Ok, here's the issue. Had the car completed last year. Took it to the track, ran a 13.0 @ 110. I know, the car's got a lot more in it but I can't drive and this was with a peg leg and a manual.

Put it in the garage over the winter. Put in an automatic, a posi Ford 9", and a 3500 rpm Edge converter. Took it out this spring to test everything. Died when I floored it. Died in park as well. Thought it was related to the new base plate I needed to get to fit the TV cable hookups. Swapped the old baseplat back on, same thing.

After months of trying to figure it out I have noticed that I now have VERY low vacuum at idle, like 1-2 inches. It used to be great 11-12. The only way I can get the vacuum back and it to not die when floored is to loosen the rockers to an undrivable point: clicking and clacking like crazy!

I took the cam out to see if there was any damage and measured the lobes, looked at the pushrods, lifters, and arms. No problems. I'm completely lost here!

What do you guys think?

I assume your sig is correct in that you have hyd-roller lifters?

Could maybe be a lifter issue...

I think i would just tighten up all the rockers to spec and start doing a leakdown test to see which valves arent closing, that might help sort this out...

Weird!
Where are you measuring the vacuum? How's it idling, with 1-2" of vac?
It should stall with 1-2" of vac at idle.

I'm guessing there's something wrong with your carb. I think when the valves are set right, they pull too much fuel through the carb, and low vac, it dies. When you set the valves loose, it barely opens the valves, you get a super strong signal through the tiny opening, and it pulls more air through, and idles better. This is a bit of a WAG, but see where it leads you...

I'd look for broken valve springs.

Thanks everybody for the suggestions. I'll try an answer in order. The sig is correct and they are hyd-roller lifter, actually a the Comp roller conversion setup as the block is a 1977 piece. A leakdown test was performed and the results were great. Doesn't seem like there's an issue there.

How's it idling, with 1-2" of vac? Like crap! We have to play with the throttle to keep her going around 700 it'll stay by itself at ~1,000. We've tried three different carbs to date, all with the exact same symptoms. My Holley 750 DP, a new Holley 650 vacuum secondary, and the ond, never fails 650 Holley vacuum secondary. We see no change with any of the carbs.

five7kid - wish it was that easy. One of the first things I looked for. I have an issues with that before on another motor but these are much better springs. No issues there unfortunately.

Question. This seems almost certainly related to the opening and closing of valves which means it can really only be caused by timing (maybe) or a physical problem affecting lift. Sound reasonable?

With that being said, I've removed the cam and measured the lobes on V-block and everything looks perfect. I mean jeez, the motor only has ~1,000 miles on it since the build and there are roller lifters. I'm lost!

Does that mean you've verified each and every one is currently okay?

Yes sir. Inner and outter.

An exhaust obstruction can make a car run like that. Ruled that one out yet?

Wouldn't be surprised to see a ratsnest in the exhuast after sitting that time.

Hmm... Interesting. I was told that before but had ruled it out because the last thing I did before pulling the car out of the garage was a complete new exhaust system. I know nothing is stuck in it but what about, and I know this is a long shot, a major restriction in the system itself? I doubt it but could it be possible? An incorrectly constructed muffler? Poorly welded headers? The system consists of Headman longtubes, a custom y-pipe, and a Hooker 3" cat-back with an Aero muffler.

It actually has never run right with this system on it....... I'll take it off and see what happens...

Ok. I work fast. I almost forgot I had cutouts right after the headers. Took'em off and no difference. I guess I could change the headers themselves. More ideas???

Did you check the timing to make sure it is correct?

Many, many, many times. Even went so far as to put a completely new ignition system in. Took out the dist, MSD box and all wires. Hooked up a separate system all together completely isolated from the car. Separate battery, coil, and all wires. Nothing changed.

I'm still stuck on this being a physical problem....

