valves floating?

[daytona kid]

Starts to cutoff at only 4300 RPM's. That is pretty low. Stock, non-adjustable rockers ? I would first put the stock ignition back on and test it. If you can make it happen while parked hook up a timing light and have someone rev the engine until it "floats" again and keep your eye on the timing light. If it is ignition, the light will stop flashing.

I'll try the timing light trick, that's a good idea! I don't have any other ignition/distributor to try as the motor was missing all that and the carb.. If it were ignition tho it seems to me it would recover as soon as rpms got back lower than 4300 or almost instantly as I let off, instead of missing till it goes dead at low rpms, unless I help it recover with throttle pumping.. The valve train is stock as well as everything else I assume. What would be the symptoms if the carb jets are to small or lean?

 

[daytona kid]

Just because you have fuel pressure doesnt mean you have sufficient flow. I think you answered your own question. "Pumping the accelerator keeps it running". In this case it's out of fuel. The only fuel is from pump shot until the bowl refills. " The fuel gauge blocks 1/3 of the line". That's not helping flow. Remove the lines at the carb itself. You haven't mentioned what type of fuel pump. Crank engine or turn the pump on. Measure the amount of fuel pumped in 30 seconds. At 300hp you need about 1/4 - 1/3 of a gallon minimum. You also need a a proper vent in the tank. Dont forget the carb. If there is a screen in the inlet or the float level is very low that will be an issue. To me valvlve float would act as Dwayne has said. Ignition would more than likely misfire.
Doug

I have a summit electric pump #sum-g3136-1, that is supposed to pump 97gph. I may do a flow check but I think it's ok.. I'll check the screens if they are there, can't remember. Fuel cell is vented good.. I put a washer/spacer on the fuel gauge which pulled it out enough, still missing.. It never pops or backfires, it just acts like a couple cylinders aren't firing.

 

[daytona kid]

If it’s truly rpm related(doesn’t want to go past a certain rpm under any condition), it’s likely ignition or valvetrain.

If it’s load related, it’s probably fuel.

My test for the fuel would be to run it at wot thru the gears, but shift at an rpm lower than the rpm where you normally see the problem.
If you can start in low, go thru the gears and make it well into high gear at wot without it nosing over....... it’s probably not a fuel supply issue.

Another rpm related test is, go along in low gear at a light throttle setting and crowd the rpm where the problem occurrs.
Lightly crowd the throttle to get to the rpm point where the problem occurs.
If it runs clean right up to just under a certain rpm, and seems to be like there is a rev limiter...... then I’d look more at ignition.
If you’ve ruled everything in the ignition out, then look at the valvetrain.

I can tell you this, on the dyno...... it isn’t that unusual to see a valvetrain issue show up very predictably at the point where things get unhappy.
Just like flipping a switch.

If I leave it in drive/3rd and let it shift itself it feels fine till 4300 in 3rd. It shifts itself to 2nd and 3rd probably a little sooner than it should, before the problem rpm. But if I shift it manually, sometimes I let it get to hi and it does it. It runs nice tho in drive/3rd shifting itself, pulls pretty hard and smooth and will only miss at the hi end of 3rd which is about 90-100mph. It's like a rev limiter except my engine misses for a while and/or goes dead unless I help it recover, and a rev limiter recovers instantly.

 

[dvw]

. It never pops or backfires, it just acts like a couple cylinders aren't firing.

If it's not miss firing it isnt losing a couple cylinders.
Doug

 

[PRHeads]

If I leave it in drive/3rd and let it shift itself it feels fine till 4300 in 3rd. It shifts itself to 2nd and 3rd probably a little sooner than it should, before the problem rpm. But if I shift it manually, sometimes I let it get to hi and it does it.

If you hold it in low and try and run it past 4300.......and it won’t do it without acting up.......
But, you can be at wot from low, thru 2nd and into 3rd, with your foot on the floor the whole time......and not go over 4300...... and it’s fine until you get to 4300...... that def does not sound like a fuel delivery issue to me.

 

[daytona kid]

Here's a look at a plug. Looks good to me. They are Accel 437s plugs, set at .035.. I'm thinking it's not the plug wires or it would backfire, carb pop, and recover almost as soon as I let off.

 

[daytona kid]

I raised the rear float level a tad, no change. I noticed the fuel pressure at almost 9 before cranking and a little over 7 when idling. I think that's ok.. What would be the symptoms if the carb jets are to small or lean?

 

[PRHeads]

I highly doubt it’s anything in the carb, but......jets are easy.
Just add 2 to 4 sizes to the secondaries and see if it changes anything.

If not, just put it back the way it was.

 

[PRHeads]

I was answering a question about a similar situation over on fabo, and remembered a few instances where customers had engines in cars at their shops that didn’t want to go over 4000-ish rpm.

There were 3 instances where the problem ended up being the cams were installed wrong.
They were installed with the bottom gear keyway straight up, and the upper gear dot straight down.
This puts the cam advanced 2.5 teeth..... roughly 35*.

In those 3 cases, the motor ran fine until you tried getting it to go over about 4000 at high throttle settings.
One of those(a 383) had been being driven like that for a couple of years.

The tell tale is usually the compression test numbers seem too high for what the motor is.

 

[daytona kid]

I was answering a question about a similar situation over on fabo, and remembered a few instances where customers had engines in cars at their shops that didn’t want to go over 4000-ish rpm.

