Hoover777

Update: From my experience chasing this gremlin, I see most people don't update threads confirming what the problem was. If you're running a 6014 check, double check your harness. I actually had a bad box first go around, always had a cam fault...but it would still cut out at 5000rpm.. Swap the power/coil harness and the problem was fixed. Never assume "it's good". I lost a lot of sleep, spent a lot of time and money, and it was a super simple fix. Hope this post helps somebody in the future.

I was going to ohm out the old harness and cross check the pinout, but decided cracking a cold one was a better idea, just glad it's fixed!

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​​​My new build has a gremlin that won't show it's face.


Sitting still, park or neutral, will rev to 7000 rpm quick, just like it should. Cranks good, runs good, idles good, everything is FINE until the car is under load..and it doesn't matter if you roll into the throttle, or mat it...at 5000 rpm and above it starts to stumble. It's not a smooth stumble, it's rough..but it doesn't spit or pop out the exhaust or intake, and if you stay in it it will continue to climb in rpm.

Here's a list of all the things that haven't made a single change in how it runs.

(Plugs look perfect by the way)

-carburetor
-6014
-less lifter preload
-coil harness
-fuel filter (fuel psi stays rock steady at 6psi)
-crank sensors (plural...gm)
-cam sensors(original 6014 always had a cam fault)
-plug wires
-checked for play in the crank front to back and there is none.
-reluctor wheel was straight as an arrow when the pan was bolted down
-map is zeroed out and not hooked up
-ect is zeroed and not hooked up
-ive played with timing, no change
- rev limiter/ launch are both moved to 7k to eliminate that as a cause
-6014 is seeing 14 volts, lowest I've seen it while running is 13.7
-1/0 ground from battery(rear) to block, 4ga from that same point to both heads, 4ga from battery to frame in rear, 6014 is grounded to head at the same place as the 4ga cable
-car has a k&r super duty relay board, off of the ignition power lug (relayed), I added a second 40 amp relay to power the 6014.
-pinouts on harnesses are correct
-coil packs are grounded at the same location as the 1/0 main ground

I'm almost certain I forgot something, will update if I did.

Today I'm running a compression check, testing the (new) valve springs, and trying a known good set of coil packs. Currently running BWD D585 coils.

If you have an idea, let me hear it, I'll try anything at this point. Thanks.

pantera_efi

iTrader: (1)

Hi, I would test the Coil Voltage when this occurs.

DID you CHECK TDC "0" needed for the Spark Advance to be correct ?

Lance

Hoover777

I don't understand. Is this something in the software???

Pop N Wood

iTrader: (1)

Fuel flow. You could be running out of gas. Don't need as much unloaded as loaded.

How is your fuel system set up and when was the last time you cleaned your fuel filters?

Hoover777

10 gallon cell, -10 to aeromotive stainless mesh filter, on the Barry grant 400, -10 to magnafuel log, Holley regulator, with -8 off each side of the regulator to the carb inlets.

yesterday...
Flushed the tank through paint strainers (pulled feed line off fuel log)... no trash.

Pulled fuel filter, it looked brand new, sprayed it out with carb cleaner anyway.

Holds fuel pressure...and will fill a 5 gallon jug QUICK. didn't even mess around with timing how fast it filled. It's FLOWING!

Pop N Wood

iTrader: (1)

Sounds like a well put together system.

Do you have an AFR gauge? That would tell you right quick if it was a lack of fuel or spark. Plugs being good is sort of confusing. You would think that either a fuel or spark issue would gunk them up some.

I've struggled with this sort of thing before as well. I can't begin to count the number of times I've wanted a real time fuel pressure reading.

Have you taken the carb apart and used carb cleaner to check for blocked passages and air bleeds?

SoFla01SSLookinstok

Just for info. My car had a similar prob. It would only break up/shake after a certain rpm at the drag strip. Where I could get traction/full load. On the road it was ok. It turned out to be a problem with the valve springs. New set took care of problem. Good luck man.

Hoover777

Pulled my carb off, and pulled a carb off a very, very good running car....put it on my car. No change...and the setups are similar.

Hoover777

Thanks man. These are new springs, still going to test them today. I'm saving a ton of money on haircuts. I've pulled all my hair out.

SoFla01SSLookinstok

No problem bud. I feel you. When my car was doing it I didn't know what to do. How it would only do it at the track. One day, when driving, one failed & I barely made it home. Then found out broken/failed valve springs. New set of BTR springs repaired problem. The ones that failed on me were PRC. Not old at all. I will never buy again. What brand springs are you running?

Hoover777

FED .660″ Dual LSX Springs with Titanium Retainers

Bowtiedford

iTrader: (9)

well you know what my problem was, have you tried moving the balancer back and forth. We used a long pry bar and then put a gauge on the end of the balancer to measure how much movenment it had back and forth. FFFFing thrust bearing. But spent a month at the shop like you trying everything first before we came to that conclusion. good luck, hope its not that.

TTur1996

Make sure both coil harnesses are not flipped over backwards. And ask MSD if its okay to use a relay on the main power wire. May be causing interference.

Hoover777

Decided to change the MSD power/coil harness...just for kicks. Turns out, that's all it was. A little more than 3 weeks of chasing this gremlin. I'm just glad it's fixed. Thanks for all the help and suggestions. Time to hook up the transbrake and let er eat!

Pop N Wood

iTrader: (1)

That is one serious vehicle!!

So just a different harness fixed the issue? Flipping weird.