb was brand new out of the box.
Edelbrock 1406.

Justice

 

I checked compression on # 4, 6, 5, 3 cylinders today.
They all checked good >140 #'s

I like your idea about the penetrating oil. I had mentioned that idea earlier to one of the guys here at work.

The only things I haven't tried replaciing were my wires.
Remember this engine and everything on it is new <500 miles.
Everything was peachy last summer, but it has refused to run right since I started it up for this summer.

I am working 12hr nights right now, so I don't have much time to fool with it. However, I will be taking 10 days off starting this coming Friday morning. I am hoping to figure it out then.

I really appreciate all of the responses. I don't really know anyone around me with any more experience than I have with SBC's , so it is a little frustrating trying to get a valid second opinion.

Justice

 

Nope, HEI

Thanks

Justice

 

[ QUOTE ]
maybe the exhaust is blocked up somewhere?

[/ QUOTE ]
Yeah, I thought about that, but the only cylinders running hot are #5 &amp; 6. I also have dual exhaust without a X-over.
I would consider this more if it were only on one side.

Keep thinkin'

Justice

 

Have you played with the timing. Advance it and see what happens?

 

U sure you don't have a plug wire crossed?

 

Yeah, I did that. It doesn't seem to make any difference.

Justice

 

[ QUOTE ]
U sure you don't have a plug wire crossed?

[/ QUOTE ]

Yep, I checked them just to be sure. I hadn't messed with the wires anyway, so they were just like they were last year.

My plugs keep fouling out like they are not getting a good spark.

As soon as I get the top of the engine back on this weekend, I am gonna check my spark strength. Of course, knowing my luck, it will probably crank up and run fine.
Then I will forever scratch my head and wander what fixed it.
Then again, I don't really care as long as it is runnning right.

Justice

 

how bout a damaged/collapsed fuel line? And to check your ground, just hook some jumper cables from the frame to the engine. you used a different cap and coil to test also? Only other thing I can think of is improper voltage to your dizzy, I'm FAR from knowledgeable about engines, but if it backfires thru the carb, doesn't that indicate a cylinder firing at the wrong time, i.e. when the intake valve is open? good luck....Toqwik

 

Bad - or stuck - PCV valve?

They'll make an engine fall on it's face.

 

[ QUOTE ]
damaged/collapsed fuel line?

[/ QUOTE ]
Nah, I don't think so. It shouldn't be fouling all my plugs out if it was lean.
[ QUOTE ]
you used a different cap and coil to test also?

[/ QUOTE ]
Nope, I used a new coil and ignition module, but not the cap. The cap I have is still new.
I am going to replace the wires and the cap when I re-assemble it this weekend though.
It will take a little bit to fit the wires. I have attached a photo of the engine that I am working on. This photo was taken last year before I dropped it in the car.

Justice

 

I have two thoughts on what it could be,

First and easiest to check would be timing/crossfiring from mositure in the distributor cap or cracks in the cap.

Second and harder to fix would be sticky valves, maybe its from when the engine was sitting for an extended period of time, rust or scale may have formed on the stem or seat and is holding the valves open enough to bleed combustibles out on the compression stroke ending with a lean mixture which is going to run real hot and have a misfire from lack of a powerful enough fuel burn. (If you are real lucky on this one it may be a collapsed lifter from the pressure on it for the last few months)

Anyway first things first.

If I was in your situation I would do the folowing diagnostics check.....

-Check for is moisture or cracks inside the distributor cap.
-Start the engine and get it up to operating tempreture, never mind the popping etc.
-Do a compression test on ALL cylinders of the engine while the engine is hot (remember to have WOT for the whole time you are doing a compression test - ie not pumping the gas open and closed)
-Check Valve Lash (if adjustable) As you are turning it over watch each rocker and see if they are getting a reasonably even amount of travel on each rocker.
-Do a cylinder leakage test listening very carefully at the carb mouth and tailpipes.
-Replace plugs with brand new set.
-Check Firing order of HT leads (someone may have been a dick head and switched them one night when the boys were on the booze.
-Static Set Timing around 8 degrees BTDC.
-Fire her up and set timing properly.
-See how she runs and if no better throw some 2nd Hand lifters into the bad cylinders (rough I know but if you want to throw in a complete brand new set of lifters - go for gold -just use heaps of cam lube)
-If still no better I would be yanking the heads and checking the valves/ valve seats.

Hope you solve the problem real soon cos I know its mega annoying having a car running like shit when cruising and nothing more embaressing than breaking down on the side of the road.

Good Luck -Chris

 

Thanks, that was a really good write up.

I still have the intake and rocker covers off. I removed all the lifters one at a time to see if the bottoms were worn (indicating a bad lobe.)
I re-installed the rockers and pushrods, and adjusted all my valves at top dead center on each cylinder.
I plan on putting the manifold back on, replacing the wires and dist. cap, and fireing it back up.
I'll then set the timing back up and see how she does.

There is one thing that I have been thinking about. I have a CLoyes quiet gear drive set. I am wondering if my bushing may have worked itself out of the cam gear from where I degreed the cam. This would allow the top gear to shift and would be the same as a chain drive jumping a tooth.

If it still runs crappy after this next try, I may just pull off the timing cover and check it. I have the re-usable one-piece pan gasket,so it isn's a big deal.

Justice