I guess I'll just have to pull it and tear it apart.

i would definitely tune/retune the carburetor. when tuning a holley after the idle speed and float level are set, then hook up that vac gauge and tune the mixture needle screws to max vacuum.

are you getting the vac off of the right port for sure?

It's not the carb. Absolutely no difference with 3 different pieces. It's got to be a mechanical issue. I vote the cam is shot but I've already proven otherwise..... This sucks!

Have you done a compression test? A good compression test would indicate the cam/valves should be working, and timed well enough that at the least, they are not the cause of this problem.

If the cam is in, undamaged, and timed correctly, the valves are working, and have no broken valvesprings, I think that is enough to rule out a physical, mechanical problem in the long block assembly, and it's time to look elsewhere.

The top three things I can think of are:

1) Major big vacuum leak
2) Severe exhaust restriction (near 100% blockage)
3) Severely retarded timing.

What is your timing set at? While you were replacing parts, did you replace the timing cover, or the harmonic balancer? A mismatch between the balancer and timing cover timing marks can give incorrect timing. I helped a friend break in a new cam a while back, and his engine ran like yours. He had replaced the stock timing cover with a chrome one that turned out to have the timing marks in the way wrong place, and the timing was off by something like 45-60 degrees retarded.

Well there's your problem, the engine is bored .40 oversize, you have no cylinder walls left and the pistons are just flopping around in the bores

It doesn't sound like he's touched the short block since it ran well...problem should not be here.

I'd imagine .040" would make for some pretty good piston slap

A compression test was actually one of the first things I did with stellar results, in the realm of 250 psi a cylinder. This motor is tight and used to run great.

I didn't replace anything touching the motor except the exhaust so the timing is as it was which is 12* advanced before any mechanical advance comes in.

I think we can rule out a 100% restriction is the exhaust system. I took the cutouts off which are right after the headers and it had no effect.

I too thought about a huge vacuum leak which is exactly what it feels like but I can't find one!

"Well there's your problem, the engine is bored .40 oversize" I wish that was it!!!

I had a similar problem when I used a cheap carb gasket and had a huge vacuum leak. I'm sure that this isn't your problem, but I figured it couldn't hurt to throw it out there. You tested all the other options, throwing in some stupid ones might help. I assume you haven't messed with the intake manifold since it ran right. All of the computer wires are hooked up to the dizzy...etc.

Yup. Checked the gasket and replace with each different carb we tried. Completely rewired ignition system so we're good there. I think it's coming out this weekend. I'll keep everybody posted.

Thank you for all your help thusfar.

????

-- Joe

I always go back to the last thing done. I know its a long shot, but what about the trans or the converter?

Did the trans spin freely before you put it in. What about the pilot bushing from changing over from manual to auto. Did the converter fit on the flexplate ok?

Which trans did you go with 700r4, th350, th400? Does it have a vacuum line for the modulator valve?
Just some ideas.

anesthes - "peg leg" = non-posi rear end.

Ahh!


-- Joe

what does the spark look like?

what does the plugs look like after running

lean or rich

Got it on a scope the whole time. Spark looks great, running a little rich.
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To reply to a previous post: Could the trans really be causing such an issue? I don't see how that is physically possible. It's a 700r4 with no vacuum lines that go to it. Everything fit well and the trans seems to be in good working order. I know it needs a rebuild but I went through and cleaned the valve body when I did the TransGo kit and rebuilt the front pump when I got the converter.

I can't see it being the issue plus I can't really run it without the trans attached. Well I guess I 'can' but should I?

I dont know that it has anything to do with the trans, but you never know. If it was fine before, then you have to go over everything you changed.

i think my car is kinda doin the same thing...i have a really bad idle...i cant seem 2 get it timed rite....and kinda like u my car will run 4 a min but it just completly runs outta gas and bogs down like its gettin 2 much fuel but its running outta fuel is the problem??
like u im completly lost

The " Loosen the rockers thing " is a real head scratcher . What type of rocker are you running ?
If you have no vacuume then that would point to a intake valve issue , how much spring are you running ? how much lift on intake ?
The leak-down test eliminated the hole in the piston or a broken piston .
What about a crack in the intake ? on the bottom maybe ?
Keep us posted ..