There were 3 instances where the problem ended up being the cams were installed wrong.
They were installed with the bottom gear keyway straight up, and the upper gear dot straight down.
This puts the cam advanced 2.5 teeth..... roughly 35*.

In those 3 cases, the motor ran fine until you tried getting it to go over about 4000 at high throttle settings.
One of those(a 383) had been being driven like that for a couple of years.

The tell tale is usually the compression test numbers seem too high for what the motor is.

Would the motor go dead?... I rerouted the plug wires and spaced them apart from each other and now they're not really touching anything, test run with no change.. I'm running an msd blaster coil with a proform electronic distributor/ignition and wondering if those are ok with each other? I think I made sure they were compatible when I bought them.

 

[Bee1971]

Correct me if I am wrong

Reading through all these posts , you never mentioned what you are running for a ignition box or module ?

You talked about the coil and distributor

Anyways , Ignition box , who what and

 

[daytona kid]

Correct me if I am wrong

Reading through all these posts , you never mentioned what you are running for a ignition box or module ?

You talked about the coil and distributor

Anyways , Ignition box , who what and

It is a proform electronic conversion kit from summit. It came with distributor and module.

 

[daytona kid]

I may be on to something that doesn't add up. I read where the voltage from the +pos side of the coil should have 7-9 volts with key in run position. I'm getting 3.3 ., What's going on there?. And I read that msd coils may ruin the ign module., What's up with that?... Anyway thought I'd start throwing money at it till it's happy. Looking at a hi-rev module and a suggested coil from jegs. If they don't cure it I'll have some good to have spares.

 

[PRHeads]

Sounds like you need to start probing the power wire at various points between the firewall connector and the coil.
I had a similar situation in my car many moons ago when I was still running an OE style box.
I only had 3v at the coil....... but I also only had about 9v at the hot side of the ballast resistor, and about 11v at the firewall connector.
The old factory wiring was all green inside and was one big resistor.
I’d had an MSD 6A box on the shelf for a while, and that was the motivation I needed to install it.
The main power wires go directly to the battery, so you bypass all the factory wiring to power the box.

When I’d discovered the 3v at the coil, it was after I had put the 340 in the car, which revved quite bit higher than the 440 did.
The problem revealed itself as a high rpm intermittent miss.
I had swapped coils when I put the 340 in........ to an MSD Blaster 2.
When I discovered the miss, I reinstalled the old coil, which was one of the big yellow Accell super coils.
The miss was still there, but maybe slightly less.

Once I tested the voltages, I knew what the problem was.

 

[Bee1971]

I questioned that ECU Ignition Module

Yes , the MSD Blaster 2 coils are intended for CD type ignition systems
Hence the low Primary resistance of the coil itself .7 ohms


Your on the right track with that Ignition Module from Jegs (Rick E)
And proper 1.5 ohm primary resistance coil

What is the ohm reading of your ballast resistor cold , key off , and when it gets hot , engine running

Also was your car running , charging system working when you measured volts at the positive side of coil , or was the key in the run position , engine off

Thanx

Your on the right track

 

[66Satellite47]

Low voltage at the coil & what looks like a real low RPM box, combined with corroded or bad wiring may be the issue? Coils do need to match the ignition controller/box. CD coils don't mix with lower perf boxes.

 

[PRHeads]

I have no problem believing a Proform box running the wrong type of coil is causing some issues......... but......

When I had the 3 volts at the coil(car running/charging), I was only seeing a very slight intermittent miss when the revs got over 6500 going down the track.

Nothing even close to the OP’s description of the motor basically shutting off.

While I do agree there are some ignition issues that really should be addressed...... I’m not totally convinced this is the root cause of the “dead at 4300” issue.

But, it sounds like we’re all going to find out.

 

[66Satellite47]

Gee, 3V doesn't seem like much to generate much secondary voltage. Low dollar boxes see questionable too. I was never a fan of the Mopar Orange boxes. Seemed like guys ran out of steam with them. My old Blue box ran past 7000 with ease & the MSD 404BC went to 8400 before the valve train destructed. Whooops! Coils were matched to the boxes.

 

[daytona kid]

Does the ign module/box need to be grounded to the car/frame? A bud said yes and now I wonder if that's true if my stainless firewall panel is not letting it ground good. I put foam seal strips under the ss to waterproof in between the it and the original firewall , ss screws holding it on also. Does stainless conduct/ground ok for this situation?

 

[1 Wild R/T]

Hard valve float allows the lifters to pump up and hold the valves open, and the motor dies.

The first time I had this happen wa on a tired old 361 and I thought I blew up the motor.

Wound it up tight and it popped a couple times and shut off like you turned the key off.

Tried restarting....... motor just freewheeled....... no compression.
I was under the hood looking for something amiss...... found nothing.
Tried starting it again ...... it started, but ran poorly for about a minute..... then it was fine.

It took a few minutes for the valve springs to bleed the lifters back down to the correct preload so the motor would run again.

I see I'm not the only one...



I was sure I'd blown up my 440.... I guess I couldn't bury the speedo on my 70 Charger R/T... Speedo got to about 135 before the engine died....Man I was sweating bullets, I knew somebody was gonna call the cops & I couldn't go anywhere..... When it started I drove off & was happy to never try a top speed run again..

Years later when I tore that engine down it had eyebrows in all eight pistons...