DNSTA, this is bad. I have the EXACT same symptoms except I'm EFI, not carb. Car was running GREAT a week ago. Now my car's idle and driving around is 1-2" of vacuum. I did a compression test and on my 8.75:1 383 I'm 160PSI +/- 3%. I haven't taken the valve covers off yet but tomorrow I'm going to put the plugs back in, let her idle, check the timing and if its fine I'll spray propane around the intake and such to try and see if I can get the RPM's to race. After that I'll test vacuum with a guage near the rear port of the plenum. Then I'll pull valve covers and see if the polylocks for some reason backed off.

If the polylocks backed off you should hear some ticking .. If you had a bad valve the needle would bounce on the vac gauge.

I wonder whats wrong. hrmm..

-- Joe

Yes, this is bad. I'll see if I can get an update out some time this week. Work's been bad.

Ok, is it possible you DO just have a bad vacume leak? Sure you didn't suck an intake gasket?

Can I ask a question????

Do any of you who are complaining of this condition run comp cams retro fit hydraulic lifters with tie bars?


Jeff

Nope. My lifters are Crane and the equivelant OEM 1991 replacement offered by them.

Did you run it on alcohol or run nitrous?

The engine has been apart after the problem started so the intake gaskets are not suspect nor is a huge vacuum leak. If it was there before it wouldn't be there now.

Jeff, your question scares me! I AM running the cams retro fit hydraulic lifters with tie bars!

Why do you ask......?

No alcohol or nitrous. All N/A power on premium fuel.

Jeff, come back! This is bother the hell out of me!!!

Is there some sort of known issue with these lifters?

I dont have definitive proof there is a problem with those lifter but I know I had a new build using them and the lifters failed at the skirt area(metal failure) and it caused my roller cam to have two wiped out lobes after only about 1 hour idle running time. I had the same condition you are describing. Drain your oil and look for glitter.

Jeff

Damn. Unfortunately not the problem here. The lifters are in perfect condition externally and there was no sign of anything in the pan. We took the cam out and physically measured every lobe to no avail. Thank you very much for the idea though.

DN, did you at one point do the propane test? Use a propane torch to spray propane around your intake gaskets and such to see if there was a vacuum leak?

I have not done any testing of the intake seal after we pulled the heads off. The problem existed before and work was done so the possibility of a major leak was there but after we pulled the heads and cam I an quite certain we do not have an external leak although I cannot rule out an internal (lifter valley?) leak.

We just unbolted the torque converter today to eliminate the transmission to no avail. We are planning on pulling the engine this week and tearing it apart again. I may have access to an engine dyno so were planning on putting it on there and diagnosing the problem sans the car altogether. Hopefully we can come up with something.

DNSTA, keep me posted. Hope you find it. I had some light. I was at 1"-2" at idle and cruise. I replaced the header gaskets and the vacuum jumped to 8"-10"...still lower than the 12-15 I was at before.

Just a long shot but my camaro had a bad brake booster and caused a huge vacuum leak. Try plugging off your vacuum lines, brakes, etc.

AC: Good to hear it's getting better for you. I'm a little curious how the header gasket made such a difference. Please fill me in on your thoughts.

big: Unfortunately I've disconnected every vacuum line there is to no avail. Pretty much had the engine running completely disconnected from the car. Separate electrical and fuel system and no trans attached. Just the exhaust..... Hmmmmm, maybe I'll look for exhaust leaks around the headers courtesy of AC.

Haven't got the engine dyno in yet. As soon as it's here, the engine comes out. Just wanted to let everyone know the saga continues.

Still waiting on the engine dyno. I'll keep everybody posted.